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TG 2Second editionMay 2009

ASPHALTACADEMY

Technical Guideline:Bitumen Stabilised Materials

A Guideline for the Design and Construction of Bitumen Emulsion and Foamed Bitumen Stabilised Materials

ASPHALTACADEMY

Asphalt Academy

CSIR Built Environment

PO Box 395

Pretoria

0001

South Africa

Tel: +27 12 841 2436

Fax: +27 12 841 2350

Email: [email protected]

www.asphaltacademy.co.za

Technical Guideline: Bitum

en Stabilised Materials

Second edition • May 2009

Published by theAsphalt Academyc/o CSIR Built EnvironmentP O Box 395Pretoria0001

First published in 2009

ISBN 978-0-7988-5582-2

Copyright © 2009 Asphalt Academy

DisclaimerConsiderable effort has been made to ensure the accuracy and reliability of the information contained in this publication. However, neither the Asphalt Academy nor any of the compilers of the document accept any liability whatsoever for any loss, damage or injury resulting from the use of this information.

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Technical Guideline: B�tumen Stab�l�sed Mater�als

PREFACEThe first TG2 was publ�shed �n 2002 and covered the des�gn and construct�on of foamed b�tumen treated mater�als. S�nce 2002, s�gn�ficant research �n b�tumen emuls�on and foamed b�tumen treatment has been done, wh�ch needed to be �ncluded �n the TG2 gu�del�ne, hence th�s update. Th�s gu�del�ne supercedes the TG2 publ�shed �n 2002 and covers the des�gn and construct�on of B�tumen Stab�l�sed Mater�als (BSMs) and �ncludes both mater�als treated w�th b�tumen emuls�on (BSM-emuls�on) and foamed b�tumen (BSM-foam).

The �nclus�on of BSM-emuls�on mater�als �nto TG2 has been done because the des�gn and construct�on of BSM-emuls�on and BSM-foam are �dent�cal �n many respects. Where there are d�fferences between the mater�als, the �nappropr�ate techn�ques are often appl�ed by �ncorrectly adopt�ng the technology for the other mater�al. For th�s reason, th�s gu�del�ne h�ghl�ghts the s�m�lar�t�es and d�fferences, wh�ch should prevent the �nappropr�ate appl�cat�on of e�ther technology.

Th�s gu�del�ne covers the uses of BSMs, the�r class�ficat�on for des�gn purposes, the m�x and structural des�gn and construct�on aspects.

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ACKNOWLEDGEMENTSThe sponsors of th�s project; Gauteng Department of Publ�c Transport, Roads and Works (GDPRW) (represented by Elzb�eta Sadz�k) and SABITA (represented by Trevor D�st�n and P�et Myburgh) are gratefully acknowledged. The project has been managed by Les Sampson of the Asphalt Academy.

The gu�del�ne has been comp�led by:

Dave Coll�ngs PDNAJoe Grobler Vela-VKEM�ke Hughes WSP GroupK�m Jenk�ns Stellenbosch Un�vers�tyFr�tz Jooste Modell�ng and Analys�s SystemsFenella Long Modell�ng and Analys�s SystemsHugh Thompson WSP Group

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SCOPETh�s gu�del�ne document covers the class�ficat�on, des�gn and construct�on of B�tumen Stab�l�sed Mater�als (BSMs), and �ncludes both b�tumen emuls�on (BSM-emuls�on) and foamed b�tumen treated mater�als (BSM-foam).

BSMs are descr�bed, and gu�del�nes for the�r appropr�ate use are g�ven. Appl�cat�ons for wh�ch BSMs are not appropr�ate are also d�scussed. The approaches to class�ficat�on, m�x and structural des�gn and construct�on are d�scussed.

The class�ficat�on of BSMs �ncludes three mater�al classes:BSM1: Th�s mater�al has a h�gh shear strength, and �s typ�cally used as a base layer for des�gn traffic appl�cat�ons of more than 6 m�ll�on equ�valent standard axles (MESA). For th�s class of mater�al, the source mater�al �s typ�cally a well graded crushed stone or recla�med asphalt. BSM2: Th�s mater�al has a moderately h�gh shear strength, and would typ�cally used as a base layer for des�gn traffic appl�cat�ons of less than 6 MESA. For th�s class of mater�al, the source mater�al �s typ�cally a graded natural gravel or recla�med asphalt.BSM3: Th�s mater�al �s typ�cally a so�l-gravel and/or sand, stab�l�sed w�th h�gher b�tumen contents. As a base layer, the mater�al �s only su�table for des�gn traffic appl�cat�ons of less than 1 MESA.

A cons�stent and rat�onal system for class�fy�ng the mater�als �s presented. Th�s system �s new and �s appl�cable to granular and cemented mater�als as well as BSMs. Full deta�ls of the method for all mater�als are g�ven �n Append�x A.

The m�x des�gn of BSMs �nvolves three levels of test�ng, wh�ch depend on the des�gn traffic level. ITS test�ng �n dry and soaked states �s used for Level 1 and 2. For Level 3 (des�gn traffic exceed�ng 6 MESA), tr�ax�al test�ng �s recommended. A s�mple tr�ax�al test has been developed to fac�l�tate such test�ng �n standard laborator�es. A method for test�ng the mo�sture sens�t�v�ty of BSMs �n the tr�ax�al test has also been developed, wh�ch ut�l�ses the MIST equ�pment for saturat�ng the tr�ax�al spec�mens. Th�s �s descr�bed �n Chapter 4.

The structural des�gn of BSMs ut�l�ses the Pavement Number (PN) des�gn method. Th�s method �s based on observed performance of field pavements and �s based on an “�ntell�gent” structural number. The PN method �s recommended for des�gn traffic between 1 and 30 MESA and for Category A and B roads. Because the PN method �s also new, and �s appl�cable for all road bu�ld�ng mater�als, the complete deta�ls of the method are g�ven �n Append�x C. For des�gn traffic less than 1 MESA, a catalogue of typ�cal des�gns �s g�ven.

The construct�on of BSMs �ncludes �n s�tu recycl�ng w�th recyclers, convent�onal construct�on equ�pment, and �n plant treatment. Qual�ty control for construct�on �s also �ncluded, and Append�x D conta�ns deta�ls on construct�on controls for BSM treatment us�ng recyclers.

Wh�le th�s gu�del�ne �s the culm�nat�on of many years of research and development, �t may be necessary to update deta�ls �n the laboratory test methods and �n the mater�al class�ficat�on system and Pavement Number method. Any such updates w�ll be posted on www.asphaltacademy.co.za/b�tstab.

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GLOSSARY OF TERMS°C degrees Celc�usτ1/2 half-l�fe% percentAASHTO Amer�can Assoc�at�on of State H�ghway and Transportat�on Offic�alsAct�ve filler F�llers that chem�cally alter the m�x propert�es. Th�s �ncludes fillers such as l�me, cement, fly ash, etc, but

excludes natural fillers such as rock flour.BSM(s) B�tumen Stab�l�sed Mater�al(s)BSM-emuls�on B�tumen emuls�on treated mater�alBSM-foam Foamed b�tumen treated mater�alCBR Cal�forn�a Bear�ng Rat�oCOLTO Comm�ttee of Land and Transport Offic�alsCS Crushed stoneDE-G1 to DE-G10 Des�gn equ�valent G1 to G10 mater�al classesDEMAC Des�gn equ�valent mater�al classELTS Effect�ve long term st�ffness. Th�s �s a relat�ve �nd�cator of the average long term �n s�tu st�ffness of a

pavement layer. EMC Equ�l�br�um mo�sture content ER Expans�on Rat�oEtan Tangent modulus, st�ffness from monoton�c tr�ax�al testEWC b�tumen emuls�on water content �nclud�ng water used for d�lut�on as percentage of dry aggregate fluff po�nt mo�sture content at wh�ch the “max�mum bulk volume of loose m�neral aggregate �s obta�nedFMC field mo�sture content of aggregateG1 to G10 Granular mater�als classes, see TRH4 for defin�t�onsGS Gravel so�lHMA Hot m�x asphaltICL In�t�al consumpt�on of l�meITSdry Ind�rect Tens�le Strength test, 100 mm d�ameter spec�mens cured for 72 hours at 40 °C.ITSequ�l Ind�rect Tens�le Strength test, spec�mens cured accord�ng to cur�ng procedure.ITSsoaked Ind�rect Tens�le Strength test, spec�mens cured accord�ng to cur�ng procedure and then soaked for 24 hours

at 25 °C.ITSwet Ind�rect Tens�le Strength test, 100 mm d�ameter spec�mens cured then soaked for 24 hours at 25 °C.L�me L�me refers to hydrated road l�meMast�c The mast�c �s the m�x of fines and b�tumen.max�mum st�ffness The max�mum st�ffness a mater�al can ach�eve depends on the mater�al qual�ty.MESA m�ll�on equ�valent standard axles, 80 kN axlesMIST Mo�sture Induced Sens�t�v�ty Test used to �nduce mo�sture �nto tr�ax�al spec�mens.mm m�ll�metersMod. AASHTO Mod�fied AASHTO compact�onModular Rat�o Rat�o of a layer’s st�ffness relat�ve to the st�ffness of the layer below.MPa megaPascals N We�nert’s N-valueNG Natural gravelOFC opt�mum flu�ds contentOMCMod-U opt�mum mo�sture content us�ng Mod. AASHTO compact�on on untreated mater�alOMCMod-BSM opt�mum mo�sture content us�ng Mod. AASHTO compact�on on treated mater�alOMCV�b-BSM opt�mum mo�sture content us�ng v�bratory hammer compact�on on treated mater�alPI Plast�c�ty IndexPN Pavement numberPTR Pneumat�c Tyred RollerRA Recla�med asphaltRBC res�dual b�tumen content as percentage of dry aggregateSSSC S�lt, s�lty sand, clayTSR Tens�le Strength Reta�ned. Rat�o of ITSwet and ITSdry.UCS Unconfined Compress�on Test

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CONTENTSpage

ACKNOWLEDGEMENTS iiSCOPE iiiGLOSSARY OF TERMS ivCONTENTS vLIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v��

1 INTRODUCTION 11.1. WHAT ARE BITUMEN STABILISED MATERIALS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2. PURPOSE OF GUIDELINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3. LAYOUT OF GUIDELINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 BITUMEN STABILISATION, USAGE AND DESIGN APPROACH 42.1. WHAT IS BITUMEN EMULSION AND FOAMED BITUMEN? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2. BEHAVIOUR OF BITUMEN STABILISED MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3. BENEFITS OF BITUMEN STABILISATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4. LIMITATIONS OF BITUMEN STABILISATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.5. MATERIALS SUITABLE FOR BITUMEN TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.6. WHERE TO USE BSMS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.6.1. CONSTRUCTION METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.6.2. CLIMATIC CONSIDERATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.6.3. GENERAL PROJECT SELECTION CRITERIA FOR IN SITU TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.7. DESIGN APPROACH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.7.1. DESIGN SEQUENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.7.2. MATERIAL CLASSIFICATION APPROACH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.7.3. MIX DESIGN APPROACH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.7.4. STRUCTURAL DESIGN APPROACH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.8. CLASSIFICATION OF BSMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3 MATERIAL CLASSIFICATION 153.1. CONCEPT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.2. MATERIAL CLASSIFICATION SYSTEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.3. TESTS AND INTERPRETATION OF RESULTS FOR BSMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.4. CONFIDENCE ASSOCIATED WITH ASSESSMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4 MIX DESIGN 214.1. MIX DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.1.1. MIX TYPE SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.1.2. OUTLINE OF MIX DESIGN PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.2. MIX CONSTITUENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.2.1. AGGREGATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.2.2. BITUMEN SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.2.3. FILLER (NATURAL AND ACTIVE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.2.4. WATER QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.3. SPECIMEN PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3.1. FLUID CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3.2. MATERIAL PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.3.3. MIXING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.3.4. COMPACTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.3.5. CURING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

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4.4. MECHANICAL TESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.4.1. INDIRECT TENSILE STRENGTH (ITS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.4.2. TRIAXIAL TEST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.5. MIX DESIGN PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.5.1. LEVEL 1 MIX DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.5.2. LEVEL 2 MIX DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.5.3. LEVEL 3 MIX DESIGN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5 STRUCTURAL DESIGN 425.1. PAVEMENT NUMBER STRUCTURAL DESIGN METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.1.1. APPLICABILITY OF PAVEMENT NUMBER METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.1.2. RULES OF THUMB / DEPARTURE POINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.1.3. PAVEMENT NUMBER CALCULATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455.2. CATALOGUE OF DESIGNS FOR LOWER TRAFFICKED ROADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465.3. APPROPRIATE SURFACINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485.4. ECONOMIC ANALYSES AND MAINTENANCE REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6 CONSTRUCTION 506.1. IN SITU TREATMENT (GENERAL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516.1.1. DILUTING BITUMEN EMULSION WITH WATER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516.2. IN SITU TREATMENT USING RECYCLERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516.2.1. FACTORS REQUIRING CONSIDERATION (PLANNING THE WORK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516.2.2. EXECUTING THE WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6.3. IN SITU TREATMENT USING CONVENTIONAL EQUIPMENT (BSM-EMULSION ONLY) . . . . . . . . . . . . . . . . . . . . . . . . . . . 666.3.1. EQUIPMENT SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666.3.2. BITUMEN EMULSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676.3.3. MIXING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686.3.4. COMPACTION, CUTTING LEVELS AND FINISHING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686.4. IN-PLANT TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696.4.1. IN-PLANT MIXING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696.4.2. TRANSPORTING BSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706.4.3. LAYER CONSTRUCTION USING A PAVER / FINISHER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716.4.4. LAYER CONSTRUCTION USING CONVENTIONAL CONSTRUCTION EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756.4.5. LAYER CONSTRUCTION USING LABOUR INTENSIVE METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766.5. CURING AND TRAFFICKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776.6. SURFACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786.7. CONSTRUCTING TRIAL SECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786.7.1. TRIAL SECTIONS FOR IN SITU TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786.7.2. TRIAL SECTIONS FOR IN-PLANT TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796.8. QUALITY CONTROL ASPECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796.8.1. QUALITY OF THE BSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796.8.2. QUALITY OF THE LAYER OF BSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826.8.3. ACCEPTANCE CONTROLS FOR PAVEMENT LAYERS CONSTRUCTED WITH BSMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

BIBLIOGRAPHY 86

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APPENDIX A: MATERIAL CLASSIFICATION SYSTEM 88A.1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88A.2. CONCEPT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88A.2.1. Assumed Mater�al Behav�our . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89A.2.2. Des�gn Equ�valent Mater�al Class. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91A.3. MATERIAL CLASSIFICATION SYSTEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91A.3.1. Theory of Hol�st�c Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91A.3.2. Step by Step Mater�al Class�ficat�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92A.3.3. Certa�nty Factors for D�fferent Tests and Ind�cators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93A.3.4. Adjustment for Sample S�ze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93A.3.5. Assess�ng the Relat�ve Certa�nty of Ev�dence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93A.3.6. Updat�ng Mater�al Class�ficat�on for Ava�lable Ev�dence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94A.4. TESTS AND INTERPRETATION OF RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95A.4.1. Granular Mater�als . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95A.4.2. B�tumen Stab�l�sed Mater�als . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101A.4.3. Cement Stab�l�sed Mater�als. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105A.5. CONFIDENCE ASSOCIATED WITH ASSESSMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106A.6. WORKED EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

REFERENCES 111

APPENDIX B: LABORATORY TESTS 112

APPENDIX C: PAVEMENT NUMBER STRUCTURAL DESIGN METHOD 113C.1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113C.2. APPLICABILITY AND LIMITATIONS OF THE PAVEMENT NUMBER METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113C.3. RULES OF THUMB / DEPARTURE POINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114C.3.1. The Effect�ve Long Term St�ffness (ELTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115C.3.2. Modell�ng of Subgrade Mater�als . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115C.3.3. The Modular Rat�o L�m�t and Max�mum St�ffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116C.3.4. The Base Confidence Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117C.4. PAVEMENT NUMBER CALCULATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117C.4.1. Comb�n�ng Pavement Layers to Form a F�ve Layer Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121C.4.2. Determ�n�ng Effect�ve Long-Term St�ffness (ELTS) Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122C.5. PAVEMENT CAPACITY CALCULATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124C.6. WORKED EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

REFERENCES 127

APPENDIX D: CONSTRUCTION CONTROLS FOR BITUMEN TREATMENT 128D.1. ESSENTIAL REQUIREMENTS FOR A SUCCESSFUL RECYCLING OPERATION USING RECYCLERS . . . . . . . . . . . . . . . . . . . . . 128D.2. PRE-START CHECKLISTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131D.2.1. In s�tu recycl�ng: BSM-foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131D.2.2. In s�tu recycl�ng: BSM-emuls�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132D.2.3. In plant treatment: BSM-foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133D.3. DAILY REPORTS FOR IN SITU RECYCLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134D.3.1. BSM-foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134D.3.2. BSM-emuls�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135D.3.3 Act�ve filler control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

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LIST OF TABLES

LIST OF FIGURES

Table 3.1 Ind�cators and Tests for Class�ficat�on of B�tumen Stab�l�sed Mater�als. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Table 3.2 Interpretat�on of Ind�cators and Tests for Class�ficat�on of B�tumen Stab�l�sed Mater�als . . . . . . . . . . . . . . . . . . . . . . 18Table 3.3 Interpretat�on of Grad�ng Rat�ng for BSMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Table 3.4 Relat�ve Confidence of Mater�als Class�ficat�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Table 4.1 Durab�l�ty M�ll Index, L�m�t for Rocks and So�ls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Table 4.2 Categor�es of B�tumen Emuls�on for Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Table 4.3 Compat�b�l�ty of B�tumen Emuls�on Type w�th Aggregate Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Table 4.4 Foam Character�st�c L�m�ts (m�n�mum values) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 4.5 Role of Flu�ds �n BSMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Table 4.6 Interpretat�on of ITS tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Table 4.7 Interpretat�on of Tr�ax�al Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Table 5.1 Modular Rat�o L�m�t and Max�mum Allowed St�ffness for Pavement Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Table 5.2 Typ�cal Future Ma�ntenance Measures for BSM Base Pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Table 6.1 D�lut�on of B�tumen Emuls�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

F�gure 1.1 Aggregate and B�nder Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2F�gure 1.2 Conceptual Behav�our of Pavement Mater�als . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2F�gure 2.1 Manufacture of B�tumen Emuls�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4F�gure 2.2 Foamed B�tumen Product�on �n Expans�on Chamber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4F�gure 2.3 Des�gn Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13F�gure 3.1 Interpretat�on of Test and Ind�cator Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16F�gure 3.2 Interpretat�on of Grad�ng to Quant�fy Relat�ve Conformance to Grad�ng (BSM) . . . . . . . . . . . . . . . . . . . . . . . . . . . 19F�gure 4.1 Factors Influenc�ng B�tumen and Act�ve F�ller Content Select�on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22F�gure 4.2 Gu�del�nes for Su�tab�l�ty of Grad�ng for Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26F�gure 4.3 Determ�nat�on of Opt�mum Foamant Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31F�gure 4.4 M�x Factors Cons�dered for Select�on of Cur�ng Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38F�gure 4.5 M�x Des�gn Flow Chart for BSM M�xes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41F�gure 5.1 Catalogue of Des�gns for BSM Pavements Carry�ng up to 1 MESA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47F�gure 5.2 M�n�mum Surfac�ng Th�ckness for BSM Pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48F�gure 6.1 BSM Construct�on Opt�ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50F�gure 6.2 Mount�ng of Cutt�ng Tools on M�ll�ng Mach�nes and Recyclers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52F�gure 6.3 Pr�mary Roller Select�on Gu�de . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54F�gure 6.4 Padfoot Roller Impr�nts on Mater�al Be�ng Compacted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55F�gure 6.5 Typ�cal Recycl�ng Cut Plan Show�ng the Overlap Relat�ve to the Outer Wheel Path . . . . . . . . . . . . . . . . . . . . . . . . 58F�gure 6.6 B�tumen Starvat�on along Long�tud�nal Jo�nt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58F�gure 6.7 Typ�cal Recycl�ng Tra�n for B�tumen Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60F�gure 6.8 Mater�al Compacted by the Rear Wheels of the Recycler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63F�gure 6.9 M�x�ng Plant for BSM-foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70F�gure 6.10 Long�tud�nal Jo�nt Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

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CHAPTER 1: Introduction – What are BSMs?

1

1 INTRODUCTIONRoad pavements constructed w�th b�tumen stab�l�sed mater�als (BSMs) us�ng e�ther b�tumen emuls�on or foamed b�tumen are env�ronmentally susta�nable and cost effect�ve; and, when good construct�on techn�ques are used, these pavements perform very well. BSMs are su�ted to both construct�on of new pavements and to pavement rehab�l�tat�on us�ng �n s�tu recyclers and/or convent�onal construct�on equ�pment. BSMs are also �deally su�ted to labour �ntens�ve construct�on. Worldw�de, the state of road pavements �s deter�orat�ng, and the demand for rehab�l�tat�ng road pavements far exceeds the demand for new roads. Th�s s�tuat�on has seen the adopt�on of �n place recycl�ng as the preferred procedure for address�ng the rehab�l�tat�on backlog by reus�ng mater�al �n the ex�st�ng pavement. B�tumen stab�l�sat�on enhances the propert�es of these recycled mater�als, prov�d�ng serv�ce l�ves that equates to or exceeds those ach�evable had v�rg�n aggregates been used, all at a lower cost.

Th�s gu�del�ne covers the approach to class�ficat�on, des�gn, construct�on and r�sk assessment of pavements us�ng BSMs. To d�fferent�ate between b�tumen emuls�on and foamed b�tumen treated mater�als, the terms BSM-emuls�on and BSM-foam are used. Where there are d�fferences �n the approach to BSM-emuls�on and BSM-foam, these are clearly h�ghl�ghted �n the text by separat�ng the text �nto columns, where BSM-emuls�on aspects are �n the left column and the BSM-foam aspects �n the r�ght column

1.1. WHAT ARE BITUMEN STABILISED MATERIALS?BSMs are pavement mater�als that are treated w�th e�ther b�tumen emuls�on or foamed b�tumen. The mater�als treated are normally granular mater�als, prev�ously cement treated mater�als or recla�med asphalt (RA) layers. Where an ex�st�ng pavement �s recycled, old seals or asphalt surfac�ng �s usually m�xed w�th the underly�ng layer and treated to form a new base or subbase layer.

The quant�t�es of res�dual b�tumen emuls�on or foamed b�tumen added do not typ�cally exceed 3% by mass of dry aggregate. In many s�tuat�ons, act�ve filler �n the form of cement or hydrated l�me �s also added to the m�x. The cement content should not exceed 1%, and should also not exceed the percentage of the b�tumen stab�l�ser, (�e. the rat�o of b�tumen percentage to cement percentage should always be greater than 1). If th�s rat�o �s less than one, then the mater�al should be cons�dered a cement treated mater�al and the gu�del�nes �n TRH13 should be followed.

The add�t�on of b�tumen emuls�on or foamed b�tumen to produce a BSM results �n an �ncrease �n mater�al strength and a reduct�on �n mo�sture suscept�b�l�ty as a result of the manner �n wh�ch the b�tumen �s d�spersed amongst the finer aggregate part�cles.

BSM-emulsion

W�th BSM-emuls�on the b�tumen emuls�on d�sperses preferent�ally amongst the finer part�cles, but not exclus�vely. There �s some “pa�nt�ng” of the larger part�cles by the b�tumen emuls�on. Th�s �s �llustrated schemat�cally �n F�gure 1.1.

W�th b�tumen emuls�ons, there �s a chem�cal bond between the b�tumen and the aggregate promoted by the emuls�fier.

BSM-foam

Foamed b�tumen d�str�butes exclus�vely to the finer part�cles, produc�ng “spot welds” of a mast�c of b�tumen droplets and fines. Th�s �s �llustrated schemat�cally �n F�gure 1.1.

Cement Contents

The cement content of BSMs should be ≤ 1%, and the

cement content should not exceed the b�tumen content.


CHAPTER 1: Introduction – What are BSMs?

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BSM-emulsion BSM-foam

Figure 1.1 Aggregate and Binder Bond

Such “non-cont�nuous” b�nd�ng of the �nd�v�dual aggregate part�cles makes BSMs d�fferent from all other pavement mater�als. The d�spersed b�tumen changes the shear propert�es of the mater�al by s�gn�ficantly �ncreas�ng the cohes�on value wh�lst effect�ng l�ttle change to the �nternal angle of fr�ct�on. A compacted layer of BSM w�ll have a vo�d content s�m�lar to that of a granular layer, not an asphalt. BSMs are therefore granular �n nature and are treated as such dur�ng construct�on. The many benefits that accrue from us�ng BSMs are d�scussed �n Chapter 2.

The behav�our of BSMs, relat�ve to other pavement mater�als �s �llustrated �n F�gure 1.2.

Figure 1.2 Conceptual Behaviour of Pavement Materials

Incr

ease

dP

Dre

sist

ance

,red

uced

flex

ibili

ty Stronglycementedmaterial

Stiff, brittlebehaviour

HighIntermediateLowNone

Temperaturedependent, visco-elastic behaviour

Stressdependentbehaviour

Increased moisture resistance, flexibility

Unboundmaterial: Highquality crushed

stone andaggregate

Moderatequality natural

gravel

Low qualitynatural gravel

Bitumen

Asphaltconcrete

(BSM-foam andBSM-emulsion)

BSMs

Cement

Presumed noteconomically

viableLightlycementedmaterial

High

Intermediate

Low

None

Incr

ease

dP

Dre

sist

ance

,red

uced

flex

ibili

ty Stronglycementedmaterial

Stiff, brittlebehaviour

HighIntermediateLowNone

Temperaturedependent, visco-elastic behaviour

Stressdependentbehaviour

Increased moisture resistance, flexibility

Unboundmaterial: Highquality crushed

stone andaggregate

Moderatequality natural

gravel

Low qualitynatural gravel

Bitumen

Asphaltconcrete


BSMs


BSMs

Cement

Presumed noteconomically

viableLightlycementedmaterial

High

Intermediate

Low

None



CHAPTER 1: Introduction – Layout and Purpose of Guideline

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Contrary to some m�sconcept�ons, the add�t�on of foamed b�tumen or b�tumen emuls�on does not change the nature of the mater�al so that �t becomes cold-m�x asphalt. BSMs rema�n granular �n nature and must be processed as such dur�ng construct�on. For th�s reason, term�nology such as “foamed asphalt” �s not recommended for BSM-foam, as �t perpetuates the m�s�nterpretat�on.

In th�s gu�del�ne, the terms stab�l�se and treat are used �nterchangeably. The d�fferent�at�on between stab�l�sat�on and mod�ficat�on used prev�ously �s no longer used because the focus �s on the behav�our of the final product, rather than the quant�ty of the const�tuents wh�ch make up the product.

1.2. PURPOSE OF GUIDELINETh�s gu�del�ne �s an update to the follow�ng manuals:

GEMS – The Des�gn and Use of Granular Emuls�on M�xes, Manual 14 (SABITA, 1993).ETB – The Des�gn and Use of Emuls�on-treated Bases, Manual 21 (SABITA, 1999). Inter�m Techn�cal Gu�del�ne: The Des�gn and Use of Foamed B�tumen Treated Mater�als, Techn�cal Gu�del�ne 2 (Asphalt Academy, 2002).

Because of the many s�m�lar�t�es between BSM-emuls�on and BSM-foam, �t �s appropr�ate to publ�sh one gu�del�ne document on b�tumen stab�l�sat�on that �ncorporates both mater�als. The advantage of the comb�ned gu�del�ne �s that the s�m�lar�t�es and d�fferences between BSM-emuls�on and BSM-foam are h�ghl�ghted. Th�s w�ll a�d �n prevent�ng the �ncorrect appl�cat�on of the technolog�es.

S�gn�ficant research �nto the behav�our and performance of BSMs has occurred �n the last five years. Much of th�s work has focussed on m�x des�gn, class�fy�ng mater�als for des�gn, and structural des�gn. Observat�ons of �n-serv�ce pavements were also made, wh�ch has contr�buted to the knowledge base of BSM pavements. All th�s research has been �ncorporated �nto th�s gu�del�ne.

The purpose of th�s gu�del�ne �s to prov�de a complete reference for the project select�on, treatment select�on, mater�al class�ficat�on, m�x des�gn, structural des�gn, construct�on and r�sk assessment of projects ut�l�s�ng BSMs. Th�s gu�del�ne should however be used �n conjunct�on w�th other establ�shed gu�del�nes, such as:

TRH4: Structural Des�gn of Flex�ble Pavements for Interurban and Rural Roads, Draft 1996.TRH12: Flex�ble pavement rehab�l�tat�on �nvest�gat�on and des�gn, Draft 1997.TRH14: Gu�del�nes for road construct�on mater�als, 1985.TRH21: Hot-m�x asphalt recycl�ng, Draft, 2008. Job Creat�on, Sk�lls Development and Empowerment �n Road Construct�on, Rehab�l�tat�on and Ma�ntenance, GDPTRW, 2008.Wirtgen Cold Recycling Manual: 2nd Ed�t�on, November 2004

1.3. LAYOUT OF GUIDELINETh�s gu�del�ne conta�ns s�x chapters, a b�bl�ography and four append�ces:

Chapter 2 descr�bes bitumen stabilisation, where BSMs are used and the approach to design.Chapter 3 presents the material classification method, w�th part�cular focus on BSMs. Chapter 4 deals w�th the mix design process for BSMs.Chapter 5 d�scusses the structural design of BSMs and prov�des the deta�ls necessary to perform the Pavement Number structural des�gn method for BSMs. Chapter 6 deals w�th the construction of pavement layers us�ng BSMs. A comprehens�ve bibliography �s g�ven. No references are c�ted �n the text of the gu�del�ne. Append�x A g�ves the background and complete deta�ls of the material classification system. Append�x B g�ves a l�st of all laboratory tests and methods referred to �n the gu�del�ne and prov�des the reference for the test method. Where the methods cannot be found �n standard test manual references, the methods can be downloaded from www.asphaltacademy.co.za/b�tstab. Append�x C g�ves the background deta�ls of the Pavement Number structural des�gn method.Append�x D conta�ns Construction Controls for B�tumen Treatment.

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BSM Behaviour

The add�t�on of b�tumen emuls�on or

foamed b�tumen does not transform the material to an asphalt l�ke mater�al. The material remains granular �n nature, albe�t w�th �mproved behav�oural character�st�cs.

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CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – What is Bitumen Emulsion and Foamed Butimen

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2 BITUMEN STABILISATION, USAGE AND DESIGN APPROACHTh�s chapter covers much of the background �nformat�on for the subsequent chapters. A descr�pt�on of b�tumen emuls�on and foamed b�tumen �s presented and the behav�our of BSMs are d�scussed. The select�on of mater�als and projects su�table for b�tumen stab�l�sat�on �s rev�ewed along w�th the benefits of us�ng BSMs and where they are most appropr�ately used. F�nally, the ph�losophy underly�ng the des�gn approach for m�x and structural des�gn �s presented and d�scussed.

2.1. WHAT IS BITUMEN EMULSION AND FOAMED BITUMEN?Both b�tumen emuls�on and foamed b�tumen are methods of reduc�ng the v�scos�ty of b�tumen, allow�ng �t to be m�xed w�th cold mo�st mater�al. They are, however, produced us�ng completely d�fferent methods.

Bitumen Emulsion

B�tumen emuls�on �s compr�ses b�tumen emuls�fied �n water. The b�tumen �s d�spersed �n the water �n the form of an o�l-�n-water type b�tumen emuls�on. The b�tumen �s held �n suspens�on by an emuls�fiy�ng agent. The emuls�fy�ng agent determ�nes the charge of the b�tumen emuls�on. Cat�on�c b�tumen emuls�ons have a pos�t�ve charge and an�on�c b�tumen emuls�on have a negat�ve charge. The manufacture of a typ�cal b�tumen emuls�on �s �llustrated �n F�gure 2.1. B�tumen emuls�on �s manufactured �n a plant and has a shelf l�fe of several months, prov�ded the manufacturer’s storage gu�del�nes are str�ctly followed.

Figure 2.1 Manufacture of Bitumen Emulsion

Foamed Bitumen

Foamed b�tumen �s produced by �nject�ng water �nto hot b�tumen, result�ng �n spontaneous foam�ng. The phys�cal propert�es of the b�tumen are temporar�ly altered when the �njected water, on contact w�th the hot b�tumen, �s turned �nto vapour, wh�ch �s trapped �n thousands of t�ny b�tumen bubbles. Th�s process �s shown �n F�gure 2.2. The foam d�ss�pates �n less than a m�nute. The foam�ng process occurs �n an expans�on chamber. The expans�on chamber developed by Mob�l �n the 1960’s �s st�ll the most commonly used system for produc�ng foamed b�tumen. Expans�on chambers are relat�vely small th�ck-walled steel tubes, approx�mately 50 mm �n depth and d�ameter, �nto wh�ch b�tumen and water (plus a�r on some systems) are �njected at h�gh pressure.

Figure 2.2 Foamed Bitumen Production in Expansion Chamber

Mill

Acid orCaustic SodaSurfactants

Water BitumenWaterWater

5 microns

Mill

Acid orCaustic SodaSurfactants

Water BitumenWaterWater

5 microns

Water

Hot bitumen

Air

Expansion chamber

Water

Hot bitumen

Air

Expansion chamber



CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Behaviour of BSMs

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When m�xed w�th aggregate, the charge on the �nd�v�dual b�tumen droplets causes them to be attracted to the aggregate part�cles, focus�ng on the smaller fract�ons due to the�r surface area and charge concentrat�on features. The mo�sture and type of aggregate �n the m�x plays an �mportant role �n d�spers�ng the b�tumen emuls�on and prevent�ng a premature “break” (separat�on of the b�tumen from the water) dur�ng m�x�ng.

Once m�xed, the b�tumen emuls�on needs to break to allow the b�tumen to act as a b�nder. S�nce the b�tumen emuls�on acts as a lubr�cant, the break should occur only after the mater�al has been fully compacted. The treated mater�al w�ll have a “speckled” appearance due to the concentrat�on of b�tumen on the finer part�cles. B�tumen emuls�ons are d�scussed �n more deta�l �n Sect�on 4.2.2.

To produce a BSM-foam, the b�tumen �s foamed on s�te and �ncorporated �nto the aggregate wh�le st�ll �n �ts foamed state. The greater the volume of the foam, the better the d�str�but�on of the b�tumen �n the aggregate.

Dur�ng the m�x�ng process, the b�tumen bubbles burst, produc�ng t�ny b�tumen part�cles, that d�sperse throughout the aggregate by adher�ng to the finer part�cles (fine sand and smaller) to form a mast�c. The mo�sture �n the m�x pr�or to the add�t�on of the foamed b�tumen plays an �mportant role �n d�spers�ng the b�tumen dur�ng m�x�ng. On compact�on, the b�tumen part�cles �n the mast�c are phys�cally pressed aga�nst the larger aggregate part�cles result�ng �n local�sed non-cont�nuous bonds (“spot weld�ng”). Foamed b�tumen product�on �s d�scussed �n more deta�l �n Sect�on 4.2.2.

2.2. BEHAVIOUR OF BITUMEN STABILISED MATERIALSThe behav�our of BSMs �s s�m�lar to that of unbound granular mater�als, but w�th a s�gn�ficantly �mproved cohes�ve strength and reduced mo�sture sens�t�v�ty. BSMs, unl�ke hot-m�x asphalt, are not black �n appearance and do not have a st�cky feel. W�th BSMs, the larger aggregate part�cles are not coated w�th b�tumen. The b�tumen d�sperses only amongst the finest part�cles, result�ng �n a b�tumen-r�ch mortar between the coarse part�cles. There �s a sl�ght darken�ng �n the colour of the mater�al after treatment. Typ�cally, small amounts of act�ve filler (cement or hydrated l�me) are added to the m�x �n conjunct�on w�th the b�tumen emuls�on or foamed b�tumen. In add�t�on to �mprov�ng the reta�ned strength under saturated cond�t�ons, such act�ve filler ass�sts �n d�spers�ng the b�tumen.

BSM-emulsion

When b�tumen emuls�on �s added to a mater�al, the charged b�tumen droplets are attracted to the smaller aggregate part�cles w�th the oppos�te charge.

Act�ve filler ass�sts the extract�on of the water phase from a b�tumen emuls�on, caus�ng break�ng.

BSM-foam

The t�ny b�tumen part�cles that are produced when the foamed b�tumen bubbles burst have only enough energy to warm the smaller aggregate part�cles suffic�ently to perm�t adhes�on.

Act�ve filler acts as a catalyst �n d�spers�ng the b�tumen part�cles.

No d�st�nct�on �s made �n these gu�del�nes between the behav�our of BSM-foam and BSM-emuls�on. Th�s assumpt�on �s based on numerous observat�ons of �n-serv�ce pavements. The ma�n features and assumed behav�our of BSMs are:

BSMs exh�b�t a s�gn�ficant increase in cohesion �n compar�son to the parent mater�al. The friction angle of the treated mater�al �s typ�cally s�m�lar to the untreated mater�al. BSMs acquire flexural strength as a result of the comb�ned effect of the v�sco-elast�c propert�es of the d�spersed b�tumen droplets. S�nce the �nd�v�dual b�tumen droplets are not l�nked and the coarser aggregate part�cles rema�n uncoated, BSMs reta�n the granular character�st�cs of the parent mater�al. It �s therefore stress dependant and �s not prone to crack�ng when subjected to tens�le stresses. BSMs perform well when cohesive strength is optimised through proper m�x des�gn (to determ�ne the opt�mal b�tumen and act�ve filler contents), wh�lst reta�n�ng enough flex�b�l�ty so that fr�ct�on res�stance �s st�ll act�vated under load. S�nce the b�tumen �s d�spersed only amongst the finer aggregate part�cles, the fines are encapsulated and �mmob�l�sed. Th�s �mproves the moisture sensitivity and durability of the treated mater�als. Prov�ded suffic�ent b�tumen �s appl�ed, the tendency for the BSM to pump under load�ng �n saturated cond�t�ons �s also s�gn�ficantly reduced because the fines are bound.

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BSM Behaviour

The behav�our of BSMs �s similar to that of

unbound granular mater�als, but w�th improved cohesive strength and reduced moisture sensitivity.

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CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Behaviour of BSMs

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S�m�lar to unbound granular mater�als, the stiffness of b�tumen stab�l�sed mater�als �s dependent on:The �nherent stiffness of the parent material.The density of the mater�al �n the layer.The quantities of binder and active filler added, and the�r d�spers�on throughout the m�xed mater�al.The local climate, part�cularly amb�ent temperature and ra�nfall.The stiffness of the support.

However, the h�gh cohes�ve strength allows the mater�al to susta�n a higher stiffness under load than the unbound parent mater�al.The pr�mary mode of failure of BSMs �s permanent deformat�on. The behav�our and st�ffness of BSMs var�es s�gn�ficantly depend�ng on the quantities of bitumen and active filler used. In part�cular, when excess�ve cement �s used, the mater�als behave more l�ke cement treated mater�als and the benefit of add�ng b�tumen �s quest�onable. For th�s reason, cement contents that exceed 1% are not recommended, and the rat�o of added b�tumen to added act�ve filler should always exceed one.

For opt�mal BSM performance, �t �s �mportant that the m�x des�gn �s balanced and the pavement �s well des�gned. For opt�mal m�x des�gns, the reader �s referred to Chapter 4 and for opt�mal pavement des�gn the reader �s referred to Chapter 5. However, �t �s �mportant to understand that there are two ways �n wh�ch opt�mal shear strength of a BSM can be comprom�sed, both result�ng from the �nclus�on of too much act�ve filler:

Excessive amounts of active filler w�ll transform the mater�al from a flex�ble to a br�ttle state. In th�s state, the cohes�ve strength w�ll dom�nate but w�ll s�gn�ficantly reduce once fracture occurs. Th�s �s l�kely to be assoc�ated w�th deformat�on and crack�ng, and w�ll result �n a mater�al cons�st�ng of large fractured clumps, w�th a low fr�ct�onal res�stance.Poorly graded or non-durable source materials (soft weathered natural gravel or mater�al w�th excess�ve fines) w�ll comprom�se the fr�ct�onal res�stance of the mater�al. Inexper�enced des�gners may be tempted to compensate for such a s�tuat�on through the add�t�on of h�gher amounts of cement. Such fine gra�ned, br�ttle mater�als w�ll be h�ghly suscept�ble to crush�ng and fat�gue fa�lure.

BSMs are clearly very d�fferent to asphalt and cement treated mater�als �n terms of behav�our and performance. In part�cular, they should not be confused w�th cold asphalt m�xes manufactured w�th cut-back b�tumen.

2.3. BENEFITS OF BITUMEN STABILISATION The pr�mary benefits of us�ng BSMs are:

The increase in strength assoc�ated w�th b�tumen treatment allows a BSM to replace alternat�ve h�gh-qual�ty mater�als �n the upper pavement. For example, a G2 qual�ty mater�al treated w�th e�ther b�tumen emuls�on or foamed b�tumen can be used �n place of an asphalt base prov�ded �t meets the layer requ�rements, thereby offer�ng s�gn�ficant cost sav�ngs.Improved durability and moisture sensitivity due to the finer part�cles be�ng encapsulated �n b�tumen and thereby �mmob�l�sed.Lower quality aggregates can often be successfully used.

BSM-emulsion

These m�xes may be used for mater�als w�th a low fines content.

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BSM-foam

These m�xes may be produced in bulk and stockpiled close to the po�nt of appl�cat�on, to be placed and compacted at a later stage. Th�s prov�des flex�b�l�ty �n m�x manufactur�ng.

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The typ�cal failure mode of a BSM (permanent deformat�on) �mpl�es that the pavement w�ll requ�re far less effort to rehab�l�tate when the term�nal cond�t�on �s reached compared w�th a mater�al that fa�ls due to full-depth crack�ng. BSMs are not temperature sensitive, unl�ke hot m�x asphalt. Th�s �s because the b�tumen �s not cont�nuous throughout the m�x.

In add�t�on, on pavement rehab�l�tat�on projects where the mater�al �n the ex�st�ng pavement �s recycled �n s�tu w�th b�tumen, the follow�ng benefits accrue:

The process has s�gn�ficant advantages in terms of environmental considerations w�th conservat�on of natural aggregates and a reduct�on �n transport, mater�al wastage, no�se, exhaust, dust em�ss�ons and traffic d�srupt�ons. Where a layer of BSM can be subst�tuted for an asphalt base, s�gn�ficant energy sav�ngs accrue through reduced heat�ng and haulage requ�rements.

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CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Benefits of BSMs

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Unl�ke a hot m�xed asphalt, BSMs are not overly sensitive mater�als. Small var�at�ons �n both the amount of b�tumen added and untreated mater�al propert�es w�ll not s�gn�ficantly change the strength ach�eved through treatment. Th�s allows the �nev�table var�ab�l�ty �n the recycled mater�al to be tolerated.

BSM-emulsion

Layers of BSM-emuls�on may be subjected to traffic within a few hours (after the b�tumen emuls�on �n the upper port�on of the layer breaks).

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BSM-foam

BSM-foam m�xes can be successfully used for treat�ng �n s�tu mater�al w�th a relatively high moisture content.After compact�on, layers of BSM-foam have sufficient strength to be trafficked �mmed�ately w�th l�ttle detr�mental effect.

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Traffic disruption and time delays are minimised by work�ng �n half w�dths and open�ng to traffic soon after complet�on. The construct�on and ma�ntenance of detours �s therefore avo�ded. Pavements show�ng a wide range of distress types can be effect�vely rehab�l�tated.The process eliminates most of the heavy construction traffic that damages newly-constructed layers and adjacent access and serv�ce roads.

Prov�ded they are used under the correct c�rcumstances, the use of BSMs normally result �n s�gn�ficant cost and t�me sav�ngs on a project. However, the overr�d�ng cons�derat�on �n the select�on of projects for b�tumen treatment �s the est�mate of the cost-benefit rat�o. A full econom�c evaluat�on should be carr�ed out, tak�ng �nto account the �nvestment cost, the ma�ntenance costs, the road user costs and the cost of rehab�l�tat�on at the end of the serv�ce l�fe. The env�ronmental benefits �n terms of energy sav�ngs and preservat�on of natural resources are often d�fficult to quant�fy, but should also be cons�dered �n an appropr�ate l�fe-cycle analys�s.

2.4. LIMITATIONS OF BITUMEN STABILISATION The follow�ng concerns need to be addressed when cons�der�ng the use of a BSM on a project:

Economics B�tumen treatment adds s�gn�ficant cost to a project due to the pr�ce of penetrat�on grade b�tumen or b�tumen emuls�on and act�ve filler (�f used), as well as related transport costs. Where sources of alternat�ve construct�on mater�als are close by (e.g. quarr�es), the cost of treat�ng w�th b�tumen compared to other pavement solut�ons may preclude th�s opt�on, espec�ally for lower category roads w�th a structural capac�ty of less than 3 MESA.Design expertise BSMs behave d�fferently from all other pavement mater�als and are not always well understood. One of the dr�v�ng forces beh�nd th�s gu�del�ne �s to prov�de des�gn eng�neers w�th the tools needed to cons�der a BSM as an opt�on �n a pavement structure.Construction expertise B�tumen treatment may be compared w�th other construct�on operat�ons that requ�re attent�on to deta�l (e.g. asphalt manufacture and pav�ng). Operators and superv�sors need spec�al�st tra�n�ng on both the equ�pment and the use of such equ�pment. Much of the requ�red expert�se comes w�th t�me s�nce many control checks are v�sual.

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Benefits of Recycling with BSMs

Environmentally friendly processCan be trafficked soon after compactionTraffic disruption minimisedDoes not requ�re heavy construction traffic

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CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Limitations of BSMs

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BSM-emulsion

Moisture content of in situ material On recycl�ng projects, the total flu�d content of the m�xed mater�al can pose a problem when treat�ng w�th b�tumen emuls�on. Where the mo�sture content of the �n s�tu mater�al �s relat�vely h�gh, add�ng b�tumen emuls�on can �ncrease the total flu�ds content to beyond the zero-vo�ds l�m�t when compact�on energy �s appl�ed. When such a cond�t�on �s encountered, the mater�al cannot be properly compacted.Bitumen emulsion stability The b�tumen emuls�on selected for use on a project must be suffic�ently stable to tolerate the pump and spraybar operat�ng pressure of the appl�cat�on system. Once m�xed w�th the mater�al, however, a qu�ck set �s requ�red to allow the mater�al to ga�n strength. To ensure that the b�tumen emuls�on breaks w�th�n a reasonable t�me per�od, the formulat�on �s cr�t�cal for th�ck layers of BSM-emuls�on (> 150 mm).Bitumen emulsion formulation The use of poorly formulated b�tumen emuls�on has caused problems on some projects. Premature break�ng (flash set) of an unstable b�tumen emuls�on prevents m�x�ng and clogs the m�ll�ng chamber on a recycler. Where the b�tumen emuls�on �s too stable or �ncompat�ble w�th the mater�al, �t may take many months (or even years) to break.

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BSM-foam

Percentage fines Foamed b�tumen requ�res suffic�ent fine part�cles to be present �n the mater�al to fac�l�tate the d�spers�on of the b�tumen. Where the mater�al �s defic�ent �n fines, a poor m�x (character�sed by many b�tumen-r�ch lumps “str�ngers”) w�ll result. For th�s reason, the m�n�mum requ�rement normally spec�fied �s 5% (by mass) pass�ng the 0.075 mm s�eve.Foaming equipment Premature fa�lures have been exper�enced on some projects due to the use of poorly eng�neered systems �ncapable of produc�ng a un�form and cons�stent supply of foamed b�tumen. Incompatibility of water and hot bitumen Foamed b�tumen requ�res spec�al�st equ�pment that has been properly eng�neered. The two l�qu�ds (water and hot b�tumen) used to create the foam are not compat�ble: water does not ex�st �n �ts l�qu�d state above 100 ºC and the grade of b�tumen normally used for foamed b�tumen treatment does not flow at such a low temperature. Unless the system �s des�gned w�th pos�t�ve measures to address th�s �ncompat�b�l�ty, system blockages are �nev�table. The foamed b�tumen system must therefore be properly des�gned and eng�neered to avo�d blockages.

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On recycl�ng projects, other l�m�tat�ons relat�ng to variability of the in situ materials are often encountered. However, such l�m�tat�ons perta�n to all recycl�ng projects and are not spec�fic to b�tumen treatment. The key to solv�ng such var�ab�l�ty problems l�es w�th the des�gn eng�neer and the attent�on to deta�l dur�ng the des�gn �nvest�gat�on and construct�on phases.

2.5. MATERIALS SUITABLE FOR BITUMEN TREATMENT The mater�als to be treated must be su�table for treatment w�th b�tumen emuls�on or foamed b�tumen. The var�ous types of mater�al that can be used successfully for BSMs vary from G1 to G6 qual�ty from cutt�ngs and borrowp�ts (normally �n the G4 to G6 range) or quarr�es (normally �n the G1 to G3 range). In add�t�on, mater�al recla�med from an ex�st�ng road pavement, generally rang�ng from G2 to G6 qual�ty, can also be treated w�th foamed b�tumen or b�tumen emuls�on, e�ther �n s�tu or �n plant.

Examples of mater�al that are usually treated w�th b�tumen are:Crushed stone of all rock types (G1 to G3).Prev�ously untreated (G4 to G6) natural gravels such as andes�te, basalt, chert, d�abase, doler�te, dolom�te, gran�te, l�mestone, nor�te, quartz, sandstone gravels and pedogen�c mater�als such as later�te/ferr�crete.

BSM-emulsion

Calcrete gravels can be successfully treated w�th b�tumen emuls�on.

BSM-foam

Exper�ence has shown that calcrete gravels should not be treated us�ng foamed b�tumen.

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Suitable Materials

Mater�als rang�ng from G1 to G6 qual�ty are su�table for BSMs.

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CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Suitable Materials

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Reclaimed asphalt (RA) mater�al (mostly blended w�th a crushed stone layer or a gravel layer beneath).Recla�med pavement layers compr�sed of previously stabilised crushed stone and/or gravel.Marginal materials, such as sands of G7 qual�ty. These mater�als could be cons�dered when the pract�t�oners have exper�ence w�th such mater�als.

For new construct�on or when �mport�ng new mater�als, the mater�al select�on cr�ter�a are d�ctated by the spec�ficat�on requ�rements to be met for construct�ng the BSM layer and the proposed mater�al must be tested by an accred�ted roads laboratory for compl�ance.

2.6. WHERE TO USE BSMS? As descr�bed above, b�tumen treatment �mproves the shear strength of a mater�al and s�gn�ficantly reduces mo�sture suscept�b�l�ty. These benefits are however, costly and BSMs are therefore best su�ted to upper pavement layers where stresses from appl�ed loads are h�ghest and mo�sture �ngress due to surfac�ng defects are most l�kely to occur.

BSMs have ma�nly been used on pavement rehab�l�tat�on projects where the ex�st�ng pavement structure �s sound (balanced) and d�stress �s confined to the upper layers. Th�s scenar�o �s common where the surfac�ng layer has aged and cracked, allow�ng water to enter the pavement and cause mo�sture-act�vated d�stress �n the underly�ng granular mater�als. Such pavements are �deal for �n s�tu recycl�ng and the b�tumen �s added to restore (and often �mprove) the structural �ntegr�ty before a th�n surfac�ng layer �s appl�ed (asphalt or ch�p seal, depend�ng on the traffic demands). Thus, most BSM projects carr�ed out over the last two decades have been concerned w�th pavement rehab�l�tat�on and upgrad�ng (strengthen�ng and/or w�den�ng) where the �n s�tu mater�al �s recycled. Due ma�nly to escalat�ng costs, a recent trend �s to use good qual�ty mater�al (RA and/or v�rg�n graded crushed stone) treated w�th b�tumen �n spec�al�sed plant as a subst�tute for asphalt base.

Some of the more �mportant factors to be cons�dered when us�ng BSMs are d�scussed below.

2 6 1 CONSTRUCTION METHODB�tumen stab�l�sat�on projects can be constructed �n several ways and the cho�ce of wh�ch way �s best su�ted to a part�cular appl�cat�on �s �nfluenced by several factors, of wh�ch the major ones are:

Size of the project The rehab�l�tat�on of a major h�ghway w�ll demand a d�fferent approach from that used to rehab�l�tate a l�ghtly trafficked res�dent�al street (refer to TRH12)The type of work to be undertaken Rehab�l�tat�on by recycl�ng mater�al from the ex�st�ng pavement w�ll be approached d�fferently from a project where a new lane �s added to an ex�st�ng carr�ageway us�ng v�rg�n aggregates.Geographic and environmental considerations The overall approach to projects located �n mounta�nous reg�ons w�th h�gh seasonal ra�nfall, sub-zero temperatures, steep grad�ents and low geometr�c standards �s d�fferent from a project located �n the m�ddle of a flat, ar�d reg�on.Locality

BSM-emulsion

B�tumen emuls�on �s not always ava�lable �n the v�c�n�ty. In add�t�on, �t can be d�fficult and expens�ve to transport the large amounts of water requ�red to a remote s�te.

BSM-foam

It may be d�fficult and expens�ve to transport hot b�tumen to a remote s�te.

Other factors Some project spec�ficat�ons demand that a certa�n construct�on method must be used (e.g. labour-�ntens�ve).

Treat�ng a mater�al w�th b�tumen emuls�on or foamed b�tumen can be ach�eved �n-plant by feed�ng the mater�al components through a m�x�ng plant or �n s�tu on the road us�ng recycl�ng techn�ques. Where the mater�al �n an ex�st�ng pavement �s su�table for recycl�ng, �n-plant treatment could �nvar�ably be more expens�ve than �n s�tu �n terms of the BSM cost per cub�c metre, pr�mar�ly due to double handl�ng and transport costs. Log�st�cally, where v�rg�n mater�als are to be b�tumen treated, the cost d�fference between �n-plant and �n s�tu treatment w�ll determ�ne the appropr�ate techn�que. Each construct�on method therefore has �ts place �n the construct�on �ndustry and the method adopted on a spec�fic project �s �nfluenced by several factors, the most �mportant be�ng:

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CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Where to Use BSMs

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Type of construction In-plant m�x�ng �s normally cons�dered for new roads, upgrad�ng projects that requ�re add�t�onal structural layers and for labour-�ntens�ve construct�on.Rehabilitation and upgrading projects Where mater�als recycled from the upper layers of an ex�st�ng pavement are to be treated w�th b�tumen, the var�ab�l�ty and/or cond�t�on of the �n s�tu mater�al w�ll normally d�ctate whether a process of select�on and/or pre-treatment �s warranted (for example, s�z�ng th�ck asphalt mater�al). Such techn�cal �ssues may preclude �n s�tu treatment.Traffic accommodation Restr�ct�ons on the accommodat�on of traffic may �nfluence the preferred construct�on method to be adopted on a part�cular project.

Unt�l the m�d-1990s, �n s�tu treatment was undertaken us�ng convent�onal construct�on equ�pment (motor graders, d�sc ploughs and rotavators). Although purpose-bu�lt recycl�ng mach�nes have generally replaced such convent�onal equ�pment, the convent�onal equ�pment rema�ns an opt�on on smaller projects where the cost of establ�sh�ng a large recycler may not always be just�fied.

BSM-emulsion

A cho�ce between these two �n s�tu opt�ons �s only ava�lable to BSM-emuls�on treatment.

BSM-foam

BSM-foam cannot be appl�ed us�ng convent�onal equ�pment and �ts appl�cat�on �s l�m�ted to the use of spec�al�sed foam�ng equ�pment mounted on a recycl�ng mach�ne.

The end spec�ficat�on requ�rements of the BSM layer must however be the same �rrespect�ve of wh�ch construct�on method �s adopted. The qual�ty l�m�tat�ons of us�ng convent�onal equ�pment versus an �n s�tu recycler must be cons�dered when select�ng the construct�on method.

2 6 1 1 In Situ versus In-plant TreatmentIn s�tu treatment saw a phenomenal �ncrease �n popular�ty dur�ng the 1990s due to the advent of modern powerful recycl�ng mach�nes that allow pavements to be rehab�l�tated at a lower cost than convent�onal reconstruct�on. In add�t�on, these mach�nes �ntroduced the capab�l�ty of construct�ng th�ck monol�th�c treated layers, thereby �ncreas�ng the�r structural contr�but�on and allow�ng eng�neers to des�gn more cost-effect�ve pavements.

As a consequence of the deter�orat�ng state of road pavements worldw�de, coupled w�th the huge financ�al �nvestment there�n, the need for the rehab�l�tat�on of ex�st�ng pavements far exceeds the demand for new roads. Th�s s�tuat�on has dr�ven the adopt�on of �n s�tu recycl�ng as a preferred procedure for address�ng the enormous backlog of rehab�l�tat�on requ�red.

In-plant m�x�ng �s an opt�on that should always be cons�dered, part�cularly where new layers of BSMs are to be constructed from v�rg�n mater�als and/or a blend of v�rg�n and recycled mater�als from a stockp�le. The ma�n benefits that accrue from �n-plant m�x�ng compared to �n s�tu treatment are:

Control of input materials In s�tu recycl�ng allows l�ttle control of the mater�al be�ng m�xed. W�th �n-plant recycl�ng, the requ�red end-product can be obta�ned by blend�ng several d�fferent aggregates �n a purpose-bu�lt plant. Input mater�als can be stockp�led and tested pr�or to m�x�ng and the �nput proport�ons determ�ned and changed as requ�red.Quality of mixing Var�ous changes can be made to the m�xer (e.g. adjust�ng the angle of �nd�v�dual paddles �n a pugm�ll type m�xer) to �ncrease the retent�on t�me �n the m�xer, thereby �mprov�ng the qual�ty of the m�xed mater�al.Stockpiling capabilities

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Stockpiling BSM-emulsion

Stockp�l�ng BSM-emuls�on �s not recommended.



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BSM-emulsion

It �s not recommended to stockp�le BSM-emuls�on. Th�s �s because the b�tumen emuls�on tends to leach from the aggregate. The aggregates should rather be pre-blended and held �n stockp�le for m�x�ng w�th the b�tumen emuls�on.

In except�onal c�rcumstances BSM-emuls�on may be stockp�led �f the follow�ng cond�t�ons are met:

The cement content is 1% or less (as recommended for BSM m�xes.The b�tumen emuls�on content �s more than 2%. The stockpile is covered w�th an �mperv�ous blanket to prevent water �ngress and water loss. The m�x �s stockp�led for a maximum of 2 days.The amb�ent temperate does not exceed 30 °C.

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BSM-foam

BSM-foam may be placed �n stockp�le and used when requ�red, thereby remov�ng the �nter-dependency of the m�x�ng process and the construct�on of the new layer. Stockp�le l�fe (the t�me that the m�xed mater�al can rema�n �n stockp�le w�thout los�ng any of �ts propert�es) �s pr�mar�ly a funct�on of mo�sture content and the amount of act�ve filler added to the m�x.

BSM-foam may be kept �n stockp�le for several days prov�ded the follow�ng cond�t�ons are met:

The mater�al �n the stockp�le must remain uncompacted. The he�ght of the stockp�le �s l�m�ted to the max�mum reach of the conveyor or loader used to place the mater�al �n the stockp�le. Veh�cles must not be allowed to dr�ve on the m�xed mater�al to end-t�p.S�nce the �nd�v�dual b�tumen droplets �n a BSM-foam m�x lose the�r adhes�on ab�l�ty when the mater�al dr�es out, the mo�sture content of the mater�al �n the stockp�le must be maintained at approximately the optimum moisture content (OMC) Th�s can be ach�eved by “sheet�ng” the ent�re stockp�le w�th an �mperv�ous blanket. Such a sheet also protects aga�nst ox�dat�on of the b�tumen near the surface of the stockp�le. If no �mperv�ous blanket can be prov�ded, stockp�les of BSM-foam can be kept wet by frequently spray�ng the surface w�th water or spray�ng a fog spray of b�tumen emuls�on over the ent�re stockp�le.

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2 6 2 CLIMATIC CONSIDERATIONSThe follow�ng cl�mat�c cons�derat�ons are �mportant when work�ng w�th BSMs:

BSM-emulsion

BSM-emuls�ons should only be constructed at temperatures exceed�ng 5 °C. At low temperatures, the b�tumen emuls�on may break prematurely result�ng �n a poor m�x. In add�t�on, the lower the temperature, the slower the rate of evaporat�on of the excess mo�sture �n the mater�al.

The mo�sture content of the pre-treated mater�al needs careful cons�derat�on when work�ng �n wet cl�mates. When the b�tumen emuls�on �s added to a mater�al that already has a h�gh mo�sture content, the result�ng flu�d content may be too h�gh for compact�on.

BSM-foam

Temperature affects the foam�ng process. If the temperature of the aggregate �s too low, the foamed b�tumen w�ll not be properly d�spersed �n the m�x. Extra care should therefore be taken when us�ng foamed b�tumen �n cold temperatures, part�cularly when the temperature of the mater�al pr�or to m�x�ng �s between 10 and 15 °C. Foam�ng should not occur at aggregate temperatures below 10 °C.

2 6 3 GENERAL PROJECT SELECTION CRITERIA FOR IN SITU TREATMENTTo date, most BSM projects have been constructed �n s�tu. For many years convent�onal equ�pment has been used for �n s�tu treatment. However, by the end of 2008, more than 50 recycl�ng mach�nes capable of construct�ng BSMs were operat�ng �n the southern Afr�can reg�on. In contrast, few �n-plant m�x�ng un�ts were ava�lable for the product�on of BSM-emuls�on and even fewer capable of produc�ng BSM-foam. Clearly the market �s geared for �n s�tu treatment.



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Although th�s focus on �n s�tu treatment can change, recycl�ng �s l�kely to rema�n the preferred construct�on method for the foreseeable future and �s therefore the centre of attent�on for these gu�del�nes. The follow�ng sect�ons summar�se the ma�n factors that need cons�derat�on when assess�ng the potent�al for us�ng �n s�tu treatment on a pavement rehab�l�tat�on project.

2 6 3 1 Type and Quality of Existing Pavement and MaterialsThe qual�ty of the untreated mater�al largely d�ctates the performance of the treated mater�al. The follow�ng s�tuat�ons that �mpact on the qual�ty of the final m�x should be noted:

Roads with shallow structures result�ng �n poor structural capac�t�es can seldom be adequately rehab�l�tated us�ng only �n s�tu recycl�ng. Where the subgrade CBR �s less than 3%, the use of �n s�tu recycl�ng �s not recommended unless the subgrade �s first �mproved w�th deep, h�gh energy compact�on or adequate cover w�th suffic�ent strength �s prov�ded. The subgrade mater�al should not be m�xed w�th mater�al from the structural layers.If the depth of the pavement structure �s adequate and structural problems are confined to the base layer, then recycl�ng �s a good opt�on and can produce a h�gh-qual�ty base. The recycl�ng process does not d�sturb the mater�al �n a sound pavement layer beneath the recycl�ng hor�zon. Pavements w�th waterbound macadam bases should not be recycled because the coarse grad�ng of such mater�al �s unl�kely to be su�table for BSMs. Pavements w�th severe crocodile cracking �n the asphalt can present problems. If the cracked segments are close to or smaller than the d�stance between the cutt�ng teeth on the recycler, the part�cles may pass through the recycl�ng process w�thout be�ng broken down. The grad�ng so obta�ned may be unsu�table and may requ�re pre-treatment by pre-m�ll�ng (as d�scussed �n Chapter 6). The thicknesses and variability of the layers ava�lable for recycl�ng play a s�gn�ficant role �n determ�n�ng the su�tab�l�ty of the project. Where two or more layers are to be recycled, the relat�ve th�cknesses and mater�al propert�es need to be �dent�fied and the extent of the var�ab�l�ty quant�fied as part of the field �nvest�gat�ons. In some cases, additional material needs to be added to that be�ng recycled to:

Increase the total pavement thickness Reduce variability of the recycled mater�al.Modify the properties (espec�ally the grad�ng) of the recycled mater�al.Prov�de the recycler w�th a working platform that conforms to the final shape requ�rements.

Such mater�al add�t�on �s normally �mported, spread as a layer on the ex�st�ng road surface and precompacted.A problem often encountered w�th �n s�tu recycl�ng �s excessive moisture or var�at�ons �n the mo�sture content of the mater�al recovered from the ex�st�ng road. Th�s needs to be evaluated pr�or to recycl�ng to determ�ne how best �t can be addressed.

2 6 3 2 Geometry of Existing Road and ServicesIn s�tu recycl�ng �s part�cularly useful on rehab�l�tat�on projects where the ex�st�ng road geometry must be reta�ned. Kerb�ng, concrete dra�ns and access ramps �n the urban env�ronment are typ�cal cases where changes �n road level should be avo�ded.

The qual�ty of the mater�al that �s recycled from a pavement w�th layers constructed to d�fferent cambers w�ll vary laterally across the w�dth. Th�s s�tuat�on needs to be recogn�sed and allowances made dur�ng the des�gn process.

Roads w�th large numbers of bur�ed serv�ces and those w�th steel manhole covers requ�re careful plann�ng and prel�m�nary work before recycl�ng can be undertaken. Careful attent�on must be pa�d to the poss�ble presence of steel manhole covers that have been bur�ed by asphalt as these can damage the recycler’s cutt�ng equ�pment.

2.7. DESIGN APPROACH The approach to des�gn�ng BSMs, �n terms of both m�x and structural des�gn, are presented �n th�s sect�on.

2 7 1 DESIGN SEQUENCE The typ�cal des�gn sequence followed �n a BSM project �s �llustrated �n F�gure 2.3. The process beg�ns w�th an �nvest�gat�on �nto the des�gn traffic, the ava�lable mater�als, the pavement structure (for recycl�ng projects) and the cl�mate. Once these parameters are known, the

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Construction Temperatures

BSM-emulsion should only be constructed at ambient temperatures > 5 °C.

BSM-foam should only be constructed at ambient temperatures > 10 °C

Buried Utilities

Roads w�th large numbers of buried services and

those w�th steel manhole covers requ�re careful plann�ng before recycl�ng can be undertaken.



CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Design Approach

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laboratory �nvest�gat�on �nto the mater�als beg�ns. The untreated aggregate �s first �nvest�gated, and �s class�fied to determ�ne the des�gn equ�valent mater�al class. Dur�ng th�s �nvest�gat�on, a prel�m�nary pavement des�gn �s necessary for recycl�ng projects as the depth of recycl�ng and result�ng layer th�ckness d�rectly �nfluence the mater�als used for the laboratory �nvest�gat�on. Follow�ng laboratory test�ng, the m�x des�gn �s done, followed by the final mater�al class�ficat�on. The structural des�gn follows. Should the econom�c analys�s show the des�gn to be �nappropr�ate, the m�x des�gn w�ll be redone or refined.

Figure 2.3 Design Sequence

2 7 2 MATERIAL CLASSIFICATION APPROACHOne of the pr�mary object�ves of th�s gu�del�ne �s to l�nk the m�x and structural des�gn of BSMs w�th the performance of these mater�als, through the�r class�ficat�on. The object�ve of the mater�al class�ficat�on method �s to prov�de a rel�able, rat�onal and cons�stent �nd�cat�on of the appropr�ate mater�al class, us�ng all the ava�lable data. The method attempts to move away from the yes/no type class�ficat�on, where one test can result �n a mater�al be�ng class�fied �n a much lower class than what �ts behav�our suggests. The method class�fies the certa�nty of a mater�al belong�ng to a mater�al class. The mater�al classes are termed des�gn equ�valent mater�al class (DEMAC). A DEMAC denotes a mater�al that exh�b�ts shear strength, st�ffness and flex�b�l�ty propert�es s�m�lar to newly constructed mater�als of the same class. A method for class�fy�ng BSMs �s g�ven �n Chapter 3 and Append�x A.

2 7 3 MIX DESIGN APPROACHThe pr�mary object�ve of the m�x des�gn process �s to create a BSM that �s fit for purpose, whether us�ng b�tumen emuls�on or foamed b�tumen. The cons�derat�ons that need to be accounted for �n the m�x des�gn �nclude:

Investigation

Laboratory Tests

Mix Design Material Classification

Pavement Design

Economic Analysis

Traffic Materials Pavement Climate

Preliminary Material ClassificationAggregate Selection

Investigation

Laboratory Tests

Mix Design Material ClassificationMix Design Material Classification

Pavement Design

Economic Analysis

Traffic Materials Pavement ClimateTraffic Materials Pavement Climate

Preliminary Material ClassificationAggregate Selection


CHAPTER 2: Bitumen Stabilisation, Usage and Design Approach – Classification of BSMs

14

Understand�ng the primary mode of failure by wh�ch the performance of a mater�al may be defined, �s �t durab�l�ty, permanent deformat�on, or some other mechan�sm?Ident�fy�ng the most appropriate laboratory tests to s�mulate the key performance cr�ter�a and fa�lure mechan�sms.Ident�fy�ng key mix properties and �ntr�ns�c material properties that can �nfluence performance. For example, gradat�on of aggregate, hardness of aggregate and b�tumen content.Tak�ng account of variability, cons�der�ng that many BSMs are prepared from recycled and reused mater�als w�th s�gn�ficantly var�able propert�es, such as percentage of RA and degree of weather�ng.Tak�ng account of the environmental factors that �nfluence the cond�t�on�ng of the mater�al and thus �ts performance, e.g. cl�mate (espec�ally temperature and mo�sture), pavement type and permeab�l�ty. These factors �nfluence the cur�ng rate and equ�l�br�um mo�sture cond�t�ons, and need to be cons�dered for short, med�um and long term effects.Effect�ve simulation of field compaction procedures �n the laboratory for the preparat�on of spec�mens for evaluat�on. Th�s �s espec�ally �mportant g�ven that current roller technology has taken the opt�m�sat�on of field dens�t�es to new levels.

The outcome from the m�x des�gn process largely depends on:The design traffic that needs to be accommodated.The quality of available material Cost considerations and budget constra�nts.

In terms of the select�on of an appropr�ate m�x compos�t�on, the opt�mum b�tumen content �s not necessar�ly selected to prov�de the peak mater�al strength, but rather to sat�sfy m�n�mum requ�rements w�th regard to m�x propert�es, for example, strength, st�ffness and durab�l�ty �nclud�ng res�stance to mo�sture. Cons�derat�on of predom�nantly strength cr�ter�a leads to the des�gn of br�ttle, �nflex�ble m�xes that are suscept�ble to crack�ng. Durab�l�ty cons�derat�ons, on the other hand, lead to adjud�cat�on of m�n�mum b�tumen contents to sat�sfy mo�sture res�stance requ�rements, wh�ch automat�cally sat�sfy the flex�b�l�ty needs. M�x compos�t�on select�on cr�ter�a that cons�der the des�gn traffic and the qual�ty of the untreated aggregate are prov�ded as part of the mater�al class�ficat�on system (Chapter 3).

2 7 4 STRUCTURAL DESIGN APPROACHThe purpose of structural pavement des�gn �s to make an unb�ased, rat�onal est�mate of the structural capac�ty of layered pavement systems. Such est�mates allow the unb�ased compar�son of alternat�ve des�gns dur�ng the structural and econom�c analyses. If the structural capac�ty of a spec�fic des�gn �s under- or overest�mated �n relat�on to the structural capac�ty of alternat�ve des�gns, that part�cular des�gn w�ll be unfa�rly penal�sed or promoted dur�ng the econom�c analys�s. A structural des�gn method that assesses the structural capac�ty of d�fferent pavement types accord�ng to the same set of rules �s prov�ded �n th�s gu�del�ne.

A pavement des�gn method has been developed for BSMs, but �s �n fact appl�cable to most pavement mater�als used �n southern Afr�ca. The method, called the Pavement Number (PN), �s an emp�r�cal method based on accepted pavement des�gn rules and uses a pavement �ndex approach. The method was developed w�th data from well-establ�shed catalogues of des�gn, long-term pavement performance data and Heavy Veh�cle S�mulator test sect�ons. Data from over twenty pavement sect�ons were used. The use of these field data, and the coarseness of the data, precluded the development of mechan�st�c-emp�r�cal des�gn models.

The structural des�gn of BSMs �s d�scussed further �n Chapter 5. The approach to structural des�gn �n th�s gu�del�ne �s complementary to TRH4 and TRH12. In conjunct�on w�th those gu�del�nes, the des�gner should ensure that all relevant aspects of pavement des�gn are �nvest�gated.

2.8. CLASSIFICATION OF BSMS BSMs are class�fied �nto three classes, depend�ng on the qual�ty of the parent mater�al and the des�gn traffic. The three classes are:

BSM1: Th�s mater�al has a h�gh shear strength, and �s typ�cally used as a base layer for des�gn traffic of more than 6 MESA. For th�s class of mater�al, the source mater�al �s typ�cally a well graded crushed stone or recla�med asphalt (RA). BSM2: Th�s mater�al has moderately h�gh shear strength, and �s typ�cally used as a base layer for des�gn traffic appl�cat�ons of less than 6 MESA. For th�s class of mater�al, the source mater�al would typ�cally be a graded natural gravel or RA.BSM3: Th�s mater�al typ�cally cons�sts of so�l-gravel and/or sand, stab�l�sed w�th h�gher b�tumen contents. As a base layer, the mater�al �s only su�table for des�gn traffic appl�cat�ons of less than 1 MESA.

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CHAPTER 3: Material Classification – Concept

15

3 MATERIAL CLASSIFICATIONThe mater�al class�ficat�on system prov�des a cr�t�cal l�nk between the m�x and structural des�gn, and construct�on qual�ty control checks. The determ�nat�on of mater�al classes for each pavement layer �s a cr�t�cal aspect of the structural des�gn process, s�nce th�s process effect�vely determ�nes the structural des�gn �nputs. In th�s chapter, a method for class�fy�ng mater�als �s presented. The object of the method �s to prov�de a rel�able, rat�onal and cons�stent �nd�cat�on of the appropr�ate mater�al class. The system can be used for all mater�als common �n southern Afr�ca and �n all pavement des�gn contexts. However, the method �s part�cularly appropr�ate for rehab�l�tat�on, spec�fically recycl�ng, as the qual�ty of the ex�st�ng mater�al �s not typ�cally eng�neered, but must be well character�sed.

The sect�ons below descr�be the method �n more deta�l and prov�de all relevant deta�ls for class�ficat�on of BSMs. The mater�al class�ficat�on system has not yet been formally publ�shed �n a gu�del�ne, and �s therefore descr�bed �n full �n Append�x A for BSMs, granular and cemented mater�als.

3.1. CONCEPTMany mater�al class�ficat�on methods are spec�ficat�on type approaches that rely on pass or fa�l type cr�ter�a. For these types of approaches, �f any one test fa�ls the cr�ter�a for the mater�al class then the mater�al cannot be class�fied �n that class. For example, �f the ITS value �s below the spec�ficat�on for a BSM1 mater�al, then the mater�al cannot be class�fied as a BSM1 even �f all other ava�lable test results do meet the BSM1 cr�ter�a.

The concept underly�ng the mater�al class�ficat�on system �s to use all ava�lable mater�al �nformat�on to g�ve a cons�stent, rat�onal and object�ve assessment of a mater�al class. The system g�ves a hol�st�c assessment, wh�ch works best when a comprehens�ve range of test �nd�cators are used. Th�s approach �s more rat�onal, albe�t less exact and can handle vagueness �n the data. Rather than g�v�ng a yes or no answer, the method �nd�cates the conformance to a mater�al class �n less restr�ct�ve terms. The approach assoc�ates a certa�nty that the mater�al can be cons�dered as a part�cular mater�al class, and uses Fuzzy Log�c and Certa�nty Theory to prov�de th�s type of assessment.

The result of the mater�al class�ficat�on process �s a Des�gn Equ�valent Mater�al Class (DEMAC). A DEMAC denotes a mater�al that exh�b�ts shear strength, st�ffness, durab�l�ty and flex�b�l�ty propert�es s�m�lar to a newly constructed mater�al of the same class. The DEMAC �mpl�es that the mater�al may not meet exact spec�ficat�ons for a part�cular mater�al class, but �n terms of expected behav�our the mater�al �s s�m�lar.

3.2. MATERIAL CLASSIFICATION SYSTEMThe mater�al class�ficat�on system for BSMs ass�gns a mater�al to one of four mater�al classes, and determ�nes the certa�nty that the mater�al can be represented by that DEMAC. The follow�ng mater�al classes (as defined �n Sect�on 2.8) are used:

BSM1BSM2BSM3 Unsu�table for treatment w�th b�tumen emuls�on or foamed b�tumen.

The DEMAC does not d�fferent�ate between BSM-emuls�on and BSM-foam.

The method works by determ�n�ng, for each test result ava�lable, the certa�nty that the mater�al falls �nto each of the four mater�al classes. Th�s �s done by us�ng the 10th percent�le, med�an and 90th percent�le of all the results from the spec�fic test, as �llustrated �n F�gure 3.1 for the DCP penetrat�on and ITS. The blue l�nes represent the 10th and 90th percent�les and the red dot the med�an. The certa�nty that a mater�al belongs to a part�cular DEMAC �s dependant on how much of the data falls �nto that class. The spec�fic deta�ls of the calculat�on are g�ven �n Append�x A. Us�ng F�gure 3.1 as an example, the DCP suggests that the mater�al �s e�ther a des�gn equ�valent BSM2 (DE-BSM2) or des�gn equ�valent BSM3 (DE-BSM3), and the ITS suggests a DE-BSM1, DE-BSM2 or DE-BSM3.

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Design Equivalent Material Class (DEMAC)

A DEMAC denotes a mater�al that exh�b�ts shear strength, st�ffness and flex�b�l�ty propert�es s�m�lar to newly constructed mater�al of the same class.

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Software

Software to determ�ne a DEMAC, and a template for data preparat�on are ava�lable on www.asphaltacademy.co.za/b�tstab

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CHAPTER 3: Material Classification – Tests and Interpretation

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Test or IndicatorMaterial Class

BSM1 BSM2 BSM3 Unsuitable

DCP Penetrat�on (mm/blow)

< 3.7 3.7 to 9.1 9.1 to 19.0 < 19.0

ITS (kPa)

> 100 75 to 100 50 to 75 < 50

Figure 3 1 Interpretation of Test and Indicator Results

Because most pavement mater�als tests prov�de only a part�al �nd�cat�on of the mater�al behav�our, each test �s ass�gned a certa�nty factor. Th�s certa�nty factor (CF) represents the subject�ve confidence �n the ab�l�ty of a test to serve as an accurate �nd�cator for mater�al strength and st�ffness �n the pavement layer. The value of CF ranges from 0 to 1, w�th a value of 1 �nd�cat�ng absolute confidence �n a test or �nd�cator (h�ghly unl�kely).

Us�ng the spread of data for each test, and the certa�nty factor, the cumulat�ve certa�nty that a mater�al falls �nto one of the four mater�al classes �s calculated. The more tests ut�l�zed, the h�gher the cumulat�ve certa�nty. The deta�ls of th�s calculat�on are g�ven �n Append�x A. The method can be done us�ng a spreadsheet. However, to make �t eas�er to ut�l�se, software to perform the mater�al class�ficat�on and a template for data preparat�on are ava�lable on www.asphaltacademy.co.za/b�tstab.

3.3. TESTS AND INTERPRETATION OF RESULTS FOR BSMSThe tests that are used for the mater�al class�ficat�on, �nterpretat�on of the test results and certa�nty factors for BSMs are prov�ded �n th�s sect�on. The values shown for the tests �ncluded �n th�s gu�del�ne were the values used at the t�me of publ�cat�on of the gu�del�ne. Although these values were well val�dated, �t may be necessary from t�me to t�me to make changes to �mprove the system. If changes are made, the mod�fied values w�ll be reflected on www.asphaltacademy.co.za/b�tstab. It �s recommended that before commenc�ng the mater�al class�ficat�on process, the webs�te �s checked for any changes �n values or tests.

The class�ficat�on for BSMs �s �ntended to assess the su�tab�l�ty of the mater�al for BSM treatment. It therefore assesses the mater�al based on many of the same tests and �nd�cators used for granular mater�als, represent�ng the mater�al before treatment, and then evaluates the BSM m�x us�ng tests from the m�x des�gn process. Although some of the l�m�ts �n the tests are d�fferent for BSM-emuls�on and BSM-foam, �n the final class�ficat�on no d�st�nct�on �s made between the two mater�als.

The �nd�cators and tests for the class�ficat�on of BSMs are deta�led �n Table 3.1 and the relevance of the test or �nd�cator �s expla�ned. The �nterpretat�on of the test results and actual l�m�ts used for each test are prov�ded �n Table 3.2. The �nterpretat�on of grad�ng requ�res the determ�nat�on of a rat�ng, wh�ch �s deta�led �n Table 3.3 and F�gure 3.2. F�gure 3.2 �s a repeat of F�gure 4.2 �n Chapter 4.

Test and Indicator Limits

www.asphaltacademy.co.za/b�tstab Conta�ns the most up to date limits and certainty factors for the selected tests and �nd�cators.

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Table 3 1 Indicators and Tests for Classification of Bitumen Stabilised Materials

Test or Indicator Relevance for Material ClassificationInterpret or Rating

Soaked CBR (untreated) When soaked, tests ma�nly the fr�ct�onal strength component of shear strength. Table3.2

Percent pass�ng 0.075 mm s�eve (F�nes)(untreated)

Impacts on the dens�ty that can be ach�eved, b�tumen content and on the bear�ng strength of the mater�al. As such, relates ma�nly to fr�ct�onal component of shear strength. Table3.2

Relat�ve Dens�ty (untreated)

Relates to the dens�ty of pack�ng of part�cles, and hence to the potent�al to develop fr�ct�onal res�stance.

Table3.2

DCP Penetrat�on (untreated)

Ind�cator for overall shear strength. Sens�t�ve to dens�ty, mo�sture content, part�cle strength, grad�ng and plast�c�ty.

Table3.2

FWD Backcalculated St�ffness (untreated)

Prov�des a d�rect but relat�ve �nd�cat�on of the st�ffness under dynam�c load�ng. L�kely to be h�ghly correlated to shear strength at small stra�ns for most mater�als.

Table3.2

Plast�c�ty Index (untreated)

Determ�nes the �nfluence of water on shear strength. For a fixed max�mum aggregate s�ze, shear strength �s greatly reduced w�th an �ncrease �n PI.

Table3.2

Relat�ve Mo�sture Content (untreated)

The relat�ve mo�sture content �s the measured mo�sture content, relat�ve to the opt�mum mo�sture content for the mater�al.

Table3.2

Grad�ng Assessment Rat�ng (untreated)

Rat�ng quant�fies the conformance of the mater�al grad�ng to appl�cable spec�ficat�ons. Good conformance to grad�ng �nd�cates �ncreased fr�ct�onal res�stance.

Table3.3F�gure 3.2

Grad�ng Modulus (untreated)

Quant�fies the relat�ve amount of fines �n the mater�al. As such, �t �nfluences the ab�l�ty of the mater�al to develop �nterlock between coarse part�cles.

Table3.2

Cohes�on, Fr�ct�on angle and Tangent Modulus (treated)

The shear parameters and mater�al st�ffness from tr�ax�al test�ng prov�de cr�t�cal performance propert�es related to res�stance to permanent deformat�on. Table3.2

ITS (treated)Prov�des a reference to the h�stor�c performance of m�xes (ITSdry and ITSequ�l) and a measure of mo�sture res�stance (ITSwet).

Table3.2

UCS (treated)Prov�des a measure of the compress�ve strength of m�xes, and a reference to the h�stor�c performance of m�xes.

Table3.2

Reta�ned Cohes�on (MIST) (treated)

The change �n cohes�on after mo�sture cond�t�on�ng from tr�ax�al test�ng prov�des a measure of mo�sture res�stance.

Table3.2



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Table 3 2 Interpretation of Indicators and Tests for Classification of Bitumen Stabilised Materials

Test or Indicator Material1Design Equivalent Material Class Not suitable

for treatmentCF

BSM1 BSM2 BSM3

Soaked CBR (%)CS (98%) > 80 25 to 80 10 to 25 < 10

0.4NG (95%) > 25 10 to 25 < 10

P0.075 (%)(B�tumen emuls�on)

CS 4 to 15 > 15

0.35

NG 5 to 25 25 to 40 > 40

GS 5 to 20 15 to 30 > 30

SSSC 0 to 20 > 20

P0.075 (%)(Foamed b�tumen)

CS 2 to 15 > 15

NG 11 to 25 23 to 40 > 40

GS 0 to 20 13 to 30 > 30

SSSC 0 to 20 > 20

Relat�ve dens�ty All > 0.98 0.95 to 0.98 0.93 to 0.95 < 0.93 0.1

DCP Pen (mm/blow) All < 3.7 3.7 to 9.1 9.1 to 19.0 > 19.0 0.1

FWD Backcalculated St�ffness (MPa)

All > 300 150 to 300 70 to 150 < 70 0.1

Plast�c�tyIndex

CS < 10 > 10

0.25NG <6 6 to 12 > 12

GS > 11 11 to 15 < 15

SSSC < 15 > 14

Relat�ve mo�sture (%)

CS < 90 > 90

0.1NG < 70 70 to 100 < 80

GS > 100 80 to 100 < 100

SSSC > 100 > 100

Grad�ng modulusNG 2.0 to 3.0 1.2 to 2.7 0.15 to 1.2 0.15

0.2GS 1.2 to 2.5 0.75 to 2.7 < 0.75

Cohes�on (kPa) All > 250 100 to 250 50 to 100 < 50 0.45

Fr�ct�on Angle (°) All > 40 30 to 40 < 30 0.4

Tangent Modulus (MPa) All > 150 50 to 150 < 50 0.1

ITS (kPa)

Dry, 100 mm 2

> 225 175 to 225 125 to 175 < 125 0.1

Equ�l�b, 150 mm

> 175 135 to 175 95 to 135 < 95 0.2

ITS (wet) kPa) 100 mm > 100 75 to 100 50 to 75 < 50 0.1

UCS (kPa) All 1 200 to 3 500 700 to 1 200 450 to 700 < 450 0.1

Reta�ned cohes�on after MIST (%) All > 75 60 to 75 50 to 60 < 50 0.45

Rat�ng All 0.5 to 1.5 1.5 to 2.5 2.5 to 3.5 3.5 to 4.5 N/A

Notes:CS = crushed stone, NG = natural gravel, GS = gravel so�l, SSSC = sand, s�lty sand, s�lt, clay; 98%, 95%, 93%, 90% are Mod. AASHTO dens�t�es.D�ameter of spec�men.

1.

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Table 3 3 Interpretation of Grading Rating for BSMs

Test or Indicator Material1Rating

CF1 2 3 4

Grad�ng (see F�gure 3.2)

CS Ideal Less su�table Marg�nal

0.4NG Ideal Less su�table Marg�nal

GS Ideal Less su�table Marg�nal

Sieve Size (mm)

Percent Passing

BSM-Emulsion BSM-Foam

Ideal Less suitable Ideal Less suitable

50 100 100

37.5 87 – 100 87 – 100

26.5 77 – 100 100 77 – 100 100

19.5 66 – 99 99 – 100 66 – 99 99 – 100

13.2 67 – 87 87 – 100 67 – 87 87 – 100

9.6 49 – 74 74 – 100 49 – 74 74 – 100

6.7 40 – 62 62 – 100 40 – 62 62 – 100

4.75 35 – 56 56 – 95 35 – 56 56 – 95

2.36 25 – 42 42 – 78 25 – 42 42 – 78

1.18 18 – 33 33 – 65 18 – 33 33 – 65

0.6 12 – 27 27 – 54 14 – 28 28 – 54

0.425 10 – 24 24 – 50 12 – 26 26 – 50

0.3 8 – 21 21 – 43 10 – 24 24 – 43

0.15 3 – 16 16 – 30 7 – 17 17 – 30

0.075 2 – 9 9 – 20 4 – 10 10 – 20

The d�fferences between the grad�ng zones of BSM-emuls�on and BSM-foam are small enough that the d�fferences cannot be d�scerned on the figure.

Figure 3.2 Interpretation of Grading to Quantify Relative Conformance to Grading (BSM)


CHAPTER 3: Material Classification – Confidence

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3.4. CONFIDENCE ASSOCIATED WITH ASSESSMENTThe confidence �n the certa�nty assoc�ated w�th the mater�al classes depends on the number of tests or �nd�cators used and the certa�nty factors assoc�ated w�th these tests and �nd�cators. The strength of confidence �n the assessment �s thus quant�fied by the certa�nty of the assessment, and th�s �s an �nd�rect �nd�cator of the rel�ab�l�ty of any des�gn based on th�s assessment. Table 3.4 prov�des some gu�del�nes to assess the confidence assoc�ated w�th the mater�al class�ficat�on.

Table 3 4 Relative Confidence of Materials Classification

Cumulative Certainty Confidence in Classification

< 0.3Very low confidence. It �s strongly recommended that more data be gathered to enable a more confident assessment to be made.

0.3 to 0.5Low confidence. Su�table only for s�tuat�ons where the ex�st�ng pavement cond�t�on and age �s such that structural rehab�l�tat�on w�ll not be cons�dered, or �s very unl�kely.

0.5 to 0.7Medium. Su�table or s�tuat�ons where the ex�st�ng pavement cond�t�on and age �s such that structural rehab�l�tat�on �s unl�kely, or for wh�ch the cond�t�on and/or other factors predeterm�nes the treatment type.

> 0.7High. Th�s �s the m�n�mum recommended certa�nty for s�tuat�ons where structural rehab�l�tat�on �s l�kely, and for wh�ch the rehab�l�tat�on des�gn w�ll rely completely on the qual�ty and state of ex�st�ng pavement layers.



CHAPTER 4: Mix Design – Requirements

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4 MIX DESIGNThe m�x des�gn of B�tumen Stab�l�sed Mater�als (BSMs) �s part�cularly challeng�ng due to the number and types of �ngred�ents that compr�se these mater�als. Each component mater�al, �nclud�ng aggregate, water, b�tumen and act�ve filler, w�th �ts own var�ab�l�ty, ava�lab�l�ty and cost, needs to be blended and processed to formulate a compos�te product for a spec�fic purpose or appl�cat�on. To produce construct�on mater�als w�th the necessary qual�ty and cons�stency to fulfil the�r �ntended funct�on, sound procedures need to be followed that ass�st �n �dent�fy�ng opt�mal formulat�on, blend�ng and product�on. Th�s process �s the m�x des�gn procedure.

The BSM m�x des�gn procedure requ�res opt�m�sat�on not only �n terms of volumetr�c and compact�on character�st�cs, but also requ�res the cons�derat�on of eng�neer�ng propert�es and durab�l�ty. It �s thus essent�al that the mater�al samples used dur�ng the m�x des�gn be representat�ve of the mater�als �n the layer or layers that w�ll be treated w�th b�tumen. At the same t�me, econom�c cons�derat�ons rema�n paramount �n the determ�nat�on of m�x des�gns. The b�tumen contr�butes s�gn�ficantly to the cost of BSMs, underly�ng the need for effect�ve opt�m�sat�on of b�tumen content.

Th�s chapter deals w�th the m�x des�gn procedure of BSMs, and �ncludes all the deta�ls necessary for perform�ng and evaluat�ng a m�x des�gn.

All test methods referred to �n th�s gu�del�ne are expl�c�tly referenced �n Append�x B. Where test methods cannot be found �n standard manuals, such as THM1, the methods have been comp�led and are on www.asphaltacademy.co.za/b�tstab from where they can be downloaded. It �s adv�sable to always check the webs�te to ensure the most up to date test method �s used.

4.1. MIX DESIGN REQUIREMENTS The complex behav�our of BSMs allows the mater�als eng�neer to des�gn a product best su�ted to the part�cular des�gn cond�t�ons. By chang�ng the m�x proport�ons of the aggregate, b�tumen and act�ve filler �t �s poss�ble to create a m�x w�th behav�our that w�ll approach the behav�our of granular mater�als, cemented mater�als or hot-m�x asphalt.

There are two fundamental fa�lure mechan�sms that need to be des�gned for �n the m�x des�gn, namely:

Permanent Deformation Th�s �s accumulated shear deformat�on w�th load�ng and �s dependent on the mater�al’s shear propert�es and dens�ficat�on ach�eved. Res�stance to permanent deformat�on (rutt�ng) �s enhanced by:

Improved aggregate angularity, shape, hardness and roughness.Increased maximum particle size.Improved compaction.Reduced moisture content (cur�ng).Add�t�on of a limited amount of bitumen, usually less than 3.5% because h�gher b�tumen contents encourage rutt�ng.Add�t�on of active filler, usually l�m�ted to a max�mum of 1% because h�gher act�ve filler contents create br�ttleness wh�ch encourages shr�nkage and traffic assoc�ated crack�ng.

Moisture Susceptibility The presence of water �n BSMs, as well as the part�ally coated nature of the aggregate makes mo�sture suscept�b�l�ty an �mportant cons�derat�on �n evaluat�on of mater�al performance. Mo�sture suscept�b�l�ty �s the damage caused by exposure of a BSM to h�gh mo�sture contents and pore-pressures, caused by traffic. Th�s results �n loss of adhes�on between the b�tumen and the aggregate. Mo�sture res�stance �s enhanced by:

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Mix Design Process

The m�x des�gn process a�ms to opt�m�se the m�x for

permanent deformat�on, mo�sture suscept�b�l�ty and durab�l�ty.BSMs.

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Laboratory Test Methods

All the laboratory test methods referred to �n th�s gu�del�ne are e�ther ava�lable �n standard manuals or are ava�lable for download onwww.asphaltacademy.co.za/b�tstab.

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Mix Design

The procedure opt�m�ses the mater�als used, and

determ�nes the b�tumen content to max�m�se the performance, w�th due cons�derat�on of the cost.

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Mix Constituents

Aggregate propert�es dom�nate rut res�stance.

B�tumen content �nfluences durab�l�ty.

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Increased bitumen content, bear�ng �n m�nd the cost �mpl�cat�ons and potent�al for permanent deformat�on.Add�t�on of active filler, usually l�m�ted to 1% by mass of dry aggregate.Improved compaction.Smooth cont�nuous grading.

4 1 1 MIX TYPE SELECTIONThe type of BSM m�x that �s selected for a part�cular des�gn �s largely governed by:

The design traffic that has to be accommodated.The qual�ty of the aggregate that �s ava�lable.Economic considerations

The three ma�n factors that �nfluence the b�tumen and act�ve filler select�on dur�ng m�x des�gn, are:Traffic, both volumes and veh�cle loads.Climate, part�cularly the mo�sture cons�derat�ons.Supporting layers, whether weak or st�ff.

As shown �n F�gure 4.1, a very �mportant factor �nfluenc�ng b�tumen content select�on �s mo�sture sens�t�v�ty and �ts �nfluence on durab�l�ty. Increas�ng the b�tumen content reduces the mater�al’s mo�sture suscept�b�l�ty, and �ncreases flex�b�l�ty allow�ng the pavement to carry more traffic on weaker support.

Where m�xes have more than 1% cement, the add�t�on of b�tumen seldom prov�des add�t�onal benefits. It �s therefore recommended that m�xes conta�n�ng more than 1% cement are cons�dered cement treated mater�als, and the gu�del�ne (TRH13) for the�r use should be followed. Therefore, th�s gu�del�ne �s appl�cable to BSMs conta�n�ng a max�mum of 1% cement.

Hydrated l�me �s often used as an act�ve filler (d�scussed �n Sect�on 4.2.3), espec�ally where the untreated mater�al �s plast�c. In such cases, the hydrated l�me content may exceed 1% �f d�ctated by the l�me demand (In�t�al consumpt�on of l�me, ICL).

It �s recommended that the b�tumen content exceeds the act�ve filler content, to ensure the benefits of b�tumen treatment are ach�eved.

Figure 4.1 Factors Influencing Bitumen and Active Filler Content Selection

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Hea

vyTR

AFF

IC

SUPPORT

CLIMATE

Ligh

t

Stiff

Weak/wet

Increasing Bitumen

Dry

Wet

Hea

vyTR

AFF

IC

SUPPORT

CLIMATE

Ligh

t

Stiff

Weak/wet

Increasing Bitumen

Dry

Wet



23

4 1 2 OUTLINE OF MIX DESIGN PROCEDURECons�der�ng the number of var�ables that need to be addressed �n the m�x des�gn and the amount of mater�al requ�red to �nvest�gate these var�ables, the m�x des�gn procedure �nvolves several steps and one or more ser�es of tests (levels), depend�ng on the magn�tude of des�gn traffic. The m�x des�gn procedure always starts by test�ng the mater�al to be treated (prel�m�nary tests) to determ�ne whether �t �s su�table for treat�ng w�th b�tumen and, �f not, the type of pre-treatment or blend�ng requ�red to make �t su�table. Follow�ng th�s, the actual m�x des�gn procedure commences w�th an �n�t�al ser�es of tests (Level 1 M�x Des�gn) that prov�des an �nd�cat�on of the appl�cat�on rate of b�tumen and act�ve filler (�f necessary) requ�red to ach�eve an �nd�cated class of BSM. Thereafter, depend�ng on the des�gn traffic, add�t�onal tests are undertaken to refine the appl�cat�on rate of b�tumen and ga�n confidence �n the performance potent�al of the treated mater�al (mater�al class�ficat�on). These are the Level 2 and Level 3 M�x Des�gns. In summary, the m�x des�gn procedure cons�sts of:

Preliminary tests: These �nclude standard laboratory tests to determ�ne the grad�ng curve, mo�sture, dens�ty relat�onsh�ps and Atterberg l�m�ts. Where the results �nd�cate that some form of pre-treatment �s requ�red, add�t�onal tests must be undertaken after such pre-treatment to ensure that the des�red result was ach�eved. Level 1 Mix Design: Level 1 starts w�th the preparat�on of samples that w�ll be used to manufacture the spec�mens requ�red for all levels of m�x des�gn test�ng. 100 mm d�ameter spec�mens (Marshall br�quettes) are compacted and cured for Ind�rect Tens�le Strength (ITS) test�ng. Test results are used to:

Ident�fy the preferred bitumen stabilising agent.Determ�ne the opt�mum bitumen content Ident�fy the need for filler, and, where requ�red, the type and content of filler.

Level 1 m�x des�gn �s suffic�ent for l�ghtly trafficked pavements, wh�ch w�ll carry less than 3 MESA.

Level 2 Mix Design: Th�s level uses 150 mm d�ameter by 127 mm h�gh spec�mens (Proctor spec�mens) manufactured us�ng v�bratory compact�on, cured at the equ�l�br�um mo�sture content and tested for Ind�rect Tens�le Strength to:

Optimise the requ�red bitumen content.

Th�s level �s recommended for roads carry�ng 3 to 6 MESA.

Level 3 Mix Design: Th�s level uses tr�ax�al test�ng on 150 mm d�ameter by 300 mm h�gh spec�mens for a h�gher level of confidence. Th�s step �s recommended for des�gn traffic exceed�ng 6 MESA.

The deta�ls of the m�x des�gn procedure for each level are g�ven �n Sect�on 4.5.

4.2. MIX CONSTITUENTS

4 2 1 AGGREGATE B�tumen treatment, us�ng e�ther b�tumen emuls�on or foamed b�tumen, �s su�table for treatment of a w�de range of m�neral aggregates, rang�ng from sands, through weathered gravels to crushed stone. Aggregates of sound and marg�nal qual�ty, from both v�rg�n and recycled sources have been successfully ut�l�sed �n the process. It �s �mportant, however, to establ�sh the boundar�es of aggregate acceptab�l�ty, as well as to �dent�fy the opt�mal aggregate compos�t�on for b�tumen treatment, recogn�s�ng d�fferences between BSM-emuls�on and BSM-foam.

The aggregate propert�es requ�red for successful treatment w�th b�tumen �nclude durab�l�ty character�st�cs of the natural (untreated) aggregate, as well as plast�c�ty, grad�ng, spat�al compos�t�on and weather�ng character�st�cs.

The recommendat�ons of TRH4 and TRH14 for granular mater�als are generally appl�cable to granular mater�als to be treated w�th b�tumen.

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Cement Contents

The cement content of BSMs should be ≤ 1%, and

the cement content should not exceed the b�tumen content.


CHAPTER 4: Mix Design – Mix Constituents

24

4 2 1 1 Aggregate Sourcei Virgin AggregateM�neral aggregates selected for BSMs should generally meet the qual�ty requ�rements of G1 to G6 mater�als (TRH14), depend�ng on the levels of traffic. Poorer qual�ty gravels, for example G7 and lower, are seldom used and, where they are, generally only used for low levels of traffic, BSM3. Spec�fic l�m�ts for tests and �nd�cators for the mater�al class of aggregates for BSM are g�ven �n Table 3.1 �n Sect�on 3.3.

Soaked CBR.Percentage passing the 0 075 mm sieve (fines). H�gher filler contents create h�gher b�tumen demands, due to the �ncreased surface area of part�cles. The fines content of BSMs �s cons�dered to be very �mportant, and �s d�scussed �n Sect�on 4.2.1.3. Plasticity Index. Plast�c�ty �s ma�nly attr�buted to the fine fract�on of the aggregate. Mater�als w�th a h�gh PI can be treated w�th l�me or other act�ve fillers before treatment w�th b�tumen.

BSM-emulsion

The PI of mater�als to be treated w�th b�tumen emuls�on should be less than 7.

BSM-foam

The PI of mater�als to be treated w�th foamed b�tumen should be less than 10.

Grading. The grad�ng of the mater�al be�ng treated requ�res careful cons�derat�on. S�eve analyses carr�ed out on representat�ve samples, taken from the layers �n the case of an ex�st�ng road or from the mater�al source for a new road, w�ll �nd�cate defic�enc�es �n the fines or filler content. Cohes�ve mater�als should be treated w�th care as wet-grad�ng tests may �nd�cate a h�gh percentage of mater�al pass�ng the 0.075 mm s�eve, wh�lst the loose filler ava�lable dur�ng full-scale m�x�ng may be less. Th�s occurs when the cohes�ve filler b�nds �tself together, render�ng th�s fract�on unava�lable for the b�tumen emuls�on or foamed b�tumen to react w�th. A compar�son of the washed and unwashed grad�ng test carr�ed out �n the laboratory can be used to �nd�cate the l�kel�hood of cohes�on prevent�ng the filler from be�ng released. The unwashed grad�ng prov�des an �nd�cat�on of the ava�lable filler.

A defic�ency �n filler content can be addressed by add�ng add�t�onal fines or by add�ng act�ve filler.

ii Recycled Granular LayersIn the case of recycled mater�als, the qual�ty and compos�t�on of the aggregates can be h�ghly var�able and w�ll depend upon:

The structure of the existing pavement (mater�als and the�r th�ckness).Construct�on variability (mater�al qual�ty and th�ckness).Depth of recycling.Age of the pavement (part�cularly for prev�ously treated mater�als and mater�als prone to weather�ng).Degree of patching and repair on the ex�st�ng pavement.Th�ckness and nature of old surfac�ng seals.

The pulver�zed aggregate after recycl�ng and �mmed�ately pr�or to treatment should be well-graded, comply�ng w�th the cr�ter�a �n F�gure 4.2 (and F�gure 3.2 �n Chapter 3). In some cases th�s may necess�tate the �ncorporat�on of a port�on of the underly�ng layer �nto the compos�te recycled layer. It �s however preferable to rather �ncorporate supplementary fines by pre-spread�ng at the surface before m�x�ng. The add�t�on of v�rg�n mater�al can be cons�dered to rect�fy non-compl�ant grad�ngs, as can the add�t�on of m�lled old ch�p seals. Caut�on should be taken when �nclud�ng the underly�ng layer where the layer �ncludes cohes�ve, plast�c mater�al. In such cases pre-treatment w�th l�me should be cons�dered.

The max�mum stone s�ze and amount of coarse aggregate �s �mportant w�th regard to the m�x compact�on and abras�on of the m�ll�ng equ�pment. The max�mum stone s�ze should be l�m�ted to 75 mm �n recycled layers. The layer th�ckness should be at least three t�mes the largest stone s�ze. In add�t�on, the mass of stone larger than 50 mm should not exceed 20% to m�n�m�ze abras�on on the recycler.

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Plasticity Index

The PI of a mater�al to be treated w�th b�tumen

emuls�on should be 7 or less.

The PI of a mater�al to be treated w�th foamed b�tumen should be 10 or less.

If the PI exceeds these l�m�ts, the mater�al should be pre-treated with lime to reduce the PI.



25

iii Reclaimed Asphalt (RA)Recycl�ng projects somet�mes requ�re the reuse of h�gh percentages of RA, 75% to 100% before blend�ng w�th add�t�onal mater�als. In such cases, the �nfluence of the aggregate (RA) compos�t�on needs to be carefully cons�dered �n the m�x des�gn, espec�ally where traffic levels exceed 6 MESA. In part�cular, the follow�ng aspects need attent�on:

Climatic region If the BSM �s �ntended for appl�cat�on �n a warm cl�mate, the shear propert�es �dent�fied through tr�ax�al tests, should be determ�ned at representat�ve temperatures. Axle loads If the BSM �s �ntended for use �n an area where overload control �s not well regulated, h�gher stress rat�os w�ll result �n accelerated deformat�on. Th�s needs to be cons�dered when analys�ng the shear propert�es. RA Composition If the above two factors are appl�cable, then the compos�t�on of the RA needs to be mod�fied (blend�ng w�th 15% to 25% crusher dust). Th�s w�ll prov�de an angular sand skeleton that w�ll �mprove the shear res�stance of the m�x.

The use of 100% RA �n BSMs has been successfully appl�ed �n reg�ons of moderate cl�mate and well regulated axle load�ng.

4 2 1 2 Sampling Sampl�ng of mater�als for BSM m�x des�gns �s very �mportant, part�cularly for recycl�ng. Refer to TMH1 for sampl�ng gu�del�nes. Cogn�sance needs to be taken of numerous factors, �nclud�ng:

The depth of recycling and proport�ons of the �n s�tu layers blended to form a representat�ve compos�te layer.The variability of material type over the length and depth of the ex�st�ng pavement, so that adjustments can be made to the m�x des�gn where necessary. Where var�ab�l�ty �s encountered, the �nd�v�dual layers should be s�eved �nto the respect�ve fract�ons and recomb�ned �n the requ�red rat�os. In th�s way a cons�stent blend can be ach�eved and the �nfluence of var�at�ons �n grad�ng on the m�x propert�es can be �nvest�gated.The crush�ng and blend�ng of existing asphalt �nto the compos�te m�x, where such asphalt �s to be �ncorporated �n the recycled layer. On-s�te m�ll�ng �s the most su�table method for ach�ev�ng representat�ve samples.For v�rg�n aggregates, a bulk sample w�th a representat�ve grad�ng must be obta�ned from the appl�cable source.

The �nclus�on of ex�st�ng seals �n the recycled mater�al �s useful for enhanc�ng the grad�ng modulus of the recycled layer. M�ll�ng and blend�ng the ex�st�ng seal together w�th the recycled layer usually �mproves the layer’s structural capac�ty prov�ded that the max�mum part�cle s�ze �s l�m�ted (large chunks of bound mater�al, greater than 50 mm, should be removed). Methods of prevent�ng overs�ze mater�als are covered �n Chapter 6.

4 2 1 3 GradingThe nature of d�spers�on of the b�tumen �n BSMs �s d�fferent for BSM-foam and BSM-emuls�on. It �s understandable, therefore, that the aggregate grad�ng requ�rements d�ffer for the two types of treatments. The purpose of fines (mater�al pass�ng the 0.075 mm s�eve) �n the aggregate used for BSMs �s dependent on the type of b�tumen be�ng used. In part�cular, the grad�ng requ�rements �n terms of the target filler content d�ffer for BSM-foam and BSM-emuls�on.

BSM-emulsion

B�tumen emuls�on coats the larger aggregate part�cles to a greater extent than foamed b�tumen.

A m�n�mum filler content of 2% �s suffic�ent.

BSM-foam

The d�spersed b�tumen droplets �n BSM-foam only part�ally coat the larger aggregate. The mast�c (filler, b�tumen and water) “spot welds” the coarser aggregate fract�ons together �n BSM-foam.

Approx�mately 5% filler �s requ�red to produce a treated mater�al that performs well. Where lower b�tumen contents are used, th�s value can be reduced to 4%.

The general grad�ng requ�rements for BSMs are �nd�cated �n terms of zones of most su�table aggregate compos�t�on �n F�gure 4.2. Th�s figure �s a repeat of Table 3.3 and �s �ncluded here for completeness. The less su�table zone �s only ut�l�sed where alternat�ves are severely l�m�ted. Where necessary, aggregates can be blended w�th m�ss�ng fract�ons to �mprove the�r grad�ng. Coarse-graded mater�als requ�re less b�tumen than finer graded mater�als.

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Binder Contents

Coarse graded materials typ�cally requ�re less bitumen than fine graded gravels.

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26

Sieve Size (mm) Percent Passing



50 100 100

37.5 87 – 100 87 – 100

26.5 77 – 100 100 77 – 100 100

19.5 66 – 99 99 – 100 66 – 99 99 – 100

13.2 67 – 87 87 – 100 67 – 87 87 – 100

9.6 49 – 74 74 – 100 49 – 74 74 – 100

6.7 40 – 62 62 – 100 40 – 62 62 – 100

4.75 35 – 56 56 – 95 35 – 56 56 – 95

2.36 25 – 42 42 – 78 25 – 42 42 – 78

1.18 18 – 33 33 – 65 18 – 33 33 – 65

0.6 12 – 27 27 – 54 14 – 28 28 – 54

0.425 10 – 24 24 – 50 12 – 26 26 – 50

0.3 8 – 21 21 – 43 10 – 24 24 – 43

0.15 3 – 16 16 – 30 7 – 17 17 – 30

0.075 2 – 9 9 – 20 4 – 10 10 – 20


Figure 4.2 Guidelines for Suitability of Grading for Treatment



27

W�th�n the envelopes prov�ded �n F�gure 4.2 above, a refined target grad�ng should be targeted that prov�des the lowest Vo�ds �n the M�neral Aggregate (VMA). M�n�m�s�ng the VMA produces the most des�rable m�x propert�es.

BSM-emulsion

The m�n�m�zat�on of the VMA �s �mportant for BSM-emuls�on, but not as essent�al as for BSM-foam.

BSM-foam

For BSM-foam, the m�n�m�zat�on of the VMA �s part�cularly �mportant �n the fract�on of m�neral aggregate smaller than 2.36 mm, as th�s �s where the b�tumen droplets d�sperse w�th�n the m�x. Where necessary, two mater�als should be blended to create a dense gradat�on.

A un�que relat�onsh�p for ach�ev�ng the m�n�mum VMA, �s shown �n Equat�on 4.1, where a value of n = 0.45 should be used.

n

D

dP ⎥⎦

⎤⎢⎣

⎡= … (4.1)

Where d = selected s�eve s�ze (mm) P = percentage by mass pass�ng a s�eve of s�ze d (mm) D = max�mum aggregate s�ze (mm) n = var�able dependent on aggregate pack�ng character�st�cs

S�eve analys�s of the aggregate �s carr�ed out w�th wash�ng of the fines. The aggregate sampled �s d�v�ded �nto three fract�ons at the 19 mm and 4.75 mm s�eves. The fract�on greater than 19 mm should be removed from the m�x des�gn. The proport�ons of the mater�al fract�ons that are now d�v�ded at the 4.75 mm s�eve should be recorded as th�s �nformat�on �s requ�red when the max�mum dry dens�ty �s determ�ned. Three s�eve s�zes should be added to the typ�cal s�eves used for grad�ng analyses of so�l, namely 0.15 mm, 0.30 mm and 1.18 mm. Th�s ass�sts �n ach�ev�ng the gradat�on w�th m�n�mum VMA more accurately. Equat�on 4.1 can be used to calculate the target grad�ng for the add�t�onal s�eves.

4 2 1 4 DurabilityOne of the most �mportant aspects of the untreated aggregate �s durab�l�ty. Durab�l�ty does not just apply to the res�stance to mo�sture of a BSM or the res�stance to age�ng of the b�tumen. It also appl�es to the durab�l�ty of the untreated aggregate before treatment. To determ�ne the durab�l�ty of the untreated aggregate, the Durab�l�ty M�ll Index (DMI) �s recommended. Th�s test �dent�fies the potent�al durab�l�ty of aggregates �n terms of breakdown and generat�on of excess�ve plast�c and non-plast�c fines. The test has the most potent�al for s�mulat�ng the l�kely breakdown of the mater�als �n serv�ce, and �s appl�cable for all mater�al types. Although the acceptable l�m�ts for these tests were �n�t�ally appl�cable to granular mater�als only, these l�m�ts have been adapted for pre-treated (natural) mater�als for use �n select�on of component aggregates dur�ng m�x des�gn. The DMI l�m�ts are shown �n Table 4.1.

Table 4 1 Durability Mill Index, Limit for Rocks and Soils

Aggregate Type Rock and Soil Group DMI Limit

Gran�tes, gne�ss, gran�te Ac�d Crystall�ne

< 420Hornfels, quartz�te H�gh s�l�ca

Dolom�te, l�mestone, Carbonate

Ironstone, magnes�te, magnet�te Metall�ferous

Calcrete, ferr�crete, s�lcrete Pedogen�c mater�als < 480

Sandstone, s�ltstone, conglomerate Sandstone

< 125Greywacke, t�ll�te D�am�ct�te

Mudrock, ph�ll�tes, shale Mudrock

Basalt, Doler�te, Gabbro Bas�c crystall�ne < 100



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4 2 1 5 Aggregate Temperature

BSM-emulsion

Typ�cally, aggregates w�th temperatures of 10 °C or h�gher can be treated w�th b�tumen emuls�on w�thout comprom�s�ng the b�tumen d�str�but�on and part�cle coat�ng.

BSM-foam

Aggregate temperature for BSM-foam product�on has a s�gn�ficant �nfluence on the degree of coat�ng and the propert�es of the m�x. H�gher aggregate temperatures �ncrease the s�ze of the aggregate part�cle that can be coated. Temperature measurements of the aggregate are therefore essent�al before laboratory or field product�on commences.

Laboratory m�xes should be produced at temperatures that reflect the expected field temperatures, tak�ng account of da�ly and seasonal effects. F�eld m�xes on the other hand, should not be attempted w�th aggregate temperatures less than 10 °C. Where the aggregate temperature ranges between 10 to 15 °C, m�xes should only be produced w�th super�or qual�ty foamed b�tumen, s super�or foam�ng character�st�cs (espec�ally the half-l�fe). Where the expected aggregate temperatures range between 10 to 15 °C the qual�ty of the m�x should be checked �n the laboratory at the ant�c�pated m�x�ng temperature before commenc�ng construct�on.

4 2 2 BITUMEN SELECTIONPenetrat�on grade b�tumen �s used to produce both the foamed b�tumen and b�tumen emuls�on that �s then used to manufacture BSMs. The types of b�tumens and spec�fic b�tumen requ�rements are outl�ned below.

Bitumen Emulsion

Bitumen emulsion category Base b�tumens w�th penetrat�on values between 80 and 100 are generally selected for b�tumen emuls�on product�on, although softer and harder b�tumens have been successfully used. The select�on of the correct grade or category of b�tumen emuls�on for the appl�cat�on �s essent�al, as outl�ned �n Table 4.2.

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Foamed Bitumen

BSM-foam only requ�res low percentages of b�tumen (typ�cally 1.7% to 2.5%) and can ut�l�se softer grades of b�tumen w�thout comprom�s�ng the stab�l�ty of the m�x.

B�tumens w�th penetrat�on values between 80 and 100 are generally selected for BSM-foam, although softer and harder b�tumen have been successfully used �n the past and may be used when ava�lable. For pract�cal reasons, harder b�tumen �s generally avo�ded due to poor qual�ty foam, lead�ng to poorer d�spers�on of the b�tumen �n the m�x.

Aggregate Temperature

Aggregates w�th temperatures lower than 10 °C should not be treated w�th b�tumen. Aggregate

temperatures �n the laboratory should match the expected field temperatures.i



29

In South Afr�ca, slow set stable grade anionic bitumen emulsions are almost exclus�vely used for BSMs as they typ�cally work well w�th dense graded aggregates or w�th aggregates w�th h�gh fines contents. These b�tumen emuls�ons have long workab�l�ty t�mes to ensure good d�spers�on and are formulated for m�x stab�l�ty. The mot�vat�ng forces �n southern Afr�ca for us�ng th�s type of b�tumen emuls�on are econom�cs and cl�mate. In the rest of the world, cat�on�c b�tumen emuls�ons are extens�vely used. The test methods for b�tumen emuls�ons are referenced �n Append�x B. Breaking rate There have been many developments �n b�tumen emuls�on technology recently to �mprove stab�l�ty of the b�tumen emuls�on w�thout prolong�ng the break t�me. These b�tumen emuls�ons are typ�cally slower sett�ng than the standard products, and should be used on projects where the treated layer can be allowed to cure for a per�od before open�ng to traffic. Dur�ng the m�x des�gn phase, and on s�te before full-scale appl�cat�on beg�ns, the break�ng rate should be tested w�th representat�ve samples of aggregate, act�ve filler and water, at real�st�c temperatures. Compatibility of bitumen emulsion and aggregate The select�on of the b�tumen emuls�on type for treatment �s �nfluenced by the type of aggregate to be treated. The gu�del�nes outl�ned �n Table 4.3 �nd�cate that certa�n aggregates are not su�table for treatment w�th an�on�c b�tumen emuls�ons. The aggregates l�sted �n th�s table have s�l�ca contents above 65% and alkal� contents below 35%, �.e. these are ac�d�c rocks. In such cases a cat�on�c b�tumen emuls�on should be used.

Manufactures normally recommend that und�luted b�tumen emuls�on �s heated to between 50 and 60 °C to prevent premature break�ng of the b�tumen emuls�on wh�le pump�ng �n the construct�on equ�pment.

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The penetrat�on value alone does not qual�fy b�tumen for use �n a foamed b�tumen m�x. The foam�ng propert�es or foamab�l�ty of each b�tumen type needs to be tested. Two character�st�cs form the bas�s of b�tumen’s su�tab�l�ty for use, namely the Expans�on Rat�o (ER) and Half-l�fe (τ½):

The expansion ratio �s a measure of the v�scos�ty of the foam and w�ll determ�ne how well the b�tumen w�ll d�sperse �n the m�x. It �s calculated as the rat�o of the max�mum volume of foam relat�ve to the or�g�nal volume of b�tumen. The half-life �s a measure of the stab�l�ty of the foam and prov�des an �nd�cat�on of the rate of collapse of the foam dur�ng m�x�ng. It �s calculated as the t�me taken �n seconds for the foam to collapse to half of �ts max�mum volume.

Append�x B references the measurement of the expans�on rat�o and half-l�fe. M�n�mum l�m�ts for ER and τ½are g�ven �n Table 4.4.

One of the dom�nant factors �nfluenc�ng the foam propert�es �s the water that �s �njected �nto the expans�on chamber (or reactor �n some plants) to create the foam as �llustrated �n F�gure 4.3. A h�gher appl�cat�on rate of foamant water creates greater expans�on (h�gher ER) but leads to more rap�d subs�dence or decay, �.e. a shorter half-l�fe (τ½). The foamant water appl�cat�on rate and b�tumen temperature are the most �mportant factors �nfluenc�ng foam qual�ty. A h�gher b�tumen temperature usually creates better foam. A sens�t�v�ty analys�s �n the laboratory �s recommended to �dent�fy a target b�tumen temperature for foam�ng. As w�th HMA product�on, temperature l�m�ts should be �mplemented to prevent damage to the b�tumen at the plant.

The var�ab�l�ty of the foam character�st�cs measured �n a laboratory and �n the field, both �n terms of repeatab�l�ty and reproduc�b�l�ty, are s�gn�ficant. At least three tests are recommended for each set of cond�t�ons, to atta�n an acceptable level of stat�st�cal rel�ab�l�ty. In add�t�on, potent�al var�ab�l�ty �n the b�tumen compos�t�on from the same source necess�tates check�ng the foamab�l�ty of each tanker.

»

»

Foaming Characteristics

The expansion ratio (ER) �s the max�mum volume of foam relat�ve to the or�g�nal volume.

The half-life (τ½) �s the t�me the foam takes to collapse to half of �ts max�mum volume.

i

Diluting Bitumen Emulsion

When d�lut�ng a b�tumen emuls�on, �t �s �mportant to add the emulsion to the water, and not the water to the emuls�on. Th�s w�ll prevent the emuls�on from break�ng.



30

Table 4 2 Categories of Bitumen Emulsion for Treatment

Bitumen Emulsion Type Anionic Cationic

Emuls�fier type Fatty ac�d or res�n ac�d Am�ne

B�tumen emuls�on charge Negat�ve Pos�t�ve

pH H�gh (alkal�) Low (ac�d)

Grades Stable m�x (slow set): recycl�ng and treatment

Table 4 3 Compatibility of Bitumen Emulsion Type with Aggregate Type

Aggregate Type Compatible With

Anionic Bitumen Emulsion Cationic Bitumen Emulsion

Doler�te ¸ ¸

Quartz�te ˚ ¸

Hornfels / Greywacke ¸ ¸

Dolom�te ¸ ¸

Gran�te ˚ ¸

Andes�te ¸ ¸

T�ll�te Var�able ¸

Basalt ¸ ¸

Sandstone ˚ ¸

Rhyol�te ˚ ¸

Marble/Nor�te ¸ ¸

Syen�te ˚ ¸

Amph�bol�te ¸ ¸

Fels�te ˚ ¸



31

Figure 4.3 Determination of Optimum Foamant Water Content

Table 4 4 Foam Characteristic Limits (minimum values)

Aggregate Temperature 10 ºC to 25 ºC Greater than 25 ºC

Expans�on Rat�o, ER (t�mes) 10 8

Half-l�fe, τ1/2 (secs) 6 6

4 2 3 FILLER (NATURAL AND ACTIVE) The types of filler used w�th BSMs are: cement (var�ous types, but not rap�d harden�ng cements), l�me, rock flour, fly ash and slagment. For the purpose of th�s gu�del�ne, the term act�ve filler �s used to define fillers that chem�cally alter the m�x propert�es. Th�s �ncludes fillers such as l�me, cement and fly ash but excludes natural fillers such as rock flour. In th�s gu�del�ne, l�me always refers to hydrated l�me.

The purpose of �ncorporat�ng act�ve filler �n BSM �s to: Improve adhesion of the b�tumen to the aggregate.Improve dispersion of the b�tumen �n the m�x.Modify the plasticity of the natural mater�als (reduce PI).Increase the stiffness of the m�x and rate of strength ga�n.Accelerate curing of the compacted m�x.

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4

5

6

7

8

9

10

11

12

13

14

15

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Water Added (%)

Expa

nsio

n (ti

mes

)

4

5

6

7

8

9

10

11

12

13

14

15

Hal

f-life

(sec

onds

)

Minimum acceptable Expansion Ratio

Minimum acceptable Half-life

Optimum foamant water content

Equal Equal

Active filler

The term act�ve filler �s used to define fillers that chemically alter the m�x propert�es. Th�s �ncludes fillers such as l�me, cement and fly ash but excludes natural fillers such as rock flour.

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32

BSM-emulsion

Control the breaking time of BSM-emuls�on.Improve the workability of BSM-emuls�on (�n some cases).

»»

BSM-foam

To ass�st �n dispersing the bitumen droplets. »

The purpose of add�ng natural filler �s pr�mar�ly to supplement the fines needed for b�tumen d�spers�on.

Var�ous types of act�ve filler can be used, both separately or �n comb�nat�on. The filler type selected for appl�cat�on w�ll depend on ava�lab�l�ty, cost and efficacy w�th the actual component mater�als. Research has shown that �t �s almost �mposs�ble to pred�ct wh�ch act�ve filler w�ll prove to be the most effect�ve w�thout exper�mentat�on dur�ng m�x des�gn. Test�ng cured and soaked 100 mm d�ameter spec�mens for Ind�rect Tens�le Strength (ITSwet) and the reta�ned cohes�on from a tr�ax�al test are useful tests to gu�de act�ve filler select�on.

When cement �s used, the appl�cat�on rate must be l�m�ted to a max�mum of 1% by mass of dry aggregate. When us�ng hydrated l�me, the appl�cat�on rate may be �ncreased to 1.5% or more where the l�me �s requ�red to mod�fy plast�c�ty. However, �t should be noted that the �ncrease �n m�x st�ffness �s comprom�sed s�gn�ficantly by a loss �n flex�b�l�ty of the mater�al. Above these appl�cat�on rates, the benefit of the b�tumen �s hardly real�zed.

Where act�ve fillers are appl�ed, the t�me delay between m�x�ng the act�ve filler w�th the mater�al and appl�cat�on of the foamed b�tumen or b�tumen emuls�on should be reduced to a m�n�mum (�n the laboratory and the field). The act�ve filler react�on beg�ns �mmed�ately upon contact w�th mo�st mater�al, promot�ng adhes�on between the fine part�cles. The longer the delay between prem�x�ng w�th act�ve filler and apply�ng the b�tumen, the lower the percentage of filler ava�lable for d�spers�on of the b�tumen �n the BSM m�x.

Where mater�als w�th unacceptably h�gh PI values are encountered, they can be treated w�th hydrated l�me to mod�fy the plast�c�ty, thereby render�ng them acceptable for treatment w�th foamed b�tumen or b�tumen emuls�on. Pre-treat�ng w�th l�me must allow for suffic�ent t�me for mod�ficat�on to take place before b�tumen treatment. Depend�ng on the mater�al type, 4 hours or more may be necessary for effect�ve l�me mod�ficat�on.

4 2 4 WATER QUALITYThe qual�ty of the water used to create the foamed b�tumen and b�tumen emuls�on �s �mportant to ensure a m�x of rel�able qual�ty. The standard COLTO requ�rements should be followed �n th�s regard.

Cement Content

When cement �s used as the act�ve filler �n BSMs, the

cement content should be l�m�ted to 1% or less.

Pre-treating with Lime

When pre-treat�ng w�th l�me, allow at least 4 hours before treat�ng w�th b�tumen.



CHAPTER 4: Mix Design – Specimen Preparation

33

BSM-emulsion

The pH levels of the water must be checked, as must the compat�b�l�ty of the b�tumen emuls�on and the water. These checks are done by perform�ng a d�lut�on test.

Dilution “can” test

The b�tumen emuls�on �s d�luted to spec�ficat�on, �n a clean conta�ner such as a can. The water �s added to the b�tumen emuls�on (not b�tumen emuls�on to water to prevent premature break�ng). The “can” �s then heated to about 60 °C, and left to stand for 20 to 30 m�nutes. The d�luted b�tumen emuls�on �s then passed through a fine s�eve (0.600 mm) to determ�ne �f any premature break�ng has taken place.

Note that the d�lut�on water for cat�on�c b�tumen emuls�on must not be alkal�ne; dam water can be rather alkal�ne espec�ally �n l�mestone areas. For a cat�on�c b�tumen emuls�on, the add�t�on of hydrochlor�c ac�d to the water w�ll reduce th�s tendency. For an�on�c b�tumen emuls�on, l�me or caust�c soda �s added to the d�lut�on water �f necessary.

»

BSM-foam

Although acceptable foam may be ach�eved us�ng water conta�n�ng �mpur�t�es, such pract�ce should be avo�ded. Impur�t�es often lead to scales form�ng on the walls of the feed p�pes and these eventually d�slodge and block the water �nject�on jets, prevent�ng the b�tumen from foam�ng

4.3. SPECIMEN PREPARATION

4 3 1 FLUID CONSIDERATIONSThe role of mo�sture �n the m�neral aggregate �s s�m�lar for BSM-emuls�on and BSM-foam �n many respects, but there are some d�fferences. The ent�re flu�d content �n the m�x, mo�sture and b�tumen, needs to be cons�dered. The role of mo�sture �n the two types of BSM �s expla�ned �n Table 4.5. Table 4 5 Role of Fluids in BSMs

Component BSM-emulsion BSM-foam

B�tumen Contr�butes to flu�ds for compact�on Negl�g�ble contr�but�on to flu�ds for compact�on

Mo�sture �n aggregate

Reduces absorpt�on of b�tumen emuls�on water �nto aggregate

Separates and suspends fines mak�ng them ava�lable to b�tumen dur�ng m�x�ng

Prevents premature break�ng Acts as carr�er for b�tumen droplets dur�ng m�x�ng

Extends cur�ng t�me and reduces early strength

Reduces early strength

Prov�des workab�l�ty of BSM at amb�ent temperatures

Reduces fr�ct�on angle and lubr�cates for compact�on

Prov�des shelf-l�fe for the m�x



34

BSM-emulsion

Changes �n mo�sture content occur �n two d�st�nct phases, namely:Breaking �s the separat�on of the b�tumen from the water phase through flocculat�on and the coalescence of the b�tumen droplets to produce films of b�tumen on the aggregate. The rate at wh�ch the b�tumen globules separate from the water phase �s referred to as the break�ng or sett�ng/settl�ng t�me.

The break�ng process w�th an�on�c b�tumen emuls�ons �s a mechan�cal process (evaporat�on), whereas cat�on�c b�tumen emuls�ons produce a chem�cal break. For dense m�xtures, more t�me �s needed to allow for m�x�ng and placement and slower break�ng t�mes are requ�red. As the b�tumen emuls�on breaks, the colour changes from d�rty brown to black. Although th�s can be observed w�th the naked eye, �t �s recommended that a magn�fy�ng glass �s used.

Curing �s the d�splacement of water and resultant �ncrease �n st�ffness and tens�le strength of the b�tumen. Th�s �s �mportant as a m�x needs to acqu�re suffic�ent st�ffness and cohes�on between part�cles before carry�ng traffic.

Some of the factors wh�ch �nfluence the whole setting process, �.e. break�ng and cur�ng of b�tumen emuls�ons, �nclude:

Rate of absorption of water by the aggregate. Rough-textured and porous aggregates reduce the break�ng and sett�ng t�me by absorb�ng water conta�ned �n the b�tumen emuls�on.Moisture content of the m�x pr�or to m�x�ng �nfluences break�ng t�me.Moisture content of the m�x after compact�on �nfluences cur�ng rate.Grading of the aggregate and vo�ds content of the m�x.Type, grade and quantity of the b�tumen emuls�on.Mechanical forces caused by compact�on and traffic.Mineral composition of the aggregate The rate of cure may be affected by pos¬s�ble phys�cochem�cal �nteract�ons between the b�tumen emuls�on and the surface of the aggregate.Intensity of electrical charge on the aggregate �n relat�on to that of the b�tumen emuls�on.Active filler percentage, the amount of cement or l�me.Temperature of aggregate and a�r. The h�gher temperature, the qu�cker the b�tumen emuls�on breaks and cures.

»

»

»

»

»

»»»»

»

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BSM-foam

Changes �n mo�sture content occur as a result of cur�ng. The rate of change of the mo�sture content of BSMs �s var�able for �n s�tu m�x�ng.

Curing �s the gradual reduct�on �n mo�sture due to evaporat�on, result�ng �n an �ncrease �n st�ffness and tens�le strength of the b�tumen. Th�s �s �mportant as a m�x needs to acqu�re suffic�ent st�ffness and cohes�on between part�cles before carry�ng traffic.

»

The mo�sture content of the aggregate to be used �n the BSM requ�res opt�m�sat�on at the d�fferent stages of prepar�ng the m�x, and these opt�mum values do not co�nc�de. D�fferent opt�mum values requ�re cons�derat�on, as d�scussed �n the follow�ng sect�ons.



35

4 3 1 1 Mixing MoistureThe mo�sture content that w�ll prov�de the best BSM m�x �s termed the opt�mum m�x�ng mo�sture content (OMMC). Th�s �s the mo�sture �n the aggregate plus, for BSM-emuls�ons, any add�t�onal mo�sture �n the b�tumen emuls�on. OMMC var�es w�th gradat�on of the aggregate and, �n part�cular, the s�ze of the fract�on smaller than 0.075 mm.

BSM-emulsion

BSM-emuls�onA m�n�mum of 1 to 2% mo�sture �s requ�red �n the aggregate pr�or to add�ng the b�tumen emuls�on.

The water and b�tumen �n the b�tumen emuls�on act as lubr�cants for BSM-emuls�on m�xes. The opt�mum mo�sture content (OMC) us�ng mod�fied AASHTO compact�on should be used for the total m�x�ng flu�d content. Th�s �s expla�ned �n Equat�on 4.2 below: OFC = OMCMOD U = FMC + EWC + RBC ... (4.2)

Where OFC = opt�mum flu�ds content (%)OMCMOD-U = opt�mum mo�sture content us�ng Mod. AASHTO

compact�on on untreated mater�al (%)FMC = field mo�sture content of aggregate (%)EWC = b�tumen emuls�on water content �nclud�ng water used for

d�lut�on as percentage of dry aggregate (%)RBC = res�dual b�tumen content as percentage of dry aggregate

(%)

BSM-foam

65 to 85% of the opt�mum mo�sture content (OMC) us�ng mod�fied AASHTO compact�on should be used for the m�x�ng mo�sture content when add�ng foamed b�tumen. The fluff po�nt mo�sture content at wh�ch the max�mum bulk volume of loose m�neral aggregate �s obta�ned, �s the m�n�mum value for the m�x�ng mo�sture content.

4 3 1 2 Compaction Moisture

BSM-emulsion

Compact�on of BSM-emuls�on can be carr�ed out at the opt�mum flu�ds content (OFC) as outl�ned �n Sect�on 4.3.1.1. Alternat�vely, a sens�t�v�ty analys�s should be carr�ed out us�ng v�bratory hammer compact�on, to determ�ne a representat�ve compact�on mo�sture content.

BSM-foam

To ach�eve the requ�red level of compact�on, the opt�mum compact�on mo�sture content (OCMC) needs to be determ�ned �n the laboratory us�ng v�bratory hammer compact�on.

A procedure for carry�ng out v�bratory hammer compact�on �s referenced �n Append�x B, and uses a Bosch® v�bratory hammer. In all cases, 150 mm d�ameter spec�mens are compacted to obta�n the most representat�ve volumetr�c results.

Modern rollers used for compact�on of th�ck pavement layers �mpart very h�gh energy. Th�s type of compact�on reduces the effect�ve opt�mum flu�ds content requ�red �n the field, relat�ve to that determ�ned �n the laboratory. For th�s reason �t �s poss�ble to compact at up to 1.5% lower flu�d contents �n the field than the opt�mum used �n the laboratory.

4 3 2 MATERIAL PREPARATIONSeveral opt�ons are ava�lable for produc�ng BSMs �n the laboratory, �nclud�ng the type of m�xer, type of compact�on as well as several other var�ables. Standard�sat�on of the apparatus and procedures �s requ�red to ensure that representat�ve m�xes are produced and relevant results are obta�ned that can be compared w�th the gu�del�ne l�m�ts. Th�s sect�on �ncludes a summary of the sample preparat�on and

Fluids Available in Mix

The water �n the BSM-emulsion �s cons�dered part of the total flu�d contents, whereas for BSM-foam the foamant water �s not part of the total flu�d content.

i



36

m�x�ng.

The general�sed procedure for mater�al preparat�on �s prov�ded below. The full deta�ls and test methods are referenced �n Append�x B and are ava�lable �n TMH1 or for download on www.asphaltacademy.co.za/b�tstab.

Step 1: Determ�ne the grad�ng curve of the aggregate and the OMC of the natural (untreated) mater�al us�ng the Mod�fied AASHTO compact�on method.

Step 2: Determ�ne the Atterberg L�m�ts of the mater�al. Where necessary, pre-treat or blend the mater�al to address any defic�enc�es.

Step 3: Determ�ne the mo�sture and dens�ty relat�onsh�p us�ng Mod. AASHTO compact�on for the untreated mater�al to obta�n OMCU-Mod.

Step 4: Determ�ne the mo�sture and dens�ty relat�onsh�p us�ng Mod. AASHTO compact�on for the treated BSM mater�al to obta�n OMCMod-BSM.

Step 5: Determ�ne the mo�sture and dens�ty relat�onsh�p v�bratory for hammer compact�on for the treated mater�al to obta�n OMCV�b-BSM.

4 3 3 MIXING Prepare the BSM-emuls�on or BSM-foam m�xes, preferably us�ng a laboratory pugm�ll m�xer.

BSM-emulsion

Blender-type laboratory m�xers and flat-pan m�xers w�th a rotary m�x�ng mot�on are su�ted to m�x preparat�on for BSM-emuls�on. Care should be taken to ensure that b�tumen does not rema�n on the m�x�ng drum or paddles, as th�s w�ll �nfluence the final b�tumen content.

BSM-foam

The m�x�ng process for BSM-foam �s a dynam�c one as the foamed b�tumen beg�ns to collapse rap�dly once contact �s made w�th the cold aggregate. D�fferent m�xers can produce d�screpanc�es of up to 25% �n mater�al strength propert�es. It �s �mperat�ve, therefore, to ut�l�se a laboratory foam�ng plant and m�xer that emulates the s�te m�x�ng.

The rotary m�x�ng mot�on of the blenders used �n the laboratory are ne�ther �deal for restr�ct�ng part�cle segregat�on nor for s�mulat�ng s�te m�x�ng. The methods used on s�te prov�de suffic�ent volume �n the m�x�ng chamber and energy of ag�tat�on to ensure that the m�neral aggregate �s a�rborne when �t makes contact w�th the foam. Blender type laboratory m�xers do not emulate th�s, and subsequently the qual�ty of laboratory m�xes �s usually �nfer�or to s�te m�xes. For th�s reason, a pug-m�ll type m�xer must be used �n the laboratory. A m�x�ng t�me of 20 to 30 seconds �s generally used �n the laboratory, wh�ch �s longer than �n s�tu m�x�ng but s�mulates the d�fferences �n the energy of the laboratory m�xer and field plant.

4 3 4 COMPACTIONSpec�al attent�on needs to be pa�d to compact�on, as �t �mproves part�cle contacts and reduces vo�ds. The dens�ty ach�eved �s cr�t�cal to the ult�mate performance of the m�x.

Mixer Types for BSM-foam

Vertical agitators, �.e. blender type m�xers must not be used for BSM-foam as they produce s�gn�ficantly �nfer�or m�xes.

A pugmill type m�xer �s recommended for produc�ng BSM-foam m�xes that are representat�ve of field m�xes.

D�fferent m�xers can produce up to 25% difference in strength.

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37

BSM-emulsion

The �nclus�on of b�tumen emuls�on typ�cally �mproves compact�b�l�ty of the m�x.

BSM-foam

Compact�on promotes adhes�on of the b�tumen mast�c to the stone.

A laboratory compact�on techn�que that not only ach�eves the dens�ty expected �n the field, but also emulates the part�cle or�entat�on after roll�ng, �s ach�eved us�ng v�bratory hammer compact�on. The v�bratory hammer compact�on procedure �s referenced �n Append�x B. V�bratory hammer compact�on �s preferred to Mod�fied AASHTO compact�on because problems are exper�enced w�th delam�nat�on w�th�n the spec�men w�th Mod�fied AASHTO compact�on. For Level 1 m�x des�gns where 100 mm d�ameter spec�mens are used, and where the necessary v�bratory hammer equ�pment �s not ava�lable, Marshall compact�on may be used.

It must be noted that the mo�sture and dens�ty relat�onsh�p, and the result�ng OMC are dependant on the compact�on method used. The OMC used �s typ�cally that of the untreated mater�al.

In terms of spec�fy�ng compact�on, absolute dens�ty us�ng the Bulk Relat�ve Dens�ty method as outl�ned �n TMH1 can be used for BSMs produced w�th G1 to G4 qual�ty mater�als. For poorer qual�ty mater�als, lower than G4, the v�bratory hammer techn�que �s preferred.

The laboratory compact�on method for BSMs should follow the v�bratory hammer compact�on procedure (ava�lable on www.asphaltacademy.co.za/b�tstab), at a mo�sture content of 80% of OMCU-Mod. Th�s fac�l�tates the compact�on of 300 mm h�gh by 150 mm d�ameter spec�mens for tr�ax�al test�ng. Compact�on should be carr�ed out at 25 ± 2 °C.

Spl�t moulds should generally be used for compact�on of 150 mm d�ameter spec�mens. Th�s �s part�cularly �mportant for the product�on of tr�ax�al spec�mens.

4 3 5 CURINGCur�ng of BSMs �s the process where the m�xed and compacted layer d�scharges water through evaporat�on, part�cle charge repuls�on and pore-pressure �nduced flow paths.

BSM-emulsion

Chem�stry plays a s�gn�ficant role �n the cur�ng of BSM-emuls�ons. Water �s an �ntr�ns�c component of b�tumen emuls�ons. Break�ng of the b�tumen emuls�on needs to take place before cur�ng v�a m�grat�on and evaporat�on.

BSM-emuls�on usually requ�res longer cur�ng t�mes than BSM-foam because of the h�gher mo�sture contents.

BSM-foam

Cur�ng takes place as a result of m�grat�on of water dur�ng compact�on and cont�nues w�th evaporat�on of the water.

The reduct�on �n mo�sture content leads to an �ncrease �n the tens�le and compress�ve strength, as well as st�ffness of the m�x. It �s �mperat�ve that th�s process �s real�st�cally s�mulated �n the laboratory for m�xes to be assessed for the�r expected field performance.

The rate of mo�sture loss from newly constructed BSM layers plays a s�gn�ficant role �n determ�n�ng the performance of the layer. It �s �n the early per�od of repeated load�ng that the major�ty of the permanent deformat�on takes place �n BSM layers. Where a new BSM layer �s to be trafficked �mmed�ately after fin�sh�ng, �t �s �mportant to m�n�m�se the mo�sture content dur�ng construct�on. The lower the degree of saturat�on of the BSM, the greater the res�stance to permanent

Compaction Equipment

Use Vibratory compact�on for both BSM-emuls�on and BSM-foam.

A new method of laboratory v�bratory compact�on has been developed us�ng a Bosch hammer

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Accelerated Curing

The accelerated laboratory cur�ng method �s a�med at represent�ng the long-term equilibrium moisture content.

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38

deformat�on. The temperature of the layer �n the field and the loss of mo�sture w�th t�me are the two factors to cons�der w�th cur�ng, and hence, st�ffness and strength ga�n. Although a BSM should have suffic�ent st�ffness and strength to w�thstand moderate levels of early traffic, the layer w�ll cont�nue to ga�n strength over several years �n the field.

The recommended cur�ng procedure d�ffers for the spec�men s�ze and b�tumen types, BSM-emuls�on and BSM-foam. Although the use of act�ve filler has an �mpact on cur�ng, �ts �nclus�on �n a BSM does not just�fy extens�ons �n the cur�ng t�me as cementat�on �s not one of the des�red propert�es of these mater�als. The two cur�ng protocols are �llustrated �n F�gure 4.4.

Figure 4.4 Mix Factors Considered for Selection of Curing Protocol

For Level 1 m�x des�gns, the 100 mm d�ameter spec�mens are cured unt�l they reach a constant (dry) mass, typ�cally w�th mo�sture contents of less than 0.5%. Test�ng follows 72 hours of cur�ng at 40 ºC w�thout seal�ng the spec�mens to determ�ne the ITSdry value. Half the spec�mens are then soaked for 24 hours before test�ng to determ�ne the ITSwet value. Th�s procedure �s a�med at evaluat�ng the mo�sture suscept�b�l�ty of the BSM.

The cur�ng procedure for 150 mm d�ameter spec�mens used �n Level 2 and Level 3 m�x des�gns typ�cally produces mo�sture contents of 43 to 50% of OMC, wh�ch represents the long-term equ�l�br�um mo�sture content of the mater�al �n the field. To ach�eve th�s, d�fferent cur�ng per�ods are requ�red for BSM-emuls�on and BSM-foam. Unsealed spec�mens are �n�t�ally placed �n a draft oven at 30 °C to allow the mo�sture content to reduce. Thereafter, they are �nd�v�dually sealed �n loose-fitt�ng plast�c bags (at least tw�ce the volume of the spec�men) and cured for a further 48 hours at 40 °C. The wet plast�c bags must be replaced w�th dry bags every twenty four hours.

Before the spec�mens are tested, they should be allowed to cool down to the requ�red test temperature wh�lst sealed �n a new dry plast�c bag to prevent any further mo�sture loss.

4.4. MECHANICAL TESTS The ITS and tr�ax�al tests are used �n the var�ous m�x des�gn levels, and are d�scussed �n the follow�ng sub-sect�ons.

4 4 1 INDIRECT TENSILE STRENGTH (ITS)The ITS test �s used as an �nd�rect measure of the tens�le strength and flex�b�l�ty of the BSM to reflect the flexural character�st�cs of the mater�al. Although th�s test does not produce h�ghly repeatable results, �t �s the most econom�cal method for �nvest�gat�ng the effect�veness of the b�tumen. In add�t�on, a background of h�stor�cal data �s ava�lable.

CURING METHOD

Preliminary Mix Design

All BSMs72 hours at

40 °C, unsealed

Level 2 & 3 Mix Design

BSM-foam20 hours at 30 °C unsealed

48 hours at 40 °C sealed

BSM-emulsion26 hours at 30 °C unsealed


Level 1 Mix Design

CURING METHOD

Preliminary Mix Design

All BSMs72 hours at

40 °C, unsealed

Level 2 & 3 Mix Design









Level 1 Mix Design



CHAPTER 4: Mix Design – Mechanical Tests

39

The 100 mm d�ameter spec�mens are used �n Level 1 to �nd�cate the opt�mum b�tumen content, the need for an act�ve filler and, �f act�ve filler �s requ�red, at what content. The 150 mm spec�mens are used to refine the opt�mum b�tumen content and prov�de add�t�onal confidence for the mater�al class�ficat�on system.

The 100 mm d�ameter and 63 mm h�gh spec�mens are cured for 72 hours at 40 °C (Sect�on 4.3.5) to reach a constant mass. ITSdry values are determ�ned from these spec�mens. The results obta�ned after soak�ng these spec�mens for 24 hours at 25 °C are termed ITSwet. The rat�o of ITSwet and ITSdry, expressed as a percentage, �s the Tens�le Strength Reta�ned (TSR).

The 150 mm d�ameter and 127 mm h�gh spec�mens are cured accord�ng to the procedure �n Sect�on 4.3.5 to s�mulate the field mo�sture cond�t�ons. The ITS results from spec�mens tested after th�s cur�ng are termed ITSequ�l. After soak�ng for 24 hours at 25 °C, the results from these tests are termed ITSsoaked.

The l�m�ts for �nterpret�ng the var�ous ITS tests, and the purpose of the tests are prov�de �n Table 4.6.

Table 4 6 Interpretation of ITS tests

Test Specimen diameter

BSM1 BSM2 BSM3 Purpose

ITSdry 100 mm > 225 175 to 225 125 to 175 Ind�cates opt�mum b�tumen content.

ITSwet 100 mm > 100 75 to 100 50 to 75 Ind�cates need for act�ve filler.

TSR 100 mm N/A Ind�cates problem mater�al where TSR < 50 and ITSdry > 400 kPa.

ITSequ�l 150 mm > 175 135 to 175 95 to 135 Opt�m�se b�tumen content.

ITSsoaked 150 mm > 150 100 to 150 60 to 100 Check value on ITSwet.

The TSR �s useful to �dent�fy problem mater�als. If the TSR �s less than 50%, �t �s recommended that act�ve filler be used. Where a mater�al has a TSR less than 50%, and the ITSdry exceeds 400 kPa, the mater�al �s l�kely to conta�n clays and the b�tumen �s �neffect�ve. In th�s s�tuat�on, the mater�al probably requ�res pretreatment.

4 4 2 TRIAXIAL TESTA S�mple Tr�ax�al Test (STT) has been developed to fac�l�tate tr�ax�al test�ng �n standard laborator�es. The STT apparatus �s only appl�cable to monoton�c tr�ax�al test�ng to obta�n cohes�on and fr�ct�on angle values. However, the monoton�c st�ffness of the mater�al, tangent modulus (Etan), prov�des an �nd�cat�on of res�l�ent response of the mater�al and to track trends �n st�ffness of d�fferent m�x compos�t�ons. The tangent modulus �s however, not a d�rect measure of the res�l�ent modulus. Advanced tr�ax�al setups may also be used for test�ng. The cohes�on, fr�ct�on angle and tangent modulus are used �n the class�ficat�on of BSMs (Sect�on 3.3). The procedures for tr�ax�al test�ng and calculat�on of the results are referenced �n Append�x B. The l�m�ts used to �nterpret the data for the three mater�al classes are shown �n Table 4.7.

4 4 2 1 Moisture Induced Sensitivity Test (MIST)Tr�ax�al test�ng also prov�des a means to a more rel�able measure of the mo�sture suscept�b�l�ty of BSMs. BSMs w�th super�or mo�sture res�stance are able to reta�n a greater percentage of the cohes�on that �s generated from the b�tumen treatment. Tr�ax�al spec�mens are cond�t�oned w�th mo�sture exposure us�ng the Mo�sture Induced Sens�t�v�ty Test (MIST) apparatus, as referenced �n Append�x B. The MIST dev�ce appl�es cycl�c mo�sture �ngress at real�st�c pore pressures. The cohes�on values are compared for spec�mens w�th and w�thout mo�sture exposure, to prov�de the reta�ned cohes�on parameter for the part�cular BSM. The reference for the reta�ned cohes�on calculat�ons �s prov�ded �n Append�x B. These values, wh�ch prov�de a measure of the relat�ve loss �n cohes�on of the BSM, ass�st �n the class�ficat�on of the m�x. The values are shown �n Table 4.7.

MIST

The MIST test procedure and l�m�ts may need rev�s�on as the test �s w�dely adopted. Check www.asphaltacademy.co.za/b�tstab for the latest test procedure and limits.

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CHAPTER 4: Mix Design – Procedure

40

The MIST test �s new and �s �ntroduced because �t g�ves the most real�st�c s�mulat�on of pore pressures generated �n BSMs that have been exposed to water under traffic. And, therefore �t g�ves the best assessment of m�x durab�l�ty. Because the test �s new, �t may be necessary to rev�se the test method, or the l�m�ts assoc�ated w�th the tests. Check the www.asphaltacademy.co.za/b�tstab to obta�n the latest values. Table 4 7 Interpretation of Triaxial Tests

Test or Indicator BSM1 BSM2 BSM3

Cohes�on (kPa) > 250 100 to 250 50 to 100

Fr�ct�on Angle (°) > 40 30 to 40 < 30

Reta�ned cohes�on (MIST) > 75 60 to 75 50 to 60

4.5. MIX DESIGN PROCEDURE The complete m�x des�gn procedure �s expla�ned by means of the flow chart �n F�gure 4.5. Each level �s d�scussed �n the follow�ng sect�ons.

4 5 1 LEVEL 1 MIX DESIGN Level 1 M�x Des�gn ut�l�ses Ind�rect Tens�le Strength (ITS) tests on 100 mm d�ameter spec�mens to:

Ind�cate the opt�mum b�tumen content us�ng ITSdry, and ITSwet and TSR.Select the act�ve filler type and content us�ng ITSwet and TSR.

The spec�mens are cured accord�ng to Sect�on 4.3.5. The opt�mum b�nder content �s determ�ned by ensur�ng the ITSwet �s suffic�ently h�gh. The l�m�ts �n Table 4.6 should be used.

4 5 2 LEVEL 2 MIX DESIGN Level 2 M�x Des�gn ut�l�ses the Ind�rect Tens�le Strength (ITS) tests on 150 mm d�ameter spec�mens. Spec�mens are cured accord�ng to Sect�on 4.3.5. The ITS allows the b�nder content to be determ�ned w�th �ncreased confidence. The procedure uses the follow�ng tests:

Tens�le strength at equ�l�br�um mo�sture cond�t�ons (us�ng ITSequ�l).Tens�le strength after mo�sture exposure (us�ng ITSsoaked).

Values of ITSequ�l and ITSsoaked used for BSM class�ficat�on are �ncluded �n Table 4.6.

4 5 3 LEVEL 3 MIX DESIGNLevel 3 m�x des�gn ut�l�zes tr�ax�al test�ng to assess the shear strength of the BSM and the mo�sture res�stance v�a the MIST apparatus.

Values of cohes�on, fr�ct�on angle, and reta�ned cohes�on for m�x assessment are g�ven �n Table 4.7.

If a Level 3 m�x des�gn �s performed, �t �s not necessary to also do a Level 2 m�x des�gn.

»»

»»

Level 1 Mix Design

All traffic levelsITSdry, ITSwet and TSR

For b�tumen type and content opt�m�sat�onAct�ve filler and amount select�on Mater�al class�ficat�on for traffic < 3 MESA

»»

•

•

•

i

Level 2 Mix Design

> 3 MESA traffic levelsITSequ�l and ITSsoaked

B�tumen content final�sat�on

»»

•

i

Level 3 Mix Design

> 6 MESA traffic levelsTr�ax�al (w�th MIST)

Shear propert�esMo�sture res�stance

»»

••

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CHAPTER 4: Mix Design – Procedure

41

Figure 4.5 Mix Design Flow Chart for BSM Mixes

PRELIMINARY STEPS•Aggregate selection and blending•Aggregate classification•Pre-treatment

LEVEL 1 Mix Design•Using Selected Aggregate Blend•Consider Climate & Early Traffic

Treatment Type Foamed BitumenBitumen Emulsion

Expansion Ratio& Half-life

Acceptable?

Aggregate-EmulsionCompatibilityAcceptable?

Compaction & CureVibratory or Marshallφ=100mm specimens•ITS dry and soak

NO

•Select bitumen type and content•Select filler type and content•Results acceptable?

LEVEL 2 MIX DESIGN

Vibratory Compaction & Cure at Optimumsφ=150mm h=127mm• ITS equil and ITS soak

LEVEL 3 MIX DESIGN

NO

Vibratory Compaction & Cure at Optimumsφ=150mm h=300mm•Triaxial (monotonic)• MIST (wet) triaxial

FINALISE MIX SELECTIONDETERMINE DEMAC AND CERTAINTY

YES

YES

NO

Done

NO

•Optimise bitumen content•Check ITS results•Results acceptable?

Design Traffic < 3 MESA

DoneDesign Traffic < 6 MESA

YES

YES

YES

NO

YES

NO





Acceptable?



NO


LEVEL 2 MIX DESIGN


LEVEL 3 MIX DESIGN

NO



YES

YES

NO

Done

NO




YES

YES

YES

NO

YES

NO





Acceptable?



NO


LEVEL 2 MIX DESIGN


LEVEL 3 MIX DESIGN

NO



YES

YES

NO

Done

NO




YES

YES

YES

NO

YES

NO


CHAPTER 5: Structural Design – General

42

5. STRUCTURAL DESIGNThe bas�c pr�nc�ple of pavement des�gn �s to prov�de structural layers to protect the pavement subgrade aga�nst the stresses �mposed by traffic. The comb�ned system, cons�st�ng of the structural layers and the subgrade, should then funct�on as a un�t �n a balanced system to ach�eve the des�red des�gn structural capac�ty. In essence, pavement balance requ�res that there should be a gradual decrease �n strength from the top to the bottom pavement layers and that the strength of the structural pavement layers should not greatly exceed that of the subgrade. The except�on to th�s �s the use of �nverted pavement structures �n South Afr�ca, although the structural layers typ�cally have more strength than the subgrade. The structural des�gn of pavements w�th BSM layers should follow these general pr�nc�ples and cogn�sance should be pa�d to general pavement des�gn and rehab�l�tat�on gu�del�nes, such as TRH4 and TRH12.

Th�s chapter presents the structural des�gn methods recommended for BSMs. For pavements carry�ng between 1 and 30 MESA and Category A (95% rel�ab�l�ty) and Category B (90%) rel�ab�l�ty, the Pavement Number Method �s recommended. Th�s �s d�scussed �n Sect�on 5.1. For pavements wh�ch have des�gn traffic less than 1 MESA and are Category B, C (80% rel�ab�l�ty) or D (50% rel�ab�l�ty), the catalogue of des�gns �s recommended. The catalogue �s presented �n Sect�on 5.2. Th�s chapter also d�scusses Appropr�ate Surfac�ngs (Sect�on 5.3) and Econom�c Analyses and Ma�ntenance Requ�rements (Sect�on 5.4).

The structural des�gn of BSMs does not d�fferent�ate between BSM-emuls�on and BSM-foam. 5.1. PAVEMENT NUMBER STRUCTURAL DESIGN METHODThe structural des�gn of pavements �ncorporat�ng BSMs uses a knowledge based approach, termed the Pavement Number (PN). The PN method �s appl�cable to Category A and B roads where the des�gn traffic �s between 1 and 30 MESA.

The PN �s based on the Structural Number concept, wh�ch was used �n the or�g�nal AASHTO methods. However, some of the shortcom�ngs of the Structural Number have been overcome �n the PN method. The complete descr�pt�on of the PN method �s g�ven �n Append�x C. The PN method was chosen for several reasons:

Data from �n-serv�ce pavements were used to develop the method. The type and deta�l of the data suggests the use of a relat�vely s�mple method and precludes the use of a Mechan�st�c-Emp�r�cal des�gn method. The method g�ves a good fit to the ava�lable field data.The method �s robust, and cannot eas�ly be man�pulated to produce �nappropr�ate des�gns.

The method �s appl�cable to all pavement mater�als commonly used �n southern Afr�ca. Th�s method rel�es on bas�c rules-of-thumb, wh�ch reflect well-establ�shed pr�nc�ples of pavement behav�our and performance, and wh�ch w�ll ensure an appropr�ate pavement des�gn solut�on �n most s�tuat�ons. The concepts �n the rules-of-thumb are quant�fied �nto spec�fic rules w�th constants or funct�ons assoc�ated w�th each rule. The rules-of-thumb are br�efly descr�bed �n the follow�ng sect�ons.

The constants shown for the PN method �ncluded �n th�s gu�del�ne and the Append�x were the values used at the t�me of publ�cat�on of the gu�del�ne. Although these values are well val�dated �t may be necessary from t�me to t�me to make changes to �mprove the system. If changes are made, the mod�fied values w�ll be reflected on www.asphaltacademy.co.za/b�tstab. It �s therefore recommended that before commenc�ng a Pavement Number calculat�on, the webs�te �s checked for any changes �n values or tests. The PN method �s des�gned to be used �n conjunct�on w�th the mater�al class�ficat�on system descr�bed �n Chapter 3.

5 1 1 APPLICABILITY OF PAVEMENT NUMBER METHODBefore the Pavement Number method �s used, the des�gner must check that the follow�ng s�tuat�ons do not apply:

Design traffic greater than 30 MESA. The method was cal�brated us�ng a knowledge base wh�ch was l�m�ted to pavements that had accommodated less than 30 MESA. Thus, �n such a des�gn s�tuat�on, the des�gn should be checked us�ng more �n-depth analys�s.

»

»»

»

BSM-emulsion ≡ BSM-foam

The structural des�gn of BSMs does not differentiate between BSM-emuls�on and BSM-foam.

i

PN Method

Complete deta�ls of the PN method are g�ven �n Appendix C.

The most recent values for the method, and software to perform a calculat�on are ava�lable on www.asphaltacademy.co.za/b�tstab

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CHAPTER 5: Structural Design – Pavement Number

43

Presence of thin, weak lenses If th�n, weak lenses of mater�al ex�st below the surfac�ng, or between stab�l�sed layers, then zones of h�gh sl�p and shear w�ll develop, and the PN calculat�ons w�ll not apply. In such �nstances, the structural capac�ty assessment of the PN method �s not appropr�ate, and spec�al treatment of the affected weak lens must be undertaken. The PN des�gn method cannot be appl�ed to s�tuat�ons where such lenses st�ll ex�st w�th�n the pavement structure, espec�ally where such lenses are located w�th�n the upper 400 mm of the pavement structure.Subgrade CBR less than 3% The knowledge base on wh�ch the PN method was cal�brated d�d not �nclude any pavements that had a subgrade CBR less than 3%. The PN method should therefore not be used �n cases where the subgrade CBR �s less than 3% at a depth 600 mm below the surface.

5 1 2 RULES OF THUMB / DEPARTURE POINTSTh�s sect�on presents a d�scuss�on of the bas�c rules-of-thumb underly�ng the method for calculat�ng the PN. These rules reflect well-establ�shed pr�nc�ples of pavement behav�our and performance. The follow�ng rules-of-thumb, w�th part�cular reference to BSMs were adopted:

Rules Relat�ng to the Pavement System in General:The structural capac�ty of a pavement �s a funct�on of the comb�ned long term load spreading potent�al of the pavement layers and the relative quality of the subgrade on wh�ch the pavement �s constructed.The relative quality and stiffness of the subgrade �s the departure po�nt for des�gn, as the subgrade �s a key determ�nant �n the overall pavement deflect�on, and �n the relat�ve degree of bend�ng and shear that w�ll take place �n overly�ng pavement layers.For pavements w�th th�n surfac�ngs, the base layer is the most critical component, and fa�lure �n th�s layer effect�vely const�tutes pavement fa�lure. Exper�ence can gu�de the relat�ve confidence �n d�fferent mater�al types to serve as base layers under heavy traffic.

Rules Relat�ng to Specific Pavement Layers:The load spreading potential of an �nd�v�dual layer �s a product of �ts th�ckness and �ts effect�ve long term st�ffness under load�ng.The Effective Long Term Stiffness (ELTS) of a layer depends on the mater�al type and class and on �ts placement �n the pavement system.F�ne-gra�ned subgrade mater�als act �n a stress-softening manner. For these mater�als, the ELTS �s determ�ned ma�nly by the mater�al qual�ty and by the cl�mat�c reg�on. Ow�ng to the stress soften�ng behav�our, subgrade mater�als w�ll generally soften w�th decreased cover th�ckness.Coarse-gra�ned, unbound layers act �n a stress-stiffening manner. For these mater�als, the ELTS �s determ�ned ma�nly by the mater�al qual�ty and the relat�ve st�ffness of the support�ng layer. The ELTS of these mater�als w�ll �ncrease w�th �ncreas�ng support st�ffness, by means of the modular ratio l�m�t, up to a maximum stiffness wh�ch �s determ�ned ma�nly by the mater�al qual�ty.BSMs are assumed to act �n a s�m�lar way to coarse granular mater�als but w�th a h�gher cohes�ve strength. The cohes�ve strength �s subject to breakdown dur�ng load�ng and thus some soften�ng over t�me can occur. The rate of soften�ng �s ma�nly determ�ned by the st�ffness of the support, wh�ch determ�nes the degree of shear �n the layer. However, ow�ng to the h�gher cohes�ve strength �n b�tum�nous stab�l�sed mater�als, these layers are less sens�t�ve to the support st�ffness than unbound granular mater�als and can therefore sustain higher modular ratio limits. If the cement content of a BSM m�x exceeds 1% then the mater�al �s assumed to behave as a cemented mater�al.

The above-noted rules-of-thumb �ntroduce several concepts such as the ELTS, modular rat�o l�m�t, max�mum st�ffness and stress-st�ffen�ng behav�our. These terms are br�efly descr�bed �n the follow�ng sect�on.

5 1 2 1 The Effective Long Term Stiffness (ELTS)The ELTS �s a model parameter wh�ch serves as a relat�ve �nd�cator of the average long term �n s�tu st�ffness of a pavement layer. As such, the ELTS averages out the effects of decreas�ng st�ffness ow�ng to traffic related deter�orat�on, as well as seasonal var�at�ons �n st�ffness. Thus the ELTS does not represent the st�ffness of a mater�al at any spec�fic t�me. The ELTS �s also not a st�ffness value that can be determ�ned by means of a laboratory or field

»

»

»•

•

•

»•

•

•

•

•

Behaviour of BSMs

BSMs can sustain higher modular ratio limits than granular mater�al because of the �mproved cohesive strength.

i

ELTS

Th�s �s a relat�ve �nd�cator of the average long term in situ stiffness, and does not represent the st�ffness at any spec�fic t�me.

i



44

test. It �s a model parameter, wh�ch �s cal�brated for use �n the PN des�gn method and �t may therefore d�ffer from st�ffness values typ�cally assoc�ated w�th mater�al classes.

5 1 2 2 Modelling of Subgrade MaterialsCharacter�zat�on of the support �s cr�t�cal to the pavement des�gn of all pavements, �nclud�ng pavements w�th BSM layers. For new construct�on, the TRH4 procedure for del�neat�on of the �n s�tu subgrade and for �mport�ng selected subgrade mater�al, �f necessary when the structural strength of the �n s�tu subgrade �s �nsuffic�ent, appl�es to the PN method. For rehab�l�tat�on projects, the gu�del�nes �n TRH12 for evaluat�ng and des�gn�ng for chang�ng support cond�t�ons should be followed �n conjunct�on w�th the PN method.

The first step �n the calculat�on of the PN-value �s the determ�nat�on of the subgrade mater�al class. To do th�s, spec�fic gu�del�nes are prov�ded �n Append�x C.

Once the subgrade class has been determ�ned, the ELTS for the subgrade �s calculated. Th�s �nvolves the follow�ng steps:Ass�gnment of a bas�c long term st�ffness based on the mater�als class.Adjustment of the bas�c long term st�ffness for d�fferent cl�mat�c reg�ons (wet, dry or moderate).Adjustment of the st�ffness determ�ned to take account of depth of subgrade cover.

The adjustment of the subgrade st�ffness to take account of the depth of cover g�ves an �nd�cat�on of the stress-soften�ng tendenc�es of fine gra�ned mater�als under load. The deta�ls on the relat�onsh�p between the cover depth and the adjustment to the subgrade st�ffness are g�ven �n Append�x C. 5 1 2 3 The Modular Ratio Limit and Maximum StiffnessThe modular rat�o �s defined as the rat�o of a layer’s st�ffness relat�ve to the st�ffness of the layer below �t. Thus, �f the st�ffness of a base layer �s 300 MPa, and the st�ffness of the support below �t �s 200 MPa, then the modular rat�o of the base layer would be 1.5.

The modular rat�o accounts for the stress-sens�t�ve st�ffness of granular and, albe�t to a lesser extent, BSM mater�als. The stress-sens�t�v�ty causes the st�ffness of the mater�al to decrease when the mater�al �s placed over a weaker (less st�ff) support. Th�s decrease �n st�ffness occurs where the support layer �s soft, caus�ng a tendency for the overly�ng layers to bend �nto the support, thereby �ncreas�ng the l�kel�hood of develop�ng h�gher shear and tens�le forces �n the overly�ng layers. Th�s effect l�m�ts the st�ffness that can be obta�ned �n a stress-sens�t�ve layer placed over a weaker support. By plac�ng a l�m�t on the modular rat�o that can be susta�ned for a spec�fic mater�al, �t �s ensured that the st�ffness value assumed for that layer �s real�st�c, g�ven the mater�al qual�ty and st�ffness of the support. In essence, the concept of a l�m�t�ng modular rat�o for mater�als ensures that stress-sens�t�ve st�ffness behav�our �s �mpl�c�tly taken �nto account.

The modular rat�o that a mater�al can susta�n var�es over the l�fe of a pavement and �n the PN method �t perta�ns to the overall long term st�ffness that a mater�al can ma�nta�n.

5 1 2 4 Maximum Stiffness Under the act�on of load�ng, there �s a max�mum st�ffness that mater�als can ach�eve. As w�th the modular rat�o, the max�mum st�ffness depends on the qual�ty of the mater�al. Less dense and angular mater�als w�ll not develop very h�gh st�ffnesses under load�ng, regardless of the st�ffness of the support.

In the PN model, the modular rat�o l�m�t and the max�mum allowed st�ffness are used extens�vely to determ�ne real�st�c ELTS values. These parameters are used �n the follow�ng way:

The stiffness of the supporting layer �s first determ�ned. Thus the PN calculat�on process starts from the subgrade and proceeds upward toward the surfac�ng.The modular ratio limit and maximum allowed stiffness for each layer are determ�ned based on the mater�al type and class.

1.2.3.

1.

2.

Subgrade ELTS

Depends on:Mater�al classCl�mateDepth of cover

»»»

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Modular Ratio

Th�s �s rat�o of a layer’s stiffness relat�ve to the st�ffness of the layer below.

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45

The ELTS for a layer �s determ�ned as the m�n�mum of the support st�ffness mult�pl�ed w�th the modular rat�o l�m�t and the max�mum allowed layer st�ffness.

The ELTS values for BSMs are h�gher than that of granular mater�als because they can susta�n a h�gher st�ffness. In the case of base layers, the ELTS �s further adjusted by means of a base confidence factor.

5 1 2 5 The Base Confidence FactorThe type of mater�al �n the base layer �s an �mportant determ�nant of the performance of the pavement because the base �s the ma�n load bear�ng element �n the pavement system and fa�lure of the base effect�vely const�tutes pavement fa�lure. Exper�ence has shown that there �s a l�m�t on the types of base mater�als that can be cons�dered for any g�ven traffic s�tuat�on. In part�cular, su�table des�gn opt�ons are s�gn�ficantly l�m�ted as the des�gn traffic �ncreases.

In the PN method, the appropr�ateness of the base mater�al �s controlled by the Base Confidence Factor (BCF) wh�ch �s used to adjust the ELTS for the layer.

5 1 3 PAVEMENT NUMBER CALCULATIONAppend�x C conta�ns the full deta�ls of the PN calculat�on along w�th a worked example. The ma�n steps are summar�zed below. In a pavement des�gn s�tuat�on, the steps descr�bed are appl�ed for each un�form des�gn sect�on. For rehab�l�tat�on des�gn s�tuat�ons, �t �s thus presumed that the des�gner w�ll have deta�led �nformat�on on the ex�st�ng pavement layer propert�es for each un�form sect�on. Step 1: Check to ensure that the des�gn method �s appl�cable for the des�gn s�tuat�on. Step 2: Determ�ne the layer th�cknesses, and ava�lable mater�al propert�es for each layer. Determ�ne the des�gn equ�valent mater�al class

(DEMAC) us�ng the gu�del�nes �n Chapter 3 and Append�x A. To prevent the use of unreal�st�c layer th�cknesses, max�mum and m�n�mum l�m�ts are g�ven. BSM layers can only have a th�ckness between 100 mm and 350 mm. Values outs�de these l�m�ts have not been val�dated.

Step 3: Comb�ne layers w�th s�m�lar propert�es to obta�n a five layer pavement system, �nclud�ng the subgrade (�.e. four layers plus the subgrade). Check that the layer th�cknesses do not exceed the max�mum for des�gn purposes.

Step 4: Determ�ne the bas�c st�ffness of the subgrade by means of the g�ven values (Append�x C). Adjust the st�ffness for the cl�mat�c reg�on and depth of subgrade cover.

Step 5: For each layer above the subgrade, determ�ne the modular rat�o l�m�t and max�mum allowed st�ffness.

Step 6: Use the modular rat�o l�m�t and max�mum allowed st�ffness to determ�ne the ELTS for each layer by work�ng up from the subgrade.

Step 7: For the base layer, determ�ne the Base Confidence Factor (BCF). Step 8: For each layer, calculate the layer contr�but�on us�ng the ELTS, layer th�ckness and BCF

(for base layers). Step 9: Add the layer contr�but�ons for each layer to get the PN.

The values used for the ELTS, modular rat�o, layer th�ckness l�m�ts and BCF are spec�fic to the PN method and should not be adjusted by the des�gner. The relevant values for BSMs are shown �n Table 5.1. BSM3 values are not g�ven as BSM3 mater�als are appl�cable to des�gn traffic less than 1 MESA and �n these s�tuat�ons the des�gn catalogue should be used.

3.

BCF

To prevent the use of inappropriate bases, a Base Confidence Factor �s ass�gned, wh�ch depends on the type of mater�als.

i

PN Inputs

The ELTS, modular rat�o, layer th�ckness l�m�ts and BCF are spec�fic for the PN method should not be changed by the user.

i


CHAPTER 5: Structural Design – Catalogue

46

Table 5 1 Modular Ratio Limit and Maximum Allowed Stiffness for Pavement Layers

Design Equivalent Material Class BSM1 BSM2

General Material DescriptionH�gh strength b�tumen stab�l�sed mater�al, normally us�ng crushed stone or recla�med

asphalt (RA) source mater�al

Med�um strength b�tumen stab�l�sed mater�al, normally us�ng natural gravel or

RA source mater�al

Modular Ratio Limit 3.0 2.0

Maximum Allowed Stiffness (MPa) 600 450

Base Confidence Factor 1.0 0.7

Thickness limit 100 mm to 350 mm

5.2. CATALOGUE OF DESIGNS FOR LOWER TRAFFICKED ROADSThe PN Des�gn Method �s only val�d for Category A and B roads that carry more than 1 MESA. For des�gn s�tuat�ons that w�ll carry less than 1 MESA, the catalogue �n F�gure 5.1 should be used. The catalogue �s only appl�cable to Category B, C and D roads.

The catalogue �s appl�cable to new construct�on, however, �t may also be used as a gu�del�ne for rehab�l�tat�on. For rehab�l�tat�on purposes, the ex�st�ng pavement s�tuat�on should be matched to the nearest catalogue des�gn, ensur�ng that the ex�st�ng mater�als are not weaker than the catalogue des�gn.

The mater�al classes shown �n the catalogue should be obta�ned from the mater�al class�ficat�on system descr�bed �n Chapter 3. The S symbol �n the catalogue represents a double seal.


CHAPTER 5: Structural Design – Catalogue

47

Figure 5.1 Catalogue of Designs for BSM Pavements Carrying up to 1 MESA

3 to 7

7 to 15

> 15D (50% Reliability)

3 to 7

7 to 15

> 15

C (80 % Reliability)

3 to 7

7 to 15

> 15B (95% Reliability)

ES1300 000 to 1 000 000

ES0.3≤ 300 000

Road Category

Foundation(CBR)

Pavement Class and Design Bearing Capacity

3 to 7

7 to 15

> 15D (50% Reliability)

3 to 7

7 to 15

> 15

C (80 % Reliability)

3 to 7

7 to 15

> 15B (95% Reliability)

ES1300 000 to 1 000 000

ES0.3≤ 300 000

Road Category

Foundation(CBR)

Pavement Class and Design Bearing Capacity

S125 BSM2S125 BSM2

S125 BSM2

150 G6

S125 BSM2

150 G6

S125 BSM2

150 G5

150 G7

150 G9

S125 BSM2

150 G5

150 G7

150 G9

40 AC

300 BSM2

40 AC

300 BSM2

S100 BSM3

125 G6

S100 BSM3

125 G6

S125 BSM3S125 BSM3

S125 BSM3

150 G6

S125 BSM3

150 G6

S150 BSM3S150 BSM3

S125 BSM3

125 G6125 G6

125 G7

S125 BSM3

125 G6125 G6

125 G7

S

300 BSM3

S

300 BSM3

S125 BSM3

150 G5

150 G7

S125 BSM3

150 G5

150 G7

40 AC

200 BSM3

40 AC

200 BSM3

S

125 G6

125 G7

100 BSM3

125 G9

S

125 G6

125 G7

100 BSM3

125 G9

40 AC

200 BSM3

40 AC

200 BSM3

S

150 BSM3

150 G5

150 G7

150 G9

S

150 BSM3

150 G5

150 G7

150 G9

40 AC

200 BSM3

40 AC

200 BSM3

S100 BSM3S100 BSM3

S100 BSM3S100 BSM3

S100 BSM3

125 G6

S100 BSM3

125 G6

S

250 BSM3

S

250 BSM3

S100 BSM3

125 G6

S100 BSM3S100 BSM3

125 G6

30 AC

150 BSM3

30 AC

150 BSM3

300 BSM3

S

300 BSM3

SS

125 G6

125 BSM3

S

125 G6

125 BSM3

S

125 BSM3

150 G6

S

125 BSM3

150 G6

30 AC

175 BSM3

30 AC

175 BSM3


CHAPTER 5: Structural Design – Appropriate Surfacings

48

5.3. APPROPRIATE SURFACINGSThe select�on of a surfac�ng type to overlay a BSM base should be based on sound structural des�gn and econom�c cons�derat�ons as well as the funct�onal requ�rements of the road. Based on observat�ons from �n-serv�ce pavements, roads carry�ng �n excess of 1 MESA had HMA surfac�ngs, often �n comb�nat�on w�th a s�ngle seal. Based on these observat�ons, recommendat�ons for the m�n�mum surfac�ng th�ckness are shown �n F�gure 5.2. For traffic less than 1 MESA, a surfac�ng seal should be adequate. For traffic between 1 and 15 MESA, the formula shown �n F�gure 5.2 should be used, w�th the th�ckness rounded to the nearest 5 mm. For traffic exceed�ng 15 MESA, an HMA th�ckness of at least 50 mm �s recommended.

Figure 5.2 Minimum Surfacing Thickness for BSM Pavements

5.4. ECONOMIC ANALYSES AND MAINTENANCE REQUIREMENTSThe purpose of structural pavement des�gn �s to �dent�fy pavements w�th the same structural capac�ty that meet the traffic demand. The present worth of the construct�on and l�fe-cycle cost of the alternat�ve des�gns are then compared to select the most cost effect�ve des�gn. The alternat�ves should be compared �n terms of total project cost. The reader �s referred to TRH4 (Table 24) and to Table 5.2 below for an �nd�cat�on of the est�mated typ�cal future ma�ntenance requ�rements for l�fe cycle cost analys�s. The est�mates �n Table 5.2 assume a 20 year structural des�gn l�fe.

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25 30 35 40 45

Traffic Allowed (MESA)

Su

rfac

ing

Th

ickn

ess

(mm

)

If traffic allowed:- < 1 MESA, surfacing seal- between 1 and 15 MESA, thickness = 1.4·MESA + 29.8- > 15 MESA, HMA thickness ≥ 50 mm

Surfacings

Pavements carry�ng > 1 MESA should have an

HMA surfac�ng.



CHAPTER 5: Structural Design – Economic Analysis

49

Table 5 2 Typical Future Maintenance Measures for BSM Base Pavements

Measures to improve the surfacing condition Structural maintenance

Original surfacingModerate distress Severe distress

Surface treatment Asphalt

S1 (9 years) 1

S1 (14 years)S1 (19 years)

S1 (12 years)S1 (17 years)2

30 to 40 mm AG, AC3> 100 mm BTB4

BSM Overlay5

Notes: 1. S1 (5 years) represents a s�ngle surface treatment after five years.2. For low trafficked roads th�s seal may be replaced w�th a 50 mm overlay to �ncrease the structural capac�ty.3. AG and AC are asphalt surfac�ngs.4. BTB �s b�tumen treated base.5. BSM overlay should be plant m�xed.

The d�scount present worth of cost approach descr�bed �n TRH4 �s recommended for the project level analys�s of pavements conta�n�ng BSM layers. The cost compar�son should not attempt to just�fy the econom�c benefits of a labour-�ntens�vely constructed pavement by compar�son w�th that of a mach�ne-constructed pavement. The dec�s�on to use labour-�ntens�ve construct�on should be taken at a pol�cy level, not at the project level.


CHAPTER 6: Construction – General

50

6. CONSTRUCTIONTh�s chapter prov�des gu�del�nes for construct�ng pavement layers us�ng BSMs. An explanat�on of the general construct�on approach to BSMs �s prov�ded, followed by spec�fic construct�on requ�rements for work�ng w�th BSMs regardless of whether foamed b�tumen or b�tumen emuls�on �s used as the stab�l�s�ng agent. Aspects spec�fic to e�ther BSM-emuls�on or BSM-foam are clearly h�ghl�ghted.

From a construct�on perspect�ve, once b�tumen emuls�on or foamed b�tumen has been m�xed �nto a mater�al, the result�ng BSM behaves �n a s�m�lar way to an untreated mater�al. The var�ous construct�on operat�ons requ�red to place the mater�al, cut levels, compact to ach�eve the requ�red level of dens�ty and fin�sh off the new layer are pract�cally the same as those that would be used had the mater�al not been treated. The performance propert�es of the layer of treated mater�al are, however, d�fferent from those of the untreated mater�al. The behav�oural character�st�cs that �nfluence the workab�l�ty of the mater�al before �t �s finally compacted and fin�shed off are s�m�lar to that of untreated mater�als. Contrary to some m�sconcept�ons, the add�t�on of foamed b�tumen or b�tumen emuls�on to a granular mater�al w�ll not create a cold-m�x asphalt look-al�ke. The treated mater�al w�ll rema�n granular �n nature and must be processed �n the same way as the untreated mater�al would be processed for layer construct�on.

The pr�mary factor �nfluenc�ng the approach to construct�on �s the type of project that �s be�ng undertaken. F�gure 6.1 �llustrates the opt�ons ava�lable for BSMs.

Figure 6.1 BSM Construction Options

The type of project and the spec�fic requ�rements for construct�ng a new layer us�ng a BSM falls �nto two pr�mary categor�es, new construct�on or pavement rehab�l�tat�on/upgrad�ng. The method selected for treat�ng the mater�al w�th b�tumen, �n s�tu or �n-plant w�ll then determ�ne the opt�ons ava�lable for process�ng the mater�al to construct the layer. In s�tu treatment requ�res a d�fferent construct�on approach to mater�al that �s treated �n-plant and these are expla�ned �n two separate sect�ons. In s�tu treatment �s covered �n Sect�on 6.1 to 6.3 and �n-plant treatment �n Sect�on 6.4. These sect�ons cover the complete construct�on procedure, �nclud�ng mater�al preparat�on, m�x�ng, plac�ng, ach�ev�ng the requ�red levels, compact�on and fin�sh�ng. Th�s �s followed by sect�ons that are common to all BSM construct�on projects, wh�ch �ncludes cur�ng the fin�shed layer, traffick�ng, surfac�ng, construct�ng tr�al sect�ons and, finally, qual�ty control requ�rements. Deta�ls for controll�ng the product (both process and acceptance controls) are �ncluded �n Append�x D.

TYPE OF PROJECT

In Situ Recyclers

Conventional Plant(BSM-emulsion only)

Paver laid

Labour intensiveconstruction

New Construction Rehabilitation / Upgrading

In Situ Treatment In-Plant Mixing

CONSTRUCTIONMETHOD

Conventional PlantIn Situ Recyclers

Conventional Plant(BSM-emulsion only)


CONSTRUCTIONMETHOD

TYPE OF PROJECT


CONSTRUCTIONMETHOD

In Situ Treatment In-Plant Mixing

CONSTRUCTIONMETHOD

TYPE OF PROJECTTYPE OF PROJECT

In Situ Recyclers

Conventional Plant(BSM-emulsion only)Conventional Plant

(BSM-emulsion only)Paver Laid

Labour intensiveconstruction

Labour IntensiveConstruction

New Construction Rehabilitation / UpgradingNew Construction Rehabilitation / Upgrading

In Situ Treatment In-Plant MixingIn Situ Treatment In-Plant Mixing

CONSTRUCTIONMETHOD

Conventional PlantConventional PlantIn Situ Recyclers

Conventional Plant(BSM-emulsion only)Conventional Plant

(BSM-emulsion only)


CONSTRUCTIONMETHOD

TYPE OF PROJECTTYPE OF PROJECT


CONSTRUCTIONMETHOD

In Situ Treatment In-Plant MixingIn Situ Treatment In-Plant Mixing

CONSTRUCTIONMETHOD



CHAPTER 6: Construction – In situ Treatment Using Recyclers

51

6.1. IN SITU TREATMENT (GENERAL)Although purpose-bu�lt recycl�ng mach�nes have generally replaced convent�onal construct�on equ�pment (graders, ploughs, rotavators, etc.) for �n s�tu treatment, convent�onal equ�pment rema�ns an opt�on for BSM-emuls�on on projects where the cost of establ�sh�ng a large recycler may not be just�fied. Construct�on w�th recyclers and convent�onal equ�pment �s d�scussed �n Sect�ons 6.2 and 6.3, respect�vely.

BSM-emulsion

Only BSM-emuls�on can be constructed us�ng e�ther of the two �n s�tu opt�ons. The use of convent�onal equ�pment needs careful process control to ensure proper m�x�ng.

BSM-foam

Foamed b�tumen cannot be constructed us�ng convent�onal construct�on equ�pment. Th�s �s because of the spec�al�sed equ�pment requ�red to foam the b�tumen and because of the short t�me requ�red to m�x the foam �nto the mater�al.

6 1 1 DILUTING BITUMEN EMULSION WITH WATERUnt�l the advent of recyclers, b�tumen emuls�on was always d�luted pr�or to m�x�ng. Th�s pract�se �s st�ll requ�red when us�ng convent�onal equ�pment.

The need to d�lute the b�tumen emuls�on when us�ng recyclers �s dependant on two factors:The application rate of the bitumen emulsion B�tumen emuls�on must always be d�luted where the appl�cat�on rate of b�tumen emuls�on (as opposed to res�dual b�tumen) �s less than 2%. Th�s �s to ensure suffic�ent spraybar pressure and adequate flu�d for effect�ve m�x�ng. The number of spraybars on the recycler When the appl�cat�on rate �s suffic�ently h�gh, b�tumen emuls�on and water can be appl�ed separately prov�ded the recycler �s fitted w�th two spraybars. In th�s case, the water must be appl�ed pr�or to the b�tumen emuls�on, wh�ch typ�cally requ�res the water spraybar to be mounted below the b�tumen emuls�on spraybar. When und�luted b�tumen emuls�on �s used, the b�tumen emuls�on must be preheated to 60 °C. Where the recycler has only one spraybar, b�tumen emuls�on must always be appl�ed �n the d�luted form. However, �t �s h�ghly recommended that only recyclers fitted w�th two �ntegrated computer-controlled spraybars are used for BSM-emuls�on. Th�s allows good control of mo�sture content adjustment dur�ng m�x�ng.

After the mater�al has been treated w�th b�tumen emuls�on, should add�t�onal flu�d need to be added, �t �s good pract�ce to use a d�luted b�tumen emuls�on (”d�rty water”) as opposed to water on �ts own.

6.2. IN SITU TREATMENT USING RECYCLERSTh�s sect�on descr�bes the operat�ons when us�ng a recycler to treat mater�al from the ex�st�ng road w�th b�tumen. Th�s �s appl�cable to both new construct�on and rehab�l�tat�on. In add�t�on to the recycl�ng operat�on that �ncorporates the m�x�ng process, th�s sect�on �ncludes plac�ng and compact�ng the treated mater�al, as well as fin�sh�ng off the treated layer. The �ntent�on here �s not to repl�cate the general�t�es of recycl�ng but rather to h�ghl�ght those �ssues that are �mportant when construct�ng a new BSM layer us�ng a recycler.

In s�tu treatment us�ng convent�onal construct�on equ�pment �s covered separately �n Sect�on 6.3.

6 2 1 FACTORS REQUIRING CONSIDERATION (PLANNING THE WORK)

The da�ly product�on of a recycl�ng tra�n can be h�gh. Add�t�onally there are demands to open the completed work to traffic at the end of each day’s work. Met�culous plann�ng and d�l�gent execut�on �s requ�red to ensure that the output potent�al �s real�sed w�thout

»

»

Conventional Equipment

BSM-foam �s not su�table for construct�on w�th convent�onal equ�pment.

Number of spraybars

It �s h�ghly recommended that recyclers are fitted w�th two spraybars.

i

Recycling Projects

Meticulous planning and diligent execution

�s requ�red for recycl�ng projects us�ng recyclers.



52

comprom�s�ng qual�ty and at the same t�me ensur�ng that the BSM product stands up to early traffic load�ng. The factors that need to be cons�dered when plann�ng recycl�ng projects are descr�bed �n the follow�ng sect�ons.

6 2 1 1 Equipment SelectionThe recycl�ng mach�ne, bulk supply tankers and large pr�mary roller are �tems of plant that are not generally used for road construct�on. In add�t�on, equ�pment used for spread�ng the low appl�cat�on rates of act�ve filler normally spec�fied w�th BSM needs careful cons�derat�on. Suffic�ent equ�pment must be ava�lable to ensure that a good qual�ty BSM can be produced w�th�n the allowed work�ng per�od. The follow�ng requ�rements for the recycler, bulk tankers, spreaders for act�ve filler and compactors are recommended:

i RecyclerThe recycler works �n tandem w�th other construct�on plant, such as water and b�tumen tankers. Several types of recycl�ng mach�nes are ava�lable, rang�ng from s�mple stab�l�sers to purpose-bu�lt tyre-mounted recyclers w�th computer controlled appl�cat�on systems. Although the dec�s�on as to wh�ch mach�ne �s best su�ted to a spec�fic project �s pr�mar�ly �nfluenced by the s�ze and type of project, �t �s a cr�t�cal dec�s�on s�nce the outcome of the project w�ll be d�ctated by the ab�l�ty of the mach�ne to do the job. The recycler used for treatment of the mater�al w�th b�tumen should meet the follow�ng m�n�mum requ�rements:

Sufficient horsepower to cut/mill �nto the pavement to the requ�red depth and s�multaneously push the recycl�ng “tra�n”.Suffic�ent volume in the milling chamber to accommodate and m�x the mater�al generated by the m�ll�ng or pulver�s�ng to the requ�red depth.Two �ndependent m�cro-processor controlled appl�cat�on systems w�th separate spray bars; one for the b�tumen and the other for apply�ng water to �ncrease the mo�sture content of the recycled mater�al.A pos�t�ve control system for ma�nta�n�ng the set-up of the recycler (depth of cut and relat�ve �ncl�nat�on).

Track-mounted recyclers are m�ll�ng mach�nes that have been adapted to s�multaneously recycle and treat the mater�al. The�r capab�l�t�es are d�fferent from tyre-mounted recyclers, pr�mar�ly due to:

The smaller diameter of the milling drum and the mounting of the cutting tools on the drum results �n a lower per�pheral speed of the tools on a track-mounted recycler compared to those on a tyre-mounted recycler. The mount�ng of the cutt�ng tools of m�ll�ng mach�nes and recyclers are �llustrated �n F�gure 6.2.

Figure 6.2 Mounting of Cutting Tools on Milling Machines and Recyclers

The d�fferences �n the cutt�ng tools have a d�rect �nfluence on the grad�ng of the recycled mater�al and on the qual�ty of the m�x. The cutt�ng tool pattern on a m�ll�ng drum w�ndrows the mater�al to the centre where �t ex�ts through a door at the rear of the m�ll�ng chamber. On a recycler, the cutt�ng tool pattern l�m�ts mater�al movement to a max�mum 200 mm hor�zontally.Large m�ll�ng mach�nes have the m�ll�ng chamber and drum attached to the chass�s whereas most recyclers have the m�ll�ng chamber attached to the chass�s w�th the drum on a sw�ng arm that moves away from the chass�s as �t �s lowered �nto the pavement. The capac�ty of the m�ll�ng chamber on m�ll�ng mach�nes �s therefore constant, and the depth of cut �s l�m�ted to the amount of mater�al that can be accommodated. Th�s �n turn �s d�ctated by the amount of bulk�ng that occurs when the mater�al �s pulver�sed.

»»

»

»

»

»»

»

Milling Machine (Track Mounted Recyclers) Recycler (Tyre Mounted)



53

The BSM produced by a track-mounted recycler w�ll therefore be d�fferent from that produced by a tyre-mounted recycler �n terms of grad�ng and m�x qual�ty. Exper�ence has shown that better qual�ty BSMs are produced by tyre-mounted recyclers on th�ck layers.

The number of recyclers deployed on a project obv�ously has a s�gn�ficant �mpact on product�on potent�al. More than one pass �s normally requ�red to cover the w�dth to be treated �n one sh�ft (for a road half-w�dth or traffic lane), therefore product�ve t�me w�ll be wasted when only a s�ngle recycler �s used, wh�ch has to reverse to make a second pass. Such wasted t�me can be el�m�nated by deploy�ng two recyclers work�ng �n echelon (one �mmed�ately beh�nd the other, but offset), thereby cover�ng the full recycl�ng w�dth as d�ctated by the geometry of the cross-sect�on. The effic�ency of such an operat�on �s further �ncreased by the �mproved effic�ency of the grader cutt�ng final levels.

ii Bitumen Application SystemThe m�cro-processor controlled pump�ng system mounted on the recycler must be des�gned to mon�tor and adjust the appl�cat�on rate of the b�tumen �n accordance w�th the volume of mater�al be�ng recovered as the recycler advances. The b�tumen �s sprayed �nto the m�ll�ng chamber and �s m�xed w�th the recycled mater�al. The b�tumen emuls�on and b�tumen used to foam must meet the requ�rements �n Sect�on 6.2.2.

BSM-emulsion

The pump �ncorporated �nto the b�tumen emuls�on system on the recycler, together w�th the �nject�on nozzles fitted on the spraybar need to be “b�tumen emuls�on fr�endly” to prevent premature break�ng. Gear-type pumps and ultra-h�gh pressure nozzles w�ll cause the b�tumen emuls�on to break �nstantly (so-called flash break). Once the b�tumen emuls�on has broken, m�x�ng �s �mposs�ble and the m�ll�ng chamber on the recycler w�ll clog up to such an extent that �t can take several hours to clear.

BSM-foam

The foamed b�tumen appl�cat�on system �s one of the most �mportant determ�nants of the qual�ty of the final m�x. Poor or �ncons�stent foam�ng w�ll produce a m�x w�th many str�ngers and, �n the worst extreme, blobs of st�cky, sh�ny b�tumen w�ll be produced �f the b�tumen �s not foam�ng. These are �nd�cators of poor foam�ng character�st�cs and �nadequate b�tumen d�spers�on. Such a m�x w�ll not meet performance expectat�ons.

Before accept�ng any foamed b�tumen system on a project, �t should be checked to ensure that �t has a proven track record of successful appl�cat�ons. Homemade and other systems, such as those that create foam by squ�rt�ng water at a spray of hot b�tumen (so-called “external foam�ng systems”) should not be used. Such systems produce �ncons�stent foam, wh�ch results �n a poor m�x.

The system must have the capab�l�ty of demonstrat�ng that �t �s free from blockages, both pr�or to work commenc�ng and at any stage dur�ng the operat�on.

In add�t�on, the system must be equ�pped w�th a “test nozzle” that operates under the same temperature and pressure cond�t�ons as the spraybar. Such a test nozzle must have the capab�l�ty of produc�ng a representat�ve sample of foamed b�tumen at any stage of the operat�on.

iii Bulk TankersB�tumen, b�tumen emuls�on and water tankers coupled to the recycler should be s�zed �n accordance w�th the scope of the work and geometry of the road. In general, s�ngle-chass�s tanker un�ts (max�mum capac�ty of 15 000 l�tres) are preferred on small projects and/or where the road al�gnment has low geometr�c standards. Large sem�-tra�ler bulk tankers are usually used on large projects through flat terra�n.



54

All tankers should be �nspected for leaks pr�or to coupl�ng �nto the recycl�ng tra�n. A b�tumen or water leak causes l�ttle harm wh�le the tra�n �s mov�ng but can g�ve r�se to wet soft spots when the tra�n �s stat�onary (e.g. when chang�ng cutt�ng tools) and the dr�p falls on loose recycled mater�al for a prolonged per�od.

iv Compaction EquipmentThe type of mater�al and th�ckness of layer be�ng compacted w�ll d�ctate the type and number of rollers requ�red on a project. Three rollers are usually used to compact the recycled mater�al. The “pr�mary” roller w�th a stat�c mass commensurate w�th the th�ckness of the layer (normally fitted w�th a padfoot drum) �s first deployed �mmed�ately beh�nd the recycler to apply h�gh-ampl�tude v�brat�ng compact�ve effort that penetrates through to the bottom of the treated layer. After final levels have been cut, a smooth drum roller w�th a stat�c mass of about 10 tons apply�ng low-ampl�tude v�brat�ng effort �s used to finally compact the upper port�on of the constructed layer. A pneumat�c-tyred roller (PTR) �s then used for fin�sh�ng the layer.

The pr�mary roller �s cr�t�cal to ach�eve dens�ty �n the lower half of the BSM layer. F�gure 6.3 �s a bas�c gu�de for select�ng the stat�c mass and type of roller for d�fferent comb�nat�ons of layer th�ckness and grad�ng character�st�cs of the mater�al be�ng compacted.

Figure 6.3 Primary Roller Selection Guide

V�brat�ng padfoot rollers tend to leave pockmarks (�ndentat�ons) �n the surface of the layer wh�ch cannot be el�m�nated when a th�n surface treatment �s appl�ed. However, such pockmarks �n a completed layer are actually an �nd�cat�on of e�ther �nsuffic�ent compact�on or poor construct�on pract�ces, or both. W�th good compact�on pract�ces, the follow�ng should be ach�eved:

As more roller passes are applied, the �ncreased compact�ve effort results �n a greater dens�ty be�ng ach�eved �n the lower reg�ons of the BSM layer. As th�s dens�ty �ncreases, so does the res�stance to penetrat�on by the �nd�v�dual pads on the roller, w�th the result that the padfoot �mpr�nts w�ll r�se h�gher and h�gher w�th�n the body of the layer as the roller “walks out” of the mater�al. These scenar�os are �llustrated �n F�gure 6.4.

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Figure 6.4 Padfoot Roller Imprints on Material Being Compacted

Elimination of such pockmarks requ�res the jud�c�ous add�t�on of water or d�luted b�tumen emuls�on sprayed from a water tanker (Sect�on 6.3.4), blad�ng w�th the grader wh�lst cutt�ng the final levels and secondary compact�on w�th a smooth drum v�brat�ng roller. It must, however, be recogn�sed that th�s operat�on requ�res exper�ence to avo�d surface lam�nat�ons or b�scu�t layers form�ng, espec�ally when work�ng w�th fine graded mater�als.

6 2 1 2 Traffic AccommodationProv�s�ons always need to be made for the safe accommodat�on of publ�c traffic. Recycl�ng work �s usually done �n half-w�dths, or by clos�ng off only a port�on of the ex�st�ng road. Correct s�gnage, del�neators and traffic control measures all need to be �n place before any work can start.

6 2 1 3 Survey ControlMost pavement rehab�l�tat�on projects call for the ex�st�ng road to be recycled �n place, thereby reta�n�ng ex�st�ng surface levels and shape. Th�s also m�n�m�ses the need for extens�ve survey and des�gn �nput. The survey �s best carr�ed out by stak�ng the ex�st�ng road and transferr�ng relevant surface elevat�ons to a ser�es of level-control posts placed at regular �ntervals outs�de both shoulder edges.Standard survey controls are recommended for new construct�on.

6 2 1 4 Material Preparation

i Recycled MaterialRecycl�ng mach�nes pulver�se the ex�st�ng pavement layer(s) to the requ�red depth, break�ng down the upper port�on of a layered pavement structure to a produce mater�al that �s essent�ally granular �n nature. The m�ll�ng drum on a recycler �s des�gned to break down prev�ously bound mater�al, such as asphalt and cement treated bases.

Due to the upward rotat�ng d�rect�on of the m�ll�ng drum, the recla�med mater�al �s l�fted and tends to “fall apart” �nto a graded mater�al, rather than be�ng crushed �nto smaller part�cles. Very l�ttle aggregate crush�ng occurs. The degree of pulver�sat�on actually ach�eved depends on the strength and cond�t�on of the �n s�tu mater�al. L�ghtly cemented mater�al generally produces an aggregate grad�ng resembl�ng that used �n the or�g�nal construct�on. The fines content should, however, be checked.

The grad�ng of recla�med asphalt (RA) �s more d�fficult to control s�nce �t �s �nfluenced by several var�ables, �nclud�ng:The degree of oxidation of the bitumen in the RA For example, recently appl�ed asphalt patches conta�n�ng fresh b�tumen w�ll break down d�fferently from the aged asphalt.The total thickness of asphalt Th�n layers tend to produce more “chunks” than th�ck layers.

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Deep imprints of padfoot roller (Initial stage of compaction)

Padfoot roller “walking out” of compacted material leaving “pockmarks”

Pockmarks from Vibrating Rollers

Pockmarks from v�brat�ng padfoot rollers are generally an �nd�cat�on of insufficient compaction and / or poor construction practices



56

The original asphalt mix, part�cularly the qual�ty and grad�ng of the aggregate.The extent and geometry of any crocodile cracking �n the upper asphalt layers.The condition of the bond between var�ous asphalt overlays �n the ex�st�ng pavement.The peripheral speed of the cutting tools on the milling drum, machine advance speed and the position of the “breaker bar” mounted at the front of the m�ll�ng chamber.The temperature of the asphalt dur�ng the recycl�ng process.

One of the ma�n reasons for conduct�ng a Tr�al Sect�on (descr�bed �n Sect�on 6.7) �s to determ�ne how the mater�al �n the ex�st�ng pavement w�ll break down when recycled. Such Tr�al Sect�ons should therefore be carefully selected to be truly representat�ve of the pavement that w�ll be recycled.

ii Pre-Milling Any pre-m�ll�ng of asphalt must be undertaken us�ng a m�ll�ng mach�ne, not a recycler. The removal of some of the asphalt mater�al �s somet�mes requ�red to ensure that the post-recycl�ng levels w�ll match w�th ex�st�ng elevat�on constra�nts (e.g. kerbs, �ntersect�on t�e-�ns, etc.). In add�t�on part�al-depth pre-m�ll�ng w�thout remov�ng the RA may be necessary to break down asphalt layers that are severely d�stressed, such as pavements w�th advanced crocod�le crack�ng. The purpose of pre-m�ll�ng such asphalt layers �s to el�m�nate overs�zed part�cles such as asphalt chunks. To ach�eve the requ�red mater�al breakdown, the depth of pre-m�ll�ng must be less than the th�ckness of asphalt.

iii Pre-PulverisingPre-pulver�s�ng an ex�st�ng pavement pr�or to recycl�ng and treat�ng w�th b�tumen �s normally only cons�dered when the follow�ng cond�t�ons are present �n the ex�st�ng pavement:

Surface irregularities are s�gn�ficant relat�ve to the depth of recycl�ng or the surface �s so badly out of shape that the recycler w�ll be unable to ach�eve a cons�stent depth of cut.The recycling depth �ncludes pavement layers that requ�re more power than the recycler can del�ver to break down the mater�al wh�lst s�multaneously ach�ev�ng suffic�ent and constant advance speed. Suffic�ent advance speed �s �mportant as th�s d�ctates the flow rate for b�tumen wh�ch, �n turn, determ�nes the operat�ng pressures. Such tough m�ll�ng cond�t�ons are usually assoc�ated w�th th�ck layers of aged asphalt and strongly cemented layers.When mater�al needs to be cross-blended across the pavement to ach�eve un�form�ty. Th�s s�tuat�on �s normally encountered where the road was prev�ously w�dened us�ng d�fferent mater�als from those used �n the or�g�nal pavement, and �s d�scussed below.For mater�als exh�b�t�ng plast�c�ty, cons�derat�on may need to be g�ven to chemical modification, typ�cally us�ng hydrated l�me. (See Sect�on 4.2.3)

Where pre-pulver�s�ng �s deemed necessary, the depth of cut dur�ng the �n�t�al pulver�s�ng pass must be carefully controlled to ensure that a th�n layer (normally 50 mm) of the ex�st�ng layer rema�ns to be recycled w�th the second stab�l�s�ng pass. In add�t�on, a water cart should be coupled to the recycler and water added wh�lst pre-pulver�s�ng so that the loosened mater�al can be compacted and levels cut to prov�de the recycler w�th the correct surface shape for the second stab�l�s�ng pass. The dens�ty requ�rement for compact�on of the pre-pulver�sed mater�al �s normally 93% of the mod�fied AASHTO dens�ty.

iv Material ImportFor the reasons expla�ned �n Sect�on 2.6.3.1, some projects requ�re v�rg�n mater�al to be �mported and spread on the ex�st�ng road surface pr�or to recycl�ng. Such mater�al �s normally hauled to s�te and dumped pr�or to add�ng water, m�x�ng and plac�ng by grader to the requ�red surface shape. The mater�al �s then compacted to 93% of the mod�fied AASHTO dens�ty.

Where the ex�st�ng road �s so badly out of shape that the th�ckness of the �mported layer w�ll vary excess�vely, the ex�st�ng pavement should be pulver�sed and shaped (as descr�bed above) pr�or to �mport�ng and plac�ng the new mater�al.

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Pre-milling Asphalt

Pre-m�ll�ng of asphalt must be undertaken us�ng a milling machine not a recycler.

Density of pre-pulverised material

The dens�ty requ�rement for compact�on of the pre-pulver�sed mater�al �s normally 93% of modified AASHTO

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The mater�al �mport and preparat�on �s normally undertaken �mmed�ately ahead of recycl�ng. When work�ng �n half-w�dths, such add�t�onal mater�al can often result �n a vert�cal step on the centre-l�ne. Where th�s presents a safety hazard, both half-w�dths should be recycled dur�ng the same work sh�ft.

v Material Cross-BlendingSome pavement layers �nclude mater�al type or qual�ty d�fferences across the w�dth of the road, often result�ng from pavement w�den�ng operat�ons. It �s not uncommon to encounter graded crushed stone �n the base layer of the carr�ageway and a natural gravel mater�al �n the shoulder base layer.

Recyclers do not cross-blend mater�als (max�mum lateral movement of mater�al part�cles �s 200 mm). Blend�ng two mater�als to ach�eve un�form�ty across the carr�ageway and shoulder requ�res one of the follow�ng two opt�ons:

Pre-pulverise the shoulder base layer only, blade the result�ng mater�al on top of the adjacent traffic lane of the carr�ageway, spread as a un�form layer and pre-compact. The depth of recycl�ng and treatment on the carr�ageway �s then �ncreased to �nclude th�s added mater�al w�th the underly�ng �n s�tu mater�al, thereby obta�n�ng a homogenous blend. Once blended, the mater�al �s spread and processed across the full w�dth of the carr�ageway and shoulder.Pre-pulverise the entire half width, cross-blend the loosened mater�al w�th a grader, spread, shape and pre-compact before mak�ng another pass w�th the recycler to add the b�tumen.

6 2 1 5 Spreading Active FillerAny act�ve filler requ�rements are usually met by accurately spread�ng the filler on the road surface �mmed�ately pr�or to commenc�ng work w�th the recycler. Such spread�ng �s normally confined to one cut w�dth at a t�me rather than spread�ng over the ent�re half-w�dth of road.

The appl�cat�on rate for cement or l�me normally appl�ed w�th BSMs �s always low (1% by mass). Such low appl�cat�on rates are d�fficult to ach�eve w�th suffic�ent accuracy when us�ng the bulk spreaders that are normally employed for cement stab�l�sat�on where h�gher percentages are spec�fied. As stated above, recyclers do not “cross or forward blend” mater�al, the max�mum part�cle movement �n the hor�zontal plane �s 200 mm. The accurate spread�ng and d�str�but�on of act�ve filler ahead of the recycler �s therefore very �mportant. Where bulk spreaders cannot ach�eve the degree of accuracy requ�red, they should not be used.

Alternat�ve appl�cat�on methods such as hand-spread�ng w�th rubber squeegees �mmed�ately ahead of the recycl�ng tra�n, purpose-bu�lt spreaders or slurry �nject�on us�ng spec�al�sed equ�pment can be �ncorporated �nto the recycl�ng tra�n. When us�ng slurry �nject�on, the part�cle s�ze of cement may vary and such var�at�on should be noted as �t may affect the accuracy of appl�cat�on. To m�n�m�se var�at�ons, the use of cons�stent sources and standard rout�nes for spread�ng are recommended.

6 2 1 6 Working on Steep GradientsIn add�t�on to recycl�ng the mater�al, the recycler �s the “locomot�ve” for push�ng (or pull�ng) two bulk tankers, one conta�n�ng hot b�tumen or b�tumen emuls�on, the other water. Where slurry �nject�on �s used for apply�ng the act�ve filler, the water tanker �s replaced w�th a heavy spec�al�sed slurry m�x�ng un�t.

The most commonly used recyclers are tyre-mounted w�th each wheel be�ng dr�ven by a hydraul�c motor. The two rear wheels always run on loose recycled mater�al. Tract�on between the front tyres and road surface can be lost on steeper grad�ents when work�ng uph�ll, part�cularly where the mater�al was pre-pulver�sed. Th�s leads to several problems, the most cr�t�cal be�ng an over-appl�cat�on of b�tumen and water due to sl�ppage of the front wheels where the speed of advance �s measured and relayed to the computer controll�ng the supply pumps. Steep grad�ents should therefore be recycled by work�ng downh�ll w�th due cons�derat�on g�ven to ma�nta�n�ng suffic�ent suppl�es �n the respect�ve tankers.

6 2 1 7 Cut Plan, Overlaps and Longitudinal JointsDue to the demand for early traffick�ng coupled w�th the configurat�on of the spraybars commonly �n use, an �mportant cons�derat�on when treat�ng w�th b�tumen �s the locat�on of the outer wheel-path relat�ve to the long�tud�nal jo�nt between adjacent cuts. Such an

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Cement Contents

The cement content of BSMs should be ≤ 1%, and

the cement content should not exceed the b�tumen content.



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overlap �nvar�ably falls �n the outer wheel-path when recycl�ng s�ngle carr�ageway roads �n half-w�dths where the overall surfaced w�dth �s between 7 and 10 metres. F�gure 6.5 g�ves an example for a 9.4 metre w�de pavement.

Figure 6.5 Typical Recycling Cut Plan Showing the Overlap Relative to the Outer Wheel Path

Over-appl�cat�on of the b�tumen and water, or d�luted b�tumen emuls�on, �n the overlap must be avo�ded to prevent the overlap mater�al from be�ng too wet. To prevent over appl�cat�on of the b�tumen, the standard pract�ce when deal�ng w�th overlaps �s to reduce the w�dth of appl�cat�on by select�vely clos�ng off nozzles at the affected end of the spray bars. Unless the w�dth of overlap �s s�gn�ficant (e.g. approach�ng half the cut w�dth), nozzles should only be closed on one of the cuts. Normally the first cut �s made to �nclude the outer wheel path w�th full-w�dth appl�cat�on (�.e. all nozzles open). The w�dth of appl�cat�on �s then reduced on the second cut by select�vely clos�ng off those nozzles co�nc�d�ng w�th the overlap. Fa�lure to ensure that the outer wheel-path rece�ves the requ�red treatment can result �n an under-appl�cat�on of b�tumen and premature fa�lure.

Th�s s�tuat�on, �llustrated �n F�gure 6.6, occurred where the overlap between two passes co�nc�ded w�th the outer wheel path. Incorrect nozzle closure caused �nsuffic�ent b�tumen to be appl�ed across the overlap and traffic has caused excess�ve ravell�ng along the outer wheel-path. The lack of ravell�ng on the �nner wheel path �nd�cates that the correct appl�cat�on of b�tumen was ach�eved.

Figure 6.6 Bitumen Starvation along Longitudinal Joint

Outer wheel -path

Carriageway

Shoulder

1000 m

3700 m~1200 m

CUT 1CUT 2

2500 m2500 m Overlap

300 m

Centreline

Outer wheel -path

Carriageway

Shoulder

1000 m

3700 m~1200 m

CUT 1CUT 2

2500 m2500 m Overlap

300 m

Centreline

Cut 1

Cut 2



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However, to ensure cont�nu�ty across the w�dth of the road, adjacent cuts must always overlap by at least 150 mm. Th�s means that the second cut must extend at least 150 mm �nto the mater�al already recycled and treated dur�ng the first cut.

BSM-emulsion

Extreme care must be exerc�sed when add�ng b�tumen emuls�on to an �n s�tu mater�al that has a relat�vely h�gh mo�sture content. An over-appl�cat�on on the overlap w�ll result �n soft spots �n the mater�al along the full length of the long�tud�nal jo�nt.

BSM-foam

As a general rule when work�ng w�th foamed b�tumen, �t �s preferable to a�m for a small (approx�mately 10%) over-appl�cat�on on the overlap rather than an under-appl�cat�on.

It �s therefore recommended that a cut plan should always be comp�led and the deta�led spraybar configurat�on show�ng each nozzle locat�on �s super�mposed on the d�agram to �llustrate the effect of clos�ng �nd�v�dual nozzles.

6 2 1 8 LogisticsThe log�st�cal requ�rements for feed�ng a recycl�ng operat�on w�th b�tumen, act�ve filler and water must rece�ve due attent�on. An average da�ly product�on rate of 5 000 m² (about 1.4 km of 3.7 m w�de lane) can be expected from a modern recycler, regardless of the depth of cut. Assum�ng a cut depth of 250 mm, an average dens�ty of 2 100 kg/m³ and appl�cat�on rates of 2.2% res�dual b�tumen and 1.0% act�ve filler (by mass) translates to the follow�ng approx�mate da�ly consumpt�on of mater�als:

BSM-emulsion

96 tons of 60% b�tumen emuls�on»

BSM-foam

58 tons of b�tumen for foam�ng»

25 tons of act�ve filler (500 x 50 kg pockets of cement or 1 000 x 25 kg bags of hydrated l�me). Th�s l�me quant�ty �s �n add�t�on to any pre-treatment requ�rements.

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These are s�gn�ficant da�ly quant�t�es. Where the s�te �s d�stant from the source of supply, temporary storage fac�l�t�es need to be made ava�lable to ensure a cons�stent supply, thereby reduc�ng the potent�al for delays caused by mater�al shortages.

6 2 2 EXECUTING THE WORKM�x�ng w�th b�tumen emuls�on or foamed b�tumen, comb�ned w�th pr�mary compact�on, shap�ng, cutt�ng final levels, secondary compact�on and fin�sh�ng should ach�eve the follow�ng object�ves:

Thorough mixing of the material with the bitumen The resultant m�x must be homogeneous w�th the same appearance throughout, w�th m�n�mal b�tumen “blobs” be�ng v�s�ble.Achieve the density requirements �n the lower two-th�rds of the layer w�th pr�mary compact�on.Achieve a layer that meets the tolerances for th�ckness, surface levels and shape that �s free from segregat�on of coarse or fine mater�al. Achieve full compaction and a uniform surface texture w�th secondary compact�on and fin�sh�ng.

To ach�eve these object�ves, there are two d�st�nct processes �nvolved when recycl�ng ex�st�ng pavement layers. The first �s the recycl�ng and m�x�ng process. Th�s �s usually accompl�shed �n a s�ngle pass w�th a recycler. The second process �s the work requ�red beh�nd the recycler, wh�ch �ncludes compact�ng the BSM, cutt�ng levels and fin�sh�ng off the constructed layer.

6 2 2 1 Occupational Health and SafetyStandard occupat�onal health and safety procedures must be followed when work�ng w�th BSMs, such as descr�bed �n the follow�ng SABITA manuals:

Manual 8: Gu�del�nes for the safe and respons�ble handl�ng of b�tum�nous products DVD 410: B�tSafe – The safe handl�ng of b�tumenDVD 420: B�tSafe – Work�ng w�th b�tumen burnsDVD 430: B�tSafe – Work�ng safely w�th b�tumen

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BSM-emulsion

Standard OHS procedures must be followed.

BSM-foam

B�tumen at temperatures �n excess of 160 °C can be dangerous. The equ�pment selected for the product�on of foamed b�tumen must be des�gned to prevent potent�al acc�dents.

6 2 2 2 Mixing and PlacingM�x�ng �s accompl�shed by assembl�ng a “tra�n” cons�st�ng of the recycler and one or two tankers. A typ�cal recycl�ng tra�n for treat�ng w�th b�tumen �s shown �n F�gure 6.7.

Figure 6.7 Typical Recycling Train for Bitumen Treatment

To reduce the potent�al for blockage, the length of the feed p�pe between the tanker and recycler should be m�n�m�sed by locat�ng the b�tumen tanker �mmed�ately ahead of the recycler. In add�t�on, to promote unrestr�cted suct�on flow to the b�tumen pump on the recycler, the �nternal d�ameter of th�s feed p�pe should not be less than 100 mm.

The water tanker can e�ther be coupled ahead of the b�tumen tanker and pushed (�mply�ng that the b�tumen tanker must be fitted w�th a front push-block) or be pulled beh�nd. E�ther locat�on requ�res a long flex�ble p�pe to feed the water to the �nlet coupl�ng located at the front of the recycler. All feed p�pes operate under suct�on and must therefore be capable of w�thstand�ng negat�ve pressure, �.e. not the “lay-flat” type of hose. F�tt�ng a valve at both ends of the water feed p�pe w�ll prevent large volumes of water from escap�ng when chang�ng water tankers. To prevent soft spots (descr�bed �n Sect�on 6.2.1), all feed p�pes must be free of leaks.

The essent�al requ�rements for a successful recycl�ng operat�on are �ncluded �n Append�x D.



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6 2 2 3 Bitumen Stabilising Agent Considerations

Bitumen Emulsion

Recycl�ng w�th b�tumen emuls�on �s often descr�bed as be�ng eas�er than foamed b�tumen. Th�s �s because a tanker conta�n�ng the b�tumen emuls�on �s brought to s�te, connected to the recycler and used w�thout the �nconven�ence of heat�ng and hav�ng to conduct a long l�st of checks. These cla�ms are largely true �f the follow�ng concerns are addressed:

Haulage and storage tankers B�tumen emuls�on �s manufactured under a spec�al�sed factory env�ronment that �s normally located �n an urban centre that may be some d�stance from the s�te. It �s therefore normally brought to s�te �n bulk tankers and e�ther used �mmed�ately by connect�ng the tanker to the recycler or pumped �nto a stat�onary tank for temporary storage. All haulage un�ts and storage tanks must be ded�cated to the sole use of one type of b�tumen emuls�on. If prev�ously used for a d�fferent type of b�tumen emuls�on (or other b�tum�nous product) the tank must first be thoroughly cleaned before be�ng used.

Use of correct bitumen emulsion Extreme care must be exerc�sed to ensure that the correct b�tumen emuls�on �s brought to s�te. Each tanker must have a del�very note �ssued at the po�nt of load�ng on wh�ch �s stated the deta�ls of the product and the load�ng cond�t�ons. Samples of each tanker load should be reta�ned for future test�ng, �f and when requ�red.

Storage and usage conditions Recommendat�ons from the manufacturer concern�ng storage and usage cond�t�ons and l�m�tat�ons must be met�culously followed to prevent product deter�orat�on or premature break�ng.

Heating requirements When und�luted b�tumen emuls�on �s used, to reduce v�scos�ty and fac�l�tate pump�ng, b�tumen emuls�on �s normally appl�ed through the recycler at 60 °C. Th�s means that the b�tumen emuls�on often needs to be heated on s�te. Such heat�ng must be undertaken under str�ct control, follow�ng the manufacturer’s gu�del�nes. As a m�n�mum, the b�tumen emuls�on needs to be c�rculated �n the tank wh�lst be�ng heated. Fa�lure to follow these gu�del�nes w�ll �nev�tably result �n a premature break.

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Foamed Bitumen

Foamed b�tumen �s “manufactured” from hot b�tumen on the recycl�ng mach�ne �mmed�ately before �t �s �njected �nto the m�ll�ng chamber. Understand�ng the process requ�res an apprec�at�on of the equ�pment deployed and the operat�ng systems on the equ�pment.

Foamed b�tumen �s produced �n a ser�es of expans�on chambers pos�t�oned equ�d�stant on a spraybars fitted to the m�ll�ng chamber. Prov�ded no ant�-foam�ng agents are present, all but the hardest b�tumens can be foamed and the foam�ng character�st�cs (expans�on rat�o and half-l�fe) are spec�fic to a part�cular b�tumen. These foam�ng character�st�cs are �nfluenced by several factors, all of wh�ch can be regulated to vary�ng extents on s�te. Although these factors were expla�ned �n Chapter 3 (M�x Des�gn), they are summar�sed below w�th part�cular emphas�s on the pract�cal s�te cons�derat�ons:

The temperature of the bitumen In general, the h�gher the temperature, the better the foam�ng character�st�cs due to the reduct�on �n v�scos�ty of the b�tumen. However, b�tumen should never be heated above 195 °C. In add�t�on to harden�ng the b�tumen, such h�gh temperatures can cause damage to the more sens�t�ve components �n the b�tumen ret�culat�on system on the recycler (e.g. flow meter sensors).

The quality of the water Relat�vely pure water should be used for foam�ng s�nce �mpur�t�es can block the water jets, prevent�ng the b�tumen from foam�ng.

The temperature of the water used for foaming Warm water, as w�ll typ�cally be exper�enced on s�te requ�res less energy than cold water, as �n an a�r-cond�t�oned laboratory, to effect the change �n state from l�qu�d to vapour.

The operating pressure in both the bitumen and water supply systems Operat�ng pressure �s a funct�on of flow and these two systems must be �nterl�nked and m�cro-processor controlled by the speed of advance of the recycler. The h�gher the pressure, the more un�form the foam due to better “atom�s�ng” of both l�qu�ds as they enter the expans�on chamber through the�r respect�ve jets. Conversely, the lower the pressure, the less un�form the foam.

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Water used for dilution D�lut�ng the b�tumen emuls�on w�th water �s often carr�ed out on s�te. Care must be exerc�sed to use relat�vely pure water because �mpur�t�es �n the water can cause the b�tumen emuls�on to break.

Addition of water during mixing D�lut�ng b�tumen emuls�on �s necessary where the recycler �s fitted w�th only one pump�ng or spraybar system and d�lut�on �s requ�red to obta�n the requ�red flu�d content �n the treated mater�al. When two spraybars are used, water �s appl�ed through one spraybar and b�tumen emuls�on the other. As d�scussed �n Sect�on 6.2.2.4, the mo�sture content of �n s�tu pavement mater�al �s never dry, nor �s �t cons�stent. Exper�ence has shown that add�ng water separately from the b�tumen emuls�on allows �mproved control �n ach�ev�ng the requ�red flu�d content �n the treated mater�al. Where the mater�al be�ng recycled �s dry (normally only encountered where v�rg�n mater�al has been �mported) an �n�t�al pre-treatment w�th the recycler add�ng only water w�ll ach�eve the correct mo�sture reg�me to accept the b�tumen emuls�on added by mak�ng a second pass w�th the recycler.

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The amount of water injected into the bitumen to create the foam The “opt�mal” amount of water add�t�on �s determ�ned �n�t�ally �n the laboratory. However, s�te cond�t�ons d�ffer from those �n the laboratory and water add�t�on often requ�res adjust�ng to ach�eve the best foam on the recycler.

In pract�ce, the foam produced �n the expans�on chambers on the recycler’s spraybar are always an �mprovement on those produced �n the laboratory. The ma�n reason for th�s �s the h�gher operat�ng pressure on a recycler (5 to 10 bars), compared to laboratory un�ts that normally funct�on at approx�mately 3 bars. In add�t�on, the temperature of the water used for foam�ng on s�te �s usually s�gn�ficantly warmer than tap water �n an a�r cond�t�oned laboratory. As a result, �t �s often poss�ble to ach�eve a workable foam at b�tumen temperatures less than the m�n�mum determ�ned �n the laboratory. It �s therefore �mportant to always check the foam�ng character�st�cs on s�te.

The recycler must be fitted w�th a funct�on�ng pressure gauge to allow the operator to ma�nta�n a m�n�mum operat�ng pressure above 5 bars. Where cutt�ng cond�t�ons become so tough that suffic�ent advance speed cannot be ach�eved to ma�nta�n such a pressure, pre-pulver�s�ng �s requ�red. Where the appl�cat�on rate of foamed b�tumen �s low (< 2%) and the depth of recycl�ng �s low (less than 200 mm), the b�tumen jets �n the expans�on chambers may need to be exchanged for ones w�th smaller d�ameters �n order to ma�nta�n suffic�ent pressure at normal operat�ng speeds. Under no c�rcumstances should the speed of advance be �ncreased above 12 m per m�nute �n order to �ncrease the b�tumen pressure as th�s w�ll negat�vely affect the qual�ty of the BSM-foam.

The foam�ng character�st�cs of each load of b�tumen must be checked us�ng the test nozzle (descr�bed �n Sect�on 6.2.1.1). In�t�al checks are normally made wh�le us�ng the test nozzle to bleed a�r from the system. Once an adequate foam �s observed, the tanker can be accepted and work commence. Defin�t�ve measurements of the expans�on rat�o and half-l�fe should only be made after the system has been �n operat�on for a few m�nutes (typ�cally 2 m�nutes) and a cons�stent operat�ng temperature and pressure have been reached.

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6 2 2 4 Moisture ConsiderationsThe mo�sture content of the m�xed mater�al �s one of the most �mportant var�ables d�rectly �nfluenc�ng the end-product. The effect�veness of b�tumen d�spers�on, the compact�ve effort requ�red to ach�eve dens�ty, and the potent�al for surface crack�ng are all s�gn�ficantly �nfluenced by not only the actual mo�sture content �tself, but also by the un�form�ty of the mo�sture content throughout the recycled mater�al.

Vary�ng mo�sture cond�t�ons �n the pavement layers must be expected. Mater�al beneath a b�tum�nous surface w�ll always be mo�st and the “equ�l�br�um mo�sture content” (EMC) relat�ve

Foaming Characteristics

The expansion ratio and half-life must be regularly checked on s�te. The recycler must be fitted w�th a test nozzle for such checks.

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Moisture Contents

Great care must be taken w�th the mo�sture content of the m�x as �t effects:

Bitumen dispersionCompaction achievedCuring time

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to the OMC of the mater�al �s pred�ctable. Hence, the EMC can be expected to be reasonably cons�stent where the mater�al �s s�m�lar. However, var�at�ons must be ant�c�pated when the follow�ng cond�t�ons are encountered:

Cracks in the surfacing allow water to penetrate �nto the underly�ng pavement layers, result�ng �n h�gher mo�sture �n the v�c�n�ty of the crack.Where the road has unsurfaced shoulders, an �ncrease �n mo�sture content at the h�gh s�de of super elevated curves should be expected.The pavement materials at the bottom of sag vertical curves �s often more mo�st than elsewhere �n the pavement.

Pavements w�th natural or crushed stone bases that have many deep asphalt patches may be prone to saturat�on when recycled. M�x�ng RA (from patches and pavement layers) w�th a granular base mater�al w�ll produce a blend that has a lower OMC value than the or�g�nal base mater�al. However, th�s �s normally only encountered where the EMC �n the base approx�mates the OMC, a cond�t�on most l�kely to be encountered dur�ng wet seasons and where the surfac�ng �s severely cracked.

Where the �n s�tu mo�sture content of the mater�al to be recycled �s above the OMC, the mater�al must first be dr�ed back before �t can be treated. Th�s �s normally ach�eved by pre-pulver�s�ng on a warm day and leav�ng the loose mater�al open to dry. When the mo�sture content has reduced suffic�ently, the pulver�sed mater�al must be shaped and pre-compacted before be�ng treated.

BSM-emulsion

Standard South Afr�can pract�ce when treat�ng w�th b�tumen emuls�on �s to target a flu�d content of 90% of OMC for m�x�ng.

BSM-foam

M�x�ng �s �deal when the mo�sture content of the mater�al �s at the “fluff po�nt” (approx�mately 70% to 80% of OMC).

6 2 2 5 Compaction, Cutting Levels and FinishingCompact�ng th�ck layers of BSM �s s�m�lar to compact�ng th�ck layers of granular mater�al. Us�ng the correct compact�on equ�pment �s cr�t�cal (number and types of rollers, drum configurat�on, stat�c mass, v�brat�on capab�l�t�es), as �s the�r correct operat�on (travel speed, roll�ng pattern and number of passes) and the sequence of roll�ng, e.g. padfoot first.

The correct roll�ng sequence �s normally determ�ned dur�ng the construct�on of a Tr�al Sect�on, as descr�bed below �n Sect�on 6.7.The mater�al ex�t�ng the recycler �s �n a “fluffed-up” loose state. As shown �n F�gure 6.8, the rear wheels on the recycler run on th�s loose mater�al and compact �t. The heav�er the recycler, the more compact�on occurs. Measurements have shown that the d�fference �n dens�ty between the mater�al �n the wheel paths and that between the wheel paths �s some 10% of the mod�fied AASHTO dens�ty.

It �s �mperat�ve that the mater�al between the wheel paths �s compacted to at least the same dens�ty as the mater�al �n the wheel paths before allow�ng the grader to start levell�ng. Fa�lure to follow th�s s�mple requ�rement w�ll result �n a permanent dens�ty d�fferent�al between the mater�al �n the wheel paths and that between the wheel paths. Th�s �s because the drum w�dth of standard rollers �s 2.14 m wh�ch �s always greater than the w�dth of uncompacted mater�al between the wheel paths. If th�s loose mater�al �s cut to the same elevat�on as the compacted mater�al �n the wheel paths, subsequent compact�on w�ll always br�dge-out across the wheel paths. The mater�al �n the wheel paths w�ll therefore be at a h�gher level of dens�ty relat�ve to the mater�al between the wheel paths.

Figure 6.8 Material Compacted by the Rear Wheels of the Recycler

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In�t�al roll�ng should always be carr�ed out us�ng a s�ngle-drum v�brat�ng roller w�th a stat�c mass that �s commensurate w�th the th�ckness of the layer be�ng compacted. The v�brat�on mode must be set on h�gh ampl�tude to ach�eve max�mum penetrat�on of compact�ve effort. The roll�ng pattern should first concentrate on the m�ddle sect�on between the rear wheel paths of the recycler, then across the full cut w�dth to ach�eve un�form dens�ty. Wh�lst compact�ng, the travel speed of the roller should never exceed 3 km/h (50 m/m�n).

Apply�ng low ampl�tude v�brat�on or us�ng a roller w�th �nsuffic�ent stat�c mass w�ll not �mpart suffic�ent compact�ve energy to penetrate through to the lower hor�zon of the layer. Only the mater�al �n the upper hor�zon of the layer w�ll dens�fy, thereby form�ng a br�dge of compacted mater�al over relat�vely loose mater�al. In t�me th�s loose mater�al w�ll dens�fy under repeated traffic loads and the result�ng settlement w�ll be regarded as a “premature fa�lure” (w�de-rad�us ruts �n the wheel paths).

When the recycler works at 10m/m�n, the pr�mary roller can make 5 (un�-d�rect�onal) passes at 3 km/h for the compact�on operat�on to keep pace w�th the recycler. Where the pr�mary roller needs to make more than 5 passes to ach�eve the dens�ty requ�rements, compact�on w�ll fall beh�nd the recycl�ng operat�on and cons�derat�on should be g�ven to us�ng two pr�mary rollers, one work�ng �mmed�ately beh�nd the other. In such cases, the second roller should be �dent�cal to the first. If the rollers fall beh�nd the recycler, the recycler must be stopped to allow the rollers to catch up.

Assum�ng that work �s be�ng undertaken �n half-w�dths, once the ent�re half-w�dth of the road has been recycled and treated, and the �n�t�al compact�on �s complete, a grader �s used to cut the final level. Recycled mater�al always bulks, part�cularly where the or�g�nal pavement �ncluded asphalt layers (due to the �ncrease �n vo�ds). A w�ndrow of surplus mater�al �s therefore always ava�lable after cutt�ng final levels to ass�st �n ach�ev�ng a t�ghtly-kn�t surface fin�sh.

S�nce there �s always a delay between recycl�ng, compact�ng and start�ng work w�th the grader, the mater�al at the surface of the layer w�ll dry out. Th�s dry�ng out �s exacerbated when us�ng a padfoot roller for pr�mary compact�on. To prevent lam�nat�ons form�ng, the surface must be g�ven a thorough wett�ng before the grader moves any mater�al.

BSM-emulsion

Before break�ng, b�tumen emuls�on can be washed out of the mater�al (leached) �f water �s used as a wett�ng agent. It �s �mportant therefore to use a water tanker conta�n�ng 10% to 15% d�luted b�tumen emuls�on for �ncreas�ng the mo�sture content of the mater�al. Th�s should be sprayed across the full recycled w�dth after the �n�t�al compact�on and �mmed�ately ahead of the grader. The b�tumen emuls�on must be evenly d�str�buted on the surface ahead of the grader do�ng the blad�ng.

BSM-foam

S�nce the b�tumen droplets adhere to the fine part�cles, they are not suscept�ble to leach�ng. Water can therefore be used for adjust�ng the mo�sture content of the mater�al.

A s�ngle smooth-drum v�brat�ng roller w�th a stat�c mass �n the order of 10 tons �s used beh�nd the grader to compact the upper hor�zon of the layer. Th�s roller works only �n low-ampl�tude v�brat�on mode. When complete, the surface �s subjected to a m�ld “slush�ng” us�ng a PTR to ach�eve a t�ghtly-kn�t surface fin�sh.

BSM-emulsion

Slush�ng �s undertaken us�ng only a 10% to 15% d�luted b�tumen emuls�on.

BSM-foam

Stra�ght water �s used, s�m�lar to fin�sh�ng off a layer of graded crushed stone mater�al (e.g. G2 mater�al).

The “m�ld slush�ng” process should not be confused w�th the “full-depth slush�ng” process assoc�ated w�th G1 crushed stone bases. The “m�ld slush�ng” �s merely a�med at �mprov�ng the cond�t�on and qual�ty of the top of the BSM base layer and kn�tt�ng together the surface.



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i Target Density for Recycled LayersS�nce the typ�cal mode of fa�lure for a layer of BSM �s pr�mar�ly permanent deformat�on, the dens�ty that �s ach�eved dur�ng construct�on �s cr�t�cal to ensure that the requ�red structural capac�ty of the layer �s reached. Increas�ng dens�ty �mproves the shear propert�es of the mater�al mak�ng �t less suscept�ble to deformat�on. Hence, the h�ghest dens�ty ach�evable should always be targeted.

Dens�ty requ�rements are usually spec�fied �n terms of a percentage of some reference dens�ty. Normally the max�mum dry dens�ty (MDD) of the mater�al �s used as the reference dens�ty and th�s MDD value �s determ�ned �n a so�ls laboratory by carry�ng out a standard mo�sture-dens�ty relat�onsh�p test on the mater�al. For base layers, at least 100% of the MDD �s the norm for BSM1 and BSM2, and at least 98% for BSM3.

The challenge �n ach�ev�ng a spec�fied dens�ty on a recycl�ng project �s twofold:Variations in the recycled material change the reference density A 5% reduct�on �n the MDD value (e.g. from 2 100 kg/m³ to 2 000 kg/m³) �s not unusual, espec�ally where the ex�st�ng road has been extens�vely patched. Us�ng an �ncorrect MDD value w�ll therefore over- or understate the dens�ty ach�eved, the latter be�ng class�fied as a fa�lure w�th the consequence that the layer could be rejected. To overcome th�s problem, a representat�ve MDD value has to be determ�ned by carry�ng out a mo�sture-dens�ty relat�onsh�p test on a sample collected from every locat�on where the field dens�ty �s measured. Th�s �s an onerous requ�rement as �t s�gn�ficantly �ncreases the amount of laboratory work requ�red on the project.The level of dens�ty that can be ach�eved �n a new BSM layer �s a funct�on of the underlying support conditions (the anv�l effect). S�nce mater�als recycled �n s�tu are compacted on top of ex�st�ng pavement layers, �t �s d�fficult to hold the contractor respons�ble for not ach�ev�ng a spec�fic level of dens�ty, prov�ded the appropr�ate equ�pment �s ut�l�sed and appropr�ate compact�on techn�ques are followed.

It �s normal pract�se to determ�ne the roll�ng sequence and number of rollers requ�red to ach�eve the target dens�ty from the tr�al sect�on.

To c�rcumvent these challenges, �t �s becom�ng �ncreas�ngly popular to spec�fy “refusal dens�ty” as the target, aga�n prov�ded the appropr�ate equ�pment �s ut�l�sed and appropr�ate compact�on techn�ques are followed. Refusal dens�ty �n th�s context �s the max�mum dens�ty that can be ach�eved on a mater�al under the preva�l�ng field cond�t�ons and takes cogn�sance of both mater�al character�st�cs and the underly�ng support cond�t�ons.

Recent developments �n compact�on technology (so called “�ntell�gent compact�on” systems) offer the opportun�ty to mon�tor dens�ty development and determ�ne when the max�mum has been ach�eved. These systems �ncorporate a “compactometer” fitted to the v�brat�ng drum to measure “rebound accelerat�on” wh�ch �s a measure of the response of the mater�al to an �mpulse (v�brat�on) wh�ch, �n turn, reflects the dens�ty of the mater�al. Coupl�ng these measurements w�th data from a dev�ce that records the prec�se locat�on of the roller (a GPS-based system work�ng w�th reference satell�tes) allows mult�ple measurements taken at the same locat�on to be compared. Us�ng a colour-coded d�splay mounted �n the cab, the roller operator can cont�nuously mon�tor dens�ty development at every locat�on. When success�ve passes of the roller show no further �ncrease �n dens�ty, the “refusal dens�ty” has been ach�eved and the roller can move forward to compact the next sect�on of work.

An add�t�onal benefit of employ�ng such a system �s the compact�on record that �s obta�ned at the end of the day’s work. Such data prov�des the follow�ng deta�led �nformat�on that covers the ent�re area where the roller worked:

Number of roller passes made (coverage) at any locat�on.The maximum compactometer reading ach�eved (an �nd�cat�on of the dens�ty ach�eved).Whether or not refusal density was actually ach�eved.

Th�s �nformat�on can then be analysed to prov�de deta�ls at any spec�fic locat�on on the s�te or the relevant compact�on stat�st�cs for a selected area. In th�s manner, reg�ons of poor support can be �dent�fied (low compactometer values) and �nvest�gated. A l�m�ted number of dens�ty tests w�ll also allow the compactometer read�ngs to be cal�brated �n terms of actual mater�al dens�ty, but only as an �nd�cator s�nce mater�al var�ab�l�ty w�ll pers�st, mak�ng any relat�onsh�p w�th an assumed MDD value mean�ngless.

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Benefits of achieving density

Increas�ng dens�ty �mproves the shear propert�es, mak�ng �t less susceptible to deformation

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Obtaining Density

To ach�eve the des�red dens�ty, �t �s essent�al that

the correct rollers, roller sequence and moisture contents are used.


CHAPTER 6: Construction – In situ Treatment Using Conventional Equipment

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It must, however, be understood that these systems are not a panacea and rely on correct roller select�on and operat�on to be effect�ve. Furthermore, �t �s v�tal that the mo�sture content of the mater�al be�ng compacted �s �n the requ�red range relat�ve to the OMC of the mater�al.

6.3. IN SITU TREATMENT USING CONVENTIONAL EQUIPMENT (BSM-EMULSIONTh�s sect�on descr�bes the operat�ons �nvolved when us�ng convent�onal construct�on equ�pment to m�x and treat mater�al.

BSM-emulsion

In s�tu treatment w�th convent�onal equ�pment can only be used for BSM-emuls�on treatment.

BSM-foam

Th�s method of construct�on cannot be used w�th foamed b�tumen because m�x�ng takes place over an extended per�od of t�me, far longer than the half-l�fe of foamed b�tumen.

Th�s sect�on focuses on the preparat�on and m�x�ng act�v�t�es wh�ch const�tutes the ma�n d�fferences �n construct�on between us�ng recyclers and convent�onal equ�pment to reuse ex�st�ng pavement mater�al for BSM-emuls�on treatment. Although recyclers have generally replaced convent�onal equ�pment for �n s�tu treatment, the use of convent�onal equ�pment rema�ns an opt�on and �s st�ll commonly used on projects where the depth of treatment �s 200 mm or less.

6 3 1 EQUIPMENT SELECTIONSuffic�ent water�ng, m�x�ng and compact�on plant �n good work�ng order must be ava�lable to ensure that the spec�fied quant�t�es of water, act�ve filler and b�tumen emuls�on can be m�xed �n and the requ�red degree of compact�on obta�ned w�th�n the work�ng per�od (8 to 10 hours) allowed by the process.

Var�ous �tems of plant can be prov�ded to cater for d�fferent methods of mater�al preparat�on, process�ng and subsequent compact�on depend�ng on the project needs. These are descr�bed �n the follow�ng sect�ons.

6 3 1 1 Self-Propelled Heavy Duty Motor GraderA heavy duty motor grader �s an essent�al �tem of plant for BSM-emuls�on treatment, �rrespect�ve of the comb�nat�on of any of the other plant �tems used. Th�s grader �s requ�red to pre-shape the mater�al pr�or to be�ng treated, for process�ng the mater�al and, thereafter, to cut the layer to final levels. Process�ng by grader �ncludes m�x�ng the mater�al pr�or to treatment and m�x�ng �n the act�ve filler and b�tumen emuls�on.

Depend�ng on the volume of mater�al be�ng m�xed and the quant�ty to be treated �n a s�ngle sh�ft, more than one grader may be requ�red.

6 3 1 2 Milling MachineA m�ll�ng mach�ne may be more cost effect�ve than a grader to break up a th�ck asphalt layer and/or a strongly cemented mater�al to produce a mater�al su�table for b�tumen emuls�on treatment. A m�ll�ng mach�ne �s generally more cost effect�ve when a prev�ously treated layer has fa�led, but rema�ns bound between the fa�led areas, w�th cube crush�ng strengths well �n excess of 5 MPa, or when an asphalt layer �s severely cracked and the large chunks need to be pulver�sed. When �n s�tu mater�al �s to be augmented w�th �mported mater�al, a m�ll�ng mach�ne can also be effect�vely used to blend the two mater�als after the add�t�onal mater�al has been levelled out on top of the �n s�tu mater�al and pre-shaped w�th a grader.

Alternat�vely, layers that have developed a h�gh �n s�tu strength can be broken down us�ng a ‘woodpecker-type’ breaker fitted to an excavator. The result�ng chunks of pavement mater�al can then be transported to a s�ngle-stage crusher to be crushed and transported back to the road for further process�ng.

6 3 1 3 Diluted Bitumen Emulsion TankersSelf-propelled water tankers, w�th a 15 000 l�tre capac�ty, are essent�al plant �tems for the successful construct�on of a BSM-emuls�on layer. In add�t�on to supply�ng the b�tumen emuls�on for m�x�ng, water tankers are requ�red to ensure proper fin�sh�ng of the treated layer of

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mater�al after the �n�t�al m�x�ng and process�ng stage has been completed. Suffic�ent water tankers must be prov�ded to ensure that the process�ng of the mater�al �s a cont�nuous procedure w�th no stopp�ng to wa�t for a tanker.

The water tankers �nvolved w�th b�tumen emuls�on treatment should only ever transport b�tumen emuls�on �n var�ous stages of d�lut�on as the need d�ctates. At no stage �n the process of mater�al be�ng treated w�th b�tumen emuls�on �s neat water to be added to the mater�al on �ts own. To �ncrease the mo�sture content of the mater�al, mo�sture can only be added �n the form of a d�luted b�tumen emuls�on, as descr�bed �n Sect�on 6.3.2.

All water tankers used for b�tumen emuls�on treatment must be equ�pped w�th a c�rculat�ng pump system to c�rculate the d�luted b�tumen emuls�on after stand�ng for an extended per�od and for c�rculat�ng dur�ng the d�lut�on process. Water tankers must not be fitted w�th a convent�onal spraybar but w�th valves (such as a clam-lock valve) wh�ch w�ll not eas�ly clog. The appl�cat�on of the d�luted b�tumen emuls�on �s a cold process and there �s always the poss�b�l�ty of the b�tumen emuls�on break�ng and caus�ng blockages. Tankers must be properly flushed should they need to stand empty for extended per�ods (e.g. overn�ght).

6 3 1 4 Static Storage TanksStat�c tanks should be prov�ded to store suffic�ent b�tumen emuls�on for the needs of the project. Normally such tanks w�ll have a capac�ty of between 60 000 and 120 000 l�tres. Stat�c tanks must be fitted w�th a c�rculat�ng pump system wh�ch w�ll enable the stored b�tumen emuls�on to be properly c�rculated from t�me to t�me �n the stat�c tank, espec�ally �f no b�tumen emuls�on has been drawn or added for a per�od of 2 to 3 consecut�ve days.

6 3 2 BITUMEN EMULSIONAt no t�me whatsoever should a standard b�tumen emuls�on w�th 60% res�dual b�tumen content be appl�ed to the layer of mater�al be�ng processed w�th convent�onal construct�on equ�pment. Such b�tumen emuls�on added w�thout d�lut�on w�th water w�ll be �ncl�ned to break too qu�ckly, part�cularly on a hot day, thereby prevent�ng the b�tumen emuls�on from be�ng thoroughly m�xed throughout the depth of the layer of mater�al. Coat�ng of all the granular part�cles w�th�n the layer w�ll not take place when the b�tumen emuls�on breaks too early and a poorly treated layer w�ll result wh�ch w�ll �n turn lead to the early fa�lure of the layer. The coat�ng of part�cles w�th b�tumen emuls�on ensures the successful construct�on of the BSM layer. As a consequence, the �n s�tu mo�sture content of the untreated layer must never be so h�gh that �t cannot accommodate a b�tumen emuls�on that has been d�luted to a res�dual b�tumen content of between 30% and 40%.

A 60% an�on�c stable grade b�tumen emuls�on �s normally d�luted by the add�t�on of clean water to at least a 40% b�tumen emuls�on (40% res�dual b�tumen to 60% water) and preferably to a 20% res�dual b�tumen content for treatment of granular mater�als. On rare occas�ons where the mo�sture content of the �n s�tu mater�al �s h�gh, �t �s necessary to d�lute the b�tumen emuls�on to a res�dual b�tumen content of 50%, but th�s should be the except�on and not the rule. The d�lut�on of the b�tumen emuls�on �s deta�led �n Table 6.1. When add�t�onal water �s added to the b�tumen emuls�on, the product should be c�rculated.

Table 6 1 Dilution of Bitumen Emulsion

Percentage residual bitumen content in the diluted bitumen emulsion (%)

Litres of water to be added to 10 litres of standard bitumen emulsion (60% residual bitumen content)

50 2

40 5

30 10

20 20

10 50

Addition of Bitumen Emulsion

B�tumen emuls�on added w�thout d�lut�on w�th water w�ll be �ncl�ned to break too quickly, part�cularly on a hot day, thereby prevent�ng the b�tumen emuls�on from be�ng thoroughly m�xed.

Once b�tumen emuls�on has been added, any add�t�onal water requ�red must only be added as a very diluted (“dirty water”) bitumen emulsion.



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6 3 3 MIXINGBlade-m�x�ng by grader �s undertaken by us�ng the blade to move the mater�al from s�de to s�de. Th�s m�x�ng process �s often supplemented w�th the use of ploughs and/or rotavators. Where the w�dth of the treatment restr�cts the hor�zontal movement of the mater�al, extra use should also be made of the grader r�ppers w�th spec�ally des�gned “shoes” welded onto the r�ppers. Such shoes are �n the shape of a hor�zontal “V”, w�th the sharp end of the V po�nt�ng �n the d�rect�on of travel of the grader. The r�ppers w�th the�r V-shaped shoes are lowered to the treated depth and the “fast forward” gear of the grader �s used to plough through the layer. In th�s manner, the mater�al �s pushed as�de, ensur�ng that proper m�x�ng �s ach�eved, even when work�ng �n confined w�dths.

Where the layer to be treated was prev�ously stab�l�sed, the r�ppers of the grader can be used to break up the layer �f the �n s�tu strength �s low enough to perm�t such an operat�on.

Standard b�tumen emuls�on must first be d�luted w�th the compact�on water to a res�dual b�tumen content of 30% to 40% and appl�ed �n several appl�cat�ons onto the mater�al after the act�ve filler has been m�xed �nto the mater�al. Water tankers are used to apply the b�tumen emuls�on and the grader(s) must travel d�rectly beh�nd the water tanker, �mmed�ately cover�ng the freshly sprayed b�tumen emuls�on w�th mater�al, thereby prevent�ng the b�tumen emuls�on from break�ng. The volume of b�tumen emuls�on appl�ed �s determ�ned by the res�dual b�tumen content requ�red, expressed as a percentage by mass of the finally treated layer. Should weather cond�t�ons be part�cularly hot or dry, then the b�tumen emuls�on must be d�luted to a b�tumen content that �s less than 30% w�th proport�onately more water hav�ng to be added to the b�tumen emuls�on.

Care should be taken to ensure that the d�luted b�tumen emuls�on �s appl�ed �n such a way that no r�vulets are formed and that the b�tumen emuls�on does not run off the layer before �t has been m�xed �n.

Dur�ng m�x�ng, attent�on must be pa�d to the flu�d content of the m�x. The flu�d content �s the total quant�ty of flu�d �n the m�x, �nclud�ng hygroscop�c mo�sture, the b�tumen st�ll �n suspens�on �n the b�tumen emuls�on and the water �n the b�tumen emuls�on. If 80 l�tres of b�tumen emuls�on d�luted to a res�dual b�tumen content of 30% �s �ntroduced �nto the BSM per cub�c metre, then 24 l�tres of res�dual b�tumen forms part of the flu�d content wh�le �n suspens�on as part of the b�tumen emuls�on. However, as �t breaks and comes out of suspens�on, the flu�d content reduces by about 1.1% (assum�ng the mater�al dens�ty to be 2 100 kg/m3). The actual mo�sture content of the mater�al �s then 1.1% less than the flu�d content.

The flu�d content should not be so h�gh as to result �n deformat�on of the surface under final compact�on. The opt�mum flu�d content determ�ned �n the laboratory may be amended, based on on-s�te observat�ons, to make allowance for the type of compact�on equ�pment be�ng used.

When work�ng w�th porous mater�al, no dry mater�al should be present at the t�me of m�x�ng �n the d�luted b�tumen emuls�on, s�nce the water absorpt�on of the aggregate may lead to the premature break�ng of the b�tumen emuls�on.

Where the ex�st�ng asphalt surfac�ng �s be�ng recycled w�th the underly�ng gravel layer us�ng convent�onal construct�on equ�pment, the asphalt layer must first be m�lled off and left �n a w�ndrow on top of the granular base that �s to be recycled. Once the asphalt layer has been m�lled off �n th�s manner then the base layer can be m�lled or r�pped and broken down. Once the m�lled asphalt layer and the ex�st�ng gravel base mater�al have been thoroughly blended, then the act�ve filler must be m�xed �n �mmed�ately ahead of the �ntroduct�on of the b�tumen emuls�on on the same day.

6 3 4 COMPACTION, CUTTING LEVELS AND FINISHINGThe procedures descr�bed under Sect�on 6.2.2.5 for �n s�tu treatment us�ng recyclers are essent�ally the same as those to be followed when work�ng w�th convent�onal equ�pment.

It must be noted that when process�ng BSMs, the mater�al behaves s�m�lar to an ord�nary granular mater�al. Once m�xed, the BSM should then be processed �n the same way as the untreated mater�al. The operat�ons �nvolved for plac�ng, compact�ng, cutt�ng levels and the fin�sh�ng requ�red to ach�eve a new pavement layer are the same, w�th or w�thout the add�t�on of a b�tumen emuls�on. The only d�fferences are:

Neat water should not be applied to the mater�al once d�luted b�tumen emuls�on has been added.10% of the b�tumen emuls�on should be held back for enrichment of the upper 5 mm to 10 mm of the layer dur�ng the fin�sh�ng (slush�ng) process.

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CHAPTER 6: Construction – In-plant Treatment

69

6.4. IN-PLANT TREATMENTIn-plant m�x�ng �s normally used on projects where:

A consistent quality BSM �s requ�red, usually us�ng graded crushed stone blended w�th processed RA mater�al for asphalt base replacement e�ther from recycled mater�als or new mater�als. Th�s �s ach�eved by stockp�l�ng the �nput mater�als pr�or to blend�ng and m�x�ng. Such pre-stockp�l�ng allows the mater�als to be tested pr�or to m�x�ng to ensure that they meet the standards requ�red.All input aggregates are available at one location M�x�ng at source reduces the transport demand and el�m�nates double-handl�ng.After treatment, the m�xed BSM product needs to be stockpiled for later use. Th�s �s an �mportant requ�rement on some projects, such as those us�ng labour �ntens�ve methods for layer construct�on.The BSM needs to be placed by paver �n order to meet str�ngent shape and level tolerances on the completed layer. Th�s s�tuat�on ar�ses where the BSM �s used as the ma�n structural base w�th a th�n surfac�ng.

Controll�ng the qual�ty of the �nput mater�als �ncreases the degree of confidence that the m�xed product w�ll meet performance expectat�ons. In add�t�on, the appl�cat�on rate of b�tumen stab�l�s�ng agent and act�ve filler can be m�n�m�sed w�th confidence by undertak�ng a ser�es of m�x des�gns on a mater�al that �s relat�vely cons�stent. The gu�del�nes �n Chapter 4 for M�x Des�gn should be followed.

Stockp�l�ng BSMs are normally undertaken only when m�x�ng �n-plant. Requ�rements for stockp�l�ng BSMs are d�scussed �n Sect�on 2.6.1.1. Sect�ons 6.4.1, 6.4.2 and 6.4.3 descr�be general requ�rements for �n-plant treatment.

6 4 1 IN-PLANT MIXINGThe plant used to produce BSMs must be capable of:

Accurately blending predetermined proportions of d�fferent �nput mater�als wh�lst s�multaneously add�ng the correct amount of b�tumen stab�l�s�ng agent, water and act�ve filler.Consistently producing a homogenous product Th�s �s normally ach�eved us�ng a h�gh-energy pugm�ll type m�xer that allows cont�nuous m�x�ng.

BSM-emulsion

Relat�vely unsoph�st�cated m�xers can be used for produc�ng a sat�sfactory BSM-emuls�on product. On smaller projects, a concrete m�xer �s often used w�th volume batch�ng. Prov�ded the const�tuent mater�als are correctly proport�oned �n the m�xer and the retent�on t�me �n the m�xer �s suffic�ent, an acceptable product w�ll normally be obta�ned.

BSM-foam

S�nce foamed b�tumen has to be produced on s�te, the m�x�ng plant needs to be more soph�st�cated than those su�table for BSM-emuls�on. The system used for produc�ng foamed b�tumen must meet all the requ�rements descr�bed �n Sect�on 6.2.1.1. To ach�eve these requ�rements, the m�xer needs to be m�cro-processor controlled. A load sensor located on the mater�al feed conveyor normally prov�des the pr�mary �nput for regulat�ng the pumps for b�tumen and water (both for foam�ng and �ncreas�ng the mo�sture content, �f necessary) as well as a cont�nuously we�ghed auger feed�ng the act�ve filler. In add�t�on, the system must be capable of automat�cally ma�nta�n�ng b�tumen operat�ng pressures above 5 bars when mater�al throughput reduces. The recommended operat�ng pressure �s between 5 and 10 bars. F�gure 6.9 �llustrates a m�x�ng plant for foamed b�tumen.

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70

Figure 6.9 Mixing Plant for BSM-foam

S�nce mater�als ly�ng �n stockp�les are more suscept�ble to chang�ng weather cond�t�ons than �n s�tu mater�al protected w�th�n a pavement, �n-plant m�x�ng requ�res add�t�onal care to mon�tor the cond�t�on of the mater�al, part�cularly �n terms of:

Temperature of the material at the time of mixing The l�m�tat�ons prescr�bed �n Sect�on 2.6.2 must be str�ctly followed. However, �t must be recogn�sed that the w�nd ch�ll phenomenon often plays a s�gn�ficant role �n reduc�ng the temperature of mo�st mater�al that �s exposed to the elements. When work�ng �n w�ndy cond�t�ons w�th an amb�ent temperature approach�ng the lower l�m�t, �t �s adv�sable to check the temperature of the mater�al as �t enters the m�xer.The moisture content of the material being mixed As expla�ned �n Sect�on 6.2.2.4, mater�al that �s too wet (over OMC) or too dry (< 50% of OMC) w�ll not produce a sat�sfactory product. When work�ng dur�ng per�ods of unstable or wet weather, cover�ng the stockp�les of �nput mater�al w�ll ass�st �n ma�nta�n�ng a constant mo�sture content.

The m�xed mater�al �s normally trucked d�rectly to s�te and used �mmed�ately to construct a new pavement layer. Alternat�vely, the treated mater�al can be stored �n a stockp�le at a strateg�c locat�on for later use. In add�t�on to the stockp�l�ng requ�rements descr�bed �n Sect�ons 2.6.1.1, the normal precaut�ons concern�ng mater�al placed �n stockp�les must be addressed. These precaut�ons �nclude the avo�dance of contam�nat�on by prepar�ng a work platform beneath the stockp�le and prevent�ng mater�al segregat�on.

6 4 2 TRANSPORTING BSMMater�al segregat�on �s a pr�mary concern, espec�ally where the mater�al �s relat�vely coarse. Where such segregat�on cannot be adequately controlled when load�ng trucks d�rectly from the del�very conveyor on the plant, the mater�al should be transferred to a temporary stockp�le. Normal load�ng procedures should then be followed when extract�ng mater�al from such a temporary stockp�le. (Note that the temporary stockp�le must conta�n suffic�ent mater�al to allow such load�ng procedures to be followed.)

Where BSMs are transported over long d�stances, mo�sture loss can be m�n�m�sed by cover�ng the treated mater�al w�th an �mperv�ous heavy duty sheet (tarpaul�n).

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Loading belt

Tw in shaft pugm ill m ixer

Transfer conveyor w ith load cell

M aterial hoppers

W ater tank

O perator’s cabin

Injection system for w ater, bitum en em ulsion and foam ed

bitum enC em ent auger

Injection system for water,bitumen emulsion and

foamed bitumen

Operator’scabin

Loadingbelt

Twinshaft pugmillmixer

Transfer conveyorwith load cell

Water tank

PowerstationMaterialhoppers

Cementauger



71

6 4 3 LAYER CONSTRUCTION USING A PAVER / FINISHERThe type of paver and screed, the cond�t�on of the equ�pment and the expert�se of those operat�ng the equ�pment are cr�t�cal factors that d�ctate the qual�ty of product ach�evable when pav�ng a layer of BSM. Unl�ke asphalt, a BSM �s not a cohes�ve mater�al. Paver set up and operat�ng procedures are therefore d�fferent.

Construct�on jo�nts are zones of potent�al weakness �n a pavement structure and should therefore be kept to the barest m�n�mum. Consequently, long�tud�nal jo�nts between success�ve paver runs (or pulls) should be l�m�ted and should never co�nc�de w�th the locat�on of trafficked wheel paths. For th�s reason, large pavers are usually used to construct layers of BSM over the full- or half-w�dth of the road.

The th�ckness of a layer that can be successfully paved �s d�ctated by mater�al coarseness and restr�cted by compact�on requ�rements. The more coarse the mater�al, the more prone �t �s to segregat�on and, the th�cker the layer paved, the more d�fficult �t �s to compact w�thout roll�ng the surface out of shape. As d�scussed �n Sect�on 6.4.3.3, these l�m�tat�ons may be overcome by pav�ng two th�nner layers to ach�eve the requ�red layer th�ckness.

BSM-emulsion

Pav�ng BSM-emuls�on �s restr�cted to a s�ngle layer.

BSM-foam

Str�ngent controls are requ�red to ensure that an �ntegral bond �s establ�shed between the two layers. Pav�ng two th�nner layers �s not recommended and should only be undertaken as a last resort when pav�ng a BSM-foam.

6 4 3 1 Paver and ScreedThe th�ckness of the layer be�ng constructed and the pav�ng w�dth d�ctate the volume of BSM that the paver has to handle. A 150 mm th�ck layer paved over a 5 m half-w�dth requ�res 0.75 m³ (about 1.6 tons) of compacted BSM per runn�ng l�near metre. To ach�eve a cons�stent mat, a heavy-duty tracked paver would normally be used to handle such a volume of mater�al and s�multaneously push the del�very truck.

Prov�ded the paver �s capable of manag�ng the amount of mater�al, �t �s the screed attached to the paver that determ�nes the qual�ty of the paved mat wh�ch, �n turn, w�ll largely d�ctate the qual�ty of the final product. A th�ck layer of relat�vely low-cohes�on mater�al requ�res a screed that �s suffic�ently l�ght to “float” on the spread mater�al wh�lst s�multaneously �mpart�ng suffic�ent pre-compact�on energy to ach�eve a un�form level of dens�ty across the paved w�dth. Ut�l�s�ng the correct screed �s therefore cr�t�cal. Screeds w�th hydraul�cally-adjustable w�dth capab�l�t�es are generally too heavy and, because they compr�se three components, are d�fficult to set up to el�m�nate steps form�ng across the paved w�dth. To get such screeds to float normally requ�res the deployment of a “screed ass�st” funct�on wh�ch, �n turn, requ�res a h�gh level of expert�se �n pav�ng BSM. S�ngle un�t screeds w�th bolt-on extens�on boxes to obta�n the requ�red pav�ng w�dth are therefore preferred. To mould the mater�al and m�n�m�se lateral movement, both ends of the screed should be fitted w�th 45° bevelled end plates.

In add�t�on to plac�ng the mater�al to the requ�red l�ne and level, the screed must un�formly pre-compact the mater�al to the h�ghest ach�evable level of dens�ty. The h�gher the dens�ty obta�ned by the screed, the less roll�ng requ�red to ach�eve the target dens�ty and the lower the r�sk of roll�ng the mat out of shape. Screeds are normally equ�pped w�th tamper bars and v�brators to effect compact�on. “H�gh Compact�on Screeds” offered by some manufacturers are fitted w�th features wh�ch �ntroduce add�t�onal compact�on energy. Where poss�ble, such a screed should be employed when pav�ng a BSM.

6 4 3 2 Compaction EquipmentUnl�ke �n s�tu treated BSMs where layer th�cknesses �n excess of 200 mm are the norm, layers of BSM placed by paver seldom exceed 150 mm �n th�ckness. Such a layer th�ckness can be compacted us�ng a v�brat�ng roller w�th a stat�c mass of between 10 ton and 12 tons. Tandem smooth-drum v�brat�ng rollers are normally used on paved mater�al s�nce the mater�al encountered beh�nd the pav�ng screen �s denser than the loose mater�al that �s typ�cal beh�nd �n s�tu recyclers. In add�t�on, tandem rollers do not d�sturb the surface of the mat as do the rear wheels of s�ngle drum rollers.

Paving Thickness

It �s adv�sable to pave BSMs �n one layer

i



72

Once compacted, the paved layer �s fin�shed off �n the same manner as an �n s�tu treated layer us�ng a pneumat�c tyred roller.

6 4 3 3 Limitations of Paving a Thick LayerIt �s always preferable to construct a pavement layer as a s�ngle monol�th�c un�t. Separat�ng the layer �nto two th�nner sub-layers �ntroduces a hor�zontal construct�on jo�nt that can become a weak hor�zon (delam�nat�on plane) when the pavement deflects under load.

Although �t �s poss�ble to pave a th�ck (> 200 mm) layer of BSM, the consequence �s �nvar�ably a loss of shape when us�ng rollers to apply the h�gh ampl�tude v�brat�ng energy requ�red to dens�fy such a th�ck layer. S�nce the amount of compact�ve energy exerted by the screed �s constant, �ncreas�ng the th�ckness of mater�al be�ng paved w�ll reduce the dens�ty that can be ach�eved by the screed. Although reduc�ng the forward speed of the paver w�ll �ncrease the amount of compact�on energy on each un�t area, such energy �s not the h�gh ampl�tude type requ�red to penetrate to the bottom of the layer and may �ntroduce a br�dg�ng problem (see Sect�on 6.2.2.5).

Pav�ng the layer as two th�nner layers �s not recommended. In theory, �t should be poss�ble to ach�eve an �ntegral bond between the two but the real�t�es of a construct�on s�te make �t all but �mposs�ble to guarantee that such a bond �s ach�eved over the full length and w�dth of the road.

BSM-emulsion

Pav�ng �n two layers cannot be done w�th BSM-emuls�on s�nce constant water�ng w�ll wash the b�tumen emuls�on out of the mater�al �n the upper hor�zon of the lower layer. Subst�tut�ng a d�lute b�tumen emuls�on for water �s not a solut�on s�nce such pract�ce may result �n a film of b�tumen form�ng at the surface wh�ch w�ll only exacerbate the r�sk of delam�nat�on.

BSM-foam

Should a s�tuat�on ar�se where two layers must be constructed on top of one another, only BSM-foam can be cons�dered because bond�ng between the two layers �s poss�ble �f the surface of the first layer �s kept cont�nuously wet unt�l the second layer �s paved.

Pav�ng BSM-foam �n two th�nner layers has been successfully ach�eved us�ng the follow�ng method:

Determine the thickness of each of the two layers, keep�ng �n m�nd that the th�ckness of each layer must be more than 3 t�mes the max�mum part�cle s�ze (�.e. where the max�mum part�cle �s 37.5 mm, the layer th�ckness must be greater than 113 mm). Always try and pave a th�cker first layer w�th the second layer kept as th�n as �s pract�cal, but never less than 100 mm. For example, where a 250 mm th�ck layer �s requ�red and the max�mum part�cle s�ze �s 25 mm, the first layer should be paved 150 mm th�ck and the second layer 100 mm.Pave the lower layer on the first half-width for a maximum distance of 200 m Compact us�ng only a smooth drum roller operat�ng �n h�gh ampl�tude v�brat�on. A PTR must not be used. Prevent the surface from dry�ng out by frequent water�ng sprayed s�deways from a water tanker travell�ng on the adjacent half-w�dth.Reverse the paver over the completed first layer and immediately pave the second lift to ach�eve the requ�red layer th�ckness. Compact w�th low ampl�tude v�brat�on and fin�sh off w�th a PTR.

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Layer thickness for paved layers

Layers of BSM placed by paver seldom exceed 150 mm.

Pav�ng �n two layers is not recommended.



73

In add�t�on to keep�ng the surface of the first paved layer constantly wet, the �mmed�ate surrounds must be kept dust free. Th�s requ�res the surface of the adjacent half-w�dth to be kept mo�st wh�lst pav�ng the first half-w�dth. It also �mpl�es that no work should be undertaken when there �s a r�sk of w�nd-blown dust contam�nat�ng the wetted surface of the first layer.As d�scussed below, the paved edge that co�nc�des w�th the centre-l�ne jo�nt requ�res constant protect�on. Trucks must not be allowed to run over th�s edge when del�ver�ng BSM-foam to the paver for the second layer. Spec�al entry / ex�t ramps need to be constructed (and removed afterwards) to fac�l�tate such mater�al �mport.

Pav�ng two layers to ach�eve one th�ck layer �s t�me consum�ng and requ�res constant attent�on to deta�l by the construct�on team. There �s always a r�sk that the two layers w�ll not bond properly and premature fa�lures may ar�se due to delam�nat�on and shear�ng. When faced w�th hav�ng to construct a th�ck layer of BSM, ser�ous cons�derat�on should be g�ven to plac�ng by grader as a s�ngle layer (as descr�bed �n Sect�on 6.4.4) rather than pav�ng.

6 4 3 4 Construction RequirementsThe follow�ng aspects are cr�t�cal when plac�ng BSMs by paver.

i Paver Set UpSett�ng up the paver and screed are fundamental requ�rements on any pav�ng job. However, sett�ng up the paver to work w�th BSMs requ�res an understand�ng of mater�al behav�our, espec�ally how the part�cular BSM w�ll flow and bulk. These mater�al character�st�cs are determ�ned pr�mar�ly by the grad�ng and angular�ty of the aggregate �n the m�x, as well as the mo�sture content. These character�st�cs �nfluence what adjustments need to be made to the screed so that �t ach�eves the cons�stent “float” that �s �mperat�ve to obta�n a smooth mat. Where the screed �s not set up properly, �t w�ll tend to s�nk �nto the mat and create undulat�ons.

Tr�al sect�ons for paved BSMs should be constructed off s�te where the consequences of vary�ng the screed sett�ngs w�ll not affect the permanent work. Th�s �s d�scussed �n Sect�on 6.7 below.

ii Paving the LayerThe same bas�c procedures followed when pav�ng hot m�xed asphalt are appl�cable to pav�ng a BSM:

Continuity of paving Suffic�ent trucks should be prov�ded to ensure a cont�nuous supply of mater�al to the paver. Irregular�t�es (bumps) �n the mat are normally created by the screed settl�ng �n to the paved mater�al when the paver stops. The b�ggest steps �n the mat, however, are caused by del�very trucks revers�ng �nto the paver, forc�ng the screed backwards �nto the paved mater�al. Trucks should always stop �mmed�ately ahead of the paver, allow�ng the paver to advance and gently engage.In rolling terrain, the paver should always advance uph�ll push�ng the del�very truck. Such pract�ce fac�l�tates mater�al feed from the truck to the augers feed�ng the screed and ma�nta�ns pressure on the screed. Pav�ng downh�ll runs the r�sk of mater�al starvat�on as the paver tends to pull away from the mater�al under the screed.

S�m�lar to pav�ng a G2 type crushed stone mater�al, mater�al segregat�on �s always a concern when pav�ng a BSM, espec�ally where the mater�al �s relat�vely coarse. Segregat�on can be m�n�m�sed by:

Maintaining the moisture content of the material above 50% of OMC Mater�al that has been allowed to dry out (normally due to stand�ng for prolonged per�ods un-sheeted �n the truck) w�ll segregate far more than mo�st mater�al. Such mater�al can be sent back to the plant and retreated.

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Segregation

To avo�d segregat�on wh�le pav�ng:

The mo�sture should be > 50 % of OMC. The mater�al �n the wings of the receiving hopper must be d�scarded.

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BSM-emulsion

Re-treat w�th d�luted b�tumen emuls�on.

BSM-foam

Re-treat w�th water.

Sacrificing the material in the wings of the paver’s receiving hopper The rece�v�ng hopper should be filled w�th mater�al from the first truck load of the day and never t�lted. Th�s mater�al must be d�scarded at the end of the work�ng sh�ft.

The surface of the layer on wh�ch the new layer of BSM w�ll be paved must be clean and free of all loose mater�al and fore�gn matter. Immed�ately pr�or to pav�ng, the surface must be thoroughly mo�stened by spray�ng w�th water. Any pond�ng water must be removed by broom�ng before the BSM �s paved. Add�t�onal water�ng �s requ�red �f the surface dr�es out.

Pav�ng �s normally undertaken �n half-w�dths. A good jo�nt on the centre-l�ne �s best ach�eved by construct�ng both halves dur�ng the same work�ng sh�ft. Th�s means that the �n�t�al half-w�dth �s first paved over the full length of road to be paved, compacted and fin�shed off, often w�th a fog spray and l�ght appl�cat�on of crusher dust to fac�l�tate early traffick�ng.

iii Construction JointsLong�tud�nal jo�nts are �nev�table s�nce few roads are paved full w�dth �n one operat�on. As descr�bed �n Sect�on 6.4.3, these jo�nts are zones of potent�al weakness and therefore need to fall outs�de the trafficked wheel paths. On a typ�cal rural road w�th two lanes, the long�tud�nal jo�nt w�ll normally be located on the centre-l�ne. Long�tud�nal jo�nts generally rece�ve the follow�ng treatment when a BSM �s paved:

Once the first half-w�dth �s paved, the outer 500 mm of mater�al closest to the centre-l�ne rece�ves only one pass w�th the roller, leav�ng �t �n a relat�vely uncompacted state, as can be seen �n F�gure 6.10. All publ�c traffic and construct�on veh�cles must be prevented from runn�ng over the step of mater�al thus formed on the centre-l�ne.Immed�ately before pav�ng the second half-w�dth, the exposed edge on the centre-l�ne together w�th the part�ally compacted str�p �s thoroughly mo�stened. Th�s �s normally undertaken by a separate team equ�pped w�th hand sprayers walk�ng ahead of the paver.

BSM-emulsion

D�luted b�tumen emuls�on �s appl�ed where BSM-emuls�on �s paved.

BSM-foam

Water �s appl�ed where BSM-foam �s paved.

Pr�or to pav�ng the second half-w�dth, the bevelled end plate �s removed from the centre-l�ne end of the screed. Th�s allows the screed to butt up aga�nst the exposed step of the first half-w�dth, as �llustrated �n F�gure 6.10.

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Figure 6.10 Longitudinal Joint Treatment

The part�ally compacted str�p of mater�al rema�n�ng on the first half-w�dth then rece�ves the full compact�on and fin�sh�ng treatment together w�th the second half-w�dth.

Lateral jo�nts occur at every locat�on where pav�ng stops and a ramp �s constructed to accommodate the traffic. The follow�ng day, or when pav�ng restarts, the mater�al �n the ramp �s removed and the paved BSM mater�al cut back to ach�eve a 45° slope. The mater�al ly�ng on the slope �s then thoroughly mo�stened before pav�ng can cont�nue.

BSM-emulsion

As w�th long�tud�nal jo�nts, d�luted b�tumen emuls�on �s appl�ed where BSM-emuls�on �s paved.

BSM-foam

As w�th long�tud�nal jo�nts, water �s appl�ed where BSM-foam �s paved.

iv Compacting the Paved BSMThe pr�mary concern when us�ng heavy v�brat�ng rollers that are requ�red to compact a paved layer of BSM �s loss of shape. The roll�ng pattern establ�shed wh�lst construct�ng a Tr�al Sect�on (see Sect�on 6.7) must be str�ctly followed, espec�ally when mak�ng the �n�t�al pass that creates the outs�de edge restra�nt.

As descr�bed �n Sect�on 6.4.3.2, tandem smooth drum rollers are always used to compact the BSM beh�nd the paver. Equ�pped w�th two v�brat�ng drums, these rollers normally ach�eve the requ�red dens�ty w�th relat�vely few passes. However, operators need tra�n�ng to prevent over-roll�ng and shape loss s�nce the techn�que requ�red to compact a BSM �s very d�fferent from compact�ng hot m�xed asphalt.Once the requ�red dens�ty has been ach�eved, the layer �s fin�shed off us�ng a PTR. The procedure �s the same as descr�bed �n Sect�on 6.2.2.5 for �n s�tu treated layers of BSM.

6 4 4 LAYER CONSTRUCTION USING CONVENTIONAL CONSTRUCTION EQUIPMENTConvent�onal equ�pment �s normally used �n preference to pav�ng where �n-plant m�xed mater�al �s used to construct th�ck layers of BSM. However, there are two l�m�tat�ons:

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Th�ck layers demand more mater�al than can be managed when work�ng �n half-w�dths. For th�s reason, plac�ng a BSM w�th convent�onal equ�pment �s normally only applicable to new construction where the full road width �s ava�lable.Work�ng w�th graders always results �n moisture loss s�nce the mater�al has to be spread out over a relat�vely large area for extended per�ods of t�me. Th�s mo�sture loss needs to be replaced by add�ng water.

BSM-emulsion

The demand for add�t�onal mo�sture makes th�s method �nappropr�ate for BSM-emuls�on.

BSM-foam

The demand for add�t�onal mo�sture l�m�ts the appl�cat�on of th�s method to BSM-foam.

Essent�ally, the procedure followed �s the same as that descr�bed �n Sect�on 6.3 for plac�ng �n s�tu treated mater�al w�th the follow�ng d�fferences:

The surface of the layer on wh�ch the new layer of BSM �s to be constructed must be cleaned and thoroughly mo�stened before the treated mater�al �s �mported and t�pped out.To limit moisture loss, the grader should start plac�ng as soon as mater�al has been �mported over a suffic�ent length of the road requ�red for th�s method of work (normally 100 m). The add�t�on of water or d�luted b�tumen emuls�on and the �n s�tu m�x�ng necessary to ach�eve a un�form mo�sture content �s always requ�red to compensate for the �nev�table loss of mo�sture due to evaporat�on.

The procedure followed for fin�sh�ng off the new layer �s the same as descr�bed �n Sect�on 6.2.2.5 for �n s�tu treated layers.

6 4 5 LAYER CONSTRUCTION USING LABOUR INTENSIVE METHODSBSMs are becom�ng popular on road upgrad�ng projects us�ng labour �ntens�ve construct�on. Most of the labour �s used for spread�ng and plac�ng the BSM pr�or to compact�ng w�th relat�vely l�ght v�brat�ng rollers. Th�s normally l�m�ts the layer th�ckness to 125 mm.

The process starts by prepar�ng the surface on wh�ch the new layer �s to be constructed. A grader and heavy v�brat�ng roller �s often used for th�s work s�nce the longev�ty of the pavement �s largely determ�ned by the competence of the underly�ng support. Alternat�vely, where the support �s competent, the ex�st�ng road surface can be tr�mmed by hand and swept clean.

Once a firm surface has been ach�eved, s�de forms are erected to conta�n the �mported BSM. S�nce these s�de forms w�ll d�ctate the l�ne and level of the new BSM layer, they need to be made out of heavy duty mater�al w�th a truly stra�ght top edge. Th�n steel shutters that are commonly used for structural work are often employed. Such s�de forms are pos�t�oned w�th the top edge at the correct elevat�on by plac�ng or excavat�ng mater�al beneath the bottom edge. S�de forms need to be firmly anchored �n place us�ng a ser�es of su�table steel stakes.

BSM-emulsion

M�x�ng the BSM-emuls�on �s usually undertaken on s�te us�ng a concrete m�xer. Input mater�als are volume batched and the m�xed product taken stra�ght to the road �n wheelbarrows. Two m�xers are often used to �ncrease the product�on rate and ma�nta�n a cons�stent flow of treated mater�al.

BSM-foam

Due pr�mar�ly to �ts ab�l�ty to be held �n stockp�le for extended per�ods, BSM-foam �s �deal for construct�ng a new pavement layer us�ng labour. Stockp�les should be kept covered unt�l the mater�al �s requ�red and then thoroughly wetted before extract�ng the mater�al. The m�x�ng plant for th�s type of work �s normally located at a central venue and the mater�al trucked to s�te, stockp�led and covered for later use.

The BSM �s �mported by wheelbarrow and t�pped between the s�de forms. Th�s mater�al �s then raked �nto place and struck off flush w�th the top of the s�de forms. It �s �mportant that a reasonably un�form dens�ty �s ach�eved �n the mater�al that �s loosely spread between the s�de forms. Mater�al ly�ng �n the mound created by t�pp�ng from a barrow w�ll be part�ally compacted by the t�pp�ng act�on, whereas

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Labour Intensive Construction

BSMs are appropr�ate for labour �ntens�ve construct�on, but the thickness of the layers is normally limited to 125 mm

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mater�al spread by hand w�ll be completely loose. Care must therefore be taken to rake all the mater�al away from the locat�on where �t was t�pped. Fa�lure to follow th�s s�mple requ�rement w�ll �nev�tably result �n a poor surface shape after the mater�al has been compacted.

As soon as the mater�al has been spread and struck off, the surface �s thoroughly mo�stened (us�ng water w�th BSM-foam and d�luted b�tumen emuls�on w�th BSM-emuls�on) before the roller starts work. The surface must be kept mo�st dur�ng the ent�re compact�on process. Pedestr�an rollers that are commonly used for trench backfill�ng are normally employed. To ass�st the operator ach�ev�ng the same compact�ve effort over the ent�re area, stakes are often pos�t�oned across the road at the same �nterval as the w�dth of the drum to act as a gu�de. The same number of roller passes �s then undertaken on each str�p, w�th the drum overlapp�ng the prev�ous str�p by 50%.

The str�p of mater�al �mmed�ately aga�nst the s�de forms normally rece�ves an add�t�onal two passes w�th the roller w�th care be�ng taken not to d�sturb the shutter. Once a sect�on has been compacted, the s�de forms can be removed and a small plate compactor employed to compact the exposed edge.

F�n�sh�ng �s usually ach�eved by deploy�ng a second pedestr�an roller together w�th add�t�onal mo�sture to ach�eve a m�ld slush.

Although labour �ntens�ve construct�on may be deemed to be benefic�al for soc�o-pol�t�cal reasons, the phys�cal l�m�tat�ons of the process must d�ctate where �t �s used. Layer th�cknesses �n excess of 125 mm cannot be properly compacted us�ng the type of equ�pment used �n th�s process. Th�s �s deemed to be a major l�m�t�ng factor. Mo�sture loss due to the slow rate of progress �s also a l�m�t�ng factor. Other l�m�tat�ons �nclude the product�on rate ach�evable, the space requ�red for work�ng w�th s�de forms and the confl�ct of labour and traffic where construct�on �n half-w�dths �s contemplated. For these reasons, th�s method of construct�on �s normally restr�cted to projects concerned w�th upgrad�ng low-volume roads. 6.5. CURING AND TRAFFICKINGOne of the ma�n benefits of us�ng BSMs on rehab�l�tat�on projects �s the ab�l�ty of these mater�als to w�thstand traffic load�ng soon after the layer has been completed. Th�s feature el�m�nates the need for extens�ve traffic d�vers�ons or detours. Rehab�l�tat�on work �s normally undertaken by recycl�ng the road �n half-w�dths w�th un�d�rect�onal traffic be�ng accommodated by means of stop/go controls on the adjacent half. Outs�de construct�on hours the full road w�dth �s open to traffic.

BSM-emulsion

After compact�on, the �ncrease �n dens�ty �s not suffic�ent to ensure res�stance to traffic damage. An �ncrease �n cohes�on �s requ�red for res�stance to traffic damage, wh�ch �s d�ctated by the t�me requ�red for the b�tumen emuls�on to break. Th�s normally takes a few hours at the surface where evaporat�on forces the break, but can take several days for the b�tumen emuls�on deeper �n the layer.

BSM-foam

On compact�on, the �nstant �ncrease �n cohes�on makes layers of BSM-foam res�stant to traffic damage. However, they rema�n “tender” unt�l the mo�sture content reduces.

The res�stance to traffic damage can be mon�tored by park�ng a heav�ly loaded veh�cle on the new layer. After a relat�vely short per�od (< 1 hour), the wheels w�ll settle �nto the mater�al, leav�ng local�sed �ndentat�ons that can be as deep as 10 mm. As the mater�al dr�es back, th�s propens�ty to deform reduces unt�l, after a day or two of warm weather, �t ceases altogether. Th�s phenomenon needs to be taken �nto account when plann�ng road closures. Stop/go controls should be pos�t�oned such that the da�ly traffic �s only allowed to stand where the layer of BSM was completed at least 24 hours prev�ously.

Allow�ng traffic to travel on BSM layers has the benefit of show�ng up construct�on defects. As was �llustrated �n F�gure 6.6, sect�ons w�th an under-appl�cat�on of b�tumen w�ll tend to ravel excess�vely under the act�on of traffic, draw�ng attent�on to any area that requ�res

Spreading the mix

A reasonably uniform density must be ach�eved �n the mater�al that �s loosely spread between the s�de forms. Th�s requ�res rak�ng of areas that are part�ally compacted by the wheel barrow and t�pp�ng act�on.

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Stop/go Controls

Stop/go controls should be pos�t�oned such that

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remed�al measures to be taken before the final surfac�ng �s appl�ed. The surface must be kept clean to prevent abras�on and ravell�ng. It �s recommended that fog spray �s appl�ed. 6.6. SURFACINGThe d�spersed nature of the b�tumen �s respons�ble for �ncreas�ng the cohes�on that g�ves BSMs suffic�ent early strength to w�thstand traffic loads w�thout a surfac�ng. S�nce the part�cles at the surface are only held �n place by such spot welds along the�r lower faces, dynam�c forces �mparted by heavy tyre loads w�ll tend to loosen and remove the coarser part�cles at the surface, caus�ng roughness. Wh�lst some remarkable successes have been ach�eved �n protect�ng the surface from such damage by us�ng a d�lute b�tumen emuls�on �n the slush�ng process and/or the appl�cat�on of a l�ght fog spray, �t �s recommended that the surfac�ng must be appl�ed between 2 and 4 weeks after compact�on to prov�de protect�on aga�nst both water �ngress and excess�ve traffic abras�on. The surfac�ng must not be placed before the mo�sture content �n the upper 100 mm of the layer has reduced to below 50% of OMC, wh�ch usually takes 2 weeks.

Asphalt surfac�ngs (30 mm th�ck) have proved to be except�onally durable on BSM layers and there are no reports of delam�nat�on. Ch�p seals, however, need to be carefully des�gned to prevent bleed�ng. The bleed�ng �s �nvar�ably the result of the stone punch�ng �nto the BSM layer. BSMs are relat�vely soft and Ball Penetrat�on measurements �n excess of 3 mm can be expected, even where the treated mater�al cons�sts of G2 qual�ty graded crushed stone. H�gh summer temperatures w�ll exacerbate th�s “softness”, espec�ally where the seal �s fresh, thereby �ncreas�ng the potent�al for �nd�v�dual stones or ch�ps to punch �nto the base when heavy loads are appl�ed. Some strengthen�ng of the surface �s requ�red to prevent stone punch�ng. 6.7. CONSTRUCTING TRIAL SECTIONSA Tr�al Sect�on should always be undertaken at the start of a new project (or when warranted by changes on s�te) to determ�ne the correct sett�ngs on the equ�pment and subsequent treatment of the mater�al. Pr�or to commenc�ng the Tr�al Sect�on, the contractor must prepare a deta�led proposal �nd�cat�ng how the var�ous operat�ons to produce the BSM layer w�ll be conducted.

6 7 1 TRIAL SECTIONS FOR IN SITU TREATMENTAs a m�n�mum, the follow�ng deta�ls should be �ncluded �n the Tr�al Sect�on proposal:

A schedule listing the plant and equipment that w�ll be used for the work. Th�s schedule must �nclude all �tems that the contractor �ntends us�ng for the permanent works. A sketch detailing the number of passes required by the recycler to cover the w�dth to be recycled together w�th all overlap deta�ls.Assumptions made regarding the maximum dry density that govern the appl�cat�on rates for the b�tumen stab�l�s�ng agent and act�ve filler, based on the �n�t�al laboratory tests.Roller details (stat�c mass and drum type), the ant�c�pated number of passes to be made by each roller, the roll�ng pattern and method to be employed �n determ�n�ng when suffic�ent compact�ve effort has been appl�ed.Sampling frequency and tests to be conducted.Tr�al Sect�ons must always be located so as to be truly representative of the recycling work, and, where poss�ble, representat�ve of the pavement support �n the determ�nat�on of the so-called target dens�ty.

Wh�le the Tr�al Sect�on �s be�ng executed, the follow�ng deta�ls need to be mon�tored:Grading of the recycled material The forward speed of the recycler, the rate of rotat�on of the m�ll�ng drum and pos�t�on�ng of the breaker-bar should be var�ed to determ�ne wh�ch comb�nat�on produces the best result �n terms of pulver�sat�on and smoothness of the result�ng grad�ng curve.Moisture addition Determ�nat�on of the opt�mum m�x�ng mo�sture content (the “fluff po�nt”) and the amount of water that needs to be added through the ded�cated water spraybar to ach�eve the requ�red mo�sture content.Mixing quality Exper�ence has shown that advance recycler speeds �n excess of 10 metres per m�nute are detr�mental to m�x�ng qual�ty. In add�t�on, the pressure exerted on the rear door of the m�ll�ng chamber can be var�ed, thereby chang�ng the degree of “chok�ng” (the amount of mater�al reta�ned �n the m�ll�ng chamber). As well as �mprov�ng the qual�ty of the m�x, these sett�ngs affect the grad�ng of the product, part�cularly of the coarser fract�on.Bulking Bulk�ng of the mater�al occurs because of the �ncrease �n vo�ds after recycl�ng. Bulk�ng of the recycled mater�al must be measured or determ�ned along w�th the consequent�al effects on level control. Where bulk�ng results �n changed final levels, the excess mater�al should be removed.

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Trial Sections

Tr�al sect�ons should always be undertaken because they prov�de valuable information for construct�on.

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Compaction requirements Adequacy of the roller for ach�ev�ng dens�ty and the number of passes requ�red can be determ�ned by mon�tor�ng the rate of dens�ficat�on. If the pr�mary roller �s not equ�pped w�th a compactometer dev�ce, a nuclear gauge can be used to determ�ne the dens�ty of the layer and the change �n dens�ty w�th each pass.Detailed records A record of the prec�se sequence of events and the relevant t�m�ngs should be taken for future schedul�ng purposes.

Invaluable �nformat�on �s obta�ned from Tr�al Sect�ons. They should always be properly planned and mon�tored. The area of the recycl�ng should be l�m�ted to one tanker-load of the b�tumen stab�l�s�ng agent. A full work�ng day should be set as�de to conduct the necessary surveys and tests w�thout product�on pressures.

6 7 2 TRIAL SECTIONS FOR IN-PLANT TREATMENTWhere the BSM �s paver la�d, the s�te selected for construct�ng the Tr�al Sect�on should be a s�de road away from the permanent work. Paver set up �s a process of tr�al and error, �nvar�ably result�ng �n the �n�t�al work be�ng out of shape w�th many undulat�ons. Tr�al Sect�ons for pav�ng appl�cat�ons are seldom fin�te �n length. The object�ve �s to fine-tune the paver and screed unt�l the correct sett�ngs for the part�cular BSM have been establ�shed. The length of sect�on paved �s therefore dependent on how long �t takes to find the sett�ngs that work. 6.8. QUALITY CONTROL ASPECTSQual�ty controls are requ�red to ensure that the end product w�ll meet the performance expectat�ons embod�ed �n the des�gn. Two aspects of qual�ty need to be mon�tored:

The quality of the BSM used to construct the pavement layer, andThe quality of the pavement layer that was constructed.

For any qual�ty control programme to be effect�ve, the spec�fic qual�ty requ�rements for each project need to be clear and unamb�guous. Project Spec�ficat�ons must therefore �nclude deta�ls of the part�cular character�st�cs of both the mater�al and the layer to be controlled. Spec�fic qual�ty requ�rements must be stated as well as the method to be followed �n determ�n�ng whether or not such requ�rements have been ach�eved. In add�t�on, the consequences of not ach�ev�ng the spec�fied qual�ty requ�rements must be stated (e.g. reject�on, part�al payment, etc.)

The qual�ty of a BSM �s a funct�on of the parent mater�al, the added stab�l�s�ng agent (and any act�ve filler) as well as the effect�veness of the m�x�ng process. Qual�ty controls need to be appl�ed dur�ng the m�x�ng process to ensure that the m�xed product �s capable of meet�ng the performance expectat�ons embod�ed �n the des�gn. Add�t�onal controls are requ�red to ensure that the BSM �s placed, compacted, shaped and fin�shed off �n such a manner that the requ�red end-product �s obta�ned. Acceptance controls are then appl�ed to the fin�shed layer to determ�ne whether such end-product requ�rements have �ndeed been met.

Sect�ons 6.8.1, 6.8.2 and 6.8.3 cons�der qual�ty controls spec�fic to the product�on of a BSM layer.

6 8 1 QUALITY OF THE BSM

6 8 1 1 Material to be TreatedRegardless of whether b�tumen emuls�on or foamed b�tumen �s appl�ed, the mater�al to be treated must be s�m�lar to that env�saged by the des�gner. Where the mater�al �s m�xed �n-plant, a test�ng programme should always be put �n place to check the qual�ty of the mater�al stockp�led pr�or to m�x�ng.

The qual�ty of mater�al recovered from an ex�st�ng pavement through �n s�tu recycl�ng cannot be controlled other than �ts phys�cal cond�t�on (degree of pulver�sat�on and mo�sture content). Th�s �mpl�es that the onus rests w�th the des�gner to determ�ne whether or not the mater�al �n an ex�st�ng pavement �s su�table for recycl�ng as a BSM. Impos�ng mater�al qual�ty controls on an �n s�tu recycl�ng operat�on �s therefore unreal�st�c, other than the degree of pulver�sat�on of prev�ously bound mater�al (asphalt and/or cemented mater�al). In spec�fy�ng such requ�rements, however, the des�gner needs to be fam�l�ar w�th the capab�l�t�es of modern recyclers; �n part�cular they are not mob�le crushers. Max�mum part�cle s�ze should therefore be spec�fied; not a grad�ng envelope.

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Representative Trial Sections

Tr�al sect�ons should be representat�ve of the recycling work and the pavement support

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CHAPTER 6: Construction – Quality Control

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6 8 1 2 Stabilising Agent and Active FillerMost stab�l�s�ng agents and act�ve fillers used to manufacture a BSM are gener�c products that conform to spec�fic �ndustry standards. It �s therefore relat�vely s�mple to spec�fy and control the qual�ty of a spec�fic add�t�ve:

BSM-emulsion

Anionic b�tumen emuls�on, SANS 309 Cationic b�tumen emuls�on, SANS 548

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BSM-foam

Penetration grade b�tumen, SANS 307 . »

Active filler: Ord�nary portland cement, SABS 471 Hydrated road l�me, SABS 824

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Where penetrat�on-grade b�tumen or b�tumen emuls�on �s not suppl�ed �n accordance w�th �ndustry standards, they need to be tested pr�or to be�ng used �n the permanent works to ensure that they w�ll ach�eve the performance requ�rements.

BSM-emulsion

Breaking characteristics In add�t�on to the charge (an�on�c or cat�on�c), the break�ng character�st�cs of the b�tumen emuls�on need to be checked. Samples of the b�tumen emuls�on are normally sent to a spec�al�sed laboratory for such tests.pH of water Where a b�tumen emuls�on �s d�luted on s�te pr�or to m�x�ng, the pH of the water to be used �n the d�lut�on process needs to be checked and, where necessary, adjusted to the part�cular b�tumen emuls�on charge by add�ng ac�d or alkal�.Dilution test After d�lut�on, the potent�al for premature break�ng must then be checked us�ng the “D�lut�on can test” (Sect�on 4.2.4). The actual d�lut�on of del�ver�es must be checked.

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BSM-foam

Penetration If the results fall outs�de the spec�fied range then cons�derat�on may be g�ven to us�ng a cut back (d�esel o�l �s normally used, not kerosene).Foaming characteristics As long as acceptable foam �s obta�ned, wh�ch �s determ�ned by the expans�on rat�o and half-l�fe, the penetrat�on of the b�tumen �s not that �mportant.

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In cases where the act�ve fillers are not suppl�ed �n accordance w�th �ndustry standards, the�r effect�veness should be tested (by repeat�ng the m�x des�gn �n the field laboratory) pr�or to be�ng used �n the permanent works. In the absence of a field laboratory equ�pped for b�tumen treatment m�x des�gn test�ng, the grad�ng and mo�sture content of the act�ve filler may be used as �nd�cators of effect�veness (more than 95% of the act�ve filler should be smaller than 0.075 mm and the mo�sture content must be less than 5% by mass). If these bas�c requ�rements are met, a test sect�on should be constructed and the m�xed mater�al tested to determ�ne the effect�veness of the act�ve filler.

6 8 1 3 Process Controls for the Mixing OperationRegardless of whether m�x�ng �s undertaken �n s�tu or �n plant, the bas�c process controls to be followed when m�x�ng a BSM are s�m�lar. Where there are d�fferences between the add�t�on of b�tumen emuls�on or foamed b�tumen, these are h�ghl�ghted �n the follow�ng sect�ons.

Append�x D �ncludes a ser�es of checkl�sts and report sheets (together w�th examples) that are normally used on s�te when work�ng w�th BSMs. These �nclude:

Appendix D1: Essent�al Requ�rements for a successful recycl�ng operat�on us�ng recyclersAppendix D2: Prestart check l�stsAppendix D3: Da�ly reports for �n s�tu recycl�ng

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Process Controls

Append�x D �ncludes a ser�es of checklists and report sheets (together w�th examples) that are normally used on s�te.

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Appendix D4: Determ�n�ng the strength of field samplesAppendix D5: Determ�n�ng the strength of core spec�mens

The pr�mary determ�nants of m�x qual�ty that need careful mon�tor�ng are d�scussed �n the follow�ng sect�ons.

i TemperaturesThe temperature of the mater�al be�ng m�xed has a s�gn�ficant �nfluence on the qual�ty of m�x. In general, the colder the mater�al, the poorer the m�x qual�ty and, conversely, the warmer the mater�al, the better the m�x qual�ty. B�tumen treatment should therefore only be undertaken when the temperature of the mater�al �s above the m�n�mum stated �n the Project Spec�ficat�ons.

BSM-emulsion

The temperature of the pretreated material should exceed 5 °C. Manufacturers of b�tumen emuls�on normally recommend that the�r product �s appl�ed through a spraybar at 60 °C when und�luted b�tumen emuls�on �s used. The pr�mary reason for adopt�ng such a temperature �s the reduction in viscosity that fac�l�tates pump�ng at reduced pressure, thereby reduc�ng the r�sk of the b�tumen emuls�on suffer�ng a premature break.

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BSM-foam

The temperature of the pretreated material must be 10 °C or more, preferably 15 °C.The bitumen temperature must be above 160 °C to prov�de suffic�ent heat energy for the water to change state and create the foam. The normal b�tumen temperature for foam�ng �s 175 °C. Although b�tumen does foam at lower temperatures, the qual�ty of such foam �s �nfer�or to that ach�eved when the b�tumen �s at h�gher temperature.

B�tumen should never be heated above 195 °C.

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ii Mixing Moisture ContentAt the t�me of m�x�ng, the mo�sture content of the mater�al must be properly controlled. As expla�ned �n Sect�on 6.2.2, the mo�sture content of �n s�tu pavement mater�als �s l�kely to vary. It �s therefore essent�al that the mo�sture content of the treated mater�al �s cont�nually assessed (espec�ally when recycl�ng �n s�tu) and the amount of water be�ng added to the m�x �s adjusted �mmed�ately a change �s detected. The mo�sture content of the treated mater�al �s eas�er to control when m�x�ng �n plant, prov�ded the stockp�les of �nput mater�als are protected from the env�ronment (ra�n). Once establ�shed, the requ�red water or d�luted b�tumen emuls�on add�t�on w�ll usually rema�n relat�vely constant.

iii Amount of Bitumen AddedIt �s �mportant to recogn�se that var�at�ons �n the parent mater�al make �t pract�cally �mposs�ble to prec�sely determ�ne the quant�ty of b�tumen added. Unl�ke a manufactured product such as hot-m�xed asphalt, the grad�ng of a recycled mater�al tends to vary cons�derably and the �nclus�on or exclus�on of a s�ngle 25 mm stone part�cle makes a s�gn�ficant d�fference when attempt�ng to determ�ne the amount of b�tumen that was added, expressed as a percentage of the mass of the sample. Inclus�on of b�tumen concentrat�ons �n the sample (str�ngers �n the case of foamed b�tumen) also makes an apprec�able d�fference. Th�s s�tuat�on �s exacerbated by the presence of old b�tumen �n the recycled mater�al, espec�ally where the ex�st�ng road was extens�vely patched w�th var�ous b�tum�nous mater�als, for example, asphalt, cold m�x and ch�p seal.

B�tumen extract�ons are therefore mean�ngless and effect�ve control can only be exerc�sed by mon�tor�ng the consumpt�on of b�tumen (b�tumen emuls�on or foamed b�tumen) to ensure that the requ�red appl�cat�on rate �s ach�eved. Such control necess�tates that every tanker load of b�tumen �s suppl�ed w�th an ass�zed we�ghbr�dge cert�ficate and that the area covered by each tanker-load �s accurately mon�tored. When a recycler �f fitted w�th a flow meter, the b�tumen used should be recorded after each run and reconc�led w�th the bulk usage.

The alternat�ve to measur�ng b�tumen consumpt�on by us�ng a d�p-st�ck to measure the contents of a tanker �s usually cons�dered to be �mpract�cal where bulk tankers are used. D�p-st�cks are used rout�nely w�th d�str�butors for ch�p seal surfac�ng, but are seldom used w�th

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Bitumen Consumption

The consumpt�on of b�tumen emuls�on and foamed bitumen must be carefully mon�tored. It �s not poss�ble to determ�ne the b�tumen content after construct�on us�ng extract�ons.



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bulk tankers that are coupled �nto the recycl�ng tra�n. Furthermore, gaug�ng the contents of a tank by d�pp�ng requ�res a reasonably level or cons�stent surface wh�ch cannot be guaranteed on most rehab�l�tat�on projects.

iv Amount of Active Filler AppliedThe relat�vely low appl�cat�on rate of act�ve filler used �n produc�ng a BSM and the encapsulat�on of the �nd�v�dual part�cles of act�ve filler �n b�tumen make �t pract�cally �mposs�ble to apply the standard control tests used when stab�l�s�ng w�th cement or l�me. Consumpt�on controls are therefore used to check that the requ�red amount of act�ve filler �s appl�ed and that the spread �s un�form.

For �n s�tu treatment, act�ve filler �s normally suppl�ed �n bags and spread by hand. To ach�eve the requ�red appl�cat�on rate, a gr�d pattern �s marked on the ex�st�ng road surface w�th each gr�d block represent�ng the area to be covered by the contents of one bag. Bags are then placed �n each gr�d block, opened and the powder carefully spread by squeegee. Process controls for th�s operat�on �nclude check�ng the d�mens�ons of the gr�d mark�ngs, ensur�ng that one bag �s placed �n each block and that a un�form spread �s ach�eved w�th�n each block.Alternat�vely, on larger projects, act�ve filler �s often suppl�ed �n bulk tankers and appl�ed us�ng a spreader attached to the rear of the tanker. The canvas patch test �s usually used to check the spread rate coupled w�th an overall consumpt�on check to ensure that the mass suppl�ed (we�ghbr�dge t�cket) �s appl�ed to the area that was spread.

Where the mater�al �s recycled �n s�tu, spread�ng should always be restr�cted to one cut at a t�me, w�th the filler be�ng spread on the road surface �mmed�ately ahead of the recycler. Constant attent�on �s then requ�red to ensure that the filler �s not moved to the s�de by the front door on the recycler’s m�x�ng chamber. Traffic must never be allowed to travel over the spread filler.

The appl�cat�on rate of act�ve filler �s usually computer controlled when m�x�ng �n plant. However, the consumpt�on rate should be checked regularly to ensure that the plant �s correctly cal�brated.

6 8 2 QUALITY OF THE LAYER OF BSMLayers constructed from BSMs must meet spec�fic geometr�c requ�rements (layer w�dth and th�ckness), mater�al cond�t�on (dens�ty and un�form�ty) and surface fin�sh (shape and level). The method employed for plac�ng the mater�al, levell�ng, compact�ng and fin�sh�ng off w�ll d�ctate the qual�ty of the final product and whether the spec�fied requ�rements are ach�eved.

Layers constructed from �n s�tu m�xed mater�al �nvolve construct�on methods that are very d�fferent from those used to construct a layer from mater�al that �s m�xed off s�te. D�fferent process controls are therefore employed to ensure the requ�red end product �s ach�eved. These are covered separately �n the follow�ng sect�ons.

6 8 2 1 Layers Constructed from In Situ Treated Material Using RecyclersProcess controls for layers constructed by �n s�tu recycl�ng are focused on ach�ev�ng the correct depth of cut that w�ll prov�de the requ�red layer th�ckness, cont�nu�ty across jo�nts and adopt�ng the correct sequence of operat�ons for compact�ng the mater�al, cutt�ng levels and fin�sh�ng off.

As descr�bed �n Sect�on 6.2.2.1, the depth of cut �s best controlled us�ng a T-bar to probe to the bottom hor�zon of the recycled mater�al. A tape �s usually attached to the T-bar to measure the depth relat�ve to a str�ngl�ne stretched between the same level references (poles) that w�ll be used to cut final levels. Such measurements should be taken at least once every 100 m of cut.

Recyclers �nvar�ably need to make more than one cut to cover the requ�red w�dth of treatment, thereby �ntroduc�ng a long�tud�nal jo�nt between adjacent cuts that always requ�res an overlap. The w�dth of overlap �s d�ctated by the gu�del�ne and �nd�cator (cha�n dangl�ng from an arm attached to the front of the recycler). These must be checked before start�ng each cut. In add�t�on, the actual overlap ach�eved must be phys�cally checked at least once every 200 m by measurements taken �n front and beh�nd the recycler.

Active Filler Application

Act�ve filler �s usually spread by hand The placement of the bags and the spread�ng of the filler must be carefully controlled

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Traffic on Active Filler

Traffic must never be allowed to travel over the spread filler.



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As descr�bed �n Sect�on 6.2.2.5, the sequence of compact�ng and level cutt�ng beh�nd the recycler �s cr�t�cal. These operat�ons need to be constantly mon�tored to ensure that pr�mary compact�on �s complete before levels are cut.

6 8 2 2 Layers Constructed In Situ Treated with Conventional Plant (BSM-emulsion)Once the mater�al has been m�xed, construct�ng a layer of BSM-emuls�on �s s�m�lar to construct�ng any pavement layer us�ng convent�onal plant. However, add�t�onal controls are essent�al to ensure that the spec�fied layer th�ckness (depth of process�ng) �s ach�eved. The depth of pre-r�pp�ng of the mater�al �n the ex�st�ng pavement must be carefully mon�tored, as must the bottom hor�zon cut by the mouldboard of the grader. These are best controlled by d�pp�ng from a str�ngl�ne stretched between the same level references (poles) that w�ll be used to cut final levels.

6 8 2 3 In Plant TreatmentBSMs treated �n plant are �nvar�ably used to construct a new layer. Before plac�ng the mater�al, the surface of the underly�ng layer must be cleaned and thoroughly mo�stened. V�sual controls are requ�red to ensure that the surface rema�ns �n such a clean and mo�st state unt�l covered by the BSM.

The mo�sture content of the BSM requ�res careful mon�tor�ng throughout the plac�ng and compact�ng process. Add�t�onal mo�sture �n the form of water or a very d�luted b�tumen emuls�on (“d�rty water”) �s sprayed on the surface of the part�ally completed layer as and when requ�red, based on an assessment made by the superv�sor.

i Paver LaidAs d�scussed �n Sect�on 6.4.3.3, constant mon�tor�ng �s requ�red to prevent segregat�on, part�cularly wh�lst the mater�al �s �n trans�t and when �t �s transferred from the supply truck to the pav�ng screed.

After the paver has been properly set up so that the screed ach�eves a cons�stent “float” on the mater�al, the process �s controlled ma�nly by observ�ng the operat�on to ensure that the correct l�ne �s followed, speed �s restr�cted to the rate of mater�al del�very, mater�al flow to the screed �s constant and that the tampers / v�brators / pulse bars are funct�on�ng. Measurements need to be taken at both ends of the screed (normally once every 50 m) to ensure that the requ�red pre-compacted th�ckness �s ach�eved.

When pav�ng aga�nst a prev�ously formed jo�nt, the face of the jo�nt must be thoroughly mo�stened and kept mo�st unt�l covered (v�sual observat�ons).

Rollers used to compact the paved mat also need to be closely mon�tored to ensure that the correct roll�ng pattern and sequence �s followed, suffic�ent passes are made and that the energy appl�ed does not roll the mat out of shape.

ii Placed by GraderWhere an �n-plant treated BSM �s dumped on the road and placed by grader, the same procedures and controls used to construct a layer from G2 mater�al are followed.

iii Placed by Labour Intensive MethodsControls are necessary to ensure that the dens�ty of the spread mater�al �s reasonably cons�stent pr�or to any compact�ve effort be�ng appl�ed. V�sual observat�ons are used to ensure that all mater�al �s moved from where �t was dumped. The “heel penetrat�on test” carr�ed out on the surface of the spread layer can also be useful as an �nd�cator of var�at�ons �n dens�ty.

6 8 3 ACCEPTANCE CONTROLS FOR PAVEMENT LAYERS CONSTRUCTED WITH BSMSThe Project Spec�ficat�ons for each project need to deta�l the relevant tolerances and qual�ty control tests that w�ll be conducted on the completed works. These w�ll normally �nclude the m�n�mum acceptance cr�ter�a and relevant tolerances relat�ng to:

Thickness of the Completed BSM Layer Th�s �s one of the most cr�t�cal parameters �nfluenc�ng the performance of the overall pavement structure. Small changes �n layer th�ckness s�gn�ficantly �nfluence structural capac�ty. Hence, layer th�ckness must be carefully mon�tored on s�te.

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Conventional Equipment

BSM-foam cannot be constructed us�ng convent�onal equ�pment.



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On �n s�tu recycl�ng projects �t �s �mportant to apprec�ate that the th�ckness of the completed layer �s not necessar�ly the same as the depth of recycl�ng. A grader �s always used to shape the mater�al beh�nd the recycler, always after �n�t�al deep compact�on has been appl�ed, and to cut the final levels. Level control pegs should always be establ�shed on s�te and checked aga�nst ex�st�ng surface levels pr�or to recycl�ng.

A m�n�mum th�ckness �s normally spec�fied. For example, where the structural des�gn requ�res a 200 mm th�ck layer, the m�n�mum requ�rement measured at any one pos�t�on should not be less than 200 mm.

Application Rates for the Bitumen Stabilising Agent and Active Filler A tolerance of ± 0.3% �s normally spec�fied for the appl�cat�on of the b�tumen stab�l�s�ng agent. When 2.5% res�dual b�tumen �s spec�fied, appl�cat�on rates of between 2.2 and 2.8%, measured on actual consumpt�on, w�ll meet the requ�red l�m�ts.

The tolerance for appl�cat�on rate of act�ve filler, also based on actual consumpt�on, �s normally spec�fied as ± 0.1%. Thus, �f the spec�fied appl�cat�on rate �s 0.7%, appl�cat�on rates of between 0.6 and 0.8% w�ll meet the requ�rements. Emphas�s must be placed on process controls to ensure that the act�ve filler �s un�formly spread on the road surface.

Mix Quality The qual�ty of m�x �s evaluated by test�ng the strength of the mater�al. Due to the lack of soph�st�cat�on found �n most field laborator�es, the strength of field samples �s normally evaluated from s�mple ITS tests carr�ed out on 100 mm d�ameter spec�mens.

Bulk samples (approx�mately 50 kg) of the BSM are usually taken from the road, pr�or to be�ng compacted, and reta�ned �n a sealed bag. Two such samples are normally taken for each day’s work. These samples are then transported to the field laboratory and used �mmed�ately to manufacture spec�mens. Append�x D4 descr�bes the procedure to be followed �n manufactur�ng and cur�ng the spec�mens and for determ�n�ng relevant ITS values. M�n�mum ITS values (dry and soaked) that must be ach�eved for the d�fferent classes of mater�als (BSM1, BSM2 or BSM3) are g�ven �n Chapters 4 and 5.

Care needs to be exerc�sed when manufactur�ng 100 mm d�ameter test spec�mens, espec�ally where the mater�al �s coarse and non-plast�c. Each spec�men should be �nspected after extrud�ng from the mould. Those exh�b�t�ng ev�dence of part�cle segregat�on or poor compos�t�on should be d�scarded and replaced by manufactur�ng add�t�onal spec�mens. There should always be suffic�ent mater�al ava�lable s�nce each 100 mm d�ameter spec�men has a mass of approx�mately 1 kg.

In the final analys�s, �f there �s any doubt about the qual�ty of the as-bu�lt product, 150 mm d�ameter cores can be extracted from the completed layer and subjected to a test�ng programme to est�mate the potent�al performance of the mater�al �n the recycled layer. S�nce a “young” BSM �s relat�vely tender and s�gn�ficantly less dense than hot m�x asphalt, cor�ng must be undertaken w�th gentle pressure appl�ed to the core barrel and m�n�mal water add�t�on. L�kew�se, the recovered spec�men w�ll be tender and needs to be handled w�th care, espec�ally wh�lst be�ng transported from s�te to the laboratory. Once �n the laboratory, core spec�mens must be �nspected for damage pr�or to cond�t�on�ng, cur�ng and test�ng (as descr�bed �n Append�x D5). Damaged spec�mens must be d�scarded s�nce any test carr�ed out on such a spec�men w�ll not be a true reflect�on of the mater�al �n the field. To ensure 100% core recovery, cor�ng should be delayed unt�l the mater�al has ga�ned suffic�ent strength.

BSM-emulsion

100% Core recovery �s normally ach�eved after four weeks.

BSM-foam

100% Core recovery �s normally ach�eved after two weeks.

Compaction Requirements The m�n�mum dry dens�ty requ�rement �s usually spec�fied, s�m�lar to the prov�s�ons conta�ned �n the Standard Spec�ficat�ons (COLTO, 1998) for pavement layers constructed from treated mater�als. The actual level of dens�ty spec�fied (as a percentage of the MDD or BRD) w�ll depend on the support character�st�cs of the underly�ng pavement. Dens�t�es between 97

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Thickness Tolerances

The tolerances allowed should ensure that the th�ckness at any po�nt �s not less than the design thickness



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and 100% of the mod�fied AASHTO dens�ty are normally spec�fied where the pavement support cons�sts of natural granular mater�al, depend�ng on the �n s�tu st�ffness, and up to 102% where a cement treated layer ex�sts �n the subbase.

Where layers th�cker than 175 mm are recycled, �t �s normal to spec�fy that a m�n�mum percentage (typ�cally 10%) of all dens�ty tests are carr�ed out on two separate hor�zons �n the layer. Thus, where the layer th�ckness �s 200 mm, one dens�ty test �s conducted on the upper 100 mm th�ck hor�zon and a second test on the underly�ng lower 100 mm hor�zon. The average of the two measurements must meet the m�n�mum spec�fied dens�ty for acceptance.

Levels, Width, Cross-Section and Surface Regularity The construct�on tolerances spec�fied �n clause 3405 of the Standard COLTO Spec�ficat�ons are usually appl�cable to the completed layer. Measurements should always be taken �mmed�ately after complet�ng the layer, before open�ng to traffic.

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BIBLIOGRAPHY

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BIBLIOGRAPHYAASHTO. 1986. Guide for Design of Pavement Structures, Amer�can Assoc�at�on of State H�ghway and Transportat�on Offic�als.

Comm�ttee of Land Transport Offic�als (COLTO), 1998 Ed�t�on. Standard Specifications for Road and Bridge Works for State Road Authorities.

EMERY, S.J. The pred�ct�on of mo�sture content �n untreated pavement layers and an appl�cat�on to des�gn �n Southern Afr�ca. CSIR Research Report 664, NITRR, Bulletin 20, Pretor�a, South Afr�ca, 1987.

Gauteng Department of Publ�c Transport, Roads and Works, 2008. Job Creation, Skills Development and Empowerment in Road Construction, Rehabilitation and Maintenance. October 2008.

HEFER, A.O. and F.J. Jooste. 2008 Development of a Pavement Performance Information System Rev�s�on of the South Afr�can Pavement Des�gn Method Project PB/2006/PBIS. South Afr�can Nat�onal Roads Agency. Report number 1998/009584/06

JENKINS, KJ. 2000. M�x des�gn cons�derat�ons for cold and half-cold b�tum�nous m�xes w�th emphas�s on foamed b�tumen. Ph. D. Thes�s, Un�vers�ty of Stellenbosch, South Afr�ca.

JENKINS, KJ, Van de Ven, MFC, Derbysh�re, R and Bond�ett�, M. 2000. Invest�gat�on of the early performance propert�es of a pavement, recycled w�th foamed b�tumen and b�tumen emuls�on through field-test�ng. In: Action in Transport for the New Millennium, South Afr�can Transport Conference, Pretor�a, July 2000, Paper 2C54 (On CD).

JENKINS, K.J., L.J. Ebels, E.T. Mathan�ya, R.W.C. Kelfkens, P.K. Moloto and W.K. Mulusa, 2008, Updating Bitumen Stabilised Materials Guidelines: Mix Design Report, Phase 2 Stellenbosch Un�vers�ty.

JOOSTE, F.J., F.M. Long, and A.O. Hefer. 2007. A Method for Consistent Classification of Materials for Pavement Rehabilitation and Design Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2007. (GDPTRW report number: CSIR/BE/IE/ER/2007/0005/B).

JOOSTE, F.J., F.M. Long and A.O. Hefer. 2007. A Knowledge Based Structural Design Method for Pavements Incorporating Bitumen Stabilised Materials Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2007. (GDPTRW report number: CSIR/BE/IE/ER/2007/0004/B).

KLEYN, E.G. 1984. Aspects of Pavement Evaluation and Design as Determined with the Aid of the Dynamic Cone Penetrometer M.Ing. Theses (�n Afr�kaans), Department of C�v�l Eng�neer�ng, Un�vers�ty of Pretor�a, Pretor�a.

LEE D.Y., 1981. Treat�ng Marg�nal Aggregates and So�ls w�th Foamed Asphalt. Association of Asphalt Paving Technologists Volume 50 pp 211-250.

LONG, F.M. and F.J. Jooste. 2007. Summary of LTTP Bitumen Emulsion and Foamed Bitumen Treated Sections Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2007. (GDPTRW report number: CSIR/BE/IE/ER/2007/0006/B).

LONG, F.M. 2009. Validation of Material Classification System and Pavement Number Method Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2009. (GDPTRW report number: CSIR/BE/IE/ER/2009/0028/C).

MULUSA, WK., 2008. Development of a Simple Triaxial Test for Characterising Bitumen Stabilised Materials. MSc (Eng) thes�s at Stellenbosch Un�vers�ty. To be publ�shed.


BIBLIOGRAPHY

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PAIGE-GREEN, P., Semmel�nk, C., Theyse, H. and Steyn, W. 2001. Pavement rehabilitation using cold recycling: A synthesis Pretor�a: CSIR Transportek. (Contract Report CR2001/45).

SABITA, 1993. GEMS - The Design and Use of Granular Bitumen Emulsion Mixes, Manual 14, 1993.

SABITA, 1999. ETB: The Design and Use of Bitumen Emulsion-treated Bases, Manual 21, 1999.

SAMPSON, L.R. and Netterberg, F, 1989. The Durab�l�ty M�ll: A new performance related test for base-course aggregates. The Civil Engineer in South Africa pp 287 – 294.

TMH1 Standard methods of testing road building materials 1986. Pretor�a: Department of Transport. (Techn�cal Methods for H�ghways: TMH1).

TMH6 Special methods for testing roads 1984. Pretor�a: Department of Transport. (Techn�cal Methods for H�ghways: TMH6).

TRH3 Design and Construction of Surfacing Seals, Techn�cal Recommendat�ons for H�ghways. 2007.

Draft TRH4 Structural Design of Flexible Pavements for Interurban and Rural Roads, Techn�cal Recommendat�ons for H�ghways, Draft 1996.

Draft TRH12 Flexible pavement rehabilitation investigation and design 1997. Pretor�a: Department of Transport. (Techn�cal Recommendat�ons for H�ghways: Draft TRH 12).

TRH13 Cementitious stabilizers in road construction 1986. Pretor�a: Department of Transport. (Techn�cal Recommendat�ons for H�ghways: Draft TRH13).

TRH14 Guidelines for road construction materials 1985. Pretor�a: Department of Transport. (Techn�cal Recommendat�ons for H�ghways: TRH14).

Draft TRH 21 Hot Mix Recycled Asphalt. 2009. (Downloadable from the Sab�ta and SANRAL web s�tes)

Wirtgen Cold Recycling Manual, 2004. 2nd Ed�t�on, ISBN 3-936215-05-7, W�rtgen GmbH, W�ndhagen, Germany, November 2004.


APPENDIX A: Material Classification System

88

APPENDIX A: MATERIAL CLASSIFICATION SYSTEM

A.1. INTRODUCTIONThe der�vat�on of the mater�al classes for each pavement layer �s a cr�t�cal aspect of the des�gn process, s�nce th�s process effect�vely const�tutes the determ�nat�on of structural des�gn �nputs. When appropr�ately done, the class�ficat�on process also prov�des a l�nk between the m�x des�gn and structural des�gn processes. In th�s Append�x, the recommended method for class�fy�ng mater�als �s presented. The object of the method �s to prov�de a rel�able, rat�onal and cons�stent �nd�cat�on of the appropr�ate mater�al class. The method �s based on the use of all ava�lable �nformat�on, and uses fuzzy log�c and certa�nty theory to assess the certa�nty that mater�als belong to a part�cular class.

The sect�ons below descr�be the method �n more deta�l and prov�de all relevant deta�ls for the �mplementat�on of the method. Although the method was spec�fically developed for use �n the structural des�gn method for pavements that �ncorporate BSMs, the approach can be used �n any pavement des�gn context w�th all common mater�al types, and �s espec�ally relevant for rehab�l�tat�on des�gn.

A.2. CONCEPTDur�ng a rout�ne pavement rehab�l�tat�on �nvest�gat�on, an eng�neer �s typ�cally faced w�th a w�de array of test parameters and cond�t�on �nd�cators. These parameters can be quant�tat�ve or qual�tat�ve, subject�vely or object�vely determ�ned, and the sample s�zes for d�fferent �nd�cator types may vary s�gn�ficantly. For example, for a spec�fic pavement layer w�th�n a un�form des�gn sect�on, an eng�neer may typ�cally be faced w�th the follow�ng set of �nformat�on:

Seven Dynam�c Cone Penetrometer (DCP) tests.F�fty Fall�ng We�ght Deflectometer (FWD) deflect�ons.Two sets of mater�al descr�pt�ons and samples from test p�ts, together w�th standard mater�als test results, �nclud�ng Plast�c�ty Index (PI), grad�ng, Cal�forn�a Bear�ng Rat�o (CBR), mo�sture content and dens�ty.One subject�ve v�sual assessment w�th a descr�pt�on of observed d�stresses.F�fty sem�-subject�vely determ�ned backcalculated st�ffnesses from FWD tests.A general descr�pt�on of the mater�al type from h�stor�cal records.A general descr�pt�on of the h�story and past performance of the pavement.

From such a set of �nformat�on, the eng�neer has to der�ve the key assumpt�ons needed for the rehab�l�tat�on des�gn. The synthes�s of the �nformat�on to arr�ve at des�gn assumpt�ons �s one of the most �mportant and d�fficult parts of the rehab�l�tat�on des�gn process. Apart from bas�c analyt�cal sk�ll, �t also requ�res cons�derable exper�ence and knowledge of the ma�n dr�vers of mater�al behav�our. When �ncorrectly done, �ncons�stent conclus�ons can be drawn and the des�gn assumpt�ons w�ll not be cons�stently supported by ava�lable ev�dence.

The concept beh�nd the mater�al class�ficat�on method �s therefore to gu�de eng�neers �n the �nterpretat�on of ava�lable pavement cond�t�on data, and to synthes�ze ava�lable �nformat�on so that key des�gn assumpt�ons can be der�ved �n a cons�stent and rat�onal manner. The object�ve of the mater�als class�ficat�on method �s therefore to prov�de a method for the cons�stent assessment of pavement mater�als us�ng rout�ne tests and �nd�cators.

Many mater�al class�ficat�on methods are spec�ficat�on type approaches that rely on pass or fa�l type cr�ter�a. For these type of approaches, �f any one test fa�ls the cr�ter�a for the mater�al class then the mater�al cannot be class�fied as that class. For example, �f the CBR value �s below the spec�ficat�on for a G6 mater�al, then the mater�al cannot be class�fied as a G6 even �f all other ava�lable test results do meet the G6 cr�ter�a.

The approach descr�bed �n th�s Append�x �s a more rat�onal, albe�t less exact method, wh�ch can handle vagueness �n the data. Rather than g�v�ng a yes or no answer, the method �nd�cates the conformance to a mater�al class �n less restr�ct�ve terms. The approach assesses the certa�nty that the mater�al can be cons�dered as the part�cular mater�al class, and uses Fuzzy Log�c to prov�de th�s type of assessment. The evaluat�on of pavement mater�als as part of rehab�l�tat�on �nvest�gat�ons poses several un�que challenges. These challenges are related to the real�t�es of pavement �nvest�gat�ons and pavement des�gn, wh�ch �ncludes the follow�ng aspects:

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Many Sources of Uncertainty: Pavement eng�neer�ng deals w�th large quant�t�es (�.e. long d�stances) of natural and thus h�ghly var�able mater�als, wh�ch are subject to h�ghly var�able loads. Risk is Poorly Defined: The r�sk assoc�ated w�th pavement fa�lure �s poorly defined. For example, what �s the consequence of 5% more crocod�le crack�ng over a twelve year per�od, and �s �t cost-effect�ve to spend an extra R10 m�ll�on now to prevent �t? Several assumpt�ons are needed to answer th�s quest�on, and many of these – although they can be est�mated – are beyond control (e.g. ra�nfall, overload�ng, future budgets, etc). Because of th�s s�tuat�on, subject�ve assessment us�ng exper�ence plays a cons�derable role �n pavement des�gn.Small Sample Sizes: Rel�ance on small samples �s part of the real�ty of pavement �nvest�gat�ons. It �s not unusual for a rehab�l�tat�on des�gn over 20 km of road, over vary�ng terra�n and geolog�cal areas to be based on ten or less tr�al p�ts. All Tests are Indicators: In pavement des�gn s�tuat�ons, the assessment of mater�als always a�ms to assess stab�l�ty and (for some mater�als) flex�b�l�ty. It does so e�ther d�rectly (as �n a stab�l�ty test) or �nd�rectly (as �n a grad�ng assessment, wh�ch w�ll �mpact on stab�l�ty). Because the actual load s�tuat�on var�es, no pavement mater�al test �s able to completely quant�fy long term stab�l�ty or flex�b�l�ty. Even a h�ghly soph�st�cated test, l�ke the repeated load tr�ax�al test, must be performed at a fixed mo�sture content and stress state wh�ch w�ll never correspond completely to the real pavement s�tuat�on that �t a�ms to assess. Thus all tests prov�de only a relat�ve �nd�cat�on of the two key propert�es to be assessed, and some tests do so very poorly.Interpretation is Vague: In pavement rehab�l�tat�on �nvest�gat�ons, an eng�neer needs to dec�de what �nformat�on �s ava�lable, and what can be done w�th �t. A yes or no �nterpretat�on �s not always appropr�ate, and a relat�ve �nterpretat�on �s needed. Th�s compl�cates the �nterpretat�on of data cons�derably, espec�ally when confl�ct�ng �nformat�on �s �nvolved. It also �ntroduces more subject�v�ty �nto the process.

The mater�al class�ficat�on system deals w�th these real�t�es. Spec�fically, the approach �ncorporates the follow�ng elements: Clear and rat�onal formulat�on of the object�ve.Ab�l�ty to handle vagueness and uncerta�nty of �nterpretat�on.Ab�l�ty to work w�th small sample s�zes.

A 2 1 Assumed Material BehaviourTo prov�de a sound bas�s for the mater�als class�ficat�on method, a model of pavement mater�al behav�our was adopted. The assumed model �s shown �n F�gure A.1, and represents the mater�al as a conglomerate of course part�cles, fine part�cles, b�tumen and a�r vo�ds. Th�s mater�al model �s the well-known Mohr-Coulomb model, wh�ch generally appl�es to compos�te mater�als cons�st�ng of a comb�nat�on of loose aggregate and b�tumen. Th�s model appl�es to almost all pavement eng�neer�ng mater�als except clay and s�lt and manufactured mater�als such as geotext�les, w�th the �mportant d�st�nct�on that the compos�t�on of the mast�c d�ffers s�gn�ficantly for d�fferent mater�als.

Figure A.1 Mohr-Coulomb Material Model

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The mater�al model shown �n F�gure A.1 can be used to expla�n the components that determ�ne the strength and st�ffness of the mater�al. There are two components that determ�ne the mater�al’s shear strength:

The cohes�ve strength, wh�ch �s determ�ned ma�nly by the mast�c (cons�st�ng of the m�xed b�tumen and fine mater�al), andThe strength prov�ded by �nter-part�cle fr�ct�on, and mob�l�zed when compress�ve stresses force the fine and coarse part�cles together.

The cohes�ve and fr�ct�onal strength components determ�ne not only the shear strength or stab�l�ty, but also the st�ffness and tens�le strength. When the mater�al �s �n compress�on, the st�ffness and shear strength �s pr�mar�ly determ�ned by a comb�nat�on of the cohes�ve and fr�ct�onal elements. When the mater�al works �n tens�on, part�cles are not pushed together and the st�ffness and tens�le strength are determ�ned ma�nly by the cohes�ve element (�.e. the mast�c). Stab�l�ty and flex�b�l�ty prov�de an �nd�cat�on of the res�stance to the two ma�n sources of pavement deter�orat�on: deformat�on (e�ther due to volume change or shear) and crack�ng (due to fat�gue �n tens�on).

The mater�als that are most res�stant to shear and tens�le fa�lure are those �n wh�ch there �s a good balance between the strength prov�ded by the cohes�ve and fr�ct�onal elements. However, some mater�als tend to be dom�nated e�ther by the fr�ct�onal or cohes�ve element, as �llustrated �n F�gure A.2.

Figure A.2 Material Composition, Showing Dominance of Friction and Cohesion

The relat�ve role that the fr�ct�onal or cohes�ve component plays �n determ�n�ng the strength and st�ffness depends almost ent�rely on the state of the mast�c. In the case of asphalt, for example, the mast�c cons�sts of the b�tumen and filler comb�nat�on. At h�gh temperatures, the v�sco-elast�c b�tumen softens. When the mater�al �s loaded �n th�s cond�t�on, load �s transferred d�rectly to the coarse aggregate matr�x, and shear strength �s almost completely from the fr�ct�onal component. A s�m�lar effect �s observed �n crushed stone and natural gravels, where excess water destroys the suct�on forces that b�nd the fine part�cles together �n a mast�c, thereby s�gn�ficantly reduc�ng the cohes�ve strength or st�ffness component.

A clear understand�ng of the role of cohes�on and fr�ct�on �n determ�n�ng the strength and st�ffness of pavement mater�als �s �mportant, as most test �nd�cators prov�de an assessment of one or both of these elements. Thus some tests, l�ke the Plast�c�ty Index (PI), relate only to the cohes�ve element, wh�le others, l�ke a grad�ng analys�s, relate to the shear strength element. A fundamental understand�ng of what �s measured by a spec�fic test can prov�de the key to a rat�onal and useful �nterpretat�on of the test’s results.

The above defin�t�on and d�scuss�on of the Mohr-Coulomb model, and the cohes�ve and fr�ct�onal components that dr�ve th�s model, are used �n Sect�on A.4 to class�fy the var�ous mater�als tests, and to gu�de the�r �nterpretat�on.

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A 2 2 Design Equivalent Material ClassThe mater�al classes for granular and cement stab�l�sed mater�als adopted for th�s mater�al class�ficat�on method are al�gned w�th TRH14 (1985). The TRH14 class�ficat�on system �s regarded as be�ng h�ghly su�table for new construct�on and rehab�l�tat�on des�gn, as the behav�our and performance patterns of each mater�al class �s known w�th some certa�nty. However, w�th the mater�al class�ficat�on method, the obta�ned mater�als class �s regarded as the des�gn equ�valent mater�als class (DEMAC) and w�ll not necessar�ly meet the spec�ficat�ons for that mater�al class as g�ven �n TRH14. However, s�nce mater�als to wh�ch des�gn equ�valent classes are ass�gned have been �n serv�ce for some t�me, the raw mater�al would conform to (or exceed) the spec�ficat�ons for the class, as stated �n TRH14, �n almost all �nstances. The mater�al classes for BSMs are defined �n Chapter 2 of the Gu�del�ne and Sect�on A.4.2 of th�s Append�x.

When a des�gn equ�valent mater�al class (DEMAC) �s ass�gned to a mater�al, �t �mpl�es that the mater�al exh�b�ts �n s�tu shear strength, st�ffness and flex�b�l�ty propert�es s�m�lar to those of a newly constructed mater�al of the same class. For example, a layer �n an ex�st�ng pavement structure class�fied as a G2 des�gn equ�valent would �nd�cate that the mater�al �s cons�dered to be equ�valent to a G2 for des�gn purposes, based on the ava�lable test ev�dence. For brev�ty, a DEMAC w�ll be denoted DE-G2, for example.

The mater�als class�ficat�on system descr�bed �n the next sect�on prov�des a cons�stent method to evaluate and document the necessary ev�dence to support the mater�al class�ficat�on.

A.3. MATERIAL CLASSIFICATION SYSTEM

A 3 1 Theory of Holistic ApproachThe mater�al class�ficat�on system prov�des a framework for the rat�onal synthes�s of several d�fferent test �nd�cators. The outcome of the assessment becomes more rel�able as more test �nd�cators are added to the assessment. Th�s �s because each test typ�cally expla�ns only a small part of the cohes�ve or fr�ct�onal elements of mater�al behav�our. More complex tests, l�ke tr�ax�al tests, may evaluate these two elements together, but w�ll do so only for a spec�fic mo�sture or b�tumen content. The use of other �nd�cators w�ll st�ll be needed to determ�ne how the mater�al w�ll behave �f the mo�sture state or b�tumen content changes. S�nce each test prov�des only a part�al explanat�on of the mater�al’s behav�our, the rel�ab�l�ty of the assessment can be greatly �ncreased by �ncreas�ng the sample s�ze, and by add�ng more �nd�cators (�.e. test types) to the assessment. The system �s therefore a hol�st�c assessment, wh�ch works best when a comprehens�ve range of test �nd�cators are used.

The theory underly�ng the method �s based on Fuzzy Log�c and Certa�nty Theory. The development of the method �s descr�bed �n deta�l by Jooste et al (2007) and the val�dat�on of the method �s descr�bed by Long (2009). A summary of the theoret�cal process to class�fy a mater�al �s as follows:1. If H �s the hypothes�s to be tested, then the certa�nty that the hypothes�s �s true �s des�gnated as C(H), wh�ch has a value of 1.0 �f H �s

known to be true, 0.0 �f H �s unknown and -1.0 �f H �s known to be false. In the context of the present study, H could for example be the hypothes�s that the base layer �s a DE-G1.

2. The value of C(H) �s determ�ned by apply�ng rules wh�ch are based on exper�ence or doma�n knowledge. Each rule has a certa�nty factor (CF) assoc�ated w�th �t, to reflect the level of certa�nty �n the ava�lable ev�dence, or �n the knowledge on wh�ch the rule �s based. A typ�cal rule may be:

If [PI < 4] then [Material is a DE-G1] With Certainty CF

3. The certa�nty factor of a rule, CF, �s mod�fied to reflect the level of certa�nty �n the ev�dence. Th�s g�ves the mod�fied certa�nty factor CF’, calculated s�mply as:

CF’ = CF x C(E) (A.1)

Where C(E) �s a number between 0 and 1, �nd�cat�ng that the ev�dence �n support of the hypothes�s �s e�ther completely absent (C(E) = 0.0) or known to be present w�th absolute certa�nty (C(E) = 1.0).



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4. To get C(H|E), wh�ch �s the updated certa�nty that the hypothes�s H �s true, g�ven the ev�dence E, the follow�ng compos�te funct�on �s appl�ed:

If C(H) ≥ 0 and CF’ ≥ 0 then: C(H|E) = C(H) + [CF’ x (1-C(H))] (A.2)

If C(H) ≤ 0 and CF’ ≤ 0 then: C(H|E) = C(H) + [CF’ x (1+C(H))] (A.3)

If C(H) and CF’ have opposite signs, then:

(A.4)

In the appl�cat�on of the above methodology for mater�al class�ficat�on, the certa�nty factor CF assoc�ated w�th a spec�fic test �s ass�gned based on doma�n knowledge and exper�ence. If the test �s known to be a good overall �nd�cator of cohes�on, fr�ct�onal res�stance or both, then CF w�ll tend to be h�gher. CF can also be adjusted based on the sample s�ze and range of sampled values. For small sample s�zes, CF can be lowered to reflect decreased confidence �n the ava�lable ev�dence.

The steps and equat�ons outl�ned above prov�de a general method for cons�stently evaluat�ng the certa�nty that a hypothes�s �s true, g�ven uncerta�n and vague rules and ev�dence. A general�zed and s�mpl�fied example of the method’s appl�cat�on for mater�als class�ficat�on �s outl�ned below:1. We want to test the hypothes�s H that the mater�al for wh�ch we have �nformat�on �s a graded natural gravel (DE-G4). To do th�s, we

formulate the follow�ng rules: If [Material is Natural Gravel] and [PI < 4] then [Material is a DE-G4] with CF = 0.4 If [Grading conforms to G4 Envelope] then [Material is a DE-G4] with CF = 0.32. We now obta�n samples and measure the PI and grad�ng. The certa�nty factors can be adjusted based on the sample s�ze.3. We start w�th the first ava�lable ev�dence (PI test). At th�s stage C(H) = 0. S�nce CF = 0.4 for the first rule concern�ng PI, we use

Equat�on 4.1 and 4.2 to calculate the updated certa�nty for the hypothes�s that the mater�al �s a DE-G4 (C(H|E)).4. The updated certa�nty C(H|E) becomes the new start�ng certa�nty C(H) for the second rule wh�ch �nterprets the grad�ng. We aga�n

apply Equat�on 4.2 to calculate the new value for C(H|E).

Th�s process can be appl�ed for each mater�al class to obta�n a relat�ve �nd�cat�on of how much the ava�lable test data po�nt to each class. The follow�ng sect�ons g�ve more deta�ls on the process, and a worked example �s �ncluded �n Sect�on A.5.

A 3 2 Step by Step Material Classification The Certa�nty Theory approach �nvolves an assessment of how well the ava�lable ev�dence su�ts a g�ven hypothes�s. In the present context, the ev�dence would be ava�lable test data, and the hypothes�s to evaluate would be that the mater�al conforms to a spec�fic mater�al class. The method �nvolves the follow�ng steps:Step 1: For each of the ava�lable mater�al tests, determ�ne and report the 90th percent�le, med�an and 10th percent�le values from the

ava�lable observat�ons. For those tests for wh�ch a rat�ng system �s prov�ded, use the rat�ngs at each observat�on to determ�ne the requ�red stat�st�cs. Where there �s only one observat�on ava�lable, s�mply report the observat�on as the med�an value.

Step 2: Determ�ne the certa�nty factor assoc�ated w�th each of the ava�lable tests (�.e. CF as defined �n Sect�on A.4). Th�s certa�nty reflects the confidence that we have �n each test to prov�de an accurate �nd�cat�on of the �n s�tu shear strength and st�ffness of the mater�al. Deta�ls related to th�s step are prov�ded �n Sect�on A.3.3.

Step 3: Adjust the relat�ve certa�nty determ�ned �n Step 2 to take account of sample s�ze. Th�s adjustment decreases the confidence for smaller sample s�zes. Deta�ls related to th�s step are prov�ded �n Sect�on A.3.4.

Step 4: Select a l�kely mater�al class (e.g. DE-G4) for the layer �n quest�on. Step 5: For each of the ava�lable tests, determ�ne the expected range of values for each DEMAC for the selected mater�al from Table

A.3 (Granular), Table A.8 (BSM) or Table A.11 (Cemented). For example, �f the mater�al �n quest�on �s a DE-G4, and the test �s the soaked CBR at 98% Mod. AASHTO dens�ty, we w�ll use Table A.3 to obta�n the expected range of CBR values for a G4 (�.e. 80 to 99%). For tests that �nvolve a rat�ng system, as defined �n Sect�on A.4, the rat�ng values correspond�ng to d�fferent mater�al classes are shown �n Table A.3 (Granular), Table A.8 (BSM) and Table A.11 (Cemented).

Some tests or �nd�cators have expected ranges for the mater�al classes for d�fferent mater�al types, compact�on levels or spec�men d�ameter. For example, �n Table A.3, the Plast�c�ty Index has d�fferent values for crushed stone, natural gravel, gravel

1

+=

−C(H ) CF 'C(H | E )

min(| C(H ) |,| CF ' |)



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sand and s�lt, s�lty sand, sand and clay. In these cases, only one mater�al type, dens�ty level or spec�men d�ameter may be selected per test or �nd�cator.

Step 6: For each test, determ�ne how much the 10th percent�le to 90th percent�le range overlaps w�th the expected range of values for the mater�al. Th�s prov�des the relat�ve certa�nty that the test data po�nts to the mater�al class �n quest�on (�.e. factor C(E) as defined �n Sect�on A.3.1). Deta�ls of how to perform th�s calculat�on are prov�ded �n Sect�on A.3.5.

Step 7: For each test, use the certa�nty factor CF from steps 2 and 3 and the certa�nty of ev�dence C(E) from Step 6, to update the certa�nty that the mater�al tested conforms to the class selected �n Step 4. Th�s calculat�on then prov�des the relat�ve certa�nty that the mater�al belongs to the selected DEMAC, g�ven the ava�lable ev�dence (�.e. C(H|E) as defined �n Sect�on A.3.1). Deta�ls on these calculat�ons are prov�ded �n Sect�on A.3.6.

Step 8: Repeat Steps 4 to 7 for each l�kely mater�al class. For example, �f we are perform�ng a class�ficat�on for an unbound granular base, we may evaluate the certa�nty assoc�ated w�th classes DE-G1 to DE-G5.

Step 9: Select the mater�al w�th the h�ghest certa�nty g�ven the ava�lable ev�dence. Th�s mater�al class �s ass�gned to the layer �n quest�on. Properly document the ev�dence and calculat�ons.

A 3 3 Certainty Factors for Different Tests and IndicatorsBecause most pavement mater�als tests prov�de only a part�al �nd�cat�on of the shear strength and st�ffness of a mater�al, a certa�nty factor �s ass�gned to each test �nd�cator. Th�s certa�nty factor represents the factor CF as defined �n Sect�on A.3.1. In essence, CF represents the subject�ve confidence �n the ab�l�ty of a test to serve as an accurate �nd�cator for mater�al strength and st�ffness. The value of CF can range from 0 to 1, w�th a value of 1 �nd�cat�ng absolute confidence �n a test or �nd�cator (a h�ghly unl�kely ass�gnment).

Suggested certa�nty factors for the tests and �nd�cators used �n the class�ficat�on system are prov�ded �n Table A.3 (granular mater�als), Table A.8 (BSMs) and Table A.11 (cemented mater�als). The rat�ngs shown �n these tables are based on a subject�ve assessment of the completeness and appropr�ateness of each test or �nd�cator. Eng�neers can adjust these values to take account of exper�ence or spec�fic project s�tuat�ons, but the assumed values should be reported to cl�ents. If the assumed values dev�ate substant�ally from those suggested �n the tables, the assumed values must be mot�vated �n the assessment report.

A 3 4 Adjustment for Sample SizeSmall sample s�zes, �.e. one or two observat�ons are not uncommon �n pavement cond�t�on assessments. However, th�s affects the certa�nty w�th wh�ch a mater�al class �s assessed. To take account of th�s, the Certa�nty Factor (CF) assoc�ated w�th each test �s adjusted to take account of the sample s�ze. Table A.1 shows the recommended adjustment factors based on sample s�ze. These factors are appl�ed by mult�ply�ng the factor from Table A.1 w�th the CF factor for the test from Table A.3 (Granular), Table A.8 (BSM) and Table A.11 (Cemented).

Table A 1 Recommended Adjustment of CF based on Sample Size

Sample S�ze (number of observat�ons) Adjustment Factor

1 0.2

2 0.3

3 0.6

4 to 6 0.7

6 or greater 1.0

A 3 5 Assessing the Relative Certainty of EvidenceThe mater�al class�ficat�on method assesses the certa�nty that a mater�al can be class�fied as a part�cular mater�al class. Th�s assessment �s vague and uncerta�n because of the �ncompleteness of most tests and because a sampl�ng est�mate �s used. The �ncompleteness �s taken �nto account w�th the Certa�nty Factor (Sect�on A.3.3), but the var�at�on �n the tests results needs to be cons�dered.

The method for ach�ev�ng th�s �s �llustrated �n F�gure A.3. The figure shows the CBR l�m�ts assoc�ated w�th mater�al classes DE-G5, DE-G6 and DE-G7. Also shown �s a tr�angle wh�ch �s determ�ned as follows: left bottom corner �s the 10th percent�le value, top corner �s the med�an value and r�ght bottom corner �s the 90th percent�le value.



94

The tr�angle represents the ava�lable ev�dence �n a relat�ve manner. The he�ght of the tr�angle �s g�ven a fixed value of 1.0. The total area of the tr�angle and the port�on of the tr�angle that falls w�th�n the DE-G6 class are calculated. The relat�ve area that overlaps w�th the DE-G6 class g�ves us a relat�ve �nd�cat�on of how strongly the CBR ev�dence po�nts to a DE-G6 class. In the context of the certa�nty theory methodology, we assume that the relat�ve area that overlaps w�th the mater�al class �n quest�on, g�ves us the factor C(E) as defined �n Sect�on A.3.1.

Figure A.3 Determining Relative Conformance of Evidence to Material Class Limits

A 3 6 Updating Material Classification for Available EvidenceThe object�ve of the assessment �s to determ�ne the certa�nty assoc�ated w�th the hypothes�s that a mater�al conforms to a selected DEMAC. For example, �f the mater�al selected for evaluat�on �s a DE-G6, and we want to obta�n the relat�ve certa�nty that the mater�al �s �ndeed a DE-G6. As defined �n Sect�on A.3.1, the certa�nty for th�s hypothes�s �s C(H), wh�ch �s �n�t�ally zero, but wh�ch w�ll �ncrease when we cons�der tests for wh�ch the results conform partly to the range expected for a DE-G6 mater�al.

The certa�nty factors for the d�fferent tests, comb�ned w�th the adjustment for sample s�ze, prov�de the certa�nty factor CF assoc�ated w�th each test (Sect�on A.3.3). The compar�son of the test results w�th the expected l�m�ts for the DEMAC �n quest�on (as shown �n F�gure A.3 and d�scussed �n Sect�on A.3.5) prov�des us w�th the certa�nty that ev�dence �s present, C(E). These are all the factors needed to calculate an updated certa�nty for the hypothes�s that the mater�al tested conforms to the selected DEMAC, �.e. C(H|E) as defined by Equat�ons A.1 to A.4 (Sect�on A.3.1).

Usually, the calculat�on of C(H|E) mostly �nvolves repeated appl�cat�on of Equat�on A.2. In�t�ally, C(H) �s zero. Then, CF’ �s calculated us�ng Equat�on A.1, and then C(H|E) us�ng Equat�on A.2. Then, the next test type �s evaluated, wh�ch has a new CF and C(E) assoc�ated w�th �t. The CF’ �s then recalculated. For the new test type, the certa�nty C(H) �s set equal to C(H|E) determ�ned from the prev�ous test type. The C(H) and CF’ �n Equat�on A.1 are used to calculate the new C(H|E). Th�s process �s repeated for each test type to obta�n an overall certa�nty that the mater�al conforms to the selected DEMAC.

Once the overall certa�nty that the mater�al conforms to the selected DEMAC �s assessed, the next l�kely class �s selected and the process repeated us�ng the same set of �nformat�on. In some �nstances, th�s evaluat�on may requ�re that the conformance to five or more classes be evaluated. Although th�s seems cumbersome, the calculat�ons are s�mple and the process can eas�ly be automated us�ng a spreadsheet macro or a computer program.

A software program to do the mater�al class�ficat�on �s ava�lable on www.asphaltacademy.co.za/b�tstab. The software runs on the webs�te and �t �s not necessary to download the software to a local computer. A M�crosoft Excel template for prepar�ng and upload�ng the data can be downloaded from the webs�te.

CBR Value

25 45 8015

DE-G7 Class DE-G6 Class DE-G5 Class

1.0

90th percentile10th percentile median

CBR Value

25 45 8015

DE-G7 Class DE-G6 Class DE-G5 Class

1.0

90th percentile10th percentile median



95

A.4. TESTS AND INTERPRETATION OF RESULTSTh�s sect�on deta�ls the tests that are used for the mater�al class�ficat�on, the �nterpretat�on of the test results and the certa�nty factors. Three mater�als are covered: untreated granular mater�als, b�tumen stab�l�sed mater�als and cement stab�l�sed mater�als.

The mater�al class�ficat�on method �s relat�vely new, and although �t has been well val�dated, espec�ally for granular and cemented mater�als (Long, 2009), �t �s poss�ble that further refinements may be necessary. If such refinements are made, the most up to date l�m�ts and certa�nty factors w�ll be posted on www.asphaltacademy.co.za/b�tstab. It �s therefore recommended that before commenc�ng the mater�al class�ficat�on process, the webs�te �s checked for any changes �n values or tests.

A 4 1 Granular MaterialsThe class�ficat�on of granular mater�als �s al�gned w�th TRH14 (1985). The �nd�cators and tests for the class�ficat�on of unbound granular mater�als are deta�led �n Table A.2, and the relevance of the test or �nd�cator �s expla�ned. The �nterpretat�on of the test results are g�ven �n Table A.3. The values shown have been val�dated and prov�de cons�stent, reasonable results (Long, 2009). The �nterpretat�on of cons�stency, v�s�ble mo�sture, grad�ng and h�stor�cal performance requ�res the determ�nat�on of a rat�ng. Deta�ls on the rat�ngs are g�ven �n Table A.4, w�th add�t�onal �nformat�on �n Table A.5 (h�stor�cal performance), Table A.6 (cons�stency) and F�gure A.4 (grad�ng).

Table A 2 Indicators and Tests for Classification of Unbound Granular Materials

Test or Indicator Relevance for Material Classification Interpretat or Rating

Comments

Soaked CBRWhen soaked, tests ma�nly the fr�ct�onal strength component of shear strength.

Table A.3Test relevance and �nterpretat�on �s based on TRH14 spec�ficat�ons.

Percent pass�ng 0.075 mm S�eve (F�nes)

Impacts on the dens�ty that can be ach�eved, and on the bear�ng strength of the mater�al. As such, relates ma�nly to fr�ct�onal component of shear strength.

Table A.3

Ideal range �s 6 to 10%. At less than 4% fines, dens�ty �s d�fficult to ach�eve. Shear strength reduces when fines exceed roughly 13% (Hefer and Scull�on, 2002; Gray, 1962).

Relat�ve Dens�tyRelates to the dens�ty of pack�ng of part�cles, and hence to the potent�al to develop fr�ct�onal res�stance.

Table A.3Test relevance and �nterpretat�on �s based on TRH14 spec�ficat�ons.

DCP Penetrat�onInd�cator for overall shear strength. Sens�t�ve to dens�ty, mo�sture content, part�cle strength, grad�ng and plast�c�ty.

Table A.3Test relevance and �nterpretat�on �s based on exper�ence and ranges publ�shed Kleyn (1984).

FWD Backcalculated St�ffness

Prov�des a d�rect but relat�ve �nd�cat�on of the st�ffness under dynam�c load�ng for most mater�als. L�kely to be h�ghly correlated to shear strength at small stra�ns.

Table A.3Test relevance and �nterpretat�on ranges based on exper�ence �n southern Afr�ca.

Cons�stency Rat�ngProv�des a rough �nd�cat�on of mater�al dens�ty and st�ffness.

Table A.4Rat�ng based on mater�al cons�stency evaluat�on from test p�ts.

Plast�c�ty Index


Table A.3

Based on TRH14. Test relevance and ma�n effects related to shear strength are reported �n Hefer and Scull�on (2002); and �n Gray (1962).

Test and Indicator Limits

www.asphaltacademy.co.za/b�tstab has the most up to date l�m�ts and certa�nty factors for the selected tests and �nd�cators.



96

Test or Indicator Relevance for Material Classification Interpretat or Rating

Comments

V�s�ble and Measured Mo�sture Content

The relat�ve mo�sture content �s the measured mo�sture content, relat�ve to the opt�mum mo�sture content for the mater�al. It prov�des an �nd�cat�on of the degree of saturat�on and the relat�ve cohes�ve strength.

Table A.3andTable A.4

Rat�ng and l�m�ts are based on exper�ence, and on spec�ficat�ons reported by Hefer and Scull�on (2002). These �nclude the spec�ficat�ons of New South Wales (1997), and Queensland (1999).

Grad�ng Assessment Rat�ng


Table A.4andF�gure A.4

Rat�ng requ�res that the relat�ve conformance to the appropr�ate grad�ng be quant�fied. Th�s value �s then used to obta�n an overall rat�ng for grad�ng based on mater�al type.

Grad�ng Modulus


Table A.3Based on TRH14 and on COLTO (1998) spec�ficat�ons.

H�stor�cal Performance

The h�stor�cal performance for the base and subgrade can be �solated w�th some confidence us�ng past traffic and observed cond�t�on.

Table A.5Based on exper�ence and ex�st�ng gu�del�nes (e.g. TRH12, 1998).



97

Tabl

e A

3 I

nter

pret

atio

n of

Indi

cato

rs a

nd T

ests

for C

lass

ifica

tion

of U

nbou

nd G

ranu

lar M

ater

ials

Abb

rev�

at�o

ns:

CS =

cru

shed

sto

ne, N

G =

nat

ural

gra

vel,

GS

= gr

avel

so�

l, SS

SC =

san

d, s

�lty

sand

, s�lt

, cla

y; 9

8%, 9

5%, 9

3%, 9

0% a

re M

od. A

ASH

TO d

ens�

t�es.

Test

or

Indi

cato

rM

ater

ial

Des

ign

Equi

vale

nt M

ater

ial C

lass

CFD

E-G

1D

E-G

2D

E-G

3D

E-G

4D

E-G

5D

E-G

6D

E-G

7D

E-G

8D

E-G

9D

E-G

10

Soak

ed C

BR

(%)

CS (9

8%)

> 10

080

to 9

945

to 7

925

to 4

415

to 2

410

to 1

47

to 9

< 7

0.4

NG

(95%

)>

4525

to 4

415

to 2

410

to 1

47

to 9

< 7

NG

/GS

(93%

)>

2515

to 2

410

to 1

47

to 9

< 7

SSSC

(90%

)>

1510

to 1

47

to 9

< 7

P0.0

75 (%

)

CS4

to 1

2

0.3

NG

5 to

15

13 to

20

15 to

25

25 to

30

30 to

40

40 to

50

> 50

GS

5 to

15

13 to

20

15 to

25

25 to

30

30 to

40

> 40

SSSC

0 to

10

10 to

15

15 to

20

20 to

30

> 30

Rela

t�ve

dens

�ty

All

> 1.

021.

00 to

1.0

20.

98 to

1.0

0.95

to 0

.98

0.93

to 0

.95

< 0.

930.

3

DCP

Pen

(m

m/b

low

)A

ll<

1.40

1.40

to 1

.79

1.80

to 1

.99

2.00

to 3

.69

3.70

to 5

.69

5.7

to 9

.09

9.1

to 1

3.99

14 to

18.

9919

.0 to

25.

0>

250.

4

FWD

Ba

ckca

lc.

St�ff

ness

(M

Pa)

All

> 60

050

0 to

600

400

to 4

9930

0 to

399

200

to 2

9915

0 to

199

100

to 1

4970

to 9

950

to 6

90

to 4

90.

3

Plas

t�c�ty

Inde

x

CS<

44

to 5

5 to

77

to 1

0>

10

0.4

NG

< 5

5 to

66

to 1

010

to 1

2>

12

GS

< 11

11 to

12

12 to

15

> 15

SSSC

< 12

12 to

14

14 to

20

> 20

Rela

t�ve

mo�

stur

e (%

)

CS<

6060

to 6

565

to 8

080

to 9

090

to 1

00>

100

0.3

NG

< 65

65 to

70

70 to

80

80 to

100

> 10

0

GS

< 80

80 to

90

90 to

100

> 10

0

SSSC

< 90

90 to

100

100

to 1

20>

120

Gra

d�ng

m

odul

us

NG

2.0

to 2

.61.

5 to

2.6

1.2

to 2

.7<

1.2

0.2

GS

1.2

to 2

.50.

75 to

2.7

0.75

to 2

.70.

75 to

2.7

< 0.

75

Rat�n

gA

ll0.

5 to

1.5

1.5

to 2

.52.

5 to

3.5

3.5

to 4

.54.

5 to

5.5

5.5

to 6

.56.

5 to

7.5

7.5

to 8

.58.

5 to

9.5

9.5

to 1

0.5

N/A



98

Tabl

e A

4 R

atin

g of

Indi

cato

rs a

nd T

ests

for C

lass

ifica

tion

of U

nbou

nd G

ranu

lar M

ater

ials

Abb

rev�

at�o

ns:

CS =

cru

shed

sto

ne, N

G =

nat

ural

gra

vel,

GS

= gr

avel

so�

l, SS

SC =

san

d, s

�lty

sand

, s�lt

, cla

y

Test

or

Indi

cato

rM

ater

ial

Rati

ngCF

12

34

56

78

910

Cons

�ste

ncy

(see

Tab

le

A.6

)

CSVe

ry

dens

eD

ense

Med

�um

de

nse

Loos

eVe

ry lo

ose

0.2

NG

Very

den

seD

ense

Med

�um

de

nse

Loos

eVe

ry lo

ose

NG

/GS

Very

den

seD

ense

Med

�um

de

nse

Loos

eVe

ry lo

ose

SSSC

Very

st�ff

St�ff

F�rm

Soft

Very

sof

t

V�s�

ble

mo�

stur

e

CSD

rySl

�ght

ly

mo�

stM

o�st

Very

mo�

stW

et

0.2

NG

Dry

Sl�g

htly

m

o�st

Mo�

stVe

ry m

o�st

Wet

GS

Dry

Sl�g

htly

m

o�st

Mo�

stVe

ry m

o�st

Wet

SSSC

Dry

Sl�g

htly

m

o�st

Mo�

stVe

ry m

o�st

Wet

Gra

d�ng

(s

ee F

�gur

e A

.4)

CS1

23

4

0.4

NG

12

34

GS

12

34



99

Table A 5 Rating of Historical Performance

Layer Condition DescriptionTraffic Accommodated to Date (MESA)

< 0 5 0 5 to 1 1 to 3 3 to 10 > 10

Base1 No v�s�ble rutt�ng, deformat�on, pump�ng or potholes, surfac�ng mostly �ntact. M�nor patch�ng only.

D�fficult to assess

2 1 1

Less than 8 mm narrow rutt�ng �n wheelpath, m�nor pump�ng and traffic-related crack�ng. M�nor patch�ng.


4 3 2 1

8 to 12 mm narrow rutt�ng �n wheelpath, some deformat�on, shov�ng and/or pump�ng. Frequent patch�ng noted.

7 5 4 3D�fficult to

assess

More than 12 mm narrow rutt�ng �n wheelpath, severe and frequent shov�ng, pump�ng and/or deformat�on. Frequent patch�ng.

9 7 5D�fficult to

assess

Subbase2

No w�de, subgrade relat�ve rutt�ng v�s�ble.D�fficult to

assess7 6 5

Suspect some subgrade deformat�on occurred, as shown by w�de, subgrade related rutt�ng (<10 mm depth), and sl�ght undulat�on and/or subgrade related fa�lures.


8 7 6

Strong ev�dence of subgrade related rutt�ng (>10 mm depth) and/or defin�te s�gns of subgrade related fa�lures.

10 9 8D�fficult to

assess

Notes: Assessment �s only val�d �f there are no surfac�ng related problems (e.g. str�pp�ng, br�ttleness, rutt�ng) wh�ch may have caused a rap�d deter�orat�on �n the base layer. Also, assessment �s not val�d �f overlay or surface seal was recently placed. Assessment �s only val�d �f an overlay or surface seal was no recently placed.

1.

2.



100

Table A 6 Guidelines for Consistency

Material Type Consistency Description of Layer Condition

Coarse granular mater�als

Very LooseVery eas�ly excavated w�th spade. Crumbles very eas�ly when scraped w�th geolog�cal p�ck.

Loose Small res�stance to penetrat�on by sharp end of geolog�cal p�ck.

Med�um Dense Cons�derable res�stance to penetrat�on by sharp end of geolog�cal p�ck.

DenseVery h�gh res�stance to penetrat�on of sharp end; and requ�res blows of geolog�cal p�ck for excavat�on.

Very DenseVery h�gh res�stance to repeated blows of geolog�cal p�ck; and requ�res power tools for excavat�on.

Cohes�ve so�ls

Very SoftGeolog�cal p�ck head can eas�ly be pushed �n to the shaft of handle; eas�ly moulded by fingers.

SoftEas�ly penetrated by thumb; sharp end of geolog�cal p�ck can be pushed �n 30 to 40 mm; moulded w�th some pressure.

F�rmIndented by thumb w�th effort; sharp end of geolog�cal p�ck can be pushed �n up to 10 mm; very d�fficult to mould w�th fingers; can just be penetrated w�th an ord�nary hand spade.

St�ffPenetrated by thumb na�l; sl�ght �ndentat�on produced by push�ng geolog�cal p�ck po�nt �nto so�l; cannot be moulded by fingers; requ�res hand p�ck for excavat�on.

Very St�ffIndented by thumb na�l w�th d�fficulty; sl�ght �ndentat�on produced by blow of geolog�cal p�ck po�nt; requ�res power tools for excavat�on.



101

Figure A.4 Interpretation of Grading to Quantify Relative Conformance to Grading (Granular)

A 4 2 Bitumen Stabilised MaterialsThe class�ficat�on for BSMs �s �ntended to assess the su�tab�l�ty of the mater�al for treatment w�th b�tumen emuls�on or foamed b�tumen and to determ�ne the DEMAC. It therefore assesses the mater�al based on many of the same tests and �nd�cators as used for granular mater�als, and then �n add�t�on evaluates the BSM m�x us�ng test results from the m�x des�gn process. Although some of the l�m�ts �n the tests are d�fferent for BSM-emuls�on and BSM-foam, �n the final class�ficat�on no d�st�nct�on �s made between the two mater�als.

The follow�ng three mater�al classes are used for BSMs:BSM1: Th�s mater�al has h�gh shear strength, and �s typ�cally used as a base layer for des�gn traffic appl�cat�ons of more than 6 m�ll�on equ�valent standard axles (MESA). For th�s class of mater�al, the source mater�al �s typ�cally a well graded crushed stone or recla�med asphalt (RA). BSM2: Th�s mater�al has moderately h�gh shear strength, and �s typ�cally used as a base layer for des�gn traffic appl�cat�ons of less than 6 MESA. For th�s class of mater�al, the source mater�al �s typ�cally a graded natural gravel or RA.BSM3: Th�s mater�al �s typ�cally a so�l-gravel and/or sand, stab�l�sed w�th h�gher b�tumen contents. As a base layer, the mater�al would only be su�table for des�gn traffic appl�cat�ons of less than 1 MESA.

A fourth opt�on �s also shown for many of the tests or �nd�cators, wh�ch �nd�cates that the mater�al �s not su�table for treatment. In these cases, the mater�al should be class�fied as a granular mater�al (Sect�on A.4.1).

The �nd�cators and tests for the class�ficat�on of BSMs are deta�led �n Table A.7, and the relevance of the test or �nd�cator �s expla�ned. The �nterpretat�on of the test results are g�ven �n Table A.8. The values shown have been val�dated and prov�de cons�stent, reasonable results (Long, 2009). The �nterpretat�on of grad�ng requ�res the determ�nat�on of a rat�ng, wh�ch �s deta�led �n Table A.9 and F�gure A.5 (wh�ch �s a repeat of F�gure 3.2 and F�gure 4.2.)

»

»

»

Sieve Size

Per

cent

age

Pass

ing

Inside Grading Envelope

Just coarse of envelope, but follows envelope closely (well-graded)

Fine of envelope, or significantly coarse of envelope

Significant deviation from specified envelope

1234

Assign 2 for conformance to grading



102

Table A 7 Indicators and Tests for Classification of Bitumen Stabilised Materials

Test or Indicator Relevance for Material Classification Interpret or Rating

Comments

Soaked CBR(untreated)

When soaked, tests ma�nly the fr�ct�onal strength component of shear strength.

Table A.8 Test relevance and �nterpretat�on �s based on TRH14 spec�ficat�ons.

Percent pass�ng 0.075 mm S�eve (F�nes)(Untreated)

Impacts on the dens�ty that can be ach�eved, and on the bear�ng strength of the mater�al. As such, relates ma�nly to fr�ct�onal component of shear strength.

Table A.8 Ideal range �s 6 to 10%. At less than 4% fines, dens�ty �s d�fficult to ach�eve. Shear strength reduces when fines exceed roughly 13% (Hefer and Scull�on, 2002; Gray, 1962). F�nes are also requ�red to d�str�bute b�tumen emuls�on and foamed b�tumen.

Relat�ve Dens�ty(Untreated)

Relates to the dens�ty of pack�ng of part�cles, and hence to the potent�al to develop fr�ct�onal res�stance.

Table A.8 Test relevance and �nterpretat�on �s based on TRH14 spec�ficat�ons.

DCP Penetrat�on(Untreated)

Ind�cator for overall shear strength. Sens�t�ve to dens�ty, mo�sture content, part�cle strength, grad�ng and plast�c�ty

Table A.8 Test relevance and �nterpretat�on �s based on exper�ence and ranges publ�shed Kleyn (1984).

FWD Back-calculated St�ffness(Untreated)


Table A.8 Test relevance and �nterpretat�on ranges based on exper�ence �n southern Afr�ca.

Plast�c�ty Index (Untreated)


Table A.8 Based on TRH14. Test relevance and ma�n effects related to shear strength are reported �n Hefer and Scull�on (2002); and �n Gray (1962).

Measured Mo�sture Content (Untreated)

The relat�ve mo�sture content �s the measured mo�sture content, relat�ve to the opt�mum mo�sture content for the mater�al.

Table A.8 Rat�ng and l�m�ts are based on exper�ence, and on spec�ficat�ons reported by Hefer and Scull�on (2002). These �nclude the spec�ficat�ons of New South Wales (1997) and Queensland (1999).

Grad�ng Assessment Rat�ng(Untreated)


Table A.9andF�gure A.5

Rat�ng requ�res that the relat�ve conformance to the appropr�ate grad�ng be quant�fied. Th�s value �s then used to obta�n an overall rat�ng for grad�ng based on mater�al type.

Grad�ng Modulus(Untreated)


Table A.8 Based on TRH14 and on COLTO (1998) spec�ficat�ons.

Cohes�on, Fr�ct�on Angle and Tangent Modulus(Treated)

The shear parameters and mater�al st�ffness from tr�ax�al test�ng prov�de cr�t�cal performance propert�es related to res�stance to permanent deformat�on.

Table A.8 Test relevance and �nterpretat�on based on global m�x des�gns and research �n Jenk�ns et al (2008).

ITS(Treated)

Prov�des a reference to the h�stor�c performance of m�xes (ITSdry) and a measure of mo�sture res�stance (ITSwet).


UCS (Treated) Prov�des a measure of the compress�ve strength of m�xes, and a reference to the h�stor�c performance of m�xes


Reta�ned Cohes�on (MIST) (Treated)

The change �n cohes�on after mo�sture cond�t�on�ng from tr�ax�al test�ng prov�des a measure of mo�sture res�stance.

Table A.8 Test �s new, selected because g�ves most real�st�c s�mulat�on of pore pressures �n BSMs trafficked �n wet cond�t�ons. Test relevance and �nterpret�on base on research test�ng of l�m�ted South Afr�can mater�als. Based on Jenk�ns et al (2008).



103

Table A 8 Interpretation of Indicators and Tests for Classification of Bitumen Stabilised Materials

Test or Indicator Material1Design Equivalent Material Class Not suitable

for treatmentCF

DE-BSM1 DE-BSM2 DE-BSM3

Soaked CBR (%)CS (98%) > 80 25 to 80 10 to 25 < 10

0.4NG (95%) > 25 10 to 25 < 10

P0.075 (%)(B�tumen emuls�on)

CS 4 to 15 > 15

0.35

NG 5 to 25 25 to 40 > 40

GS 5 to 20 15 to 30 > 30

SSSC 0 to 20 > 20

P0.075 (%)(Foamed b�tumen)

CS 2 to 15 > 15

NG 11 to 25 23 to 40 > 40

GS 0 to 20 13 to 30 > 30

SSSC 0 to 20 > 20

Relat�ve dens�ty All > 0.98 0.95 to 0.98 0.93 to 0.95 < 0.93 0.1

DCP Pen (mm/blow) All < 3.7 3.7 to 9.1 9.1 to 19.0 < 19.0 0.1


All > 300 150 to 300 70 to 150 < 70 0.1

Plast�c�tyIndex

CS < 10 > 10

0.25NG < 6 6 to 12 > 12

GS > 11 11 to 15 < 15

SSSC < 15 > 14

Relat�ve mo�sture (%)

CS < 90 > 90

0.1NG < 70 70 to 100 < 80

GS > 100 80 to 100 < 100

SSSC > 100 > 100

Grad�ng modulusNG 2.0 to 3.0 1.2 to 2.7 0.15 to 1.2 < 0.15

0.2GS 1.2 to 2.5 0.75 to 2.7 < 0.75

Cohes�on (kPa) All > 250 100 to 250 50 to 100 < 50 0.45

Fr�ct�on Angle (°) All > 40 30 to 40 < 30 0.4

Tangent Modulus (MPa) All > 150 50 to 150 < 50 0.1

ITSdry / equ�l (kPa)100 mm 2 > 225 175 to 225 125 to 175 < 125 0.1

150 mm > 175 135 to 175 95 to 135 < 95 0.15

ITS wet (kPa) 100 mm > 100 75 to100 50 to 75 < 50 0.1

UCS (kPa) All 1 200 to 3 500 700 to 1 200 450 to 700 < 450 0.1

Reta�ned Cohes�on (%) All > 75 60 to 75 50 to 60 < 50 0.45

Rat�ng All 0.5 to 1.5 1.5 to 2.5 2.5 to 3.5 3.5 to 4.5 N/A

Notes:CS = crushed stone, NG = natural gravel, GS = gravel so�l, SSSC = sand, s�lty sand, s�lt, clay; 98%, 95%, 93%, 90% are Mod. AASHTO dens�t�es.D�ameter of spec�men.

1.

2.



104

Table A 9 Rating of Indicators and Tests for Classification of Bitumen Stabilised Materials

Test or Indicator Material1Rating

CF1 2 3 4

Grad�ng (see F�gure A.5)

CS Ideal Less su�table Marg�nal

0.4NG Ideal Less su�table Marg�nal

GS Ideal Less su�table Marg�nal

Sieve Size (mm)

Percent Passing



50 100 100

37.5 87 – 100 87 – 100

26.5 77 – 100 100 77 – 100 100

19.5 66 – 99 99 – 100 66 – 99 99 – 100

13.2 67 – 87 87 – 100 67 – 87 87 – 100

9.6 49 – 74 74 – 100 49 – 74 74 – 100

6.7 40 – 62 62 – 100 40 – 62 62 – 100

4.75 35 – 56 56 – 95 35 – 56 56 – 95

2.36 25 – 42 42 – 78 25 – 42 42 – 78

1.18 18 – 33 33 – 65 18 – 33 33 – 65

0.6 12 – 27 27 – 54 14 – 28 28 – 54

0.425 10 – 24 24 – 50 12 – 26 26 – 50

0.3 8 – 21 21 – 43 10 – 24 24 – 43

0.15 3 – 16 16 – 30 7 – 17 17 – 30

0.075 2 – 9 9 – 20 4 – 10 10 – 20


Figure A.5 Interpretation of Grading to Quantify Relative Conformance to Grading (BSM)



105

A 4 3 Cement Stabilised MaterialsThe class�ficat�on of cement stab�l�sed mater�als focuses on the degree of cementat�on st�ll present. The mater�al �s class�fied as a rat�ng, from 1 to 3. Th�s rat�ng scheme has the follow�ng relat�onsh�p between the rat�ng and the mater�al classes as defined �n TRH14 (1985).

Rating 1: Ind�cates cond�t�on s�m�lar to recently constructed C1, C2, or C3 mater�al.Rating 2: Ind�cates cond�t�on s�m�lar to recently constructed C4 mater�al.Rating 3: Ind�cates mater�al �s e�ther �neffect�vely stab�l�sed, or has deter�orated to an equ�valent granular state. These mater�als should be regarded as unbound granular mater�als and the class�ficat�on gu�del�nes �n Sect�on A.4.1 should be appl�ed.

The �nd�cators and tests for the class�ficat�on of cemented mater�als are deta�led �n Table A.10, and the relevance of the test or �nd�cator �s expla�ned. The �nterpretat�on of the test results are g�ven �n Table A.11. The values shown have been val�dated and prov�de cons�stent, reasonable results (Long, 2009).

Table A 10 Indicators and Tests for Classification of Cement Stabilised Materials

Test or Indicator Relevance for Material Classification Rating Comments

DCP Penetrat�onInd�cator for overall shear strength. Sens�t�ve to dens�ty, mo�sture content, part�cle strength, grad�ng and plast�c�ty.

Table A.11Test relevance and �nterpretat�on �s based on exper�ence and ranges publ�shed Kleyn (1984).

FWD Backcalculated St�ffness


Table A.11Test relevance and �nterpretat�on ranges based on exper�ence �n southern Afr�ca.

Cons�stency Rat�ngProv�des a rough �nd�cat�on of the degree of cementat�on of the mater�al.

Table A.11Rat�ng based on mater�al cons�stency evaluat�on from test p�ts and on the SANRAL M1 Manual (SANRAL, 2004)

Ev�dence of Act�ve Cement

Quant�fies the confidence that mater�al �s act�ng as a cohes�ve, cement stab�l�sed layer.

Table A.11 None

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106

Table A 11 Interpretation of Indicators and Tests for Classification of Cemented Materials from Field Observations

Test or Indicator

Rating

CF

1 2 3

Indicates condition similar to recently constructed C1,

C2 or C3 material

Indicates condition similar to recently constructed C4

material

Indicates material is either ineffectively stabilised, or

deteriorated to an equivalent granular state

Cons�stency

Hand-held spec�men can be broken w�th hammer head

w�th s�ngle firm blow. S�m�lar appearance to concrete.

Mater�al crumbles under firm blows of sharp geolog�cal p�ck po�nt. Gra�ns can be d�slodged

w�th some d�fficulty under a kn�fe blade.

Some mater�al can be crumbled by strong pressure between fingers and thumb. D�s�ntegrates under a kn�fe

blade to a fr�able state.

0.2

F�rm blows of sharp geolog�cal p�ck po�nt.

Cannot be crumbled between strong fingers. Some mater�al can

be crumbled by strong pressure between thumb and hard surface. D�s�ntegrates under l�ght blows of a hammer head to a fr�able state.

DCP Penetrat�on (mm/blow)

< 1.50 1.5 to 3.0 > 3 0.4


> 1 200 500 to 1 200 < 500 0.3

Ev�dence of Act�ve Cement

Clearly v�s�ble �n mater�al colour and cons�stency. Clear �nd�cat�on of act�ve cement,

based on chem�cal tests.

No cementat�on v�s�ble, sl�ght �nd�cat�on of act�ve cement, based

on chem�cal tests.

No �nd�cat�on of act�ve cement, e�ther �n mater�al colour and cons�stency or from chem�cal

tests.

0.3

A.5. CONFIDENCE ASSOCIATED WITH ASSESSMENTThe confidence �n the certa�nty assoc�ated w�th the mater�al classes depends on the number of tests or �nd�cators used and the certa�nty factors assoc�ated w�th the tests and �nd�cators. The strength of confidence �n our assessment �s thus quant�fied by the certa�nty of the assessment, and th�s �s an �nd�rect �nd�cator of the rel�ab�l�ty of any des�gn wh�ch �s based on th�s assessment. Table A.12 prov�des some gu�del�nes to assess the confidence assoc�ated w�th the mater�al class�ficat�on.

Table A 12 Relative Confidence of Materials Classification

Final Value of C(H|E) Confidence in Classification

< 0.3Very low confidence It �s strongly recommended that more data be gathered to enable a more confident assessment to be made.

0.3 to 0.5Low confidence Su�table only for s�tuat�ons where the ex�st�ng pavement cond�t�on and age �s such that structural rehab�l�tat�on w�ll not be cons�dered or �s very unl�kely.

0.5 to 0.7Medium. Su�table or s�tuat�ons where the ex�st�ng pavement cond�t�on and age �s such that structural rehab�l�tat�on �s unl�kely, or for wh�ch the cond�t�on and/or other factors predeterm�nes the treatment type.

> 0.7High Th�s �s the m�n�mum recommended certa�nty for s�tuat�ons where structural rehab�l�tat�on �s l�kely, and for wh�ch the rehab�l�tat�on des�gn w�ll rely completely on the qual�ty and state of ex�st�ng pavement layers.



107

A.6. WORKED EXAMPLEThe follow�ng paragraphs �llustrate the appl�cat�on of the method descr�bed �n Sect�on A.3. Th�s example uses data from an actual pavement rehab�l�tat�on �nvest�gat�on, but w�th some sl�ght adjustments to clearly �llustrate the concepts of the method. The example �nvolves an assessment of an upper subbase layer for the eastbound lane of a planned rehab�l�tat�on project 18 km long.

Based on the cond�t�on of the road, the construct�on h�story and the deflect�on patterns, the road was des�gnated as a s�ngle un�form des�gn sect�on. All ava�lable results are therefore assessed together. The ava�lable �nformat�on cons�sts of the follow�ng:

Materials test data from nine test pits Ava�lable test data �nclude: mater�al descr�pt�on, relat�ve dens�ty, mo�sture content, DCP penetrat�on, grad�ng analyses, CBR and PI.173 FWD deflections w�th backcalculated st�ffnesses for all layers.

Table A.13 summar�zes some of the test �nd�cators. The grad�ng analyses are summar�zed �n F�gure A.6. In the test p�ts, the mater�al was descr�bed as a dense weathered doler�te natural gravel �n all �nstances and therefore the class�ficat�on system for granular mater�als �s appropr�ate.

Table A 13 Example Materials Test Data

Station (Km)Relative Density

CBR (%)

% Passing 0 075 mm

Sieve

Moisture as % of

OptimumGM PI

Consistency Rating1

Grading Rating2

DCP Pen (mm/blow)3

1.5 1.03 70 11 70 2.34 9 4 4 1.8

2.7 0.87 24 4 108 2.7 10 4 6 4.8

4.3 0.94 64 5 91 2.67 9 4 5 -1

4.9 1 66 6 96 2.65 7 4 5 -1

7.9 1 70 13 67 2.17 8 4 4 -1

9.2 1 100 3 75 2.68 8 4 5 -1

12.5 1 90 12 63 2.24 5 4 4 2.4

14.3 0.98 80 6 72 2.59 8 4 4 1.4

17.5 0.94 N/R 10 48 2.24 6 4 5 -1

10th Percent�le 0 93 52 3.8 60 2 2 6 4 4 -1 0

Med�an 1 00 70 6.0 72 2 6 8 4 5 -1 0

90th Percent�le 1 01 93 12.2 98 2 7 9 4 5 2 9

Observat�ons 9 8 9 9 9 9 9 9 9

Note: 1. Cons�stency rat�ng determ�ned from Table A.4 and Table A.6. 2. Grad�ng rat�ng determ�ned from Table A.4 and F�gure A.4. 3. For DCP penetrat�on, a value of -1 �nd�cates refusal.

The backcalculated st�ffnesses for the subbase were as follows:10th Percent�le = 189 MPaMed�an = 466 MPa90th Percent�le = 581 MPa

For most of the ava�lable tests, the results can be d�rectly evaluated by means of the �nterpretat�on gu�del�nes prov�ded �n Sect�on A.4. However, for the cons�stency and grad�ng, the test results first have to be converted to a rat�ng, to fac�l�tate a numer�cal evaluat�on of results. The rat�ngs ass�gned for these �nd�cators are summar�zed �n Table A.13.

»

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108

Once all the tests have been quant�fied, we can summar�ze the ava�lable tests, the�r certa�nty factors and the�r sample stat�st�cs. For th�s example, the certa�nty factors from Table A.3 were adopted. S�nce the sample s�ze exceeds s�x for all tests, the adjustment factor for sample s�ze (from Table A.1) �s 1.0 �n all cases. The ava�lable test data and certa�nty factors are summar�zed �n Table A.14.

Figure A.6 Grading Analyses for Worked Example

Table A 14 Worked Example, Summary of Test Data and Certainty Factors

Test CF CF’ 10th % Median 90th % C(E) DE-G4 C(E) DE-G5 C(E) DE-G6

DCP Penetrat�on 0.4 0.4 -1.0 -1.0 2.9 0.05 0.00 0.00

CBR (NG) 0.4 0.4 52 70 93 0.18 0.79 0.0

P0.075 (NG) 0.3 0.3 3.8 6.0 12.2 0.92 0.0 0.0

Relat�ve Dens�ty 0.3 0.3 0.93 1.00 1.01 0.20 0.21 0.02

FWD St�ffnesses 0.3 0.3 189 466 581 0.30 0.11 0.00

Cons�stency Rat�ng 0.2 0.2 4 4 4 1.0 0.0 0.0

PI (NG) 0.4 0.4 6 8 9 0.0 1.0 0.0

Rel. Mo�sture (NG) 0.3 0.3 60 72 98 0.33 0.54 0.08

Grad�ng Rat�ng 0.4 0.4 4 5 5 0.25 0.75 0.0

GM (NG) 0.2 0.2 2.2 2.6 2.7 0.44 0.50 0.06

Column 1 2 3 4 5 6 7 8

In Table A.14, CF �s the certa�nty factor related to the test type, and CF’ �s s�mply CF adjusted to take account of sample s�ze. In th�s case, CF’ �s equal to CF because the sample s�ze �s greater than 6 �n all cases. Columns 6, 7 and 8 represent the relat�ve certa�nty that the test ev�dence po�nts to a DE-G4, DE-G5 or DE-G6 des�gn equ�valent mater�al class.



109

The factors C(E) are determ�ned us�ng the method descr�bed �n Sect�on A.3.1. F�gure A.7 shows an example of the deta�led calculat�on of C(E) for FWD Backcalculated St�ffness. Th�s calculat�on rel�es on the FWD st�ffness l�m�ts recommended �n Table A.3 and on the sample stat�st�cs shown h�ghl�ghted for FWD st�ffness �n Table A.14.

Figure A.7 Example of C(E) Calculations for FWD Backcalculated Stiffness Sample

Table A.15 shows the final adjusted certa�nty factors (CF’) for a DE-G4, DE-G5 and DE-G6 mater�al, and also the cumulat�ve certa�nty that the mater�al �s a DE-G4, DE-G5 or DE-G6 (�.e. C(H|E)). The final cumulat�ve certa�nty for these three mater�al classes �s shown �n the bottom row. The class�ficat�on method shows that most of the ev�dence po�nts to the mater�al be�ng a DE-G5, and some ev�dence also po�nts to a DE-G4. In compar�son to a DE-G4 and DE-G5, there �s comparat�vely l�ttle �nformat�on to suggest that the mater�al �s a DE-G6.

FWD Stiffness

200 300 600150

G6 Class G5 Class G4 Class

1.0

G3 Class G2 Class

400 500

10th % = 189 Median = 466 90th % = 581

Portion of evidence corresponding to G6 = C(E:G6) = [0.5 x (200-189) x Ya] / 196 = 0.001

Ya= 0.040

Yb= 0.401

Yc= 0.762

Total “evidence area” = 0.5 x (581-189) x 1.0 = 196

Portion of evidence corresponding to G5 = C(E:G5) = [(300-200) x (Ya + Yb)/2] / 196 = 0.113

Portion of evidence corresponding to G4 = C(E:G4) = [(400-300) x (Yb + Yc)/2] / 196 = 0.297



110

Table A 15 Worked Example, Summary of Certainty Associated with DE-G4, DE-G5 and CE-G6

Test CF’ C(H-DEGX|E)

DE-G4 DE-G5 DE-G6 DE-G4 DE-G5 DE-G6

DCP Penetrat�on 0.02 0.00 0.00 0.02 0.00 0.00

CBR 0.00 0.40 0.00 0.02 0.04 0.00

P0.075 0.28 0.00 0.00 0.29 0.4 0.00

Relat�ve Dens�ty 0.13 0.11 0.02 0.38 0.47 0.02

FWD St�ffnesses 0.09 0.03 0.00 0.44 0.49 0.02

Cons�stency Rat�ng 0.20 0.00 0.00 0.55 0.49 0.02

PI 0.00 0.40 0.00 0.55 0.69 0.02

Measured Mo�sture 0.06 0.13 0.09 0.58 0.73 0.11

Grad�ng Rat�ng 0.10 0.30 0.00 0.62 0.81 0.11

GM 0.16 0.09 0.20 0.68 0.83 0.29

Final Assessment of Relative Certainty for DE-G4 = 0 68 DE-G5 = 0 83 DE-G6 = 0 29

Most likely Materials Class is a G5 Design Equivalent ClassRelative Certainty associated with this outcome = 0 83Confidence assoc�ated w�th th�s outcome �s High.Assessment �s su�table for s�tuat�ons where structural rehab�l�tat�on �s requ�red, or for wh�ch the rehab�l�tat�on des�gn w�ll rely completely on the state of ex�st�ng layers.

Note: CF’ calculated w�th Equat�on A.1 C(H-G4/G5/G6|E) calculated w�th Equat�on A.2, A.3 or A.4



BIBLIOGRAPHY

111

REFERENCESCOLTO. 1998. Standard Specifications for Road and Bridge Works for State Authorities Comm�ttee of Land Transport Offic�als, Halfway

House, South Afr�ca.

GRAY, J.E. 1962, Character�st�cs of Graded Base Course Aggregates Determ�ned by Tr�ax�al Tests. National Crushed Stone Association, Engineering Bulletin No 12, Nat�onal Crushed Stone Assoc�at�on, Wash�ngton, D.C.

HEFER, A and Scull�on, T. 2002. Materials, Specifications, and Construction Techniques for Heavy Duty Flexible Bases: Literature Review and Status Report on Experimental Sections Texas Transportat�on Inst�tute, The Texas A&M Un�vers�ty System, College Stat�on, Texas (Report 0-4358-1), October, 2002 (Resubm�tted: July 2005).

JENKINS, K.J., L.J. Ebels, E.T. Mathan�ya, R.W.C. Kelfkens, P.K. Moloto and W.K. Mulusa, 2008, Updating Bitumen Stabilised Materials Guidelines: Mix Design Report, Phase 2 Stellenbosch Un�vers�ty.

JOOSTE, F.J., F.M. Long, and A.O. Hefer. 2007. A Method for Consistent Classification of Materials for Pavement Rehabilitation and Design Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2007. (GDPTRW report number: CSIR/BE/IE/ER/2007/0005/B).

KLEYN, E.G. 1984. Aspects of Pavement Evaluation and Design as Determined with the Aid of the Dynamic Cone Penetrometer (In Afr�kaans). Pretor�a: Transvaal Roads Department, Mater�als Branch, May, 1984 (Report L6/84).


Roads and Traffic Author�ty of New South Wales. 2001. RTA Conditions of Contract and Quality Assurance Specifications, Rev 2001 Roads and Traffic Author�ty of New South Wales (web reference: http://www.rta.nsw.gov.au).

SANRAL. 2004. Geotechnical and Materials Investigations, Design and Documentation South Afr�can Nat�onal Roads Agency L�m�ted. Pretor�a, South Afr�ca (M1 Mater�als Manual).

Standard Spec�ficat�ons Roads, 3rd Ed�t�on, Queensland, Department Ma�n Roads. Web reference http://www mainroads qld gov au.

THEYSE, H.L. , De Beer, M. and Rust, F.C. 1996. Overview of the South African Mechanistic Pavement Design Analysis Method Paper Number 961294 Presented at the 75th Annual Transportat�on Research Board Meet�ng, January 7 to 11, 1996, Wash�ngton, D.C.

TRH12. 1998. Flexible Pavement Rehabilitation Investigation and Design Comm�ttee of State Road Author�t�es. Pretor�a, South Afr�ca. (Techn�cal Recommendat�ons for H�ghways Ser�es, TRH 12).

TRH14. 1985. Guidelines for Road Construction Materials Comm�ttee of State Road Author�t�es. Pretor�a, South Afr�ca. (Techn�cal Recommendat�ons for H�ghways Ser�es, TRH 14).


APPENDIX B: Laboratory Tests

112

APPENDIX B: LABORATORY TESTS

Test Test Method

Website1 TMH1 Other

Atterberg L�m�ts A1, B4

Bulk Relat�ve Dens�ty B14

Cal�forn�a Bear�ng Rat�o (CBR) - Soaked A8

D�lut�on Test for B�tumen Emuls�ons Method 1

Dynam�c Cone Penetrometer (DCP) TMH6

Dry dens�ty vs mo�sture curve A7

Durab�l�ty M�ll Index (DMI) CSIR TS/20/85

B�tumen emuls�on typeAn�on�cCat�on�c

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SANS 308SANS 548

Expans�on Rat�o Method 2

Fractured Faces ASTM D5821-01

Grad�ng Modulus TRH14

Half-l�fe Method 2

Ind�rect Tens�le Strength (ITS) Method 3

Ind�rect Tens�le Strength – wet (ITSwet) Method 4

Laboratory Pugm�ll M�x�ng Method 6

Preparat�on of field cores for test�ng Method 9

Preparat�on of field mater�al for manufacture of spec�mens Method 10

Reta�ned Cohes�on (MIST) Method 7

Mod�fied AASHTO compact�on A7

Mo�sture contents Method 8 A7

Plast�c�ty Index A1, B4

S�eve Analys�s / Grad�ng A1, B4

S�mple Tr�ax�al TestCohes�onFr�ct�on AngleTangent Modulus

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Method 7

Unconfined Compress�ve Strength (UCS) Method 5

V�bratory Hammer Compact�on Method 8

Note: 1. These tests are ava�lable for download on www.asphaltacademy.co.za/b�tstab.



APPENDIX C: Pavement Number Structural Design System

113

APPENDIX C: PAVEMENT NUMBER STRUCTURAL DESIGN METHODC.1. INTRODUCTIONThe bas�c pr�nc�ple of pavement des�gn �s to prov�de structural layers to protect the pavement subgrade aga�nst the stresses �mposed by traffic. The comb�ned system, cons�st�ng of the structural layers and the subgrade, should then funct�on as a un�t �n a balanced system to ach�eve the des�red des�gn structural capac�ty. In essence, pavement balance requ�res that there should be a gradual decrease �n strength from the top to the bottom pavement layers and that the strength of the structural pavement layers should not greatly exceed that of the subgrade. The except�on to th�s �s the use of �nverted pavement structures �n South Afr�ca, although the structural layers typ�cally have more strength than the subgrade.

The structural des�gn of pavements �ncorporat�ng B�tumen Stab�l�sed Mater�als uses a knowledge based approach, termed the Pavement Number (PN). The PN �s based on the Structural Number concept, wh�ch was used �n the or�g�nal AASHTO methods (AASHTO, 1996).

However, some of the shortcom�ngs of the Structural Number have been overcome �n the PN method. The PN method was chosen for several reasons.

Data from in-service pavements were used to develop the method. The type and deta�l of the data suggests the use of a relat�vely s�mple method and precludes the use of a Mechan�st�c-Emp�r�cal des�gn method. The method g�ves a good fit to the ava�lable field data.The method �s robust, and cannot eas�ly be man�pulated to produce �nappropr�ate des�gns.

The development and val�dat�on of the PN method are descr�bed �n Jooste, et al (2007) and Long (2009). The method �s appl�cable to all pavement mater�als commonly used �n southern Afr�ca. Th�s method rel�es on bas�c po�nts of departure, or rules-of-thumb, wh�ch reflect well-establ�shed pr�nc�ples of pavement behav�our and performance, and wh�ch w�ll ensure an appropr�ate pavement des�gn solut�on �n most s�tuat�ons. The concepts �n the rules-of-thumb are quant�fied �nto spec�fic rules w�th constants or funct�ons assoc�ated w�th each rule. The rules-of-thumb are descr�bed �n the next sect�on.

The PN method was cal�brated by calculat�ng the PN value for several pavements extracted from the TRH4 catalogue (TRH4, 1996), and for wh�ch the structural capac�t�es were known w�th some certa�nty from exper�ence. Us�ng these data, the quant�fied rules-of-thumb were adjusted to opt�m�ze the correlat�on between PN and structural capac�ty. The final rules were then val�dated us�ng observed pavement performance data. The development of the rules-of-thumb and the cal�brat�on and �n�t�al val�dat�on processes are descr�bed by Jooste and Long (2007). The add�t�onal val�dat�on process and final values for the rules-of-thumb are descr�bed by Long (2009).

The constants shown for the PN method �ncluded �n th�s gu�del�ne were the values used at the t�me of publ�cat�on of the gu�del�ne. Although these values were well val�dated (Long, 2009), �t may be necessary from t�me to t�me to make changes to �mprove the system. If changes are made, the mod�fied values w�ll be reflected on www.asphaltacademy.co.za/b�tstab. It �s therefore recommended that before commenc�ng a Pavement Number calculat�on, the webs�te �s checked for any changes �n values or tests.

The PN method �s des�gned to be used �n conjunct�on w�th the mater�al class�ficat�on system descr�bed �n Append�x A. The method �s appl�cable to both new construct�on and rehab�l�tat�on. For rehab�l�tat�on projects, the mater�al class would be the des�gn equ�valent mater�al class (DEMAC). For brev�ty, �n th�s Append�x, the term mater�al class �s used for both new construct�on and rehab�l�tat�on, but �t should be understood that the term �mpl�es the DEMAC for rehab�l�tat�on projects.

C.2. APPLICABILITY AND LIMITATIONS OF THE PAVEMENT NUMBER METHODBefore the calculat�on of the pavement number �s started, the des�gner should check to ensure that the des�gn method �s appl�cable to the pavement s�tuat�on and that none of the follow�ng s�tuat�ons apply:

Design traffic greater than 30 MESA The PN method was cal�brated us�ng a knowledge base wh�ch was l�m�ted to pavements that had accommodated less than 30 m�ll�on standard axles (MESA). Thus, �n such a des�gn s�tuat�on, the des�gn must be checked us�ng more �n-depth analys�s.

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114

Presence of thin, weak lenses If th�n, weak lenses of mater�al ex�st below the surfac�ng, or between stab�l�sed layers, then zones of h�gh sl�p and shear w�ll develop, and rout�ne des�gn calculat�ons w�ll not apply. In such �nstances, the structural capac�ty assessment of the PN method w�ll not be appropr�ate, and spec�al treatment of the affected weak lens must be undertaken. The PN des�gn method cannot be appl�ed to s�tuat�ons where such lenses st�ll ex�st w�th�n the pavement structure, espec�ally where such lenses are located w�th�n the upper 400 mm of the pavement structure.Design traffic less than 1 MESA In cases where the des�gn traffic �s less than 1 MESA, the des�gner should use the des�gn catalogues �n Chapter 5.Subgrade CBR less than 3% The knowledge base on wh�ch the PN method was cal�brated d�d not �nclude any pavements that had a subgrade CBR less than 3%. The PN method should therefore not be used �n cases where the subgrade CBR �s less than 3% at a depth less than 600 mm below the surface.

C.3. RULES OF THUMB / DEPARTURE POINTSTh�s sect�on presents a d�scuss�on of the bas�c rules-of-thumb underly�ng the method for calculat�ng PN. These rules-of-thumb reflect well-establ�shed pr�nc�ples of pavement behav�our and performance. The follow�ng rules-of-thumb were adopted as the po�nts of departure for the calculat�on of the Pavement Number:

Rules Relating to the Pavement System In General:1. The structural capac�ty of a pavement �s a funct�on of:

The comb�ned long term load spread�ng potent�al of the pavement layers. The relat�ve qual�ty of the subgrade on wh�ch the pavement �s constructed.

2. The relat�ve qual�ty and st�ffness of the subgrade �s the departure po�nt for des�gn, as the subgrade �s a key determ�nant �n the overall pavement deflect�on and �n the relat�ve degree of bend�ng and shear that w�ll take place �n overly�ng pavement layers.

3. For pavements w�th th�n surfac�ngs, the base layer �s the most cr�t�cal component, and fa�lure �n th�s layer effect�vely const�tutes pavement fa�lure. Exper�ence can gu�de the relat�ve confidence �n d�fferent mater�al types to serve as base layers under heavy traffic.

Rules Relating to Specific Pavement Layers:4. The load spread�ng potent�al of an �nd�v�dual layer �s a product of �ts th�ckness and �ts effect�ve long term st�ffness under load�ng.5. The Effect�ve Long Term St�ffness (ELTS) of a layer depends on the mater�al type and on �ts placement �n the pavement system.6. F�ne-gra�ned subgrade mater�als act �n a stress-soften�ng manner. For these mater�als, the ELTS �s determ�ned ma�nly by the mater�al

qual�ty and by the cl�mat�c reg�on. Ow�ng to the stress soften�ng behav�our, subgrade mater�als w�ll generally soften w�th decreased cover th�ckness.

7. Coarse-gra�ned, unbound layers act �n a stress-st�ffen�ng manner. For these mater�als, the ELTS �s determ�ned ma�nly by the mater�al qual�ty and the relat�ve st�ffness of the support�ng layer. The ELTS of these mater�als w�ll �ncrease w�th �ncreas�ng support st�ffness, by means of the modular rat�o l�m�t, up to a max�mum st�ffness wh�ch �s determ�ned ma�nly by the mater�al qual�ty.

8. Cement stab�l�sed mater�als �n�t�ally act as a st�ff, glassy mater�al, but gradually deter�orate �nto a mater�al cons�st�ng of loose clumps or separate blocks that can be sol�d or deter�orated �nto a granular state. For a spec�fic DEMAC, the rate of deter�orat�on depends ma�nly on the th�ckness of the layer and on the st�ffness of the support.

9. Th�n asphalt surfac�ngs act as e�ther st�ff, glassy mater�al, or as sem�-st�ff, rubbery mater�al. The mater�al state depends pr�mar�ly on the temperature and b�tumen content. Over t�me, the mater�al �s subject to deter�orat�on ow�ng to age�ng and fat�gue. Fat�gue breakdown �s pr�mar�ly dependent on the st�ffness of the support�ng layer.

10. B�tumen stab�l�sed mater�als w�th low cement contents (≤ 1%) are assumed to act �n a s�m�lar way to coarse granular mater�als, but w�th a h�gher cohes�ve strength. The cohes�ve strength �s subject to breakdown dur�ng load�ng, and thus some soften�ng over t�me can occur. The rate of soften�ng �s ma�nly determ�ned by the st�ffness of the support, wh�ch determ�nes the degree of shear �n the layer. However, ow�ng to the h�gher cohes�ve strength �n b�tum�nous stab�l�sed mater�als, these layers are less sens�t�ve to the support st�ffness than unbound granular mater�als, and thus can susta�n h�gher modular rat�o l�m�ts.

The above-noted rules-of-thumb �ntroduce several concepts, l�ke the ELTS, Modular Rat�o L�m�t and Stress-st�ffen�ng behav�our. These aspects w�ll be d�scussed �n more deta�l �n the follow�ng subsect�ons.

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115

C 3 1 The Effective Long Term Stiffness (ELTS)The ELTS �s a model parameter wh�ch serves as a relat�ve �nd�cator of the average long term �n s�tu st�ffness of a pavement layer. As such, the ELTS averages out effects of long term decrease of st�ffness ow�ng to traffic related deter�orat�on, as well as seasonal var�at�ons �n st�ffness. Thus the ELTS does not represent the st�ffness of a mater�al at any spec�fic t�me.

The ELTS �s not a st�ffness value that can be determ�ned by means of a laboratory or field test. It �s a model parameter, wh�ch �s cal�brated for use �n the PN des�gn method and �t may therefore d�ffer from st�ffness values typ�cally assoc�ated w�th mater�al classes. (e.g. Theyse et al, 1996).

The ELTS concept �s espec�ally needed �n the case of cement stab�l�sed mater�als, where a s�gn�ficant change �n the effect�ve st�ffness of the mater�al can be expected dur�ng the course of a pavement’s des�gn l�fe (de Beer, 1990; Theyse et al, 1996; TRH4, 1996). Th�s concept �s �llustrated �n F�gure C.1, wh�ch shows the reported breakdown of a cement stab�l�sed mater�al under traffic, w�th the ELTS represent�ng an average effective long term stiffness.

Figure C.1 Application of the ELTS Concept for Cement Stabilised Materials

C 3 2 Modelling of Subgrade MaterialsCharacter�zat�on of the support cond�t�on �s cr�t�cal to the pavement des�gn. For new construct�on, the TRH4 procedure for del�neat�on of the �n s�tu subgrade and for �mport�ng selected subgrade mater�al, �f the structural strength of the �n s�tu subgrade �s �nsuffic�ent, appl�es to the PN method. For rehab�l�tat�on projects, the gu�del�nes �n TRH12 (1997) for evaluat�ng and des�gn�ng for chang�ng support cond�t�ons should be followed �n conjunct�on w�th the PN method.

The first step �n the calculat�on of the PN-value �s the determ�nat�on of the subgrade mater�al class. To do th�s, spec�fic gu�del�nes are prov�ded �n Append�x A.

Once the subgrade class has been determ�ned, the ELTS for the subgrade �s calculated. Th�s �nvolves the follow�ng steps:Ass�gnment of a bas�c long term st�ffness based on the mater�als class.Adjustment of the bas�c long term st�ffness for d�fferent cl�mat�c reg�ons (wet, dry or moderate).Adjustment of the st�ffness determ�ned �n step 2 to take account of depth of subgrade cover.

1.2.3.

Effe

ctiv

e St

iffne

ss

Axles Accommodated

Pre-Cracked Phase (E > 3000 MPa)

Effective Fatigue Phase (E = 800 to 2000 MPa)

Equivalent Granular Phase (E = 200 to 400 MPa)

ELTS



116

The adjustment of the subgrade st�ffness to take account of the depth of cover takes account of the stress-soften�ng tendenc�es of fine gra�ned mater�als, �n wh�ch these mater�als tend to soften under load. The relat�onsh�p between the cover depth and the adjustment to the subgrade st�ffness �s g�ven �n Sect�on C.4.

C 3 3 The Modular Ratio Limit and Maximum StiffnessThe modular rat�o �s defined as the rat�o of a layer’s st�ffness relat�ve to the st�ffness of the layer below �t. Thus, �f the st�ffness of a base layer �s 300 MPa, and the st�ffness of the support below �t �s 200 MPa, then the modular rat�o of the base layer would be 1.5.

The modular rat�o accounts for the stress-sens�t�ve st�ffness of granular mater�als, wh�ch causes the st�ffness of a granular mater�al to decrease when the mater�al �s placed over a weaker (less st�ff) support. Th�s decrease �n st�ffness occurs because, �n s�tuat�ons where the support layer �s soft, the overly�ng layers tend to bend more �nto the support, thereby �ncreas�ng the tendency to develop h�gher shear and tens�le forces �n the overly�ng layers. Th�s effect l�m�ts the st�ffness that can be obta�ned �n an unbound layer placed over a weaker support. By plac�ng a l�m�t on the modular rat�o that can be susta�ned for a spec�fic mater�al, �t �s ensured that the st�ffness value assumed for that layer �s real�st�c, g�ven the mater�al qual�ty and st�ffness of the support. In essence, the concept of a l�m�t�ng modular rat�o for granular mater�als ensures that stress-sens�t�ve st�ffness behav�our �s �mpl�c�tly taken �nto account.

The modular rat�o that a mater�al can susta�n w�ll vary over the l�fe of a pavement. The concept of pavement balance, as d�scussed by Maree (1982) and Kleyn (1984) essent�ally assumes that the modular rat�o of d�fferent unbound layers �n a pavement system w�ll decrease over t�me, as the traffic moulds and dens�fies the mater�al �nto a more un�form or balanced system.

Thus wh�le �t �s poss�ble for a h�gh qual�ty crushed stone to ma�nta�n a modular rat�o of 4 to 5 r�ght after construct�on, over t�me the mater�al w�ll be moulded and weakened by traffic �nto a more balanced state where a modular rat�o of 3 or less �s l�kely to be observed. It �s thus �mportant to note that the use of a modular rat�o l�m�t, as defined for the PN method, perta�ns to the overall long term st�ffness that a mater�al can ma�nta�n over t�me.

Under the act�on of load�ng, there �s a max�mum st�ffness that mater�als can ach�eve. As w�th the modular rat�o, the max�mum st�ffness depends on the qual�ty of the mater�al, and less dense and angular mater�als cannot develop very h�gh st�ffnesses under load�ng, regardless of the st�ffness of the support.

In the PN model, the modular rat�o l�m�t and the max�mum allowed st�ffness are used extens�vely to determ�ne real�st�c ELTS values. These parameters are used �n the follow�ng way:

The st�ffness of the support�ng layer �s first determ�ned. Thus the PN calculat�on process starts from the subgrade and proceeds upward toward the surfac�ng.The modular rat�o l�m�t and max�mum allowed st�ffness are determ�ned based on the DEMAC.The ELTS for a layer �s determ�ned as the m�n�mum of

The support st�ffness mult�pl�ed w�th the modular rat�o l�m�t.The max�mum allowed layer st�ffness.

In the case of base layers, the ELTS �s further adjusted by means of a base confidence factor, wh�ch �s d�scussed �n more deta�l �n Sect�on C.4. The use of the modular rat�o l�m�t and max�mum allowed st�ffness �s also appl�ed to cement stab�l�sed and hot m�x asphalt mater�als, as expla�ned below.

C 3 3 1 Modular Ratio Limit for Cement Stabilised Materials and Hot Mix AsphaltModular rat�o l�m�ts do not normally apply to cohes�ve mater�als such as cement stab�l�sed layers and hot m�x asphalt. Th�s �s because of the h�gh cohes�on �nherent �n such mater�als, wh�ch effect�vely removes the stress-sens�t�v�ty and ensures that these mater�als can ma�nta�n a relat�vely h�gh st�ffness under load�ng, even over weak support.

However, when the long term st�ffness of these mater�als �s cons�dered, then the st�ffness of the support aga�n becomes relevant. Th�s �s because weaker support layers w�ll lead to �ncreased fat�gue and hence faster breakdown of stab�l�sed layers. Thus, when these mater�als are used �n a s�mpl�fied model, the modular rat�o l�m�t can serve to m�m�c the long term fat�gue effect that w�ll lead to qu�cker reduct�on of the st�ffness when these mater�als are placed over softer support.

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2.3.

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117

Th�s effect �s �llustrated schemat�cally �n F�gure C.2, wh�ch shows a case where the same cement stab�l�sed mater�al �s placed over a st�ff and soft support. Because the cement stab�l�sed mater�al �s the same �n both �nstances, the �n�t�al and final st�ffness values are the same. However, the mater�al on soft support exper�ences more rap�d st�ffness reduct�on, and thus the effect�ve st�ffness over the long term �s lower than for the mater�al on the st�ff support.

Another factor wh�ch determ�nes the rate and degree of breakdown �n cement stab�l�sed mater�als �s the th�ckness of the layer. To m�m�c the �nfluence of layer th�ckness on the rate of deter�orat�on, the PN model adjusts the ELTS of cement stab�l�sed layers for layer th�ckness. Deta�ls of th�s adjustment are prov�ded �n Sect�on C.4.

Figure C.2 Modular Ratio Limit for Cement Stabilised Materials

C 3 3 2 Modular Ratio Limit for Bitumen Stabilised MaterialsThe modular rat�os of BSMs and the ELTS values are h�gher than that of granular mater�als for the reasons g�ven �n Sect�on C.3, Rule 10.

C 3 4 The Base Confidence FactorThe type of mater�al �n the base layer �s an �mportant determ�nant of the performance of the pavement because the base �s the ma�n load bear�ng element �n the pavement system, and fa�lure of the base effect�vely const�tutes pavement fa�lure. Exper�ence has shown that there �s a l�m�t on the types of base mater�als that can be cons�dered for any g�ven des�gn traffic. In part�cular, su�table des�gn opt�ons are s�gn�ficantly l�m�ted as the des�gn traffic �ncreases.

In the PN method, the appropr�ateness of the base mater�al �s controlled by the Base Confidence Factor (BCF). The BCF �s used to adjust the ELTS value for the base layer. Th�s �s done s�mply by mult�ply�ng the �n�t�al ELTS for the base w�th the BCF.

C.4. PAVEMENT NUMBER CALCULATIONIn th�s sect�on, the stepw�se method for calculat�ng the PN �s deta�led. Deta�ls relat�ng to d�fferent steps or concepts �n the method are d�scussed �n the subsect�ons that follow. In a pavement des�gn s�tuat�on, the steps descr�bed are appl�ed for each un�form des�gn sect�on. For rehab�l�tat�on des�gn s�tuat�ons, �t �s thus presumed that the des�gner w�ll have deta�led �nformat�on on the ex�st�ng pavement layer propert�es for each un�form sect�on.

Step 1: Check to ensure that the des�gn method �s appl�cable for the des�gn s�tuat�on (see Sect�on C.2 for deta�ls). If the des�gn method �s not appl�cable, a more deta�led analys�s should be performed, and the PN method should not be used.

Step 2: Determ�ne the layer th�cknesses, and ava�lable mater�al propert�es for each layer. Use the mater�al propert�es to obta�n a DEMAC for each layer (see Append�x A for deta�ls). To prevent the use of unreal�st�c layer th�ckness assumpt�ons, max�mum and

Axles Accommodated

Effe

ctiv

e St

iffne

ss

ELTS of cement stabilized material on stiff support

ELTS of cement stabilized material on soft support

Note: For hot mix asphalt and stabilized layers, the modular ratio limit ensures that faster breakdown of stiffness due to weaker support is incorporated



118

m�n�mum pract�cal des�gn th�ckness are prescr�bed for d�fferent mater�al types. The l�m�ts are also constra�ned by the data used to cal�brate and val�date the PN method (Long, 2009). The layer th�ckness l�m�ts are shown �n Table C.1.

Step 3: Comb�ne layers w�th s�m�lar propert�es to obta�n a five layer pavement system, �nclud�ng the subgrade (see Sect�on C.4.1 for deta�ls). Check that the layer th�cknesses do not exceed the max�mum for des�gn purposes (see Table C.1 for deta�ls).

Step 4: Determ�ne the bas�c st�ffness of the subgrade by means of Table C.2. Adjust the st�ffness for cl�mat�c reg�on (Table C.3) and depth of subgrade cover (F�gure C.3) by mult�ply�ng the bas�c st�ffness by the cl�mate adjustment factor and add�ng the subgrade cover adjustment factor. The result�ng st�ffness �s the ELTS for the subgrade.

Step 5: For each layer above the subgrade, determ�ne the modular rat�o l�m�t and max�mum allowed st�ffness from Table C.4.Step 6: Use the modular rat�o l�m�t and max�mum allowed st�ffness to determ�ne the ELTS for each layer by work�ng up from the

subgrade (see Sect�on C.4.2 for deta�ls on the process).Step 7: For the base layer, determ�ne the Base Confidence Factor (BCF) from Table C.4. For cement stab�l�sed layers, also determ�ne the

adjustment factor based on th�ckness from F�gure C.4.Step 8: For each layer, calculate the layer contr�but�on by mult�ply�ng the ELTS w�th the layer th�ckness and d�v�d�ng th�s by 10 000. For

the base layer mult�ply th�s product w�th the BCF, and for any cement stab�l�sed layers, mult�ply w�th the th�ckness adjustment factor.

Step 9: Add the layer contr�but�ons for each layer to get the PN.

The constants shown �n Table C.2 to Table C.4 and the relat�onsh�ps �n F�gure C.3 and F�gure C.4 were obta�ned through an �terat�ve cal�brat�on process. The values are spec�fic to the PN method and should not be adjusted by the des�gner.

Table C 1 Recommended Layer Thickness Limits for Design Calculations

Material Type Layer Situation

Thickness Limits Allowed for PN Calculation (mm)

Minimum Maximum

Hot M�x Asphalt Surfac�ng Layers 20 50

Surface Seals Surfac�ng Layers 5 5

B�tumen Stab�l�sed Layers Base and Subbase 100 350

Cement Stab�l�sed Layers Subbase 100 400

All Unbound Mater�als (G1 to G10)Subbase 100 300

Selected Layer(s) 100 300

Table C 2 Stiffness Determination for the Subgrade

Design Equivalent Material Class for Subgrade Stiffness Value (MPa)

G6 or better 180

G7 140

G8 100

G9 90

G10 70

Note: Subgrade st�ffness value should be adjusted for cl�mate (Table C.3) and cover depth (F�gure C.3).



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Table C 3 Climate Adjustment Factors

Climate and Weinert N Values (after TRH4, 1996) Adjustment Factor

Wet (We�nert N < 2) 0.6

Moderate (We�nert N = 2 to 5) 0.9

Dry (We�nert N > 5) 1.0

Table C 4 Modular Ratio Limit and Maximum Allowed Stiffness for Pavement Layers

General Material Description Material Class1 Modular Ratio Limit

Maximum Allowed Stiffness

(MPa)

Base Confidence

Factor

Hot m�x asphalt (HMA) surfac�ng and base mater�al AG, AC, AS, AO 5.0 3500 1.0

Surface sealsS1, S2, S3, S4, S5,

S62.0 800 N/A

H�gh strength b�tumen stab�l�sed mater�al, normally us�ng crushed stone or recla�med asphalt (RA) source mater�al

BSM1 3.0 600 1.0

Med�um strength b�tumen stab�l�sed mater�al, normally us�ng natural gravel or RA source mater�al

BSM2 2.0 450 0.7

Crushed stone mater�al

G1 2.0 700 1.1

G2 1.9 500 0.8

G3 1.8 400 0.7

Natural Gravel

G4 1.8 375 0.2

G5 1.8 320 0.1

G6 1.8 180 -2.0

Gravel-so�l blend

G7 1.7 140 -2.5

G8 1.6 100 -3.0

G9 1.4 90 -4.0

G10 1.2 70 -5.0

Cement stab�l�sed crushed stone C1 and C2 9 1500 0.8

Cement stab�l�sed natural gravelC3 4 550 0.6

C4 3 400 0.4

Note: 1. Des�gn equ�valent mater�al class (DEMAC) for rehab�l�tat�on projects.



120

Figure C.3 Adjustment of Subgrade Stiffness Based on Cover Thickness

Figure C.4 ELTS Adjustment Factor for Cement Stabilised Layers based on Layer Thickness

-15

-10

-5

0

5

10

15

400 450 500 550 600 650 700 750 800 850 900

Thickness of Subgrade Cover (mm)

Adj

ustm

ent t

o Su

bgra

de S

tiffn

ess

(MPa

)

If Cover Thickness (in mm) is:> 800, then Adjustment = +10 MPa< 500, then Adjustment = -10 MPaelse:Adjustment = -10 + [(Cover-500)/300] * 20 MPa

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350 400 450

Layer Thickness (mm)

Ad

jus

tme

nt

toS

ub

gra

de

Sti

ffn

es

s(M

Pa

) If Thickness (in mm) is:> 300, then Adjustment Factor is 1.0else:Adjustment = 1- [(300-Thickness)/50] * 0.3to a minimum of 0.2

(Multiply adjustment factor with layer ELTS)



121

C 4 1 Combining Pavement Layers to Form a Five Layer ModelBy defin�t�on, the PN cons�sts of the sum of the load spread�ng contr�but�ons of four pavement layers above the subgrade. To apply th�s defin�t�on cons�stently, the pavement model used �n the PN calculat�on must cons�st of four pavement layers plus the subgrade. In cases where the pavement cons�sts of more than four layers, two or more layers w�ll need to be comb�ned. To do th�s, the follow�ng gu�del�nes should be adhered to:

Only comb�ne layers that cons�st of the same general mater�als class. In th�s respect, the follow�ng general mater�al classes can be used:

Hot m�x asphalt and surfac�ng sealsCrushed stone mater�al Natural gravel mater�alCement stab�l�sed mater�al B�tumen stab�l�sed mater�al Gravel-so�l, s�lt or clay mater�als

The surfac�ng should be modelled as a separate layer �n all cases. A surface seal should be modelled as a 5 mm th�ck layer.Where there �s a need to comb�ne pavement layers, the des�gner should first comb�ne sub-layers below the subbase, followed (�f needed) by sub-layers �n the subbase zone.The mater�al class ass�gned to the comb�ned layer should be the class of the th�cker of the two layers. Thus, �f a 150 mm G6 �s comb�ned w�th a 120 mm G7, then the mater�al ass�gned to the 270 mm comb�ned layer should be G6.Where the two layers to be comb�ned are of equal th�ckness, the lower mater�al should be ass�gned to the comb�ned layer. Thus, �f a 150 mm G7 �s comb�ned w�th a 150 mm G8, then the mater�al class ass�gned to the 300 mm comb�ned layer should be G8.When a pavement layer �s comb�ned w�th the apparent natural subgrade, the mater�al class of the comb�ned subgrade layer should be the class of the uppermost layer.When a pavement cons�sts of only two or three pavement layers, a four layer pavement system should be constructed by subd�v�d�ng the top of the subgrade �nto two or more layers, each w�th a th�ckness of 100 mm. The mater�al class ass�gned to these sub-layers should be that of the subgrade.The th�ckness of the comb�ned layers should not exceed the l�m�ts g�ven �n Table C.1. These th�ckness l�m�ts are only appl�cable to the des�gn calculat�ons.

F�gure C.5 shows an example �n wh�ch there are several selected layers that are comb�ned to form a five layer system. Th�s example also shows the appl�cat�on of the l�m�t�ng th�ckness to the selected layers, wh�ch also determ�nes the amount of cover on the subgrade for modell�ng purposes. Even w�th the above gu�del�nes taken �nto account, some pavement s�tuat�ons w�ll allow more than one approach to the comb�nat�on of layers. In such cases, the des�gner should exper�ment w�th d�fferent approaches and adopt the most conservat�ve model for des�gn purposes.

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122

Figure C.5 Example of the Combining of Pavement Layers to Form a Five Layer Model

C 4 2 Determining Effective Long-Term Stiffness (ELTS) Values The ELTS and modular rat�o l�m�t are essent�al to the PN-method. For the subgrade, the ELTS �s first determ�ned us�ng the mater�al class. Th�s value �s then adjusted for cl�mate and for depth of subgrade cover.

The cl�mate adjustment of the subgrade st�ffness takes �nto account the �ncreased frequency and r�sk of hav�ng a soft subgrade �n wet reg�ons. The cl�mate adjustment factors are shown �n Table C.3 and are mult�pl�ed by the ELTS assoc�ated w�th the mater�al class.

The adjustment for subgrade cover takes �nto account the behav�our of finer-gra�ned mater�als wh�ch tend to soften under �ncreased stress. A relat�ve adjustment (decrease) of the subgrade st�ffness �s therefore made to s�mulate the effect of stress-soften�ng for pavements w�th less subgrade cover (�.e. where shear stresses are greater). The adjustment of the subgrade st�ffness for depth of cover �s shown �n F�gure C.3 and �s added to the ELTS that has already been adjusted for cl�mate.

For pavement layers above the subgrade, the max�mum allowed st�ffness and modular rat�o l�m�t for each mater�al are obta�ned from Table C.4 us�ng the ass�gned mater�al class. The st�ffness can then be determ�ned by work�ng from the subgrade upwards, us�ng the modular rat�o l�m�t and the max�mum allowed st�ffness. The ass�gned ELTS �s determ�ned as the m�n�mum of the max�mum allowed st�ffness, and the st�ffness of the support layer mult�pl�ed by the modular rat�o l�m�t.

An example of th�s procedure �s shown �n F�gure C.6 and F�gure C.7 for a structure �n a wet and dry cl�mate, respect�vely. A compar�son of these figures shows the �mpact of cl�mate on the subgrade, and the subsequent �mpact on pavement layer st�ffnesses. These examples show how the modular rat�o effect�vely takes �nto account the st�ffness of the support layer, thereby reduc�ng the ass�gned ELTS when the support st�ffness reduces, even though the mater�al class rema�ns unchanged.

50 mm Continuously Graded Asphalt

150 mm BSM2 Material

180 mm C4 Material

G9 Material (Apparent natural subgrade)

Proposed Design, using test pit profiles

230 mm G7 Material

120 mm G8 Material

110 mm G6 Material



180 mm C4 Material

Pavement converted to a five layer system

340 mm G7 Material

G8 Material (assigned subgrade)



180 mm C4 Material

Check thickness limit on selected layer

300 mm (thickness used in design calculations)

G7 Material

G8 Material (assigned subgrade)



123

Figure C.6 Example of ELTS Determination (Wet Climate)

Figure C.7 Example of ELTS Determination (Dry Climate)



150 mm C4 Material

G8 Subgrade

Climate = Wet

Emax = 450; MR = 2;

Emax = 3500; MR = 5;

Emax = 400; MR = 3;

E = 100 MPa;

Climate Factor = 0.6

Stiffness adjustment for depth of subgrade cover = - 10 MPa

Obtain design equivalent material classes

Determine stiffness determination factors

ELTS = (100 x 0.6) – 10

= 50 MPa

Determine ELTS values for each layer

ELTS = min(400, 3 x 85)

= 255 MPa

ELTS = min(3500, 450 x 5)= 2250 MPa

ELTS =min(450, 2 x 255)

= 450 MPa

150 mm G7 Material Emax = 140; MR = 1.7; ELTS = min(140, 1.7 x 50)

= 85 MPa

Etc.

Determine subgrade ELTS first, then work upwards

Table C.19

Table C.19

Table C.19

Table C.17 and Table C.18

Table C.19



150 mm C4 Material

G8 Subgrade

Climate = Wet

Emax = 450; MR = 2;

Emax = 3500; MR = 5;

Emax = 400; MR = 3;

E = 100 MPa;





ELTS = (100 x 0.6) – 10

= 50 MPa


ELTS = min(400, 3 x 85)

= 255 MPa

ELTS = min(3500, 450 x 5)= 2250 MPa

ELTS =min(450, 2 x 255)

= 450 MPa


= 85 MPa

Etc.


Table C.19

Table C.19

Table C.19


Table C.19



150 mm C4 Material

G8 Subgrade

Climate = Dry

Emax = 450; MR = 2;

Emax = 3500; MR = 5;

Emax = 400; MR = 3;

E = 100 MPa;





ELTS = (100 x 1.0) – 10

= 90 MPa;


ELTS = min(400,3 x 140)

= 400 MPa

ELTS = min(450, 2 x 400)

= 450 MPa


= 140 MPa

Etc.


ELTS = min(3500, 450 x 5)= 2250 MPa

Table C.19

Table C.19

Table C.19


Table C.19



150 mm C4 Material

G8 Subgrade

Climate = Dry

Emax = 450; MR = 2;

Emax = 3500; MR = 5;

Emax = 400; MR = 3;

E = 100 MPa;





ELTS = (100 x 1.0) – 10

= 90 MPa;


ELTS = min(400,3 x 140)

= 400 MPa

ELTS = min(450, 2 x 400)

= 450 MPa


= 140 MPa

Etc.


ELTS = min(3500, 450 x 5)= 2250 MPa

Table C.19

Table C.19

Table C.19


Table C.19



124

C.5. PAVEMENT CAPACITY CALCULATIONThe calculat�on of the pavement capac�ty depends on the Pavement Number and the Road Category. The relat�onsh�p �n Equat�on C.1 �s used, �n conjunct�on w�th the constants �n Table C.5 or Table C.6. The relat�onsh�p between the PN and the pavement capac�ty does not g�ve a pavement l�fe pred�ct�on, but rather prov�des a lower l�m�t for wh�ch the pavement should carry the des�red traffic suffic�ently. The cr�ter�a are only appl�cable to Category A and B roads and for des�gn capac�t�es between 1 and 30 MESA. For Category C and D roads, a catalogue of des�gn �s recommended, see Chapter 5.

Nallow = N1 + (PN - PN1) x Slope (C.1)

Where: Nallow = Allowed pavement capac�ty (MESA) N1 = Lower l�m�t for the capac�ty range from Table C.5 or Table C.6 PN = Calculated pavement number PN1 = Lower l�m�t for the PN range from Table C.5 or Table C.6 Slope = Slope for the PN range from Table C.5 or Table C.6

The values N1, PN1 and Slope are obta�ned from Table C.5 or Table C.6 (depend�ng on the Road Category), after first determ�n�ng the range w�th�n wh�ch the calculated PN falls. F�gure C.8 shows the cr�ter�a �n a graph�cal format.

Table C 5 PN Criteria for Category A Roads

PN Range N1 PN1 Slope

PN < 15 Less than 3 MESA, not su�ted for Category A roads

15 < PN ≤ 23 3 15 0.00

23 < PN ≤ 25 3 23 3.50

25 < PN ≤ 32 10 25 0.00

32 < PN ≤ 35 10 32 6.67

PN > 35 30 35 0.00

Table C 6 PN Criteria for Category B Roads

PN Range N1 PN1 Slope

PN < 3 Less than 1 MESA, use Des�gn Catalogue (F�gure 5.1)

3 < PN ≤ 8 1 3 0.00

8 < PN ≤ 11 1 8 0.67

11 < PN ≤ 15 3 11 0.00

15 < PN ≤ 25 3 15 0.70

PN > 25 Use Category A Cr�ter�a



125

Figure C.8 Criteria for Determining Allowed Capacity from PN

C.6. WORKED EXAMPLEAn example of the PN calculat�on �s shown �n F�gure C.9. In the figure, the assumed values are shown �n yellow, values obta�ned from tables and figures are shown �n green and calculated values are shown �n blue.

For the example, the follow�ng �nformat�on was assumed:

Climate: Moderate

Pavement Structure: 30 mm Asphalt Surfac�ng 175 mm BSM2 (B�tumen Stab�l�sed Natural Gravel) 200 mm G6 (Gravel So�l Blend) 180 mm G7 Selected Layer G8 Subgrade

Step 1 Check the number of pavement layers and thicknesses The pavement has five layers �nclud�ng the subgrade, and does not need adjustment us�ng the gu�del�nes �n Sect�on C.4.1. The

layer th�cknesses are w�th�n the spec�fied l�m�ts for each mater�al type g�ven �n Table C.1.

Step 2 Calculate the Subgrade ELTS Th�s �s shown �n the topmost sect�on of F�gure C.9. The �n�t�al st�ffness �s first determ�ned from Table C.2, mult�pl�ed by the cl�mate

adjustment factor (Table C.3) and then the cover depth adjustment factor (us�ng F�gure C.3) �s subtracted. The subgrade ELTS �s then entered �nto the last row of column 4 of the lower table �n F�gure C.9.

0

5

10

15

20

25

30

35

0 10 20 30 40 50Pavement Number

Min

imum

Str

uctu

ral C

apac

ity (M

ESA

) h

Category ACategory B



126

Step 3 Calculate the ELTS for each layer F�rst, the modular rat�o l�m�t and max�mum allowed st�ffness are determ�ned from Table C.4. The ELTS �s then calculated as the

m�n�mum of:The max�mum allowed st�ffness.The st�ffness of the support layer mult�pl�ed by the modular rat�o l�m�t.

The calculat�on starts at the subgrade and then moves upward. For example, the ELTS of the selected layer �s the m�n�mum of 146 (�.e. 86 * 1.7) and the max�mum allowed st�ffness of 140 MPa.

Step 4 Determine the Thickness Adjustment Factor and Base Confidence Factor The th�ckness adjustment factor �s determ�ned from F�gure C.4 and entered �n column 5. Th�s factor appl�es only to cement

stab�l�sed mater�als and �s therefore shown as 1.0 for all layers �n th�s example. The BCF for the base layer �s determ�ned from Table C.4 and �s only val�d for the base layer.

Step 5 Calculate Layer Contribution The layer contr�but�on �n column 7 �s calculated for each layer by mult�ply�ng the th�ckness, the ELTS, the th�ckness adjustment

factor and the BCF (where appl�cable). Th�s product �s then d�v�ded by 10 000 to scale the number to a real�st�c value. For example, the base layer contr�but�on �s (175 * 360 * 1 * 0.7) / 10 000 = 4.4.

Step 6 Calculate the Pavement Number The layer contr�but�ons are added to obta�n the PN (5.4 + 4.4 + 3.6 + 2.5 = 15.9).

Step 7 Determine the Pavement Capacity Equat�on C.1 and the constants g�ven �n Table C.5 for Category A roads or Table C.6 for Category B roads are used to calculate the

pavement capac�ty. For example, for Category B, the pavement capac�ty �s 3 + (15.9 – 15) * 0.7 = 3.6 MESA.

Subgrade Class G8

Initial Stiffness 100 (from Table C.2)

Climate Moderate

Climate Adjustment 0.9 (from Table C.2)

Cover Depth 585 mm (sum of layer th�cknesses above subgrade)

Cover Adjustment - 4 (from F�gure C.3)

Subgrade ELTS 86 (100*0.9 – 4)

Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 Column 9

Layer Thickness (mm)

material class

Modular Ratio

(Table C.4)

Maximum Stiffness

(MPa) (Table C.4)

ELTS (MPa)

Thickness Adjustment (F�gure C.4)

BCF (Table C.4)

Layer Contribution

Surfac�ng 30 AC 5.0 3 500 1 800 1.0 N/A 5.4

Base 175 BSM2 2.0 450 360 1.0 0.7 4.4

Subbase 200 G6 1.8 180 180 1.0 N/A 3.6

Selected 180 G7 1.7 140 140 1.0 N/A 2.5

Subgrade N/A G8 N/A N/A 86 Pavement Number = 15.9

Pavement Capac�ty =(Equat�on C.1)

3.0 MESA (A)3.6 MESA (B)

Figure C.9 Example Showing Determination of the Pavement Number

••



BIBLIOGRAPHY

127

REFERENCESJOOSTE, F.J, Long, F.M. and Hefer, A.. 2007. A Method for Consistent Classification of Materials for Pavement Rehabilitation Design

Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca (study funded by Sab�ta and Gauteng Department of Publ�c Transport, Roads and Works). (Gautrans report: CSIR/BE/IE/ER/2007/0005/B).

JOOSTE, F.J., F.M. Long and A.O. Hefer. 2007. A Knowledge Based Structural Design Method for Pavements Incorporating Bitumen Stabilised Materials Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2007. (GDPTRW report number: CSIR/BE/IE/ER/2007/0004/B).

LONG, F.M. and F.J. Jooste. 2007. Summary of LTTP Bitumen Emulsion and Foamed Bitumen Treated Sections Techn�cal Memorandum. Modell�ng and Analys�s Systems, Cull�nan, South Afr�ca. SABITA/Gauteng Department of Publ�c Transport, Roads and Works, Pretor�a, 2007. (GDPTRW report number: CSIR/BE/IE/ER/2007/0006/B).


Techn�cal Recommendat�ons for H�ghways, 1996, Structural Design of Flexible Pavements for Interurban and Rural Roads, TRH4, Draft, 1996.

Techn�cal Recommendat�ons for H�ghways, 1997, Flexible pavement rehabilitation investigation and design, TRH12, Draft, 1997.

THEYSE, H.L., De Beer, M. and Rust, F.C. 1996. Overview of the South African Mechanistic Pavement Design Analysis Method Paper Number 961294 Presented at the 75th Annual Transportat�on Research Board Meet�ng, January 7 to 11, 1996, Wash�ngton, D.C.


APPENDIX D: Contruction Controls for Bitumen Treatment

128

APPENDIX D: CONSTRUCTION CONTROLS FOR BITUMEN TREATMENTD1 Essential Requirements for a successful recycling operation using recyclers

D2 Pre-start check lists (example sheets) D2.1 In s�tu recycl�ng: BSM-foam D2.2 In s�tu recycl�ng: BSM-emuls�on D2.3 In plant treatment: BSM-foam

D3 Daily reports for in situ recycling (example sheets) D3.1 BSM-foam D3.2 BSM-emuls�on D3.3 Act�ve filler control

D.1. ESSENTIAL REQUIREMENTS FOR A SUCCESSFUL RECYCLING OPERATION USING RECYCLERS

The follow�ng are some of the essent�al requ�rements for a successful recycl�ng operat�on:Operator and supervisor training Recycl�ng should never be undertaken by a work crew that has not rece�ved the necessary tra�n�ng. In add�t�on to techn�cal aspects of the work, safety �s a major factor when work�ng w�th large mach�nery. Th�s �s compounded when work�ng w�th the hot b�tumen requ�red for BSM-foam. Everyone �nvolved �n the operat�on must be adequately tra�ned to use all the equ�pment properly, and all the r�sks must be emphas�sed to prevent acc�dents.Operating procedures These must be str�ctly adhered to, part�cularly those relat�ng to start-up. Feed l�nes requ�re bleed�ng and checks must be carr�ed out to ensure that the spraybars are free of �nternal blockages. Blockages are frequently exper�enced when these procedures are not followed. External blockages caused by mater�al bu�ld-up �ns�de the m�ll�ng chamber must be checked and removed where necessary. In add�t�on, the var�ous sett�ngs �.e., drum rotat�on speed, breaker-bar sett�ng, rear-door pressure, etc. should be preset as per those establ�shed dur�ng the construct�on of the Tr�al Sect�on, as dealt w�th �n Sect�on 6.7. Computer �nput data, such as mater�al dens�ty and appl�cat�on rates, need to be set and checked.Connecting tankers to the recycler Before coupl�ng a b�tumen tanker to the recycler, the valve at the rear of the tanker should always be carefully opened to allow a small quant�ty of b�tumen emuls�on or hot b�tumen to flow out �nto a drum. Th�s �s an �mportant procedure as �t prevents a plug of cold b�tumen from enter�ng and block�ng the feed l�ne. Although such cold plugs are more often exper�enced when work�ng w�th foamed b�tumen, th�s check w�ll also draw attent�on to b�tumen emuls�on that has broken prematurely �n the tanker.Temperature checks The follow�ng temperature checks should be rout�nely undertaken:

Material prior to treatment Where low temperatures are suspected (normally est�mated from the surface temperature) the temperature of the mater�al be�ng recycled can be measured soon after start�ng work by l�ft�ng the drum and us�ng a hand-held d�g�tal thermometer focused on the cut face. Where the temperature �s below the m�n�mum recommended (Sect�on 4.2.1.5), work should not proceed.Hot bitumen or bitumen emulsion The temperature of the b�tumen �n each tanker load should be checked before connect�ng to the recycler. When the temperature �s below the m�n�mum spec�fied, the tanker must be sent off s�te. Temperature gauges permanently fitted to tankers are notor�ously �naccurate. A hand-held d�g�tal thermometer should therefore be used to measure the temperature of the contents of the tanker through the fill�ng hatch. The mixed product A hand-held d�g�tal thermometer should be used to measure temperature var�at�ons across the w�dth of treatment �mmed�ately beh�nd the rear door of the m�ll�ng chamber. Ensure that the laser “spot” (locat�on of temperature read�ng) �s kept off coarse part�cles. The temperature read�ngs should not vary by more than 5 °C across the recycled w�dth. Any decrease of more than 5 °C �s an �nd�cator of under appl�cat�on by a blocked nozzle. S�nce recyclers do not move mater�al more than 200 mm �n the transverse d�rect�on, the offend�ng nozzle can be �solated and the cause of the problem addressed.

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129

BSM-emulsion

Not relevant.

BSM-foam

An �ncrease �n temperature �nd�cates a lack of foam�ng s�nce unfoamed hot b�tumen �s be�ng appl�ed.

Lateral joints Jo�nts are formed at r�ght-angles to the d�rect�on of travel every t�me the recycl�ng process �s stopped and, s�m�lar to all other stab�l�s�ng processes, cont�nu�ty across these jo�nts �s an �mportant factor �n avo�d�ng local�sed fa�lures. To ensure cont�nu�ty of treatment, �t �s essent�al that the operat�ng character�st�cs of the appl�cat�on system be�ng used are fully understood, part�cularly the b�tumen appl�cat�on system. As the recycler accelerates from stat�onary to the normal operat�ng speed, the b�tumen appl�cat�on system needs to respond cont�nuously to ensure that the correct appl�cat�on rate �s ach�eved and ma�nta�ned. Where the system only starts funct�on�ng above a m�n�mum advance speed (thereby ensur�ng suffic�ent pressure on the spraybar), the recycler must be pos�t�oned at least 1 metre back �nto mater�al that has already been treated to ensure cont�nu�ty of b�tumen treatment. When the recycler moves forward, the m�n�mum advance speed �s generally atta�ned w�th�n the first metre and the appl�cat�on system starts funct�on�ng. Fa�lure to adhere to th�s s�mple requ�rement can result �n a patch of untreated mater�al.Containing the recycled material Recycled mater�al ex�ts the recycler �n a loose state and must be compacted �mmed�ately back �nto the cut from whence �t came. Bulk�ng w�ll result �n th�s mater�al be�ng proud of the adjacent un-recycled road surface. Mater�al must not be spread �nto the path of the adjacent un-recycled cut because th�s w�ll result �n double dosage and saturat�on when the next cut �s recycled.Thickness control Although recyclers are usually equ�pped w�th automat�c sensors, the depth of recycl�ng �s cr�t�cal and should therefore be regularly checked and any necessary adjustments made. To ensure that the correct layer th�ckness �s ach�eved, the same survey reference poles used for cutt�ng final levels should be ut�l�sed, employ�ng a po�nted T-bar as a probe, as �llustrated �n

A trench, 0.5 m, w�de should be dug through the ent�re layer of loose BSM across the full cut w�dth at least once every 500 m. When opened, the cond�t�on of the top surface of the underly�ng �n s�tu mater�al can be checked as well as the layer th�ckness and the qual�ty of the recycled and treated m�x. These trenches must be dug, �nspected, measured, v�ewed, recorded and closed before the pr�mary roller makes the first pass.

Figure D.1. Where check measurements are taken on the side face of the cut, cognisance must be taken of the increase in surface elevations of recycled material caused by bulking.

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130

Speed of advance The qual�ty of the recycled and b�tumen treated m�x �s a funct�on of the advance speed of the recycler. Although the recycler may be capable of work�ng at far h�gher speeds, exper�ence has shown that opt�mal m�x�ng �s ach�eved at forward speeds of between 7 and 10 metres per m�nute, depend�ng on the nature of the mater�al to be recycled and the depth of cut.“Bulldozing” the active filler Where act�ve filler �s pre-spread on the road surface ahead of the recycler, the rubber flap fitted to the bottom of the front door of the m�ll�ng chamber must be l�fted to prevent �t from act�ng as a dozer blade, sp�ll�ng a w�ndrow of the act�ve filler on e�ther s�de of the chamber. Th�s w�ndrow tends to be bur�ed by fines thrown forward through the s�des of the front door and not eas�ly v�s�ble. If not detected and el�m�nated, such a concentrat�on of act�ve filler w�ll not be properly d�spersed when recycl�ng the adjacent cut and can be the cause of a long�tud�nal crack that follows the l�ne of the jo�nt.Change in recycling conditions Should unforeseen cond�t�ons ar�se that result �n slow operat�ng speeds or var�at�ons �n the recycled and treated mater�al, the recycler can always be stopped and the drum l�fted for a qu�ck �nspect�on.Moisture control As expla�ned �n Sect�on 6.2.2.4 �n Chapter 6, �t �s �mpract�cal to attempt to accurately pred�ct var�at�ons �n the mo�sture content of mater�als �n the pavement layers, regardless of how many tests are done �n advance. On most recycl�ng projects, the requ�red mo�sture content of the recycled mater�al �s approx�mated by vary�ng the add�t�on of water wh�lst recycl�ng and constantly “measur�ng” the mater�al “by feel”. Th�s requ�res the operator to vary the amount of water added, only upon �nstruct�on of a superv�sor who has suffic�ent exper�ence to be able to gauge mo�sture content. Equ�pp�ng the superv�sor and operator w�th walk�e-talk�e rad�os allows �nstant commun�cat�on.Visual observations whilst the recycler is working:

The consistency in the colour of the mater�al �mmed�ately beh�nd the recycler w�ll usually �nd�cate whether or not the mach�ne �s set up properly. A gradual change �n colour across the w�dth normally �nd�cates that one end of the drum �s lower than the other. A l�ghter appearance �nd�cates d�lut�on (under-appl�cat�on of water and b�tumen stab�l�s�ng agent) caused by the drum not penetrat�ng too deep �nto the pavement. A darker colour �nd�cates an over-appl�cat�on due to the drum not penetrat�ng to the requ�red depth.B�tumen treated mater�al �s not sticky and should therefore not adhere to the rear wheels of the recycler. The left p�cture �n F�gure D.2 �llustrates what should be seen beh�nd the recycler. The r�ght p�cture shows mater�al st�ck�ng to the rear wheels �nd�cat�ng that the treated mater�al �s poorly m�xed. Th�s operat�on should be stopped �mmed�ately to determ�ne the cause. Such poorly m�xed mater�al w�ll also st�ck to the drum of the roller, caus�ng mater�al bu�ld-up and further problems.

BSM-emulsion

Th�s �s not usually a problem w�th BSM-emuls�on.

BSM-foam

Mater�al st�ck�ng to the rear wheels of the recycler �nd�cates a poor m�x. Th�s �s the consequence of the b�tumen not foam�ng or too few fines are ava�lable to d�sperse the amount of added b�tumen.

Figure D.2: Observations behind the recycler

The ball test Th�s s�mple test requ�res a round spec�men the s�ze of a fist to be made from a sample of mater�al p�cked up from beh�nd the recycler and firmly squeezed between both hands. Once a ball has been formed, the follow�ng v�sual observat�ons can be made:

»

»

»

»

»•

•

»

Minimal material sticking to the wheels of the recycler Material sticking to the wheels of the recycler



131

BSM-emulsion

Place the ball �n the sun and leave to dry for at least 30 m�nutes to allow the b�tumen emuls�on to break before carry�ng out the “test” descr�bed below.

BSM-foam

Clean all loose mater�al from the palms of the hands and observe the b�tumen spots. The warmth of the hands and pressure appl�ed w�ll perm�t the b�tumen to st�ck. Lots of t�ny spots �nd�cate good d�spers�on wh�lst larger “blobs” are the str�ngers result�ng from poor d�spers�on. The ball does not need cur�ng and can be tested �mmed�ately as descr�bed below.

The “test” cons�sts of hold�ng the ball between the thumb and �ndex finger and gently apply�ng pressure on oppos�te s�des of the ball to gauge the cohes�veness of the mater�al. The ball should deform before fall�ng apart. Inspect the face of the broken ball too see how well the b�tumen has d�spersed. If no b�tumen can be seen, the m�x �s perfect. The more b�tumen blobs or str�ngers there are that can be observed, the worse the qual�ty of the m�x.

D.2. PRE-START CHECKLISTSThe follow�ng checkl�sts are examples of the k�nds of checks that should be followed pr�or to start�ng the recycl�ng.

D 2 1 In situ recycling: BSM-foam

IN SITU RECYCLING / FOAMED BITUMEN S/visor:

PRE-START CHECK LIST Date:

1. Check the bitumen system heaters are operational

2. Check the temperature of the road surface (digital thermometer) 18° C 07 :00

3. Check that the foam-water tank is full

4. Remove and clean the foam-water filter

5. Remove and clean the bitumen filter

6. Lift machine / lower drum / open chamber doors for visual inspection

Check: all foamed bitumen nozzles clear

all water injection nozzles clear

7. Check each expansion chamber for blockages using "pre-water" functionSwitch # 1 2 3 4 5 6 7 8

Nozzle # 1 & 3 2 & 4 5 & 7 6 & 8 9 & 11 10 & 12 13 & 15 14 & 16

8. Obtain loading / weighbridge certificate for bitumen tanker 21.96 tons

9. Calculate cut lengths / finalise cut plan (with the operator)

10. Reset the on-board computer, enter data and check

Density 2150 Cut depth 200mm 2.5m

2.20% 2.50%

SETTING UP THE RECYCLING TRAIN (Each new cut / tanker load)

1. Check cut guideline and position recycler on first cut

2. Check bitumen temperature in tanker (loading hatch) 17 3°C

3. Check bitumen tanker for leaks. Crack valve, check for cold plug

4. Check water tanker is full and free of leaks

5. Couple up bitumen tanker and bleed air from system

6. Check that the bitumen foams using test nozzle Good

7. Couple up water tanker and bleed air from system

8. Check all supply lines and feed pipes for leaks

9. Confirm cut plan / check computer settings & nozzle closure All open

10. Check solenoid lights controlling spraybars / nozzle closure # 4 out ( water)

11. Close front & rear doors. Lower recycling drum to cut depth

12. Lift drum and measure temperaure of material on cut face N/A

13. Roller in place. Drivers ready. Level control team standing by

(Start of shift)

Application width

Bitumen application rate Foam water

E XAMPL E S HE E T

Note any blockages:# 15 block ed. R emoved water jet, cleaned dirt f rom jet

23 March 2009

W irtgen 2500 S # 00593Machine ID:RECYCLER



132

D 2 2 In situ recycling: BSM-emulsion

IN SITU RECYCLING / BITUMEN EMULSION S/visor:


1. Check the bitumen emulsion system has been flushed

2. Check the temperature of the road surface (digital thermometer) 19° C 07 :20

3. Lift machine / lower drum / open chamber doors for visual inspection

Check: all bitumen emulsion nozzles clear


4. Obtain loading / weighbridge certificate for bitumen tanker 21.62 tons

5. Calculate cut lengths / finalise cut plan (with the operator)

6. Reset the on-board computer, enter data and check check

Density 2060 Cut depth 150mm 2.1m

3.33 (percentage emulsion)

SETTING UP THE RECYCLING TRAIN (Each new cut / tanker load)

1. Check cut guideline and position recycler on first cut

2. Check emulsion temperature in tanker (loading hatch) 59° C

3. Check emulsion tanker for leaks. Crack valve, check flow

4. Check water tanker is full and free of leaks

5. Couple up emulsion tanker and bleed air from system

6. Couple up water tanker and bleed air from system


8. Confirm cut plan / check computer settings & nozzle closure

9. Check solenoid lights controlling spraybars / nozzle closure

10. Close front & rear doors. Lower recycling drum to cut depth

11. Lift drum and measure temperaure of material on cut face OK

12. Roller in place. Drivers ready. Level control team standing by

RECYCLER (Start of shift)

Emulsion application rate

Application width

E XAMPL E S HE E T

25 February 2009

W irtgen 2100 DCR # 0593Machine ID:



133

D 2 3 In plant treatment: BSM-foam

IN PLANT TREATMENT / FOAMED BITUMEN S/visor:


1. Check the bitumen system heaters are operational

2. Check the temperature of the material stockpiles 17 °C

3. Check that the water tank is full

4. Remove and clean the foam-water filter

5. Remove and clean the bitumen filter

6. Aggregate feed bins.

SETTING UP THE PLANT FOR MIXING (Each new batch / tanker load)

Application rate:Active filler:

(Start of shift)

Material density

Foam waterBitumen application rate

Note any blockages:

Machine ID:MIXING PLANT

Check for material packing / blockages

Bin # 1. Material:

Bin # 2. Material:

Setting 15 %

Setting 85 %

7. Check the active filler bin and auger feed system

8. Open pugmill hatch and visually inspect for blockages

Check: all foamed bitumen nozzles clear


9. Check each expansion chamber for blockages using "pre-water" function

Nozzle # 1 2 3 4 5 6

10. Obtain loading / weighbridge certificate for bitumen tanker B ulk

11. Check delivery conveyor is clean and running free

12. Reset the computer, enter data and check

2150 L ime 0.7 %

1.9 % 2.0 %

1. Check bitumen temperature in tanker (loading hatch) 181 °C

2. Couple up bitumen tanker and bleed air from system

3. Check that the bitumen foams using test nozzle Good

4. Water supply. Open valves and bleed air from system


6. Check ancillary plant and equipment is ready for mixing

NOTES Two wheel loaders. Material run to stock pile

< 6.7 mm crusher dust

< 19mm S creened R AP

E XAMPL E S HE E T

All clear

Friday 20 March 2009

W irtgen K MA 200 # 0063



134

D.3. DAILY REPORTS FOR IN SITU RECYCLING

The follow�ng are examples of report that should be completed da�ly dur�ng recycl�ng operat�ons.

D 3 1 BSM-foam

Project: Date

Recycler make / model

Type of Bitumen

Weather conditions

Road surface temp oC

Bitumen temp (flowmeter) oC

Active filler Type / %

Start

Finish

Start

Finish

Length of section m

Application width m

Recycling depth m

Volume of section m3

Density of material kg/m3

Mass treated tons

Computer Actual Computer Actual Computer Actual Computer Actual

19 900 19 600 13 900 Part 5 700 Part 8 000 Part

Bitumen application rate % 2.23 2.2 2.29 tanker 2.26 tanker 2.26 Tanker

Design requirement %

Remarks:

Sketch plan:

150mm

Drum cut width 2.5m

C/line

OPC / 0.7%

33+240

32+410

33 800

19 900

2150

282.2

0.2

830

1.7

830

892.25

2.2

Supply tanker ID / bitumen temp ND 635 / 170° C

19.60 tonsWeighbridge ticket mass

Emulsion consumedlitres

2.5

DAILY FOAMED BITUMENAPPLICATION RECORD

LHS

1

Machine Serial No.

Producer / Batch No80 / 100 Pen

Sunny and warm

Lane (see sketch) LHS

2

Distance covered (chainagemarkers)

Bitumen consumptionreading (computer)

Time

185°C

19 900

32+410

33+240

Wirtgen 2500 S

18°C

Engen, Durban, 0067/338/21

06-WR-593-067

09:20

Cut no. (see sketch)

9.86 tons

15:30

27°C

11:45

3

? s ame

? s ame

13:15

26°C23°C

172°C

NP 4439 / 165° C

19.38 tons

Total bitumen used±47 tons for 830m. (38.98 + 8 approx) Average application for day : 2.29%

0.2

117.3

2150

252.2

415.0

2150

0.2

606.73

2.2

CUT # 1. Full bar

CUT # 3. Shut switches 6 7 8

CUT 2. Close switches 6.7.8

800mm O/lap

Spray 1700mm

800mm overlap

2.2

LHS

32+410

32+755

345

1.7

168°C

OPC / 0.7%

33 800

39 500

166°C

1.7

0.2

3

LHS

OPC / 0.7%

39 500

OPC / 0.7%

Reset 0

164.9

47 500

32+755

33+240

485

Width to be recycled and stabilised 5 750mm

23 March 2009Rehab of N2 Section 21, Kokstad

Total pockets of cement spread : 280 (14 tons). Average application for day 0.68%

354.54

Tanker # 3 sent away with about 2 tons remaining (computer says 1.86 tons)

2150

2.2

ND 4004 / 170° C



135

D 3 2 BSM-emulsion

Project: Date

Recycler make / model

Type of Emulsion

Weather conditions

Road surface temp oC

Emulsion temp (flowmeter) oC

Active filler Type / %

Start

Finish

Start

Finish

Length of section m

Application width m

Recycling depth m



Mass treated tons

Computer Actual Computer Actual Computer Actual Computer Actual

21 400 21620 17 500 Part

Emulsion application rate % 3.30 3.33 3.33 tanker

Residual bitumen content % 60 60 60

Bitumen application rate % 1.98 2.00 2.00

Design requirement %

Remarks:

C/lineSketch plan:

Drum cut width 2.1m 100mm

400mm overlap

25 February 2009Rehab of Munyawaneni Road, Durban

Total cement spread by hand: 220 pockets (11 tons). Average application for day 0.94%

Tanker # 2 not emptied - about 3 tons remaining (computer indicates 3.43 tons)

CUT # 1. Switch off # 1, 2

CUT 1. Full bar open

OPC / 1.0%

Reset 0 21 400


Lane (see sketch)

21.62 tonsWeighbridge ticket mass

Emulsion consumedlitres

59°C

21 400

0+340

1+340

315

2060

0.15

Supply tanker ID / emulsion temp ND 123 / 62°C

Distance covered (chainagemarkers)

Emulsion consumptionreading (computer)

Time

19°C

07:20

DAILY BITUMEN EMULSIONAPPLICATION RECORD

LHS

1

Machine Serial No.

Producer / Batch NoCSS-60

Partly cloudy and windy

Wirtgen 2100 DCR

JJ Emulsions, Durban, 3/2009/593

03-WDC-00593

10:10

24°C

64°C

2060

255

0.15

1000

1.7

OPC / 1.0%

0+340

LHS

2

NP 456 / 61°C

20.93 tons

Shoulder

Width of recycling / treatment 3 800mm

Spray 2100mm

1+340

2.1

Total emulsion used 38.9 tons for 1000m. Average application for day 3.31% (1.99% residual)

38 900

1000

648.9

3.33 / 2.0 net

525.3

3.33 / 2.0 net



136

D 3 3 Active filler control

Project: Date

Type of Active Filler

Wind conditions

Length of section m

Application width m

Recycling depth m



Mass treated tons

Active filler required tons

Mass per pocket kg

Pockets required No

Spacing per pocket m

Total pockets for day No

Total tonnage used tons

Total volume treated m3

Tons of material treated tons

Tons of cement required tons

Difference tons

Actual application rate %

Remarks:

Sketch plan:

150mm

Drum cut width 2.5m

C/line

CUT #2.S pread 17 00mm

14.37 - 14.0 = 0.37 UNDER APPLIED

14.0 / 2052.2 x 100 = 0.68 %

120 80 80

Width to be recycled and stabilised 5 750mm

23 March 2009Rehab of N2 Section 21, Kokstad

CONTROL SHEET FOR SPREADING BY HAND

14.0

280

LHS

50

10.38

830

1.7

4.25

CUT # 1.

CUT # 3.

800mm O/lap

S pread 17 00mm

800mm overlap

S pread 2500mm

0.2

282.2

2150

606.73

415.0

2150

0.2

606.73

0.70%

830 x 5.75 x 0.2 = 954.5

954.5 x 2.15 = 2,052.2

2,052.2 x 0.007 = 14.37

3

0.70%

NPC, Durban


6.25

50

6.92

DAILY ACTIVE FILLERAPPLICATION RECORD

LHS

1

SourceOPC in 50kg pockets

Light NE

Lane (see sketch) LHS

2

830

892.25

Required application rate 0.70%

2.5

2150

282.2

0.2

830

1.7

10.38

50

4.25

Published by theAsphalt Academyc/o CSIR Built EnvironmentP O Box 395Pretoria0001

First published in 2009

ISBN 978-0-7988-5582-2

Copyright © 2009 Asphalt Academy

DisclaimerConsiderable effort has been made to ensure the accuracy and reliability of the information contained in this publication. However, neither the Asphalt Academy nor any of the compilers of the document accept any liability whatsoever for any loss, damage or injury resulting from the use of this information.

TG 2Second editionMay 2009

ASPHALTACADEMY

Technical Guideline:Bitumen Stabilised Materials

A Guideline for the Design and Construction of Bitumen Emulsion and Foamed Bitumen Stabilised Materials

ASPHALTACADEMY

Asphalt Academy

CSIR Built Environment

PO Box 395

Pretoria

0001

South Africa

Tel: +27 12 841 2436

Fax: +27 12 841 2350

Email: [email protected]

www.asphaltacademy.co.za

Technical Guideline: Bitum

en Stabilised Materials

Second edition • May 2009