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TG 2 Second edition May 2009 ASPHALT ACADEMY Technical Guideline: Bitumen Stabilised Materials A Guideline for the Design and Construction of Bitumen Emulsion and Foamed Bitumen Stabilised Materials

Technical Guideline: ASPHALT Bitumen Stabilised Materials ... · 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

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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.

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

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

    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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  • �v

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

    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

  • v

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

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

    page

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

    page

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

    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

    page

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

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

    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.

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

    CHAPTER 1: Introduction – What are BSMs?

    2

    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

    (BSM-foam andBSM-emulsion)

    BSMs

    (BSM-foam andBSM-emulsion)

    BSMs

    Cement

    Presumed noteconomically

    viableLightlycementedmaterial

    High

    Intermediate

    Low

    None

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

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

    CHAPTER 1: Introduction – Layout and Purpose of Guideline

    3

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

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

    4

    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

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

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

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

    5

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

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

    6

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

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

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

    7

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

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

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

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

    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.

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

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

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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.

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

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

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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 t