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Technical Guideline:The use o Modied Bituminous Binders in Road Construction

TG1

Second edition

November 2007

ASPHALT

ACADEMY

Technical Guideline:

The use of

Modied Bituminous Binders

in Road Construction


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Published by theAsphalt Academy

c/o CSIR Built EnvironmentP O Box 395Pretoria0001

First published in 001

ISBN 978-0-7988-5572-3

Copyright 007 Asphalt Academy


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PREFACE

The publication o the rst edition o Technical Guideline N 1 (TG1): The use o Modied BituminousBinders in Road Construction in 001 was a major step towards achieving a unied approach to thespecication and use o modied binders in South Arica. The classication o modied binders intovarious generic classes which are, to some extent, polymer blind, is now rmly entrenched in theindustry.

Since the introduction o TG1 in 001, the modication o bituminous binders has become anincreasingly more dynamic eld. In addition, new modiers have been introduced into the roadconstruction sector and are being specied on a more regular basis. As a result, in 005 the Road

Pavement Forum (RPF) reconstituted a task group with a mandate to review the 001 edition and torevise the document to reect the improved knowledge obtained in promoting current industry best-practice.

This nd Edition (007) is the culmination o the task groups eorts. However, notwithstandingadvances made internationally and locally with respect to an improved understanding and predictiono the behaviour o modied products, the ultimate goal o speciying pure perormance-drivenproperties has not yet been ully realised. As a result, the product property requirements togetherwith their associated limits, as recommended in this document, are still largely empirically based.Nevertheless, the sections covering aspects such as HSE, selection criteria, design inuences as well asspecic construction constraints have been considerably expanded in order to assist practitioners in

optimising their use.

While it is elt that the requirements and/or limitations as recommended in this document shouldsuce in the majority o applications o these products, it is accepted that speciying agencieswith adequate experience may prescribe other limits based on their own specic circumstances,environment and experiences.


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ACKNOWLEDGEMENTS

On behal o the road construction industry represented by the RPF, AsAc wishes to acknowledge,with thanks, the time and eort given by the ollowing members o the Task Group responsible orcompiling this important guideline document or the industry:

DR Rossmann, SANRAL (Chair)TR Distin, SabitaTM Gilbert, Much AsphaltJA Grobler, Vela VKEKJ Jenkins, University Stellenbosch

J Lansdell, KenzamJG Louw, ColasCH Loots, SRTJ Muller, TosasDE Sadler, TosasLR Sampson, Asphalt AcademyBMJA Verhaeghe, CSIR Built EnvironmentIH Wiese, SANRALN Wilcocks, Basil ReadMP Zacharias, Shell

Some o the aspects incorporated into the original document were based on guidelines developedby Austroads and the Australian Asphalt Pavement Association (AAPA). Their permission to do so isgrateully acknowledged.


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SCOPE

This technical guideline covers the requirements or generic classes o homogenous (thermoplasticpolymers) and non-homogenous (bitumen-rubber) modied binders or use in hot mix asphalt,surace seals and crack sealing applications. It includes recommendations related to the appropriateselection criteria, product property requirements, HSE and quality control measures or theprocurement and application o modied binders.

Methods or the sampling, preparation and common test procedures o these products have beenincluded as an Appendix to the document. The intention is that these tests will be incorporated intothe South Arican National Standards (SANS) standard test methods or compliance with South Arican

National Accreditation Systems (SANAS) requirements.

It should be noted that aggregate selection, mix design, nal product composition and constructionlimitations are not addressed here. It is recommended that practitioners reer to the relevant manuals/guidelines, or appropriate research, covering these aspects. However, the scope o this documenthas been extended to include requirements or special applications related to uel resistance, bondcoats, high modulus asphalt and microsuracing. These were not previously covered under the genericspecication ramework.

Furthermore a protocol or conducting a eld evaluation or introducing new modied binderproducts is also provided as a guideline.

Similarly, proprietary products oering enhanced perormance criteria above that o the genericclasses proposed in this document are also not covered. It is expected that they would ollow acertication process such as Agrment, which could possibly include the provision o appropriateperormance guarantees.


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GLOSSARY OF TERMS

ASTM Method : The latest test method published by the American Society orTesting and Materials.

Base bitumen : Penetration grade bitumen o various grades conorming toSABS 307.

Bitumen-rubber binder : A blend o bitumen and rubber, containing, where necessary,extender oil and/or diluent, blended in such properties as tocomply with the prescribed requirements.

COLTO : Committee o Land Transport OcialsDiluent/cutter : A petroleum hydrocarbon distillate.

Elastomer : A thermoplastic polymer which producers mainly elasticproperties at in-service temperatures.Ethylene Vinyl Acetate (EVA) : An ethylene and vinyl acetate co-polymer.Extender Oil : A petroleum-derived material o high aromaticity.F-T waxes : High molecular weight waxes derived or the Fischer-Tropsch

processHomogenous binder : A blend o polymer and bitumen where two distinct phases

cannot be detected.Hydrocarbon modiers : Naturally occurring hydrocarbon products.Latex : Natural or synthetic emulsion containing rubber particles.Morphology : Chemical structure o a material.

Non-homogenous binder : A blend o modier and bitumen where there are two distinct,detectable phases in the nal product.Plastomer : A thermoplastic polymer where the elastic deormation is

accompanied by a component o permanent deormation.Rubber crumb : Vulcanised rubber, rom recycled pneumatic tyres that has

been reduced to small particles by mechanical means.Sabita : Southern Arican Bitumen AssociationSANS : South Arican National StandardsSANAS : South Arican National Accreditation SystemSHRP : The Strategic Highway Research Programme o the US Federal

Highway Authority.

Styrene Butadiene Rubber (SBR) : A random co-polymer o styrene and butadiene.Styrene Butadiene Styrene (SBS) : A di-block or tri-block copolymer o styrene and butadiene.Thermoplastic Polymers : Polymers that liquey and become malleable.

Reversible when heated.TRH : Technical Recommendations or Highways: Committee o Land

Transport Ocials.


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CONTENTS

1 INTRODUCTION 1

2 OCCUPATIONALHEALTH,SAFETYANDTHEENVIRONMENT 3

.1 Manuacture o modied binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Modiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Extender oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Adhesion agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

. Spraying operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 COMPOSITIONANDCHARACTERISTICS 53.1 Composition o bitumen modiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.1.1 Homogenous Binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.1. Non-Homogenous Binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1.3 Naturally Occurring Hydrocarbon Modiers . . . . . . . . . . . . . . . . . . . . . .103.1.4 High molecular weight waxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

3. Behavioural Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13..1 Rheology (ow behaviour) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133.. Elasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143..3 Cohesion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .153..4 Adhesion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

3..5 Ageing and durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173.3 Use o cutters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193.3.1 Factors aecting the cutting back o modied binders . . . . . . . . . . . . . . .19

4 MANUFACTURE 22

4.1 Homogenous binders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1.1 SBR modied bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1. SBS modied bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1.3 EVA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34.1.4 Hydrocarbon modied binders and high molecular weight waxes. . . . . . . .34.1.5 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

4. Non-homogenous polymer modied binder . . . . . . . . . . . . . . . . . . . . . . . . . .34..1 The Wet Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44.. The Dry Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

5 MODIFIEDBINDERCLASSIFICATION 26

6 PRODUCTREQUIREMENTS 28

6.1 Special Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346.1.1 Modied emulsions or microsuracings . . . . . . . . . . . . . . . . . . . . . . . .346.1. Hydrocarbon modied bitumen or high modulus asphalt. . . . . . . . . . . . .356.1.3 Modied binders or uel resistant suracings . . . . . . . . . . . . . . . . . . . . .36

6.1.4 Modied bitumen emulsion or tack coat . . . . . . . . . . . . . . . . . . . . . . .36

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7 SELECTIONCRITERIA 37

7.1 Suracing Seal Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377.1.1 Environmental inuences during application . . . . . . . . . . . . . . . . . . . . .397.1. Aggregate inuences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .407.1.3 Substrate inuences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .407.1.4 Project location and programming inuences. . . . . . . . . . . . . . . . . . . . .47.1.5 Trac inuences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47.1.6 Design inuences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437.1.7 Selection guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

7. Hot mix asphalt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .447..1 Resistance to permanent deormation (rutting). . . . . . . . . . . . . . . . . . . .467.. Cracking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .467..3 Mix type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .477..4 Design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .477..5 Production criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

8 CONSTRUCTION 48

8.1 Surace Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .488. Hot Mix Asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

9 QUALITYASSURANCEINSTORAGEANDHANDLING 509.1 Heating o modied binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.1.1 Hot-applied polymer modied binders . . . . . . . . . . . . . . . . . . . . . . . . .519.1. Polymer modied emulsions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59.1.3 Bitumen rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

9. Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .549.3 Quality assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .559.4 Site quality control plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58

10 SAMPLINGANDTESTING 59

10.1 Sampling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

10.1.1 Saety precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5910.1. Monitoring o product during handling. . . . . . . . . . . . . . . . . . . . . . . . .5910.1.3 Storage o samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6010.1.4 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

10. Testing o modied binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6110.3 Asphalt mix design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

11 PROTOCOLFORINTRODUCINGANEWMODIFIEDBINDER 62

11.1 Laboratory testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611. Field trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

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APPENDIX: Sampling and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

METHOD MB-1: Sampling o modied binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65METHOD MB-: Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67METHOD MB-3: Modied rolling thin lm oven test. . . . . . . . . . . . . . . . . . . . . . . . . . . .69METHOD MB-4: Elastic recovery o polymer modied binders by ductilometer . . . . . . . . . .71METHOD MB-5: Torsional recovery o polymer modied binders . . . . . . . . . . . . . . . . . . .74METHOD MB-6: Storage stability o polymer modied binders. . . . . . . . . . . . . . . . . . . . .77METHOD MB-7: Modied Vialit adhesion test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

METHOD MB-8: Pull out test method or suracing aggregate . . . . . . . . . . . . . . . . . . . . .80METHOD MB-9: Pliers test or assessment o adhesion properties. . . . . . . . . . . . . . . . . . .83METHOD MB-10: Ball penetration and resilience o bitumen-rubber blends . . . . . . . . . . . . .85METHOD MB-11: Compression recovery o bitumen rubber binders . . . . . . . . . . . . . . . . . .87METHOD MB-1: Flow test or bitumen-rubber binders . . . . . . . . . . . . . . . . . . . . . . . . . .89METHOD MB-13: Dynamic viscosity o bitumen-rubber binders. . . . . . . . . . . . . . . . . . . . .90METHOD MB-14: Particle size distribution and loose bre content o rubber crumbs . . . . . . .9METHOD MB-15: Resilience o rubber crumbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93METHOD MB-16: Bulk density o rubber crumbs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95METHOD MB-17: Sotening point o modied bitumen by ring and ball method . . . . . . . . . .96METHOD MB-18: Dynamic (Apparent) viscosity o polymer modied binders . . . . . . . . . . . .96

METHOD MB-19: Low temperature ductility o polymer modied binders . . . . . . . . . . . . . .96METHOD MB-0: Recovery o residue o modied bitumen emulsion . . . . . . . . . . . . . . . . .97METHOD MB-1: Viscosity o modied bitumen emulsions by means o the

Saybolt -Furol viscometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98METHOD MB-: Water content o modied bitumen emulsions . . . . . . . . . . . . . . . . . . . .98METHOD MB-3: Residue on sieving o a modied bitumen emulsions . . . . . . . . . . . . . . . .98METHOD MB-4: Particle charge o modied bitumen emulsions. . . . . . . . . . . . . . . . . . . .99

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LIST OF TABLES

LIST OF FIGURES

Table 1: Requirements or rubber crumbs or modiying bitumen. . . . . . . . . . . . . . . . . . . . 9Table : Composition o Bitumen Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10Table 3: Comparison o the composition o naturally occurring hydrocarbons. . . . . . . . . . . .11Table 4: Modied Binder Classication System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Table 5: Properties o hot applied polymer modied binders or suracing seals . . . . . . . . . .9Table 6: Properties o polymer modied emulsions or suracing seals . . . . . . . . . . . . . . . .30Table 7: Properties o polymer modied binders or hot mix asphalt . . . . . . . . . . . . . . . . . .31Table 8: Properties o bitumen rubber or suracing seals and asphalt . . . . . . . . . . . . . . . . .3Table 9: Properties o hydrocarbon modied binders or hot mix asphalt . . . . . . . . . . . . . . .33Table 10: Properties o modied binder crack sealants . . . . . . . . . . . . . . . . . . . . . . . . . . .34Table 11: Properties o polymer modied emulsions or machine-applied microsuracing. . . . .35Table 1: Advantages and disadvantages o modied binders compared with

conventional binders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Table 13: Minimum road surace temperatures or surace sealing . . . . . . . . . . . . . . . . . . . .40Table 14: Selection criteria or surace seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

Table 15: Common Binder Modiers and Additives used in HMA . . . . . . . . . . . . . . . . . . . . .45Table 16: Typical temperature/time limits or polymer modied binders . . . . . . . . . . . . . . . .5Table 17: Typical temperature/time limits or polymer modied emulsions . . . . . . . . . . . . . .53Table 18: Typical temperature/time limits or bitumen rubber. . . . . . . . . . . . . . . . . . . . . . .54Table 19: Test requencies or hot polymer modied binders . . . . . . . . . . . . . . . . . . . . . . .56Table 0: Test requencies or polymer modied emulsions . . . . . . . . . . . . . . . . . . . . . . . .57Table 1: Testing requency or bitumen rubber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Table : Sample monitoring during handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Figure 1: Typical eect o SBS on the sotening point o bitumen with dierentasphaltene contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure : Typical eect o F-T wax on viscosity over temperature. . . . . . . . . . . . . . . . . . . . 1Figure 3: The typical eect o various modiers on bitumen viscosity. . . . . . . . . . . . . . . . . 13Figure 4: The typical eect o various modiers on bitumen sotening point . . . . . . . . . . . . 13Figure 5: Typical orce-ductility curves or various modied binders. . . . . . . . . . . . . . . . . . 15Figure 6: Adhesion characteristics o latex modied emulsions. . . . . . . . . . . . . . . . . . . . . 17Figure 7: Typical viscosity o a binder over its working temperature range. . . . . . . . . . . . . . 18Figure 8: Schematic o a typical high speed bitumen rubber blender . . . . . . . . . . . . . . . . . 5Figure 9: Process ow or handling modied binders . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Figure 10: Typical changes in viscosity values or bitumen rubber at dierent

temperatures over time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

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1 INTRODUCTION

Modied binders have the ability to oer improved perormance over conventional binders, but arenot a solution or panacea or all situations. Benets that may be derived rom binder modicationinclude:

Improved consistency;Reduced temperature susceptibility;Improved stiness and cohesion;Improved exibility, resilience and toughness;Improved binder-aggregate adhesion;Improved resistance to in-service ageing.

However, irrespective o the improvement in binder characteristics, the undamental rules o mixdesign or hot-mix asphalt or surace dressings (including aggregate quality, mix stiness/exibilityand workability) should not be ignored.

Modied binders are generally more expensive than conventional binders; hence, their correctapplication does not lie in the simple substitution o conventional binders, but requires appropriatedesign o the nal product in order to maximise the benets appropriate to the specic need. Veryoten perormance requirements or routine situations can be met with the use o appropriateconventional binders. There are, however, particular situations where modied binders could oercost-eective solutions. Typical conditions where such binders should be considered are as ollows:

SuraceSealsIn areas o high stress such as heavy trac, steep inclines, intersections (modied tack coat orCape Seals) and sharp curves;In areas experiencing large daily/seasonal temperature uctuations or high ambienttemperatures or long periods;As a Stress Absorbing Membrane Interlayer (SAMI);For sealing over active cracks o up to 3 mm without pre-treatment (Stress Absorbing Membrane,SAM);In slurry seals or heavy duty applications (eg rut lling);In remote areas where improved durability is required.

Hot-MixAsphaltOn relatively highly exible pavements;In areas o high stress such as heavy trac, steep inclines, intersections and sharp curves;In asphalt bases which are subjected to high loading under slow moving trac;In areas experiencing large daily/seasonal temperature uctuations or high ambienttemperatures or long periods;In areas that are subjected to uel spillages;In open graded mixes requiring a high lm thickness;In areas where thin layer overlays are required.


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TackCoatAs a tack coat under very thin asphalt suracings to reduce the risk o de-lamination.

CrackSealingFor cracks wider than 3 mm;For highly active cracks.


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2 OCCUPATIONAL HEALTH, SAFETY

AND THE ENVIRONMENTHot modied binders are generally applied at higher temperatures than conventional binders to osetthe increase in viscosity. The concomitant use o extender oils and additives with higher temperaturestend to produce an increase in the umes. Hence, extreme care is required to reduce the workersexposure to these umes and it is the responsibility o the binder manuacturers to exclude the use oingredients which have known adverse eects on workers health. Similarly, it is the responsibility othe applicator to ensure that the relevant precautions as set out in the suppliers Material Saety DataSheet are ollowed.

The main hazards and dangers associated with the handling o modied binders are similar to thato conventional binders, namely the risk o workers being burnt when their skin comes into contactwith the hot product. To this end the wearing o appropriate Personnel Protective Equipment (PPE) isrecommended at all times when handling hot modied binders in order to protect workers againstbeing burnt.

Modied binders are handled below their minimum ash point requirement o 30C (Pensky-Martensclosed cup ASTM D93) and thereore i handled correctly present a low re risk. However the risk oa re or explosion occurring is increased i petroleum cutters are used to reduce the viscosity o thebinder or spraying or cleaning operations. For more details on Guidelines or the sae and responsible

handling o bituminous products reer to Sabita Manual 8.

21 Manuactureomodiedbinders

The blending o modied binders is usually carried out in a actory but may sometimes be carried outon site in a mobile blending plant. It is important that all the workers associated with the blendingand handling o modied binders undergo saety training in order to be made aware o the potentialhazards and dangers.

211 Modiers

The handling o the modiers used in the manuacture o modied binders requires special attention.The most commonly used modiers are:

Rubber crumbs;Styrene Butadiene Styrene (SBS) pellets or powder;Ethylene Vinyl Acetate (EVA) pellets;Styrene Butadiene Rubber latex;Natural hydrocarbon modiers;F-T synthetic waxes.

Care must be taken to ensure that the rubber crumbs are dry as the presence o moisture could lead

to a boil-over during blending with the hot bitumen. The addition o SBR latex into hot bitumen alsorequires special blending equipment to eliminate the entrapment o moisture which can result inexcessive oaming during the blending process. SBS and EVA polymers are very ammable and mustbe stored in a location where they will not be exposed to a source o heat or ignition.


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212 Extenderoils

Small quantities o extender oils are used in the manuacture o bitumen rubber and some SBS

modied binders. Some o these extender oils contain high concentrations o harmul PolycyclicAromatic Hydrocarbons (PAHs) and every precaution must be taken to reduce the exposure o workersto ume inhalation and/or skin contact.

213 Adhesionagents

It is becoming more common or chemical additives to be incorporated into the binder to improve theadhesion characteristics o relatively highly modied binders, or where dicult aggregates are to beutilised. Inormation on the composition and handling conditions or these agents must be obtainedrom the suppliers as certain additives could be toxic.

22 Sprayingoperations

The spraying o bitumen rubber or hot polymer modied binders by hand is not recommended as thespray temperature o the product is in the region o 00C. In the event that small areas need to besprayed during the application o hot modied binders, then a sprayer which allows individual nozzlesto be cut o should be used. Alternatively, the use o low viscosity emulsion (SC-E1) modied binderswith binder contents in the range o 6568% are recommended as the required product applicationtemperature is only 60C.

I the modied binder has to be cutback due to the onset o cooler weather, then the blending othe cutter should be undertaken in a blending plant. In the event that the latter is not practical, thenthe cutting back o hot binder in a sprayer on site should only be permitted i a method statement isprovided by the binder supplier or undertaking this operation.

No heating o the product should take place during transportation or spraying operations. The heatingo the product must only take place:

In a storage tank, a stationary haulier or sprayer whilst under supervision.When the ue pipes are covered by at least 00mm o product and the product is beingcirculated.

I a load is discharged within an hour, the burners must be switched o and the product circulated or

an hour beore commencing the spray work.

Heating o uncovered burner ue pipes must be prevented as this will cause sel ignition o the vapourspace resulting in an explosion.

Drip trays should be used on site or testing spray bars. The sprayed product in the drip tray mustbe sucked back immediately into the spray tanker or reuse. Any spillages that occur during producttranser or due to leakages and the associated waste products resulting rom the cleaning upoperations (eg soiled bituminous paper) must be collected and disposed o at a legal waste disposalsite. Contact Sabita or visit www.sabita.co.za or a list o waste disposal sites to identiy the site closestto the project.


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3 COMPOSITION AND CHARACTERISTICS

Bituminous binders behave dierently under dierent temperature and load conditions. At lowertemperatures or short duration o loading, the binder tends to be sti and elastic while at highertemperatures or prolonged loading, there is more ow or plastic behaviour. At intermediate caseso temperature and loading, the binder will act as a combination o the two behaviour conditions.Further details o the viscoelastic characteristics o bitumen can be ound in Sabita Manual .

Similar to conventional binders, the physical properties o modied binders are largely controlled bythe undamental properties related to temperature, viscosity and phase transition. The purpose o themodier is to extend the plastic phase and depending on the type, concentration and modier used,

the viscoelastic range will vary. Modied bitumen provides the technology to produce a bituminousbinder with improved viscoelastic properties which remain in balance over a wider temperature rangeand loading conditions.

There are our distinct modes o interaction between bitumen and modiers:The modier is present as a separate phase within the bitumen.The bitumen is present as a separate phase in the modier and the product will display theproperties o the modier rather than the bitumen.The modier will orm an interace with the bitumen giving greater elasticity due to changes inthe mechanical structure o the material.The modier will orm a molecular bond with the bitumen giving greater elasticity and stiness

to the material.

31 Compositionobitumenmodiers

Modied binders have been divided into the ollowing two broad compositional groups:

Homogenous binders which are dened as a blend o polymer and bitumen where two distinctphases cannot be detected on a microscopic level, or, where the two phases are interwovento such an extent that the material behaves as a single-phase material rom a small, localisedviewpoint. Examples o homogenous binders are EVA, SBR and SBS polymer modied binders;Non-homogenous binders are where there are two distinct, detectable phases and where there

will be localised dierences in properties depending at what stage a test is perormed. Bitumen-rubber alls into this category as it consists o rubber crumbs partially dissolved in a bitumenmatrix.

They can also be considered in two distinct areas; those which are hot applied and those which arecold applied either by emulsiying and/or cutting back.

In terms o hot applied modied binders, polymer modication and rubber modication was untilrecently the only two types o modication considered. However, in recent times, naturally occurringhydrocarbons (with high asphaltene contents) and long chain, high molecular weight paran (poly-alkanes) components are also used to introduce other unique eatures into the rheological behaviouro bituminous binders and will be considered separately in this chapter.


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Cold applied products in the orm o bitumen emulsion or cutback bitumens are also available or usein the road building industry. Only bitumen emulsions are normally modied to improve the residualbitumens viscoelastic properties. Cutters are sometimes added to hot binders to reduce their viscosity

and improve their ability to wet the stone aggregates during chip and spray applications in coolerweather conditions.

The homogenous polymer modiers typically used in bitumen modication are thermoplasticpolymers such as:

Styrene-butadiene-styrene (SBS) block copolymers (Elastomeric).Synthetic styrene-butadiene-rubber (SBR) latex (Elastomeric).Natural rubber latex (Elastomeric).Ethylene-vinyl-acetate (EVA) block copolymers (Plastomeric).

The non-homogenous bitumen rubber utilises crumbed rubber rom recycled tyres.

For cold applied products, the rheological properties o bitumen in the emulsion can either bemodied by the pre-modication o bitumen or by the post-modication o the bitumen emulsion.In South Arica, the post-modication o the bitumen emulsion is the most popular practice. Naturalrubber or synthetic rubber latexes such as SBR or SIR (Styrene Isoprene Rubber) can be used toimprove the properties o bitumen in the various applications.

Each o the dierent types o modied bitumens will be discussed separately in order to describe thebenets and sensitivity to use o each o the various modiers.

NOTE: MODIFICATION OF FOGSPRAY EMULSIONS IS NOT RECOMMENDED.

The latex emulsion breaks rst, orms a skin and prevents the bitumen emulsion rom breaking. Thiscauses the rubber to lie on top o the road surace, where it is picked up by trac.

311 HomogenousBinders

Styrene-Butadiene-Styrene(SBS)

SBS is a block copolymer and can be classied as either linear or radial. A radial blocked copolymerresults in much higher viscosities and sotening point or the same addition o polymer making itmore dicult to mix with bitumen, compared with the linear block copolymers.

SBS can be considered as a thermoplastic rubber and is characterised by its glass transition point (Tg).

Coherent cross-linking points provide high stinesses below the glass transition point. The process isreversed by melting (> 100C) the copolymer which causes it to dissociate, become sot and start toow. On cooling the copolymer, it regains strength and elasticity.

Styrene and butadiene are mutually incompatible and attempt to separate in the modied bindermix. However, as the copolymers are chemically linked, styrene end blocks agglomerate and ormthree dimensional cross-linked polystyrene domains which give the polymer mechanical propertiescomparable to cross-linked rubber (vulcanisation). Since the cross-linking is physical rather thanchemical, the process is reversible.

At elevated temperatures above the glass transition point o the polystyrene domains, the physical

cross-links dissociate. On cooling, the domains reorm and the physical cross-links with longcontinuous elastic networks reorm and are restored within the bitumen.


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SBS absorbs the maltenes in the bitumen, swells and, at higher dosage levels, orms a continuousmolecular network in the bitumen phase which makes up a major raction o the bitumen by volume.At lower concentrations (3 to 4%) the SBS will only orm a ragmented molecular network. At higher

concentrations (4 to 6%) a continuous network orms which results in a dramatic increase in thesotening point. The molecular networks increase the elastic component o bitumen which assistswith recovery ater deormation. As the SBS content is increased, the elastic recovery also increases.

The eect that an increase in the amount o SBS polymer on the sotening point o a base bitumenwith varying asphaltene contents is shown in Figure 1. The rate o increase in the sotening point andthus, the shape o the curve, is dependent mainly on the asphaltene content o the base bitumen, thetype and grade o the SBS polymer and the percentage thereo. Typically, the curve assumes an S-shape as the SBS structure changes rom a ragmented orm to a continuous network in the modiedbinder.

Softeningp

oint

SBS content

Asphaltene content

Figure 1: Typical eect o SBS on the sotening point o bitumen with dierent asphaltene contents

There is a direct correlation between elastic recovery and deormation resistance in that an increasein elastic recovery provides or better deormation resistance. Cohesive strength also increases withthe increased elastic recovery. SBS hot modied binders are generally preerred to SBR due to therehigher sotening points and higher elastic recovery properties, which in turn can be applied at lowertemperatures as a result o there lower relative viscosities.

At low temperatures, the addition o SBS improves the exibility o the bitumen which inhibitscracking and improves the resistance o the binder to crack reection.

Styrene-Butadiene-Rubber(SBR)

SBR latex consists o styrene butadiene polymer which is emulsied with a solids content greaterthan approximately 50% depending on the grade. The SBR latex is manuactured through thecopolymerisation o the hard styrene monomer and the sot butadiene monomer. The butadienecontributes to the elasticity and makes the binder more exible whereas the styrene gives stinessand strength to the material.


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The mechanical bonding mechanisms and chemistry o SBRs is very similar to that o SBS with theexception that during the co-polymerisation o the butadiene, the poly-butadiene molecules arenot blocked by the polystyrene at both ends o the elastomeric butadiene strands. In this case, the

polystyrene and poly-butadiene is intermingled and thereore, to a large extent, cross-linking pointsare absent.

SBR latex is used in both hot and cold modied binders. However, the emulsier type becomes veryimportant when selecting the SBR-latex or the modication o bitumen emulsions. Anionic latexemulsiers are used with anionic emulsion and similarly, cationic latex emulsions are used withcationic bitumen emulsion grade.

SBR modied binders are predominantly used in cold applied binders or seals, bond coats, cracksealants and microsuracings. Hot modication o bitumen with SBR is still commonly used or sealsand to a lesser extent in asphalt. With the modication o hot bitumen the amount o SBR latex that

can be added is limited by:the rapid increase in the binders viscosity which is in turn restricted by the spray temperature;andthe evaporation o the water content o the latex when blending with the hot bitumen.

SBR polymers improve adhesion o the binder with the aggregate in sealing applications whichresults in better chip retention. It also provides improved elasticity and exibility to the binder, sealscracks and prevents water ingress into the pavement. In hot mix asphalt applications they reduce thedeormation resistance, enhance atigue properties and retard crack reection.

NaturalRubber

Natural rubber latex consists o polymerised isoprene monomers which increase the elasticity o thebitumen. However, the natural rubber latex is more sensitive to heat and is thereore mainly usedin the modication o cold bituminous binders. The addition o latex to emulsion also provides anexcellent cold product which can be used or the sealing o small cracks less than 3mm width.

EVA(Ethylene-Vinyl-acetate)

EVA is a polymeric plastomer which consists o two monomers ethylene and vinyl-acetate (VA). Thetwo monomers orm long crystalline molecular strings which dissociate when the temperature isincreased above the materials glass transition point.

The morphology o EVA is semi-crystalline and interconnected by polyethylene crystalline molecules

and vinyl-acetate molecules which orm amorphous chains contributing to the exibility.

The polyethylene provides the stiness to the material with cohesion provided by the crystallinity andchain length. The copolymers are polar and together with the maltenes rom the bitumen will dictatethe compatibility and adhesive properties o the binder. The ollowing main parameters control theproperties o EVA:

VAcontent: The more the VA content increases, the higher the proportion o rubbery regions(ie an increase in exibility) and the lower the proportion o crystalline regions (ie a decrease instiness).Molecularweight: Standard practice or EVAs is to measure melt ow index (MFI); the higherthe MFI the lower the molecular weight and viscosity.


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EVA modied bitumens have the ability to provide improved resistance to rutting in hot-mix asphaltcompared to conventional bitumen along with improved compatibility, saer handling and betterworkability compared to the SBS and SBR modiers. Some grades o EVA also increase the resistance

to damage caused by uel spillages and pose no problems with uture recycling o the material.However, it should be noted that the properties o EVA vary or dierent grades depending on thechain length and molecular weight o the polymer, the vinyl acetate (VA) monomer content and thecrystallinity. In terms o the EVAs the VA content and melt ow rate (MFR) are as important as theStyrene content and linear or radial structure in SBSs, when determining specic properties.

EVA modied bitumen is also more heat stable and does not deteriorate at elevated temperaturesduring storage as ast as SBR and SBS modied bitumen products. Storage stability will thereore bebetter than that o SBS and SBR.

312 Non-HomogenousBinders

BitumenRubber

Bitumen rubber products combine rubber crumbs (with a specic, grading, morphology andcomposition) with bitumen at high temperatures to achieve a complex two phase product whichhas both the elasticity and stiness o tyre rubber, and the ow characteristics o bitumen. However,it is important to note that the type o tyre rubber varies depending on the sources and make o thetyre. The natural rubber and synthetic rubber content will also vary depending on the source. Themorphology o the rubber particles signicantly inuences the composition o crumbed rubber atermechanical grinding. Table 1 shows the requirements or rubber crumbs or modied bitumen.

Table 1: Requirements or rubber crumbs or modiying bitumen

Property Requirement TestMethod

Sieveanalysis (% mass)Passing screen (mm)1.1800.6000.075

10040 -700 - 5

MB - 14

Poly-Isoprenecontent (%m/m totalhydrocarbon)

5 min Thermo Gravimetric Analysis

Fibrelength (mm) 6 max

Bulkdensity (g/cm) 1.10 1.5 MB - 16

The rubber crumbs and bitumen are blended at a temperature in excess o 180C and involves theabsorption o some o the maltene-raction o bitumen into the rubber. The rubber particles swellwith some becoming totally digested by the bitumen, but most are only partially digested andincreases the viscosity o the bitumen dramatically.

Digestion o the rubber is a continuous process and occurs at a higher rate at higher temperatures.Should the rubber crumbs become totally digested by the bitumen, the desired properties that therubber crumbs give to the bitumen will be lost. Hence, special care is required during the manuacture


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and application o bitumen rubber. The product will have a shel-lie that varies depending on themanuacturers technology, time and temperature at which the product is stored.

When the bitumen rubber blend cools down the course rubber particles orm a rubber networkwhich is lled with bitumen and it is the rubber network that contributes to the improved cohesion,elasticity, exibility, re-healing capabilities and strength o the material. Bitumen rubber has beenused successully in seal and hot-mix asphalt applications due to its improved elasticity and stinessand can be used as a stress absorbing membrane interlayer (SAMI). The stone retention properties,resistance to bleeding and resistance to deormation are also enhanced.

The typical composition o bitumen rubber is shown in Table . However, the ratio o componentsvaries depending on the bitumen source, the climatic conditions and the application. With theaddition o extender oil the maltenes in bitumen remains virtually unaected and improves theatigue and durability characteristics o the binder. The requirements o the extender oil are such that

it should have a ash point o greater than 180C and the percentage by mass o aromatic unsaturatedhydrocarbons be greater than 55.

Table 2: Composition o Bitumen Rubber

Component %bymass

Bitumen 80/100 7-8

Extender oil 0-4

Rubber crumbs 18-4

The rubber crumbs also contain other components that may improve the properties o bitumen. Forexample, the crumbs contain in excess o 30% carbon black which has been shown to add reinorcingproperties to bitumen and antioxidants in the rubber contribute to the durability o bitumen rubber.

313 NaturallyOccurringHydrocarbonModiers

Naturally occurring hydrocarbon products are mainly used to reduce the temperature susceptibility oasphalt mixes by increasing the sotening point, stiening or hardening the bitumen giving increased

viscosity and reduced penetration values.

North American Asphaltum is a natural, resinous hydrocarbon ound in Utah, USA, soluble in aromaticand aliphatic solvents and is requently used to harden petroleum products. The black, shiny,ree-owing, granular substance is brittle and easily crushed into a dark brown powder that is ullycompatible with bitumen, has a high asphaltene (71%) and nitrogen (3%) content and essentiallysulphur-ree (0.3%). It is 99% pure in its natural state, is low in toxicity and is non-carcinogenic.

South American Asphaltums originate rom Argentina and are natural bitumens o high purity,composed o hydrocarbons, asphaltenes and aromatics o high molecular weight. Table 3 shows acomparison o the composition between Asphaltums and a typical bitumen.


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Table 3: Comparison o the composition o naturally occurring hydrocarbons

Component% Asphaltum

ExNorthAmerica

Asphaltum

ExSouthAmerica

TypicalBitumen

Asphaltenes 71 >80% 8-18

Resins & Aromatics 7High molecular weightaromatics

70-90

Saturates 4-10

Asphaltum can provide increased mix stability, helps to reduce rutting and shoving because it

increases the load bearing capability, reduces temperature susceptibility o hot-mix asphalt, improvedaggregate adhesion and improved resistance to water stripping. It is ully compatible with bitumenallowing or good stability in storage.

314 Highmolecularweightwaxes

In general, practitioners will not generally consider waxes or use in bitumen. However, there is a verydistinct dierence between wax derived rom a crude source and the high molecular weight waxesrom the Fischer-Tropsch (F-T) process which are used as bitumen modier.

The F-T waxes are long carbon chain alkanes or iso-alkanes which originate rom the coal gasication

process. The chain lengths o these waxes are between 40 and 100 carbon atoms compared to crudewax with typical carbon numbers between 0 and 40 carbon atoms.

The F-T waxes acts as a ow improver and have the ability to reduce the viscosity o the modiedbitumen during mixing and compaction o hot-mix asphalt and do not have a negative eect on thebitumens characteristics at low temperatures.

At service temperatures below 80C the F-T waxes increase the sotening point and decrease thepenetration value, improving the high temperature perormance and deormation resistance o hotmix asphalt.

Figure shows the eect o viscosity change o F-T wax modied binder compared to a conventionalbitumen over the in-service and application temperatures zones.


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Viscosity

Temperature

Application temperature

F-T wax modied bitumen

Bitumen

In-service temperature

Figure 2: Typical eect o F-T wax on viscosity over temperature

The F-T wax modied bitumen has good aggregate adhesion, provides satisactory stiness at thehigher operating temperatures and resistance to cracking at low operating temperatures. It also hasthe ability to allow or lower compaction temperatures through the reduced viscosity o the bitumen,yet it produces a bituminous binder that has a much higher stiness at high service temperatures thanconventional bitumen. F-T modied bitumen is also uel resistant.

The F-T waxes are completely compatible with bitumen and are stable in storage. They can also beused as a co-modier with polymer modied bitumen to produce hybrid products that could betailored or specic engineering requirements to improve the long-term perormance o asphaltpavements.

32 BehaviouralCharacteristicsThe main purpose o bituminous products is:

To act as an organic glue and water proong agent when combined with naturally occurringinorganic stone and sand.To provide appropriate behavioural characteristics to the materials in service that will improvetheir ability to withstand the environmental conditions to which they may be exposed.

The most important characteristics that will be considered are:RheologyElasticity

CohesionAdhesionAgeing and durability


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321 Rheology(owbehaviour)

Rheology is the study o the ow and deormation behaviour o materials. Bituminous binders

behave as visco-elastic materials, with their behaviour inuenced by the loading time as well as thetemperature. At high temperatures or long loading times, binders behave as viscous liquids, andconsequently produce large permanent deormation. At low temperatures or short loading times,binders behave as elastic (brittle) solids, with most deormation recovered at the end o the loadingperiod.

The rheology o unmodied binders is relatively simple, and behaviour can be predicted through theuse o simple tests such as Penetration, Sotening Point and Viscosity at various temperatures. Therheology o modied binders on the other hand is highly complex, and, although the results romconventional tests may indicate a signicant improvement in properties, the in-service perormance othese binders is not easily categorised. The typical inuence o type, as well as amount o modier on

viscosity and sotening point properties is shown in Figures 3 and 4, respectively.

Viscosity

Polymer content

SBR

SBS

EVA

F-T wax

Figure 3: The typical eect o various modiers on bitumen viscosity

Softeningp

oint

Polymer content

SBR

SBS

EVA

F-T wax

Figure 4: The typical eect o various modiers on bitumen sotening point


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Selection o polymer type and grade as well as the amount will be dictated largely by the need tosatisy the minimum sotening point requirement as well as achieving the specied applicationviscosity within the recommended maximum temperature limits, to prevent degradation o the

product. This certainly is the case with SBR modied binders, as can be seen in Figures 3 and 4, andusers must be cautioned that by increasing the amount o polymer to meet the minimum soteningpoint requirement will lead to a concomitant dramatic increase in the viscosity rendering the nalproduct dicult to apply.

Experience has shown that there is a general tendency or the sotening point values o polymermodied binders to decrease in storage over time. Where long haul distances, or lengthy delays, areexpected, it may be necessary to slightly increase the percentage o modier added. When assessingthe acceptability o this product property (as with any other properties) cognisance should always betaken o the inherent standard deviation applicable to the test method.

Unlike conventional bitumen which displays Newtonian behaviour above its sotening pointtemperature, modied binders tend to display shear thinning behaviour thus rendering dynamicviscosity measurements at normal shear rates o limited useulness, particularly below applicationtemperatures. Thus the use o the standard protocol o the Brookeld viscosity test at one shear rateto determine asphalt mixing and compaction temperatures or modied binders is not appropriate.Using the viscosity limits commonly used or conventional binders, based on a single shear rate, leadto too high temperatures when compared to eld experience and producers recommendations. Theinternational tendency is to replace the Brookeld test with the Low Shear Viscosity test to determinetemperature viscosity measurements at low shear rates. There is also a concept or using the DynamicShear Rheometer to determine dynamic viscosity at a specied shear stress or estimating the mixingand compaction temperatures or modied binders.

In most instances, the addition o a polymer results in the binder having lower moduli at lowtemperatures, and is thereore more exible. At high temperatures, however, the binder exhibits animproved stiness and elasticity when compared to the unmodied bitumen. The most commonway o measuring rheological properties was through the use o the Dynamic Shear Rheometer(DSR), which applies a range o shear stresses at various requencies (loading time) and temperatures.However there are serious doubts about the use o the complex modulus and phase angle or accurateprediction o the eect o modied bitumens on rutting resistance. The ailure o these parametersto take into account the asymmetric behaviour o the stiness during loading and unloading o amodied binder or a variety o loading intensities and temperature conditions has lead to a searchor a more reliable test to replace the protocol o modulus and phase angle used in the DSR or to

amend the DSR measurement with an elastic recovery test. A creep and recovery procedure called theMultiple Stress. Creep and Recovery (MSCR) has been introduced as an AASHTO standard in early 007.

322 Elasticity

Elastic behaviour indicates that the binder recovers most or all o its initial shape when the load thatcaused the deormation is removed. The elastic recovery o a binder is commonly used to measurethe atigue resistance o a binder or its ability to absorb large stresses without necessarily crackingor deorming. Particular modiers have unique elastic recovery characteristics depending on themorphology o the modier/binder system. For example, SBS orms a three-dimensional networko highly elastic, butadiene chains connecting sti styrene domains, resulting in very high elastic

recoveries. SBR has random styrene/butadiene molecules, resulting in relatively lower elastic recovery.EVA orms a rigid three-dimensional network, imparting no elastic recovery properties to the basebinder but provides a high stiness.


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The elastic property o a binder is generally inuenced by the type o modier as well as the degree omodication and is determined by measuring the recovery o a sample which has been extended in alow temperature ductilometer. In general, there is a direct relationship between elastic recovery and

the degree o modication.

323 Cohesion

Cohesion is a measure o the tensile stress required to break the bond between molecules o thebituminous binder. The inherent strength, tenacity and toughness o the bituminous binders areimproved by modication with thermoplastic polymers and rubber crumbs. Hence, a greater orce ortensile stress is required to break the molecular bonds o modied binders and cause ailure comparedwith a lower tensile stress required to break the bonds o conventional binders.

A orce-ductility test is used to determine the cohesive strength o a modied binder and involves the

elongation o a sample with the orce measured at very small elongation intervals. Figure 5 shows agraph o the typical prole o various modied binder types obtained during the test.

Force

Ductility

EVA modied bitumen

SBR modied bitumen

Bitumen

F-T wax modied butimen

Figure 5: Typical orce-ductility curves or various modied binders

As shown in Figure 5, the maximum orce is reached early in the elongation process. The elastic phaseis represented by the area beore the initial peak and the total area under the curve can be used

to calculate toughness. This is a good indication o the energy required to extend the binder andthereore provides a good estimation o resistance to cracking.

The energy required to elongate elastomeric modied binders is generally signicantly more than thator conventional binder. Plastomeric modied binders will impart stiness to the bituminous bindersbut not necessarily improve its cohesive nature. Such modied binders may well perorm in a brittlemanner in tension.

The cohesive properties o modied binders provides guidance to practitioners related to how soonater construction a seal could be opened to trac as well as providing an assessment o the ability othe binder to withstand shear stresses imparted by heavy trac.


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324 Adhesion

Adhesion is the measure o the stresses required to break the bonds between the bituminous binder

and mineral aggregate. It is largely dependent on the physical chemistry as well as the chemicalnature o the bituminous binder and aggregate type when combined or application.

The ollowing actors have an impact on adhesion at the stone/bitumen interace:The presence o dust and/or moisture which could reduce adhesion at the bitumen/aggregateinterace.The level o modication that inuences the viscosity o bitumen which in turn aectsthe wetting ability or time to coat the road stone with bituminous binder. Wetting is aninstantaneous process but i the viscosity o modied binder is too high during application,wetting takes longer and poor adhesion can be expected.Ambient road and air temperatures and, especially overnight temperatures. Temperature related

adhesion ailures o suracing seals are typically associated with two actors:For homogenous modied binders, the higher the level o modication, the higher the risko adhesion ailure due to decreased wetting ability and increased stiness.At colder temperatures, the higher stiness o the binder results in a decreased adhesion.

By increasing the lm thickness o the binder layer the adhesion is improved. The lm thickness o thebinder layer can be increased by;

Reducing the time-lag between the binder application and the stone application in suracingseals.Using pre-coated stone.Using emulsion cover (og) sprays to increase or correct the nal binder application rate.

Pre-blending an adhesive agent with the modied binder prior to spraying.

Temporary reduction o the viscosity by the addition o cutters during colder weather conditions alsoimproves the adhesion properties. However, care should be taken in areas with hot humid climatesand/or heavy trac conditions.

It should also be noted that dierent types o aggregates exhibit dierent adhesion behaviourdepending on the chemical nature o the parent rock in terms o its hydrophilic (water-attractive) oroleophobic (oil-repelling) nature. Depending on the chemistry o the parent rock, the nature o theaggregate could vary. However, bitumen is oleophilic (oil-attracting) or hydrophobic (water-repelling).Thereore, based on the inherent character o the aggregate it may or may not react (orm chemical,

charge-related bonds) with water but the presence o water will have a negative inuence on theadhesion properties and it will repel the bitumen.

Acidic aggregates are more hydrophilic than basic aggregates. Acidic aggregates will thereore havepoor adhesion properties in the presence o water. Cationic spray grade emulsion overcomes thistendency when the ree electrons on the aggregate orm physical/electrical bonds with the positivelycharged bitumen and SBR latex droplets as shown i Figure 6.

Similarly and, especially in high risk applications and under dicult construction conditions, suraceactive chemicals in commercially approved adhesion promoters and pre-coating uids have beenused eectively to improve the adhesion properties. However, i these are used in conjunction with

bitumen emulsions in the construction o a suracing seal, they are known to retard the breakingcharacteristics o the emulsion.


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Strong chemical

attraction

Aggregate

Bitumen droplet

Latex droplet

Figure 6: Adhesion characteristics o latex modied emulsions

325 Ageinganddurability

The change in properties o bituminous binders over time is termed ageing and is normally expressedas the dierence between the original properties and the derived properties exhibited over time.Typical actors aecting the ageing o bituminous binders are the temperature and time-relatedconditions which results in a change in the viscoelastic behaviour. In-service ageing describes thehardening (increase in stiness and reduction o elastic properties) o a binder during its lie on the

road when exposed to constant trac and ultra-violet radiation.

Degeneration and adverse changes in the properties o modied binders are also observed whenbituminous products are stored at high temperatures. Durability o bituminous binders thereorerelates to the ability o a particular binder in a specic application to resist the negative inuence oageing.

Temperaturesusceptibility

This is characterised by the variation in consistency (stability) o the bitumen related to temperatureand is governed by the sotening point at high temperatures and the ragility point at lowertemperatures. The window between the two extremes is called the service temperature o the

bitumen with the two extremes being dependent on the crude source and bitumen grade. Shouldthe binder be exposed to temperatures above the sotening point bleeding/rutting could occur andbelow the ragility point, cracking may be observed (see Figure 7).


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Consistency

Temperature

Bitumen

Required binder

Solid

Fluid

too sti = cracks

too soft = ruts,

bleeding, shoving

too viscous = not

workable

Bitumenperformance

range

Required

performance

range

Figure 7: Typical viscosity o a binder over its working temperature range

By adding polymers to bitumen the in-service temperature range is widened. The increased stinesscompared to conventional bitumen enhances the perormance characteristics o the modiedbitumen and provides better protection against increased trac loads and adverse climate conditions.

In addition, thinner asphalt layers could be considered during design and construction/rehabilitationto reduce the cost o the pavement.

Bitumen rubber, SBS and SBR materials are generally sensitive to oxidation and thermal degradation.It is thereore important to careully monitor temperature during all stages rom production, storage,mixing and the laying o these modied materials.

Compatibilityandstability

Chemical compatibility relates to a stable homogenous blend which is important during handling andstorage. The polymers must be chemically stable at the standard bitumen processing temperatures.

The denition o compatibility is the ability o a polymer to remain distributed in the bitumen withoutphase separation occurring. However, the degree o compatibility varies by bitumen and by type andgrade o polymer used in the ormulation o the polymer modied product. Compatibility also varieswith concentration o the polymer and the higher the concentration o the polymer, the lower thedegree o compatibility. Should total incompatibility occur, this could result in segregation and evengelling.

In the modied bitumen there is competition between the modier (rubber crumbs, SBS or SBR) andthe naturally occurring asphaltenes or the available maltene portion (resins and aromatics) o thebitumen. This competition varies with the type and source o both the bitumen and the polymer andthis will aect the compatibility o the nal product. Thereore any changes in the crude type andrening process used during the manuacture o the base bitumen could aect the compatibility othe polymer bitumen system.


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The stability or homogeneity test as described in MB-6 is used to determine the hot storage stabilityo a material which, in eect, is an indication o compatibility. The use o mechanical stirring willprevent the segregation o the dierent components during storage. As a guide to manuacturers,

the stability test should be used as an indicator o whether stirring is required or not. The tests shouldbe conducted to determine the suitability o the base bitumen with the polymer. Whenever there isany reason to believe that the chemistry o the base bitumen has changed, the test should also beconducted.

33 Useocutters

As discussed in the previous sections, modication o bitumen with polymers or rubber crumbstends to increase the binders cohesion and render them more viscous at the expense o reducing thebinders ability to wet the aggregate, resulting in the possible reduction o adhesion between thebinder and stone. The reduction in adhesion could become critical when constructing a seal duringcooler weather conditions. It is not uncommon or some modied binder seals to perorm adequatelyin warm and dry conditions but lose a considerable portion o aggregate during the rst cold wetweather i appropriate work practices are not adhered to.

Polymer modied binders are normally produced with 80/100 penetration grade bitumen. Duringlower temperature conditions it is necessary to soten the binder by utilizing an appropriatehydrocarbon cutter, such as illuminating paran, to prevent stone loss by improving the adhesionproperties o the binder and promoting the early ormation o a stable mosaic o aggregate.

It is also possible to manuacture the binder with 150/00 penetration grade bitumen, but this gradeis unortunately not always available rom the reneries and it may also, to some degree, negate theimproved in-service perormance properties required o the binder. For light trac conditions themodied binders can be sotened with up to 5% cutter by volume o binder, but or heavier tracconditions it is recommended that not more than 3% cutter be added.

From a saety perspective, the practice o cutting back hot binders is a hazardous operation as theblending temperature o the binder is well in excess o the cutters ash point. Ideally, this operationshould only be undertaken under controlled conditions such as in a blending plant. However, ithe blending o the cutter has to be undertaken on site in a sprayer, then the binder supplier mustproduce a written method statement o his blending procedures or cutting back modied bitumen.

It should also be noted that there is always the real risk that the use o a cutter can lead to bleedingo the newly constructed seal with the onset o warmer weather conditions under heavy trac. Thusspecial care must be taken o all the actors that could aect the perormance o the new seal i themodied binder is cutback.331 Factorsaectingthecuttingbackomodiedbinders

The ollowing actors will inuence whether it is necessary to cut back binder and provides guidanceon the appropriate quantity o cutter to use.

Roadsuracetemperature

The road surace temperature at time o spraying and the projected temperature or the next 4 hoursis a critical actor with respect to risk o early stone loss. I the trac spectrum dictates that the use ocutters would be inappropriate then no spraying o hot modied binders should be done i:


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The expected maximum road temperature does not exceed 30C or several hours during theapplication period. Sealing should only commence when the road surace temperature reaches5C and continues to rise above 30C; or

The expected minimum air temperature in the ollowing 48 hours is expected to drop below10C. To this end the weather orecast or the ensuing week should be obtained to ensure thatthe minimum temperatures are not expected to all below this value.

Shadyareas

Where the road will be in shade during the day it is likely that the maximum road temperature in theshaded area would be below 5C. In such locations cutting back should be considered providedthat the areas are large enough. However, these areas are oten isolated in comparison to the overallproject e.g. areas under bridge decks and thus the ollowing options are recommended in place ocutting back:

Increase the binder application rate by up to 0% or large areas. Otherwise, split the binder

application by reducing the application rate o the tack spray and spraying a diluted emulsion asa cover spray.Start the application in the shaded areas and ensure that the distance between the sprayer andchip spreader is kept to a minimum.Where a signicant length o the project is expected to be in shade, consider using an emulsionor the project and covering the seal with no-nes grit ater the emulsion has broken and keepthe shaded areas o the road closed to trac or 48 hours. Care must be taken when usingmodied emulsions in cooler locations because the latex in the emulsion orms a skin whichinhibits the breaking process.

Timeotheyear

Cutting back o binders should not take place later than the beginning o September because it cantake up to 3 months or the volatile ractions o the cutters to evaporate rom the layer. The amounto cutter used should also be tapered o with the onset o warmer weather as spring approaches. Assome areas in South Arica experience night temperatures below 10C in March it is recommendedthat the minimum temperatures rom the closest weather station or the preceding 10 year period beobtained prior to making any decisions as to whether to cutback or not.

Typeosuracing

The type o suracing will also inuence whether or not a cutter can be used. Cutters should not beused in the spray applications or:

Cape seals, tack sprays or double seals, geoabric seals and SAMIs as they will be covered by a

slurry, binder or asphalt which would lead to the entrapment o the volatiles.Seals to be placed over resh asphalt or slurry suraces (excluding texture slurries o less thanmm) as it could lead to premature embedment o the new seal. A ball penetration test shouldbe done to determine the hardness o a new asphalt or slurry surace beore resealing with acutback modied binder.

Spray grades o modied emulsions usually contain - 4% m/m o cutter (ux), which is variedseasonally to enhance the breaking and adhesion characteristics. The presence o cutter in theemulsion may cause bleeding in cape seals carrying very heavy trac as well as instability in geoabricseals during warmer weather.

ExpectedtrafcvolumeThe expected trac volume, especially the number, type and load o heavy trucks and the speed atwhich they will travel on the seal is a critical actor in determining whether to cut back or not. Modied


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binders that have been cut back tend to bleed where there is a high volume o heavy vehiclestravelling at speeds below 40 km/h.

As a general guide, the use o cutters should be restricted to roads carrying less than 5 000 elv/day andthe amount o heavies should be less than 15% o the trac volume. Furthermore their use in highstress areas like climbing lanes and busy intersections should be avoided. The application o modiedbinders incorporating a cutter on residential streets during cooler temperatures as experienced in thewinter months generally presents a low risk or bleeding.

Modied binder seals incorporating up to 3% cutter have been successully applied on roads carryingrelatively high trac. A reduction in the amount o cutter which would normally be added, as well asa possible reduction in binder application rate, must be made to accommodate the eects o heavierand higher trac volumes over and above 5 000 elv/day.

AmountocutterIn the absence o a proven test method to determine the equivalent low temperature adhesionproperties o modied binders with cutters, it is recommended that reerence is made to the bindersupplier or guidelines on the amount and type o cutter to be used or the respective modied binderin accordance with the expected road temperature.

Constructionconstraints

The cutting back o modied binders does not negate the need to ollow good construction practices.Specic constraints based on local experience are given in Chapter 8: Construction


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4 MANUFACTURE

The processes being used to manuacture polymer modied bitumens are proprietary and dierentprocesses are used by the various suppliers. Some aspects are, however, common to all manuacturersand the basic requirements or a blending plant or homogenous polymer modied bitumen are:

Mixing vessels should ideally be heated with hot oil coils, instead o direct ame heating, tominimize the degradation o the polymer at the actory. Once on site, ame heating is the norm;The heating mechanism should be capable o raising the temperature o the contents o the tankrom to 5 to 10C per hour;The manuacturing vessels should be tted with:

Calibrated thermometers and temperature controllers;

A mixing system which is capable o eectively mixing the polymer into the bitumen;A mechanism or eeding the polymer into the bitumen;A calibrated dipstick.

A general overview o the manuacture o the various types o polymer modied binders is givenbelow:

41 Homogenousbinders411 SBRmodiedbitumen

This type o binder is produced by adding SBR latex, containing approximately 35% water, to hotpenetration grade bitumen and, being a liquid, the latex is usually pumped into the hot bitumen.During the addition o the latex, the water component is converted to steam with concomitantrothing and an increase in the volume o the binder. The addition rate o the latex is usually careullycontrolled to prevent boil-over in the manuacturing vessel. Plants used or the manuacture o theSBR modied binder should be designed in such a way to enable the steam component to escaperom the manuacturing vessel to avoid entrapment o the moisture in the binder.

The residual SBR component is dissolved in the bitumen by agitation and pump circulation. Theagitation/circulation time and manuacturing temperature required is a unction o the polymer/bitumen compatibility, with extended mixing times and higher mixing temperatures being required

or less compatible bitumens.

I the heated, manuactured product has to be stored in the manuacturing vessel or any reason,it is advisable to agitate/circulate the nal product during storage, to prevent possible polymersegregation.

It is important that the water is completely expelled in the manuacturing vessel beore discharge.Residual water can cause urther oaming during heating in binder distributors and hauler tanks, withthe possibility o boil-over

412 SBSmodiedbitumen

SBS polymers are available in pellet, in crumb or powder orm. I pellet or crumb polymer is used, themanuacturing plant should be tted with a high speed shearing device that will reduce the polymer


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particles suspended in bitumen, to a size suitable or easy solubility in the binder. The powdered gradeis already o the correct particle size and can be incorporated into the binder by simple agitationat the required temperature. The manuacturing temperature and time required or dissolving o

the polymer is lower than that required or SBR modied bitumen. Polymer degradation is thusconsiderably slower.

The addition o the polymer to the manuacturing vessel should be careully controlled. I the additionrate is too high, polymer conglomerates could orm on the surace, resulting in lumps, which could beproblematic during application o the binder.

Similar to SBR modied bitumen, it is advisable to have some means o circulation in the vessel toprevent possible polymer segregation during storage o the heated binder.

413 EVA

EVA polymer is incorporated into the bitumen by adding the polymer pellets while stirring orcirculating the contents o the mixing vessel. The polymer melts into the bitumen and a short periodis required or the polymer to completely dissolve in the bitumen. As with SBR and SBS modiedbitumen, the compatibility o EVA with the base bitumen should be assessed.

414 Hydrocarbonmodiedbindersandhighmolecularweightwaxes

Hydrocarbon modiers and high molecular weight waxes can be added to the heated bitumen whilestirring or circulating the contents o the mixing vessel. Similar to EVA, the hydrocarbon modierdissolves in the bitumen ater a short mixing period. No compatibility problems have been detected in

with modication o locally produced bitumens.

415 General

The quantity o polymer required is derived rom either the mass o binder placed in the mixing vesselor volumetrically, using the necessary temperature correction actors to determine the mass o thebinder. The quantity o polymer required should be weighed o accurately or the number o bags ordrums o polymer required should be established.

The nal product should be inspected visually to conrm that the polymer has been completelydissolved. The product can also be examined microscopically to assess the degree o solution o the

polymer. A Ring and Ball sotening point test will also conrm that the correct quantity o polymer hasbeen added and that the polymer has been completely dissolved.

Should small quantities o modied binders be required or carrying out emergency work, SBR latex ornatural occurring hydrocarbon modiers can be added directly into the pugmill during mixing o hotasphalt.

42 Non-homogenouspolymermodiedbinder

Bitumen-rubber is manuactured by adding graded crumbed rubber, obtained rom grinding vehicle

tyres, to hot bitumen which contains a quantity o heavy extender oil. Following the addition o therubber, a digestion period is required or the rubber to swell and partially dissolve in the bitumen/extender oil blend. The rubber never completely dissolves in the bitumen and the product is thusclassed as a non-homogenous binder.


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Special manuacturing equipment is required to manuacture this highly viscous material. Theproduct has a limited useable lie o 4 to 6 hours and thereore, manuacture usually takes place on-site or very close to the construction site.

Bitumen rubber binder can be used or surace dressing operations, in which case it is applied withbinder distributors specially designed to handle this highly viscous binder. For surace dressingapplications, the bitumen-rubber binder is manuactured using the wet method. Two processes canbe employed or the manuacture o bitumen-rubber hot-mix asphalt, the wet method and the drymethod with the wet method being used in the majority o cases.

421TheWetMethod

A typical bitumen-rubber blending unit (Figure 8) consists o:a tank or super-heating the bitumen;

a blending unit;a suitable rubber eeding mechanism;transer pumps;a digestion tank equipped with an agitators and a super-heater.

The extender oil could either be added to the penetration grade bitumen beore delivery or tothe bitumen on site. The bitumen is pumped into the small blending tank at a temperature o notmore than 0C or short periods beore the introduction o rubber; where the rubber is added inproportion to the bitumen ow rate. The blending unit consists o a small tank equipped with a highspeed stirring device that ensures proper wetting o the rubber by the binder and prevents theormation o rubber lumps in the nal product. During the addition o the rubber component, the

blend cools down considerably and has to be re-heated to a temperature o 190 to 00C to ensureproper digestion o the rubber in the bitumen. From the blending tank the product is transerred to adigestion tank which could also be a specialised binder distributor. In the digestion tank the product iscontinually agitated while being heated to the nal temperature.

On completion o the digestion period, a hand-held Haake viscometer is used to perorm a viscositytest on the product to conrm that sucient digestion has taken place. I approved, the product isready or application.


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Auger feeder

Primary rubber

crumb hopper

Secondary rubber

crumb hopper

Rubber crumbinlet

High speed

mixing chamber

Superheated bitumen

inlet High speed

mixerBlended bitumen rubber

to reaction vessel

3000 rpm

Figure 8: Schematic o a typical high speed bitumen rubber blender

422TheDryMethod

The dry method is only used with a hot-mix plant using a batch mixer and not with a drum orcontinuous type mixer. The plant must also be tted with the necessary equipment to eed accuratequantities o crumbed rubber directly into the pugmill. The temperature o the aggregate in thepugmill should be within the range 190 10C. The correct quantity o crumbed rubber is added tothe hot aggregate in the pugmill and mixed or 5-7 seconds, ollowing which, the bitumen is added.

Sucient mixing time should be allowed to ensure acceptable distribution o the bitumen throughoutthe aggregate/rubber blend. The bitumen temperature should be 145165C and the asphalt leavingthe pugmill should be at a temperature ranging rom 19010C. The mix is then transerred to thehot-storage bins where it is let or at least an hour to allow or the digestion o the rubber by the

bitumen. The asphalt is drawn rom the bins and transported to site as required.

Practitioners tend to be sceptical o the dry blend method, because o the inability to determine theproperties o the bitumen-rubber binder in the mix. The use o this method is generally only justiedi small quantities o bitumen-rubber asphalt are required or emergency repairs. The wet blendmethod usually involves substantial establishment costs o the blending unit, which are only justiedor larger demands.


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5 MODIFIED BINDER CLASSIFICATION

The intention is to provide a binder classication system that does not dictate the type and quantity opolymer to be used but rather ocuses on the end property perormance requirements o the binder.To this end a generic system has been developed or classiying modied binders according to ourmain criteria based on application type and temperature, polymer used and a numerical value. To thisend the ollowing codes are used to designate the dierent classes o modied binders:

The type o application in which they are intended to be usedSeal (S),Asphalt(A)

Crack sealant (C)

The type o binder systemEmulsion (colder applied) - I the product is an emulsion then the letter C would ollowdirectly ater the letter indicating the type o application.Hot applied No letter is used ater the letter indicating the type o application.

The predominant type o modier usedElastomer (E) eg A-E1Plastomer (P) eg A-P1Rubber (R) eg A-R1

Hydrocarbon (H) eg A-H1

The level o modicationThe higher the numerical number the higher the sotening point value but this does no necessarilyimply improved overall perormance properties. The intention is that higher order modied bindersshould be able to be included in the classication ramework in uture should the need arise byincreasing the numerical value.

The ollowing additional code can also be used or classication purposes to indicate whether or notthe use o a uxing agent or cutter is permitted:

Should the binder application not permit the use o ux or cutter the letter t should be shown

in brackets ater the classication.

For example a classication o SC-E(t) indicates that the binder is:

S - intended to be used or a suracing chip sealC - it is an emulsionE - the main modier is an elastomer - it has a higher sotening point than an SC-E1(t) - the use o a uxing agent or cutter is prohibited

Table 4 summarises the dierent classes o generic modied binders according to thei

Documents

TG1 (2007) Modified Binders