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5. Binders Questions and Responses AAPA 2011 Study Tour Group ReportQ 9. How is crumb rubber included in sprayed sealing? Direct mixing in bitumen sprayers?Terminal blending and long distance hauling? Field blending at point of application?The crumb rubber is preblended with the bitumen in high speed mobile blenders close to the pointof use. Sometimes it is digested in the sprayer before spraying otherwise a compartmented tank isused. Sometimes the CRB is transported to remote sites if it can be used within 6 hours before theproperties degrade at elevated temperatures.The use of CRB is also influenced by size and location of the project given the high establishmentcosts. Typically more than 1.5 million litres would be required to justify the establishment of amobile blending unit on-site.Q 10. Does environmental benefit or sustainability enter into consideration in the selection ofbinders?Consideration is given to using locally produced crumb rubber from recycled tyres to save onimportation of expensive polymers, assist with the disposal of used tyres and extend the life of thesurfacing.Q 11. What efforts are being made to use alternatives to crude oil sourced bituminous binders?Are there binders commercially available?We did not come across the use of any alternative binders to bitumen excepted the limited use ofShell’s Mexaphalt C coloured synthetic binder to demarcate a dedicated bus lane in Durban. Theuse of coal tar binders have also been discontinued due to environmental and health reasons.Q 12. What modified binders are commonly used in asphalt manufacture? Is the selection basedon performance? Have long term performance trials been undertaken to assess theadvantages?SBS and CRB are the most popular modified binders used for asphalt wearing courses whilst EVA isused mostly in base courses.SANRAL makes exclusive use of modified binders to reseal their road network of 16 170 km. TRH3Surfacing Seals for Rural & Urban Roads provides guidance for the selection of the mostappropriate binders for given traffic and climatic conditions. TG1 provides additional guidelines forthe selection of the most appropriate binder for a given stress condition and differentiatesbetween the different modified binder classes currently available.We did not come across any long term performance trials for monitoring modified asphalt.Q 13. Has accelerated pavement testing (HVS) been used to assess the performanceimprovements for modified and bitumen rubber for seal and asphalt? If yes, have theresults been included in design guides?Modified binders have been included in HVS testing and the pavement performance included inthe national and provincial design pavement design guides. Details are covered in the CSIRpresentation by Benoit Verhaeghe and in Chapter 6 Question 5.V4-2 Page 56
5. Binders Questions and Responses AAPA 2011 Study Tour Group ReportQ 14. Do specifications, test procedures and best practice guides exist for crumb rubber binders(bitumen rubber)?TG1 contains specifications and test methods for CRB for use in spray seal and asphalt.Sabita Manual 19 provides guidelines for the design, manufacture and construction of bitumenrubber asphalt wearing courses.Q 15. What attempts have been made to improve the plastomeric properties of crumb rubberbinders?CRB modified asphalt by nature is elastomeric and this results in resilient modulus values @ 25°Cof 1500 to 2500 MPa which is similar to SBS. Sasol indicated that they were doing work inGermany to produce a hybrid CRB with a polymer for use in asphalt.Q 16. What attempts have been made to lower the handling temperature and improve the selflife of crumb rubber binders?CRB are sprayed and mixed at temperatures between 190 – 210°C. At this temperature the binderhas a limited shelf life of up to 6 hours. To extend the self life the temperature must be dropped to165°C so that it does not degrade over time.Source: TG1V4-2 Page 57
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Contents1. EXECUTIVE SUMMARY 22. IN
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1. Executive Summary AAPA 2011 Stud
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8. CAPSA’11 & General AAPA 2011 S
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8. General - Questions & Responses
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8. General - Questions & Responses
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Appendix 9.1 - Detailed ItineraryAA
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Appendix 9.1 - Detailed ItineraryAA
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Appendix 9.2 - Study Tour Delegates
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Appendix 9.2 - Study Tour Delegates
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Appendix 9.3- Question ListAAPA 201
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Appendix 9.4 - South African Acrony
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Appendix 9.4 - South African Acrony
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Appendix 9.5 - ReferencesAAPA 2011
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Australian Asphalt Pavement Associa
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