4.6.3 Polymer Modified Binder (PMB)
PMB consists of bitumen blended with a synthetic polymer or crumb rubber. PMBs are used to enhance the performance of binders on heavily trafficked or distressed pavement surfaces, often in adverse climatic conditions. Property improvements include reduced temperature susceptibility, increased elasticity or resilience, increased cohesion and improved tenacity once a bond has been established. In terms of sprayed sealing, performance improvements include lower risk of bleeding, improved crack resistance, better aggregate retention and less deformation at high temperatures. These improvements are the basis of the use of PMBs in strain alleviating membranes (SAMs), strain alleviating membrane interlayers (SAMIs) and high‑stress seals (HSSs).
Polymer groups are coded as follows:
- E for elastomeric polymers including styrene-butadiene-styrene (SBS), styrene-butadiene rubber (SBR) and polybutadiene (PBD). Binders modified with elastomeric polymer have improved resilience or elasticity, are less temperature susceptible, and are widely used as HSSs, SAMs and SAMIs.
- P for plastomeric polymers including ethylene vinyl acetate (EVA), ethylene methacrylate (EMA), atactic polypropylene (APP), and polypropylene (PE). Binders modified with plastomeric polymer have increased stiffness and are may be used in HSSs.
- R for crumb rubber materials. Crumb rubber is generally obtained from shredding and grinding of scrap rubber from vehicle tyres. When blended with bitumen the rubber behaves as a form of elastomer and is used in HSSs, SAMs and SAMIs.
More information on various types of PMBs is provided in the Guide to Pavement Technology Part 4F: Bituminous Binders (Austroads 2017). The properties of PMBs are specified in Austroads (2014c).