Research was undertaken at WSP Opus Research in 2018 to investigate evidence from field studies supporting the performance benefits of polymer modified binders (PMBs) in thin asphalt and chipseal road surfacings. Improved performance benefits claimed for the use of PMB modified thin surfacings include reduced rutting and fatigue cracking in dense asphalt, reduced chip loss in chipseals and open graded porous asphalts and reduced flushing in seals.
The use and specification of PMBs internationally was reviewed and compared with practice in New Zealand. New Zealand follows international practice in that elastomeric polymers (typically SBS, SBR type), at 3–5% concentration are most widely used. In New Zealand, the physical requirements for PMBs are usually based on softening point and torsional recovery and limits are set based on past experience but contrary to many overseas jurisdictions the NZ Transport Agency does not have a specification or provide any formal guidance for the use of PMBs.
Although site and construction variables can have a significant influence on performance, there exists a good body of evidence supporting anecdotal observations that PMBs provide significant benefits to thin asphalt surfacings compared with unmodified binders. In contrast there is very little data available from field studies showing significant improvements in chipseal performance from use of PMBs.
Keywords: asphalt; binder performance; chipseals; elasticity; elastomer; plastomer; polymer modified binders; polymer modified bitumen; polymer modified emulsions