Researchers have identified polymer additives that increase the storage stability of asphalt rubber.
Christopher Williams, Eric Cochran and colleagues wanted to identify polymer alternatives that mitigated the problems of ground tyre asphalt, namely its high viscosity and its tendency to separate into rubber and bitumen layers during storage.
The researchers studied the stability of rubber asphalt made by blending and extruding different amounts of the polymers cis-isoprene, trans-isopreme, polybutadiene or polyisobutylene with ground tyre rubber.
The team found that, when mixed with asphalt, blends of ground tyre rubber with trans-isoprene or polybutadiene in a 3:1 ratio performed the best.
These mixtures reduced the density of ground tyre rubber so that it was similar to asphalt and did not settle during storage.
The polymers also helped reduce the viscosity of the rubber asphalt so that the material was easier to work with.
According to the researchers, the polymer additives are cost effective resulting in tables of about 77 to 10 per cent compared with regular asphalt.