Properties of polymer modified bitumen after rubber-bitumen interaction

This paper describes results from a laboratory investigation into the effects of the interaction between a styrene-butadiene-styrene (SBS) modified bitumen and recycled crumb rubber on the mechanical performance of impact absorbing asphalt (IAA), an asphaltic material that has applications as a sports and safety surface. Curing tests at high temperatures have been undertaken using different rubber-bitumen ratios to assess the amount of bitumen absorbed by the rubber. The changes in bitumen constitution through this interaction have been monitored and related to changes in the rheological characteristics of the residual bitumen. The results show that significant absorption takes place and that the residual bitumen undergoes alterations in terms of its stiffness and viscoelastic balance, together with a reduction in cohesion. A significant finding has been the loss of the polymeric nature of the residual SBS polymer modified bitumen. This has been due to the precipitation of the SBS polymer as the compatibility between the base bitumen and polymer has decreased following the absorption of the lighter, solvating fractions of the binder. To assess the effect of the rubber-bitumen interaction on the mechanical durability of IAA, an abrasive wear test has been developed to simulate the contact between a twisting foot and the surface. This test has been used to compare the mechanical durability of laboratory prepared specimens that have been artificially aged at high temperatures (to simulate the mixing and transportation period before the material is laid and compacted). Results show that there is a detrimental effect on the mechanical durability of the aged material due to the interaction between the rubber and the bitumen.