SBS Polymer Modified Asphalt Binder and Its Implications on Overlay Design

Book excerpt: Substantially improved overlay mixes, required by the modern road industry should be highly resistent to reflection cracking. The mix must contribute significantly to the stiffness of the pavement, even when it is applied in relatively thin layers. The binder should possess a high softening temperature to reduce the sensitivity for rutting and corrugation, and it should have a reasonable penetration value to minimize the chances of cracking. In this paper attention is paid to the manner SBS polymer modified asphalt binders cope with this set of requirements. The basic principles of this modification are outlined and emphasis is laid on the rheological and mechanical properties: viscosity and penetration test results are presented. Burgers' model for viscoelastic materials is used in an attempt to describe the visco elasticy. Results of indirect tensile tests are reported, including the tensile strengths and the elastic moduli. Repeated loading tests have been done on polymer modified and plain asphaltic concrete mixes. The results are mutually compared concerning fatigue behaviour, elastic moduli and crack propagation characteristics. The paper describes various trial sections, with special attention to comparative tests carried out in an Australian accelerated loading facility.