Material Characterization and Balanced Design of Asphalt–Rubber Binders

Abstract

Current specifications for asphalt–rubber (AR) binders is designate the degree of rubberized modification of the asphalt cement at a specific temperature. It is necessary to investigate the performance-based properties of the AR binders by means of advanced test methods. In this research, three types of asphalt binder with different crumb rubber concentration levels were produced and tested. The base asphalts chosen for the study were 60/70 penetration-grade (Pen 60/70) and 20/40 penetration-grade (Pen 20/40) asphalts and a polymer-modified bitumen (PMB). Test results showed that penetration-grade asphalt blended with rubber appeared to have improved toughness with increasing rubber content, whereas a reduction in toughness was found for the PMB mixed with rubber. At high temperatures, the addition of rubber improved the resistance to permanent deformation of the asphalt binders. However, the AR binders showed relatively poorer delay elastic behavior compared to the PMB, reflecting that the crumb rubber acted mainly as flexible filler. In addition, equiviscous temperature (EVT) was used for grading asphalt binders because it took slow-moving traffic into account at high pavement service temperatures. In terms of balanced design method, the results demonstrate that the performance of the AR binder was asphalt dependent. The Pen 20/40 asphalt modified with rubber was found to be more rut-resistant than the AR binder including the Pen 60/70 asphalt, but little difference in crack resistance was shown between them. The PMB modified with rubber had good resistance to rutting, but a decline in fatigue performance was found with increasing rubber content.