Abstract
Crumb rubber modified (CRM) bituminous binders have been used successfully in asphalt pavements to significantly enhance durability and cracking resistance properties. However, the rubber contents required (>20%) and their associated costs are generally prohibitive for use on local roads. It is therefore of interest to determine the performance and anti-aging benefits that may be realized from low-dose (≤15%) CRM dense grade asphalt (DGA) in these applications. In this study, a typical local road DGA mixture was prepared with low-dose CRM binders (5%, 10%, and 15%) using both short and long binder blending durations, to simulate field and terminal blends, respectively. Compacted asphalt specimens were oven aged for a duration of 0, 5, and 15 days, in accordance with the AASHTO R30 conditioning method. Test specimens were then subjected to mechanical performance testing, including resilient and flexural modulus, and IDEAL-CT to determine cracking resistance benefits. The relative performance and the changes to these mechanical properties were used as indicators of the resistance to thermo-oxidative aging effects imparted by the CRM binders. It was found that increasing rubber contents resulted in improved mechanical performance properties, relative to the unmodified control mixture, and that the reduction in dissolution of the rubber crumb from short-duration (field-blended) binders generally resulted in improved performance, compared to their long-duration (terminal-blended) equivalents. Similarly, with increasing rubber content, it was found that the resulting CRM DGA mixtures showed a reduced level of stiffness increase and improved retention of cracking resistance with age. Analysis of variance of the test results indicated that the CR content had a statistically significant effect on the relative aging of the CRM DGA mixtures. Consequently, it was concluded that the incorporation of low-dose CRM binders in local roads may significantly reduce the aging process and improve pavement life and should be encouraged in the future.