Secondary-Reaction Method to Improve Performance of a Compound Modified Rubber Asphalt after Short-Term Aging

Abstract

Asphalt aging occurring during the mixing and transportation of a mixture will decrease the performance. In this study, a compound modified rubber asphalt containing crumb rubber modifier (CRM), styrene-butadiene-styrene (SBS), and naphthenic rubber oil was obtained from a company, and a secondary-reaction method was proposed to improve its performance after short-term aging. Secondary reaction means that in preparation of the modified asphalt, CRM is given an incomplete reaction; then, the reaction continues at high temperature during mixing and transportation. In this research, an inadequate reaction was achieved by controlling the reaction time in preparation, and the secondary reaction was simulated by rotating film oven heating (RTFOT). The rheological performance was evaluated using a dynamic shear rheometer (DSR). Moreover, a Fourier transform infrared spectrometer (FTIR) was employed to research the mechanism. According to the results, if secondary-reaction time (mixture mixing and transportation) is 1 h, all samples with 20% by weight CRM present aging resistance, but for a longer secondary-reaction time of 5 h, blending time should also be controlled as 0.5 h. FTIR results show a decreased carbonyl index and an increased sulfoxide index, indicating desulfurization and degradation of CRM during the secondary reaction.