Short-Term Aging of High-Content SBSMA

Abstract

Highly modified styrene-butadiene-styrene–modified asphalt (SBSMA) with an SBS content of 6–9% is gaining popularity in China as an efficient binder for open graded friction course pavement. However, the short-term aging of highly modified SBSMA cannot be properly simulated in the lab because it is too stiff to flow inside the rolling thin-film oven test (RTFOT) aging bottle. To investigate the short-term aging of conventional as well as high SBS content SBSMA binders, an innovative thin-film aging was proposed. It was not affected by the high viscosity and can age all binders at the same film thickness, providing them with the same level of aging severity. Two SBSMA binders with SBS contents of 4.5 and 7.5% (coded as SBS45 and SBS75, respectively) were investigated. To compare them with the actual short-term aging, their corresponding loose mix was collected in actual field projects for binder recovery. The binder’s chemical and rheological evolutions during aging were monitored using infrared spectra and master curves. The test results indicated that the thin-film aging was much more severe than the RTFOT and provided the SBS45 and SBS75 with a similar aging severity. For the SBS45, this aging severity was more serious than the actual short-term aging. However, for the SBS75, it was similar to the actual short-term aging; this was ascribed to the higher mixing and paving temperature of the SBS75 mixtures. Moreover, a similar logarithmic correlation between the asphalt carbonyl growth and SBS polymer degradation rate were observed for both SBS45 and SBS75, suggesting that high SBS content SBSMA may be more vulnerable to aging.