Effect of Aging on Foamed Warm Mix Asphalt Produced by Water Injection

This study evaluated the aging characteristics of foamed warm mix asphalt (WMA) produced by water injection in comparison to traditional hot mix asphalt (HMA). Two asphalt binders (PG 70-22 and PG 64-22) and one aggregate (12.5-mm NMAS limestone aggregate) were used in this study. The short-term and long-term aging of the two asphalt binders were simulated using the rolling thin film oven (RTFO) and pressure aging vessel (PAV), respectively, while AASHTO's standard practice for mixture conditioning for hot mix asphalt was used to simulate the short-term and long-term aging of the laboratory-prepared asphalt mixtures. The dynamic shear rheometer (DSR) was used to characterize the viscoelastic behavior of the original (unaged, RTFO-aged, and PAV-aged) and recovered asphalt binders; Fourier-transform infrared (FTIR) spectroscopy was used to identify and quantify the amount of functional groups present in the asphalt binders; and gel permeation chromatography (GPC) was used to determine the molecular size distribution within the asphalt binders. In addition, this study investigated the effect of the extraction and recovery procedures on the recovered binder properties. It was observed that the extraction and recovery procedures had little effect on the rheological properties of PG 70-22, but a significant effect on PG 64-22. In addition, G*/sin and G*sin values were obtained for the asphalt binders recovered from short-term and long-term oven-aged HMA mixtures that were comparable to or slightly higher than those recovered from foamed WMA mixtures. This indicates that foamed WMA mixtures undergo comparable or lower levels of aging than traditional HMA mixtures. The DSR test results were confirmed by the FTIR and GPC test results. (C) 2016 American Society of Civil Engineers.