Investigation of the rheological modification mechanism of warm-mix additives on crumb-rubber-modified asphalt

Studies in recent years have proved that warm-mix asphalt (WMA) additives can effectively improve the rheological properties of crumb-rubber-modified asphalt (CRMA) without significantly affecting its engineering properties. However, limited research has been done to investigate the rheological modification mechanism of WMA additives on CRMA. In this study, CRMA was prepared by mixing PG64-22 asphalt with 18% crumb rubber by weight of asphalt. Evotherm-DAT, a typical WMA additive, was added to CRMA at four percentages: 0, 8, 10, and 12%. Various conventional rheological tests were performed to evaluate the performances of the CRMA with and without Evotherm-DAT additives at different temperatures. In addition, a series of unconventional tests; including environmental scanning electron microscopy (ESEM), chemical composition, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) spectroscopy; were conducted to investigate the interaction mechanism of Evotherm-DAT and CRMA from the viewpoints of thermal effects, microscopic morphology, chemical composition, and molecular structure. This study concluded that there is no complex chemical reaction between Evotherm-DAT and CRMA. However, Evotherm-DAT affects the state of aggregation of the crumb rubber and the intermolecular forces of CRMA, which in turn changes the rheological properties of CRMA.Department of Civil and Environmental Engineerin