Viscosity evolution and separation behaviour of high content rubber modified asphalt under thermal storage

High content rubber modified asphalt (HCRMA) has raised concerns about viscosity evolution and separation behaviour under thermal storage. This study used Soxhlet extraction test to separate liquid phase asphalt and undissolved crumb rubber from HCRMA. The viscosity relationship among the liquid phase asphalt and HCRMA was analysed. The composition of undissolved crumb rubber and the functional groups of HCRMA were detected using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). To evaluate the separation behaviour of HCRMA, the rheological separation indicators were analysed. The results indicate that as the thermal storage time increases, the viscosity of HCRMA decreases, while the viscosity of the liquid-phase asphalt increases. The content of undissolved crumb rubber decreased. Both natural rubber and synthetic rubber in HCRMA undergo desulphurisation and degradation during the thermal storage process. As the storage time increases, the desulphurisation and degradation rates of natural rubber accelerate. This finding indicates that desulphurisation and degradation of natural rubber are the primary causes of the viscosity reduction in HCRMA during thermal storage. With extended storage time, the rheological property difference between the top and bottom increases. This indicates that the separation behaviour of HCRMA intensifies with prolonged thermal storage time, primarily due to the sedimentation of crumb rubber.