Investigation of the Thermal Degradation of SBS Polymer in Long-Term Aged Asphalt Binder Using Confocal Laser Scanning Microscopy (CLSM)

Styrene–butadiene–styrene (SBS) polymer is extensively employed for asphalt pavement construction, and its degradation significantly damages the durability of asphalt concrete. However, the effect of aging protocols on the degradation of SBS polymer in asphalt binder has not been thoroughly investigated. In this study, confocal laser scanning microscopy (CLSM) was applied to characterize the change in morphology with SBS polymer degradation. Various aging protocols were considered, including accelerated aging processes in laboratory- and field-aged samples from three highway sections with different in-service periods. Scanned images of the polymer phase in the 2D plane at different depths were processed and further reconstructed in three dimensions. Furthermore, the three-dimensional polymer morphology indices derived from the semi-quantitative analysis of the images were correlated with the rheological indices. The results show that the polymer particles change from a relatively large ellipsoidal shape to a relatively small spherical shape as aging proceeds. The increase in aging temperature appears to accelerate the degradation of the polymer at the same rheological level. The effect of the laboratory aging method on the polymer was more pronounced during the early stages of aging compared to that in the field aging process.