Research on the field aging gradient behavior of SBS-modified bitumen at different depths of pavement by rheological and microscopic characterization

Abstract

This study investigated the aging behavior of styrene–butadienestyrene copolymer (SBS)-modified bitumen with different depth after exposure in the field. The SBS-modified bitumen after construction aging (CA), field aging for 1 year (1Y) and field aging for 5 years (5Y) was obtained and analyzed. Samples were divided into three layers (upper/middle/lower) according to depth. Dynamic shear rheometer (DSR), infrared spectroscopy (IR), bending beam rheometer (BBR) and fluorescence microscopy (FM) experiments were used to observe the trends and changes of the rheological properties and microscopic performance of SBS-modified bitumen with depth. The test results showed that in the CA stage, the SBS-modified bitumen had no aging gradient behavior in the depth direction. The SBS-modified bitumen had a gradient change with depth direction during the 1Y, but the gradient behavior had not evolved to the middle and lower layers. After 5Y the effects of deep aging behavior gradually emerged, showing a distinct gradient behavior. The molecular change characteristics of SBS modified bitumen showed obvious gradient behavior after 5Y, and the change trend was consistent with the aging trend of bitumen. Compared with the aging index of rheological properties, it was found that the most serious degree of aging was on 5Y-upper, followed by 1Y-upper, 5Y-middle and 1Y-middle. It can be seen that the influence of direct contact with aging factors on the degree of aging was greater than the influence of aging time on the depth of aging. Therefore, in the road maintenance process, only the milling surface could be considered for the restoration of the SBS modified bitumen pavement after 5 years of field aging.