Optimizing Thermosetting Epoxy Asphalt with Styrene–Butadiene Rubber and Styrene–Butadiene–Styrene Modifiers for Enhanced Durability in Bridge Expansion Joints

The high- and low-temperature performance of asphalt-based seamless expansion joints seriously affects road performance. The purpose of this paper is to explore the application of thermosetting epoxy asphalt-based materials in bridge expansion joints. The composite modification of asphalt was performed using Styrene–Butadiene rubber (SBR) and Styrene–Butadiene–Styrene (SBS) copolymer. The study then investigates the impact of five different dosages of SBR/SBS-modified asphalt on the performance of epoxy asphalt. The results of the cone penetration test, tensile test, and stress relaxation test of SBR/SBS-modified epoxy asphalt (SSEA) and BJ200 (a commercial Seamless expansion joint material) were comparatively analyzed. The Marshall test, rutting test, three-point bending test, and freeze–thaw split test were used to evaluate the road performance of SSEA mixtures. The test results show that with the increase in asphalt content, the shear resistance and tensile strength of SSEA decrease, and the low-temperature relaxation ability and elongation at break increase. The content of SBR/SBS-modified asphalt has a positive effect on the low-temperature performance of SSEA mixtures, and the residual stability in water and freeze–thaw splitting strength ratio (TSR) are higher than that of BJ200. Based on the requirement of balancing high and low-temperature performance, SSEA-3 has the best overall performance, and the dosage of SBR and SBS modifier is 12% and 2.5%, respectively. The ratio of epoxy resin, SBR/SBS-modified asphalt, and the curing agent is 1:4:1.6, and its use is recommended in areas with slight temperature differences.