Evaluating fracture performance of stone mastic asphalt with SBS and SEBS modifications

This study investigates the effects of styrene–butadiene–styrene (SBS) and styrene-ethylene-butylene-styrene (SEBS) on the fracture properties of stone mastic asphalt (SMA) at various loading rates. Semi-circular bending (SCB) tests were performed at 25 °C with notch angles of 0° and 45° at loading rates of 0.5, 1, and 5 mm/min. Key parameters such as maximum load, ductility, and fracture energy were derived from force-displacement curves. The results showed that SEBS-modified samples consistently exhibited higher fracture energy than SBS-modified samples, particularly at lower loading rates. Specifically, at a 45° notch angle, the fracture energy of SEBS was 43 % and 68 % higher than SBS at loading rates of 0.5 and 1 mm/min, respectively, attributed to the higher tensile strength and modulus of SEBS, allowing greater energy absorption before failure. However, at the highest loading rate (5 mm/min), SBS outperformed SEBS by 25 %, attributed to its superior viscoelastic properties and hardness, which improve energy absorption and distribution at higher speeds. While SBS specimens exhibited lower ductility compared to SEBS, SEBS propagated cracks earlier due to limited time for plastic deformation, whereas SBS, with its higher elongation at break and greater viscosity, slowed crack propagation by accommodating larger deformations before failure. The fracture energy-CMOD index effectively evaluated the impact of polymer additives on the fracture behavior of SMA, with higher values indicating improved performance under load. SEBS outperformed SBS at a 0° notch angle due to its higher tensile strength, While SBS excelled at a 45° notch angle, this advantage was not solely due to its greater hardness but also attributed to its higher viscosity, greater elongation at break, and viscoelastic behavior, which allowed it to better resist crack propagation under combined tensile and shear forces.