Assessing Pavement Structural Changes Due to Trafficking and Ageing

Stone Mastic Asphalt (SMA) is widely used in high-traffic pavements due to its superior rutting resistance and durability. However, its porous structure makes it vulnerable to chemical pollution from fuel spills and coolant leaks, which can accelerate structural degradation. This study investigates the effects of aging, trafficking, and chemical pollution on the 3D microstructure of SMA asphalt using X-ray microtomography and Avizo 3D. Eleven cylindrical SMA core samples (100 mm dia) were analyzed, representing different combinations of aging, trafficking, and pollution states. A standardized workflow quantified total porosity, connected porosity, void morphology (equivalent diameter and sphericity), and binder film thickness. 3D void networks were visualized to compare damage patterns. The results reveal distinct damage mechanisms. Petrol pollution causes the most severe damage, increasing porosity from 4.90% (healthy control) to 15.44% (aged + trafficked + petrol), a 3.2-fold increase. Petrol-damaged samples exhibit void coalescence (average equivalent diameter up to 2.49 mm) and nearly complete connectivity (96.8%), indicating aggressive binder dissolution. EV Coolant causes moderate damage (porosity 8.86–11.81%) with uniform binder thinning (thickness reduced from 8.57 mm to 8.09 mm after spillage). Aging and trafficking alone cause mild damage (porosity 6.40–6.45%), with voids remaining small, round, and isolated (no connected network detected). Vertical scan analysis reveals damage is non-uniform along core height, with petrol-spilled samples showing a "bathtub" profile (highest porosity at top and bottom, lowest in the middle). The "before vs. after" spillage comparison confirms the pollutant itself, not just aging or trafficking, is responsible for the additional damage. These findings provide quantitative evidence of the distinct damage mechanisms induced by petrol and EV coolant, offering insights for pavement management and spill response strategies.