The effect of surface electric charges in tack coat and aggregate on the interlayer shear-bond strength of asphalt pavements

This study investigates the influence of surface electric charges of tack coat emulsions and aggregates on the interlayer shear strength (ISS) of asphalt pavements. Three types of aggregates (andesite, sandstone, limestone) and three types of tack coat emulsions (cationic, cationic polymer, and anionic) were used. The electrical charges of these materials were determined using X-Ray Fluorescence (XRF) and Zeta Potential tests. The ISS was measured at different temperatures (25 °C and 60 °C) and normal loads (0 kN, 1 kN, and 2 kN) using the Leutner shear device. XRF results showed that andesite and sandstone had mixed charges due to high silica content, while limestone, high in alkaline-earth oxides, exhibited a positive charge. Zeta potential tests revealed positive values for cationic emulsions and a negative value for the anionic emulsion. ISS tests showed cationic emulsions had strong bonding at lower temperatures but weakened at higher temperatures, while anionic emulsions were consistent across temperatures. Statistical analysis (R² and Spearman's Rho) indicated significant electrostatic interaction effects on ISS at 25 °C but diminished at 60 °C. Additionally, when normal loads are applied, the electrostatic interaction effects at 60°C are significantly more pronounced. This study highlights the importance of selecting appropriate tack coat emulsions to ensure optimal interlayer bonding and enhance pavement durability. © 2025 Elsevier Ltd