Role of interface bonding in the early-stage mechanical response of geogrid-reinforced asphalt overlays

Abstract

This study investigates the importance of interface bonding on early-stage mechanical response and fatigue performance of geogrid-reinforced asphalt overlays, using Digital Image Correlation (DIC) as strain-based assessment tool. By integrating interface shear tests with cyclic four-point bending fatigue tests monitored by DIC, the research evaluates how shear bond strength enables the initial mobilization and effectiveness of reinforcement mechanisms in double-layer asphalt systems. Double-layer asphalt systems reinforced with polyester, polyvinyl alcohol, and fiberglass geogrids were evaluated. Leutner shear tests confirmed that all reinforced systems achieved adequate interlayer bonding, satisfying the necessary condition for effective stress transfer and initial reinforcement mobilization. Notably, reinforcements with distinct tensile stiffness levels, exhibited identical strain reduction efficiency, indicating early-stage strain mitigation is primarily associated with interface bonding rather than with the tensile stiffness of the geogrid. Fatigue life results, evaluated using the Simplified Flex Point criterion, showed that tensile stiffness becomes increasingly influential at advanced damage stages, which may not be entirely compatible with the strain regimes typically targeted in pavement design aimed at preventing crack initiation. Consequently, a combined evaluation of interface quality and strain response is essential for a mechanistically consistent interpretation of reinforcement effectiveness and for the reliable design of geogrid-reinforced asphalt overlays.