Study on the bonding performance and micromechanism between alkali-activated mortar and rock

Alkali-activated mortar (AAM) has emerged as a sustainable alternative to ordinary Portland cement (OPC) for rock-based applications, yet its bonding behavior with rock remains underexplored. This study investigates the interfacial performance between AAM and sandstone through orthogonal experiments, Brazilian splitting tests, and microstructural analyses (SEM-EDS, XRD). Results show that binder formulation and mortar composition significantly affect bond strength: slag content dominates early-age bonding, while the binder-to-sand ratio controls long-term strength. The optimal mixture (80% slag, water-to-binder ratio 0.35, binder-to-sand ratio 1.5) achieved a 28-day bond strength of 2.67 MPa, surpassing the sandstone’s tensile strength (2.42 MPa). Failure mode shifted from interfacial debonding to cohesive fracture within sandstone, accompanied by a wider interfacial transition zone (ITZ), indicating enhanced physicochemical integration. These findings improve the scientific understanding of the bonding mechanism between AAM and rock and may provide useful implications for rock engineering applications.