Effects of Surface Roughness and Interfacial Agents on Bond Performance of Geopolymer–Concrete Composites

This study investigates the effects of surface roughness and interfacial agents on the bond performance of geopolymer–concrete composites (GCCs). Firstly, cement concrete substrates with four surface roughness conditions, including cast surface, drawn surface, chiseled surface and split surface, were prepared and their surface roughness was quantitatively characterized by the Joint Roughness Coefficient (JRC) based on the 3D surface morphology reconstruction technique. The GCC specimens were prepared by casting geopolymer concrete on cement concrete substrates and using three interfacial agents in the bonding interface. Then, the splitting tensile tests were conducted on GCC specimens and the effect of surface roughness and interfacial agents on the bonding strength and failure behavior of GCC was discussed. Finally, the empirical model of the bonding strength of the GCC was proposed by considering surface roughness, interfacial agent, and geopolymer tensile strength simultaneously. The results show that with increasing JRC, the bonding strength of GCC shows a trend of slow increase followed by significant increase, and the failure modes transitioned from interfacial debonding to concrete matrix failure. Among the bonding agents, geopolymer slurry achieved the highest bonding strength, followed sequentially by untreated interfaces, SBR-modified cement paste, and expansive agent-modified cement paste. The results also show that the empirical model can accurately predict the interface splitting tensile strength of GCC under different surface roughness and interfacial agents, with a prediction accuracy of 0.92.