The early bonding performance of geopolymer for repair: Effect of mix proportion of cement substrate

Geopolymer can be potential Portland cement alternatives or supplement for concrete repair. In order to understand the bonding mechanism of geopolymer repairing materials, the effect of the mix proportion of cement mortar substrate on the early bonding performance was studied. For repaired composites by geopolymer, with the increase of sand‐to‐cement ratio of cement substrate from 1.5 to 2.5, the trends in the interfacial flexural‐tensile strength and slant shear strength were the same, both decreasing, which may be explained by the combined effect of surface porosity and the amount of surface cement pastes. And with the rise of the water‐to‐cement ratio of cement substrate from 0.4 to 0.5, the interfacial flexural‐tensile strength also increased mainly because of the increase in the surface porosity of the substrate, while the slant shear strength decreased resulting from the impact of compressive strength of the substrate. This indicates that the interfacial flexural‐tensile test is more suitable for the evaluation of the bonding performance than the slant shear test when the mix proportions of substrate vary.