Repair of ordinary Portland cement concrete using ambient-cured alkali-activated concrete: Interfacial behavior

Abstract In this paper, alkali-activated concrete (AAC) mixtures synthesized using five different class C fly ashes (FAs) were used as a repair material for structures constructed using conventional Portland cement concrete (CC). The bond strength between ambient-cured AAC and CC was evaluated using slant shear and pull-off tests. Three inclination angles of 45°, 33.75°, and 22.5° were examined during the slant shear test. For the pull-off test, no surface treatment, bonding adhesive treatment, or sandblasting surface treatment were applied to the CC substrate before applying the ACC repair. Full-height cylinders and full-depth beams were also tested as references for comparison purposes. Repairing CC using AAC yielded results similar to those of repairing CC with CC. Using the slant shear test at different angles, the average adhesion between the CC and AAC was found to be 5.8 MPa with a slight increase when increasing the calcium content in the precursor. The average coefficient of friction of the repaired specimens was approximately 0.64. The pull-off test results were sensitive to the surface treatment with sandblasting, which yielded the highest direct tensile strength. The direct and indirect tensile strengths were also analytically correlated to the adhesion from the slant shear test. The SEM results displayed new products such as calcium aluminate silicate hydrate (CASH) at the interface surface, and no sign of visible gap between the substrate and repair materials: i.e., CC and AAC, was observed.