Kaolinite based admixture for rapid hardening high strength concrete

Abstract Early-stage hardening with high-strength concrete is required in many construction applications. In this study, we develop and evaluate a kaolinite-based, low-dosage (2 wt% of cement) chemical admixture designed to accelerate early-age strength development in Portland cement concrete (cement: sand: stone = 1:2:2.73). The admixture increased compressive strength by about 61% in 3 days and by more than 30% in 28 days, reaching nearly 44 MPa. FT-IR, WD-XRF, XRD, and XPS analyses were used to interpret the hydration mechanism. The results indicate that the admixture accelerates early hydration and promotes rapid formation of a compact C-S-H network, while the reduced water absorption measured by ASTM C642 supports microstructural densification and lower pore connectivity. Overall, the proposed admixture provides a practical route to rapid hardening without compromising later-age performance.