Ceramics-Silikáty 69, (3) 418 - 435 (2025)

Potassium magnesium phosphate cement (MKPC) is an excellent concrete repair material due to its high early strength, rapid hardening, and superior bonding strength. However, its poor water resistance remains a critical issue that requires serious attention. This study investigated the effects of two organic waterproofing agents-sodium methyl silicate (SM) and isobutyltriethoxysilane (IBTOS)-on the compressive strength, water resistance, and workability of MKPC. The analysis also explored the underlying mechanisms from the perspectives of the hydration products and microstructure. The results indicated that SM significantly enhanced the water resistance of MKPC and simultaneously increased the compressive strength under both air and water curing conditions. This improvement might be attributed to SM′s excellent water solubility and shorter hydrophobic groups, which facilitated the better dispersion in the mixture and the formation of a more compact hydration product structure. In contrast, IBTOS reduced the compressive strength of MKPC, but markedly improved its water resistance. Both SM and IBTOS formed hydrophobic layers on the surface of hydration products, effectively preventing water ingress and thereby enhancing the overall water resistance of MKPC.