An investigation on the formation of Friedel’s salt in tricalcium silicate combined with metakaolin and limestone systems

Abstract

Supplementary cementitious materials of calcined clay combined with limestone show an excellent improvement for chloride resistance. Understanding the process of Friedel’s salt formation in calcined clay and limestone system is essential for chemical bound chloride quantification, which is beneficial for binding capacity enhancement. This study selected tricalcium silicate, metakaolin, and limestone powder as the primary research objects to exclude other factors (such as ettringite) effect. Calorimetry test was applied to analyze Friedel’s salt formation kinetics during early hydration. Meanwhile, X-Ray powder diffraction, combined with Rietveld analysis, was used to quantify Friedel’s salt content. Thermodynamic modeling (GEMS) was taken as a complementary method to better understand Friedel’s salt formation under various conditions. The results suggest that pure Friedel’s salt is formed in C3S + MK system, while in systems with limestone, solid solution of Friedel’s salt and hemicarboaluminate is found. Carbonate participates in the Friedel’s salt formation process and results in the overestimation of Friedel’s salt content. The finding of this research is helpful for the chemical bound chloride quantification.