Influence of low concentration calcium formate on the hydration process of tricalcium aluminate-gypsum system

The effect of low concentration (not exceeding 2%) calcium formate (CF) on the hydration process of tricalcium aluminate (C3A, Ca3Al2O6, the fastest hydrating component in cement)-gypsum systems was investigated in this study using methods such as isothermal calorimetry, XRD, TGA-DSC and SEM. Results demonstrate that a higher dosage of CF corresponds to a more pronounced enhancement in C3A hydration. Furthermore, CF inhibits the initial formation of hydrogarnet (C3AH6, Ca3Al2(OH)12) and promotes the formation of ettringite (AFt) in C3A-gypsum system at 2 h hydration. However, after 1 d hydration, CF facilitates the conversion of excess C3A to C3AH6, which delays the transformation of AFt to AFm. SEM observations reveal that the CF-induced reduction in the size of AFt crystals, formed during C3A hydration, facilitates their more effective filling of interstitial voids within the hydration products, thereby contributing to the formation of a more resilient interlocking structure.