Enhancement of Hydration Activity and Microstructure Analysis of γ-C2S

This paper investigated the combined effect of chemical activators and nano-SiO2 on the hydration reaction and the microstructure of gamma-C2S. The hydration reaction of gamma-C2S slurry activated with chemical activators (NaHCO3, NaOH, K2CO3, and KOH at 1 mol/L) was enhanced by 1% nano-SiO2. The hydrate reaction rate was determined by isothermal calorimetry, and the hydrated samples were characterized by XRD, TGA/DTG, SEM-EDS, and Si-29 MAS/NMR. The results revealed a substantial enhancement in the hydration activity of gamma-C2S due to the presence of the alkaline activator. Furthermore, nano-SiO2 did not alter the composition of gamma-C2S hydration products, instead providing nucleation sites for the growth of hydration products. Incorporating nano-SiO2 promoted the formation of C-(R)-S-H gel with a low calcium-to-silica ratio and increased its polymerization levels, resulting in more favorable structures. Among all the activators used in this study, potassium salts had a better activation effect than sodium salts. After 28 days of curing, the degree of hydration reaction in the KC+Si group was 48% and about 37% for the NHC+Si group. Whereas, the KH+Si and NH+Si groups only reached approximately 20% after the same hydration duration.