Hydration of tricalcium silicate in the presence of synthetic calcium–silicate–hydrate

The early age-hydration of tricalcium silicate, the main chemical compound in Portland cement, was studied in the presence of synthetic calcium silicate hydrate (C–S–H) addition having C/S ratios = 0.8 and 1.2. Isothermal conduction calorimetry, scanning electron microscopy, differential scanning calorimetry and 29Si MAS NMR were employed in order to investigate events occurring during various stages of the hydration. The results that were analyzed using novel methods in cement chemistry showed that the addition of seeds of synthetic C–S–H significantly accelerated the hydration of C3S. The extent of the acceleration was dependant on the amount and chemical composition of the C–S–H seeds. It was suggested that the synthetic C–S–H significantly increased the rate and degree of dissolution of the C3S particles. It was also found that the nucleation and silicate polymerization of the C–S–H that formed during the hydration of the C3S phase was promoted. Direct evidence of the seeding effect was provided. The properties of the resulting C–S–H hydration products seemed to be dependant on the lime-to-silica ratio of the synthetic C–S–H. It was suggested that the silicate polymerization and chemical composition of the hydration products of silicate phases may be manipulated through C–S–H seeding. As the chemical and mechanical properties of C–S–H are largely controlled by its C/S ratio, this method should provide a unique tool for tailoring the nanostructure of the hydration products of Portland cement through the addition of selective C–S–H seeds for optimum engineering and durability performance.