Antagonistic effect of superplasticizer and colloidal nano-silica in the hydration of Alite and Belite pastes

The dependence on the hydration rate for Alite and Belite clinker phases in the presence of a polycarboxylate superplasticizer PC SP upon addition of colloidal nano-silica CNS were monitored by means of Diffuse Reflectance Infrared spectroscopy DR-FTIR. Spectral signatures of clinker dissolution and product formation were acquired for both materials. The rates for the build-up of product vibrational band intensities were found to depend sensitively on addition of CNS. The hydration product was proposed to be calcium-silicate-hydrate C–S–H. Details in the spectral signatures were found to differ. Quantum chemical calculations were employed and found to be consistent with the interpretation that small clusters dominate the Alite C–S–H spectrum, whereas the Belite C–S–H spectrum results from extended polymers.