Influence of Nanosilica and Superplasticizer Incorporation on the Hydration, Strength, and Microstructure of Calcium Sulfoaluminate Cement Pastes

This study investigated the effect of incorporating three types of nanosilica (NS), two powders, and one colloidal suspension on the hydration, strength, and microstructure of calcium sulfoaluminate (CSA) cement pastes prepared with and without a superplasticizer (SP). X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and compressive strength tests were performed after 2, 5, and 28 days of hydration. The results showed that both NS powders delayed cement hydration at an early age, which was attributed to particle agglomeration (confirmed by dynamic light scattering). Whereas well-dispersed colloidal NS did not significantly affect the hydration of CSA at the investigated ages. SP incorporation improved the dispersion of CSA cement particles, resulting in a 10% increase in the degree of hydration of ye'elimite at 28 days for the system without NS. Conversely, when the SP was incorporated in NS-containing mixtures, it hindered cement hydration of the systems with powdered NS, but did not significantly affect the cement hydration of the system containing colloidal NS. The SEM images suggested that the SP changed the ettringite morphology, thereby negatively affecting the mechanical strength of the CSA pastes.

Automated summary

This study investigated the impact of three types of nanosilica on the hydration, strength, and microstructure of calcium sulfoaluminate cement pastes with and without a superplasticizer. The results showed that powdered nanosilica delayed cement hydration, while colloidal nanosilica had little effect. The superplasticizer improved the dispersion of cement particles and increased the degree of hydration. However, when the superplasticizer was used with powdered nanosilica, it hindered cement hydration, while it had little effect on the system with colloidal nanosilica. The SEM images indicated that the superplasticizer altered the morphology of ettringite and negatively affected the mechanical strength of the cement pastes.