Mechanical properties and hydration characteristics of sulfoaluminate cement-based materials containing nano silica

This paper examines the effect of nano silica (NS) on the mechanical properties and hydration characteristics of materials based on sulfoaluminate cement (SAC). The compressive strength and flexural strength of mortars were measured with different NS addition levels ranging from 0 to 3%. The results indicate that the compressive strength and flexural strength are significantly improved with increasing NS content up to 2% and then decrease slightly with a further increase in NS content (e.g. at 3%). The strength loss of SAC-based materials can also be avoided when NS is added. The underlying mechanism was then analyzed by mercury intrusion porosimetry (MIP), microcalorimetry, X-ray diffraction (XRD), differential thermogravimetry (DTG), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results indicate that the microaggregate filling effect and nucleation effect of NS act as the major factors in the early stages while the pozzolanic effect plays a dominant role in the later stages. These effects are beneficial in improving the compactness of SAC-based materials, and thus in increasing the strength and avoiding the strength loss at all ages. These results could also be expected to provide guidance on the use of NS in SAC-based materials.