Use of nano-silica sol in concrete: Performance and influence mechanisms

Abstract

Nano-silica sol (NSS) is an aqueous liquid containing colloidal nano-silica in dispersed state. It has been reported to offer better effects to the cement-based materials compared with nano-silica powder, which is by far the most widely studied nanomaterial for concrete applications. To identify the optimal type of NSS (acidic/ neutral/ alkaline) for use in cement-based materials, its effects on the performances and the influence mechanisms, a three-staged research program for testing the workability, strength, durability and chemo-physical properties of mixes with various types and contents of NSS at various ages has been completed. Generally, the addition of NSS decreased the workability and increased the strength and durability of concrete. It was found that alkaline NSS was the desirable type from the viewpoint of highest workability and strength. X-ray diffraction patterns, wet packing density, scanning electronic microscope images and mercury intrusion porosimetry tests verified the pozzolanic reaction effect, nucleation effect, densification effect and pore modification effect brought about by NSS. In-depth analysis revealed that the NSS induced nucleation effect at early age and pozzolanic reaction effect at later age, densified the microstructure and reduced both volume and size of pores. These effects explained the improvement of strength and durability of concrete by using NSS.