Title: Study on early stage hydration of cementitious system in presence of silica nanoparticles

Abstract

Application of silica nanoparticles (SNPs) in cementitious system has been widely explored during last decades as they provide higher mechanical strength and acceleration in hydration process (1-7). However, size, shape and physical state of SNPs in cementitious system have not been well understood. Most of the researchers used colloidal nanosilica which causes agglomeration and therefore weaker zone formation takes place (6-10). We have prepared cost effective uniform size (30-70nm) SNPs, which can be well mixed with cementitious materials. A systematic hydration study has been carried out on tricalcium silicate (C3S) (major component of Portland cement) so as to understand the kinetic behaviour of cementitious system in first 24h. The present work is focused on the effect of particle size and form (i.e. colloidal and powder) of silica nanoparticles (SNPs) on its early age reactivity. Three different types of commercially available SNPs i.e. Elk microsilica (100-300 nm), colloidal SNPs (8- 15 nm) and powder SNPs (10- 70 nm) were used for the study. The results showed that the colloidal and the powder SNPs have higher reactivity than the microsilica. Furthermore, FTIR and 29Si-NMR results revealed that in the presence of the colloidal and the powder SNPs, the structure of C-S-H gel was more ordered as the Q2 and Q3 peaks were very shaper and intense. However, with microsilica, unreacted silica peak Q4 peak was present showing the slower reactivity of microsilica. Further, it was also observed that in presence of powdered SNPs, the polymerization rate of silicate chain is higher as compared to the colloidal SNPs.