Studies on optimization of silica nanoparticles dosage in cementitious system

•SNPs show its nucleation effect at 8 h of hydration and pozzolanic effect at 24 h of hydration.•Nucleation and pozzolanic effect of SNPs is increased with the increasing dosages of SNPs.•With 10% SNPs addition, these effects are less significant showing the optimised dosage of SNPs is being ~5% in C3S.•SNPs accelerate the polymerization of silicate chain, which increases its crystallanity with higher dosage of SNPs.•Capillary porosity is reduced ∼58% with 10% addition at 24 h of hydration.•The compressive strength results show that optimised dosage of SNPs in cement is 2–3%.

Optimization of silica nanoparticles (SNPs) dosage in cementitious system was carried out analytically as well as experimentally by understanding the early stage hydration reaction of tricalcium silicate (C3S). XRD and TGA results show the maximum nucleation effect of SNPs at 8 h, when the rate of product formation was higher than the control (∼66% additional CSH and ∼61% more CH with 10% SNPs addition). While at 24 h of hydration, ∼25% additional CSH was formed and CH content reduced by ∼32% with 10% addition showing the pozzolanic effect of SNPs. Further, FTIR results reveal that SNPs accelerate the polymerization in silicate chain and with 10% SNPs addition more crystalline (probably tobermorite like) structure is formed. This is responsible for the formation of highly compact and dense microstructure at 24 h as observed in electron micrographs, which may be responsible for the slow hydration rate at later age. XRD, FTIR and TGA studies on C3S revealed that up to 5% addition of SNPs is beneficial, whereas higher dosages do not contribute significantly. Based on these investigations, studies were performed on cement paste, mortar and concrete samples, which revealed that 2–3% addition of SNPs is the optimum quantity for significant contribution in strength properties.