Functionality of silica nanoparticles on hydration mechanism and microstructure of tricalcium aluminate

•SNPs shows nucleation effect at early stage (10 min of hydration).•Reverse pattern of C3A reaction is observed at 1 hr of hydration.•Slow C3A hydration is observed in presence of SNPs.•Formation of C-S-H and C-A-S-H might be responsible for slow C3A hydration. In this paper, a detailed reaction mechanism of tricalcium aluminate (C3A) in presence and absence of silica nanoparticles (SNPs) within 24 hr of hydration was studied. The effect of SNPs on an early stage of hydration was assessed through XRD (mineralogical analysis), TGA (quantification of hydrated products), FTIR (analysing chemical bonding) and FESEM (morphological study). The results indicate that SNPs promote C3A hydration at the very early stage of hydration (10 min of hydration), after that retardation in C3A hydration was observed and the pattern of reaction is consistent up to 24 hr of hydration. The retardation might be due to the surface coverage of C3A grain by calcium silicate hydrate (C-S-H) and calcium alumina silicate hydrate (C-A-S-H), thus, the reactivity of C3A decreases. This study presents a detailed inside reaction mechanism of C3A hydration with SNPs, which will help in understanding the influence of other admixtures (such as superplasticizers, accelerators and retarders) in SNPs modified cementitious system.