Synergistic effect of colloidal nano and micro-silica on the microstructure and mechanical properties of mortar using full factorial design

The optimum interaction of colloidal nano-silica (CNS) and micro-silica (MS), which is a function of W/C and cement fineness, has an exclusive effect on the particular properties of cement composites, such as strengths, porosity, and microstructure. For sensitivity analysis, a full factorial design was applied wherein two water-to-binder (W/B) ratios were applied inconstant workability, and four levels of CNS and MS were produced and tested at different ages through many specimens. The results show that the synergistic effect of CNS and MS leads to higher performance of mechanical strength and porosity at all ages of curing when compared with their individual use. Using silica particles more than optimum values leads to inverse behavior in strength while the porosity continues to improve. Wider particle size distribution in ternary mixtures creates cement composite more dense and homogeneous, which was also confirmed by microstructure tests (MIP and SEM). Besides, according to XRD and MIP tests, the further production calcium silicate hydrate (C-S-H) gel is believed to be the reason for this improvement. Sensitivity analysis and analysis of variance also showed that the contribution of CNS to improving strength is greater than that of MS, while MS is more effective in decreasing porosity. (C) 2020 Elsevier Ltd. All rights reserved.