Effect of colloidal nanosilica as an admixture on chloride ion diffusion of Portland cement–fly ash mortars

Abstract

The properties of the ordinary Portland cement (OPC) mortar having a water–cement (w/c) proportion of 0.450 and cement/sand ratio of 1:2 are altered by replacing cement with 25% fly ash and adding 2% colloidal nanosilica separately and in a combined form. The changes were studied experimentally. Cured specimens at different ages were subjected to compressive strength test, split tensile test, and durability tests such as sorptivity, water absorption, and chloride penetration. The impact of the addition of colloidal nanosilica on the permeability of the mortar matrix, estimated by the coefficient of absorptivity, was computed by performing a water absorption test for 60 min. It was observed that in the initial curing regime, fly ash expansion causes a decrease in strength and an increase in water permeability. The addition of 2% colloidal nanosilica proves to be advantageous in the hardened OPC and fly ash mortar as it increases the materials characteristic strength by conferring it a dense microstructure. Nanosilica in the cement matrix with and without fly ash assists the rapid growth of hydrated products by creating additional nucleation sites and improving the durability properties of the material as anodic polarization decreases under impressed voltage. The microstructure was analyzed by SEM and found to have the refinement of a pore structure and densification of binding gels in the colloidal nanosilica -incorporated samples.