Synergistic cementing efficiencies of nano-silica and micro-silica in carbonation resistance and sorptivity of concrete

Abstract

Nano-silica (NS) and micro-silica (MS) are both effective in improving the strength and durability of concrete, but their combined effect on a particular performance attribute may not be the same as the sum of their respective individual effects. In this research, the individual and combined effects of NS and MS on the carbonation and sorptivity of concrete were studied by conducting carbonation and water absorption tests of concrete mixes with different cement, NS, MS and water contents, and SEM imaging of the microstructural changes due to the addition of NS and/or MS. Then, the cementing efficiencies of NS and MS in carbonation resistance and sorptivity were assessed in terms of cementing efficiency factors (CEFs). It was found that the CEFs of NS were higher than those of MS, and, more importantly, were at least 48% higher when co-added with MS due to microstructure densification arising from the successive filling of voids by the superfine MS and then the ultrafine NS. Hence, for improving the durability of concrete, it is better to co-add NS and MS so as to exploit their synergistic effects.