Combined usage of micro-silica and nano-silica in concrete: SP demand, cementing efficiencies and synergistic effect

It is well known that the addition of micro-silica (MS) can improve the strength and durability of concrete and the addition of nano-silica (NS) can also improve certain properties of concrete. However, systematic research is still needed to exploit the benefits of combined usage of MS and NS, and more specifically, to evaluate their cementing efficiencies and synergistic effect. In this study, an experimental program was launched to investigate the combined effects of MS and NS on the compressive behaviour of concrete. Concrete mixes with varying water/cementitious materials (W/CM) ratio, MS content and NS content but similar workability were produced for testing. It was found that NS has much higher superplasticizer (SP) demand and cementing efficiency than MS. Nevertheless, at the same strength, the SP demand of (MS + NS) is not higher than that of pure cement. More importantly, the combined usage of MS and NS offers certain synergistic effect, as evaluated by a new formula proposed in this study.