Performance Enhancement in Concrete Using Nano Silica and Fly Ash

To improve the concrete performance, combining nano materials with mineral admixtures is quite effective in refining the fresh as well as hardened properties. However, the combined effects of nano and micro level materials on the concrete performance needed to be investigated for better understanding of their synergistic effects. In this paper fly ash (FA) is blended with nano silica (NS) replacing ordinary Portland cement (OPC) grade 43 to produce high performance concrete (HPC). Experiment was conducted at fixed water binder ratio with varying percentage of superplasticizer to produce workable and cohesive mix. Ternary blending with NS gave better cube strength at early stage than the binary blended mix. Even at later stage there was enhancement in the strength at 15% FA and 2% NS replacement. This could be due to seeding effects of ultra fine NS particles providing favourable hydration conditions for FA. Nano modified concrete gave lower strength at higher proportions due to the inherent problem of agglomeration. Durability of the mix was investigated by the rapid chloride penetration test (RCPT). Also, ultrasonic pulse velocity (UPV) test was conducted to observe the homogeneity of the mix. Ternary mix of 1.5% NS and 20% FA with OPC was the optimum dosage as it showed enhanced strength and durability. The images obtained from scanning electron microscope (SEM) was analysed to understand the CSH gel formation and the hydration process. These results showed that the combined usage of NS and FA has synergistic effects which could be utilized for maximum performance.