Effect of nano-SiO2 (NS) on dolomite concrete towards alkali silica reaction

The aim of this work was to study the effect of nano silica on the physico-mechanical properties of concrete containing dolomite coarse aggregate and its effect on alkali silica reaction. In this work, Portland cement is replaced by 1, 2 and 4 wt.% nano silica (NS). It is clear that nano silica up to 2 wt.% leads to increase the compressive strength and decrease the total porosity up to 180 days of curing in tap water. This is due to that nano silica content acts as pozzolanic material and nucleating sites for the hydration products, which enhances the cement hydration rate. A 4 wt.% NS led to reduce the mechanical properties but is still higher than dolomite control because it leads to coating of the cement grains, retarding its hydration rate and therefore, decreases the hydration products formation. The resistivity of dolomite concrete control against 1 N NaOH up to 6 months of immersion has been carried out. The results show that all concrete mixes have high resistivity towards 1 N NaOH up to 6 months of immersion. The compressive strength development rate of dolomite concrete control containing 2 wt.% of nano silica is higher than that of control. This is due to the continuous activation and accumulation of hydration products. This indicates that the NaOH has marginal compacts on the mechanical properties reduction, and this result confirmed that dolomite aggregate has higher resistivity to alkali silica reaction. XRD and SEM photograph are applied to investigate the formed hydration products.