Effect of Nano-Silica in Performance of Recycled Aggregate Concrete

The effect of recycled coarse aggregate in nano silica solution on the properties of recycled aggregates concrete is compared with the direct mixing of NS in concrete. In this study, four series of concrete are considered. The first and second series are control series containing 100% natural coarse aggregate (NCA) and 100% RCA, respectively. The third and fourth series are similar to the second series in every aspect except that 2 wt% NS is added through direct mixing in concrete and presoaking of RCA in 2 wt% NS solution of 24 hr, respectively. Results show that the measured 7-day compressive strength of recycled aggregate concrete containing presoaked RCA is higher than that containing direct mixing of NS in concrete. The total porosity of mortar adjacent to RCA is also found to be significantly lower than the same, where NS is mixed directly. The concentration of pores in the matrix adjacent to RCA is also shifted to medium capillary pores from the large capillary pores of matrix adjacent to RCA containing no NS. The volume of medium capillary pores reduced significantly in the matrix adjacent to presoaked RCA compared to the same, where NS is mixed directly.