An Experimental Investigation to Enhance the Strength of Recycled Aggregate Concrete Using Silica Fume

Abstract

Burying construction waste in the soil causes a negative environmental impact. Therefore, it is essential to find effective disposal methods, such as recycling and reuse. This study investigates the effect of using recycled concrete aggregate (RCA) at 25%, 50%, and 75% on the mechanical properties of new concrete, as well as substituting of a 10% and 20% of the cement with silica fume to compensate for the expected decrease in concrete strength when using RCA. The results showed that replacing 25% of the natural coarse aggregate (NCA) with RCA does not significantly affect compressive strength. Replacement percentages of 50% and 75% caused a greater decrease in strength. These ratios have a greater impact on tensile and flexural strength than on compressive strength. A 25% replacement ratio yields better results than other ratios. Adding silica fume has a positive effect; replacing 10% of the cement with silica fume increases compressive strength by 12% as compared to ordinary concrete, by 8% compared to concrete treated with 25% RCA, and by 9% compared to concrete treated with 50% RCA. However, replacing 20% of the cement with silica fume reduces strength compared to ordinary concrete. Therefore, the reductions resulting from replacing 25% and 50% of the RCA with NCA can be repaid by replacing 10% of the cement with silica fume.