Effect of mixing sequence on fresh and hardened state properties of concrete with recycled aggregate

Abstract

The aim of this work is to compare two methods of incorporation of concrete recycled coarse aggregate (CRCA) in the concrete mixture: at the beginning and at the end of the mixing stage. Concrete mixtures with 0% and 50% of CRCA were developed, with three water/cement (w/c) ratios. Slump loss and electrical resistivity were measured in the fresh state. Compressive strength and water absorption by capillarity were also measured in the hardened state, after 28 days of wet curing. Mixture water absorption by CRCA during mixing was decreased when the insertion was at the end of the mixture, as evidenced by better reduced slump loss. Electrical resistivity measurements are also consistent with this observation. Capillarity absorption and compressive strength, however, showed better results when CRCA was inserted at the start, due to the reduction of w/c ratio caused by the CRCA water absorption during mixing.