Steel fibre-reinforced concrete with fully recycled coarse and partially recycled fine aggregates

The construction industry is showing an increasing interest in the integration of Recycled Aggregate (RA) into concrete as a substitute for natural coarse aggregate, whether in full or in part, with the aim of reducing dependence on virgin aggregate. This shift seeks to alleviate the environmental impact associated with the extraction of aggregates from natural resources and address the environmental challenges related to concrete waste. However, there is limited research on concurrently replacing both natural fine and coarse aggregate in concrete. This study investigates the effects of substituting natural aggregates with recycled aggregate concrete, specifically using 100% recycled coarse aggregate in combination with 10% recycled fine aggregate, and further examines the influence of steel fibres on the resulting mix. Replacing natural aggregates with recycled aggregates (100% coarse, 10% fine) leads to an increase in slump value, indicating enhanced workability. However, the addition of steel fibres reduces the slump by 21.12% to 33.33%, reflecting the impact of fibre reinforcement on the mix's flow characteristics. Mechanical testing reveals that the use of recycled aggregates alone generally reduces concrete strength. Specifically, the replacement leads to reductions in compressive strength, split tensile strength, and flexural strength by 48.19%, 76.53%, and 71.96%, respectively, at 28 days. Importantly, incorporating steel fibres into the recycled aggregate concrete mitigates this strength loss, enhancing compressive strength, split tensile strength, and flexural strength by 16.51%, 6.12%, and 7.55% at the 28-day. These findings demonstrate that steel fibres effectively reinforce recycled aggregate concrete, compensating for strength reductions and improving overall performance.