Experimental investigation and code-based assessment of the shear behavior of steel fiber-reinforced concrete beams with recycled aggregates

This paper investigates the shear behavior of steel fiber-reinforced concrete (SFRC) beams made of conventional concrete (CC) with natural aggregate and with 50% replacement using coarse recycled aggregate concrete (RAC). The experimental program comprised 12 simply-supported beams without transverse reinforcement, with depths of 300, 400, and 500 mm, tested under four-point bending and designed to failure in shear. For each beam height, two nominally identical beams were tested, considering both conventional and recycled aggregates. The material characterization showed that both mixtures met the performance requirements of ABNT NBR 16940:2021. Although the RAC mixture exhibited a greater dispersion of results during the characterization tests, the beam’s load-bearing capacity was not affected. Experimental tests confirmed that the RAC beams achieved ultimate shear capacities comparable to or higher than those of the CC beams for all depths investigated. Moreover, the beams became increasingly fragile with increasing height. The experimental shear strengths were compared with the predictions from the SFRC shear model recommended in ABNT NBR 16935:2021. For both concretes, code-based shear resistances accounted for only about 30-45% of the mean experimental capacities, indicating markedly conservative estimates. The results demonstrate that partial replacement of natural coarse aggregates with recycled aggregates does not affect the shear performance of SFRC beams and can be safely combined for sustainable structural applications.