Shear strength of recycled aggregate concrete beams containing stirrups

This paper reports the findings of an experimental study of the shear behavior of reinforced concrete beams produced using recycled coarse aggregates (RCA). A total of eighteen test results from three series of beams containing transverse and longitudinal reinforcement are presented. The variables in the tested beams were the percentage of replacement (PR) of natural coarse aggregates (NCA) with RCA in the concrete mixes, and the amount of stirrups provided. The percentage of replacement in the three series was 0%, 20% and 100%. The ratio of the longitudinal reinforcement in all the beams was 1.38%. The experimental results showed that incorporating RCA at the rates of PR = 20% and PR = 100% in the concrete caused 5% and 9% average reductions in the shear strength relative to the natural aggregate concrete (NAC) beams respectively. The results also showed negligible effects of PR on the shear cracking patterns, the critical shear cracks, the longitudinal steel strains and the mode of failure. However, the midspan deflections of the beams were increased considerably for PR = 100%. Beams that are reinforced with both longitudinal as well as transverse reinforcement are shown to be less affected by the incorporation of recycled aggregates than beams reinforced only with longitudinal reinforcement. The observed ultimate shear strengths were also compared with the calculations of shear equations from the ACI, CSA, MC2010 and EC2 codes. The calculations were conservative for the level of approximation II of the MC2010 model code, but were slightly unconservative for the rest of the methods checked, especially for the beams with recycled aggregates.