Biaxial shear behavior of recycled concrete aggregate reinforced concrete beams

The study aimed to investigate the capacity of reinforced concrete beams that include Recycled Coarse Aggregates (RCA) when subjected to biaxial shear loading. Nine beams of square cross-section 300 mm x 300 mm were tested until failure under three different load inclinations angles. The specimens were divided into three groups based on the aggregate type: 100 % Natural Concrete Aggregate (NCA), 100 % RCA, and a combination of 60 % RCA and 40 % NCA. The experimental results indicated that the uniaxial shear capacity of the 60 % RCA and 40 % NCA specimen was higher by about 8 % compared to the uniaxial shear capacity of the NCA and RCA specimens. Additionally, the 60 % RCA and 40 % NCA specimens showed better performance in terms of capacity and deformation than the RCA specimens under all load inclinations. This outcome is also supported by literature investigating the flexural and uniaxial shear capacity of reinforced concrete beams that incorporate 60 % RCA and 40 % NCA. Furthermore, the study revealed that the biaxial shear capacity generally decreased as the load inclination angle increased, and there was a quadratic relationship between the biaxial shear capacity of the tested beams and the load inclination. Theoretical values of the biaxial shear capacity based on the cross-section geometry, material, and load inclination were determined using equations proposed by Tinini et al. and were found to give conservative predictions of the biaxial shear strength. Therefore, the study highly recommends the use of the 60 % RCA and 40 % NCA combination in reinforced concrete beams and the equations proposed by Tinini et al. for biaxial shear capacity.