Tensile damage development and constitutive relationship establishment of recycled coarse aggregate concrete based on a double-interface numerical model

The tensile constitutive relationship is essential for determining the ductility and restoring force characteristics of seismic-resistant concrete structures and studying the mechanisms causing damage and fracture to concrete structures. This study investigates the axial tensile stress-strain curves of mortar, the interface between new and old mortar, and recycled aggregate concrete (RAC) with different water-binder ratios and ages. First, the tensile constitutive relationships of mortar and new-old mortar interface were established. Then, based on the experimental results and the random aggregate model, a double-interface numerical model of RAC was established to investigate the development of tensile damage in RAC and the influence law and mechanism of the old mortar strength, thickness and curing age on the curve of the tensile stress-strain of RAC. The results are a comparison of the peak tensile strengths at the same age and water-binder ratio for the above three mortar types, where new mortar > RAC > new-old mortar interface. Under the same thickness of old mortar, the peak stress, elastic modulus and peak cutline modulus of RAC increased with the increase of old mortar strength, and the amplitude of change increased with the increase of mortar thickness. Based on the tensile constitutive relationship of ordinary concrete, the tensile constitutive relationship of recycled coarse aggregate concrete is proposed by combining the experimental results and numerical analysis results.