Fracture behaviours of sustainable multi-recycled aggregate concrete under combined compression-shear loading

Abstract

The mechanical properties and strength failure criteria of natural coarse aggregate and multiple recycled coarse aggregate concrete under the combined compression and shear loading states are investigated in this study. The failure pattern, peak shear strength, and peak shear displacement are compared in terms of the number of regeneration cycles and normal compressive stress ratios. The results reveal that both the peak shear strength and peak shear displacement of concrete increase with the enlarged normal stress ratio. The shear failure pattern with higher severity corresponds to more spalling powder and debris deposited on the shear fracture surface. When the times of coarse aggregate regeneration increase, the peak shear strength decreases, and the descending trend becomes more evident with the increased vertical compressive stress ratio, whereas the peak shear displacement significantly fluctuates, regardless of the regeneration time and the normal compressive stress ratios. With normal compressive stress, the contact friction strength becomes the dominated component of peak shear strength consisting of cohesive strength, contact friction strength, and shear dilation strength. Based on the different stress expressions, three compression-shear failure criterion models considering the times of coarse aggregate regeneration under planar stress state were established for concrete. Despite the strong correlation with the correlation factors (R2) larger than 0.96 for all the models, the failure criterion model based on stress invariance and failure criterion model based on octahedral stresses in the quadratic parabolic functional forms provides the highest predictive accuracy. The related outcomes are expected to fill the gap of the related research on recycled aggregate concrete.