Triaxial mechanical behaviours and life cycle assessment of sustainable multi-recycled aggregate concrete

Multi-recycling of concrete waste presents a promising avenue for carbon-negative development and a circular economy. This study comprehensively assesses the triaxial mechanical performance and environmental impact of multi-recycled concrete (Multi-RAC) through three recycling cycles. The results reveal a triaxial failure mode similar to natural aggregate concrete (NAC). The peak stress and peak strain monotonically increase with confinement stress, showing a significant impact (enlarged by 171.4 % to 280.6 % and 397.4 % to 412.0 %, respectively) from 0 to 20 MPa. All P-values for recycling cycles and confining pressure are less than 0.05, with the confining pressure having a more significant effect. Three best-fit multivariate mixed models predict mechanical properties, and a modified elastoplastic model introduces the recycling cycles factor. Numerical simulations confirm the model's accuracy in predicting the triaxial mechanical properties of Multi-RAC. Comparative analysis reveals that the elastoplastic model-derived non-integral high order failure criterion outperforms the Willam-Warnke failure criterion and other conventional criteria. Regarding environmental impact, all indicators (GWP, POCP, AP, EP, and CED) decrease favourably with the increasing number of recycling cycles, with CED and EP playing the most significant roles. Compared to NAC, the five environmentally favorable indicators for RACIII decrease by 3.24 % to 50.6 %, respectively. These findings provide valuable insights for future research on developing eco-friendlier Multi-RAC for sustainable and green infrastructure.