Carbon footprint accounting for recycled aggregate concrete with multi-mix designs considering carbonation absorption effect

The accurate accounting of carbon footprint is crucial for promoting the "dual control " of energy consumption to the "dual control " of total carbon emissions and intensity in the construction industry. To address the limitations of the current life cycle assessment (LCA) framework of recycled aggregate concrete, this study established a general calculation model of carbon footprint that incorporated carbonation absorption effect. The model integrated both carbon sources and sinks throughout the life cycle of recycled concrete, based on the theory of LCA. Combined with the actual production conditions in Taiyuan City, the carbon footprint of 500 recycled aggregate concrete and 150 natural aggregate concrete designs with different mix ratios was calculated. The grey model was employed to clarify the emission reduction advantages and environmental benefits of recycled aggregate concrete. The results showed that the average comprehensive carbon footprint of 1 m³ recycled concrete was 326.79 kg CO₂e, which was 13.56 % lower than that of natural aggregate concrete. In terms of emission reduction contribution, the environmental benefits of shortened transportation distance, enhanced carbonation absorption, and the avoidance of landfill accounted for 2.83 %, 23.55 %, and 73.62 %, respectively. Predictions using the grey model indicate that the output of waste concrete in Taiyuan City will reach 26.75 million tons in 2030, achieving a carbon emission reduction of 3.02 million tons at a 60 % resource utilization rate. Therefore, promoting the application of recycled concrete is of great practical significance for the construction industry to implement the “Carbon Peak and Carbon Neutrality” goals.