A carbon footprint assessment for usage of recycled aggregate and supplementary cementitious materials for sustainable concrete: A life-cycle perspective in China

Recycled coarse aggregates (RCA) from construction and demolition (C&D) waste have emerged as a sustainable solution to the challenges of natural resource depletion and C&D waste disposal. However, amidst the global push to reduce carbon emissions, the embedded carbon in the recycling and transport processes of RCA has prompted questions about their effectiveness in mitigating concrete-related emissions. This study first compares the carbon footprint of RCA sourced from fixed and mobile plants with that of natural aggregates (NA). A two-stage transport model is incorporated to highlight the contrasting carbon emission characteristics of recycling RCA via these two modes in urbanized areas. Since supplementary cementitious materials (SCMs) are commonly used in concrete to improve performance and significantly reduce carbon emissions, the life cycle assessment (LCA) is further performed to explore the synergistic potential of combining RCA with SCMs for greater carbon mitigation. The results underscore the potential for reducing emissions from concrete by substituting NA with RCA recycled from both mobile and fixed plants. Sensitivity analysis further illustrates that the carbon reduction benefits of RCA can be enhanced by optimizing waste recycling programs. Considering both the technical characteristics and emissions of concrete, a combination of RCA and SCMs emerges as a more effective solution to mitigate emissions sustainably. It is anticipated that the results will provide valuable data and technical insights for policymakers.