Sustainability assessment of recycled concrete aggregate in the Kathmandu Valley: a comparative analysis with natural coarse aggregate

Increasing construction and demolition waste (CDW) disposal issues in landfills necessitate exploring sustainable solutions in developing nations like Nepal. The reason for this investigation is to assess the sustainability of natural coarse aggregate (NCA) and recycled concrete aggregate (RCA) and examine the practicality of recycled aggregate concrete in the Kathmandu Valley. This sustainability evaluation of RCA and NCA is carried out through qualitative and quantitative assessment across social, environmental, economic, and technical terms. The study uses NCA of Naubise and Dolalghat (nearby quarry sites), and RCA from crushed concrete debris. A total of 28 sub-criteria are identified for the study: 25-qualitative and 3-quantitative. Qualitative analysis is based on a two-level questionnaire survey where experts rate the importance level and scores for each qualitative sub-criteria, whereas the quantitative analysis evaluates the score of sub-criteria: embodied energy (EE), embodied carbon (EC) and strength. The EE and EC values are derived from literature review and primary data, while strength scores are assigned based on the aggregate physical and mechanical properties. The sustainability index is determined by aggregating the scores across all criteria. The results show a sustainability index of 0.872 for NCA and 0.96 for RCA, suggesting that RCAs are socially acceptable, environmentally safe, and economically and technically viable. The study further evaluates the strength of 24 concrete specimens with varying replacement percentages of RCA (0%, 25%, 30% and 50%) for NCA. The results suggest that replacing up to 50% of NCA with RCA achieves a comparable strength to conventional concrete.