Quantifying carbon emissions from different urban slurry resource utilization pathways: a life cycle assessment approach

Abstract Efficient utilization of waste slurry resources is a pivotal strategy in urban engineering construction, aligning with the global “dual carbon” goals of sustainability and carbon neutrality. To quantitatively assess the carbon emission intensity and mitigation potential associated with the utilization and disposal of urban waste slurry (UWS), a life cycle assessment (LCA) framework was adopted. A partial cradle-to-site LCA was conducted for a representative project in Shanghai, China, encompassing all key stages from material extraction to on-site application. An inventory of the materials and fossil fuel energy utilized during construction was compiled to calculate the primary energy consumption and the corresponding embodied carbon. Carbon emission accounting using SimaPro software was conducted for three UWS resource utilization methods: subgrade backfill material (SBM), scour protection backfill material (SPBM), and fluid self-compacting backfill material (FSCBM). Based on the analysis results, recommendations were proposed to enhance carbon emission reduction measures for utilization. The results indicate the following order of carbon emissions from UWS: SPBM (93.1 kg CO 2 -eq/m 3 ) > FSCBM (47.1 kg CO 2 -eq/m 3 ) > SBM (41.8 kg CO 2 -eq/m 3 ). The solidification treatment of UWS has emerged as the dominant contributor to carbon emissions across all utilization pathways, accounting for 59.33%, 61.33%, and 64.12% of the total emissions for SBM, FSCBM, and SPBM, respectively. Notably, in the SPBM route, transportation emissions alone account for 37.8% of the total emissions. These findings suggest that the adoption of low-carbon curing agents and the optimization of transportation methods can significantly reduce overall carbon emissions. Furthermore, from a long-term environmental perspective, direct landfill disposal of UWS constitutes the least sustainable management option, with the highest carbon emissions at 123.62 kg CO₂-eq/m 3 . Compared to plain concrete and recycled aggregate concrete per unit volume, SBM achieves significant carbon reductions of 51.3% and 22.0%, respectively. Consequently, the resource utilization of UWS, especially through SBM, demonstrates significant potential to mitigate environmental impacts, offering a promising pathway for sustainable development in the construction materials sector.