Integrated carbon assessment for sludge-derived concrete: Modelling and a comparative study

Concrete, a cornerstone of modern construction, bears a significant responsibility for global carbon emissions due to its energy-intensive pyroprocessing processes and the direct carbon emissions associated with limestone decomposition. With increasing global of awareness environmental sustainability, the imperative to decarbonise concrete production is becoming evident. Recent research highlights the significance of producing eco-friendly "green" concrete by incorporating treated alum sludge, a by-product of drinking water treatment often discarded in landfills, within the framework of sustainable construction. This research endeavours to develop a comprehensive model for the integrated carbon assessment of sludge-derived concrete products. By conducting scenario and sensitivity analyses, the study explores the decarbonisation potentials and quantifies the impacts of diverse variables on carbon output across the entire lifecycle of concrete products. These variables encompass supply chain dynamics, cement replacement ratio, carbon intensity of local grid mix, and the utilization of alternative fuels. Findings reveal that in comparison to general purpose (GP) cement production, sludge treatment has the potential to achieve an impressive 83.48% reduction in carbon emissions. Moreover, a modest 10% substitution of cement with treated sludge would contribute to 9.07% overall carbon reduction. The transition to full renewable energy consumption holds the potential for a remarkable 41.97% carbon reduction, while the integration of photovoltaic (PV) electricity and biogas heating offers a substantial 30.57% carbon reduction in the manufacturing of sludge-derived concrete. Nonetheless, supply chain alterations demonstrate limited impacts, given the prevalence of locally sourced raw materials and the low embodied carbon contents of transportation-intensive ingredients such as sand and aggregate. Despite discernible progress achieved through cement substitution and renewable energy penetration, full carbon neutrality remains an elusive goal.