Sludge valorization towards sustainable concrete: a biochar-based framework integrating life cycle assessment, and socio-economic impacts

Abstract

While recent studies have demonstrated that biochar supplementation to the cement mixture positively impacted the concrete mechanical properties, there is a research gap in exploring various environmental burdens, human health impacts, and resource consumption patterns accompanying biochar-concrete composite manufacturing. Hence, this study introduces a novel evaluation framework by integrating biochar-concrete properties, life cycle assessment (LCA) criteria, and economic considerations with sustainable development goals (SDGs) achievement. The control mix (C mix) was prepared using 100% cement, and the other mixtures were arranged using different sludge biochar (SB) replacement levels (5–20% w/w). A LCA model was employed to select the best sludge valorization approach, regarding two scenarios: (i) cement mixture (C mix) with sludge landfilling, and (ii) sludge biochar mixture (SB mix). The 5% SB mixture exhibited functional characteristics nearly comparable to those of the C mix, particularly in terms of compressive strength at 7 and 28 days, split tensile strength (3.5 MPa at 28 days), water penetration depth (≈ 2.8 mm), and durability. Applying this mixture in concrete maintained LCA endpoint categories of 0.005 DALY, 3.7 × 103 PDF m2 yr, 7 × 103 kg CO2 eq, and 70.6 × 103 MJ primary for human health, ecosystem quality, climate change, and resources, respectively. This mixture scenario could also fulfill 11 SDGs, including human health protection (SDG_3), resource recovery (SDG_12), climate change mitigation (SDG_13), and ecosystem preservation (SDG_14). Because the combined technical/LCA/SDG framework could maintain a sludge management approach for biochar-concrete industrialization, future work should focus on quantifying other scenarios related to energy, climate, urbanization, transport, and low-carbon cement development.