Evaluating environmental and economic benefits of using biochar in concrete: A life cycle assessment and multi-criteria decision-making framework

While several studies have assessed the applicability of using biochar in cement mortar and concrete preparation based on the best mechanical properties, this evaluation method should be improved to consider the techno-economic feasibility and the environmental impacts. To address this research gap, this study attempts to compare between the conventional concrete with 100 % cement as a control mixture (CM) and dumping of sludge into open sites (scenario_1), and biochar concrete using alum sludge biochar (ASB) as a partial cement replacement (scenario_2), regarding the project life cycle assessment (LCA) and economic feasibility. A multi-criteria decision-making (MCDM) framework was used to assign scores to the environmental LCA criteria, material functional performance tests, and cost considerations. The two scenarios were arranged in SimaPro LCA software, and then the different criteria were analyzed using the TOPSIS technique to choose the best alternative. The study demonstrated that the functional properties of the cement mixture containing 5 % of ASB were almost comparable to those of CM, owing to the presence of significant amounts of quartz (SiO2) that bonded strongly with cement molecules. This ASB mixture also enjoyed the least environmental impacts, reducing the global warming potential (GWP) by 32.2 % compared with the CM scenario. The scores of the "Cost" criterion, considering the price of raw materials, energy, production, and maintenance, for the two alternatives were almost comparable, depicting that scenario_2 achieved the highest closeness coefficient of 0.95 in the MCDM overall scoring. This study concluded that biochar could be incorporated into cementitious mixtures due to its lower impact on global warming to maintain a sustainable and economic concrete industrial strategy. Future studies should focus on studying the long-term durability of the biochar-based concrete mixtures and integrating into the MCDM strategy; in addition, determining the correlation between sustainable construction implementation and sustainable development goals achieved.