A novel environmental framework for cleaner cement production in a cement plant

Abstract

Meeting the Paris Agreement goal of maintaining the global temperature ‘less than 2°C and towards 1.5°C above preindustrial temperatures requires combined CO2 emissions from all countries and sectors to fall to zero and then become progressively negative by 2050–2055 (1.5°C) to 2070–2075 (2°C). Cement production is a critical component of modern infrastructure but is associated with significant environmental impacts, including high greenhouse gas (GHG) emissions, substantial energy consumption, and excessive resource usage. To address these challenges, this doctoral study proposes a novel environmental framework for cleaner cement production, structured into four integrated components: (i) Environmental Impact Assessment, (ii) Material Substitution Strategies, (iii) Optimized Production Model, and (iv) Validated Cleaner Production System. The urgency of mitigating these environmental consequences necessitates a comprehensive assessment of cement production, particularly within the South African (SA) context, where research remains limited. This study conducts a Life Cycle Assessment (LCA) of SA cement plants utilizing both midpoint and end-point approaches of the Life Cycle Impact Assessment (LCIA). A cradle-to-gate analysis of 1 kg of cement produced in a typical South Africa plant revealed that 0.993 kg CO2 eq emissions are released per kilogram of cement, with 98.8% attributed to actual CO2 emissions, significantly contributing to global warming. Furthermore, emissions of 1.6 kg of 1,4-Dichlorobenzene (1,4-DCB) eq into air and water exacerbate toxicity levels, while 0.139 kg of oil eq is linked to fossil resource scarcity. The end-point analysis highlights the potential endangerment of 55,404 human lives and 133 species annually, with a projected economic impact of R6.2 billion due to resource scarcity. To mitigate these environmental concerns, material substitution emerges as a viable strategy. This study reviews the effectiveness of various material replacement approaches, including waste and recycled materials, in reducing energy use and GHG emissions in cement production. Findings indicate that partial (1%-60%) and total material substitution can reduce energy consumption by 5.5%-40% and GHG emissions by 1%-94%. To determine the most environmentally beneficial method of cement manufacturing, an integrated life cycle assessment multi-criteria decision-making technique was employed. The LCA is employed to quantitatively evaluate the environmental effects of ten different methods of cement production across eighteen distinct categories. Meanwhile, the CRITIC weighted TOPSIS and EDAS MCDM approaches are utilized to rank the various alternatives by determining their proximity to the optimal solution. The LCA results showed that CEM III/A slag cement had lower environmental impacts than Portland cement. With a ranking score of 0.9094 and 1.7228 for EDAS and TOPSIS techniques, respectively, both MCDM identified CM10: ground granulated blast furnace slag (GGBFS) as the most recommended. Also, material substitution strategies were assessed through the valorisation of industrial waste as supplementary cementitious materials (SCMs) for sustainable concrete was carried out using two-step framework and screening over 25 waste materials, followed by a multi-criteria decision-making (MCDM) analysis using the EDAS method to rank top-performing SCMs Fly Ash, GGBFS, Silica Fume, Calcined Clay, and Metakaolin with Fly Ash emerging as the most suitable SCM. The evaluation incorporated technical parameters, pozzolanic reactivity, environmental benefits, and regulatory compliance. These findings are validated by life cycle assessment (LCA) results indicating major carbon and energy savings and highlights the importance of waste consistency, regional supply chains, and performance-based material standards in scaling SCM implementation. To systematically optimize cement production processes, this study employs Mixed-Integer Linear Programming (MILP) to model adaptive fly ash substitution strategies. The MILP model minimizes GHG emissions while maintaining production efficiency, with optimal substitution rates of 30%-40% reducing CO2 emissions by 33% and energy consumption by 19.8%. Coupled with LCA, this approach ensures a quantitative evaluation of environmental impacts, aligning industry practices with sustainability goals. In the LCA of 1 ton of cement production process with and without replacement shows that estimated amount of 80% of the impact categories reduced by 100% in the system that incorporates the partial replacement when compared to the one that doesn’t. Global warming potential and Terrestrial ecotoxicity reduces by 41% and 38% respectively. Significant reduction in CO2 as a major contributor to GW was observed. However, further analysis on TE suggests that partial replacement of clinker with fly ash (30-40%) can slightly increase the amount of some heavy chemicals (Lead, Mercury, Nickel, Vanadium and Zinc) that is emitted into the environment. In conclusion, this research provides a holistic evaluation of cement production’s environmental footprint and offers practical mitigation strategies. It underscores the urgent need for sustainable practices in cement production, highlighting material substitution as a key strategy to mitigate environmental impacts. By integrating LCA methodologies with optimization technique, the study analyses the potential of material substitution in reducing energy consumption and GHG emissions, thereby promoting a more sustainable cement industry. In conclusion, this research presents a novel environmental framework for cleaner cement production, integrating LCA, SCM screening with MCDM, MILP-based optimization, and validation through impact reduction. The framework both improves environmental performance and supports industry alignment with global sustainability goals through actionable, evidence-based strategies.