Synergistic optimization of multi-waste low-carbon concrete using response surface methodology

The adverse environmental effects of conventional concrete manufacturing demand sustainable solutions, including the substitution of Portland cement and aggregates with waste materials. This approach not only minimizes landfill waste but also mitigates resource depletion and environmental risks. Incorporating multiple waste materials like biomass fly ash (BFA) and glass powder (GP) in place of cement, along with shredded rubber (SR) as aggregate, has the potential to enhance cement substitution and support low-carbon concrete production. However, achieving optimal environmental, mechanical and durability standards remain challenging when using multiple waste materials. This study investigates optimal concrete mix designs that incorporate SR, BFA, and GP. Nineteen mixtures were developed using the Response Surface Method (RSM) to model the interactions between these materials. Workability and mechanical properties were evaluated through slump and compressive strength tests, while durability was assessed using Rapid Chloride Migration (RCMT) and bulk electrical resistivity tests. Environmental impact, including Global Warming Potential (GWP) and service life, was also examined, contributing valuable insights toward the development of sustainable concrete solutions. The results demonstrate that GP enhances concrete properties and, when combined with BFA and SR, partially offsets their adverse effects. This allows a greater proportion of waste materials to replace cement, potentially reducing carbon emissions by 30% per 1m³ during the life cycle compared to the control sample. The optimal design space was achieved at 11–20% GP, enabling BFA up to 15% and only SR < 2% to satisfy combined mechanical, durability, and environmental constraints.