Development of sustainable ash and Calcined Clay Cement (C3) based composites and building units: An effort towards low-cost housing solutions

This research investigates the potential of supplementary cementitious materials (SCMs) in the composites and building units involved in housing and building e.g., mortar: used for plaster and masonry work, concrete: used for flooring and roofing, bricks: used for masonry, blocks: used for load and non-load-bearing walls and pavers: used for pathways and driveways. OPC is partially replaced by SCMs in composites and building units with SCMs such as fly ash, bagasse ash, and calcined red mud (Calcined Clay Cement C3) at multiple replacement levels. Three techniques vibration, energy-intensive, and vibro-compaction—were employed, with vibration applied to composites, both vibration and energy-intensive techniques applied to laboratory-scale units, and vibro-compaction applied to industrial-scale production. Laboratory testing identified optimum mixes, which were then upscaled for industrial applications. The results showed that 20 % replacement of fly ash (F20C) achieved a 90‑day compressive strength of 37 MPa while reducing CO₂ emissions by 61 kg m⁻³ and lowering cost from PKR 420 m⁻³ to PKR 374 m⁻³ (cost index reduced from 12.73 to 10.10). Similarly, 20 % calcined red mud (RM20C) achieved 38 MPa at 90 days. For mortar, the F20M mix reached 27.3 MPa at 90 days and reduced CO₂ emissions by 84.5 kg unit⁻¹ , lowering the cost index from 0.97 to 0.88. The OB‑4 brick mix (5 % OPC, 20 % fly ash, 25 % bagasse ash, 30 % fines, and 20 % coarse aggregates) achieved a 56‑day compressive strength of 12.1 MPa, reduced CO₂ emissions from 585 kg to 202.5 kg per 1000 units, and lowered the cost index from 1.75 to 1.46. The optimized paver mix (F20P‑E2) reached 29.5 MPa at 56 days and reduced CO₂ emissions by 116 kg unit⁻¹ . Optimized building units exhibited reduced cost indices, making them viable for low-cost housing applications. Compressive strength tests revealed that vibration techniques were more effective for coarse aggregate-rich units, while energy-intensive techniques performed better for finer aggregates. The incorporation of SCMs led to a significant reduction in CO₂ emissions and overall material costs. These findings support the development of sustainable, eco-friendly construction materials that align with cost reduction goals and carbon footprint minimization, promoting sustainable development in the construction industry. In addition, this study aligns with of Sustainable Development Goals (SDGs): SDG 11 (Sustainable Cities and Communities), SDG 12 (Responsible Consumption and Production), and SDG 13 (Climate Action).