Mechanical, Durability and Environmental Performance of Concrete Incorporating Sawdust Ash as Partial Cement Replacement

Abstract

Cement production contributes approximately 5–8% of global CO₂ emissions, while the timber industry generates substantial sawdust waste, presenting dual environmental challenges. This study investigates the mechanical, durability, and environmental performance of concrete incorporating Sawdust Ash (SDA) — a pozzolanic by-product of controlled sawdust incineration — as a partial cement replacement at levels of 0%, 5%, 10%, and 15%. Concrete mixes were designed using the Department of Environment (DOE) method targeting 30 MPa characteristic compressive strength at 28 days (w/c = 0.48), with specimens comprising 150 mm cubes, 100×200 mm cylinders, and 100×100×400 mm beams cured at 7, 14, 28, and 56 days. Tests conducted included compressive strength, flexural strength, split tensile strength, and water permeability. Compressive strength decreased progressively with increasing SDA content; however, the 10% replacement mix achieved 29.53 MPa at 28 days, satisfying the minimum structural-grade threshold of 25 MPa. Flexural strength peaked at 13.0 MPa with 10% SDA at 28 days, exceeding the control mix value of 10.3 MPa, attributable to enhanced microstructural densification and interfacial transition zone refinement. Water permeability improved progressively with SDA content, with penetration depth reducing from 6.3 mm (control) to 5.5 mm at 15% SDA, reflecting pozzolanic pore refinement and C–S–H gel densification. A cradle-to-gate embodied carbon assessment demonstrated up to 13.02% CO₂ reduction at 15% SDA replacement (from 443.12 to 385.46 kg CO₂/m³); these values are indicative rather than absolute, as transport emissions and full life-cycle stages were outside the defined system boundary. Quadratic regression modelling confirmed non-linear compressive strength behaviour (R² = 0.41), presented as a trend-identification tool within the tested parameter range. Overall, 10% SDA replacement is identified as the structural optimum, offering a viable balance of mechanical performance, durability enhancement, and embodied carbon reduction for sustainable concrete construction.