Performance optimisation and field assessment of ternary-blended sandcrete blocks with calcium carbide residue and sawdust

Abstract

Cement production contributes significantly to global greenhouse gas emissions, creating a need for sustainable alternatives. Calcium carbide residue (CCR) and sawdust remain underutilised in Nigeria despite their potential in cement-based applications. This study evaluates physical, mechanical, and economic performance of hollow sandcrete blocks incorporating CCR and sawdust, with emphasis on full-scale production and field application. A total of 206 standard hollow blocks (225 mm) were produced and used in a building extension from damp-proof course to lintel level. Laboratory tests include water absorption (WA), density and compressive strength (CS) followed the Nigerian Industrial Standard (NIS). Blocks with 30% CCR exhibited density comparable to the control but lower CS, falling 18% below the NIS minimum of 1.5 MPa at 28 days. Sawdust-based blocks showed reduced density and easier handling but exhibited high-WA and CS reductions exceeding 40% relative to the control. Mixture design modelling revealed cement had the strongest positive effect on strength (R2 = 0.917), while WA models showed excellent fit (R2 = 0.919). Numerical optimisation identified an optimal mixture of 1063 g cement and 37 g CCR per 1100 g binder, predicting 28-day strength of 1.70 MPa and WA of 7.97%. Economic analysis showed the CCR-modified mix achieved the highest performance-to-cost ratio, followed by control while sawdust-based mixes ranked lowest. Qualitative field observations were consistent with laboratory findings: carbide blocks showed no dampness, while sawdust blocks exhibited dampness after rainfall. CCR is a viable sustainable material, while sawdust requires careful consideration due to its negative effects on strength and absorption.