Optimization of Atterberg Limits and Structural Reliability of Cement–Water Treatment Sludge Stabilized Abuja Laterite For Structural Earth Block Production

This study examines the optimization of Atterberg limits and structural reliability of lateritic soil stabilized with Ordinary Portland Cement (OPC) and Water Treatment Sludge (WTS) for structural earth block production in Abuja, Nigeria. The research aimed to characterize the materials mineralogically, establish mixture compositions using Scheffé’s polynomial model, evaluate Atterberg limits and 28-day compressive strength, and determine the optimal mix ratio. Laboratory analyses showed that the laterite contained a combined pozzolanic oxide content (SiO₂ + Al₂O₃ + Fe₂O₃) of 76.22%, meeting pozzolanic standards, while WTS recorded 68.93% with notable sulphate content (0.97%), indicating limited suitability as a standalone binder. The raw laterite exhibited a low plasticity index (0.42%), while stabilization with OPC and WTS improved shrinkage resistance and moisture stability. Compressive strength tests revealed that the control sample attained 3.508 MPa, whereas optimized mixes B12 and D12 achieved 3.469 MPa (98.9% of control) with enhanced dimensional stability. Scheffé’s optimization yielded coefficients of determination (R²) above 99%, confirming strong model reliability. The optimal mix composition was approximately 0.39 OPC, 0.08 WTS, 0.53 water, and trace laterite. The study concludes that controlled incorporation of WTS (≤8%) with OPC effectively stabilizes lateritic soil for durable, sustainable, and low-cost earth block production, demonstrating Scheffé’s model as a robust optimization tool for material design.