A Regression-Based Predictive Model for the Compressive Strength of All-in-Laterite Concrete

Abstract

All-in-laterite concrete, in which lateritic material supplies both the fine and coarse aggregate fractions, is an attractive, low-cost, locally sourced alternative to conventional concrete in tropical regions, yet its adoption is constrained by the lack of a validated tool to predict compressive strength from mix-design variables. This study characterises all-in-laterite concrete produced from laterite from Idah (Kogi State, Nigeria) and develops a regression-based predictive model of its compressive strength. Laterite fine and laterite rock aggregates were tested for specific gravity, water absorption, particle-size distribution, abrasion resistance, and oxide composition. A total of 108 cubes were cast across three mix proportions (1:2:4, 1:1½:3, 1:1:2) and water–cement ratios from 0.65 to 1.25, and tested for compressive strength at 7, 14, 28, and 64 days, alongside slump and hardened density. The aggregates were normal-weight (bulk specific gravity 2.32–2.48) but highly absorptive (7.95–13.5%), and the coarse fraction was mechanically sound (Los Angeles abrasion 25.56%). Strength followed the classical inverse relationship with the water–cement ratio, with peak 28-day strengths of 18.8–23.4 MPa rising to 21.0–26.9 MPa at 64 days. Twelve mixes (48 strength observations) were pooled and fitted by ordinary least squares to a model of the form fc = β₀ + β₁(w/c) + β₂(a/c) + β₃ln(t), which achieved R² = 0.936 (adjusted R² = 0.932, RMSE = 1.26 MPa); a simplified 28-day model achieved R² = 0.942. Leave-one-mix-out cross-validation returned Q² ≈ 0.91 for both models. All-in-laterite concrete from the studied source is a viable normal-weight structural material for lightly-loaded and non-structural applications when proportioned on an effective-water basis, and its 28-day strength can be predicted to within about ±1.3 MPa from three routinely available mix-design variables.