An Exploratory Structural Performance Index for Reinforced All-in Laterite Aggregate Concrete Beams Under Low Shear-Span-to-Depth-Ratio Loading

Abstract

All-in Laterite Aggregate Concrete (AILAC), in which both the coarse and the fine fractions are drawn from a single weathered laterite deposit, is a low-cost, locally available material for tropical regions, yet its shear behaviour has received little experimental attention. Because the shear strength, service stiffness and deformation capacity of a beam do not in general vary together, no single measured quantity ranks specimens on its own. This paper converts a small laboratory investigation of the shear behaviour of reinforced AILAC beams into an exploratory, within-sample Structural Performance Index (SPI). Four beams of 150 × 150 × 900 mm; three reinforced with 2Ø10, 2Ø12, and 2Ø16 mm tension bars (B_₁-10_, B_₂-12, and B_₃-16) and one plain beam (B_₄), one specimen per condition and without web reinforcement, were tested under symmetric two-point loading. With a shear span a = 150 mm and effective depth d ≈ 100 mm, the shear-span-to-depth ratio is a/d ≈ 1.5, placing the specimens in the short-beam / arch-action regime. Surface strains measured with 60° rosette gauges were reduced, under a pre-crack linear-elastic assumption, to principal strains, principal stresses, and the maximum shear stress; mid-span deflection tracked serviceability. The measured principal stress–strain response is strongly linear and indicates an effective elastic modulus of about 14 GPa and a shear modulus of about 5.8 GPa for the mix. The index combines three normalised, non-dimensional pillars: nominal shear strength, service-load secant stiffness, and ultimate deformation capacity, using a weighted geometric mean, chosen because it penalises imbalances among the pillars. Within the unreplicated series tested, the SPI ranks the beams B_₃-16 (0.93) > B_₁-10 (0.69) ≈ B_₂-12 (0.69) > B_₄ (0.20); the top and bottom ranks are stable across a range of weightings, while the two intermediate beams exchange places depending on the weights. Ultimate nominal shear strength increased with reinforcement ratio across the four specimens, and the principal-analysis shear stress rose with principal strain; an association that is expected, because the stress is computed from the strain through the assumed elastic relations, and is therefore reported as a descriptive consistency check rather than an independent result. Its ordering was consistent with the corresponding energy rankings and observed failure descriptions. The index should presently be interpreted as an exploratory within-sample decision aid; independent testing across laterite sources, reinforcement ratios, and shear-span-to-depth ratios is required before broader validation or design use.