Modelling the effect of water–binder ratio on target strength and volumetric conversion factor of normal strength concrete

Concrete performance is governed by the interaction of its constituent materials, among which the water–binder (w/b) ratio plays a dominant role in hydration, workability, compaction efficiency, and strength development. Conventional quality control frameworks relate target strength primarily to characteristic strength and statistical dispersion, without explicitly accounting for the influence of w/b ratio on volumetric conversion during batching. This study investigates the effect of varying w/b ratio on the target strength and volumetric conversion factor (VCF) of normal-strength concrete grades M20–M35. Laboratory experiments involving slump tests, volumetric measurements, and compressive strength tests at 7, 14, and 28 days were conducted in accordance with BS EN standards. Results show that target strength decreases exponentially with increasing w/b ratio, while VCF follows a quadratic trend with a distinct optimum around w/b = 0.55. Statistical models were developed and validated, demonstrating strong predictive capability (R² > 0.90). The study establishes w/b ratio as a critical independent variable for both strength optimization and accurate volumetric estimation, with direct implications for concrete quality control and bill of engineering measurement and evaluation (BEME).