Unified Electrical Resistance Model for Non-Destructive Strength Prediction of B40 and B50 Concrete

Electrical impedance measurements offer a promising non-destructive approach for monitoring concrete strength development during hydration. Building on a previous impedance spectroscopy study of B40 concrete [9], this work extends the analysis to B50 concrete (w/c = 0.505) and develops a unified predictive model. Capacitance shows strong frequency dispersion and non-monotonic behaviour, limiting its direct use. Active resistance increases monotonically with strength (R² > 0.98). Separate power-law maturity models are calibrated for each mix. A unified model incorporating cement content correction is proposed: P = 15.49·(C/400)1.35·[ln(R/R 0 )]1.57. Evaluated on the combined B40 and B50 data sets (1.4–60 MPa), the model achieves R² = 0.996 and mean absolute error of 0.80 MPa. With one-time calibration of initial resistance on a given batch, the approach supports continuous on-site strength monitoring and optimised formwork removal; transferability to subsequent batches requires further verification.