Development of a field water/cement ratio test using time domain reflectometry

Abstract

A reliable and nondestructive method is needed to determine the water-to-cement or water-to-cementitious material ratio (w/cm) of fresh concrete for performance-based quality assurance. This study developed and validated a Time Domain Reflectometry (TDR) based method to quantify the real-time w/cm ratio of fresh concrete. Forty-eight concrete mixtures with varying w/cm ratios, air contents, and cementitious binder types (cement-only, fly ash, and slag) were tested, and TDR measurements were synchronized with conventional tests to establish a calibrated model between the apparent dielectric constant (K_a) and volumetric water content (θ_v). Data were analyzed using the statistical software R, employing group standardization, ordinary least-squares regression, and the Simulation–Extrapolation (SIMEX) method to correct for measurement-error bias. Four models developed for different cementitious binder systems showed strong consistency between measured and predicted results, confirming the reliability of the proposed calibration framework. However, as an empirical model, its applicability may be limited to the specific material range for which it was tested. Future studies should incorporate additional laboratory and field experiments, as well as explore physics-based dielectric modeling, to enhance prediction accuracy and generalization.