Monitoring of Microwave Properties of Early-Age Concrete and Mortar Specimens

Microwave noninvasive and evaluation techniques have shown to be promising for characterization of cement-based materials (CBMs). In the construction industry, the determination of initial water-to-cement (w/c) ratio and cure-state monitoring of early-age CBMs are still challenging tasks. In this paper, measurement results of monitoring of reflection coefficients, electrical conductance and susceptance of early-age concrete, and mortar specimens with different w/c ratios and constituent ratios are presented. The comparative measurements are conducted using a microwave near-field noninvasive testing technique at two frequency bands, namely, R-band (1.7 - 2.6 GHz) and X-band (8.2 - 12.4 GHz). Statistical analysis and exponential curve fitting have been performed on the temporal measurements of early-age (a few first days) CBMs. The results demonstrated that the dynamic ranges, the initial values, and the initial slopes of measurement curves can be used for cure-state monitoring, hydration rates prediction, and initial w/c ratio determination.