Electromagnetic sensing and modeling for cement paste moisture estimation

Electromagnetic sensing techniques, such as ground-penetrating radar and imaging radar, are capable of both surface and subsurface sensing of concrete structures, such as bridges, roadways, and tunnels, etc. However, the performance and effectiveness of electromagnetic sensing techniques for concretes highly depend on a fundamental understanding of the material's dielectric properties as a function of the water-to-cement (w/c) ratio and moisture content. The aim of this paper is to investigate the combined effects of the w/c ratios (0.35, 0.42, 0.45, 0.5, 0.55) and moisture content in cement paste within the frequency range of 1-4.5 GHz. Twelve cement paste specimens were analyzed: six were oven-dried, and six were conditioned at room temperature. The dielectric properties of the twelve specimens were measured in a frequency range of 1-4.5 GHz. Subsequently, the dielectric constants were modeled and discussed. The model was used to estimate the moisture content of the cement paste. The estimated moisture contents were compared with the actual results. The results indicate that for most samples, the estimated results match very well with the actual results. However, with a lower moisture content, the model tends to exhibit a bias toward underestimation.