TDR-based measurements of water content in construction materials for in-the-field use and calibration

In this paper, a time domain reflectometry (TDR)-based system for measuring water content of raw construction materials is presented. The proposed system relies on the fact that the presence of water leads to an increase of the dielectric permittivity of materials; therefore, from TDR-based permittivity measurements, it is possible to infer the water content value. In practical applications, the proposed system could be used for assessing the intrinsic water content of construction materials before they are poured into the concrete mixture. Knowing the intrinsic water content of the raw materials, in fact, would allow to evaluate the optimal amount of water that should be added to the mixture in order to achieve the desired waterto-cement ratio. This, in turn, would permit to fine-tune and control the mechanical properties of the final concrete structures. For assessing the feasibility of using the proposed system for the intended purpose, water content measurements were carried out on three construction materials, namely, sand, gray cement, and white portland cement. For each of these materials, a calibration curve relating water content to the apparent dielectric permittivity was derived; additionally, through repeated measurements, also a confidence interval was associated with the calibration curves.