Determination of water content in fresh concrete mix based on relative dielectric constant measurement

The volumetric water content in the concrete mix affects greatly both the fresh and hardened properties, rendering which one of the most important factors on quality control in concrete production. A method for determining the water content in fresh concrete mix is established with Ground Penetrating Radar (GPR) to measure the Relative Dielectric Constant (RDC) of the fresh mix. The RDC is measured by calculating the propagation time of the electromagnetic impulse in the material. A hybrid capacitor model is proposed to correlate the composition of the fresh mix to its RDC. Test results have shown that the water content has a strong influence on the RDC of fresh concrete mix. Temperature of the mix must be considered in the RDC test as it has a dominant effect as well. Effects of fly ash and ground granulated blastfurnace slag on the test results are investigated, which are shown to be rather limited compared to those of water and temperature. While the volumes of cement and aggregates in a fresh concrete mix are to a much less extent subject to variations, the volumetric water content can be determined with the hybrid capacitor model proposed in this study.

► A setup for measuring the dielectric constant of fresh concrete is developed.
► Effects of temperature and water content on the dielectric constant are investigated.
► Effects of fly ash and blastfurnace slag on the dielectric constant are investigated.
► A model for the dielectric constant of fresh concrete mix is established.
► Water content in fresh concrete mix can be determined with the setup and model.