Effective medium theories in electromagnetism for the prediction of water content in cement pastes

International audience; Permittivity is a widespread property used to estimate the water content in concrete. To improve the reverse conversion from permittivity measurements to moisture content, we suggest the building of an electromagnetic model of concrete. In this paper, such a model is developed for the case of cement pastes. It relies on electromagnetic homogenization schemes which require an information about the permittivity of the predominant species in the material. Estimating those properties over the frequency range [200 MHz; 1 GHz] was achieved by synthesizing model cementitious binders (C-S-H and portlandite mixtures), by characterizing their macroscopic permittivity with an open-ended coaxial probe and by identifying their intrinsic permittivity with a specific homogenization procedure combining effective medium equations. The identified values are used as inputs for a homogenization procedure estimating the water content in cement pastes. For a wide range of water content, the simulated and measured real parts of permittivity show a good agreement.