Développement d'une méthode diélectrique radiofréquence (RF) pour le suivi de l'hydratation des matériaux cimentaires

The development of the microstructure of cementitious materials at a young age is responsible for the development of these materials' properties, particularly mechanical and rheological. It is therefore important to be able to use measurements to monitor the hydration processes of cementitious materials, i.e. the chemical reaction between cement and water at the beginning of the life of such a material. The calorimetric methods usually used provide information on the evolution of the reaction and the degree of hydration. However, they are destructive and unsuitable for in-situ application. This thesis proposes a method of RF dielectric measurement for the non-destructive monitoring of hydration in cementitious materials. It is based on experimental and modelling developments. We have designed a probe and a broadband RF measurement protocol from 50 MHz to 3 GHz adapted to measurements on cement paste during hydration. The model developed is a multi-scale model for predicting the evolution of the dielectric permittivity of a cement paste during hydration. It combines molecular dynamics simulations at the nanometric scale, homogenisation models to pass to the mesoscopic scale of the hydrated calcium silicate (C-S-H) gel, and then to the macroscopic scale of the cement paste. Finally, we present and analyse RF dielectric spectroscopy measurements of hydration monitoring, carried out over 28 days, on different cement pastes (differing in their water/cement mass ratios). The RF measurements proved to be sensitive to variations in hydric properties during hydration, as well as to various changes in the material, such as those affecting the connectivity of its capillary network, or the setting of the cement paste. In addition, the measurements are in good agreement with the predictions of the multi-scale model, particularly when it takes into account the densification of C-S-H.