Abstract: In recent years, many studies have been done on concrete about the detection of its water content, since it is one of the main causes of degradation. In this study, an experimental set-up of imbibition by capillary effects is used to model the water transfer in concrete. The main objective is to monitor the water transfer through time by electromagnetic (EM) guided waves. The new empirical model-arctan(x) was applied to the experiments on concrete slabs of imbibition. The water content distributions measured by gammadensimetry are set as reference. The results show that the combination of the multi-layer waveguide (WG) model and ground penetrating radar (GPR) measurements allowed to estimate the gradient curves inside concrete slabs.