Use of electromagnetic waves propagating in multilayer waveguide to characterize water transfer in concrete

Water content, known as one of the most important durability monitoring parameters of concrete, has been widely studied by GPR under homogeneous conditions. In this paper, we employ an experimental protocol by its capillary effects to monitor the water penetration into a porous concrete. In this case, concrete cannot be considered as homogeneous anymore. An innovative technique is developed here for extracting and exploiting the Electromagnetic (EM) waveguide dispersion of civil engineering materials with GPR, which enables us to study the water gradient inside a concrete. This technique is based on a new inversion procedure that relies on the Electromagnetic Waveguide Model (WGM) inverting the phase velocity dispersion curves in their modal form to estimate the dielectric constants and geometric parameters of the propagation medium. A homogenization Parallel model, derived from the well-known Lichtenecker-Rother equation is employed to develop the waveguide from a one-layer medium into a multilayer medium. The multi-layer WGM outputs offer a primary application on monitoring water transfers in concrete through water ingress cycles. This procedure is validated with GPR measurements on homogeneous materials. Then it is applied on concrete to monitor the water ingress front during an absorption process. The results of gammadensimetry, measured on cores monitoring the same imbibition process, are used as reference. Both results are found to have good agreements with each other, providing some key information of the studied concrete on conditioning states.