Modeling of moisture diffusion in FRP strengthened concrete specimens

Modeling the movement and distribution of moisture in the fiber-reinforced polymer (FRP) composites strengthened concrete structure is important because the interfacial adhesion between FRP and concrete is susceptible to moisture attack. Using relative humidity as the global variable, the moisture diffusion governing equation was derived for the multilayered system in this study. The moisture diffusivity (diffusion coefficient) and the isotherm curve, which correlates the moisture content to environmental relative humidity, of each constitutive material (concrete, epoxy, and FRP) were experimentally determined. A multilinear diffusivity model was developed for concrete based on desorption test, and a linear diffusivity model was proposed for epoxy adhesive based on absorption test. A simple method was developed to directly measure the FRP/concrete interface region relative humidity (IRRH). Finite-element analysis was performed to study the moisture diffusion in the FRP-adhesive-concrete system. The IRRH values were obtained for different environmental relative humidity in the numerical study. The error between the experimental and numerical results of IRRH at test locations was less than 5% RH. The good agreement between experimental and numerical results indicates that the approach developed in this study worked well.