Long-term moisture absorption and durability of FRP pultruded rebars

Up to 15-years long moisture diffusion into carbon, glass, and aramid fiber reinforced plastic (FRP) rebars is studied. To eliminate uncertainties in identification of the radial and axial diffusivities, a successive methodology for determination of the diffusion coefficients is proposed. The concept of apparent diffusivity taking into account anisotropy and edge effects is extended to cylindrical samples. The ratio of the axial and radial diffusivities is the lowest for carbon (3) and the highest for glass (81) FRP rebars. Durability performance of the rebars is estimated by monitoring their interlaminar shear strength (ILSS). Long-term exposure of FRP rebars in a humid environment resulted to a decrease of their ILSS for 10–50%. Retention of properties after drying of samples was about 90% irrespective of the amount of absorbed moisture and the ratio of anisotropy of the diffusion coefficients.