Investigation of 3D moisture diffusion coefficients and damage in a pultruded E-glass/polyester structural composite

As civil engineers seek to improve buildings and bridges, they are turning to composite materials for some structural components. Thus the long-term life of these materials in damp highly acidic conditions (from concrete pore solutions) is critical. This article presents a study of moisture ingression and damage in a pultruded compression element under exposure to pore solution. The goal was to experimentally find the orthotropic diffusion coefficients for pore solution in the composite material and to evaluate the damage in the composite using SEM. A method for calculating 3D diffusion coefficients based on weight measurements by selectively sealing some surfaces against moisture ingression was successfully employed. This research extends the application of the 3D diffusion solution developed by Pierron et al. to selectively sealed specimens of fixed dimension. The Arrhenius equation was then used to model the diffusion coefficients with respect to temperature. For the first time, sequential SEM images were performed in the same location before and after specimen exposure in an attempt to identify damage development separately from initial damage. These images showed little if any change in specimens exposed at room temperature over the first 19 days: however, characteristically different damage was notable at elevated temperature and for a specimen exposed for 650 days.