Understanding Water Diffusion Characteristics in Civil-Grade Epoxy Materials: A Comprehensive Study Through Microscopic Observation and Numerical Analysis

The utilization of civil-grade thermosetting materials encounters constraints due to their vulnerability to various environmental factors, primarily water absorption. Thus, a comprehensive investigation of water diffusion characteristics is imperative to fully understand the underlying mechanisms and devise effective strategies for mitigating water-induced challenges. This research aims to investigate the water diffusion characteristics (e.g., diffusivity, solubility) and associated damage of a civil-grade epoxy resin. A series of room-temperature diffusion tests were conducted over two months under deionized and tap water to observe the water diffusion characteristics of the epoxy resin. An in-house MATLAB code was developed to compute water diffusion coefficients utilizing the 1D Fickian equation. A baseline representative volume element-based finite element (RVE-FE) diffusion model was formulated based on micro-computed tomography (micro-CT) image analysis of the specimens, facilitating a detailed comprehension of water diffusion characteristics associated with manufacturing defects (i.e., porosity). Results show that the epoxy is more susceptible to tap water than deionized water; all specimens experienced water gain of approximately 50% of their initial weight, resulting from internal porosity. A porosity content determined from micro-CT observation confirmed that the civil-grade epoxy has a greater porosity than conventional industry epoxy systems, rendering it more susceptible to water diffusion. This research will establish a foundation for the development of a thermoset with enhanced environmental resistance by modifying the epoxy resin system.