Long-term behaviour of particulate-filled epoxy-based polymers

Long-term behaviour of particulate-filled epoxy-based polymers

Epoxy-based polymers are now widely used in civil engineering applications including bonding of structural elements, filling for structural repair, and coating for railway sleepers. Recently, different particulate fillers were introduced to reduce the cost of epoxy-based polymers. While the optimum amount of fillers was found to enhance the short-term properties of epoxy-based polymers, their effect on the long-term properties is still unknown. Understanding the long-term behavior of epoxy-based polymers is important as this material is subject to different environmental conditions, which can limit their application range.

This study systematically investigated the long-term durability through deep understanding of the mechanistic response of particulate-filled epoxy-based polymer coating containing fire retardant (FR) and fly ash (FA) fillers. It focused on the weathering effects of high moisture, elevated in-service temperature, and solar ultraviolet (UV) radiation, and the synergistic effects of these severe environmental conditions on the mechanical, physico-chemical and microstructure behavior of particulate-filled epoxy-based polymer. New empirical models were also developed to predict the changes in the mechanical characteristics of epoxy-based polymers when exposed to harsh environmental conditions.

The effect of in-service elevated temperature (from room temperature to 80°C) was evaluated as the first study. FR and FA filler materials were increased from 0% to 60% (with an increment of 20%) in the epoxy based matrix. The physical, mechanical and microstructure of particulate-filled epoxy polymers epoxy-based polymer matrix was examined. The results showed that sensitivity of epoxy resin against in-service temperatures can be significantly improved by the inclusion of fillers by up to 60% by volume. A simplified prediction equation based on power function showed a strong correlation to the experimental strength properties of particulate-filled epoxy based resin at different levels of in-service elevated temperature.

The effect of the combined moisture and temperature (hygrothermal conditioning) on the durability of particulate-filled epoxy resin was investigated as the second study. The epoxy resin was conditioned for up to 3000 h at temperatures up to 60ºC and a relative humidity of 98%. Inclusion of fillers was found to decrease the moisture absorption, increase the glass transition temperature and slightly reduce the mechanical properties after hygrothermal conditioning. Based on the Arrhenius model, the filled epoxy polymers can retain more than 70% of their mechanical properties at 100 years of service in the Australian environment.

The behaviour of the particulate filled epoxy polymer coating when exposed to UV was investigated as the third study. Epoxy-based resin system filled with FR and FA was exposed to UV for up to 2000 h. It was found that adding up to 60% by volume of FR and FA reduced the UV degradation to 0.5 mm, which is 5 times less than that of the neat epoxy resin. The developed prediction equation showed that providing a polymer coating of 11 mm will result in up to 100 years UV resistant materials.

Finally, the synergistic effect of temperature, moisture and UV on the long-term performance of the particulate filled epoxy polymer coating was evaluated. The polymer coating was conditioned at a relative humidity of 98% and temperature of 60ºC for 2000 h (HG). These specimens were then exposed to UV for 2000 h. It was found that not all environmental conditions were detrimental to the properties of particulate filled epoxy, indicating its suitability as a protective coating material.
An in-depth understanding of the long-term behaviour of particulate filled epoxy polymer coating was the significant outcome of this study. The results from this
work provided a good representation and comparison of the long-term properties and durability performance of particulate filled epoxy polymer coating in different harsh environments. The experimental data, theoretical models and predictions equations derived from this study are critical for a safe mix design and use of epoxy-based polymers as coating for civil infrastructure.