Prediction of durability of cold-curing epoxy resins: comparison between natural and artificial weathering

In recent years, epoxy resins, widely employed in many industrial fields, have been used in several civil engineering applications. Structural repairs are often carried out by either injection of the neat resin or application of fiber-reinforced composites based on epoxy matrix. These materials are also used for restoration works of historic buildings. Despite their wide spread, their durability in the field of built structures is not well documented yet. Since many years of natural exposition would be necessary to evaluate the long-term behavior, artificial aging is usually used to simulate the environment in service conditions and predict the changes in properties of the materials. In these tests, higher environmental stress levels than those achieved in the natural exposure are employed, in order to obtain accelerate aging. Several papers dealing with the artificial weathering are reported in literature; however, they hardly explain how these tests can be correlated to the real long-term natural exposure. In this report, the first results of a research on the behavior of three cold-curing epoxy resins subjected to aging, either artificial or natural, are presented. The variations of thermal and mechanical properties, as well as color changes, after aging at 70°C and 75% relative humidity and after natural weathering, were compared.