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Characterization of Ambient Temperature Cure Epoxies Used in Adhesive Anchor Applications

Thermo-viscoelastic properties of two commercial, ambient temperature-cure epoxy structural adhesives were analyzed and compared. The adhesives were formulated by the same manufacturer and appeared to have the same base chemistry; however, one system contained accelerators for shorter cure times. In the laboratory, dynamic mechanical temperature/frequency sweeps were performed on both systems to generate dynamic mechanical data and predict creep compliance master curves using frequency-temperature superposition principles. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and moisture sorption analysis were also used to assess the thermal and hygroscopic properties of the materials. Differences were observed in the thermal, hydrolytic, and dynamic mechanical properties of the two adhesive systems as well as in their estimated creep compliance behavior, which were attributed to differences in the curing agent(s) and accelerator(s) used in the adhesive systems. In most cases the differences in the properties of the epoxies were small, but a few properties, particularly the predicted creep behavior, exhibited very large differences. Results from laboratory creep testing confirmed the predicted difference in creep behavior. The data also suggest that dynamic mechanical testing combined with frequency-temperature superposition may be a useful metrology for predicting trends for in-service creep behavior from short term tests.