Mechanical Performance of Polyurethane and Epoxy Adhesives in Connections with Glued-in Rods at Elevated Temperatures

Glued-in rods have successfully been used for connections or reinforcement of timber structures due to their high strength and stiffness. However, their performance is potentially sensitive to temperature. This paper deals with an experimental investigation of the connections and adhesives in elevated temperatures. First, dynamic mechanical analysis (DMA) tests were performed to characterize an epoxy (EPX) and a polyurethane (PUR) adhesive. The evolution of the stiffness and the glass transition temperature, T-g, were measured in the range of 30 degrees C to 120 degrees C. Then, a total of 66 specimens with glued-in rods and the same adhesives were tested under a static tensile load at 20 degrees C, 40 degrees C, 50 degrees C, 60 degrees C, and 70 degrees C. In both types of tests, the EPX outperformed PUR due to its higher stiffness at temperatures of up to 40 degrees C; however, it showed a more rapid degradation of the stiffness and strength than the PUR at higher temperatures. No direct correlation was established between the Tg and the performance of the connections. The test results suggest that timber structures with glued-in rods may be vulnerable in service at temperatures above 40 degrees C.