Effect of moisture and temperature on the thermal and mechanical properties of a ductile epoxy adhesive for use in steel structures reinforced with CFRP

CFRP has proven to be a material capable of being used in many engineering applications, highlighting its good properties for reinforcement of steel structures. In this study, a new CFRP-steel adhesive joint is evaluated by using a structural and ductile epoxy adhesive to join the CFRP reinforcements to the steel structure. On the one hand, the epoxy adhesive has been thermally characterized by means of its kinetics of curing (Kissinger and Model Free Kinetics methods), finding behavior similar to other epoxy adhesives. On the other hand, different surface treatments are studied in order to achieve the best mechanical properties of the joint. In addition, the suitability of this kind of joints is assessed under durability conditions (60 degrees C and 99% relative humidity) and under thermal fatigue. Shear tests are realized on specimens subjected to different exposure times, studying the mechanisms that affect the degradation of the adhesive joint in each environment. Breaking surfaces were analyzed by Scanning Electron Microscopy (SEM) and by Energy-dispersive X-ray Spectroscopy. A simplified Weibull model is used to evaluate the reliability of the joints during both durability and thermal fatigue processes. The thermal and mechanical properties of the adhesive are determined, showing better behavior against thermal fatigue because moisture in the durability process accelerates degradation of the adhesive joint.