Mechanical behavior of concrete–resin/adhesive–FRP structural assemblies under low and high temperatures

The application of FRP to the strengthening of existing reinforced concrete structures entails the inevitable exposure of the layered structure to temperature changes. This paper takes another step in investigating the behavior of the structural assembly under the combined effect of temperature change and load. The investigation tests double lap shear joints a temperature-controlled chamber under temperatures in the range of −40–120 °C. Two FRP systems are examined. The first combines unidirectional carbon fiber sheets and epoxy resin applied in a wet lay-up technique, and the second uses pre-fabricated FRP strips or laminates applied by an adhesive bonding technique. The emphasis in this paper is on the response of the layered structure to the combined mechanical and environmental loading. The experimental sections of the paper characterize the mechanical properties of the resin used in the wet lay-up system and the adhesive used in the bonded system under the examined range of temperatures. Next, the paper explores the response of the two assembled FRP–adhesive/resin–concrete systems under the thermo-mechanical load. The analytical section of the investigation also includes two phases. First, the paper examines three empirical formulae for the assessment of the failure load. Then, the paper investigates the results of an analytical approach that uses a high-order fracture mechanics model. The experimental and analytical results reveal a gradual degradation under both low and high temperatures and a behavior that is different from the glass transition effect, which characterizes certain components of the layered system.