Effects of Elevated Temperatures and Fire on Bond Strength of Prestressed Steel and Carbon FRP Bars in High Performance Self-Consolidating Concrete

Abstract

Novel structures are emerging utilizing high performance, self-consolidating, fibre-reinforced concrete (HPSCC) reinforced with high-strength, lightweight, and non-corroding prestressed reinforcement. One example of this is a new type of precast carbon fibre reinforced polymer (CFRP) pretensioned HPSCC panel intended as load-bearing panels for building envelopes. As for all load-bearing structural members in building applications, the performance of these members in fire must be understood before they can be used with confidence. In particular, the bond performance of CFRP prestressing reinforcement at elevated temperatures is not well known. This paper examines the fire performance of these new types of structural elements, placing particular emphasis on the bond performance of CFRP and steel wire prestressing reinforcement at elevated temperatures. The results of large scale fire tests and bond-pullout tests on CFRP and steel prestressing bars embedded in HPSCC cylinders are presented and discussed to shed light on the fire performance of these structural elements. An analytical model is proposed to determine the temperature at which first appearance of the cracking phenomenon and concrete cover failure occurred, in the large scale fire tests, due to incompatibility of thermal expansion between CFRP tendons and HPSCC. From this research it is proposed that temperatures in range of the glass transition temperature (Tg) of the CFRP tendon’s epoxy matrix are critical for the bond strength capacity of the CFRP tendons in reinforced or pretensioned concrete members.