Strength evolution after high temperature exposure of coated carbon fiber rovings used for a fiber-reinforced cementitious matrix (FRCM)

This paper presents experimental results of the tensile strength decrease of coated Carbon Fiber rovings after high temperature exposure up to 1000°C. The composite material is used as a mesh reinforcement for various shotcrete applications (FRCM - Fiber Reinforced Cementitious Mortar) in structural retrofitting projects. In case of a fire accident, it is mandatory to dispose of a certain residual strength after high temperature exposure in order to guarantee structural safety. The current investigation treats unidirectional tensile strength tests on Carbon Fiber rovings carried out at Empa. The investigation was performed at room temperature on Carbon Fiber rovings after having been thermally subjected to constant temperature of 300, 500, 700 and 1000°C in a tube furnace for 30 minutes. It can be observed that an exposure at 300°C for half an hour does not affect the mechanical properties of the analyzed reinforcement. However, a further increase in temperature starts seriously damaging the material's ability at 500°C, whilst no residual strength is left at 700 and 1000°C, respectively. Additionally, reinforced concrete plate strips were strengthened with a fiber-reinforced-cementitious-matrix (FRCM) layer and subsequently subjected to fire at the 'Versuchsstollen Hagerbach' (CH), temperature was controlled according to the European ETK-temperature curve. The measured temperature evolution on the Carbon Fiber rovings (under a total concrete/shotcrete cover of 40 mm for the steel reinforcement) together with the previously performed tensile tests lead to the conclusion that the inner steel reinforcement, for which temperature was also monitored, is partially protected by the FRCM layer and does not trespass 250°C in this case.