Fire behaviour of rc slab strips strengthened with advanced cfrp strengthening systems

Carbon fibre reinforced polymer (CFRP) composite systems are widely used to strengthen reinforced concrete (RC) structures through bonding strips/sheets on the concrete surface – externally bonded reinforcement (EBR) technique, or through strips/rods bonded inside slits in the concrete cover – near-surface mounted (NSM) technique. Although both techniques provide high strength increases, it is usually not possible to use the CFRPs’ full strength due to premature debonding, especially with EBR. This limitation can be overcome when using CREatE (continuous reinforcement embedded at ends) technique (developed by the last three authors), which consists of (i) bonding the central part of the CFRP strip (as in EBR), or the CFRP rod (as in NSM), and (ii) anchoring both ends of the strip/rod inside the concrete section, after a transition curve, enhancing its anchorage capacity. However, all these techniques are susceptible to fire, due to the polymeric nature of CFRP materials and epoxy adhesives. This paper presents the results of an experimental study regarding the fire behaviour of RC slab strips strengthened with EBR, NSM and CREatE techniques, in which the influence of applying different fire protection systems was investigated. The specimens were strengthened with those systems and simultaneously subjected to a service load and the ISO 834 fire curve. The following main results were obtained: (i) without fire protection, the CREatE technique presented the highest fire resistance due to the better anchorage of the CFRP; (ii) when protected, the NSM technique presented higher fire resistance compared to EBR and CREatE techniques; and (iii) “critical” temperatures were proposed for each technique, 1.0T_g, 2.5T_g, and 3.0T_g for EBR, NSM and CREatE techniques, respectively.