Influence of High Temperatures on Concrete Pillars Confined with CFRP

Abstract

Concrete is a quite recent material in the history of architecture. However, there are a large number of buildings whose structure consists on this material nowadays. Despite its excellent performance, concrete has a useful lifetime. When this time comes to its end, the structural element needs to be treated, repaired or replaced. We are getting to the point at which many of the concrete constructions are reaching, or already surpassing, the useful lifetime of the material. At this point, the Carbon Fiber Reinforced Polymer (CFRP) takes on importance, appearing on the market as a modern and high performance tool, in terms of structural reinforcement of the concrete. Nevertheless, this relatively new system presents yet some aspects to study and research, such as its long-term behaviour under extreme conditions. This is the departure point of our research, focused on the response of the CFRP system, both fiber and matrix, to adverse temperature conditions. This high and maintained temperature can be reached in places such as structures undergone to large periods of solar radiation around Equator latitudes, machinery installations enclosures which generate high temperatures focused on specific points, and brief small fires, among other situations, which surpass the maximum service temperature recommended by the manufacturers. In order to study this influence, a comparison of the compressive strengths of three groups of standard concrete test specimens has been carried out. Each group consisted of three cylindrical specimens, all manufactured on the same date. The first two groups were tested after their 28 day curing in chamber: one of them without any confinement and the other with CFRP sheet applied according to the manufacturer's specifications. The third group of specimens spent 90 days on a climatic chamber subjected to a temperature of 75°C, above the maximum temperature recommended by the manufacturer, 50°C. This third group was tested 388 days after their manufacture. In order to obtain a reliable basis on which to compare the effective strength provided by the deteriorated CFRP, it was needed to calculate the acquisition of theoretical strength that the concrete would have reached after the mentioned period of time without any added reinforcement. With all the results, it is possible to conclude that, after this period of heat attack, despite having produced an aesthetic degradation of the CFRP sheets, most of the compressive strength of the specimens remains.