Análise do desempenho mecânico de CUAD com a adição de fibras de aço carbono e de polipropileno frente exposição à elevadas temperaturas

Abstract

The constant development of society demands improvement in all areas of knowledge. The need to use concrete with high mechanical strength to guarantee the slenderness of constructive elements or even to meet architectural decisions can often compromise the fire resistance percentages. In this context, the work evaluated the behavior of ultra high performance concrete (UHPC) subjected to temperatures of up to 600°C. The samples were composed by a fixed content of carbon steel fibers of 75 kg/m³ and variation of the content of the addition of polypropylene fibers in 0,0%, 0,2%, 0,6% and 1,0%, allowing to verify the interference of the additions against the performance in the fresh state, determined by the mini-slump test where, with the increase of the amount of PP fibers, there was a significant reduction in the workability of the concrete. In the hardened state, through tensile tests in flexion and compression, UHPC presents high resistance properties linked to the concrete formulation and the presence of fibers. For the high temperature exposure test, the samples were subjected to room curing, 7 days before the test, and curing in an oven at 60ºC, for 48 hours before exposure. The samples without the incorporation of PP fibers, in both curing regimes, suffered the occurrence of the spalling effect, demonstrating that the melting of the polypropylene fibers, due to the effect of the high temperature, reduced the risk of fragmentation, due to the increase in the porosity of the samples and, therefore, decrease the internal pressure of the cement matrix. After exposure, samples with the addition of 1.0% of polypropylene fibers showed better performance in terms of maintaining flexural tensile strength. Analyzing the residual compressive strength, the samples submitted to oven curing showed higher resistance rates as a function of the acceleration of cement hydration during the curing process and exposure to temperatures of up to 600°C, according to the process visualized in the scanning electron microscopy (SEM). [resumo fornecido pelo autor]