Comportamento mecânico de concretos com substituição parcial de cinza de casca de arroz e adição de fibras de polipropileno em altas temperaturas

Abstract

The incorporation of rice hush ash (RHA) when incorporated into concrete create benefits with respect to durability in room temperatures situations, due to the densification of the cemente matrix. However, on fire situations, the densification of the cement matrix ends up becoming an obstacle to the exit of watwe vapors when the concrete is heated, increasing the internal pressure in the pores, which can lead to the appearance of explosive spalling. Research shows that the use of polypropylene fibers can help reduce the likelihood of spalling in concrete, because they create channels interconnected with the pores facilitating the exit of water vapors. Although the incorporation of RHA in concrete is addressed in numerous researches, a limited number are concerned with analyzing its behavior at high temperatures and, even more limited, with the addition of polypropylene fibers. In this research, the influence of the partial substution of Portalnd cement by RHA and the addition of polypropylene fibers on the mechanical resistance to compression, weight loss and occurrence of spalling in concrete after being submitted to high temperatures is investigated. For this, specimens with a/agl fixed ratio of 0,45, 25% substitution of cement by RHA and addition of 1,5 kg/m³ of polypropylene fibers were molded. The samples were heated at a rate of 1°C/min, according to RILEM TC 129-MHT (RILEM Technical Committee, 2004) until they reached the temperature levels of 200ºC, 400ºC, 600ºC and 900ºC, where they remained for 60 minutes. The tests were performed after the specimens were slowly cooled down. With the results obtained, it was noticed that the incorporation of CCA improves the performance regarding the mechanical resistance to residual compression and loss of mass. Finally, the occurrence of spalling was not evidenced in the samples tested due to the preheating conditions of the specimens.