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

Abstract

The incorporation of rice hush ash (RHA) into concrete create benefits for its durability in usual situations, because it leads to the refinement of the pore structure. However, on unusual situations, such as a fire, the refinement of the pore structure makes it difficult for water vapor that arise when the concrete is heated to escape, increasing the pore’s internal pressure, that may contribute to the appearance of explosive spalling. Researches show that the using of steel fibers may help to decrease the susceptibility of appearance of spalling on concrete, because they help controlling the occurrence of cracks. Despite the incorporation of RHA in concrete is discussed in many researches, just a few worries about analyzing its behavior at high temperatures and even less when steel fibers are added. In this research, the influence of the partial replacement of Portland cement for RHA and the addition of steel fibers on mechanical compressive strength, modulus of elasticity, weight loss and occurrence of spalling in concretes, after its exposed to high temperatures, are analyzed. For this purpose, it was made specimens with fixed water and binder ratio of 0,45, 25% of replacement of cement for RHA and addition of 10 kg/m³ of steel fibers. The specimens were heated with a heat rate of 1ºC/min, according to the RILEM TC 129-MHT (RILEM Technical Committee, 2014), till the temperatures levels of: 200ºC, 400ºC, 600ºC and 900ºC, in which they remained for 60 minutes. The tests were made after its cooling. Based on the tests, it was noted that the incorporation of RHA improves performance in terms of residual mechanical resistance to compression and mass loss, however it did not influence on modulus of elasticity. The addition of steel fibers showed improvement on mechanical compressive strength, this benefit was evident above 400ºC, but, in the other hand, it did not influence the result of modulus of elasticity and weight loss. Finally, the occurrence of spalling was not observed on the specimens due to its preheat stowage conditions, as well as due to the heating rate used