Concreto reforçado com fibras de aço: influência do modo de resfriamento na resistência à compressão após exposição a elevadas temperaturas

Abstract

Concrete is the most consumed construction material in Brazil and the world due to its properties in the fresh and hardened states, in addition to presenting great versatility. However, this material has some limitations, such as the fragile rupture mode. Because of this, technological alternatives have emerged to overcome these limitations. One option is steel fiber reinforced concrete (CRFA). In Brazil, this type of concrete is widely used in pavements, shotcrete and prefabricated concrete. However, there is still no complete regulation for this material. There is still a lack, for example, of a standard on CRFA in fire situations. The rapid heating caused by fire, followed by cooling, can seriously compromise a concrete structure. As a result, this research analyzes the influence of the cooling mode on the compressive strength of concrete reinforced with steel fiber after exposure to high temperatures. For this purpose, 66 cylindrical specimens with five centimeters in diameter and 10 centimeters in height were molded. A ratio of 1: 1.53: 2.12: 0.56 was used (Cement CP II-F-32, fine sand, coarse basaltic aggregate and water). The proportion of steel fiber was 1% concerning the volume of concrete. The samples were subjected to five different temperatures (200 °C, 400 °C, 600 °C, 800 °C and 1000 °C) for seven hours. After this stage, the specimens were cooled under two regimes: slow and abrupt. The results showed that up to 400 °C, the type of cooling has a greater influence than at temperatures above 400 °C. From 600 °C the results become very close; at this temperature, in particular, the residual resistances were 76.35% and 77.72% for slow and sudden cooling, respectively. For temperatures of 800 °C and 1000 °C, the results confirmed the decomposition of the concrete constituents. The consequence of this was a drastic reduction in compressive strength.