Mechanical properties and flexural toughness evaluation method of steel fiber reinforced concrete after exposure to elevated temperatures

Abstract

To investigate the mechanical properties of SFRC after exposure to elevated temperatures, tests on 108 cubes and 30 flexural specimens with three steel fiber volume ratios (SFVRs) (i.e. 0 %, 1.0 % and 1.5 %) after elevated temperatures (i.e. 200 ℃, 400 ℃, 600 ℃, 800 ℃ and 1000 ℃) were conducted in this study. The results showed that the enhancement effect of SFVR was most obvious within the temperature range of 600 °C – 800 °C, while it basically disappeared at 1000 °C. Due to the influence of temperature on the formation and decomposition of hydration products, the cubic compressive strength (CCS), peak flexural load (PFL), equivalent flexural strength and initial flexural toughness ratio firstly decreased at 200 °C, and then increased again at 400 °C, and finally decreased rapidly after 600 ℃. The splitting tensile strength (STS) of SFRC initially increased before 200 ℃ and then decreased. After 1000 ℃, the CCS, STS and PFL were merely 26.7 %, 15.9 % and 12.2 % of those at room temperature, respectively. Moreover, the samples which suffered 1000℃ had poor integrity relative to the samples experienced lower temperatures. The empirical models of the CCS and STS with different kinds of fibers after elevated temperatures were proposed. Meanwhile, the expression of STS with respect to CCS was established. Furthermore, a method to evaluate the flexural toughness of SFRC after elevated temperatures was proposed based on equivalent elastic-plastic energy method, which could well reflect the influences of SFVRs and elevated temperatures.