Effect of low temperatures on fracture properties of steel fibre reinforced rubberised concrete

Low temperatures, recognised as one of the more extreme environmental conditions, significantly influence the fracture properties of concrete structures. In this study, three-point bending tests were performed on 25 steel fibre reinforced rubberised concrete (SFRRC) notched beams, each containing 10 % crumb rubber, to investigate the effect of various low temperatures (20 degrees C, 0 degrees C, -20 degrees C, -40 degrees C, -60 degrees C) and steel fibre volume fractions (0 %, 0.5 %, 1.0 %, 1.5 %, 2.0 %) on their fracture properties. Four critical parameters (fracture energy, fracture toughness, equivalent flexural strength, and characteristic length) were calculated to comprehensively evaluate the fracture behaviour, while the microstructure response of the SFRRC beams was examined using Scanning electron microscopy (SEM), facilitating an in-depth analysis of the corresponding damage alterations. The experimental results indicate that low temperatures can have a positive impact. As the temperature decreases to -60 degrees C, the fracture energy, initial fracture toughness, unstable fracture toughness and equivalent flexural strength show an increasing trend, and the maximum increase is 355.5 %, 161.8 %, 173.0 % and 254.4 %, respectively. Conversely, the characteristic length exhibits a substantial decrease, reaching a maximum reduction of 58.9 %, which results in a significant increase in the brittleness of the SFRRC. The increase in brittleness, however, can be mitigated by maintaining the steel fibre content within a range of 1.0-2.0 %. Whilst the SEM observations further reveal that low temperatures may potentially inflict damage on the SFRRC, the addition of steel fibres can also offset this adverse effect.