Residual fracture properties of normal- and high-strength concrete subject to elevated temperatures

Abstract

The effects of elevated temperatures (Tm), related to the exposure period (th) and the curing age (ta), on the residual fracture properties of normal-strength concrete (NSC) and high-strength concrete (HSC) were investigated by conducting three-point bending tests on 87 notched preheated beams. Most beams were exposed to temperatures between 100°C and 600°C for 12 h at 14 days, while some NSC beams were heated either for various exposure periods up to 168 h at 14 days or for 12 h at 7, 28 and 90 days. The weight loss (ω) was also monitored. The measured residual properties included the energy parameter (fracture energy GF), a number of strength parameters (compressive strength fcu, tensile strength f′t and modulus of rupture fr), stiffness parameters (Young's modulus Ec and Poisson's ratio νc) and the brittleness parameter (the characteristic length lch). ω increased with Tm and th but decreased with ta. There existed a transition point for ω at 200°C which could mark a distinction between physical and chemical processes. GF increased with Tm and ω up to 300°C and then decreased. GF also increased with th at lower temperatures but decreased at higher temperatures, and increased with ta as well; fcu, f′t and fr did not change very much with Tm up to 200°C and decreased thereafter. A longer th had an intensifying effect on all strengths at lower temperatures but a damaging effect at higher temperatures. All strength parameters increased with ta. Ec and νc decreased continuously with Tm, th and ω. Ec increased whereas νc decreased with ta. The concrete became less brittle with increasing Tm, th and ω or with decreasing ta. In this study, all fracture parameters tended to become stable at 90 days. Finally, a linear relationship between GF and fcu existed not only for room temperature but also for higher temperatures.

Fracture properties of geopolymer paste and concrete

“…Brittleness is commonly understood to be the tendency of a material to fracture abruptly before significant irreversible deformation occurs (Zhang et al, 2000). To evaluate the degree of brittleness B of a concrete structure, Bache (1986) proposed:…”

Gradient enhanced thermo‐mechanical damage model for concrete at high temperatures including transient thermal creep

“…This term has been made here temperature dependent in order to capture the change in ductility that occurs as temperature increases [26]. The value of this parameter is dependent on the size of the localization zone and will be quantified in the next section.…”

“…Zhang et al [26] have undertaken a number of experiments on notched beams (both normal and high strength concrete) that have been exposed to temperature up to 6008C: The results of these experiments show that there is a general increase in the fracture energy release rate ðG f Þ up to approximately 3008C; after which there is a gradual decline. In order to capture this dependence of the fracture energy on temperature, the softening parameter, which reflects mechanical damage, should be made temperature dependent.…”

Residual fracture energy of high-performance and normal concrete subject to high temperatures

“…The GF tests reported herein are carried out as a part of an ongoing research work at the Department of Civil Engineering, University of Glasgow, to assess the fracture energy of concrete subject to high temperatures [7,8]. The experimental findings suggest that the fracture energy, based on the work of fracture method, increases with exposure temperature.…”

“…The experimental findings suggest that the fracture energy, based on the work of fracture method, increases with exposure temperature. Furthermore, [7] and [8] report that GF tested under hot conditions is generally lower than under residual conditions, i.e. the damage introduced by the cooling process increases Gr.…”