Compressive and hydration behavior of steel fiber-reinforced concrete under high geothermal environment

The unique challenges presented by high geothermal environments in tunnel construction are becoming increasingly evident, particularly in the context of the high geothermal conditions in western China. In this paper, the uniaxial compressive properties, and stress-strain relations of steel fiber-reinforced concrete (SFRC) in high geothermal environment are studied. The effects of the volume fraction of steel fiber (0.5%/1.0%/1.5%/ 2.0%) and the heat damage temperature (40 degrees C/60 degrees C) on the peak stress, peak strain, and the stress-strain curve of SFRC under uniaxial compression are analyzed. The results show that the fracture and spalling of concrete around the main crack increase due to the heat damage after uniaxial compression test. Compared to 20 degrees C, the peak stress, bending strength, and limit flexural toughness of SFRC significantly decrease (45.9%, 29.5%, and 72.1%, respectively) after 60 days of exposure to a high geothermal environment of 60 degrees C. Moreover, while the addition of steel fiber can enhance the peak strain and limit flexural toughness of concrete, the decline in peak stress and bending strength of SFRC becomes more pronounced as the duration of heat damage increases. Based on the P-K hydration kinetics model, the ettringite content in cement without an accelerator is determined to decrease by 66.35% after 28 days of hydration at 60 degrees C, indicating in the change of the concrete's material properties.