Abstract
High temperatures impose a negative effect on the mechanical properties of concrete. An experimental setup designed by the theory of nonlinear resonance vibration, the method of mercury intrusion porosimetry (MIP) and split Hopkinson pressure bar (SHPB) were used to test damage, porosity and mechanical properties of the pre-heated Brazilian discs of 10-year-old concrete respectively. According to the nondestructive test, the hysteretic nonlinearity parameters βh became larger as the temperature went up. The damage calculated by βh, which was 0, 0.57, 0.88 and 0.95 at 20 °C, 200 °C, 400 °C and 600 °C respectively, could be fitted by a power function. Based on MIP, the compound lognormal distribution model was used to simulate the pore size distributions. The quantitative relationship between porosity and damage was established by a power function, with the porosities of 13.96% at 20 °C, 15.77% at 200 °C, 19.17% at 400 °C and 20.22% at 600 °C. Finally, by the method of impact splitting tensile tests under gas pressures of 0.3 MPa, 0.4 MPa and 0.5 MPa, which represented impact velocity of 7.11 m/s, 10.26 m/s and 13.02 m/s respectively, the dynamic tensile strengths were obtained and the quantitative relationship between damage and macroscopic splitting tensile strength was established and the average value of exponential parameter b was 0.281.
Highlights
Fire often occurs in concrete structures when they are in service and the mechanical properties of concrete decrease obviously after exposure to high temperatures, the material appears a good performance of resistance to fire and heat (Bažant and Kaplan 1996; Gao et al 2017; Eunmi et al 2018)
Chen et al (2015) performed a dynamic compression test of plain concrete based on the split Hopkinson pressure bar, and established a relationship between the dynamic compressive strength and the porosity obtained by mercury intrusion porosimetry (MIP)
The nonlinear resonance vibration, MIP, and split Hopkinson pressure bar (SHPB) technique were used for damage evaluation, pore size distribution study and impact splitting tensile test, respectively
Summary
Fire often occurs in concrete structures when they are in service and the mechanical properties of concrete decrease obviously after exposure to high temperatures, the material appears a good performance of resistance to fire and heat (Bažant and Kaplan 1996; Gao et al 2017; Eunmi et al 2018). During the process of fire, the magnitude of temperature and the duration of the fire can cause different degrees of damage to concrete structures. Such conditions may result in cement paste. The mercury intrusion porosimetry (MIP), which is widely applied to the study of the pore structures of concrete materials, is a vital means of analyzing the microstructure of concrete and is well-received in the research field of concrete. Chan et al (2000) studied the variation of porosity and pore structure by utilizing MIP and established the quantitative relationship between porosity and compressive strength of concrete after the concrete was exposed to high temperatures. The applicability and the accuracy of mercury intrusion, the research method has been widely received by researchers
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