Research on uniaxial mechanical performance of high-performance concrete after high temperature rapid cooling and damage mechanism analysis

High-performance concrete (HPC) is widely used in civil and hydraulic engineering, with durability as its main indicator. During the service life of high-performance concrete structures, there is a risk of extreme fire incidents. The fire department generally adopt water cooling to quickly control the fire after a fire occurred. Studying the mechanical property of high-performance concrete after high temperature and rapid cooling is of great significance for evaluating the safety performance of high-performance concrete structures after a fire. Therefore, three types of uniaxial loading modes (uniaxial compression, pure shear, uniaxial tension) and five temperatures (20OC, 200OC, 400OC, 600OC, 800OC) were considered in this study. Hydraulic servo machine was used to conduct experimental research on the uniaxial mechanical properties of high-performance concrete after high temperature and rapid cooling. In addition, digital image correlation (DIC) and acoustic emission technology (AE) were combined to analyze the external and internal damage evolution processes of concrete during loading process. The experimental results are as follows: as the temperature increases, the compression strength of high-performance concrete under uniaxial compression is initially increased and then decreased, with a maximum reduction of 62.02%; however, the strength of high-performance concrete under pure shear and uniaxial tension conditions are gradually decreased, with maximum reduction of 76.12% and 81.26% respectively; compared to room temperature cooling conditions, the strength of high-performance concrete under water cooling condition is decreased more greatly, but this difference gradually decreases with the increase of temperature; combined with the analysis of DIC and AE, under different stress states, the surface main cracks of HPC become more tortuous and accompanied by more micro-cracks under the influence of high temperature, and the evolution process of cracks inside HPC also changes significantly with the temperature. At the same time, the surface damage process of HPC under the influence of load has obvious lag compared with the internal damage process. Finally, based on the cumulative ringing count obtained by AE, the damage process of high-performance concrete under different loads is characterized, and the constitutive model of high-performance concrete after high temperature and rapid cooling under different loading modes is established. The research results provide a theoretical basis for the safety evaluation and calculation of high-performance concrete structures after fire.