Failure behavior and strength deterioration model of high-performance concrete under coupled elevated temperature, biaxial constraint and impact loading

This research investigates the effects of high temperatures, multiaxial stress constraints, and impact loads on the failure behavior and strength deterioration of high-performance concrete. Combined with scanning electron microscopy and ultrasonic testing, the microscopic deterioration characteristics of thermally damaged concrete were revealed. Dynamic compression tests were performed on concrete, after exposed to elevated temperatures (from 25 degrees C to 750 degrees C), using a true triaxial Hopkinson pressure bar test system. The study analyzes the effect of temperature and strain rate on dynamic failure behaviors of concrete under biaxial stress constraints. The study establishes models for predicting the evolution of dynamic strength deterioration and strain rate. Additionally, the research discusses the mechanisms of influence of stress constraint states on the dynamic increasing factor (DIF) and failure modes of concrete. Results indicate that concrete's strength under biaxial stress constraints increases with the load rate and is hardened or weakened by changes in temperatures (taking 300 degrees C as a demarcation point). The strain rate effect of concrete becomes more significant with increasing temperature. Stress constraint states significantly affect the dynamic strength of concrete, and the DIF of concrete grows quasi-linearly with the logarithm of strain rate at different temperatures. Under biaxial stress constraints, concrete is dominated by oblique shear failure, and damage is less severe with the increase in the intermediate principal stress & sigma;2. Macro-fractures are unlikely to appear under true triaxial stress constraints.