Microstructure and fatigue performance of high strength concrete under compression after exposure to elevated temperatures

Abstract

The fatigue tests of high-strength concrete after exposure to elevated temperatures of 200 °C, 500 °C, and 800 °C under low cyclic compression at different stress levels were carried out by an electro-hydraulic servo fatigue tester. The microstructure of high-strength concrete specimens during fatigue was studied with the aid of five comprehensive microscopic research methods—scanning electron microscopy, X-ray diffraction, ultrasonic, microhardness testing, and mercury intrusion porosimetry. By measuring the microscopic parameters such as ultrasonic velocity, microhardness, and the most probable aperture, the variation of microstructure during the fatigue process was analysed. It was found that with the increase of fatigue cycles, the variation speed of microscopic parameters follows a three-phase trend. The relationship between microscopic parameters and residual strain or elastic modulus ratio was established, and the fatigue damage models based on the microscopic parameters were obtained. A simplified mean damage variable was proposed and the residual life of concrete was predicted. The research results can provide reference for non-destructive testing, fatigue damage analysis and structural evaluation of high-strength concrete structures subjected to elevated temperature processes.