Compressive properties and micro-structure of high ductility concrete exposed to elevated temperature

In order to study the compressive properties of high ductility concrete (HDC) exposed to elevated temperature, 49 groups of cubic specimens were designed considering three factors:temperature, cooling and curing mode, and standing time. And their compressive strength was tested. The relationship among compressive strength, maximum temperature, ultrasonic velocity and rebound value of HDC was studied by ultrasonic rebound test of five groups of prism specimens. The results show that the temperature has significant impact on compressive strength, and with the increase of temperature, the compressive strength decreases; the influence of cooling mode cannot be neglected when the temperature is below 200℃ and the standing time has a great impact on the natural cooling specimens when the temperature is 400℃. Ultrasonic rebound test shows that the compressive strength of HDC is well correlated with the ultrasonic velocity and rebound value. Based on the regression analysis of test data, the strength curve of HDC exposed to elevated temperature and the formula for estimating the highest exposure temperature were established. The effect mechanism of elevated temperature on the mechanical properties of HDC was revealed by using XRD, SEM and thermogravimetric-differential thermal analysis (TG-DSC).