Effects of fly ash on the mechanical and impact properties of recycled aggregate concrete after exposure to high temperature

Experiments were conducted on 180 specimens to investigate the mechanical and impact properties of recycled aggregates (RAs) concrete with different fly ash (FA) contents after exposure to temperature at 20??C (room temperature), 200??C, 400??C, 600??C and 800??C. The compressive strength, elastic modules, peak strain, ultimate strain, Poisson?s ratio and recovering effect of air curing time on the tested specimens were analysed. The impact numbers and impact energy under the repeated drop-weight test were obtained. Test results showed that the numbers of blows causing the first and final crack decreased gradually with the increasing temperature and FA contents, and the temperature of 200??C had a great influence on the impact resistance of RA concrete. The weight loss and compressive strength of the specimens suffering from high temperature alone decreased with the increasing FA content. The compressive strength of unheated specimens for 118?days curing was about 0.045?0.196% higher compared to that for only 28 days curing. The Poisson?s ratio of RAs concrete at 400??C was less than half of that at 20??C. Results of this study provided certain theoretical basis for research on fire-resistant design of concrete structures.