Concrete is frequently subjected to various adverse environmental effects throughout its service life such as fire and high temperature. Although the resistance of concrete against fire is superior to many other construction materials up to a certain temperature, its performance starts to decrease at temperatures above 400 o C. Serious physical and mechanical damage starts to take place particularly above 400 o C and the performance of concrete decreases due to such impacts. Fly ash is an

more »

... cial pozzolanic material that can be used as a mineral additive in making concrete. Fly ash has on the one hand a beneficial effect on the performance of the concrete and allows economy by saving cement on the other hand as it is a waste product of thermal power plants. In this study, the compressive strength and ultrasonic pulse velocities of concrete containing fly ash subjected to high temperatures was investigated. The measurements were taken at the end of 28 days of standard curing and 28 days of standard curing plus 90 days of air curing in a laboratory condition. Concretes of 300 kg/m 3 were produced and fly ash was replaced with cement at ratios of 20%, 30% and 40% by weight of cement. The ultrasonic and compressive strengths measurements were taken on 100 mm cubes. The temperatures applied to concrete were 200 o C, 400 o C, 600 o C, and 800 o C, respectively. It has been found that fly ash substitution does not have a beneficial effect on concrete subjected to high temperature both in ultrasonic pulse velocity and compressive strength.