Assessing Fire Damage of Concrete by the Ultrasonic Pulse Technique

Abstract When a concrete member is exposed to fire, the exterior of the member is heated up drastically, while the interior remains at a relatively low temperature. Only a thin surface layer of the concrete is subjected to severe damage. Knowledge of the extent of damage is most useful to the engineer in estimating the repair work. Thickness of the damaged layer can be expediently assessed by measuring the velocity of ultrasonic pulses along the surface. Accuracy of this technique has been investigated with a series of tests in which the concrete was heated to various temperatures. Test results indicate that the method of assessment is reasonably accurate. However, extensive cracking of concrete at very high temperatures may make the ultrasonic measurements very difficult and, hence, limits the applicability of the technique.