Acoustic methods for the assessment of fire damage in concrete structures

The possibility to reuse a concrete structure after fire is mainly dependent on the residual load bearing capacity and on acceptable residual deflections and/or deformations. The degree of damage due to fire, possible repair measures and the corresponding repair costs are decisive parameters in the decision to reuse or demolish the structural member. This thesis presents a practical and efficient way of analyzing the damage thickness of concrete elements that can be applied to reasonable costs. The experimental studies using indirect Ultrasonic Pulse Velocity for fire damaged concrete were presented in this thesis. The reliability and accuracy of the experimental techniques were improved by adopting wedges. The merits and limitations of this technique for the assessment of fire-damaged concrete were discussed. 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. 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.