Ultrasound tomography applied to AAR-affected concrete structures

This paper discusses the potential application of ultrasound tomography and scientific visualization for evaluating the internal condition of massive concrete structures affected by AAR and other deterioration processes. Ultrasound measurements have been used in the evaluation of concrete structures for many decades. Traditional transmission ultrasound measures the average velocity of stress waves between two points on a concrete structure - the velocity being related to concrete quality - but provides no information on the distribution of velocity (and hence quality) between those two points. However, if sufficient measurements are made to form a network of velocities across a single cross-section, tomographic methods can be applied to produce a two-dimensional image of the spatial distribution of velocity data within the section. Results are presented from a preliminary study carried out to assess the potential application of this technique for evaluating the internal condition of large concrete elements. Overall, the initial results are promising, indicating that the presence and location of internal defects can be determined and visualized using this technique. Features of the transmitted wave, other than velocity, are currently being examined to assess their sensitivity to internal micro-cracking of concrete. The frequency content of the received wave may be amore » more sensitive indicator of AAR microcracking and the potential application of spectral analysis in tomographic surveys is discussed.« less