This study evaluated various techniques that use mechanical waves for the evaluation of critical concrete properties, such as proper consolidation of the concrete during placement and strength development; changes in modulus; and the detection of cracks, voids, and delaminated regions. The methods evaluated were ultrasonic shear-wave tomography, ultrasonic pulse velocity, crosshole sonic logging, sonic echo-impulse response, spectral analysis of surface waves, and the use of an impact echo scanner on pavements and bridge structures.
Ultrasonic shear-wave tomography can be successfully used to determine the major distressed areas in pavements. Crosshole sonic logging can detect voids in drilled shafts and can indicate concrete performance and quality. Sonic echo-impulse response can reliably detect voids but is not always able to establish a precise location because of the potential variability in wave velocity. However, it can still provide useful thickness or depth information. In addition, detection of distress is limited by the embedded length-to-diameter ratios of the foundation element being examined. The use of ultrasonic pulse velocity can improve the accuracy of sonic echo–impulse response measurements by providing the actual velocity of the concrete being evaluated. Use of the impact echo scanner can provide delamination data for structures with smooth surfaces.
In addition to detecting the condition of the concrete elements, these methods can be used to help determine compliance with end-result specifications. Quality control and acceptance using end-result specifications requires at least three test results to determine variability, which can be easily obtained using nondestructive test methods.
The results regarding spectral analysis of surface waves were promising, but additional validation work is required to determine the abilities of this technique to assess asphalt-overlaid concrete decks.
This study showed that nondestructive mechanical wave methods can be successfully used in determining concrete quality and the extent of distress in concrete structures. The study recommended that these methods be used by the Virginia Department of Transportation for condition assessment. The next step is to continue collecting data on pavements and bridge structures using these techniques.
