SBIR-STTR Award

Residual lifetime evaluation of existing nuclear facilities requires detailed information regarding condition of containment and support structures. Current nondestructive methods for subsurface evaluation of reinforced concrete use complex equipment and rely heavily on interpretation by the operator. A research effort is proposed to examine the use of computerized tomographic imaging for locating subsurface features in reinforced concrete structures. Acoustic pulse velocity data will be used as the base information for image reconstructions. The approach would provide a cross-sectional image of the mass being investigated, showing the velocity distribution throughout the interior of the concrete. The image of concrete condition can be analyzed and used as a basis for determining the internal concrete condition and the necessity of repairs. A number of initial problems will be addressed, pertaining to determination of appropriate stress wave parameters and optimization of data gathering techniques. A mass concrete specimen will be constructed to incorporate features of interest, such as reinforcing steel, density variations, cracks, and voids. The main portion of the study will concentrate of determining the ability of acoustic imaging techniques to identify the presence and location of such features.

Anticipated Results:
The research will investigate the feasibility of a velocity-based imaging procedure for in situ evaluation of concrete structures. A method for on-site global imaging is needed not only for the evaluation of nuclear structures, but for all types of large-scale civil structures such as bridges and dams. Tomographic imaging could also be applied to quality control during construction or repair of nuclear facilities.

The preliminary Phase I study has shown that acoustic tomography can locate subsurface faults and anomalies in concrete laboratory test sections. The proposed Phase II research will seek to advance acoustic tomography to a level of development where it can be used for practical evaluation of real reinforced concrete structures. This will be accomplished by improvements to the existing software which was developed for geophysical applications. Improvements to ultrasonic pulsing and receiving equipment, sensors and sensor coupling, and practical application procedures will also be made. Tests will be carried out on large laboratory specimens and field specimens to evaluate the technique under realistic conditions. At the end of the program an application manual will be prepared giving practical guidance on the use of the acoustic tomographic technique, on the types of structures where the technique may be applied and on the functional and theoretical limitations of the technique.

Anticipated Results:
Acoustic tomography, when successfully developed, will provide a nondestructive means for internal examination of mass concrete section. No other technique having the capabilities of acoustic tomography for this purpose presently exists. Considerable commercial potential exists for examination of existing structures including power plants (nuclear and conventional), bridges, and navigational structures.