| Problems with corrosion of steel strands in grouted bridge cable stays have raised concern about the integrity of the grout layer protecting the strands. Bleed water that may accumulate in the grout layer if voids or bubbles are trapped during the grouting process can lead to corrosion and reduced fatigue life of the cables. This research study was undertaken to evaluate various nondestructive evaluation (NDE) methods for inspection of this protective grout layer. Methods which were studied include ultrasonics, film radiography, computed tomography (CT), and neutron radiography.; The feasibility of using computed tomography for inspection of the grout layer has been demonstrated. Voids as small as 0.04 in. (1 mm) in diameter were identified in both the annular region of grout and inside the steel cable bundle. Although some of these voids were manufactured, many of those found were a result of the grouting operation during fabrication of the specimens, an observation which lends urgency to the need for an inspection system.; Laboratory experiments were conducted with a prototype ultrasonic inspection unit which utilizes two rolling contact probes with 500 kHz transducers. A digital signal subtraction technique was found to be particularly useful in analyzing the received signals. The ultrasonic system was successful in identifying the location of defects, but information regarding the size and content of the defects was inconclusive.; Three distinct regions exist along the cable which will most likely require different inspection schemes. It is envisioned that the main section of cable will be inspected by one technique, possibly ultrasonics, while the lower regions of cable, where extra layers are added for fire and crash protection, will require a radiographic technique. The third region, which includes the saddles and anchorages, will likely require a third inspection technique, such as a portable linear accelerator. |
