EVALUATION OF NDE TECHNIQUES FOR DETECTING GROUT DEFECTS IN CABLE STAYS

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 may accumulate in the grout layer if voids o r bubbles are trapped during the grouting process, leading to localize d corrosion of the cables. A research study has been undertaken to ass ess various nondestructive evaluation (NDE) methods for inspection of this grout layer. Methods studied include ultrasonics, X-ray radiograp hy, computed tomography, and neutron radiography. Representative model s of grouted cable stays were prepared with manufactured defects to in vestigate the feasibility of these techniques. There are two distinct regions along the cable length that most likely will require different inspection schemes. The main section of cable will be inspected by on e technique, possibly ultrasonics, while the lower regions of cable, w here extra layers are added for fire and crash protection, may require a radiographic technique.