Non-Destructive Evaluation of Bridge Stay Cable and External Post-Tensioning Systems



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Non-destructive evaluation (NDE) of bridge stay cable and external post-tensioning (PT) systems is an essential tool to thorough bridge inspections and also eliminates any necessary repair of destructions made during evaluation. Conditions such as corrosion, steel strand and wire breakage, tendon section loss, voids in the grout, water infiltration, and other undesired grout conditions can go undetected in nontransparent stay cable and external PT ducts without proper inspection. In this research, sounding, ultrasonic tomography, infrared thermography, and ground penetrating radar are evaluated for their applicability to identify selected conditions in a mock-up specimen representative of both a stay cable system and an external PT system. A borescope is also used to collect ground truth data for comparison with the NDE results. The conditions are fabricated in the mock-up specimen to closely represent conditions in the field so that the NDE results are directly applicable to bridge construction quality control and in-service bridge inspections. Locations of corrosion, breakage, and section loss are established prior to grouting. These conditions are combined with both foam void locations and an air-filled void in the grout along the top of the duct.

The sounding method was extremely applicable in accurately detecting air voids in the grout and the sounding results matched closely with the ground truth data of the air void extent collected by the use of a borescope. This research concludes that the infrared thermography and ground penetrating radar devices used did not identify any of the corrosion, section loss, or breakage locations within the specimen. However, both of these methods identified air voids and foam voids in the duct free span during both the quality control testing period and inspection testing period, although GPR did not provide accurate void depth. In addition, infrared thermography was able to identify air voids within the grout caps at each anchorage end. The ultrasonic tomograph used in this research, designed for use on concrete rather than stay cables and external PT, produced inconsistent results when used on the specimen. In future research, a different means of ultrasonic tomography testing may be applicable to identifying voids in the grout.