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1 S U M M A R Y The inspection guidelines are aimed in assisting bridge owners in selecting the most appro- priate nondestructive evaluation (NDE) method or combination of methods for the condi- tion assessment of in-service post-tensioning and stay cable systems. The recommendations in the inspection guidelines are based on the findings from NCHRP Project 14-28, âCondi- tion Assessment of Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods.â The tendons and grout to be inspected are typically embedded in massive concrete (inter- nal tendons) or opaque ducts (external tendons or stay cables) making it difficult to evaluate the true condition of the post-tensioning and stay cable systems by visual inspection alone. NDE methods can serve to identify detrimental conditions at an earlier stage in order to mitigate reduced bridge safety and load capacity, costly rehabilitation actions, and traffic disruptions. The inspection guidelines will allow bridge owners to take timely, proactive actions to prevent further deterioration and unanticipated failure of the post-tensioning and stay cable systems. The deteriorated conditions that are of interest are strand defects that result in a loss of metallic area of the tendon which may be due to corrosion, section loss, or breakage of the strands; compromised grout such as unhydrated, over-hydrated or gassed grout; voids in the grout; and water infiltration into the tendons. Various NDE methods that are capable of evaluating these conditions are explored. These include electromagnetic methods such as Ground Penetrating Radar (GPR), Infrared Thermography (IRT), and Electrical Capaci- tance Tomography (ECT); magnetic methods such as Magnetic Flux Leakage (MFL) and magnetic main flux method (MMFM) using permanent magnet and solenoid; mechanical wave and vibration methods such as Impact Echo (IE), Ultrasonic Tomography (UST), Ultrasonic Echo (USE), Sonic/Ultrasonic Pulse Velocity (S/UPV), Low Frequency Ultra- sound (LFUT), and sounding; visual methods such as Visual Testing (VT) and borescope; and electrochemical methods such as electrochemical impedance spectroscopy (EIS). A combination of the above methods to utilize the advantages of multiple methods are also explored. These include a combination of GPR/USE, GPR/IE, MFL/sounding, MFL/IE, and IRT/USE. Based on the findings from this investigation flowcharts are presented to aid in the selection of the most appropriate NDE method to evaluate specific deterioration condi- tions. Flowcharts are also presented to help end users determine the different defects that may be detected by a particular NDE technique. Testing procedures for each of the NDE methods, and their combinations are also presented. Inspection Guidelines for Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods
