Using Nondestructive Test Methods to Determine Voiding in Grouted Post-Tensioned Tendons

Forensic investigation after the failure of a bonded post-tension (PT) tendon has shown that in most cases, these failures occur because the strands were not properly protected by the grout. There is often a void or deficient grout which provides an environment that will lead to strand corrosion, and if left unmitigated, eventually failure. Identification of PT tendon grout defects is very difficult to perform with standard inspection techniques and these PT issues are commonly not identified until a serious failure occurs. This paper will review the innovative ways nondestructive testing can locate voided or defective grout and document corrosion in external and internal PT tendons. The paper will focus on the use of the acoustic method, impact echo/pulse velocity (IE/PV), which can determine voiding by analyzing the amplitude and frequency of the resonating compressional, and shear waves along the PT tendons. Through analysis of these stress waves, a trained practitioner can locate defects in the grouting of both internal and external tendons. The paper will provide case studies of two different bridges where a failed PT tendon on each structure prompted an investigation into the condition of the other tendons. It was discovered that grout voids were a prominent issue throughout the structures and that corrosion was at advanced stages.