Impact echo scanning technology for internal grout condition evaluation in post-tensioned bridge ducts: Fid-Bau Portal

Impact echo scanning technology for internal grout condition evaluation in post-tensioned bridge ducts

Tinkey, Y. / Olson, L.D. / Bedon, R. / Lieberle, C.

This paper focuses on imaging and scanning technology based on the rolling Impact Echo (IE) method. The basic background of the Impact Echo technique and its implementation with a rolling scanning transducer are discussed. A 2D imaging display using the amplitude normalization technique and typical results in time and frequency domains from case histories and a university research project are also included in the paper. Impact Echo is generally used to either determine the internal condition of the concrete structures or measure the thickness of the structures. The rolling transducer in the IE scanner expedites the IE test process by allowing for rapid, near-continuous testing. Several nondestructive testing techniques were used in a research project to locate/evaluate the grout condition inside post tensioned ducts. Then, an Impact Echo Scanner was used to scan along and across a duct for internal grout condition evaluations. Other NDT techniques such as Ultrasonic Tomography Imaging using Ultrasonic Pulse Velocity equipment and Spectral Analysis of Surface Waves were also used in the investigation. The results from Impact Echo scanning with an automatic filtering and the 2D image display produced good accuracy in locating voids in both plastic and steel ducts. Secondly, actual NDE results from post-tensioned steel ducts in a bridge are discussed. Ground Penetrating Radar (GPR) was first used to locate the ducts. Next, IE Scanning was done to locate anomalies indicative of void. Drilling and borescope examination were used to confirm voids. Also, another NDT technique using a vacuum pressure system was used in the project to measure the volume of air (void) inside the duct before the vacuum injection repair process was done.