Impact Echo Scanning for Discontinuity Defection and Imaging in Posttensioned Concrete Bridges and Other Structures

摘要

This paper focuses on experimental results from two scanning impact echo systems on the internal condition of posttensioned ducts. The first system uses an impact echo head attached to an X/Y scanner and the second system is a rolling impact echo scanning system. The experimental tests were performed by two different research agencies and comparisons of the blind interpretation and the actual design conditions of the posttensioned ducts and slab are included herein. Background of the impact echo technique and its implementation with a rolling scanning transducer are discussed in the paper. The impact echo technique is generally used to either determine the. internal condition of concrete structures or to measure the thickness of concrete members. The rolling transducer in the impact echo scanner expedites the test process by allowing for rapid, near continuous testing. The results from the rolling impact echo scanning system are presmted in a three dimensional fashion to provide better interpretation of the internal conditions of the ducts.In these studies, the impact echo results from both research agencies show good agreement in correctly identifying grouting discontinuities in tendon ducts. Discontinuities of grout in bridge ducts are located based on an indirect indication of a void due to an apparent impact echo increase in bridge wall/skb thickness that actually reflects the lower resonant echo frequency due to the decreased stiffness associated with the duct void. No direct reflection from the duct with grouting discontinuities was observed in these experiments.