IMPACT ECHO (IE)
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ABSTRACT
This paper presents the findings from a research project titled “Non-destructive Evaluation Method for
Determination of Internal Grout Conditions inside Bridge Post-tensioning Ducts using Rolling Stress
Waves for Continuous Scanning”. This project was funded by the NCHRP – IDEA Program. This paper
discusses the experimental results from the studies which involved a defect sensitivity study of an Impact-
Echo (IE) Scanner to detect and image discontinuities in post-tensioned ducts of a mockup U-shaped
bridge girder and a mockup slab. Different sizes of ducts were included in this study as well as varying
sizes of void defects. Detailed sensitivity study of non-destructive grout defect detection with Impact-
Echo Scanning of 8-four inch diameter ducts with constructed defects was the main focus in this study.
Comparisons of the IE defect interpretation and the actual design conditions of the ducts inside the bridge
girder/slab are presented. The IE results are presented in a three-dimensional fashion using thickness
surface plots to provide improved visualization and interpretation of the internal grout to void defect
conditions inside the ducts of the girder. The Impact-Echo tests were performed with a Scanner which
greatly facilitates the Impact-Echo test process by allowing for rapid, near continuous testing and true
“scanning” capabilities to test concrete structures. The paper summarizes the general background of the
Impact-Echo technique and the Impact-Echo Scanner. Descriptions of two mock-up specimens used in
the experiment and the discussion of the results from the Impact-Echo Scanner are presented herein.
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