Impact-Echo Scanning for Grout Void Detection in Post-Tensioned Bridge Ducts — Findings from a Research Project and a Case History

Abstract

This paper presents the findings from a research project 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 nondestructive 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 ImpactEcho Scanner are presented herein. Finally, a case study using an Impact Echo Scanner to locate grout voids inside the Orwell Bridge in UK is included in this paper.