QUANTIFYING SHALLOW DEPTH CONCRETE DELAMINATIONS USING IMPACT ECHO

Abstract

Delamination is a type of deterioration commonly found in concrete structures. It may form due to corrosion of embedded steel, poor construction, excessive vibration, or lack of bonding in composite construction. Impact echo (IE) is a simple and straightforward non-destructive testing (NDT) technique that is used to detect the presence and extent of delamination within concrete structures. It is capable of detecting its presence of delaminations in deep depths, but cannot accurately measure the defects that are near the surface. This phenomenon occurs due to the differences in the vibration modes of deep and shallow depth delaminations. The objective of this study was to quantify the depth of shallow depth delaminations, using the IE method. Four slab samples containing 12 near- surface delaminations were cast, and the impact echo test was performed on each of them. Frequency contour maps were drawn for each slab from which the average frequency of each delamination was determined. A numerical formulation that correlated the average vibration response over the delaminated region, obtained from the IE test, and the geometry of the delaminations was suggested, based on the theoretical solution of flexural mode of vibration of thin rectangular plates. Regression analysis was performed for three selected dimensional parameters, and six regression functions (three logarithmic and three exponential) were suggested. The depths of the delaminations were predicted with these functions. It was observed that the exponential function correlating the flexural mode of vibration and the perimeter-to-depth ratio yielded the smallest percentage error in predicting the depths. As a result, this exponential equation was finalized as the flexural mode vibration equation for shallow depth delaminations, and recommendations for further work were suggested.