Experimental and Numerical Studies on Nondestructive Evaluation of Grout Quality in Tendon Ducts Using Impact-Echo Method

Abstract

The impact-echo method is applied to evaluate the grout quality in tendon ducts of posttensioned structures nondestructively in the present study. As the main evaluation index, the dominant frequency (DFQ) is obtained from the frequency-domain spectrum, which is transformed from the original time-domain signal. The influences of several factors on the DFQ are investigated in detail both experimentally and numerically. These factors include size effect, slab thickness, tendon duct depth, affected range, DFQ shift, and grout strength. The experiments are conducted in the construction field on posttensioned box girders under various grouting conditions. The DFQs of each test point in a test area are integrated to draw a contour image based on their coordinates. Through the analysis of the contour image, grout quality in the tendon ducts can be evaluated accordingly. Grout defects are detected in some box girders and verified by chiseling these suspected ducts. The numerical studies, which can provide some insights into the experimental findings, show good agreement between the experimental and numerical results.