Nondestructive Testing of Cable Ducts in Concrete Columns and Walls Using the Impact-Echo Method

Abstract

This paper describes how the appearance of cracks and spalling in concrete columns in a new eight-story office building brought about concerns that the injection of the ducts in the columns was of poor quality. The cracks were mainly present at one floor, and trial drillings into the ducts on columns with severe cracks disclosed the presence of water and loose gravel and aggregates. Opening a duct revealed that the duct was either partially empty, filled with compacted gravel, or fully grouted. It was decided to use the impact-echo (IE) method to investigate the columns and ducts. Each column contains four ducts with a 25 mm (1 in.) diameter reinforcing bar for distribution of the shear stress at the lower and upper 1.0 m (3 ft) to each floor. Testing was performed for each 0.1 m (4 in.) elevation in these areas. The criterion to approve the injection was that at least 0.7 m (2 ft) of the column at the floor or the ceiling was fully injected. After testing the columns on 3 floors, it was decided to investigate the ducts in the walls of the three stairwells of the building, as they were vital for transferring the stresses of the reinforcement down through the building. Verification of the IE-system by drilling cores showed that is possible to distinguish between empty ducts, fully injected ducts, and ducts with compacted gravel. More than 35,000 measurements were made. The examination of the ducts showed that approximately 63% of tests at the top and approximately 86% at the bottom of the columns and walls indicated full injection.