TECHNIQUE TO DETERMINE DEPTH OF DEFECTS IN CONCRETE USING INFRARED THERMOGRAPHY – A SIMULATION STUDY

Abstract

The cracks and damages in concrete can occur during the construction, placement, curing or any time during the service life of the structure. Cracks and damages can indicate concrete deterioration. Structural engineers are interested in the identification of damage location and crack depth measurement. The crack and damage depth measurement can help contractor in evaluating the repair costs. There are different methods to measure the crack depth like Impact-Echo Method, Ultrasonic Pulse Velocity (UPV) which can be employed where location of the cracks and damages are accessible. However, sometimes location of crack and damage in the concrete is inaccessible and this requires non contact measurement methods for identifying damages. Infrared thermography can be effectively used in identifying subsurface cracks and damages in such cases. The research work reported in this study is to identify depth of sub-surface defects located in concrete structures. The depth of damage is identified by taking infrared images of concrete surface. A pseudo experiment of thermal imaging was conducted on concrete surface using FEM simulations. A concrete slab model having inbuilt defects of known thicknesses and at known depths from the surface is used. The surface of slab is subjected to thermal excitation of varying amplitude and time period. The temperature contours on vertical sections passing through the defects are used to accurately determine the depth of damage. Using this technique depth of defect could be determined with a least amount of error up to 2% of actual depth. The results of simulation study are reported.