Moisture-Insensitive Procedure for Determining the Air Void Distribution in Concrete

An infrared thermography (IRT) based procedure, that relies on detecting temperature differences due to air voids, is developed to detect improperly compacted concrete. Unlike previous attempts to detect isolated delaminations, the object of the present work is to reconstruct the random void distribution inside concrete. A correlation function of thermal contrast-based approach is adopted. However, the basic method is shown to have several limitations. Enhancements are proposed which use a combination of techniques to remove background noise and improve the thermal contrast. The enhanced method is tested on laboratory specimens. The void distributions obtained are compared with those obtained from micro x-ray computed tomography (CT) scans of the specimens. The algorithm is further validated using the results of finite element simulations of concrete specimens with synthetic void distributions. It is found capable of distinguishing air voids from moisture-filled areas, thereby adding to its usefulness.