Determination of Favorable Time Window for Infrared Inspection by Numerical Simulation of Heat Propagation in Concrete

Abstract

Every bridge is subjected to a thorough inspection process every other year at most. Nondestructive evaluation techniques, especially noncontact methods, are gaining popularity to take part in structural health monitoring of existing bridges for expediting the inspection process. Infrared thermography is one of the noncontact testing methods; it is based on capturing and processing the thermal gradient on a radiant surface which is highly affected by the ambient environmental conditions. The objective of this study is to numerically search for an appropriate time window to carry out infrared inspections. To this end, a numerical model of a bridge deck with certain initial and boundary conditions was used to numerically obtain temperature differentials at any nodes across the model for a period of 24 h. A delamination with a constant thickness was positioned in the concrete deck. The transient solutions of the nonlinear partial differential equation were obtained by utilizing the finite element method. The numerical results point to afternoon as the most favorable time window to conduct infrared inspections; this result coincides with some of the experimental research found in literature. Additionally, it was shown that the existence of water in the defect greatly affected the heat conduction process.