Principal Component Thermography for Defect Detection in Concrete

Abstract

The goal of the condition assessment of concrete structures is to gain an insight into current condition of concrete and the existence of defects, which decrease durability and usability of the structure. Defects are quite difficult to detect using infrared thermography when concrete elements cannot be thermally excited with the Sun, together with unfavorable thermophysical properties of concrete structures. In this paper, principal component thermography (PCT) is applied as a post-processing method to a sequence of thermograms in order to enhance defect detectability in concrete structures. Defects are detected by analyzing a set of empirical orthogonal functions (EOFs), which were acquired by applying principal component analysis to a sequence of thermograms. The research was performed using concrete samples containing known defects, which were tested using a step heating thermography setup. The results of presented research show that PCT is an effective post-processing method to improve defect detection in concrete structures. By effectively improving the defect detection, PCT has a potential to improve the non-destructive testing (NDT) accuracy of using infrared thermography (IRT) on concrete structures, especially in shaded areas of such structures. The research also shows the defect detectability depending on concrete type thermal excitation setup and defect geometry.

A Review of Infrared Thermography for Delamination Detection on Infrastructures and Buildings

“…It reaches 700 W/m 2 on a south elevation and 1300 W/m 2 on a horizontal surface at noon [88,148,159]. Previous studies have demonstrated that the larger the energy input is, the higher thermal contrast and SNR are generated in laboratory tests [10,85,139,157,169,170]. In contrast, delamination is difficult to be detected under low or no solar irradiation conditions [20,148,162].…”

“…Positive SNR means detectable delamination, and negative SNR means undetectable. The advantage of the SNR is that because of signal level evaluation, the metric and criterion can be applied not only to raw IR images but also processed images, such as PPT or PCT [10,169].…”

Drone-Based Non-Destructive Inspection of Industrial Sites: A Review and Case Studies

“…Flights conducted during the experiment have demonstrated the difficulty of manually flying a UAV while capturing NDI data. The data were subject to standard post-processing procedures, such as Principal Component Thermography (PCT) [151] or Pulsed Phase Thermography (PPT) [152]. However, the data were essentially useless due to the noisy sequence, and could not provide accurate results.…”

Latest Advances in Common Signal Processing of Pulsed Thermography for Enhanced Detectability: A Review

“…Each M column vectors are then subjected to a standardization process to ensure uniformity on a pixel-by-pixel basis. [33,39], This standardized matrix A is then reduced by singular value decomposition as follows:…”

“…This polynomial is referred to as the TSR polynomial. Suggestions based on analytical studies [39] have been made, to determine the degree n of the TSR polynomial that should ideally be used. The optimal degree n depends on the sample under consideration and measurement acquisition parameters, but it is in the range of n = 7 to n = 9 [43].…”