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.
Highlights
Today concrete is understood to be one of the most widely used materials in civil engineering structures around the world [1,2]
It is evident that some defects can be detected using these optimal thermograms, but there is a significant effect of uneven heating and reflectance, which hinder defect detection
As can be seen (Figure 16), principal component thermography (PCT) did not manage to detect the smallest defects in samples BM x-1 and the specimens at largest depths. It can be concluded from the presented research that PCT is an effective post-processing method to improve defect detection in concrete structures
Summary
Today concrete is understood to be one of the most widely used materials in civil engineering structures around the world [1,2]. Concrete is by its nature a nonhomogeneous composite material whose composition varies and a material that utilizes diverse raw materials in its production This causes quite a lot of complications when one tries to apply non-destructive testing (NDT) methods to detect defects in concrete structures. Since work on in-situ casting is often performed by unskilled workers, the resulting hardened concrete is highly variable and often contains defects, which can influence its durability. This means that concrete structures are often not constructed in a way that would meet the designed parameters [4]
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