Application of numerical procedure for thermal diagnostics of the delamination of strengthening material at concrete construction

Abstract

Purpose Large structural objects, primarily concrete bridges, can be reinforced by gluing to their stretched surface tapes of fiber-reinforced polymer (FRP). The condition for this technology to work requires the quality of the bonding of FRP and the concrete to be perfect. Possible defects may arise in the phase of construction but also as a result of long-term fatigue loads. These defects having different forms of voids and discontinuities in the bonding layer are difficult to detect by optical inspection. This paper aims to describe the development of a rapid and nondestructive method for quantitative assessment of the debonding between materials. Design/methodology/approach The applied technique belongs to the wide class of active infrared (IR) thermography, the principle of which is to heat (or cool) the investigated object, and determine the properties of interest from the recorded, by an IR camera, temperature field. The methodology implemented in this work is to uniformly heat for a few seconds, using a set of halogen lamps, the FRP surface attached to the concrete. The parameter of interest is the thermal resistance of the layer separating the polymer tape and the concrete. The presence of voids and debonding will result in large values of this resistance. Its value is retrieved by solving an inverse transient heat conduction problem. This is accomplished by minimizing, in the sense of least squares, the difference between the recorded and simulated temperatures. The latter is defined as a solution of a 1D transient heat conduction problem with the already mentioned thermal resistance treated as the only decision variable. Findings A general method has been developed, which detects debonding of the FRP tapes from the concrete. The method is rapid and nondestructive. Owing to a special selection of the compared dimensionless measured and simulated temperatures, the method is not sensitive to the surface quality (roughness and emissivity). Measurements and calculation may be executed within seconds. The efficiency of the technique has been shown at a sample, where the defects have been artificially introduced in a controlled manner. Originality/value A quantitative assessment procedure which can be used to determine the extent of the debonding has been developed. The procedure uses inverse technique whose result is the unknown thermal resistance between the member and the FRP strip.

Wheeled Robot Dedicated to the Evaluation of the Technical Condition of Large-Dimension Engineering Structures

“…This was the motivation to the Silesian University of Technology team to work on the methods and tools making such inspection possible. One of the promising non-destructive methods of quality assessment is infrared thermography (IRT) [7] The proposed method [8] base on that, is currently at the stage of patent applications [9,10] whose co-author is one of the co-authors of this publication. This solution was adopted as the primary diagnostic tool used in the diagnostic robot.…”

“…As a consequence, it can result in local delamination of material which means that composite connection does not meet the required criteria anymore. The proposed diagnostic method bases on thermal diagnostic [8] and it was installed on the robotic platform. The test procedure involves even heating of the element, followed by observation of the surface cooling process (Figure 16).…”

Increasing the Performance of a Fiber-Reinforced Concrete for Protective Facilities

“…New fiber-reinforced concretes are still being researched [5][6][7]. Fibers that are overly long and not adequately treated at the time of processing, on the other hand, tend to "ball" in the mix and cause problems with workability [8]. Fibers are added to concrete for long-term durability by controlling the size of cracks, by which the transport of corrosive materials into the concrete is reduced [5,6,8].…”

“…Fiber-reinforced building materials for special structures, created taking into account transdisciplinary positions and micromechanics of composite media, are of significant interest as a new generation of composites [5,6,8]. At the same time, it becomes possible to Fibers 2021, 9, 64 2 of 13 achieve the target characteristics of static and dynamic strength, impermeability to toxic vapors and gases, as well as durability, which will make it possible to operate structures in extreme conditions and, accordingly, preserve the life and health of people in protective shelters [9][10][11].…”

“…At the same time, it becomes possible to Fibers 2021, 9, 64 2 of 13 achieve the target characteristics of static and dynamic strength, impermeability to toxic vapors and gases, as well as durability, which will make it possible to operate structures in extreme conditions and, accordingly, preserve the life and health of people in protective shelters [9][10][11]. Transdisciplinary positions that combine the theoretical foundations and technical justification for the creation of multicomponent composites from the standpoint of reducing the economic and environmental burden, provide the ability to control structure formation in order to achieve high values of operational characteristics [7][8][9][10][11][12][13][14][15].…”