Author: Inspector-Analyst. José López, September 6, 2023.
Introduction
Non-Destructive Testing (NDT) is gaining more and more relevance in the detection of defects and evaluation of the integrity of bridges and concrete structures. These test methods allow obtaining information about the internal conditions of the bridge decks, identifying damage and non-visible deterioration due to corrosion.
These infrastructures are constantly exposed to various environmental conditions and loads that can trigger deterioration over time. Therefore, timely and accurate detection of faults, structural weakening, and other problems has become a critical priority to ensure public safety and long-term sustainability.
Deteriorated and damaged bridges represent a significant concern in the area of transportation infrastructure. According to the American Highway and Transportation Association (ARTBA) Bridge Report, it is estimated that approximately one in three bridges in the United States require intervention for repair or replacement, and there are more than 46,100 bridges with structural deficiencies. .
Substantial financial resources are allocated annually to preserve the structural integrity and functionality of these bridges, since their deterioration is usually the result of a confluence of various factors.
In this context, this article will discuss the conventional methods and the most recent advances in Non-Destructive Testing technology applied to bridges and concrete structures, to identify and evaluate in a non-intrusive and precise way the defects and cracks that can undermine structural integrity.
These technological advances not only allow for more effective and efficient maintenance, but also contribute to extending the useful life of these important infrastructures, reducing long-term costs and improving the safety of the people who depend on them.
Conventional Methods of Non-Destructive Testing (NDT)
The first place is occupied by visual inspection; which is a direct and simple method that is commonly used to detect visible damage such as potholes in concrete bridges. However, it is limited in identifying more subtle problems such as cracks and corrosion, as it is based on naked eye observation and does not provide a complete assessment of the internal structural integrity of the infrastructure, focusing mainly on obvious problems that require immediate repairs.
In the field of bridge inspection, conventional Non-Destructive Testing (NDT) methods have historically been used to assess the integrity of structures. One such traditional approach is liquid penetrant testing (PT), which involves the application of a liquid dye to reveal surface cracks in welds. Although PT is an inexpensive and versatile technique in terms of applicability to different materials, it has limitations as it focuses solely on the detection of surface cracks, without taking subsurface cracks into account. In addition, it requires direct access to the surface under inspection, and the roughness of the surface can influence the sensitivity of detection.
Another conventional method is radiography, which has been used in the inspection of bridges, although its use is gradually being discontinued. Radiographic tests use X-rays to obtain a radiographic image of the internal structure of welds or bolts, making it possible to determine the existence of discontinuities in the joints. However, this method carries safety risks associated with the emission of radiation and the generation of chemical residues. In addition, it requires the obtaining of additional licenses and the evacuation of areas near the site of the radiographic inspection.
Advanced NDT Methods
To overcome the limitations of conventional methods, multi-element ultrasound assays (Phased Array or PAUT) have emerged as a reliable and safe alternative. These tests use a multi-element ultrasonic defect detector (Phased Array) that emits high-frequency sound waves towards the bridge structure. When a defect is detected, such as a crack or corrosion, the probe records disturbances in the sound waves. The resulting data is transmitted back to the defect detector, which processes it into a visual representation that allows inspectors to accurately identify defects.
Another advanced NDT technique widely used by inspectors is Eddy Current (EC) testing. This method is especially valuable for the detection of subsurface cracks, a capability often overlooked by liquid penetrant tests. A highlight of the eddy current test is its ability to be applied to painted or coated surfaces, which significantly reduces time and cost as coatings do not need to be removed prior to inspection.
These advanced NDT techniques, such as multi-element ultrasonic testing and eddy current testing, have evolved to overcome the limitations of traditional methods and offer higher data quality in bridge inspection, supporting the safety and durability of bridges. these critical structures.
Amongst other of the various more advanced Non-Destructive Testing (NDT) techniques used to assess the integrity of bridges, Infrared Thermography has stood out as a valuable and highly effective tool. Through the thermal radiation emitted by objects, images are created that represent the temperature differences on a surface.
In the context of bridge inspection, these temperature differences on the bridge surface can reveal areas where moisture accumulates or where there is a loss of insulating material, which could indicate corrosion or moisture problems in the concrete. Infrared thermography can identify the presence of subsurface corrosion by detecting irregular thermal patterns on the surface; This is important to prevent undetected structural deterioration that could endanger the safety of a bridge.
These techniques allow inspectors to fully assess defects found during a visual inspection and also allow inspections to be carried out on items that are not easily accessible. They require trained technicians to perform the tests and a professional with experience in interpreting the results.
Application of the techniques
It is important to take into account the element to be inspected for the application of the technique.
In the case of concrete elements, the following advanced inspection techniques are available: resistance methods, such as sclerometric and Windsor test; sonic pulse velocity methods, to detect delaminations; ultrasound techniques, which allow obtaining resistance values and detecting large cracks and voids; magnetic methods, for the determination of the position of the reinforcement; electrical methods, to determine corrosion; nuclear methods, for the determination of moisture content; infrared thermography, for detection of delaminations in boards; radar, to detect deterioration, especially on dashboards; radiography, to determine the distribution pattern of reinforcement; endoscopy, for a close examination of those parts of the structure that otherwise could not be visualized.
On the other hand, for metallic bridges there are: radiography, for the detection of cracks or inclusions of slag, or porosity in welding; magnetic particle examination, to locate defects on or near the surface; eddy current examination, to detect defects in depth; penetrating ink test, for surface defects; ultrasound examination, for the detection of internal defects.
Conclusion
Advances in Non-Destructive Testing have significantly increased the ability to inspect and evaluate bridges and concrete structures, allowing for more accurate and earlier detection of failures. These advanced technologies not only improve the security of our critical infrastructure, but also reduce costs in the long run by preventing larger problems. As we continue to innovate in this field, we can expect greater efficiency in the management and maintenance of these essential structures for our development and security.
References:
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