7 NDT Methods for Accurate Corrosion Evaluation in Concrete Structures

Early detection of corrosion in concrete structures is crucial for preventing extensive damage and ensuring the longevity of infrastructure. Non-Destructive Testing and Evaluation (NDT) methods play a pivotal role in identifying the onset of corrosion without damaging the structure. In this article, we will quickly review 7 Essential NDT Methods for Accurate Corrosion Evaluation in Concrete Structures.

NDT Methods for Accurate Corrosion Evaluation in Concrete Structures

1. Half-Cell Potential Measurement

Overview: Half-cell potential measurement is a widely used electrochemical method for detecting active corrosion in the reinforcing steel within concrete structures. Read More
How It Works: This method measures the electrical potential difference between the embedded steel reinforcement and a reference electrode placed on the concrete surface. Areas with lower potential readings indicate active corrosion.
Advantages: It is a quick and relatively simple technique that provides a good indication of corrosion activity, allowing for identifying areas at risk.

2. Ground Penetrating Radar (GPR)

Overview: GPR uses electromagnetic waves to scan the subsurface of concrete structures and detect anomalies that may indicate corrosion.
How It Works: GPR sends radar pulses into the concrete. The reflected signals are analyzed to identify changes in the material’s properties, such as moisture content or voids, which could indicate the presence of corrosion.
Advantages: GPR can provide detailed images of the subsurface, allowing for the identification of the location and extent of potential corrosion-related damage.

3. iCAMM

Overview: iCAMM is a novel Canadian technology for evaluating the corrosion activity of embedded steel reinforcement in concrete.
How It Works: uses the magnetic properties of ferromagnetic objects to identify not only the extent and location of degradation and defects, but also the distribution of stress within the specimen. Because materials such as concrete are non-ferromagnetic, the technology can readily be used to detect corrosion and cracking of metalic objects (Pipes, Reinforcement, etc) under any covering materials such as insulation or concrete to identify and locate their degradation.
Advantages: The key advantage of the iCAMM technology is the fact that it does not require establishing an electrical connection with steel bars. The iCAMM sensor senses the electromagnetic field on or around the rebar as the sensor rolls over the concrete surface, producing heat maps of corrosion activity and intensity. Read More

4. Corrosion Rate Measurement

Overview: Corrosion rate measurement quantifies the rate at which steel reinforcement within concrete is corroding, providing a direct assessment of the ongoing degradation.
How It Works: One common technique is the Linear Polarization Resistance (LPR) method, where a small electrical current is applied to the reinforcing steel, and the resulting potential difference is measured. The polarization resistance gives an estimate of the corrosion rate in terms of the amount of steel lost per year.
Advantages: This method provides a quantitative measure of corrosion activity, allowing engineers to assess the urgency of repairs and monitor the effectiveness of corrosion protection systems. It is especially useful for ongoing monitoring and maintenance planning, helping to extend the lifespan of structures by addressing corrosion before it reaches critical levels.

5. Surface Electrical Resistivity Testing

Overview: Surface electrical resistivity testing measures the electrical resistance of the concrete surface, which is influenced by its moisture content and the presence of chlorides—both key factors in corrosion.
How It Works: A resistivity meter is used to pass a small current through the concrete surface. Lower resistivity indicates higher moisture content and a greater likelihood of corrosion.
Advantages: This method is non-invasive and provides valuable insights into the concrete’s permeability and potential for corrosion, making it an excellent tool for early detection and ongoing monitoring.

6. Infrared Thermography

Overview: Infrared thermography is a technique that detects surface temperature variations on concrete structures to identify areas of potential corrosion.
How It Works: Thermal cameras capture infrared radiation emitted from the surface of the concrete. Temperature differences may indicate areas of moisture ingress or delamination, both of which are often associated with corrosion.
Advantages: This method is non-invasive, fast, and can be used to inspect large areas of a structure, making it ideal for preliminary assessments.

7. Ultrasonic Pulse Echo

Overview: UPE testing measures the velocity of ultrasonic waves traveling through concrete to assess its integrity and detect defects.
How It Works: The UPE uses shear waves to identify internal defects, such as delamination in concrete decks, and identify potential voids in concrete. Ultrasonic Pulse Echo is particularly useful in detecting corrosion and defects in post-tensioning ducts, as well as in concrete slabs and walls. This method allows for the identification of voids, delamination, and the presence of corrosion by analyzing the reflections of ultrasonic waves from internal features. In post-tensioning ducts, it can help detect tendon fractures or corrosion, which are critical for structural integrity. In slabs and walls, it is effective in locating areas of corrosion that may not be visible from the surface.
Advantages: Ultrasonic Pulse Echo provides a non-invasive means of assessing the internal condition of concrete structures, especially in areas that are difficult to access or inspect using other methods.