Concrete corrosion testing is the assessment of whether, where, and how fast the steel reinforcement inside a concrete structure is corroding. Modern practice does this non-destructively, using electrical, electromagnetic, or thermal signals read through the concrete surface, so the structure is not cored or cut. Five methods dominate: corrosion rate measurement, half-cell potential mapping, electrical resistivity, ground penetrating radar, and infrared thermography. They answer different questions, so most real assessments use two or more together, and this page explains which to choose for which situation.
When steel reinforcement within concrete structures corrodes, it compromises the integrity, leading to safety risks and costly repairs. But how can you assess corrosion without causing further damage to the structure? That’s where non-destructive testing (NDT) methods come into play, offering innovative solutions for corrosion assessment.
Why Does Corrosion in Reinforced Concrete Matter?
Concrete structures rely on embedded steel reinforcement to maintain strength. However, factors like chloride ingress and carbonation can trigger corrosion in the steel, leading to cracks, spalling, and eventual failure if not addressed promptly. If you rely on traditional destructive tests, such as coring or cutting sections out, you risk damaging the structure you are trying to assess. Non-destructive concrete testing gives you a way to diagnose corrosion before it becomes a structural problem, without leaving new damage behind.
Why Choose Non-Destructive Concrete Testing Over Destructive Methods?
For decades, engineers assessed corrosion by coring or cutting sections out of the concrete. These destructive methods give detailed information, but they are invasive, expensive, and leave the structure compromised. Sustainable, cost-effective alternatives now exist, and non-destructive concrete testing has become the standard first-line approach for corrosion assessment.
NDT offers a solution that balances precision with preservation. These advanced techniques enable the evaluation of concrete’s condition without affecting its structural integrity.
What Are the Top Non-Destructive Concrete Testing Methods for Corrosion?
Each method answers one question well and the others poorly. Read down the second column first.
| Method | The question it answers | What it does not tell you | Typical standard | Best used for |
|---|---|---|---|---|
| Corrosion rate measurement (polarization resistance) | How fast is the steel corroding right now? | Where the bar is, how deep the cover is | There’s no consensus standard for measuring corrosion rate in the field. ASTM C876 addresses half-cell potential instead, which indicates where corrosion is likely occurring, not how fast it’s progressing. | Prioritising repair versus monitor decisions, tracking a structure over years |
| Half-cell potential mapping | Where is corrosion probable across this area? | How fast it is progressing | ASTM C876 | Screening large decks and walls to find hot spots worth measuring properly |
| Electrical resistivity | How easily can corrosion sustain itself in this concrete? | Whether corrosion is actually active | AASHTO T358 (surface), ASTM C1876 (bulk) | Durability screening, quality control, interpreting a corrosion rate reading in context |
| Ground penetrating radar (GPR) | Where is the reinforcement, and are there voids or delaminations? | Anything electrochemical | ASTM D6087 (bridge decks) | Locating bar and cover depth before an electrochemical survey, mapping delamination |
| Infrared thermography | Where is subsurface delamination or moisture, over a large area quickly? | Corrosion rate, corrosion probability | ASTM D4788 (bridge decks) | Fast first-pass screening of large decks, especially where access time is limited |
A practical sequence on an in-service structure is: thermography or GPR to find where to look, half-cell potential to confirm the probable zones, then corrosion rate measurement at the confirmed hot spots to decide what happens next.
1. Electrochemical Measurements
Electrochemical methods are commonly used to measure the corrosion rate of the steel embedded in concrete. One of the most efficient tools in this category is Giatec’s iCOR®, which employs patented CEPRA technology to provide wireless, non-invasive corrosion rate measurements. Unlike traditional methods, iCOR® offers real-time data with minimal surface preparation, making it a powerful solution for engineers looking to monitor corrosion over time.
2. Half-Cell Potential Mapping
Half-cell potential testing involves placing a reference electrode on the concrete surface and measuring the potential difference between the electrode and the embedded steel. This method can indicate areas where corrosion is likely to occur, though it doesn’t measure the corrosion rate directly. However, it’s a useful tool for identifying at-risk zones in large structures.
3. Ground Penetrating Radar (GPR)
GPR is another popular NDT method that can detect anomalies in concrete structures, such as voids, cracks, and delaminations that may be caused by corrosion. It works by sending radar waves into the concrete and interpreting the reflected signals. GPR provides an excellent overview of the internal state of the concrete and can help in identifying areas that may need further testing.
4. Infrared Thermography
This method uses infrared cameras to detect temperature variations on the concrete surface, which may indicate underlying issues such as moisture ingress or corrosion. Infrared thermography is a useful tool for initial inspections, offering a quick and visual way to assess large areas.
Where iCOR Fits in This Comparison
iCOR is a field device that returns three of the measurements in the table above from a single reading: corrosion rate, half-cell potential, and in-place electrical resistivity of the concrete. It takes the reading through four probes on the concrete surface, with no electrical connection to the rebar, so the same grid points can be resurveyed later without any breakout or patch repair.
That covers the electrochemical half of an assessment. It does not replace GPR or thermography, which answer geometric and thermal questions that no electrochemical method can. If you are locating bar before a survey or screening a whole deck for delamination, you still need those. If you are deciding whether a confirmed corrosion zone needs repair now or monitoring for another two years, you need a rate.
For how the connectionless measurement works, see our explanation of the rebar corrosion test technique. For how to read the numbers it produces, see our guide to interpreting concrete corrosion rate.
What’s Next for Non-Destructive Concrete Testing?
As the demand for sustainable infrastructure grows, the need for innovative, non-destructive corrosion monitoring tools becomes even more crucial. The future lies in integrating advanced technologies like artificial intelligence and machine learning into NDT systems, enabling predictive maintenance and minimizing the risks associated with corrosion-related failures.
Giatec continues to develop NDT and monitoring solutions built for that shift, including iCOR and SmartRock® sensors, ensuring that concrete structures remain safe, durable, and efficient for years to come.
Frequently Asked Questions
What is concrete corrosion testing?
Concrete corrosion testing determines whether the steel reinforcement inside a concrete structure is corroding, where in the structure it is happening, and how fast. It is done with instruments that read electrical, electromagnetic, or thermal signals through the concrete surface, so the structure is not damaged by the test itself.
What are the main methods of concrete corrosion testing?
Five methods cover most of the field: corrosion rate measurement, half-cell potential mapping (ASTM C876), electrical resistivity (AASHTO T358 for surface resistivity, ASTM C1876 for bulk), ground penetrating radar, and infrared thermography. Each answers a different question, so an assessment usually combines a screening method with a confirming electrochemical measurement.
Which concrete corrosion test should I use first?
Start with the question you need answered. If you do not yet know where to look on a large deck or wall, screen with infrared thermography or GPR. If you know the area but not whether corrosion is active, map half-cell potential. If you already know corrosion is active and need to justify a repair budget, measure corrosion rate. Testing out of that order usually means paying for readings you cannot act on.
Does concrete corrosion testing damage the concrete?
Non-destructive methods do not. They work through the cover using electrical, electromagnetic, radar, or infrared signals, so the structure keeps its integrity and the same point can be tested again later to see how corrosion has progressed. Destructive alternatives, such as coring for chloride profiling, do leave damage and need patch repair, and they give a single snapshot rather than a repeatable series.
How often should a structure be corrosion tested?
Frequency depends on age, exposure, and what the last survey found. Structures in chloride-heavy environments, such as marine exposure, de-icing salt, or parking decks, warrant more frequent assessment than sheltered structures in mild conditions. The value of corrosion rate testing comes from repeating the same grid over time, so a fixed interval you actually keep to is worth more than an occasional intensive survey. Follow the owner’s inspection programme and the applicable governing standard.
Editor’s Note: This post was originally published in October 2024 and has been updated for accuracy and comprehensiveness in September 2026.
