Concrete tests answer two different questions. For new concrete: does what was delivered and placed meet the specification? For existing concrete: what condition is it in, and why is it deteriorating? Different tests suit each question, and the best results come from combining a visual inspection with a few well-chosen tests rather than running everything.
Testing new concrete
On new construction, the project specification sets which tests are required, usually referencing CSA A23.1 for concrete materials and construction and CSA A23.2 for test methods. Check the current editions your project specifies.
Fresh concrete tests
Done on site by a qualified technician as concrete is delivered:
- Slump: a measure of workability and consistency between loads.
- Air content: concrete exposed to freezing needs entrained air to resist freeze-thaw damage, so air content is checked against the specification.
- Temperature: concrete that is too hot or cold can have problems with setting and strength.
- Density: sometimes measured as a check on the mix.
Strength cylinders
Samples are cast into cylinders, cured in a controlled way and crushed in a lab at set ages. Results show whether the concrete as delivered achieved the specified compressive strength. Cylinders reflect the concrete delivered, not necessarily how it was placed and cured in the structure.
Testing existing concrete
Visual inspection and sounding
The starting point. An inspector maps cracks, spalls, scaling, stains and exposed reinforcing, and sounds the surface by tapping or dragging a chain. Hollow sounds reveal delaminations, where a layer has separated below the surface, often due to corroding steel.
Cores
Cylinders are drilled from the structure and tested in a lab. Cores are the most direct way to measure in-place strength and can also be examined for depth of deterioration, air void system, carbonation and cracking. They cause local damage, so locations need to be scanned and chosen carefully. See cutting and coring concrete safely.
Rebound hammer
A spring-loaded hammer strikes the surface and measures the rebound. It is quick and non-destructive and useful for comparing areas, but it only reflects near-surface hardness and needs correlation with cores to estimate strength.
Ultrasonic pulse velocity
Measures the time for a sound pulse to travel through concrete. Lower velocities can indicate cracking, voids or poor quality. It is useful for checking uniformity across a member.
Cover meters and scanning
Cover meters measure how deep reinforcing sits below the surface. Low cover lets water and chlorides reach steel sooner. For locating embedded items in more detail, see concrete X-ray vs GPR scanning.
Testing for corrosion
Corrosion of reinforcing steel is the main cause of deterioration in parking structures, balconies and other salt-exposed concrete.
- Chloride content: powder or core samples taken at increasing depths are tested in a lab. High chloride levels at the steel indicate a high risk of corrosion.
- Half-cell potential: measures electrical potential across the surface to map where corrosion is likely active.
- Carbonation depth: a chemical indicator sprayed on a fresh break or core shows how far carbonation has progressed. When it reaches the steel, protection is lost.
- Corrosion rate measurements: specialized tests that estimate how quickly steel is corroding.
Freeze-thaw damage is a major cause of deterioration in Canadian concrete. See freeze-thaw damage to concrete and masonry.
Choosing the right tests
| Question | Useful tests |
|---|---|
| Did the new concrete meet spec? | Fresh tests, cylinders, cores if results are low |
| How strong is this existing concrete? | Cores, with rebound hammer to compare areas |
| Why is the slab spalling? | Sounding, cover, chlorides, half-cell, carbonation |
| Where can I safely core or cut? | GPR or X-ray scanning |
| Is the damage from freezing? | Visual, cores examined for air voids and damage depth |
Start with the question. Testing without a clear question produces numbers that are hard to use. Decide what decision the results will support, then choose tests and sampling locations to answer it.
Who does the testing
Fresh concrete testing and cylinder testing are done by certified field technicians and testing laboratories. Lab tests on cores and chloride samples are done by laboratories. Interpretation of structural capacity, and design of repairs, belongs with a structural engineer.
How ehZee can help
We inspect concrete, recommend the tests that answer your question, coordinate sampling and lab work, and explain the results in plain terms. See our concrete inspections and X-ray, or call 1-833-888-0091.
Common questions
My cylinder results were low. Is the structure weak?
Not necessarily. Low cylinder results can come from sampling, handling or curing of the cylinders. Cores from the structure are usually the next step, and an engineer interprets them against the design.
Can a rebound hammer replace cores?
No. It is a useful comparative tool, but strength estimates from it are rough unless correlated with cores from the same concrete.