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Concrete Carbonation Testing

Concrete Carbonation Testing

Concrete carbonation is easily measured by applying Phenolphthalein solution to concrete. We offer concrete carbonation testing kits for hire to perform this on site.

The best method is to drill two holes a set distance apart and break the concrete away between them. Drilling a single hole to a specified depth and performing the test in that location is not recommended. A single drilled hole is a small test area and is at risk of contamination from potentially contaminated drilling dust from a shallower part of the hole. Concrete Carbonation Testing 2

By drilling two (or a cluster of holes) and breaking between them, ‘fresh’ concrete is exposed providing a more accurate carbonation penetration reading. This ‘cluster’ of holes can also be used for sampling concrete for chloride ion content.

Carbonation testing can also be performed on cores recovered from site by cutting them open in a lab. Again this must be done in a controlled manner to avoid any cross contamination from potentially carbonated areas on the surface.

The recommended Phenolphthalein solution to be used is in a 1% mix solution. For example 1g of indicator in a 100 ml mix of alcohol and water.

The Phenolphthalein solution gives a very clear contrast on the concrete. Carbonated areas will remain clear and alkaline (non carbonated) areas will show as bright pink.

The tests must be done at various locations across the substrate alongside a cover meter or Ferroscan survey. The cover readings at each sample location can then be compared to the measured carbonation depth indications to estimate the extent in which carbonation has reached the re-bar. Also to estimate the possible future carbonation rate.


Some aggregates can confuse Phenolphthalein indicator readings. Some concrete mixes can be dark in colour and determining the colour change accurately can be difficult.

Cross contamination of the sample area is another potential limiting factor. Care must be taken to ensure the freshly exposed concrete remains ‘clean’.

We can also offer a sample testing service, if you would like to discuss or hire a concrete carbonation testing kit please don’t hesitate to contact us today.

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