Carbonation in concrete is measured by applying Phenolphthalein solution to exposed concrete. We carry out concrete carbonation testing to difficult access areas using our experienced Rope Access Team, usually to High Rise structures but also to more easily accessible areas where no specialist equipment is needed.
In the first instance, a defect survey of the building or structure is carried out, logging distressed areas. A desktop study is normally used to reference locations on where Carbonation sampling is to be carried out, this is the easiest method of undertaking a survey.
Once locations have been decided on, using a Cover Meter, or rebar locator, which is a gauge that measures the thickness of concrete cover over steel reinforcement bars is used. The cover meter can tell you the depth of the rebar, the location and orientation of reinforcement bar (rebar) and determine the diameter of the rebar. Once the area that has the lowest concrete cover is recorded, the method we use, is to drill two holes a set distance apart and remove the concrete 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 potential contamination. By drilling two or more holes and breaking between them, fresh concrete is exposed providing a more accurate carbonation penetration reading.
The number 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, this also 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. The Phenolphthalein solution gives a very clear contrast on the concrete. Carbonated areas will remain clear and alkaline, non-carbonated areas will show as pink.
The tests should be carried out at various pre-determined locations across the building substrate, to both good and bad locations. 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.