We were tasked to undertake a feasibility survey on whether a concrete walkway was fit to remain in service and receive extensive repairs or whether the walkway was to be replaced in its entirety.

In the first instance, a defect survey of the structure was carried out, logging all 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 an electromagnetic 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 reinforcement bar, 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.

By drilling two or more holes and removing the area between them, fresh concrete is exposed providing a more accurate carbonation penetration reading.
Phenolphthalein solution is sprayed onto the open area.

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, as demonstrated in the picture.