Nicholls Colton Depth of Carbonation Measurement

Depth of carbonation measurement

The depth of carbonation measurement can be found by applying phenolphthalein solution to a freshly exposed concrete surface, the more alkaline concrete (with a pH in the region of 9 or above) showing pink, the carbonated more acidic concrete remaining clear.

A hydrated Portland cement concrete is highly alkaline in nature creating a passive environment for embedded reinforcement, allowing an oxide film to form on the surface of the steel which in turn provides protection from corrosion.

However acidic atmospheric gases will react with hydrated cement and in particular, carbon dioxide which will diffuse into the concrete and if combined with moisture will react with the hydrated cement to form calcium carbonate, reducing the alkalinity of the concrete.  This carbonation advances as a front into concrete from exposed surfaces, in itself not having a detrimental effect on the concrete, but on reaching the level of reinforcing steel, will in time reduce the alkalinity of the concrete along with the protection provided to the steel leaving it vulnerable to corrosion.

When taken into consideration with Depth of cover to reinforcement measurements, depth of carbonation measurements can provide further information as to the susceptibility of reinforcement to corrosion.

Results are presented as the maximum depth of carbonated concrete measured at a test location.

Testing is undertaken in accordance with a documented in-house method based on the requirements of BRE information paper 6/81 and is covered by our *UKAS accreditation