Depth of Carbonation

Carbonation testing is performed to determine the depth to which atmospheric carbon dioxide has reduced the alkalinity of concrete. Carbon dioxide reacts with components of the cement paste over time, lowering the concrete's pH from the highly alkaline environment that normally protects embedded reinforcing steel from corrosion.

A pH indicator, Phenolphthalein, is applied to a freshly exposed concrete surface to distinguish carbonated concrete from concrete that retains a highly alkaline environment. The measured carbonation depth can then be compared with the depth of reinforcing steel.

When the carbonation front reaches the reinforcement, the protective passive layer surrounding the steel can become unstable, increasing the potential for corrosion when sufficient moisture and oxygen are present. Voss Labs commonly observes carbonation induced corrosion in industrial environments, structures greater than 100 years old, and especially in structures where concrete cover is shallow or insufficient.