Carbonation

Mineral construction material, example concrete During the process of carbonation, the highly alkaline calcium hydroxide (pH-value ≥ 12) reacts with carbon dioxide contained in the air and water and converts into pH neutral calcium carbonate and water. The carbonation process proceeds from the outside to the inside and results in strength and compactness of the concrete but also in a decrease of alkalinity. With a pH value of ≤ 10 the untreated reinforcing steel starts to corrode. The carbonation speed is highest when the air moisture content ranges between 45 % and 75 %. Thus, the application of a surface coating is an effective protective measure. An adequate concrete cover helps to maintain the alkaline environment of the reinforcing steel for as long as possible. The increasing age of the concrete reduces the carbonation speed.