Prevention of Carbonation of RC Structures (Critical Review)

Carbonation of concrete is traditionally defined as the chemical reaction between atmospheric carbon dioxide and the products of cement hydration, particularly calcium hydroxide. This phenomenon will reduce an alkaline pH of concrete of approximately 12.6, whereas the carbonated concrete is more neutral with a pH value which may decrease to 8.3. The degradation mechanism which threatens the reinforcement is corrosion, but the alkaline environment will safeguard the protective film as the pH of the surrounding solution remains within certain limits. Carbonation is a threat as it lowers pH and so may bring the steel within the corrosion boundary. Thus, carbonation may be a factor in the initiation of corrosion. Carbonation itself does not attack the reinforcement but it may contribute significantly to a lowering of the defense mechanism inherent in the synergetic relationship between steel reinforcement and concrete. This paper presents literature review of different methods which can be used to prevent the carbonation of concrete of existing structures and new one. The prevention methods include the use of protective coatings, anti-carbonation coatings and admixtures. From the literature review, it can be concluded that carbonation of concrete can be eliminated and prevented by using some anti-carbonation coatings. Also, using of protective coatings and/or cement plastering will reduce the carbonation depth. Moreover, concrete quality and good construction practices are governing factors on the rate of carbonation. The treatment of existing carbonated reinforced concrete structures is discussed.