Carbonation of Concrete Exposed to Hot and Arid Climate

A long-term investigation into the carbonation of concrete exposed to natural weather conditions in Kuwait was undertaken. Forty-four concrete mixes were prepared, and prisms were made and exposed to natural weather after a 28-day period of laboratory air and/or moist curing. Parameters investigated included water/cement ratio, type of cement, type and dosage of admixture, water-curing period, type of curing aid, and special coatings. The admixtures included water-reducers, retarders, and superplasticizers (i.e., high range water-reducers). Carbonation measurements up to a maximum age of 600 days are reported. The results show that the most significant factors influencing concrete carbonation were the use of surface coating, water/cement ratio, water-curing period, and the season when the concrete was initially made and exposed. The use of specialized surface coatings completely prevented carbonation. A decrease in the water/cement ratio and an increase in the water-curing period resulted in a decrease in concrete carbonation. Concrete initially cast and exposed during the winter season exhibited lower carbonation than concrete cast during the summer season. Other parameters, such as the type of cement, admixture, or curing compound used, also influenced the carbonation, although to a lesser extent.