Influence of Cyclic Humidity on Carbonation of Concrete

Carbonation of concrete under various humidity conditions was examined in this study. Cylindrical specimens were subjected to accelerated carbonation using 50% carbon dioxide by volume at 25°C. Two relative humidities (RHs) (70 and 90% RH) and two humidity cycles (70–90% and 50–90% RH) were applied during the process. The results showed that carbonation of concrete was affected by the ambient humidity, humidity cycles, and surface geometry. The extent of carbonation was quantified using the coefficient of carbonation, which is the ratio of the carbonation depth to the square root of time. The maximum coefficient of carbonation occurred at 70% RH, and humidity cycles induced coefficients of carbonation between those induced at 70 and 90% RH. Specimens with curved surfaces had higher coefficients of carbonation than specimens with plane surfaces. The carbonation coefficients measured in the accelerated tests were also related to the carbonation of on-site concrete, which indicates that taking humidity cycling into account results in better prediction of accelerated carbonation than assuming a single humidity.