A study on carbonation depth prediction for fly ash concrete

Carbonation of fly ash concrete is studied by using two types of fly ash with different CaO contents. It is observed that under natural exposure environments, the carbonation rate is the highest when specimens are exposed in the city. The decreased ratio of water to binder and fly ash content leads to a better carbonation resistance. For the same fly ash content, specimens of high-CaO fly ash show a better carbonation resistance than those of low CaO fly ash. However, when compared at an equal strength, the effect of the type of fly ash on carbonation becomes insignificant. When comparing the carbonation results of concrete and mortar specimens, results of mortar show similar trends as those of concrete. However, the test results on mortar are worse by the use of fly ash than those of concrete. In addition, the carbonation tests in an accelerated environment are also conducted. It is found that there exist strong relations between carbonation depths of concrete exposed in natural and in accelerated environments. A mathematical approach to predict the carbonation depth in the natural environments is proposed based on the accelerated tests and the square-root-t-law.