Influence of Curing in Early-Age and Drying to Microstructure of Fly Ash Concrete

Abstract

The global warming is one of the most important problems for many countries. It is necessary to use fly ash instead of cement to decrease CO2 emission. This study shows influence of curing conditions in early-age on the pore structure of concrete with fly ash. The microstructure of dried concrete can be divided into 2 parts, if the volume of macro pore having larger than 50nm diameter and mode pore diameter are considered. One is porous microstructure because of drying. The other is the microstructure of concrete in which the hydration continues even after finishing moist curing. When the concrete blended fly ash in 15% of binder is cured in moisture for 7days, fly ash reacts effectively and the depth of parts influenced by drying is the same as that of concrete used only cement. If the mixture includes fly ash in 30% of binder and it is cured in moisture for 3 or 7 days, the microstructure is more porous than the other mixture. When the concrete is cured in moisture for 28 days, all microstructures have almost the same pore structures. Carbonation of dried concrete is also focused on in this study. Then, it evaluates the contribution of fly ash as a binder to carbonation rate with k-value. As fly ash fraction increases, carbonation depth becomes larger. However, when fly ash fraction is 15% and the concrete is cured in moisture for 7 days, the carbonation depth is almost the same as that of concrete used only cement. If fly ash is used in this condition, k-value shows 0.4 and k'-value, which is in the case of considering inhomogeneous of structure, shows the almost 1.0. The fly ash could be used as a general material if the fraction is 15% and the period of the moist-curing is 7days.