A review on effects of curing, sheltering, and CO2 concentration upon natural carbonation of concrete

In the literature, the effects of curing, sheltering and CO2 concentration under natural carbonation are not fully understood. There is either controversy or limited research available regarding these factors, while most investigations are based on accelerated carbonation. The currently available research on natural carbonation is particularly constrained and limited. From a practical viewpoint, natural carbonation is more important as it represents the behavior of real structures. This paper reviews the influences of different curing methods and their durations; sheltered and unsheltered exposure conditions, and different atmospheric CO2 concentration levels, on carbonation of concrete under the natural outdoor exposure environment. The various curing methods examined are moist-curing, steam-, air- and oven-curing. It is found that curing effects are coupled with the type of cement. For cements containing no more than 30% fly ash or 50% slag, three-day curing is sufficient to stabilize long-term strength and carbonation behavior of concrete under site conditions. Different types of normal curing do not significantly alter natural carbonation behavior. An equation is suggested which accounts for the effect of unsheltered outdoor exposure on carbonation. Also, correction factors are proposed to account for different atmospheric CO2 levels under natural carbonation. (C) 2016 Elsevier Ltd. All rights reserved.