Theoretically identified strong coupling of carbonation rate and thermodynamic moisture states in micropores of concrete

T. Ishida, K. Maekawa and M.Soltani Journal of Advanced Concrete Technology, 2(2) 213-222, 2004 In order to predict the chemo-physical process of carbonation, a finite element based computational method is implemented based upon multi-phase/scale governing equations of moisture and flux of both heat and carbon dioxide. Influencing parameters of carbonation involving reaction rate, CO2 diffusivity and the reduction of porosity are discussed. It is found that such modeling can accurately show high nonlinearity among carbonation reaction, pore structure development and moisture distribution in micropore structures. By using the proposed assumptions, the reliability of the predictive method of the carbonation mechanism in cementitious materials under arbitrary environmental and curing conditions is examined by comparing available experimental results with theoretical ones. Through sensitivity analyses that focus on the nonlinearity of the moisture profile and local carbonation, it is clarified that different moisture distribution may bring the opposite trend of the carbonation depth under low and high CO2 concentrations.

Carbonation is the subject of many papers but usually the physico-chemical background is not treated in depth. This contribution fills this obvious gap. The understanding of this important process in concrete is placed on a solid basis. This is an excellent paper for reference. (Prof. F. H. Wittmann, Aedificatio Institute Freiburg) This paper describes an impressive attempt to model the effects of natural and accelerated carbonation under varied conditions. The assumptions are clearly stated and, although some of these are accepted to be provisional, the work provides convincing evidence of the need for caution, for example, when applying accelerated carbonation tests to compare the performance of materials made from different types of cementitious binder (Prof. C. L. Page, University of Leeds)