The carbonation processes of concrete modelled by the diffusion of CO₂ gas inwards into concrete from the surface under various conditions are analyzed theoretically based upon unsteady state dynamics, taking account of the chemical reaction of CO₂ with Ca(OH)₂ which is assumed to diffuse slowly backwards from the inner layer of concrete. Analytical solutions were obtained by Laplace transformation method which involve error functions concerning time and depth from the surface. For the progress of carbonation (neutralization) of concrete,the parabolic law concerning time involving constant term was derived.Making use of this law, the influence of various extrinsic and intrinsic factors(concentration of CO₂ gas, temperature, water content, and surface mass transfer resistance) on the progress of carbonation has been evaluated by inserting numerical values into such material property constants as diffusion constants.Theoretical results are compared with some field research results. This parabolic law involving constant term well explains the influence of various factors on the progress of carbonation.

Key_Words : Concrete, Carbonation, Neutralization, Prediction, Unsteady State Dynamics, Theoretical Model, Parabolic law

* This paper was revised and reproduced from the manuscript prepared for the Fourth International Conference on Durability of Building Materials and Components, held in Singapore, on November 4-6, 1987.
^*1 Head of Inorganic Materials Division of Materials department, Dr. Eng.