The mechanism of the effect of mortar coating on carbonation of concrete is investigated. Theoretical methods of Fick's first and second laws of linear diffusion are used to calculate the carbonation depth of concrete without and with mortar coating, respectively. Theoretical analyses are also done to obtain the carbonation retard coefficients of mortar coating on concrete with surface coatings. A great deal of well organized experimental tests are carried out to verify the values of calculation. The results of present study indicate that the suitable mortar coating on concrete can effectively delay carbonation of concrete. The carbonation depth is inversely proportional to the thickness of surface coating with mortar. The average values, measured from experiment and predicted from Fick's first and second laws of linear diffusion, of carbonation retard coefficient of mortar coating are 1.70 and 2.19, respectively.

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