Carbonation process involves the reduction of surface pH of concrete and is the prerequisite to microbial corrosion to occur. The highest carbonation rate was found in specimens exposed to 0.5% CO2 gas, followed by 5% and control (0.03%) specimens. The carbonation rates for 5%, 0.5%, and control were 7.1, 16.4, and 4.3mm/year, respectively. Microbial corrosion experiment showed that 0.5% specimens had the highest corrosion rates and percentage mass loss of 3.8mm/year and 13.9 percent/year,

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... ctively. It can be concluded that carbonation stimulated microbial corrosion process. However, under quite high CO2 gas concentration (5%), corrosion process was reduced due to formation of much calcite in the carbonated zone. Growth of T. thiooxidans was stimulated on the reduced pH of carbonated surface.