Evaluation of carbonation resistance of paint coated concrete for buildings

• Carbonation depth of C35 standard cured concrete is 56% smaller than that of C25.
• Accelerate curing increases carbonation depth of C25 concrete by 61%.
• Paint coating can reduce 28-day carbonation depth of concrete by 46% at least.
• Carbonation suppression ratio varies with exposure time and quality of substrate.
• Exterior paint coating has a longer blockage time and a smaller carbonation rate.

When evaluating the carbonation resistance of paint coated concrete, the effects of both the strength grade and the curing conditions (standard curing and accelerated curing) of concrete substrate on carbonation resistance of paint coated concrete were investigated. The concept of the carbonation suppression ratio of paint was presented for evaluation of the anti-carbonation performance of the two types of paints (exterior and interior paints) when applied to a reference concrete substrate. The test results showed a good linear relationship between the carbonation depths of the paint coated concrete and the square root of exposure times. Concrete with higher strength grade exhibited greater carbonation resistance. The carbonation depth of the C35 standard cured concrete was reduced by 56% in comparison with that of the C25 standard cured concrete. It was found that concrete substrate prepared by accelerated curing method displayed lower carbonation resistance than standard cured concrete. Compared with the standard cured specimen, the carbonation depth of the accelerated cured specimen increased by 61% for the control C25 concrete and by 56% for the control C35 concrete. This phenomenon was attributed to the formation of a higher volume of capillary pores in concrete prepared by accelerated curing. Additionally, the exterior paint had a higher carbonation suppression ratio than the interior paint. The suppression ratios of the exterior and interior paint coatings applied on C25 standard cured concrete were 71% and 56%, respectively. The exterior paint coated concrete had a better carbonation resistance with longer effective blockage time and smaller carbonation rate.