Time dependence of carbonation resistance of concrete with organic film coatings

• Organic film coatings can remarkably improve concrete carbonation resistance.
• Organic film coatings’ carbonation resistance will decrease with aging.
• Coating’s carbonation resistance exhibits an S-shaped curve with aging time.
• S-shaped curve models can be used to predict organic coatings’ service lives.

Concrete specimens with three types of organic film coatings, namely, polyurethane (PO), epoxy resin (EP), and chlorinated rubber (CR), were fabricated to study the time-dependent relationship between the aging of organic film coating and the corresponding degradation of concrete carbonation resistance. Then, three coating aging methods were adopted: artificial ultraviolet radiation, coupled ultraviolet radiation and moisture, and natural outdoor climate exposure. After different aging stages, the specimens were subjected to accelerated carbonation experiments, and partial specimens were examined by scanning electron microscopy. Results indicated that organic film coatings can significantly improve concrete carbonation resistance, and a thicker film coating can obtain better improvement. According to the parameter α for the improvement of concrete carbonation resistance per unit thickness, the ranking order of the three types of coatings is as follows: PO > CR > EP. Defects in organic coatings caused by aging, such as granulation, porosity, and cracking, are the causes of degradation of coating carbonation resistance. As an organic film coating ages, its carbonation resistance gradually decreases and exhibits an S-shaped curve. On this basis, regression models for the carbonation depth with aging time of the coated specimens were established. These models were used to predict the service lives of the coatings. The ranking order of the service lives of the coatings is PO > EP > CR. Increasing the thickness of a coating can enhance its service life.