Enhancing the carbonation and chloride resistance of concrete by nano-modified eco-friendly water-based organic coatings

To effectively improve the carbonation and chloride resistance of concrete with eco-friendly waterborne organic coatings, two nanomaterials (i.e., nano-SiO2 and nano-TiO2) were utilized to modify the water-based polyurethane and epoxy resin paints at dosages of 1 wt%, 2 wt%, and 3 wt%, and the coated concrete specimens were fabricated. Then, accelerated aging experiments of ultraviolet irradiation were conducted on the coated concrete specimens, followed by accelerated carbonation or Coulomb electric flux experiments. In addition, partial coating film samples were analyzed by scanning electron microscopy and Fourier transform infrared spectroscopy. Results show that the application of water-based organic coatings can substantially improve the carbonation and chloride resistance of concrete. The two-component water-based epoxy resin coating exhibited a higher quality than the one-component water-based polyurethane coating, thus resulting in better improvement of the carbonation and chloride resistance of concrete. However, the anti-aging capability of water-based epoxy resin coating is lower than that of water-based polyurethane coating, resulting in the rapid decline of the carbonation or chloride resistance of coated concrete after ultraviolet aging. The addition of nano-SiO2 or nano-TiO2 to the water-based organic coating can reduce the defects in the coating, effectively improve the density of the coating, and further improve the carbonation and chloride resistance of the coated concrete, with average improvement ranges of 51-74 % and 24-27 %, respectively. Meanwhile, the addition of nano-SiO2 or nano-TiO2 can help reduce the damage of water-based coatings caused by ultraviolet irradiation, thereby improving the long-term carbonation and chloride resistance of coated concrete, among which the improvement effect of nano-TiO2 is higher than that of nano-SiO2.