Impact of marine atmospheric corrosion on the thermophysical properties of building coatings

Coastal structures are subjected to substantial thermal and solar loads, as well as relentless erosion from salt sprays originating from the ocean. This erosion poses a significant threat to the integrity of the surface coatings. However, the examination of the impact of salt spray on coatings from a heat-transfer perspective is limited. The objective of this study is to quantitatively evaluate the influence of ocean salt spray on the thermal properties of building coatings by investigating the modifications in surface thermal properties and heat transfer performance. Specifically, water-based polyurethane coatings, water-based acrylic coatings, and solvent-based coatings was subjected to corrosion through indoor accelerated aging tests and wind tunnel experiments. After a 30-day expose to ultraviolet ageing and salt spray corrosion, noticeable discoloration, and a substantial reduction in surface glossiness of up to 84 % are observed in the coating samples. The change in reflectance ratio before and after corrosion was measured using a spectrophotometer, indicating a maximum reduction of 9.4 %. To analyse the variations in the dynamic heat transfer performance of the samples before and after corrosion, this study employed the heat balance equation and conducted dynamic wind tunnel tests. The corrosion process appears to increase heat transfer along the coating's surface, evident from the consistent elevation in heat transfer capacity coefficients (CHTC) of the specimens after corrosion. Notably, these increases, particularly pronounced during nighttime, reveal substantial and consistent gaps in coefficients, reaching values of up to 10 W/m2 (WP1), 12.5 W/m2 (WA1), and 10 W/m2 (S2), respectively.