Analysis on the cooling effect of a heat-reflective coating for asphalt pavement

Abstract

A type of self-made heat-reflective coating was applied on the surface of different types of asphalt concrete. The temperature of the asphalt mixture specimens with coatings that have different application rates was measured. By calculating the temperature difference between the specimen with and without the coating, the results show that the cooling value first increases and then becomes flat as the application rate of the coating increases. With the same coating application rate, dense-graded asphalt mixture has the best cooling effect, followed by the stone matrix asphalt (SMA) mixture, and finally, the open-graded friction course (OGFC) asphalt mixture has the lowest cooling effect of the tested specimens. The reason is that the OGFC asphalt mixture has a high per cent of air voids and part of the coating will penetrate into the air voids, so less coating is available to reduce the temperature. The SMA mixture has a higher texture depth than the dense-graded asphalt mixture, which compromises the cooling effect of the coating. The cooling mechanism was analysed through microscopic analysis methods, and the reflective spectrum was measured by ultraviolet–visible–near-infrared spectrometer. Results show that the coating has a high reflectivity due to the addition of fillers, which reduces the heat absorption of pavement. The Infrared spectra of the coating and fillers in the middle infrared region were tested by the Fourier transform infrared spectrometer. It indicates that the fillers have good thermal radiation ability in the atmospheric window. Accordingly, the coating presents a good cooling ability in this region, which can further reduce the temperature of the pavement. Pictures from the scanning electron microscope prove that there are many fillers scattered on the surface of the coating, which can bring about a good cooling effect.