Study on the effect of M/P ratio of magnesium phosphate cement coatings on reducing urban heat absorption

Abstract

Using reflective coatings to enhance the reflective ability of urban underlying surface can effectively reduce building energy consumption and alleviate urban heat island effect. Magnesium phosphate cement (MPC), which consists of high near-infrared reflectivity magnesium oxide (MgO) and phosphate as the main raw materials, is a potential reflective coating. This paper studied the reflection characteristics and mechanisms of MPC with different mass ratios of MgO to phosphate (M/P). The reflectivity test results indicated that the reflectivity of MPC increased with the increase of M/P ratio, with a near-infrared reflectance of 71.74% at an M/P of 10. This was mainly related to its surface chromaticity and micromorphology. In the matter of color characteristic, it was found that the increase of M/P ratio improved the brightness and weakened the performance of other colors, which was conducive to improving the reflective effect. In the matter of micromorphology, scanning electron microscopy and energy dispersive spectrometer (SEM-EDS) analysis confirmed that there were more unreacted MgO particles and less hydration products on the MPC surface with high M/P ratio, which resulted in higher reflectivity and lower bonding strength. Finally, indoor irradiation experiments were conducted to verify the heat reduction effect of MPC coating on asphalt pavement. The results indicated that the surface temperature of the specimen coated with MPC decreased by 15.3 ℃ compared to the control specimen. Therefore, it could be concluded that MPC is a promising reflective coating that can be used to reduce urban heat absorption.