Study on air-purifying performance of asphalt mixture specimens coated with titanium dioxide using different methods

Titanium dioxide (TiO₂) has been employed to degrade hazardous materials since its photocatalytic ability was discovered. In recent years, attempts have been made to apply TiO₂ onto road surfaces to degrade the harmful compounds (such as NO and NO₂) from vehicle emissions. As a photocatalyst, the NO_X degradation efficiency of TiO₂ largely depends on its surface area exposed to sunlight. However, the effective coating methods to enlarge the contact area between the coated TiO₂ and sunlight have not been well studied, especially for asphalt pavements. To fill this gap, this study aims to investigate the photocatalytic performance of three TiO₂ coating methods for asphalt pavements, including the conventional water-solution-based TiO₂ (WT) coating, and the innovative glass-bead-based TiO₂ (GT) coating and porous TiO₂ (PT) coating. A custom-designed environmental test setup was used to determine the NO_X degradation efficiency of the specimens with TiO₂ coating, and the durabilities of the coating materials were characterized by measuring their NOx degradation efficiency subjected to different numbers of lab-simulated tire abrasion. It was found that the PT and GT methods provided not only better NO degradation efficiency but also improved durability compared to the conventional WT method.