Evaluation of In-Situ NOx Removal Efficiency of Photocatalytic Concrete in Expressways

In areas of high-volume traffic, such as the proximities of expressways in large urban areas, the amounts of nitrogen oxides (NOx) emitted into the atmosphere significantly contribute to air pollution. As NOx gas is a major cause of smog and acid rain, this pollutant is considered to be particularly harmful, and therefore, increasing attention has been focused worldwide on the elimination of NOx from the air. Titanium dioxide (TiO 2 ), a photocatalytic reaction material, is particularly effective in the removal of NOx. As the solar photocatalytic reaction of TiO 2 is the mechanism that eliminates NOx, the TiO 2 in concrete road structures needs to be exposed to the ultraviolet rays (UV) of sunlight to be activated. Generally, TiO 2 concrete is produced by replacing a portion of the concrete binder with TiO 2 . However, a considerable amount of the TiO 2 in the concrete is not exposed to either the air pollutants or the UV. Therefore, as an alternative method, surface penetration agents are used to add TiO 2 to the surface of the concrete structure. This study aims to evaluate the in-situ NOx removal efficiency of the TiO 2 penetration method in a field application. Accordingly, the TiO 2 penetration method was tested on the retaining wall of the Gyeongbu expressway in Korea. The results of this study indicated that the quantity of sunlight influenced the NOx removal efficiency rate. Furthermore, it was c that the TiO 2 penetration method can be an alternative to the existing TiO 2 concrete, which produced by replacing a portion of the concrete binder with TiO 2 , for removing NOx gas from the air.