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

Abstract

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 (TiO₂), a photocatalytic reaction material, is particularly effective in the removal of NOx. As the solar photocatalytic reaction of TiO₂ is the mechanism that eliminates NOx, the TiO₂ in concrete road structures needs to be exposed to the ultraviolet rays (UV) of sunlight to be activated. Generally, TiO₂ concrete is produced by replacing a portion of the concrete binder with TiO₂. However, a considerable amount of the TiO₂ 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 TiO₂ to the surface of the concrete structure. This study aims to evaluate the in-situ NOx removal efficiency of the TiO₂ penetration method in a field application. Accordingly, the TiO₂ 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 TiO₂ penetration method can be an alternative to the existing TiO₂ concrete, which produced by replacing a portion of the concrete binder with TiO₂, for removing NOx gas from the air.