Estimation of Nitrogen Oxides (NOx) Removal Efficiency for TiO 2 Concrete

Nitrogen oxide (NOx) is a significant precursor of particulate matter (PM), particularly in high-traffic areas. Accordingly, this study aimed to reduce the presence of nitrogen oxide (NOx) along roadsides. Titanium dioxide (TiO 2 ) is used as a photocatalyst to remove NOx through a chemical reaction. Typically, concrete and TiO 2 are mixed to create TiO 2 concrete. However, air pollutants or UV rays cannot be allowed to come into contact with a significant amount of TiO 2 . Thus, the TiO 2 surface penetration method was used to fix TiO 2 to the surface of the concrete. In this method, surface penetrants and TiO 2 are combined and sprayed onto the concrete surface, enabling the possibility of NOx reduction using relatively less TiO 2 . When the fixation method is applied to vertical concrete structures, however, a peeling issue arises. To address this, a pressurized TiO 2 fixation method was applied to vertical concrete structures. This method uses external force to penetrate and fix TiO 2 to a specific depth. In the instance of the pressurized TiO 2 fixation method, which was tried for the first time, penetration depth was used to ensure long-term durability as well as NOx removal efficiency. To investigate TiO 2 distribution characteristics, the penetration depth and mass ratio of TiO 2 particles in TiO 2 concrete were measured using a scanning electron microscope (SEM/EDX). In addition, NOx removal efficiencies were evaluated using the NOx analyzing system (ISO 22197-1 standard). The experimental results showed that NOx removal efficiency increased with an increasing TiO 2 mass ratio. When the TiO 2 fixation method was used, the NOX removal efficiency was 32% when the TiO 2 mass ratio at the surface was 50%, and the efficiency was 61% when the TiO 2 mass ratio was 70%. This is attributed to the increase in NOx removal efficiency as TiO 2 content at the concrete surface increases. This study analyzed and forecasted the NOx removal efficiency of TiO 2 concrete based on the mass ratio of TiO 2 on the surface. As the TiO 2 mass ratio increased, the NOx removal efficiency improved, and it was determined that the surface TiO 2 mass ratio significantly influences the NOx removal efficiency. Consequently, this study developed an equation to estimate NOx removal efficiency, making it possible to determine a suitable maintenance interval for TiO 2 concrete.