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 (TiO₂) is used as a photocatalyst to remove NOx through a chemical reaction. Typically, concrete and TiO₂ are mixed to create TiO₂ concrete. However, air pollutants or UV rays cannot be allowed to come into contact with a significant amount of TiO₂. Thus, the TiO₂ surface penetration method was used to fix TiO₂ to the surface of the concrete. In this method, surface penetrants and TiO₂ are combined and sprayed onto the concrete surface, enabling the possibility of NOx reduction using relatively less TiO₂. When the fixation method is applied to vertical concrete structures, however, a peeling issue arises. To address this, a pressurized TiO₂ fixation method was applied to vertical concrete structures. This method uses external force to penetrate and fix TiO₂ to a specific depth. In the instance of the pressurized TiO₂ 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 TiO₂ distribution characteristics, the penetration depth and mass ratio of TiO₂ particles in TiO₂ 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 TiO₂ mass ratio. When the TiO₂ fixation method was used, the NOX removal efficiency was 32% when the TiO₂ mass ratio at the surface was 50%, and the efficiency was 61% when the TiO₂ mass ratio was 70%. This is attributed to the increase in NOx removal efficiency as TiO₂ content at the concrete surface increases. This study analyzed and forecasted the NOx removal efficiency of TiO₂ concrete based on the mass ratio of TiO₂ on the surface. As the TiO₂ mass ratio increased, the NOx removal efficiency improved, and it was determined that the surface TiO₂ 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 TiO₂ concrete.

Recently, air pollution is increasing sharply in Korea, caused by fine particulate matter. Nitrogen oxides (NOx) are particulate matter precursors that significantly contribute to air pollution. They are transmitted into the atmosphere by a large amount, especially in high-volume traffic areas. This pollutant is particularly harmful. Therefore, there are increasing efforts focused on NOx removal from the air. As the photocatalytic reaction of titanium dioxide (TiO₂) is the mechanism that eliminates NOx, the ultraviolet (UV) rays in sunlight and TiO₂ in existing concrete structure need to be contacted for reaction process. Generally, TiO₂ concrete is produced by mixing the concrete binder with TiO₂. However, a significant amount of TiO₂ in the concrete cannot be exposed to air pollutants or UV. Additionally, this technique may not be applicable to existing structures. Therefore, an alternative method that utilizes surface penetration agents is used to add TiO₂ to the concrete surface of the structures. This proposed method may not only be economical but also applicable to various types of structures. The applicability of the TiO₂ penetration application method to existing concrete road structures for reducing NOx is the purpose of this study. The penetration depth of TiO₂ particles was measured using scanning electron microscopy (SEM) combined with energy dispersive analysis of X-rays (EDAX). Additionally, the NOx removal efficiency was evaluated using the NOx analyzing system. The results of this study showed that the TiO₂ penetration method was advantageous in removing NOx effectively and securing economic feasibility.

Concrete pavement growth can cause blow-ups and other pressure-related issues, such as concrete buckling and crushing at the transverse cracks or joints. In addition, these issues result in damaged to adjoining structures, such as bridge abutments, decks, and access structures in the pavement. However, available theoretical solutions and methods for evaluating pavement growth and predictions of concrete pavement blow-up are considerably limited. In this study, therefore, the pavement growth and blow-up analysis model was developed to predict the blow-up potential due to concrete pavement growth. This model considered factors such as the pavement structure and materials, climatic conditions, configuration of expansion joint, base friction characteristics, geometric imperfection, rotational stiffness of joints, and design reliability. In addition, the pavement growth and blow-up analysis model can be used to predict the service life of expansion joints and the blow-up occurrence time by considering the factors affecting it. Using the developed model, various sensitivity analysis was performed to investigate the factors affecting the potential concrete pavement growth and blow-up occurrence. It was found that the factors of substrate type, coefficient of thermal expansion, precipitation, and alkali–silica reaction had a significant effect on pavement growth and blow-up occurrence times.