PURPOSES : Nitrogen oxides (NOx) are the main precursors to generate fine particulate matter, which significantly contribute to air pollution. NOx gases are transmitted into the atmosphere in large quantities, especially in areas with a high volume of traffic. Titanium dioxide (TiO2), which is a photocatalytic reaction material, is very efficient for removing NOx. The application of TiO2 to concrete road structures is a good alternative to remove NOx. Generally, TiO2 concrete is produced by mixing concrete with TiO2 . However, a significant amount of TiO2 in concrete cannot be exposed to air pollutants or UV. Therefore, an alternative method of penetrating TiO2 into horizontal concrete structures using a surface penetration agent was proposed in a previous study. This method may not only be economical but also applicable to various types of horizontal concrete structures. However, the TiO2 penetration method may not be applied to vertical structures because it has a mechanism for the penetration of TiO2-containing penetration agents via gravity and capillary forces. Therefore, this study aimed to evaluate the applicability of the pressurized TiO2 fixation method for existing vertical road structures.
METHODS : For the application of vertical concrete structures — such as retaining walls, side ditches, and barriers — the applicability of a static and dynamic pressurized TiO2 fixation method was evaluated according to the experimental conditions, considering the amount of pressure and time. The penetration depth and distribution of TiO2 particles in the concrete specimen were measured using SEM/EDAX. In addition, the NOx removal efficiencies of TiO2 concrete were evaluated using the NOx analysis system.
RESULTS : As a result of measuring the penetration depth and distribution of TiO2 in the concrete, it was found that the surface-predicted mass ratio increased with increasing pressure and time. In the case of the static pressurized fixation method, it was confirmed that a pressure time of at least 10 s at a pressure of 0.2 MPa and 5 s at a pressure higher than 0.3 MPa were required to achieve a NOx removal efficiency higher than 40 %. Conversely, for the dynamic pressurized fixation method applying a hitting energy of 16.95 J, NOx removal efficiencies higher than 50 % were secured in a pressure time of more than 3 s.
CONCLUSIONS : The results of this study showed that the static and dynamic pressurized TiO2 fixation method was advantageous in penetrating and distributing TiO2 particles into the concrete surface to effectively remove NOx. It was confirmed that the proposed method to remove NOx was sufficiently applicable to existing vertical concrete road structures.

ABSTRACT
1. 서론
2. 이론고찰
    2.1. 질소산화물(NOx)과 TiO2 정의 및 특성
    2.2. 국내·외 TiO2 콘크리트 적용 기술 및 한계
3. 수직 콘크리트 구조물에 TiO2 고정화를 위한가압식 실험
    3.1. 가압 침투식 TiO2 고정화 기술 전략
    3.2. 시편 제작
    3.3. 실험 방법
4. 소재의 침투 분포 및 질소산화물(NOx) 제거효율 평가
    4.1. 정적 가압 침투식 TiO2 고정화 기술 적용결과
    4.2. 동적 가압 침투식 TiO2 고정화 기술 적용결과
    4.3. 가압 침투식 TiO2 고정화 기술 적용 가능성 검토
5. 결론
REFERENCES

• 안희락(강릉원주대학교 토목공학과) | Ahn Hui Rak
• 이승우(강릉원주대학교 토목공학과) | Lee Seung Woo
• 김영규(강릉원주대학교 토목공학과) | Kim Young Kyu 교신저자