Pervious concrete with titanium dioxide as a photocatalyst compound for a greener urban road environment

Maria Christina Burton

The United States is facing the problem of controlling air pollution from vehicle emissions, especially in growing urban areas. The photocatalyst, titanium dioxide (TiO2), activates with ultraviolet (UV) radiation to oxidize air pollutants, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). Applying the photocatalytic effect of TiO2 onto pervious concrete pavement to remove pollutants from the air appeared to be a promising alternative to remove pollutants from street level. This study compared different methods to apply TiO2 onto the surface of pervious concrete and measured the effectiveness of the surface coating materials in removing air pollutants, maintaining infiltration properties, and withstanding environmental weathering. A brief analysis on the material cost of each application method is also presented. High pollutant reductions were seen with a driveway protector mix, a commercial water based TiO2 preparation, TiO2 in water, a cement-water slurry with low cement concentration, and the commercial PURETI coating. It was found that nitric oxide (NO) was efficiently removed with each of these treatments, while VOCs displayed more variability in removal efficiency. When pervious concrete was compared to traditional concrete, pervious concrete showed higher NO reductions. Most coating methods maintained an acceptable level of infiltration rate for pervious concrete pavements. The driveway protector mix had the highest resistance against freeze-thaw testing with deicing chemical and environmental weathering. The evaluated coating methods are recommended for different applications. The driveway protector mix resists environmental weathering well and can be used for highway shoulders and locations where weathering could be a concern. The transparent color of the commercial water-based TiO2 could be used for aesthetic reasons. The cement aggregate mixes could be used as a thin pervious concrete overlay to at the same time address minor pavement surface distress. The PURETI treatment is a cost-effective alternative, where the surface abrasion is low. More studies need to be done to optimize each application method and confirm their resistance against live traffic and environmental damage. Fundamental research should also be conducted to investigate the sequential chemical reactions during the complex photocatalytic process to substantiate the environmental benefits of the photocatalytic materials in the field.

Pervious concrete with titanium dioxide as a photocatalyst compound for a greener urban road environment

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