Smog-Battling Concrete Gains Support
Titanium dioxide-laced concrete could help cut down air pollution when incorporated into roads, lab and field tests in the Netherlands have concluded.
Researchers found that nitrogen oxide (NOx) could be reduced by up to 45 percent in perfect conditions with air-purifying concrete stones containing titanium dioxide, a photocatalytic material that removes the NOx from the air and converts it into a harmless nitrate with help from the sun.
While the potential of photocatalytic materials to reduce air pollution has been studied for several years, the newly published research supports titanium dioxide as an effective smog reducer.
A Year of Testing
For the project, researches from Eindhoven University of Technology (TU/e) covered 1,000 square meters (about 10,764 square feet) of a road surface in Hengelo, the Netherlands, were covered with air-purifying concrete paving stones. Another area of the same size was surfaced with normal paving stones for a control group.
"The air-purifying properties of the new paving stones had already been shown in the laboratory, but these results now show that they also work outdoors," said Prof. Jos Brouwers in an earlier press release from TU/e.
Brouwers has been a professor of building materials in the TU/e Department of Architecture, Building and Planning since September 2009.
Researchers carried out three air-purity measurements on the surfaces at heights betwen a half and one-and-a-half meters. The area covered with the air-purifying concrete had a NOx, the reactive gas air pollutant given off by car emissions, content that was 25 to 45 percent lower than the one surfaced with normal concrete.
The outdoor monitoring was done for 26 days, spaced out for over a year in order to monitor performance in different seasons and weather conditions. Measured parameters included traffic intensity, nitric oxide, nitrogen dioxide and ozone concentrations, temperature, relative humidity, wind speed and direction, and the visible and UV light irradiance.
Areas with a lot of air pollution from car emissions could benefit from the concrete, as well as other products developed with photocatalytic materials, industry professionals say.
Before and during the street test, the concrete was also tested for the same measurements in the lab. Researchers found that, on average, the NOx concentration was 19 percent lower of the course of the day and 28 percent lower in the afternoons only compared to the control street. Under ideal weather conditions, which researchers consider high radiation and low relative humidity, a 45 percent decrease in NOx concentration could be observed.
Future of Street Design
Brouwers says he sees potential for numerous applications, particularly in areas where the maximum permitted NOx concentrations have been exceeded. The air-purifying concrete can also be mixed with open asphalt for use on roads that require asphalt and can also be used in self-cleaning and air-purifying building walls.
According to Brouwers, the overall cost of using the concrete on roads is only 10 percent higher, although the stones themselves are 50 percent more expensive than normal concrete stones.
"Preventing air pollution is clearly important to our long-term health and environmental protection, but this latest research shows the potential of chemically engineered surfaces to further improve our quality of life, especially in major urban areas where traffic emissions are high," said David Brown, chief executive of the Institution of Chemical Engineering (IChemE), in a press release.
Brown said that further studies are needed to assess photocatalytic materials. "However, the potential is there and gives a strong indication of how streets may be designed in the future," Brown said.
IChemE is a society for chemical, biochemical and process engineering professionals worldwide.
The research, "Full scale demonstration of air-purifying pavement," authored by M.M. Ballari and Brouwers, was published in June in the Journal of Hazardous Materials.