February 23, 2012
ONTARIO MINISTRY OF TRANSPORTATION
FEATURE | Roadbuilding
Ontario transportation ministry tests photocatalytic concrete designed to mitigate smog
Photocatalytic concrete — a material laced with nano-sized particles of titanium dioxide — has been valued over the past decade for two of its demonstrated properties. The material is self-cleaning and “eats” smog particles by converting them to less harmful chemicals under the effect of direct sunlight. A recent trial application by the Ontario Ministry of Transportation (MTO) is designed to see just how effectively the material might perform alongside roads in the province’s climate.
MTO partnered on the project with the Ontario Ministry of Environment, the University of Toronto, Essroc Italcementi Group (the North American division of an international supplier of photocatalytic Portland cement), and noise barrier specialist Armtec Durisol of Hamilton. The trial location: a section of noise barrier installed in the summer of 2011 on Highway 401, east of the Highway 404 interchange in Toronto.
“We chose the location for several reasons,” says Shawn Smith, project engineer, highway engineering, with MTO’s highway standards branch. “There’s a high volume of traffic at the interchange, pollution levels are high, and there’s a safe area behind one of the barriers where we can park and locate our test equipment. The area gets most of its direct sunlight during the summer months, but that’s when pollution is also at its worst.”
While the technology requires only a thin coating of photocatalytic concrete to work effectively, the coating process is most economical when applied in large-scale projects. In this case, it proved less costly for Armtec Durisol to cast 54 test panels entirely of the material.
When activated by the sun’s ultraviolet rays, the titanium dioxide acts as a catalyst to speed up the oxidation of such pollutants as nitrogen oxides, carbon monoxide, sulfur dioxide and particulate matter, converting them to less harmful materials. As a catalyst, the titanium dioxide is never exhausted, changing the nature of the contaminants without changing itself.
“The surface cleaning capabilities of the material are a bonus,” says Smith. “The concrete is self-cleaning, depending on conditions. It doesn’t do big stuff like graffiti or gum, but it will remove many of the compounds that form on it, relying to some degree on the rain to wash them away. A lot of buildings in Europe use the product to keep buildings looking white.”
The Missouri Department of Transportation was the first North American jurisdiction to use the material on a roadway. Previous European demonstration projects have shown an improvement in air pollution ranging between 20 and 70 per cent in the vicinity of the material, depending on the level of sunlight that activates the process.
“European research shows that photocatalytic concrete placed in an area the size of a soccer field can remove emissions equal to approximately 190,000 car-kilometres per year,” says Smith.
One square metre of photocatalytic concrete can likewise remove up to 60 mg of nitrogen dioxide in 12 hours, with the best results demonstrated in urban areas closest to the source of pollution. The photocatalytic effect is strongest in confined areas with high light intensity at temperatures above 10 C, and at a relative humidity of less than 65 per cent, with wind blowing perpendicular to the concrete’s surface.
MTO plans to extensively evaluate the self-cleaning and smog-eating capabilities of the photocatalytic sound barrier this summer, including careful air quality monitoring at the test site and at a nearby control site. Those results will be compared against test benchmarks achieved in other countries.
“If we do get good results, there’s the potential for more widespread application of this green technology,” says Smith.
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