Interest Increases in 'Smog-Eating' Pavements
A road in Cary, N.C., is one of several sites testing titanium dioxide.
PHOTO COURTESY OF PTI
Airports, highways and civic structures are serving as testbeds for a patented technology that uses titanium dioxide to capture pollutants, particularly nitrogen oxides, in pavements—creating “smog-eating roads.” The concept of photocatalysis with titanium dioxide is receiving increasing attention for its photoreactive effectiveness in degrading greenhouse gases.
At Orlando International Airport last year, a Texas A&M Transportation Institute (TTI) report found that taxiway pavements sprayed with two titanium dioxide products provided by Pavement Technology Inc. (PTI) reduced nitrogen oxide rates by approximately half.
“I had read some articles about titanium dioxide in concrete in Europe,” recalls Sandeep Singh, president of Avcon Inc., an Orlando-based aviation planning and engineering firm. Avcon convinced the Orlando airport to try PTI’s applications on two 500-sq-ft sections of pavement. “We were worried about unintended impacts like reducing friction on a runway, or [the products being] absorbed and having no impact.”
But tests on both asphalt and concrete did not reveal negative impacts, he notes. “One thing we found, which was interesting, many pavements in Florida build up algae during wet season. It leaves a black shadow. The unintended effect here was the algae disappeared a couple days after application,” Singh says.
Pavement Technology Inc., one of many providers of asphalt rejuvenators, in 2017 branched out to use titanium dioxide to focus on reducing pollution and heat island effects.
The material, when light-energy activated, creates a chemoelectric energy field atop pavement that captures and converts harmful gases emitted through motor exhaust into harmless compounds easily absorbed by surrounding foliage, according to PTI.
“In good conditions, we can achieve 60% reduction” in those gases, says Michael Durante, PTI vice president of finance and strategic planning. “We’re also testing to see if there can be a meaningful reduction of heat islands.”
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Chris McGee, assistant director of transportation with the city of Raleigh, N.C., pitched the technology to the city last year. If all goes according to plan, the city will test some 425,000 sq ft of pavement, half using PTI’s standard rejuvenation application and the other using the titanium infusion, he says.
The company observed related research done at Louisiana State University several years ago. “LSU was testing titanium dioxide with a water-based solution on streets. It didn’t last very long; it wore off,” Durante said. “We decided to look into [applying titanium dioxide to] the wearing course of roads so that it is more permanent.”
Cores from a Cincinnati client are currently being analyzed at TTI, and other sites include Charlotte and Cary, N.C.; Akron, Ohio; and St. Petersburg, Fla., says Durante. The Ohio Turnpike “would be the first toll road in the world to test photocatalytic technology,” he adds.
