Designing components that breathe
Photocatalytic pavement speeds up nature’s process of breaking down pollution
By Michael Hughes
Industrial engineers know that better tools and better components help make for better systems.
In a world of increasing environmental awareness, facility planners and construction teams have to be cognizant of outdoor and indoor air quality. Those who design infrastructure must be wary about how the network of highways and bridges increase ambient air pollution that affects climate change.
Marwa Hassan, an assistant professor of construction management and industrial engineering at Louisiana State University, is working to give those system designers a hand. She is testing asphalt and concrete photocatalytic pavement on two sites in Louisiana. The nanotitanium dioxide in the pavement accelerates the decomposition of pollutants – volatile organic compounds (VOCs), sulfur oxides and dioxide and nitrogen oxides and dioxide – into their base elements.
Elsewhere, materials integrated into wood beams could work on indoor air pollution. Applied post-construction, such a coating would consist of one coat of paint that would last 10 years, Hassan said. She points to the federal government’s disastrous purchase of formaldehyde-contaminated trailers to house Hurricane Katrina victims in 2005. By 2008, the Federal Emergency Management Agency, which spent $2.7 billion on the 145,000 units, ordered them abandoned, according to The Washington Post.
The wood used in the homes was imported from China and glued with a material that produces formaldehyde, which can cause cancer, Hassan said. The Washington Post reported that formaldehyde
levels in the trailers were five times greater than the average in modern homes.
But the coating needed ultraviolet radiation from the sun to activate the process that oxidized formaldehyde into carbon dioxide. Because of skin cancer, Hassan said, people don’t want rows of ultraviolet lamps in their homes. Now, Hassan is researching a different material that works under normal, indoor light.
“You can get rid of sick building syndrome,” she said.
Hassan credits professor Yvan Beliveau, her advisor at Virginia Tech, with sparking her interest in sustainability. He told his students that the old cliché of thinking outside the box was one way of looking at problems differently. But he challenged them to create buildings and structures that could be part of nature.
“‘Can we create buildings that breathe,’ and I’m actually quoting what he used to say,” Hassan recalled. “Innovative or visionary or crazy as that might sound, it was quite inspiring.”
Since then, she has worked to enhance sustainability by integrating advanced materials into different processes or practices. Photocatalytic pavement falls under that umbrella. All volatile organic compounds, including oil spills, eventually decompose into carbon dioxide, Hassan said.
“For us to be able to compare apples to apples in … layman’s terms, you have to convert everything you are producing into one reference substance,” Hassan said. “That one reference substance for greenhouse gases is carbon dioxide. That’s why you hear about it all the time, although it is not the most dangerous greenhouse gas.”
In fact, hydrocarbons and other pollutants are much more severe in terms of their effects on global warming. According to Slate.com, nitrous oxide, one form of nitrogen oxide, has a global warming potential (GWP) of 310 compared to carbon dioxide’s one. The hydrocarbon methane has a GWP of 21.
“I’m not saying that all roads in the U.S. should be photocatalytic,” she said. “We only have to target the urban areas, high pollution, high population. And if you do that right you’ll see a drastic drop in national [pollution] levels.” In the U.S., large cities like Atlanta, Los Angeles, New York and even parts of Louisiana have been out of compliance with Environmental Protection Agency pollution levels for years, she noted. And the mandates are going to get stricter. Hassan has started quantifying the level of photocatalytic
pavement needed to improve ambient air quality.
“But we’re not finished yet because it requires quite a bit of urban planning,” she said. “We have to look at all the places that are not compliant from an EPA perspective, and we have to look at their major interstates, and then we have to look at the amount of traffic that is on their major interstates.”
She also is developing a design method that uses equations to quantify the reduction in different pollutants. Then the practitioners, engineers and designers can use the equations in the design and cost-analysis phase. New photocatalytic pavement adds $1.95 to the current cost of $50 per square yard of pavement. Spraying the 1-micron thick substance onto existing pavement costs $2 per square yard.
The photocatalytic process initially came with two concerns: the possibility of increasing eutrophication and the exposure of construction workers to nanomaterials.
In eutrophication, algae growth sucks oxygen from lakes and oceans, leaving fish-killing dead zones. But Hassan’s team has quantified the amount of nitrates produced by the decomposition process. The minimal increases will not enhance man-made eutrophication, she said.
The team has been checking the size, diameter and morphology of the nanoparticles being spread on the road and how much of it would be in the breathing zone of the construction workers. Those results will be published later.
“We try to look at it for all aspects, safety, environment performance, economics as well as durability,” she said.
Still, any change in technology encounters resistance. Japan and Europe, especially London, France and Italy, are farther ahead in implementation, with the European Union sponsoring a 400 million euro project. Field studies are under way in Kansas City, Mo., and a green initiative in Chicago includes photocatalytic pavement.
Hassan has been working with different Department of Transportation research facilities. As the Federal Highway Administration is funding a $10 million sustainability effort, these projects will raise the possibility of using photocatalytic pavement and other improvements related to infrastructure sustainability.
“And I’m seeing interest and slow adoption,” Hassan said. “If we get the political drive, and then the DOT started investing in it more, it would happen.”
Michael Hughes is managing editor of the Institute of Industrial Engineers.