The Kentucky Ready Mix Concrete Association is renewing an advertising campaign to inform the public about Louisville’s recurring problems with the urban heat island effect.
It might seem an unlikely campaign for a non-profit that promotes concrete. Urban heat islands (UHIs) are areas where urban cores warm at a faster rate than surrounding areas. A study conducted ranked Louisville’s UHI effect as the worst in the nation. The problem is caused mainly by changes humans have made to our environment: building roads, paving parking lots, roofing large buildings with black, heat-trapping materials.
But Brett Ruffing of the Kentucky Ready Mix Concrete Association says concrete isn’t the problem…but rather, a solution. He says asphalt and concrete shouldn’t be lumped together as “pavements.”
“Concrete’s white, it’s cement based, so it has a higher solar reflective index number,” he said. “Whereas asphalt is black. So it’s like you learned in grade school: white reflects, black absorbs.”
Thus, the association’s ad campaign. Ruffing says obviously tearing up paved surfaces and replacing them with trees and vegetation is the best solution to mitigate the urban heat island effect. But if Louisville is going to replace or add any paved surfaces, he says using concrete will help keep the city cool.
The association was lobbying for the use of concrete in the Ohio River Bridges project, but to no avail. Ruffing says concrete isn’t necessarily more expensive; he’s had similar projects cost comparable amounts, and because concrete has a longer lifespan, overall it can cost less over the life of the structure.
But in Louisville, Ruffing says concrete should definitely be a viable option for infrastructure projects, if only because of its heat-reflecting properties.
“People say they’re sustainable, they say they’re green, but they don’t practice what they preach,” he said. “So we’re trying to teach people how in the architecture, engineering, construction industry, you can do all this. It can be done.”
But obviously Ruffing and the Readymix Concrete Association promote concrete, and there’s conflicting information online about the relative benefits in using concrete over asphalt. Predictably, the Asphalt Pavement Alliance is touting the results of a study from Arizona State University on its website, looking at the differences in temperatures in the air above asphalt and pavement.
The findings from ASU’s research were recently presented at the 2013 Transportation Research Board Annual Meeting in Washington, D.C. ASU’s findings are paralleled by a similar study from the University of California at Davis, which concluded that air temperatures 1 foot or more above light-colored and dark-colored pavements were not significantly different. In fact, reflective pavements were shown to heat up adjacent buildings, actually increasing the UHI effect.
But Stuart Gaffin, a research scientist at Columbia University says measuring the heat in the air above paved surfaces is tricky. He was the lead author on a study of New York City rooftops in 2011, which concluded that white roof coverings were on average 43 degrees Fahrenheit cooler than black roofs.
Gaffin says there are two kinds of temperatures: radiometric, or skin, temperature, and air temperatures. They aren’t the same, and the prevailing science on urban heat island mitigation focuses on lowering the surface temperature.
“You try to lower that skin temperature as much as possible, and by doing that, you’re hoping to lower the air temperature above and away from it,” Gaffin said.
There aren’t many ways to cool air directly, and Gaffin says it’s trickier to measure because there are numerous factors that affect air temperature. He says his research suggests that using concrete over asphalt would, in fact, help reduce the urban heat island effect. Another way concrete could help involves using pervious pavement. Besides helping Louisville reduce storm water runoff, when moisture is allowed into paved surfaces, it helps cool the surface temperature.