A reply written by Jen Gaugler to Concrete vs. Asphalt, one that I did not want to get lost in the comments section. Following the reply is another short discussion, inspired by a reader comment.
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Economics and durability aside, I agree that the environmental factors of choosing asphalt vs. concrete are very important to take into consideration. You are right about the heat absorption properties of the two materials being very different. The “heat island effect” is the tendency of paved areas and building rooftops to absorb the sun’s energy and result in the microclimate of that area being several degrees warmer than it would be otherwise. Believe it or not, this can have a big negative impact on the surrounding ecosystem. The albedo, or solar reflectance, of a material is its ability to reflect the visible, infrared, and ultraviolet wavelengths of sunlight. Concrete has a significantly higher albedo and therefore it is definitely better to use it in warm, sunny climates to mitigate the heat island effect. It may be more acceptable to use asphalt in northern climates (like Alaska) where it may help with snow and ice, as you suggested. But I think for most of the continental U.S. it is probably more environmentally sound to use concrete.
However, there are also systems available which are similar to dirt parking lots but slightly more durable (important in some places, for example where erosion may be a factor) and they consist of open-cell concrete systems (to form a grid pattern) with grass in between. This absorbs less heat AND allows storm water to be re-absorbed into the ground to recharge underwater aquifers. Pervious concrete – made with extra large aggregate and little or no sand, to make a very water-permeable paving substance – is another good compromise between durability and sustainability.
And of course the most important factor in decreasing the heat island effect – shade, a.k.a. trees! So lining our streets with mature trees is the way to go!
-Jen Gaugler
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See also, an article from The Boston Globe on December 7, 2008, Architect Finds Beauty in the Asphalt Jungle. An assistant professor of landscape architecture from Harvard’s Graduate School of Design is taking another look at asphalt and our the public views it, since it is our most commonly used landscape. This professor and her students are taking a new look at the “jungle” without vilifying it. One of the projects include “Steamroller Printing.” It’s something that most preservationists, including me, would have never considered; but, to step and work with the existing environment is possibly just as important as our other endeavors. Regardless of opinions, it’s something neat to explore and ponder. See also the onasphalt website. Thank you to reader, Melsiel, for adding a comment with the article.
-Kaitlin
Preservation in Pink 