The "urban heat island" effect, in which the heat that builds up in a city's buildings and structures during the course of a day gets to a point where it affects the natural weather patterns around the city's metropolitan area, may soon be an odd footnote in the history of the twentieth century, ended by human innovation.
An experiment is currently underway on the highways and city streets of Arizona's largest urban center - one that has the potential to change how every road in every major city in the United States is paved. Road crews the Phoenix metropolitan area are resurfacing the region's major highways with a compound that combines traditional asphalt with particles of rubber recycled from old tires.
The resulting rubberized asphalt is proving to have some remarkable qualities. Initially intended as an experiment in reducing the noise of traffic on the area's major highways, the new material is demonstrating that it can improve traffic safety, and most surprisingly in one of the U.S.' hottest cities, it appears to be able to reduce the amount of heat that is absorbed by the road's underlying concrete during the day.
The Arizona Republic describes the unexpected benefits of the new road-paving material:
Life in the southeast Valley means life in an urban heat island. Every day, with every passing sun-drenched hour, our buildings, environment, roads and all things out of doors collect heat, sending surface temperatures well above the standard mercury reading and keeping things warmer than intended after the sun goes down.
Rubberized asphalt's porous top layer cools down quicker than concrete, cooling our roads and diminishing heat island effects. The cooling effect isn't on par with a full-blast air-conditioner, but when summer temperatures reach fatal highs, every little bit helps.
And with the soaring temperatures and unmerciful sun of the Arizona summer comes the inevitable - the monsoons. The porous surface of rubberized asphalt acts like the sponge from our opening analogy, soaking water in, dispersing it to roadsides from the crowned base level and diminishing retained street water. The tackier street surface provides good traction for treads against road, preventing some hydroplaning and keeping roads safer overall.
Of all its benefits, its the heat insulation properties of the rubberized asphalt that promises the most far-reaching change for the construction of roads in the U.S.' major cities. Given the role that the large masses of concrete that make up American roads has in creating the urban heat island effect, the ability of the material to more quickly shed the heat it builds up during the day could go a long way to cooling down urban centers in the U.S.
All-in-all, rubberized asphalt represents a neat example of how even a low-tech material can have serendipitous benefits (less heat buildup, safer roads) that were never considered by its original inventors.
Labels: technology
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