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Cool pavement research builds as temperatures rise

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Dive brief:

  • Recent research from cities and academic institutions suggests that the implementation of cold pavements and related technologies can help reduce urban heat island effects locally while providing a broader benefit for change. climate. Questions remain as to whether people actually feel fresher in the presence of these materials and the longevity of their benefits.
  • The city of Phoenix, in partnership with researchers at Arizona State University (ASU), last week present lessons from a cold pavement pilot program that began in 2020. After implementing reflective cold pavements in eight cities, the team found that the material resulted in lower surface temperatures at all times of the day. compared to traditional asphalt counterparts. Most brutally, around noon and in the afternoon cool pavements have average temperatures of nearly 12 degrees Fahrenheit cooler than traditional asphalt.
  • Separately, the Massachusetts Institute of Technology Concrete Sustainability Hub (MIT CSHub) presented its analysis of the potential for cold pavements in Phoenix and Boston during a webinar on Thursday. While the study suggested that using cold pavements in these cities could lead to reductions in air temperature and greenhouse gas (GHG) emissions, the researchers expressed the importance of taking into account the characteristics of different neighborhoods and other climate impacts of technology.

Dive overview:

After the United States had a summer of record temperatures, the risks and difficulties that heat poses for communities are a priority for many municipal officials. Phoenix is ​​seen the hottest american city. In June, it experienced six straight days where the high temperature was at least 115 degrees F. But this year’s heatwaves also hit areas of the country less accustomed to long periods of triple-digit temperatures, to know the Pacific Northwest.

Paved surfaces in Phoenix roofing 40% of the city’s urban area, serving as a main contributor to the urban heat island effect. The idea behind the rollout of cool sidewalks, which involved applying a The water-based treatment called CoolSeal on asphalt was to have a lighter colored pavement that reflected more incoming sunlight, thus absorbing less heat. On standard streets, nighttime temperatures can rise when much of this heat is released.

Among the lessons of the program’s first year were that optimal locations for implementation include open, unshaded land and low-rise residential areas where sunlight can be reflected, said Jennifer Vanos, Assistant Professor in the School of Sustainability, ASU, during the last presentation of the week. Conversely, shaded areas may not benefit as much.

Also, sports grounds or parks where people spend time in the middle of the day may not be the best setting, as people can feel that heat. An earlier pilot program in Los Angeles found that even though the material resulted in lower surface temperatures because the pavement reflected heat better, there is a possibility that humans will absorb it afterwards.

In a separate webinar on Thursday, the co-director of MIT CSHub Randolph Kirchain noted that cold pavements are a tool that can complement other heat mitigation strategies, each with shortcomings. Adding trees, for example, is very effective, but the benefits take time to develop. Adding cooling centers can also help, but has its own carbon footprint.

Recent research from MIT looked at different types of pavements and concrete, and took into account other characteristics besides color, such as surface texture, that could impact the climate. Rough pavement, for example, can cause a vehicle to expend more energy when going up and down on grooves instead of being able to move more efficiently. on smooth pavement.

Going forward, one area that MIT researchers want to explore further is “How low carbon concrete mixes and network decarbonization can change the preferred cold paving alternative over time when looking to minimize life cycle emissions” according to MIT CSHub Communications Coordinator Andrew Logan.

For the Phoenix-ASU research team, recommendations and next steps following the first year results include performing longer term tests to see how pavement properties potentially change with the aging.