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AZ Approaches Completion of Cool Pavement Program

Thursday, November 5, 2020

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Working in collaboration with Arizona State University, the Phoenix Street Transportation Department has reported it is nearing the completion of a series of “cool pavement” applications around the city.

The cool pavement treatments are a part of the city’s pilot program, where ASU will study the pavement coatings' possible impact regarding the area’s heat island effect over the course of several years. According to the Department, the applications were slated to reach completion by the end of October.

Cool Pavement Pilot Program

The idea for the pilot study was launched following a ASU-led study on solar reflective coatings back in July 2019. For the study, ASU researchers took two mobile biometeorological instrument platforms (MaRTy 1 and MaRTy 2) to Los Angeles in order to read how the city’s streets affected radiant heat and ultimately, pedestrians’ comfort.

At the time, the Los Angeles Bureau of Street Surfaces was pioneering the use of solar reflective coatings in a quest to cool city streets.

The study was the first to measure the thermal performance of solar reflective coatings using instruments that sense meteorological variables relevant to a pedestrian’s experience: radiant heat, ambient temperature, wind and humidity.

In the study’s findings, researchers found that the temperature of the coated asphalt road was up to 6 degrees C (almost 43 degrees F) cooler than the regular road in the afternoon. However, the radiant heat over coated asphalt was 4 degrees higher than non-coated areas. Additionally, the study also found that the coating didn’t have a big impact on air temperature, only half a degree in the afternoon and 0.1 degree at night. 

“We need more of these experiments,” Ariane Middel, assistant professor in both the School of Geographical Science and Urban Planning and the School of Arts, Media and Engineering said at the time. “There have been a lot of large-scale modeling studies on this. So, we don’t know in real life if we get the same effects. The urban environment is so complex, and models have to always simplify. So, we don’t know what really happens on the ground unless we measure, and there haven’t been these types of measurements in the past.”

The research study, “Solar reflective pavements — A policy panacea to heat mitigation?” was published in April of this year in the journal Environmental Research Letters.

In developing the Cool Pavement Pilot Program from the study, the City of Phoenix Street Transportation Department selected portions of eight neighborhoods and one city park to receive cool pavement treatment as part of the project. The portions cover 36 street miles at a cost of $3.3 million, which has come from the city’s street maintenance budget.

The nine areas chosen as they were already due for resurfacing and money would have gone toward rehabilitating those areas regardless of the material used, reported David Sailor, director of the Arizona State Urban Climate Research Center.

However, instead of using the reflective solar coatings like in Los Angeles, the city announced that it would be using cool pavement technology, CoolSeal, developed by California-based GuardTop LLC.

According to the Department, the application is made up of asphalt, water, an emulsifying agent (soap), mineral fillers, polymers and recycled materials. It contains no harmful chemicals, is compatible with traditional asphalt and can be spray- or squeegee-applied.

The city adds that it chose to use this form of cooling technology as opposed to the reflective coatings because, “Cool pavement reflects back the sunlight that hits it. Because the surface reflects rather than retains heat, cool pavement has the potential to offset rising nighttime temperatures in Phoenix. The use of cool pavement technology may help reduce the heat island effect and reduce temperatures in the city. It is also useful to cool neighborhood areas that don’t have much shade from the sun.”

Since announcing the program’s endeavors, the city has reportedly completed the application of cool pavement coatings to seven of its nine locations. However, those locations were slated to reach completion by the end of October.

A team from ASU intends to study the cool pavement’s effects over the next several years, with early results slated to be posted on the Street Transportation Department website by the end of 2021.

In addition to the Street Transportation Department and ASU, the City of Phoenix Office of Sustainability have also partnered on the project to see if the technology can help with the city’s continuing efforts to be environmentally sustainable while improving the quality of life for all who enjoy Phoenix.


Tagged categories: Coating Application; Colleges and Universities; NA; North America; Reflective coatings; Research; Research and development; Roads/Highways; Solar reflectance

Comment from William Cornelius, (11/5/2020, 8:22 AM)

There is an error in the math. The difference between C and F is eleven degrees. The problem is that if you punch 6C (the freezing Point being 0) into to a calculator you get 42.8F but you have to subtract the 32F difference to get the actual number.

Comment from Tom Schwerdt, (11/5/2020, 8:29 AM)

The simpler answer is to just ask Google "6C in F"

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