Cool-Pavement: An Option to Combat Climate Change

Across America, cities are partnering with Arizona State University to combat climate change in areas known as “urban heat islands”. 

The solution involves America’s most recycled material: Asphalt.

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The Global Institute of Sustainability and Innovation, Healthy Urban Environments, and the Urban Climate Research Center at AZU concluded the initial pilot program in 2021 , after partnering with Phoenix to study eight neighborhoods already in need of asphalt updates.

What is Cool Mix & How Does it Work?

Cool pavement is a water-based asphalt treatment that uses asphalt, water, an emulsifying agent, mineral fillers, polymers, and recycled materials. It is compatible with traditional asphalt and offers solar reflectance. By absorbing less energy, cool pavements trap less heat in subsurface layers, allowing cities to cool down after hot days. Traditional black-top asphalt absorbs sunlight and  the heat radiates. The promising feature of cool pavement is that it reflects sunlight so less radiation is converted to heat.

Does It Actually Work? The Pilot Program Results

Phoenix treated eight neighborhoods with cool pavement treatment, aiming to preserve pavement. The city and ASU researchers conducted scientific tests to study its performance and potential mitigation of the urban heat island effect. Data collection included thermal imaging, temperature sensors, and MaRTy, a mobile weather station. The study involved vehicles and air and surface temperature sensors to gather data during four different times a day.

The study found that cool pavement consistently had lower surface temperatures compared to traditional black-top surfaces. Surface temperatures were 10.5-12 degrees lower during early afternoon and midday hours, and averaged 2.4 degrees lower at dawn. The median sub-surface temperatures were 4.8 degrees lower in cool asphalt regions. Solar reflectivity declined from 33-38% to 19-30% over a year, compared to untreated black-top.

The Disadvantages

As always there are trade-offs, the reflective feature is the main drawback. The brightness can obstruct visibility and cause glare. The life expectancy can vary especially in areas with high traffic because the reflective surface requires maintenance to remain effective compared to traditional hot-mix. Rain water caused the coating to wash away in some areas. Researchers are still determining the lifecycle. Admittedly, cool pavements less versatile and not ideal for places such as playgrounds or tracks. The jury is out on human experience as well. While some residents agreed they prefer cool pavement over black-top, longevity is still is a concern.  Contractors may be reluctant to sacrifice quality or assume risks on larger projects.

My Two Cents

Cool-pavement does not contain harmful chemicals and can provide residents with relief in urban heat islands making it a viable and innovative option. Asphalt industry leaders should pave the way… (pun intended) and consider collaborating on additional studies and modifications to provide sustainable high-quality infrastructure that provides solutions the areas that need it most.  Any effort made to combat climate change is valiant.

Source:

https://www.fox10phoenix.com/news/is-phoenixs-cool-pavement-program-working-heres-what-one-expert-is-saying.amp