BOSTON, MASSACHUSETTS & PHOENIX, ARIZONA—‘Cool pavements’ could reduce summer heat
Record-breaking heat waves summer of 2021—”hottest July on record globally”—made walking outside in cities almost unbearable for many residents. The weather itself scorching, but the asphalt roads heated up so much that doctors warned that pedestrians were getting burned by the surfaces that reached 170°F to 180°F under the baking afternoon sun. An MIT Concrete Sustainability Hub (CSHub@MIT) study concluded that ’Cool pavements’ could reduce summer heat by 3°F in Boston, Massachusetts, USA. Replacing asphalt pavements with “cool pavements” would reduce the air temperature in the summer by 3.7° and reduce the carbon dioxide emitted.
To counter the rising extreme temperatures on paved surfaces, researchers at the CSHub examined using ‘cool pavements’ and found they emit less heat by reflecting more solar radiation.
Led by Hessam AzariJafari, Postdoctoral Associate-MIT, the the study’s main objective was to assess the effectiveness of cool pavement strategies for reducing the temperature and urban heat island effects in Boston and Phoenix as well as how they could help with greenhouse gas mitigation in the cities. They also examined the interconnections between pavements and other aspects of the city, such as the shadows and reflections from nearby buildings and the vehicles driving on the pavement.
In both cities, researchers observed and tested 3 different types of cooling techniques on pavements:
• Reflective asphalt
• Concrete
• Reflective concrete
Boston—found that replacing asphalt pavements with cool pavements would reduce the air temperature in the summer by 3°F (1.7° C)
Phoenix—found that it would be reduced by 3.7°F (2.1°C)
Cool pavements would:
• Reduce the carbon dioxide emitted in the cities
• Improve the impact of cars on climate change
• Lower carbon footprints
The team developed a metric to measure how reflective each surface was and how much light was absorbed in each type of pavement and found that cool pavements materials:
• Had the ability to reflect much higher levels of radiation and sunlight
• Emitted much less heat than normal asphalt concrete
• Surface of the pavements also impacted excess fuel consumption—“pavements with smooth surfaces and stiff structures cause less excess fuel consumption” for vehicles on the road
Randolph Kirchain, Co-Director-MIT CSHub, told Boston.com, “Our group is generally trying to push the boundaries of how to do a better job of understanding the environmental impact of technology choices in buildings and infrastructure, that’s what we do. And so this was just sort of the next biggest challenge.”
The team hopes to inspire other cities to conduct similar research that will provide them with adequate information to propose cool pavements in urban areas, mitigating the effects and impact on climate change. Since pavements cover almost half of the surface areas of cities, AzariJafari said it is important to consider the whole life cycle of the materials’ emissions. He stated,
“One of the most important things that we observed is that
there is a net zero goal defined by different cities.
We think cool pavement can be a part of this solution
to achieve net zero goals for cities.”
PHOENIX, ARIZONA—Infrared Drone Testing Confirms that Concrete is ALWAYS Cooler!
The International Grooving and Grinding Association (IGGA) along with the American Concrete Pavement Association (ACPA) recently used drone technology to conduct infrared testing of diamond ground concrete and asphalt rubber surfaced pavements in the Phoenix, Arizona, USA area to evaluate if the asphalt rubber ever achieves a cooler temperature throughout the day. The camera system captures both RGB photos and infrared images.
Larry Scofield, P.E., Director of Engineering-IGGA and Director of Pavement Innovation-ACPA, organized and executed the project to evaluate two sections of the Phoenix freeway system. Utilizing drone technology allowed for the infrared imaging to be performed during live traffic and evaluate the impact of convection cooling from the moving vehicles.
Larry Scofield will be presenting during the final day of the 12th ICCP 2021!
Register for the Virtual 12th ICCP 2021 to attend his WORKSHOP:
Workshop #10: Pavement Preservation (Sponsored by IGGA)
“Finding Cool Buried Treasure”
Larry Scofield (30 minutes)
FRIDAY, OCTOBER 1, 2021:
6:00 AM Los Angeles | 9:00 AM New York | 2:00 PM London | 4:00 PM Nairobi
6:30 PM Mumbai | 9:00 PM Beijing | 11:00 PM Brisbane:
www.12thiccp.concretepavements.org/program/
Click to download Larry Scofield’s REPORT
The purpose of the testing was to compare the temperature of the asphalt rubber surface to that of the diamond-ground concrete surface. Executed by the CSHub@MIT and sponsored by the Portland Cement Association (PCA) and the Ready Mixed Concrete Research & Education Foundation (RMCREF), the research study found that even with the cooling impact of the traffic:
• Asphalt rubber surface remained hotter than the concrete pavement throughout the course of the entire day
• Although testing was interrupted by monsoons, Asphalt was found to range from 2 to 6 °F hotter than the adjacent concrete pavement travel lanes throughout the day
• Convection cooling from traffic does occur and reduces travel lane temperatures when compared to the auxiliary lanes and shoulders—up to 5° to 10° OF difference based on the time of day
• Asphalt surface ranged up to 10° higher on the asphalt shoulder
• Just prior to sunrise, the asphalt rubber was still hotter than the diamond ground surface even after cooling all night
• Results confirm earlier research efforts conducted with stationary testing by ASU,ACPA, and the medical profession
• Higher temperatures of the asphalt rubber contribute to the urban heat island in the valley area—Possibility that most meaningful temperature for comparing the two surfaces’ contribution to the urban heat island, is the shoulder where minimal convection cooling occurs and is more representative of the actual heat energy put into the environment
• The 8,000 acres of Maricopa Association of Governments (MAG) freeway system contributes to the urban heat island effect in the valley. As the freeway continues to expand, this impact will only increase. Currently, the global warming potential of the MAG Freeway system could be reduced 2,712,238 tons of CO2 emissions by having a1 diamond ground concrete surface instead of asphalt rubber .
• The use of drone IR testing is a very definitive measure of the impact of pavement temperature differences between pavement surface types
To view Larry Scofield’s REPORT, please click image above, or go to: https://72aeb35d-270f-43cf-a58b-ddde7e42c0eb.usrfiles.com/ugd/72aeb3_db263c0f6c8947df8efb551cd4c9df8a.pdf
Click to download 2-page CASE STUDY BRIEF
An MIT Case Study Brief titled “Quantifying the impact of pavement reflectivity on radiative forcing and building energy demand in neighborhoods” recently found that the Phoenix area freeway system could reduce over 2.7 million tons of CO2-eq emissions by having an exposed concrete surface.
The study states Albedo is the measure of the fraction of solar energy reflected by the Earth’s surface, and
High-Albedo Surfaces are:
• Lighter in color
• Absorb less sunlight energy
• Reflect more shortwave radiation
The change in radiative energy balance—called radiative forcing (RF)—reduces nearby air temperatures and impacts the surrounding building energy demand (BED), including heating and cooling energy loads. The impact of reflective surfaces on RF and BED has been investigated by researchers through modeling and observational studies, however previous studies have not assessed RF and BED impacts under the same context and therefore cannot be directly compared. This case study takes a more comprehensive approach in assessing the net impacts of pavement albedo modification strategies in urban areas. The impacts of RF and BED are translated into global warming potential (GWP) savings and normalized to kg CO2 equivalent per square meter of pavement modified (click on Fig. 1 above to see the 2-page report).
This CASE STUDY BRIEF creates a foundation for future research taking into account various neighborhood characteristics. Making use of GIS data is necessary in order to demonstrate the impacts of reflective pavements accurately at urban scale. Results show:
• Evaluating the effectiveness of albedo modification strategies (changing surface reflectivity) involves quantifying the net impacts from both radiative forcing (RF) and building energy demand (BED).
• The relative magnitude of RF and BED depends on context, but usually RF is more significant.
For the BOSTON.COM online article titled “‘Cool pavements’ could reduce summer heat by 3 degrees in Boston, MIT study finds“, please go to: http://realestate.boston.com/news/2021/08/25/mit-studies-cool-pavements-summer-heat-boston/
For Larry Scofield’s FULL REPORT on the infrared drone testing, please click on first image above, or go to: https://72aeb35d-270f-43cf-a58b-ddde7e42c0eb.usrfiles.com/ugd/72aeb3_db263c0f6c8947df8efb551cd4c9df8a.pdf
For the MIT CASE STUDY BRIEF, please go to: https://72aeb35d-270f-43cf-a58b-ddde7e42c0eb.usrfiles.com/ugd/72aeb3_9cb6946a6c4242e7b72961faa5c5e065.pdf