Cool Pavements – Melvin Pomerantz


In Berkeley, we are fortunate to have such events as Science at the Theater, where Lawrence Berkeley National Lab researchers give talks on their work at the Berkeley Repertory Theatre. The lectures are free and get a pretty sizeable audience.

On Monday, October 11, I was in the audience as researchers from Lawrence Berkeley National Laboratory (and the beloved Art Rosenfeld) gave a presentation titled “Cool Roofs, Cool Cities.” The post below consists of Part 3 of my record of the presentation – Melvin Pomerantz gives an overview of cool pavements. All portions are included in chronological order.

An ellipsis (…) indicates that I was not able to capture the words or thoughts skipped. The presentation is transcribed as accurately as possible – punctuation choices are mine. I also added any images.

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Now we’re talking about cool pavements … because they are a significant fraction of a city … including the streets, parking lots, driveways, and sidewalks.

We need to understands that they are a composite material … they are aggregate, an array rocks of different sizes … We then have to hold them together. So we have to glue the rocks and sand together by coating each rock with a  binder of some sort. For “asphalt”, the binder is asphalt, which is a petroleum product …  We can also bind the rocks together with cement, which is a mineral product, and we call that concrete … The key thing is that because you’re coating the aggregate, you mostly see the color of the binding … Our target is the binder.

Of the third of the city that is covered with pavements of various kinds, 50% is streets, 40% are exposed parking, and about 10% are sidewalks … Because it covers about 90% of the paved city streets, our target is the asphalt concrete.

Image credit: Wikimedia Commons

Start with fresh asphalt concrete … which is very black and has a solar reflectance of about 5%. As it ages, sunlight breaks it downs … Typically, its solar reflectance goes up to about 15% … The question is can we do any better … If you use a light-colored aggregate, it will show as the binder wears off … can use seashells, or porcelain … For old pavement, which required resurfacing periodically … we can put on a layer of asphalt emulsion, and put light-colored aggregate on top. That is called a “chip seal” … One issue is that aggregate is heavy, so it’s expensive to ship. So we want to use rock that’s nearby, and it may not be white … If the road stay cool, it doesn’t deform as much …

An example is from San Jose … They happen to have a quarry nearby that has white rock, and they’ve used a chip seal …

The other type of road, a little less common, is cement concrete … Fresh cement has a solar reflectance of about 35% … as it ages, it gets darker and reflectance drops to about 20% … The fine aggregate tends to float to the top … If you have light-colored fine aggregate, you can get an initial solar reflectance of about 40% …

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Part 1 is posted here. Part 2 is posted here. Part 4 is posted here.

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Upcoming Bay Area Events

A few (free!) events that I thought would be of interest to Zero Resource readers. If you know of other events you think folks might be interested in, let me know at anna AT zeroresource DOT com.

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September 22, 2010

CPUC Thought Leaders event – Dr. Peter Fox-Penner, The Brattle Group

10:30 am – 12:00 pm @ the CPUC Auditorium, 505 Van Ness Ave, San Francisco

The Brattle Group provides consulting and expert testimony in economics, finance, and regulation to corporations, law firms, and governments around the world.    Mr. Fox-Penner is recognized as an international authority on energy and environmental policies and electric regulatory planning and competition issues. He will discuss his vision for electric utilities as described in his new book, Smart Power: Climate Change, the Smart Grid, and the Future of Electric Utilities. This will include business models that reflect the new roles and abilities required of utilities adopting Smart Grid technology: balancing and dispatch of energy across a changing grid and management of advanced end-use technologies for energy consumption. According to Dr. Fox-Penner, adopting and adapting to these changes will be one of the primary challenges the industry will face for the next 20 years.

More information and links to register here.

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October 1-2, 2010

The Philomathia Foundation Symposium at Berkeley: Pathways to a Sustainable Energy Future

9:00 am – 5:00 pm both days @ Berkeley Repertory Theatre, Berkeley

Can we emulate the ability of green plants to harness solar energy? Can we create intelligent materials, buildings, and even entire communities that generate their own energy? Can we put a price on greenhouse gases in order to reduce emissions? Can the technology used to produce an inexpensive anti-malaria drug also extract fuel from agricultural waste?

Hear world-renowned experts in solar energy, synthetic biology, climate science, urban design, and other critical areas discuss the best courses of action to achieve a sustainable energy future.

More info and links to register here.

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October 11, 2010

Science at the Theater – Cool Cities, Cool Planet, featuring Art Rosenfeld

7:00 pm – 9:00 pm @ Berkeley Repertory Theatre, Berkeley

How can white roofs cool your building, your city…and our planet? What’s the role of the other carbon – black carbon – in global warming?

More information here.

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