MAKING BLACK TOP GREEN

When Craig Benson started working on reusing industrial waste to rebuild infrastructure 20 years ago, he says, “I didn’t even know the word sustainable.”  He just knew that there were valuable materials going into landfill from places like the paper industry and the coal-burning power plants.  “Trying to find ways to use them just made sense.”  Dr. Benson has focused his efforts on transportation infrastructure.

..Making electricity and making roads at the same time. (photo credit: FreeFoto.com)

He is now Director of the Recycled Materials Resource Center (RMRC)  , which pools the resources of the University of Wisconsin-Madison, The University of New Hampshire and the Federal Highway Administration.

I listened to Benson explaining his work yesterday at the first Weston Roundtable Lecture of the year, “The Role of Recycled Materials in Sustainable Infrastructure, ”  co-sponsored by the Nelson Institute Center for Sustainability and the Global Environment (SAGE)  and the Department of Civil and Environmental Engineering.

The RMRC has been exploring uses for combustion products from coal-burning power plants.  One of these by products is fly ash, the fine particles that rise with the flue gases as coal burns.  Fly ash used to be released into the atmosphere, but now it is filtered out and is often landfilled.

..Fly ash particles at 2,000x magnification. Fly ash is typically finer than portland cement and lime. Fly ash consists of silt-sized particles which are generally spherical, typically ranging in size between 10 and 100 micron . These small glass spheres improve the fluidity and workability of fresh concrete.

Fly ash, it turns out, is very useful stuff.  Scientists are finding ways to use this in concrete and wallboard production.  The RMRC website says that reusing this material makes a big difference in energy consumption, water use, greenhouse gas emissions and just plain dollars spent.

The use of fly ash as a cement substitute annually:

Saves more than 55 trillion Btus of energy, enough to power 600,000 households

reduces greenhouse gas emissions  by 9.6 million tons of CO2 – equivalent to 1.7 million passenger cars

That’s just the beginning!

Benson is thinking fly ash and  transportation infrastructure.  We all dread road construction on our usual routes, but all those orange barrels and heavy equipment slogging about is more than just a nuisance.  There is an enormous expenditure of energy, materials and major CO2 emissions every time we have to rebuild a road.

Benson is working on making black top a little greener.  When roads are rebuilt, a monster machine comes along and chews off the old surface.  That stuff is called Recycled Pavement Material (RPM).  Most black top roads have a 4” layer of asphalt on top of an 8” granular layer.  This base needs to be strong enough to support the asphalt surface.  Traditionally that base would be freshly quarried gravel.

Benson’s been experimenting with making that base of either all RPM or RPM mixed which fly ash (which tends to set up when water is added to create a very firm, long-lasting base).

It turns out that plain RPM is better than the usual gravel, and RPM with fly ash is MUCH better.  Both are mechanically superior, use less energy, create fewer emissions, and last longer.  By monitoring the water that migrates through the material, studies are showing that the arsenic and mercury levels are lower than the drinking water standard.

What is not to like?

Let’s hope this new approach becomes common practice.  This is a step in the right direction.

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