The Overhead Wire Daily: Greening Asphalt and Concrete

We are still catching up on a bit of news from last week while we were at Mpact so some of the stories might have a bit older dates, but of course they are still very relevant! Looking at you Austin and your fun plans for Congress Avenue.

I also want to circle two items I think are important. A lot of the discussion around climate change often centers on emissions from transportation sources such as tailpipes, but less talked about from my perspective watching the news is from construction of the transportation infrastructure that facilitates those trips.

Often times that is road building but it can also be the construction of your favorite subway line or other infrastructure we think of as sustainable. And there are two ways I think of infrastructure construction from an ecological standpoint.

First is the impact those roads have after they are constructed such as on the urban heat island, the facilitation of driving, and on biodiversity and the free movement of animals. We talked with Ben Goldfarb (Transcript | Audio) about his book Crossings which covers this phenomenon in great, and often sad, detail.

But second is the impact of construction itself. In order to get emissions down to a reasonable amount or zero, it’s clear there needs to be a focus on sustainable construction and materials. The two materials most used for this are concrete and asphalt.

Asphalt as we found out talking with Kevin O’Reilly about his book on the topic (Transcript | Audio) has an interesting history and wild connections to politics all around the world.

There are naturally occurring versions of it including in Canada’s tar sands for example, but what we know of it now is mostly the process of asphalt extraction from refining crude oil to make gasoline. The good thing about it is that when you put it on the ground as a road it acts as kind of a carbon sink in that it never gets burned and released into the atmosphere and can mostly be reused over and over again. As Kevin said “…and so when you’re driving your car, the asphalt under your car wheels, that’s a carbon sink, but the asphalt that’s powering your engine is a carbon bomb.”

That’s why it was interesting to me when I saw the article about New York City deciding to test 50% mixes of recycled asphalt of low traffic streets. Reusing the material means that it isn’t being extracted. And although it has a big impact on the urban heat island, 200 tons of waste can also be diverted from landfills and reused.

The other material we use for infrastructure and roads and buildings is concrete. Unlike asphalt, concrete is not refined but the emissions come from limestone mined and baked at 1500 degrees Celsius usually using fossil fuels. Cement is the binder that when mixed with a specific kind of sand and gravel and water creates concrete.

And its emissions are skyrocketing. Between 2011 and 2013 China used as much concrete as the United States did in the whole 20th century. Other countries are following suit as demand for building roads and infrastructure and homes grows exponentially.

But the process is likely to get greener as companies look for ways to reduce emissions through either the heating process or by capturing emissions at creation of cement and storing it underground. Of course this isn’t a perfect solution and there are still risks of creating emissions. But I’m glad to see that solutions are sought.

This topic could prompt whole books to be written but I thought these two articles on asphalt recycling and greening concrete coming into the news list at the same time prompted some connections, especially since it’s something we’d chatted about before on the podcast in great detail. It’s definitely something to consider when thinking about emissions and lifecycle costs and impacts of these materials that are everywhere in our lives.