Courtesy Miguel Tremblay
We've all been there. You're driving along, bobbing your head along to the music, when suddenly you hit a pothole and it feels like your suspension is coming apart. It's especially bad here in Minnesota, because our extreme winters take their toll on worn asphalt. What's a gal to do?
One possible solution is a better way to fix potholes. In Duluth, MN, MNDOT workers are experimenting with new ways to hot patch asphalt with recycled materials and microwaves. In wintertime, crews usually have to patch potholes temporarily until summer comes along and they can use hot asphalt to make a more permanent patch. By using a special microwave, they can make hot patches even in bitter cold temperatures, and the recycled materials make for less waste and pollution. The new fix is also faster and cheaper than current methods.
My friend Wendie pointed out some billboards that went up recently in the metro area to promote concrete as a pothole-free alternative. (Wendie also passed along a handful of the articles in this post--thanks, Wendie!)
On the Think Concrete website, there's loads of info about how concrete lasts longer and saves money. But the question on my mind is, "Which is better for the environment?"
A life cycle assessment comparing the environmental impacts of asphalt and steel-reinforced concrete was completed in 1998. It showed that while producing asphalt required more energy input, concrete required more ore and fertilizer inputs, and gave off more toxic emissions. On the other hand, asphalt was associated with higher levels of hazardous waste generation and management needs. The authors concluded that over the life of each material, the environmental impacts were roughly equal, but they also mentioned that asphalt was recycled more often than concrete, potentially turning the sustainability tide in its favor.
However, two separate studies have shown that concrete provides a better driving surface, decreasing the fuel needed to move a car down the road and thereby its emissions. (Both of the studies were completed in cooperation with cement associations, so throw some grains of salt in there). But there are other examples of concrete's environmental benefits.
And that's not all--there are some great innovations afoot with concrete. Some researchers are working to make cement with carbon absorbing properties, while others have found ways to make flexible concrete that heals itself, reducing the need for new materials and increasing safety.
Of course, there's also the pie-in-the-sky option: solar highways.
The air around us is not as clean as it could be. Scientists are looking for ways to remove toxins, like nitrogen oxide, from the air we breathe. One of the main sources of nitrogen oxide is automobile traffic. A solution to this problem might be found under our very wheels.
How does it work? Concrete pavers are coated with nanoscale particles of titanium dioxide (TiO2). Kicked off with the energy from sunlight, TiO2 converts nasties, like nitrogen oxides, into much less harmful nitrates via a chemical reaction. Nanoscale particles have lots of surface area where a chemical reaction can occur. Also good? It seems that this coating remains stable. Tests conducted almost two years later show no change.
My favorite part of this article...they did not stop there. They asked "What about the nitrates we are introducing into the system? Where's that going?" Rain sweeps the nitrates off the road, into ditches and on to waste water treatment facilities.
Courtesy anjouwuEver stand on a sidewalk and wonder about the concrete beneath your feet? Where did it come from, and how did this hard grey material get to be pretty much everywhere? Though you may not think about it at all, concrete is used more than any other building material in the world. In fact, concrete is so ubiquitous that the production of concrete contributes 5% of the world's human-caused carbon dioxide emissions to the atmosphere.
Add it all up and it starts to look like concrete is more than just the stuff of sidewalks and building blocks. Concrete is a V.I.P. (which is how I like to refer to Very Important Polluters).
While concrete is a huge contributor of CO2, it also has loads of potential to be an innovative and important "green" material that helps us to build stronger and more environmentally friendly roads, bridges and buildings. This really great article from the New York Times science section explains the basics of concrete chemistry, and how new concrete mixes are being developed that are not just stronger and better for buildings, but that also can scrub carbon from the air.
Here in the Twin Cities we have our own example of cutting-edge concrete in the I-35W bridge, which was built to replace the bridge that collapsed in 2007, killing 13 people. You might not realize it as you pass over this bridge, but it's made of many different mixes of concrete, each developed to do a particular job.
Some of the concrete in the I-35W bridge was mixed and cured (that's what they call the hardening process) to be strong and stable, others to resist the road salts and other effects of weather and climate in Minnesota. The wavy concrete sculptures on the bridge even scrub pollutants from the air, In fact, they stay white because of a chemical process that uses the sun to help break down staining pollutants. Who knew concrete could be so fascinating?!
More Than You Ever Wanted to Know About Concrete
"Researchers have figured out a way to use 30 percent less reinforcing steel in the manufacture of the concrete beams, or spandrels, used in the construction of parking garages.
In addition to using less steel, the new design cuts labor and manufacturing time in half – significantly decreasing costs." North Carolina State University
Washington D.C. and other communities are installing rubber sidewalks. Rubber sidewalks are composed of ground-up tires. They are able to withstand tree roots and climatic fluctuations better than concrete. Not only are rubber sidewalks environmentally friendly (recycling old tires) they also serve as a shock-absorber for our joints.