Rethinking the Way We Repave

 Close up image of lines on a road angling towards the horizon.

Asphalt! It’s gooey. It’s black. It’s one of America’s most common road paving materials. But it turns out that there’s more we all should know about asphalt than meets the eye. So “stick around,” and we’ll tell you why everyone’s favorite bituminous substance has young transportation engineers like Nassim Sabahfar and Danniel Rodriguez searching for clues that could reduce our environmental impact in a big way.

Did you know that about 93% of roads in the United States are paved with asphalt cement? Asphalt (also known as bitumen) is a sticky substance derived from petroleum. Petroleum is a natural resource buried within the earth’s crust.

To put it simply, a road starts out as a layer of crushed rock, which is compacted and then paved with a layer of asphalt cement. Asphalt cement is a mixture of hot, gooey asphalt and rocky gravel, or aggregate. The asphalt acts like a glue that holds the aggregate together. When the mixture is smoothed and allowed to dry, it hardens into the tough, water-resistant road surface we’re all used to driving on: asphalt concrete.

Simple enough. But nothing’s perfect—which is why young transportation engineers like Nassim and Danniel are looking closely at the environmental impact of the way our roads are built.

Image taken from our interview with Danniel Rodriguez.

Click a button to watch an interview with Danniel Rodriguez:

Image taken from our interview with Nassim Sabahfar.

Click a button to watch an interview with Nassim Sabahfar:

You see, asphalt is hard at normal temperatures, which means road crews have to do something to keep it gooey enough to work with. Most of the time, this is done by keeping the asphalt hot all the way from the factory where it was made. Unfortunately, there’s a negative side effect of heating up petroleum (asphalt’s main ingredient): it releases a lot of carbon dioxide (CO2) into the atmosphere. And as you probably know, CO2 is the major cause of global warming.

Considering the fact that the United Sates has somewhere around 2.4 million miles of asphalt-paved roads and highways, the combined greenhouse gas emissions from hot asphalt is enough to have researchers like Nassim and Danniel—as well as states and the Federal Government—looking for more environmentally sustainable ways to manufacture and use it.

That’s why at the University of Texas at El Paso, Danniel Rodriguez is exploring recipes for more durable, longer-lasting asphalt concrete. In his view, a perfect road would be paved just once, with little to no need for future repairs. If this vision were made a reality, it could save millions of tons of asphalt from needing to be produced each and every year, which would greatly reduce the emission of greenhouse gasses from road construction and maintenance.

Nassim Sabahfar, from Kansas State University, is taking a different approach. She is researching the properties of recycled and reclaimed asphalt. If worn-out roads are torn up and repaved across the United States every day, why not recycle the old asphalt pavement instead of sending it to a landfill? Through her research, Nassim hopes to give a definite solution to what you can really do with recycled asphalt. Is it just as strong as new asphalt? Is it as easy to work with? What are its strengths and weaknesses? Doing so could encourage cities and states to pave more of their roads with reclaimed asphalt material.

Nassim and Danniel’s type of research is already making an impact. In Florida, for example, the Department of Transportation (FDOT) has been investing time and resources into sponsoring more and more research on environmentally sustainable asphalt concrete. One study released by FDOT has already proven that roads paved with 30% reclaimed asphalt can be just as durable as roads made with 100% new asphalt. In another study, scientists proved that asphalt pavement mixed at lower temperatures could reduce greenhouse gas emissions, energy consumption, and workers’ exposure to toxic fumes.

This work of young transportation engineers could end up making a huge dent in our global greenhouse gas emissions. But there’s still work to be done to reduce the way transportation impacts our environment. Non-polluting vehicles and greener construction materials may just be the first step. Perhaps in the future there will be better ways to build roads that haven’t even been imagined yet. It’s only a question of who imagines them. Will it be you?

Check out Danniel and Nassim’s videos to learn more, and keep following Fast Forward for the latest news and stories on transportation careers!

Aaron Mack
Fast Forward: Volume 3 Number 1 - National Transportation Week