The Road to Sustainability is Paved with Harder Surfaces

Developing new forms of energy is the ticket to a sustainable future, but reducing energy and fuel consumption is also of paramount importance. In fact, it can be done more quickly as the technology is already available.

Now the brains at MIT (Massachusetts Institute of Technology) have found out that stiffer pavements could make travelling in the U.S. more sustainable by saving three percent in fuel consumption. That doesn’t sound like a lot but it equals to 273 million barrels of crude oil per year, or US$15.6 billion. The environmental benefit is also huge: 46.5 million metric tons of carbon prevented from going into the atmosphere.

The study looked at the effect of pavement deflection on vehicle fuel consumption. To do that, it took a different route from traditional roadway experiments and used mathematical modeling instead. It modeled the physical forces at work when a rubber tire rolls over pavement.

Study authors Professor Franz-Josef Ulm and PhD student Mehdi Akbarian concluded that because of the way energy is dissipated, the maximum deflection of the load is behind the path of travel. This has the effect of making the tires on the vehicle drive continuously up a slight slope, which increases fuel use. They compare it to the deflection of beach sand underfoot. With each step, the foot tamps down the sand from heel to toe, requiring much more energy than when walking on a hard, even surface.

The solution then lies in stiffer pavements, which can be achieved by improving the material properties or increasing the thickness of the asphalt layers, switching to a concrete layer or asphalt-concrete composite structures, or even changing the thickness or composition of the sublayers of the road. The researchers say the initial cost outlay for better pavements would quickly pay for itself not just in fuel efficiency and decreased CO2 emissions, but also in reduced maintenance costs.

This research was conducted as part of the Concrete Sustainability Hub at MIT, which is sponsored by the Portland Cement Association and the Ready Mixed Concrete Research & Education Foundation with the goal of improving the environmental footprint of that industry. The study was released in a recent peer-reviewed report. A paper on this work has also been accepted for publication later this year in the Transportation Research Record.

Image credit: RMC