Can Building Concrete Roads Save 50 Million Tons of CO2?
May 31, 2012 at 3:50 PM
What if we, as a nation, could collectively reduce vehicle fuel consumption by 3%?
What if this reduction lowered annual carbon dioxide emissions by 46.5 million metric tons per year, an amount greater than the combined CO2 output of all the cement plants in the U.S.?1
What if this saved $15.6 billion annually in fuel, which is about 40% of the total annual U.S. gasoline/fuel tax revenues2 ($0.184 per gallon)?
What if the technology to do this existed now?
Should we do it?
The study uses a mathematical, mechanistic model3 to look at the effects of pavement deflection on vehicle fuel consumption, and applied the results across the entire U.S. road network.
The analysis, performed by MIT Professor Franz-Josef Ulm and Ph.D. student Mehdi Akbarian, shows that pavements which deflect more under a vehicle load, cause a depression that makes the vehicle perform as if it were continuously driving uphill. The stiffer the pavement, the less the effect.
This effect is both calculable and significant: 7,000 to 8,000 gallons of fuel per lane mile can be saved annually on high volume roads. This data was gleaned from the researchers analyzing 5,643 representative sections of the nation’s roadways taken from Federal Highway Administration data sets.
But how do you get stiffer pavements? Two principal options exist: Use a rigid concrete pavement, or increase the thickness of the asphalt pavement. To make an asphalt pavement's stiffness equivalent to a similarly-designed concrete pavement, "asphalt pavements need to be 25-60% thicker to display same fuel consumption performance as concrete," according to Ulm and Akbarian (in a previous MIT fact sheet on mechanistic pavement deflection modeling).
If achieving fuel, emissions, and cost savings are important to a community, local and state transportation agencies can either choose to build concrete roads, or thicken the asphalt pavement designs. You get the fuel savings benefits on a concrete road for "free," while you have to pay extra for this on an asphalt pavement (because of the greater thickness required).
With significant cost increases in asphalt (and virtually none for concrete over the last three years), inch for inch, concrete is less expensive than asphalt (see my previous blog on this). Choosing concrete for our road infrastructure seems like a no-brainer: less expensive and more sustainable.
1 Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2010, Table 4.1 (EPA 430-R-12-001).
2 Urban Institute and Brookings Institution Tax Policy Center, State and Motor Fuel Tax Revenue Selected Years 1997 - 2009.
3 Akbarian, M. and Ulm, F., "Model Based Pavement-Vehicle Interaction Simulation for Life Cycle Assessment of Pavements," MIT Concrete Sustainability Hub (2012).
Jan is the executive director of the Cement Council of Texas. He can be contacted at firstname.lastname@example.org or 817-540-4437.