The Greening of Asphalt

There are more than 4 million miles of paved roads in the United States alone. That's enough asphalt to build a paved road that would wrap the earth 160 times or to build 16 bridges between the earth and the moon. That's alot of asphalt. So it's no wonder that researchers are experimenting with ways to make paved roads more sustainable.

In the Netherlands, Dutch company Ooms Avenhorn Holding BV has created the Road Energy System (RES). The RES lays a water piping system within concrete or asphalt to heat the water The water is then used for heating and cooling in buildings and to keep the road ice-free in winter. The system is also being used in Scotland.

Similarly, researchers at Worcester Polytechnic Institute are working to use asphalt as an solar energy source and to heat water. Roads are resurfaced every 10-12 years and could be retrofitted within that cycle. An added benefit is that removing heat from the asphalt could reduce the urban 'heat island' effect.

At the University of Wisconsin-Madison, the Asphalt Research Consortium hopes to develop “cold-mix” asphalts that use more recycled materials and require significantly less energy than conventional asphalt to apply.

Meanwhile, Dutch researchers at the University of Twente have refined air-purifying concrete paving stones. The concrete stones convert nitrogen oxide from exhaust fumes into harmless nitrates which is then washed away by rain. In the city of Hengelo, streets are being half paved with the stones to test the effect and results should be available by summer 2009.