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New research targets "greener” roads

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May 29, 2008

Varying mixtures of aggregate, sand and other binder materials used to create asphalt conc...

Varying mixtures of aggregate, sand and other binder materials used to create asphalt concrete samples Photo: Jeff Miller

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May 29, 2008 A great deal of effort is being invested towards discovering ways to make our world greener, with cars in particular being the focus of research and development initiatives. But what about the green credentials of the millions of miles of roads which carry our vehicles from A to B? This question is being addressed by researchers at the University of Wisconsin-Madison (UW-Madison) who are investigating ways to make asphalt environmentally friendly.

With more than 90% of roads in the US being paved with asphalt, any effort to boost its recycled content, lengthen its life, or cut the energy needed to manufacture it could have significant environmental and financial impacts. Hussain Bahia, a professor of civil engineering at UW-Madison, says that it is because asphalt is so common that we have much to gain from making it more eco-friendly. As part of a new national research program called the Asphalt Research Consortium (ARC), Bahia will use $5 million in funding to study ways of making asphalt more environmentally sustainable. According to Bahia, one of his first goals is to develop so-called "cold mix" asphalts for widespread introduction into the US. Places like Africa and India have used them for decades, and research shows they can save up to seven times the energy of their hot mix counterparts. However, Bahia believes the greatest challenge will be to show through advanced design of these materials that the performance is equal to that of hot asphalt.

Asphalt is a byproduct of oil refining and its thickness means that in places like the United States and Europe, it's first heated to temperatures as high as 300 degrees Fahrenheit, making it easy to pump and apply. Other parts of the world have taken a very different approach such as in South Africa where it is made workable by shearing it into fine particles, and then mixing it with water and soap-like chemicals called surfactants. The surfactants keep the asphalt in solution until it's laid, after which it hardens to form the road surface. Studies by Canada's Office of Energy Efficiency and others have found that paving with these cold mixes (also called emulsions) saves significant amounts of energy, especially when combined with recycling efforts. These asphalts also cut emissions of carbon dioxide and other gases.

A number of issues still remain for cold mix asphalt and Bahia hopes his research can address those problems. Eventually he'd like to experiment with adding materials to cold mixes, such as polymers or plastics, which can make pavements quieter, safer and more durable. These "modified" asphalts are the major thrust of a new campus center he's establishing called the Modified Asphalt Research Center (MARC). The first step is to develop quality control tests and standards that will encourage industry to adopt cold mix asphalts. This means defining the critical ways in which these asphalts fail, and designing systems for detecting the failures. The final step will involve simulating various climate conditions in the laboratory to see how failure limits change with freezing cold or blazing heat.

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