By Deborah Parker
The proverbial bend in the road may soon have a little bounce to it, thanks to polymer scientists at the University of Massachusetts Amherst. Alan J. Lesser of the Department of Polymer Science and Engineering at UMass has discovered a way to take discarded plastic milk jugs and soda bottles, melt them down, and use the resulting polyolefin goo to add a little give to the asphalt used to pave highways. The result is a stronger, stretchier highway that can better survive the freeze and thaw cycle of a New England winter. What’s more, the poly-goo seems to make asphalt more impervious to the heat of a Texas summer as well. The new technology promises safer driving conditions, reduced costs for contractors - and the municipalities that pay them - and last, but not least, a significant reduction in the amount of traditional asphalt required to maintain the nations roadways.
Rich in environmentally threatening napthenes and asphaltines, asphalt is basically left over oil that cannot be refined further for any other useful purpose. Its a toxic mess, Lesser explains. Yet contractors put more than seven million tons of these materials on Massachusetts highways and roads each year. Weve had to tolerate the toxins because asphalt is all we had to work with. And, quite simply, people really wanted roads.
The roads people got, however, often left much to be desired. Federal Highway Administration specifications required only that a certain grade of asphalt be used to pave its roadbeds; contractors in New England thus used the same AC-20 that contractors in Texas did. In New England, the material grew brittle in the cold, cracked, and eventually caused the potholes that wreak havoc on the suspension systems of cars. In hotter climates the asphalt would melt, causing waves in the road that didn’t do the suspension systems much good either, not to mention releasing more of those napthene fumes into the environment.
Scientists had tried using plastics to address some of these problems, but the resulting mixes just didn’t work. The plastic would rise to the surface - Think no traction! Lesser says with a smile - and the composites would eventually crumble. Lesser wanted to know why, and what polymer science could do about it. Armed with funding from NETI and the corporate support of Shell Oil and Morton Chemical, Lesser launched an investigation into the polymer/asphalt failure.
The answer? Size counts, says Lesser. The researchers discovered that if the recycled plastics are ground to the correct particle size - much smaller than the particles tried in earlier experiments - the polymers would stay in solution within the asphalt blend, while offering a significant increase in road surface strength and flexibility. The team is now continuing its research so that exact recipes for the additives can be given to meet the diverse roadbed demands of the nation.
Basically, here in Massachusetts, were figuring we can replace about five percent of the asphalt now used with the polymer additive, which has no toxicity associated with it. While five percent may not sound like a lot, when you realize that some seven million tons of asphalt is now used in roads and on roofs just in Massachusetts each year, you’re talking about a meaningful reduction, Lesser notes. And when you multiply that by 50 states, youve got a significant reduction in toxic impact. You’re also increasing the life-span of all these roads by many years, reducing the need to repave them, and all the energy consumption that goes into that.
Lesser’s research has also attracted the attention of some companies that don’t have anything to do with asphalt at all. Solutia - which makes the nylon fiber for carpets - wants to know if discarded carpets could be melted down and used to fill the nations roadbeds. Which got Lesser to thinking that the manufacturer also produces the nylon filaments used to strengthen radial tires. So now I'd be delighted to undertake further research on behalf of a tire company, if any are interested, Lesser concludes. If we can melt down tires? Not only would the fire hazard, the environmental hazard posed by tire dumps, be addressed, but the concept just appeals to me, he notes. Ashes to ashes, tires to roads, it just has a nice ring to it, don’t you think?
The research means recycled polyolefins - the plastics used in milk jugs and soda bottles - can successfully be used as an additive in asphalt road covering. The polyolefin additive has no toxicity associated with it, and adds increased strength and flexibility to the roadbed. Researchers now want to explore whether used carpeting - and even used tires - could be turned into a roadbed additive, or high-tech roofing materials, as well.
While five percent may not sound like a lot, when you realize that some seven million tons of asphalt is now used in roads and on roofs just in Massachusetts each year, you’re talking about a meaningful reduction. And when you multiply that by 50 states, you’ve got a significant reduction in toxic impact.
Dr. Alan J. Lesser
UMass Amherst