How to thaw icy roads without rusting cars
Boston — Even in the middle of summer's heat, public works departments are thinking winter. They're testing de-icing chemicals and paving materials as alternatives to road salt.
The quest for a new way to de-ice roads stems largely from environmental side effects of road salt. Salt may help speed the melting process, but it also pollutes water supplies, corrodes cars, and helps cause potholes.
Dr. Lloyd Smith, Federal Highway Administration (FHwA) research chemist, says that costs from salt damage are extensive - especially in the Northeastern United States, where about 90 percent of all road salt is used. Although experts say it is impossible to assess the costs fully, vehicle damage is estimated at $ 3 billion a year.
Among possible alternatives to salt, CMA, a combination of calcium and magnesium acetates, is currently receiving the most attention. In 1978, researchers commissioned by the FHwA reported that CMA most nearly duplicated the de-icing properties of salt without salt's side effects.
Probably 10 years of research is needed before will CMA replace any portion of the 10 million tons of salt annually spread, according to experts.
To begin with, there is a cost problem. Estimates on the price of CMA run from seven to 25 times that of road salt, which sells for $20 a ton. The acetic acid used in CMA production is relatively expensive, says Dr. W. Clayton Ormsby, an FHwA research chemist.
Several processes might reduce the cost of the acid. Dr. Smith says that acetic acid can be produced from used newsprint. However, he notes that there may not be enough waste newsprint to meet demand.
Scientists at SRI International, an international consulting research company , are testing a fermentation process to make the acid from corn. Acetic acid can also be produced from natural gas, where this product is widely available and inexpensive. Dr. Michael Economides, a petroleum engineering professor at the University of Alaska, is testing the process. He says that CMA might eventually drop to $150 a ton if manufactured in this way.
Dr. Economides says that CMA should not have to meet the same cost standards as salt because the substitute mixture saves costly automobile, bridge, and road repairs.
CMA would be especially useful in Alaska, where airplanes are used for much transportation, Dr. Economides points out. Airports cannot coat icy runways with salt because of the damage it would do to airplane engines.
Iowa's Department of Transportation (DOT) is testing another cost-reducing method: extending CMA by coating it on sand.
Coating has other advantages, says Charles L. Huisman, Iowa DOT's state materials engineer. The dark sand aids melting on sunny days. Also, the gritty mixture can be spread more easily than can plain CMA, which he says ''looks like baking soda that's been in the refrigerator too long.''
Besides considering cost, Dr. Smith of FHwA notes that the chemical has to be tested for possible environmental effects. ''We want to make sure we are not replacing one problem with another,'' he says.
California's DOT is studying how CMA affects roadside vegetation, soils, and water supplies. No environmental problems have yet been identified. However, most results are not in, says Earl Shirley, manager of physical and environmental studies at the state agency.
Meanwhile, two other road salt alternatives are being studied.
One is rubber asphalt, a paving mixture of tiny pieces of old tires in asphalt. According to David Esch, the chief of highway research for Alaska, rubber asphalt ''looks like small raisins sticking out of a cookie.''
Rubber asphalt breaks and deflects ice when ice is under pressure from vehicles. Tests in Alaska have shown that rubber asphalt decreases automobiles' breaking distances by a fifth, according to Esch.
The cost of rubber asphalt - one and a half times that of plain asphalt - limits its potential use. But Esch says lab tests show the mixture may last much longer than plain asphalt.
If so, rubber asphalt will be useful everywhere, he says. Otherwise, it might be best used on bridge decks, according to Esch.
Another de-icer, Verglimit, is incorporated in asphalt paving. Verglimit surfaces depend on heavy traffic to wear the road surface and expose tiny pellets of the material. Here again, the material is expensive. It can double the cost of a road surface compared to standard concrete, Dr. Ormsby says.