Ice-Control Choices

Dec. 28, 2000
Gravel and salt used to be the mainstay of ice-control regimens for most DOTs. However, the world has become increasing sophisticated, and so have the methods of controlling ice on bridges and pavements. Prewetting salt has grown in popularity; this process increases the efficacy of salt, which is an especially large concern when temperatures begin to plummet.

Another trend is the increased use of nonsalt deicers, such as calcium chloride and calcium magnesium acetate (CMA).

Gravel and salt used to be the mainstay of ice-control regimens for most DOTs. However, the world has become increasing sophisticated, and so have the methods of controlling ice on bridges and pavements. Prewetting salt has grown in popularity; this process increases the efficacy of salt, which is an especially large concern when temperatures begin to plummet.

Another trend is the increased use of nonsalt deicers, such as calcium chloride and calcium magnesium acetate (CMA). While Andy Briscoe, director of public policy at the Salt Institute, Alexandria, Va., says alternative deicers have not hurt the salt industry-he projects record salt use next winter-the use of such materials is on the increase.

In response to this growing demand, Cryrotech Deicing Technology, Leawood, Kan., began the expansion of its CMA manufacturing facility in Fort Madison, Iowa. This expansion will allow the company to upgrade its equipment to produce a product that is shaped differently than the spherical look of the past.

"Physically, this CMA will be a relatively flat and rigid angular granule that more closely resembles road salt," explains Roxanna Huffman, Cryotech operations manager. "We expect it to work faster than the original product and to say in place better once it hits the [road] surface." The company plans to start up the new process during the second quarter of the year; the new CMA formulation should be available for shipment in June.

CMA was originally identified by the U.S. FHWA in the late '70s, when the agency was looking for a low-corrosion alternative to road salt that was safe to use. Today, CMA is often selected for environmentally sensitive areas (such as roadways through wetlands) or for areas where corrosion or concrete spalling is a concern.

The deicer is known to cause virtually no steel corrosion; one of its lesser-known qualities is its low impact on concrete. A recent study by the United Kingdom Department of Transportation concludes, "With the exception of CMA, all of the deicing chemicals tested in this investigation resulted in a greater deterioration of the concrete than water alone in the freeze/thaw cycle." The test included 3% solutions of deicers such as salt (sodium chloride) and calcium chloride (chart, above).

As a result of this test and others, states such as Iowa, Michigan and West Virginia have designated certain bridges as "salt free" structures; the only deicer permitted on these structures is CMA. In Oregon and Washington, liquid CMA is a fundamental ingredient in environmentally sensitive winter maintenance programs.

Cost is always a primary concern for DOT and other state agencies, especially in these times of federal and state "fiscal belt-tightening." CMA has often been perceived as a costly alternative; however, the experiences of the Oregon DOT and Washington DOT show that, economically, liquid CMA can be competitive with salt-if used properly. While the cost of granular CMA remains higher than that of common salt, CMA's price will probably dip as demand-and supply-for the product rises.