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Road Management & Engineering Journal
Copyright © 1997 by TranSafety, Inc.
February 1, 1997
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402

FHWA Field Tests Anti-Icing in 15 States: New Winter Maintenance Methods Look Promising
Iowa's Old-fashioned, Corny Snow Fences
Army Corps of Engineers "Pothole Primer" Is a Good Source Booklet

Prewetting with Salt Brine for More Effective Roadway Deicing

Iowa's use of salt brine to prewet deicing salt has been so effective in the Council Bluffs, Atlantic, and Des Moines areas that the Iowa Department of Transportation is buying salt brine systems for its 30 garages that service interstate highways. In the October 1995 issue of Technology News, the Iowa Transportation Center at Iowa State University described the background for this decision.

Iowa has found that "prewetted salt . . . works faster and at lower temperatures than does dry salt, with less waste." Instead of bouncing off the road or being swept away by traffic like dry salt, prewetted salt clings. Using less salt saves money and exposes the environment to fewer toxic chemicals. In addition, prewetted salt works under conditions that render dry salt ineffective. Roadway salting only performs effectively when moisture releases the heat from dissolving salt. At temperatures below freezing, prewetting insures moisture will be present to dissolve the salt. Salt alone would not do the job.

Since the late 1960s, Iowa has used liquid calcium chloride to prewet salt. Calcium chloride remains wet at low temperatures and is itself a deicing agent. However, it leaves the road wet even after snow and ice have broken up, resulting in blowing snow sticking to the road and creating a hazard to drivers. Calcium chloride costs about 63 cents a gallon. Although salt brine's freezing temperature is not as low as calcium chloride's (salt brine freezes at about -6 degrees Fahrenheit), salt brine has a much lower freezing temperature than salt alone. In addition, when ice and snow are gone, salt brine leaves a dry pavement. Finally, salt brine costs only about 6 cents per gallon, a considerable savings over calcium chloride.

The salt brine system Iowa will use in its garages has a 600-gallon stationary salt-brine maker. In addition, 60-gallon prewetting applicators will be mounted on highway department trucks. The truck-mounted applicators spray a 23 percent solution of salt and water onto rock salt as it goes to the spinner. A brine maker costs about $5,000, and an applicator about $1,100. Given the savings in materials costs, Tom Donahey, Iowa Director of Maintenance Programs, estimated the systems will pay for themselves in a year.

Donahey pointed out that overhead bar systems can also be used to spray brine on truckloads of salt; however, these systems would be less effective because the prewetting is less uniform. Emphasizing the importance of prewetting the salt in some manner, Donahey said, "In fact, just wetting down a load of salt with a water hose is preferable to laying down dry salt."

Technology News invited readers to contact Tom Donahey at (515) 239-1388 for information about salt-brine prewetting systems. Information about building a brine maker is available from Charles Pickett, highway maintenance supervisor at the Iowa Department of Transportation Des Moines garage. Pickett's telephone number is (515) 225-3322.

Copyright © 1997 by TranSafety, Inc.

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