ANTI-ICING WITH SALT BRINE: A KEY TOOL FOR WINTER MAE NTENANCE ARSENALS.
Anti-icing measures take place before snow falls and ice forms on the roadway. They aim to prevent the bond of frozen precipitation to the road surface. In some circumstances, anti-icing can dramatically cut the cost of maintaining a safe road surface over conventional deicing. Anti-icing chemicals are supplied in liquid form (brine) to road surfaces just before a snow or ice storm. Liquid sodium chloride (NaCl) is an effective choice for anti-icing above 15[degrees]F.
* The roadway surface is never "lost." Snowfighters react proactively.
* Anti-icing returns road surfaces to normal faster, resulting in fewer accidents and delays.
* Using a liquid ice-melter jumpstarts the melting process because salt needs moisture to be effective.
* Brine does not bounce or blow off the road surface so material is more efficiently used.
* If the storm is delayed, salt residue remains on the road ready to begin work when precipitation begins.
* Crews can cover more territory by beginning treatment in advance of a storm.
* Increased efficiency results in use of less salt, minimizing environmental concerns.
SALT BRINE MANUFACTURE
Salt brine is made by mixing rock salt or solar salt with water. Brine concentration should be approximately 23 percent NaCl. The proportion of salt to water is critical to the effectiveness of the brine. Too much or too little salt affects the freeze point depressing qualities of the brine. The proper brine mixture is 23.3 percent salt content by weight. This is the concentration at which salt brine has the lowest freezing point, -6[degrees]F. It is known as the eutectic point. Salt concentration is measured with a salometer, a specialized hydrometer. Salt is added to the water until an 88.3 percent salometer reading is obtained. This results in the proper 23.3 percent salt content.
Commercial brine makers are available at a cost of about $5,000. Many agencies have less costly do-it-yourself brine makers, assembled using water tanks and PVC pipe. Brine is usually made at the local maintenance facility sites and stored in large tanks in locations convenient for loading into saddle tanks on the sides of the V-box or anti-icing equipment.
Brine applicators are commercially available for about $1,000. Some agencies have manufactured their own application equipment using large tanks and PVC piping. Some equipment is designed to be loaded onto the bed of spreading trucks, towed behind maintenance equipment, or permanently mounted on truck beds. It can be as simple as a gravity fed spraying system with an operator controlled cut-off valve or a more complex (and more controllable) pump driven sprayer system. Control should be available to vary spreading rates from 25 to 60 gallons per lane mile.
If large, horizontal tanks are used in the design, consider installing baffles inside the tanks to help prevent the liquid from suddenly shifting in the tank, creating a hazardous control situation for the operator.
Accurate weather and road surface information are critical for the efficient use of anti-icing chemicals. Road surface temperatures, precipitation amounts and form, wind conditions, and road environment (sunlight exposure, surface condition, bridges, etc.) all affect the use and application of anti-icing measures.
Understanding the freeze point depressing qualities of brine is important to its use and application as an anti-icing agent. As shown in Figure 1, the minimum freeze point of salt brine is-6[degrees]F at a concentration of 23.3 percent NaCl. Road surface temperatures are indicated on the side of the chart, solution concentrations along the bottom. The line represents the freeze point of the solution at a given temperature. The colored portion in the center of the chart shows the melting range of brine solutions. The area to the left shows the results of a solution with too little salt; the road surface will refreeze unless more salt brine or deicing salt is applied. The area to the right shows the results with too much salt, and once again the surface will freeze without the introduction of more moisture. Additional precipitation and heavy traffic can dilute the brine solution allowing the road to refreeze. Additional precipitation always results in a dilution of brine at the road surface.
Weather information is getting better with the introduction of doppler radar reports, often distributed over the Internet or to subscribers of weather service providers. Roadway information system costs continue to drop as the technology becomes more frequently deployed. Everything from air temperature, dew point, optical weather identifiers, to pavement temperature, surface status, and chemical information is available. Some agencies use remote television cameras to monitor traffic and bridge conditions. This information will help agencies accurately determine the appropriate application of anti-icers.
SUCCESS STORIES AND RESOURCES
More than 16 states regularly use anti-icing or are experimenting with how it fits into their winter maintenance programs. Leading the way are Iowa and Illinois.
Iowa was one of 15 states involved in a three-year SHRP anti-icing project starting in the winter of 1993 to 1994. Iowa chose to test salt brine as its anti-icing test material. The pilot results were so successful that Iowa continued to use salt brine and expanded its use to the point that during the 1998 to 1999 winter season IA DOT used 4.5 MG of salt brine. Its fleet of 1,000 snowplows all have the capability to apply liquid for prewetting and a number of units are designated strictly for anti-icing. For more information on Iowa's programs, contact: IA DOT Winter Operations Administrator Dennis Berkheimer in Ames at 515/239-1355 or fax 515/239-1005; Tom Donahey, director of maintenance programs at IA DOT at 515/239-1388; and Charles Pickett, highway maintenance supervisor for IA DOT, who can provide you information on building your own brine maker, 515/225-3322. The Iowa DOT has a 30-minute video of the particulars of its anti-icing operations also available.
The Illinois Department of Transportation, Division of Highways, Bureau of Operations, has produced a 68-page manual entitled, "Guidelines for Liquid Chemical Application for Snow and Ice Control." Contact Elizabeth Hawk at the Illinois DOT, 217/782-2984 for information.
The Federal Highway Administration promotes the use of anti-icing in a video titled, "The New Generation of Snow and Ice Control," which can be obtained by calling the FHWA at 202/366-1557 or faxing them at 202/366-9981.
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|Date:||Apr 1, 2000|
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