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Hitting the high points.

Last month's article on anti-icing (Anti-Icing Part One: Relieving the Pressure) addressed the questions of "What is anti-icing?" and "Why should I consider it?". The objective of this article is to answer the questions "How do ice melt products work?", "How does that impact application decisions?", and "How can I learn from experience?".

This article is not written to provide specific application guidelines. Its focus is to provide a basic understanding of how products work and a methodology to begin your own program. Application decisions for your area should come from your own experiences. This article cannot give you experience. Experience comes from your own activities. Anti-icing is not a cure-all, it is a tool that when used appropriately can provide significant savings and improved service levels.

How do ice melt products work? All ice control products work the same. Their function is to lower the freeze point temperature of water. This ability is dependent upon the percentage of chemical in solution and is expressed as the "eutectic temperature" of the solution.

Webster's defines "eutectic" as "relating to an alloy or solution or its melting or freezing point." For our purposes, let us describe eutectic temperature as the freeze point temperature of a solution based on the percentage of material in solution, not volume.

While this may seem complex, the freeze chart on an antifreeze container is an example. To explain further, let us say you have a 12-quart capacity radiator system. You fill it with 6 quarts of antifreeze and the remainder with water. This is a 50 percent solution that provides protection down to -34 [degrees] F. If you fill the same system with four quarts of antifreeze and the remainder water, the volume of material is the same. However, this 25 percent concentration protects only down to + 10 [degrees] F.

The same holds true for all ice control products. These products melt snow, which creates water and dilutes the concentration. As the concentration changes, so does melting temperature of the material. The freeze point chart shown [ILLUSTRATION FOR FIGURE 1 OMITTED] illustrates a eutectic curve for magnesium chloride.

Dilution of Solution (DOS). As the solution concentration changes, so does the temperature at which it melts ice. Dale Keep of Washington State DOT calls this "DOS" or "Dilution of Solution."

Understanding DOS provides the key for understanding how ice control products work. Specifically, an ice control product will work until the eutectic temperature of the solution meets the pavement surface temperature. At this point, the material will stop melting and refreeze. Refreeze occurs when an ice-control product dilutes to the point that it can no longer melt ice at the given surface temperature.

How does that impact application decisions? DOS is the basis for deciding how long a product application will last. Let us say, for example, that your own experience shows that it will take 0.2 in. of water to dilute your application to the point of refreezing. Let us also say that each inch of snow contains 0.1 in. of water. How long will the application last before it refreezes?

The answer: As long as it takes to snow 2 in. Two inches of snow provides 0.2 in. of water to dilute the application to the point of refreeze. If it takes 12 hours to snow 2 in., then the application lasted 12 hours. If it takes one hour to snow 2 in. then the application lasts 1 hour.

DOS also explains why one application rate will not fit all storm events. The temperature and moisture of each storm event vary, therefore, the application needed to control each storm varies.

How can I learn from my experience? To learn from the past you should first keep an accurate record of it. Documentation will enable you track the storm event, applications, and results. This information can help you understand why an application performed the way it did and make decisions for future applications.

There are many variables that can impact the success of an anti-icing application. Documenting every possible variable is cumbersome and may not provide much value. Instead, the effectiveness of any deicing chemical can be boiled down to four basic factors: surface temperature, application rate, moisture, and beginning concentration.

To be effective, you need an easy-to-use tool to document meaningful and accurate information. Dale Keep presented a tool that meets these needs during one of his training session. His TAPER chart is a tool for the person in the truck seat to track the storm event, applications, and results. TAPER is an acronym that stands for Temperature, Application Rate, Product, (Storm) Event, and Results. This information is entered on the TAPER chart.

No one application rate will work for all storm events. Your own experience will provide proper application rates. The proper application rate for one area may not be the correct one for another. Your climate crews, equipment, and cycle times all impact the application rates that are right for you. Completing TAPER charts for several different storm events will allow you to develop a customized table for your area that provides application guidelines based on precipitation and temperature.

What now? This article is a beginning point in understanding anti-icing, how it works, and how to learn from your experience. The information provided here is not enough to go out and start an anti-icing program. The following are some steps to proceed:

* Evaluate your present winter maintenance program and the potential benefits of anti-icing.

* Obtain additional anti-icing training for crews and management.

* Set up a trial program and document your activities vs. traditional practices.

* Conduct evaluations after each storm event and after the winter.

* Expand after your successes.

* Tell the public what you are doing and why.

The use of anti-icing is growing across the country. Many agencies already have realized the economic, service, and environmental benefits of including anti-icing as a winter maintenance tool. Several resources are available to help you initiate an anti-icing pilot program. To learn more about how to meet your winter maintenance objectives, contact Great Salt Lake Minerals Corporation, 8300 College Boulevard, Overland Park, Kansas 66210; telephone 913-344-9302; fax 913-338-7919.

Scott Barger is a Market Development Specialist with Great Salt Lakes Minerals Corporation, Overland Park, Kansas.
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Title Annotation:Anti-Icing, part 2
Author:Barger, Scott
Publication:Public Works
Date:Feb 1, 1997
Words:1040
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