ANTI-ICING TECHNOLOGY By WILLIAM T. SUNLEY, Engineer of Local Roads and Streets Credits to: Technology Transfer Center, Van Vieregge, Program Development Technician and Willy Scheller, Program Coordinator.

Anti-icing is the practice of preventing the formation of bonded snow or ice to the pavement by timely applications of a chemical freezing-point depressant. This proactive approach differs from conventional de-icing practices which requires the application of a melting agent as a reaction to the accumulation of snow and ice on the pavement.

The anti-icing practice has become a viable strategy as a result of field-tests conducted in 15 states during the winters of 93/94 and 94/95. These tests were sponsored by the Federal Highway Administration (FHWA) as a continuation of a Strategic Highway Research Program (SHRP) project. Though not a new concept, the FHWA/SHRP program dramatically advanced this practice using a variety of equipment and materials, notably liquid anti-icers.

Anti-icing is a systematic approach to winter road maintenance that can be adapted to an agency's unique conditions and available tools. It includes three critical components: operations, decision making and personnel. The operations component consists of the winter maintenance forces' capability for the timely application of chemicals to the roadway in a solid, prewetted solid, and/or liquid form. This component also includes plowing accumulated snow and ice from the pavement so that a second application of chemicals can be applied to a clear-as-possible pavement surface if necessary. The equipment and materials needed to support these activities consists of spreaders, anti-icing materials, solid and liquid chemical storage facilities and plows with appropriate cutting edges. Anti-icing materials include liquid sodium chloride, liquid calcium chloride, liquid magnesium chloride, liquid calcium magnesium acetate, liquid potassium acetate and fine-graded salt prewetted with some liquid. Some liquids are used to prewet salt, and some are sprayed directly on the road surface as the anti-icing agent.

Decision-making components necessary to support anti-icing include weather service forecasts, real-time conditions of pavement surfaces and road weather information as determined from road weather information systems if available, nowcasting (the use of real-time data for short-term forecasting), traffic information, information on present pavement observations and friction measurements from patrols, and post-storm evaluations of treatment effectiveness. Anti-icing demands accurate, local weather and storm prediction data. Applying the material on the roadway too early or too late may be wasteful and ineffective.

The personnel component consists of stand-by and call-in procedures, and staff trained to use available weather and pavement data in the decision making process. After the initial application of anti-icing material, personnel, materials and equipment must be

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available and prepared for re-application as the conditions dictate.

One major benefit to be derived from the use of anti-icing technology is a better understanding of the conditions under which anti-icing operations should, and should not be used. Additional benefits are:
• Improved efficiency and effectiveness of highway agencies' winter maintenance operations and cost savings in time, labor, materials and equipment.
• Improved vehicle traction and consequently, highway safety during winter-time conditions.
• Improved levels of service of highways during winter-time conditions.
• Reduction in certain locations of the U.S. in the quantity of materials (both chemicals and abrasives) used in snow and ice control,
• Reduced environmental and infrastructure impact of snow and ice control operations in sensitive areas.
• Improved knowledge concerning the use of liquid chemicals and prewetted solids in anti-icing operations.

The FHWA/SHRP field tests have shown that while an anti-icing strategy may not be appropriate for every storm, it is a valuable tool for fighting some winter storms, for pavement frost control operations and to help eliminate "black ice" conditions. The tests indicate that anti-icing materials are most effective when applied prior to the pavement temperature reaching the freezing point and remain effective until temperatures reach -6 degrees C (20 degrees F). For storms initiating at or continuing into temperatures below -6 degrees C (20 degrees F), agencies should switch to their deicing program. High winds, heavy drifting and prolonged heavy snow conditions have also limited the effectiveness of anti-icing practices. However, applying anti-icing chemicals to the pavement prior to the storm will hinder the snow pack from bonding to the pavement and will aid in snow removal once conditions improve.

Several agencies participating in the tests noted that anti-icing must be a team effort and that everyone associated with the anti-icing process must be involved from the very beginning. Everyone must understand the new technology and the expectations of new methods to achieve the desired results. The more information everyone has the easier it is to establish a program which achieves a higher level of service at potentially less cost. Total team involvement also provides a greater chance of program success.

Another important element of any anti-icing program is advance public information. The public seeing chemicals spread (especially if the chemical is liquid) before the snow accumulates will generate some inquiries if not complaints. Advance information can turn negative attention into positive public reaction. •

Page 16 / Illinois Municipal Review / November 1996