In 2009 and beyond, elevated costs combined with fiscal and materials shortfalls — think salt shortages — may well continue. Managing the winter animal without going broke requires taking a second look at current and past practices as well as new approaches.
Using liquid anti-icers and de-icers closes the gap between services needed and what an agency can afford to provide. For example, pre-wetting salt with a de-icer solves the basic problems inherent in spreading a granular material from a moving vehicle onto a static surface: The particle bounces when making contact with the pavement, while traffic and wind blow dry particles off the pavement.
In tests conducted by the Michigan DOT, 60% to 70% of dry salt remained on the pavement. But when pre-wet, salt retention rose to 96%. This means operators can cut salt usage by 26% to 36% without affecting effectiveness, resulting in significant cost savings while maintaining a predetermined level of service.
Just as important, pre-wetting also reduces stress on the environment, making it a best-management practice. Because less salt is used, the amount of corrosive salt potentially entering surface water is reduced. Further, adjacent soil and vegetation isn't subjected to elevated levels of airborne chemical contamination. Read on for more about the benefits of winter liquids.
ANTI-ICING: BEFORE THE STORM
Applying anti-icing liquids to pavement before an event can prevent, or at least reduce, snow-pack and ice bonding. When done properly, anti-icing minimizes black ice and frost formation on bridge decks and pavements.
Winter crews must know how and when to use this tool. Using the right product at the right time in the right amount affects success levels significantly. Too small an application amount will have little to no effect. Excessive application can result in slippery conditions. And if rain is expected — which typically washes the winter liquid away, rendering it ineffective — choose a different snow-fighting method.
To know how and when to apply these liquids, crews need to be trained. The Federal Highway Administration (FHWA) and the American Public Works Association (APWA) offers several training programs.
To help personnel determine the right amount of product to use, manufacturers of anti-ice units offer systems that match desired spread rates to the varying speed of the vehicle. Plus, storm management programs such as customizable, computer-based Maintenance Decision Support Systems (MDSS), provide route-specific weather forecast information and treatment recommendations. For more information on MDSS, go to www.fhwa.gov.
PRE-WETTING FOR MORE EFFECTIVE SALT
In this process, de-icing liquids such as salt brine are applied to salt particles, rather than the pavement itself, as spreading takes place. Pre-wetting improves service levels because it speeds the ice-melting process and often eliminates the need for additional application of materials.
A dry particle of salt placed on a dry surface just sits there until it absorbs enough thermal energy from the surrounding environment to the point where a liquid is formed on its surface. Applying blended liquids or salt brine (sodium chloride) to particles jump-starts the solution process. The initial brine formation then triggers the solution to the rest of the salt. By pre-wetting, the salt solution process starts working immediately.