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.
Some agencies buy pretreated salt; others apply liquids to the salt at the time of delivery before storing it. Many advise applying additional liquids during storm operations. The method of pre-wetting and the location of the application point vary considerably.
For high-volume applications, many mangers advocate applying liquid in the controlled environment of the auger in an under-tailgate spreader, which achieves a pug mill type of mix. The process of multiple spray points and elevations in a V-body spreader chute also improves product mixing and provides consistent application. Manufacturers of spreader control systems now match the speed of the vehicle to the desired spread and liquids application rate as determined by the operator.
High-volume liquid systems can also be combined with roller systems that spread slurry, further reducing lost granular material. This process uses less salt while taking advantage of inexpensive site-produced liquids.
ONSITE BLENDING = COST SAVINGS
Winter liquids have evolved from the choice of three or four single-component products to blends of multiple components. Some manufacturers promote their products as effective in severe-cold conditions, while others emphasize “green” qualities.
The key when evaluating a product is to ask, “What will provide the level of service desired for the conditions present?” Cost and availability must also be factored as well as the environmental and infrastructure impacts.
Every storm event is different, and conditions — i.e., temperature, precipitation, type of storm event — drive which product or blend best fits. For example, multi-product liquid blends of 85% salt brine, 10% agricultural protein, and 5% calcium chloride are used extensively in the Midwest because the recipe has proved successful for the region's typical pavement temperature ranges of 18° to 32° F. But this blend may not be so effective in colder temperature ranges with different humidity levels, and it would definitely be overkill in warmer regions. The key is using the right product or blend at the right time.
Although agencies can purchase pre-blended liquids, onsite blending provides flexibility and cost savings. Transportation costs are higher for ready-to-use winter liquid products, as most are diluted. With concentrations varying from 23% to 55%, you are basically paying for water. Agencies that blend onsite can get more product for their buck by purchasing higher-concentrated products using state, county, and city agreements, locking in price and delivery dates.
Onsite production systems pay back in two to three seasons, with the service life directly related to routine maintenance. Onsite production of 23% brine (including equipment, labor, and materials) routinely falls in the range of 6 to 14 cents/gallon.
Whatever product or blend you're considering, review the product for certification with an organization such as the Pacific Northwest Snowfighters (PNS). These organizations ensure that consistent testing protocol and practices are used to provide nonbiased statistics. PNS documentation will assure you of product performance, corrosiveness, handling practices, and environmental impact.
No one product, or blend of products, will fit all your needs and funding. Extremes will take place that are well outside your plan. One of the products you have on hand — that may routinely be a component in your blended-product operation —may be the single product that best addresses the conditions present.
— Williams is a retired Illinois DOT field technician and co-author of IDOT's practices and procedure manual on liquids for snow/ice control. He owns Concept to Project Management, a design-build consulting firm, and presents winter operations seminars for public agencies nationwide.
How to move from being “storm fighters” to “event managers.”
Developing a combined approach of blended winter liquids, trained staff, storm management practices, and proper equipment reduces costs by about a third.
When developing a service level plan for winter maintenance, review the history of pavement temperatures, types of precipitation, inches of snow received, and average number of events per year. This helps determine how many pounds of salt will be needed to melt a determined amount of snow for the upcoming season.
Add the service target — for instance, to have arterial roadways clear at all times and enough snow removed from residential roads to maintain public safety — to generate parameters for determining how many and what kinds of trucks, plows, end loaders, de-icing products, liquid and granular products, and staffing are needed in a particular situation. Don't forget meteorological services that provide a blueprint of what to expect with each storm.
After all your investigation, remember that you must also have salt storage equal to a full season's average needs.