Deicing and Winter Maintenance
Salt and sand are two traditional materials used in winter maintenance to combat snow and ice. Salt is used to melt snow and ice while sand is applied to provide traction for cars and pedestrians. When snow and ice melt, the water becomes stormwater runoff, which eventually ends up in local water bodies such as lakes and rivers. As the runoff moves over paved surfaces, it collects sand, salt, and other materials and deposits them into surface waters, causing adverse effects on the environment. In addition, salt and sand also have the potential to cause building and infrastructural deterioration.
To address these issues, the University of Michigan (U-M) created the Salt Use Improvement Team (Salt Team) in 1995. By researching alternative ways to melt snow and ice, the Salt Team is working to reduce the amount of salt and sand used without jeopardizing pedestrian safety and the environment. The Salt Team has developed Best Management Practices (BMPs), used alternative chemicals, tested alternative equipment, and employed alternative procedures to allow snow removal crews to use salt and sand more effectively.
Impacts of Salt and Sand
Salt and sand have traditionally been perceived as the cheapest and most effective materials for de-icing surfaces such as highways, walkways, and parking lots. However, many people do not realize that they have hidden impacts that can detract from their overall effectiveness. Even when applied in relatively small quantities, salt can:
- Deplete the oxygen supply needed by aquatic animals and plants
- Leach into the ground and change the soil composition, making it hard for plants to survive
- Leach into the groundwater, which sometimes flows to surface water; both are sources of drinking water
- Deteriorate paved surfaces, buildings, infrastructures, and the environment
- Bury the aquatic floor life, fill in habitats, and cloud the water
- Erode the stream banks and other landscapes as it is carried to the surface waters by stormwater runoff
- Cause premature deterioration of floor surfaces as it is tracked into buildings
- Lose its effectiveness after becoming embedded in snow and ice
- Enter catch basins, storm drains, and surface waters if it is not swept up each spring
- Contribute to plugged storm drains, which can cause flooding
Snow and Ice Removal Techniques
When de-icing products are applied to snow and ice covered surfaces, a brine solution is created. As the brine solution penetrates through the icy surface, it lowers the freezing point of the water and disrupts the bond between the pavement and the snow or ice. Once the bond is broken, the removal equipment is able to remove the layers of snow and ice more easily.
Anti-icing works on the same principles as de-icing by using a brine solution to lower the temperature at which water freezes. However, anti-icers are applied prior to snowfall to prevent snow and ice from bonding to the pavement ; it is easier and quicker to prevent a bond from forming than to break a bond that has already formed. Anti-icing techniques also usually require less de-icing materials than traditional practices.
Snow and Ice Removal Product Selection
It is important to note that each de-icing and anti-icing product has unique abilities in lowering the freezing point of water. The following questions may be used to decide which type of product is most appropriate for a particular situation:
- Does snow or ice need to be removed? If so, how much?
- What is the surface temperature (surface temperature is lower than air temperature)?
- Will the surface be exposed to the sun, or shaded by trees or buildings?
- What is the temperature range when the deicing product is most effective?
- How much product is needed to be effective for a given temperature range?
The use of different products may be preferable depending on the temperature. Some products are more effective at lower temperatures than other products. The amount of product that is needed for de-icing will increase with lower temperatures and increased precipitation.
LIQUID DE-ICERS AND GRANULAR DE-ICERS
Before granular de-icers can melt snow and ice, they must first dissolve to form a brine solution. If the air temperature or the temperature of the pavement is below freezing, water may be unavailable to dissolve the granular de-icer, thus reducing its effectiveness. This can be avoided by applying a liquid de-icer or a pre-wetted solid de-icer.
There is also a difference between liquid and granular de-icers in terms of the amount of material that is applied. While liquid and pre-wetted de-icers often remain on the surface they are applied to, granular de-icers have a tendency to "bounce" off surfaces and be moved by vehicles and plows. As the material is shifted to untargeted areas, plow operators are required to make additional passes over the affected surfaces. As a result, more material is needed when using granular de-icers.
Common De-icing Chemicals*
|Sodium Chloride (Rock Salt), NaCl||Use:||Plain
Wetted w/ CaCl 2
Wetted w/ NaCl Brine
|Advantages:||Low purchase price|
|Disadvantages:||Can be corrosive to concrete and structural steel in bridges and cars
Potentially harmful to roadside vegetation
Can contaminate surface water and drinking water supplies
|Notes:||Workhorse of De-icing chemicals
Works to 15 degrees F
Sodium Chloride (salt) Brine, NaCl
Pre-wetting other chemicals
|Advantages:||Low purchase price
Little to no residue on pavement
Doesn't draw moisture, so doesn't leave road wet and slick
|Disadvantages:||Corrosive to concrete and cars and bridges|
|Notes:||Used primarily as pre-wetting and/or anti-icing agent
Works to 15 degrees F
|Calcium Magnesium Acetate (CMA), Ca(O2CCH3)2, Mg(O2CCH3)2||Use:||CMA liquid mixed with salt or sand
|Advantages:||Less corrosive than salt
Reduces corrosion on steel bridges
|Disadvantages:||Use twice as much CMA as salt
High concentrations can reduce oxygen levels in streams and lakes
Pavement appears wet
|Notes:||Best thing going from an environmental standpoint
Works to 15 degrees F
|Magnesium Chloride, MgCl 2||Use:||Sprayed directly on road
Mixed with sand or other de-icers
|Advantages:||Attracts moisture from the air, which hastens dissolving and melting
Does not require post distribution clean up
Doesn't appear to contribute to air pollution
|Disadvantages:||Keeps pavement wet if it attracts too much moisture from the air
Corrosive to metal
|Notes:||Liquid used as an anti-icing agent when air temperatures exceed 10 degrees F
Can be applied to busy streets and intersections before light snow storms to melt snow as it hits the pavement
Works to -13 degrees F
Costs approximately two times more than salt
|Calcium Chloride, CaCl2||Use :||Mixed with salt
Used to pre-wet salt
Straight/alone or in solution
|Advantages:||Releases heat when it dissolves
Reduces the amount of salt used by 10-15%
Attracts moisture so it helps snow melt
Less harmful than salt to vegetation
Keeps pavement wet
Corrosive to metal
Leaves residue harmful to carpet
|Notes:||Can be used to pre-wet salt
Sprayed in approximately 32% solution for winter use
Must be covered and kept in a dry place
Works to -25 degrees F
Costs approximately three times more than salt
|Potassium Acetate, KO2CCH3||Use:||Used as a pre-wetting agent for solids like sand, salt, urea, sand, or CMA|
|Advantages:||Requires fewer applications
Performs very well
Safer than salt for structural steel and reinforcing steel
Noncorrosive and biodegradable
Could cause slickness on pavement
Lowers oxygen levels in bodies of water
|Notes:||Liquid works best as a de-icer if applied in narrow bands
May be used alone if needed
Work to -75 degrees F
Costs approximately eight times more than salt
|Carbohydrate Based Solution (corn or beet based)||Use :||Liquid typically mixed w/ MgCl2 and other salts|
No adverse effects on roads and infrastructures
|Disadvantages:||Some products may have an odor|
|Notes:||Liquid is thick
Biological and environmentally safe
Contains agricultural by-products
|Disadvantages:||Clean up cost of sediment in storm drains|
|Notes:||Some products are available that have a mix of other de-icing materials and sand|
*Chart adapted with permission from: Technology News, August 1995, Iowa Transportation Center, Iowa State University; Safer De-icing Chemicals - Home Steading. Mother Earth News, December 2003; and the University of Minnesota Extension Service Yard & Garden Brief: Effects of De-icers on Trees and Shrubs.
Note: Material Safety Data Sheets are only required to list ingredients if 1% or greater of the material is contained in the product. Therefore, please be aware that there could be trace amounts of other chemicals or metals within anti-icing/de-icing mixes.
Snow and Ice Removal at the University of Michigan
SALT USE IMPROVEMENT TEAM
In 1995, U-M established the Salt Use Improvement Team (Salt Team) to research alternative ways to melt snow and ice in conjunction with salt and sand, without jeopardizing pedestrian safety and the environment. The team was comprised of representatives from Building Services, Grounds and Waste Management (G&WM), the Office of General Counsel, Risk Management, Plant Operations, the School of Natural Resources and Environment, and Occupational Safety and Environmental Health (OSEH). Using the input from all these groups, G&WM has started to implement the alternative methods discussed and created by the team. G&WM and OSEH continue to look for alternative de-icing practices and improving the implementation of these practices.
The team developed Best Management Practices (BMPs) in order to help snow removal crews to use salt and sand more efficiently, reduce its overall use, and minimize its undesirable effects. BMPs currently used include: closing areas that are not frequently traveled; initiating night time snow removal crews; training snow removal crews in effective salt and sand application; alternative de-icing products; anti-icing techniques; and innovative application equipment.
UM PILOT PROJECTS
U-M started testing alternative de-icers and anti-icers in the 1995-1996 winter season. Since then, U-M has implemented calcium magnesium acetate (CMA) in granular form; potassium acetate; magnesium chloride in granular and liquid form; and carbohydrate based solution (corn or beet by products). These materials are less corrosive, more effective, and less harmful to the environment than other products currently available.
CMA works best as an anti-icer because it leaves a residue on the pavement, thus preventing any future precipitation from bonding. However, due to its spherical shape, it is difficult to walk on and often rolls off dry surfaces.
Potassium acetate works well as a de-icer and anti-icer. Like CMA, it leaves a residue on the pavement allowing it to work as an anti-icer. When it is applied as a de-icer, it starts to melt the ice immediately. However, its effectiveness is somewhat reduced where the ice is covered with snow. Also, the high initial cost of potassium acetate and the cost advantages of other alternative products prevent U-M from using it.
With its competitive price and low freezing point, magnesium chloride works well as both a de-icer and anti-icer. It contains a corrosion inhibitor making it less damaging to concrete than other products and it is less harmful to the environment than calcium chloride and sodium chloride. However, magnesium chloride does have some disadvantages. One hidden cost is its corrosive effects on floors. Magnesium chloride can be inadvertently tracked into buildings and deteriorate the floors. The cost of replacing floors and increased cleaning services can detract from the overall cost effectiveness of this product. Also, magnesium chloride must be agitated periodically to keep the product in suspension. If over applied, the surface can become even more slippery than wet pavement.
Carbohydrate based solution (corn or beet by products) blended with magnesium chloride can be used both as a de-icer and anti-icer. The product U-M purchases comes pre-mixed at 10% Carbohydrate based solution / 90% Magnesium chloride. U-M has been adding this solution to a 23% salt brine at 10%. This final product gives us the low cost benefits of salt brine and the additional benefits of working at lower temperatures. When using carbohydrate based solutions, surfaces become less slippery or even tacky. Carbohydrate based solutions are most effectively used when mixed with magnesium chloride. This mixture is less corrosive than using only magnesium chloride. Carbohydrate based solutions are also less expensive than some other alternative products.
In addition to testing alternative de-icing and anti-icing chemicals, U-M has also been investigating different mechanical equipment for removing snow and ice. This element of the program focuses on reducing injuries and expenditures while increasing the level of service and improving environmental quality.
The Bobcat Toolcat below has been outfitted with a rotary broom and 200 gallon sprayer to perform a “one pass operation”. They are able to sweep the snow and apply liquid de-icers at the same time. They can also be outfitted with mowers and other attachments for summer use. This ability saves us additional manpower and equipment. U-M plans on purchasing more of these units in the future.
The pickup truck mounted sprayers below are used to apply de-icers or anti-icers to sidewalks and plazas. The hydraulically driven sprayers have a six-foot spray boom mounted on the bumper of the truck. They are also equipped with a hose reel for steps and entryways.
The salt truck below is equipped with state-of-the-art ground speed control, ambient air and pavement temperature monitors, and pre-wetting equipment. The ground speed control equipment regulates a consistent flow of material out of the chute at any speed. The ambient air and pavement temperature monitors alert the operator of areas where snow and ice could potentially be bonded to the pavement. The monitors may also alert the operator to areas that do not need a large amount of de-icers or anti-icers, such as steam tunnel areas or areas not shaded by trees.
The 950 gallon liquid tanker truck is also equipped with the same controls listed above. It has the ability to apply liquid de-icers directly to the roads and parking lots at rates from 10 gallons per lane mile up to 150 gallons per lane mile. U-M uses this for anti-icing before the storm as well as direct applications to smaller, warmer snowfalls and transporting liquid de-icers to various storage tanks on campus.
The snow melting machine is used to collect and melt the shoveled snow in parking lots and on the top of parking structures. This machine has two major benefits. First, it eliminates the need to use dump trucks to haul the snow away, which would otherwise melt, refreeze and occupy valuable parking space. Second, it prevents sand from entering the stormwater drainage system and surface waters. As the snow melting machine melts the snow, the water is separated from the sand. The water is then diverted to the stormwater system while the sand is collected for reuse or proper disposal. By using this machine, less salt and sand are needed in parking lots and on tops of parking structures. It consequently reduces the amount of sweeping needed each spring, the amount of salt and sand entering the surface waters, and the possibility of parking structure deterioration.
FUTURE OF SALT REDUCTION ON CAMPUS
By establishing the Salt Use Improvement Team, U-M has been able to research and implement alternative ways to melt snow and ice in conjunction with salt and sand while still concentrating on pedestrian safety and the environment. The team's goal was to reduce the salt used in winter maintenance activities by half. This reduction goal was based on an average annual use of 2600 tons per year.
The goal for salt reduction was set at 50% of the ten-year average salt usage dating from 1989 to 1999. In 2002-2003, salt use was reduced by 35% of this average. In 2004, salt use was reduced by 42% of this average. Since 2001, the use of sand has dropped from 483 tons to less than 15 tons by alternatively using liquid de-icers.
The University of Michigan continues to expand its de-icer and anti-icer alternatives program while continuing to promote Best Management Practices to minimize deterioration to buildings, infrastructures, and the environment.