How salt works and overview of deicing chemicals
| Solid deicers work by lowering the freezing point of water, creating a brine with the chloride that bores through snow and ice and breaks the bond between ice and the pavement. The exact choice of ice melt product to use is dependent upon the pavement temperature, current conditions and moisture or precipitation. Rock salt will melt ice to around 15 degrees. For a comparison of different deicers, see this table |
Winter weather conditions in Minnesota can cause icy roads and walkways, leading to dangerous conditions for drivers and pedestrians. In order to combat this situation, municipalities, businesses, and individuals often employ the use of deicers. A deicer is a substance that melts or prevents the formation of ice, and does so by lowering the freezing point of water and preventing a bond between ice and paved surfaces. A study by Marquette University found that deicing roads with salt reduces accidents by 88 percent and injuries by 85 percent (Kuemmel and Hanbali, 1992).
While deicers have the ability to greatly improve road and walkway safety, they can also have negative effects on the environment and surrounding infrastructure. Once applied, deicers move with melt water to our surface and groundwater. In addition, some deicers are corrosive and will negatively impact roads, bridges, and other structures, as well as automobiles. Efforts are underway to minimize these environmental and infrastructure impacts, including optimizing deicer application and using of alternative deicing chemicals. Despite these negative effects, the benefits of deicers to public safety ensures they will be utilized for years to come.
The Iowa Department of Transportation prepared a winter maintenance training series that includes a video titled How Deicing Chemicals Work.
Contents
Overview of Deicing Chemicals
Several different types of deicing chemicals exist. Those covered in this section include chloride-based deicers, acetate-based deicers, and carbohydrates. A list of the chemicals approved for use by the Minnesota Department of Transportation (MnDOT) can be found here. Link here for a discussion on environmental impacts of deicers.
Chlorides
The chloride-based deicers discussed in this section are sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2). In general, chloride-based deicers are the least expensive and most used deicers on the market.
- Sodium Chloride. Sodium chloride is the most common deicer used in Minnesota and across the U.S. (Sleeper, 2013). The Water Resources Center at UMN estimates that 403,600 tons of road salt are used each season in Minnesota, and that 249,100 tons of road salt are used in the TCMA (Overbo et al. 2019). Sodium chloride(rock salt) is a granular product. It is used to make brine (liquid sodium chloride) and there are many additives that can be mixed into brine to enhance its performance. The lowest practical melting temperature for dry rock salt is 15 degree pavement temperature (Local Road Research Board, 2012).
- Magnesium Chloride. Magnesium chloride can be purchased as either flakes, pellets, or a liquid. Magnesium chloride’s lowest practical melting pavement temperature is -10°F.
- Calcium Chloride. Calcium chloride can be purchased as either flakes, pellets, or as a liquid. Its lowest practical melting pavement temperature is -20°F (Local Road Research Board, 2012).
- Complex Chloride Minerals: These are products mined from the earth that are not pure rock salt but rather have a variety of other minerals mixed in. Overall they have been shown to increase performance in colder pavement temperatures as compared to rock salt. [ http://clearroads.org/wp-content/uploads/dlm_uploads/FinalReport_CR.13-02_Revised-Apr16_with-cover.pdf Chloride Liquid Agricultural By-Products and Solid Complex Chloride/Mineral Products].
Acetates
Acetate-based deicers are often used in areas where the use of chloride-based deicers is limited. Acetate-based deicers include calcium-magnesium acetate (CMA), potassium acetate (KAc), and sodium acetate (NaAc). Much of the information provided here is based on studies and experiences using CMA.
Advantages of acetates include the following.
- Marginally corrosive to steel (Fortin, et al 2014).
- Biodegradable (Road Research Board, 2012)
Disadvantages of acetates include the following.
- Reacts with and corrodes zinc so it would affect galvanized steel (Fortin, et al 2014).
- Potentially results in anoxic conditions as they break down (Levelton Consultants Ltd., 2008).
- Requires more material relative to salt to get comparable ice melting. An extra 20 to 70 percent more by weight is estimated to be needed (NRC, 1991).
- Does not perform as well as chloride based deicers at pavement temperatures below -5°C during heavy snowfall and freezing rain events (NRC, 1991).
Acetates include the following.
- Calcium-magnesium acetate (CMA). CMA is probably the most common acetate-based deicer. It can be purchased as either a powder, crystals, pellets, or liquids. CMA has a lowest practical melting pavement temperature of 20°F (Local Road Research Board, 2012).
- Potassium Acetate (KAc). KAc is usually purchased as a liquid and has a lowest practical melting pavement temperature of -15°F (Local Road Research Board, 2012).
Carbohydrates
Carbohydrate-based deicers are an agricultural product often made from the fermentation of grains or the processing of sugars such as cane or beet sugar (Rubin et al., 2010). Small quantities of carbohydrates are sometimes used with other deicers.
There are pros and cons about blending an agricultural additive into your brine or rock salt. Alone, carbohydrates do not aid in melting ice or snow. Agricultural products may have short term negative environmental impacts, including noticeable algal blooms or fish kills. However, mixed into chloride products, they have the potential to reduce deicer application rates and increase deicer performance for a variety of situations. The most common positive aspects of these additives include the following (Fortin et al, 2014; Rhodan and Sanburn, 2014).
- interference with ice crystal formation
- reducing the freeze point of your brine
- increased "sticking" to surfaces
- reducing corrosion
For information on this topic, see Understanding the Effectiveness of Non-Chloride Liquid Agricultural By-Products and Solid Complex Chloride/Mineral Products at the ClearRoads website.
Waste stream products
Other deicer options include free or low-cost cheese brine, pickle juice or other industry by-products on your surfaces for anti-icing or deicing. However, these should not be used without taking appropriate steps. Steps to take before using a waste stream product include but are not limited to the following [1].
- Determine if each batch of the waste product is consistent in chemical make up
- Determine the side effects of this product
- Determine what must be blended with it and in what amount to achieve optimal performance
- Get approval to apply it in your area
- Test it in a small area and learn how it works
Link here for additional information
Summary
Table summarizing of properties of deicing agents. Adapted from Local Road Research Board, 2012, Ketcham et al., 1996 and Levelton Consultants Ltd., 2008.
Link to this table
| Category | Type | Lowest Practical Melting Pavement Temperature | Potential for corrosion impairment3 | Environmental Impact | |||||
|---|---|---|---|---|---|---|---|---|---|
| Atmospheric Corrosion to Metals | Concrete Matrix | Concrete Reinforcing | Water Quality/Aquatic Life | Air Quality | Soils | Vegetation | |||
| Chloride Based Deicers | Sodium Chloride | 15°F | High; will initiate and accelerate corrosion | Low/moderate; Will exacerbate scaling; low risk of paste attack | High: Will initiate corrosion of rebar | Moderate: Excessive chloride loading/metals contaminants; ferrocyanide additives | Low: Leads to reduced abrasives use | Moderate/High: Sodium accumulation breaks down soil structure and decreases permeability and soil stability; potential for metals to mobilize | High: Spray causes foliage damage; osmotic stress harms roots, chloride toxicosis |
| Calcium Chloride | -20°F | High; Will initiate and accelerate corrosion; higher potential for corrosion related to hydroscopic properties | Low/moderate; Will exacerbate scaling; low risk of paste attack | High: Will initiate corrosion of rebar | Moderate: Excessive chloride loading; heavy metal contamination | Low: Leads to reduced abrasives use | Low/Moderate: Improves soil structure; increases permeability; potential for metals to mobilize | High: Spray causes foliage damage; osmotic stress harms roots, chloride toxicosis | |
| Magnesium Chloride | -10°F | High; Will initiate and accelerate corrosion; higher potential for corrosion related to hydroscopic properties | Moderate/high: Will exacerbate scaling; risk of paste deterioration from magnesium | High: Will initiate corrosion of rebar, evidence suggest MgCl2 has the highest potential for corrosion of chloride produces | Moderate: Excessive chloride loading; heavy metal contamination | Low: Leads to reduced abrasives | Low/Moderate: Improves soil structure; increases permeability; potential for metals to mobilize | High: Spray causes foliage damage; osmotic stress harms roots, chloride toxicosis | |
| Acetate Based Deicers | Calcium Magnesium Acetate | 20°F [2] | Low/moderate; Potential to initiate and accelerate corrosion due to elevated conductivity | Moderate/high: Will exacerbate scaling; risk of pate deterioration from magnesium reactions | Low; probably little or no effect | High: Organic content leading to oxygen demand | Low: Leads to reduced abrasives use | Low/Moderate: Improves soil structure; increases permeability; potential for metals to mobilize | Low: Little or no adverse effect; osmotic stress at high levels |
| Potassium Acetate | -26°F [3] | Low/moderate; Potential to initiate and accelerate corrosion due to elevated conductivity | [4] | Low; probably little or no effect [5] | High: Organic content leading to oxygen demand | Low: Leads to reduced abrasives use | |||
| Sodium Acetate | 0°F [6] | Relative aquatic toxicity: high | |||||||
| Carbohydrates | Beet Juice | NA | Low; Potential to initiate and accelerate corrosion due to elevated conductivity clams of mitigation of corrosion require further evaluation | Low; Probably little or no effect | Low; Probably little or no effect; claims of mitigation of corrosion require further evaluation | High Organic matter leading to oxygen demand; nutrient enrichment by phosphorus and nitrogen; heavy metals | Low: Leads to reduced abrasive use | Low: Probably little or no effect; limited information available | Low: Probably little or no effect |
| Molasses | NA | ||||||||
| Corn Syrup | NA | ||||||||
Related pages
- Overview and impacts of road salt and deicers
- Smart Salting Best Management Practices (BMPs)
- Management tools
- Smart Salting (S2) training program
- Educational resources for Smart Salting (S2)
- Cost-benefit considerations for Smart Salting (S2) and road salt winter maintenance
- Case studies for Smart Salting (S2) and road salt winter maintenance
- Chloride TMDL projects
- Links for Smart Salting (S2) and road salt winter maintenance
- References for Smart Salting (S2) and road salt winter maintenance