How salt works and overview of deicing chemicals

How do deicers work?

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

File:Ice melting from road salt.png

Deicers lower the freezing point of water, resulting in melting of ice when weather conditions are favorable.

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.

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.

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 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].

1. Determine if each batch of the waste product is consistent in chemical make up
2. Determine the side effects of this product
3. Determine what must be blended with it and in what amount to achieve optimal performance
4. Get approval to apply it in your area
5. 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
  • How salt works and overview of deicing chemicals
  • Environmental impacts of road salt and other de-icing chemicals
  • Other impacts of road salt use
• Smart Salting Best Management Practices (BMPs)
  • Snow and salt storage
  • Salt application BMPs
  • Technology-based deicing BMPs
  • Non-chloride chemical alternatives for deicing
  • Emerging and non-traditional deicing BMPs
• Management tools
  • Chloride Management Plan
  • Winter Maintenance Assessment tool (WMAt)
• Smart Salting (S2) training program
  • Winter Parking Lot and Sidewalk Maintenance Manual
  • Winter Parking Lot and Sidewalk Maintenance Factsheet
  • Smart Salting (S2) training information
  • Smart Salting (S2) training certificate holders
• 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