How salt works and overview of deicing chemicals

How do deicers work?

Deicers work by lowering the freeze point of water. There are many factors to be considered when choosing a deicer, one of the most important factors is the pavement temperature and pavement temperature trend. For example, Rock salt can melt to -6 oF pavement temperatures but the colder the pavement the slower it works. A best practice is to avoid using dry rock salt at pavement temperatures below 15 oF because it is too slow. The most common approach to speed up the melting processes is to add a liquid deicer to your granular product or use straight liquids (DLA - Direct Liquid Application). Liquids are much faster acting than granular products. They type and gradation of your granular product also will influence the speed of melting. If you commonly have salt left on dry pavement after the snow is gone it is time to revisit your strategies. One easy step is to attend the smart salting training classes where you will learn more about deicer selection and application rates. Link to smart salting training calendar. 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. Deicers are used to combat this situation. 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 soils, vegetation, and infrastructure. By integrating scientific principles into winter maintenance, we can reduce deicer use while not decreasing safety. Despite many 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 education series that includes a video titled How Deicing Chemicals Work.

A list of the chemicals approved for use in deicing by the Minnesota Department of Transportation (MnDOT) can be found here. Link here for a discussion on environmental impacts of deicers and deicing additives.

Chloride deicers

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. Magnesium chloride is often used as a blend rather than as a straight product.

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). Calcium chloride is often used as a blend rather than as a straight product.

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. Chloride Liquid Agricultural By-Products and Solid Complex Chloride/Mineral Products.

Non-chloride deicers

There are several categories of non-chloride deicers (acetates, formates, glycols, succinates, and urea). Non-chloride based deicers are less commonly used than chloride based deicers on roadways, parking lots, sidewalks and trails due to cost and availability. Airports use almost entirely non-chloride based deicers. Bridge spray systems, parking ramps and areas with low corrosion goals often turn to non-chloride products

Acetates for deicing

In Minnesota, acetates are more commonly used in winter maintenance of roads then other non-chloride deicers. Within the acetate family there is sodium acetate, calcium magnesium acetate, and potassium acetate (KAC).

• Calcium-magnesium acetate (CMA). CMA 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).

Potassium acetate has received the most attention for roadways. It is being used in automated bridge deicing systems and the Minnesota Department of Transportation (MnDOT) District 1 is running a KAC only route in the Duluth area. Because of the cold temperature range effectiveness and increased use and success of this product, studies are underway to better understand the side effects of KAC on the environment and infrastructure (MnDOT and UMN St. Anthony Falls Laboratory; Xie et al., 2017.

Airports are more heavily invested in non-chloride deicer use than the road/parking lots/sidewalk maintenance industry, with potassium acetate being the leading liquid runway decier, sodium acetate being the leading granular decier, and glycols commonly used for airplane deicing. For more details visit Snow and Ice control for airport operations. For an overview of the use and study of non-chloride deicers see Field Usage of Alternative Deicers for Snow and Ice Control and Chloride Free Snow and Ice Control Material, 2014.

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).

Deicers from waste stream products

Waste stream products for deicing have historically included chloride- and non-chloride compounds. Other deicer options include free or low-cost cheese brine, pickle juice or other industry by-products 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

For more information, see the following.

• Reuse of Aqueous Waste Streams For Transportation-Related Applications
• Clearroads testing and quality assurance criteria

Deicing additives

Carbohydrates are an additive to deicers and 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.

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 deicer use
• Information on costs and economic impacts of road salt
• Management tools
  • Minnesota Statewide Chloride Management Plan
  • Smart Salting Assessment tool (SSAt)
  • Model Ordinances
  • Model Snow and Ice Policies
• MPCA Smart Salting Training Program
  • Smart Salting Training Program
  • Smart Salting Training Calendar
  • Resources for Winter Maintenance Professionals
  • Chloride Reduction Assistance
• Education Resources
  • Educational resources for Smart Salting (S2). For more information on chloride resources, see Statewide chloride resources
  • Success stories: salt reduction and cost saving examples
  • Technical reports and Chloride TMDLs
  • Chloride and NPDES Permits
• References for Smart Salting (S2) and road salt winter maintenance
• Chloride and groundwater
  • Impacts of stormwater infiltration on chloride in Minnesota groundwater - White paper produced for the Minnesota Groundwater Association
  • Calculator for estimating chloride loading to groundwater
  • Guidance for calculator to estimate chloride loading to groundwater from infiltration