|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 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. Sodium chloride for example, which is one of the most commonly used deicing agents, can be used to reduce the freezing point of water to 15°F (Local Road Research Board, 2012). 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 dissolved in the melting snow and ice are carried away with runoff to surface and/or 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.
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.
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 deicers on the market.
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.
Disadvantages of acetates include the following.
Acetates include the following.
Carbohydrate-based deicers are 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. Alone, carbohydrates do not aid in melting ice or snow; however, their use can help reduce the freezing point of ice further than salt and can help salt stick better to the road surface (Fortin et al, 2014; Rhodan and Sanburn, 2014). Carbohydrates are not corrosive to steel, and at high concentrations, carbohydrates can act as a corrosion inhibitor for salt brines.
There is evidence that the use of carbohydrates in the United States is increasing. For example, sales of a beet based product called Beet Heet were around 900,000 gallons at the end of the winter season in 2013. By February of 2014, 1.5 million gallons of Beet Heet had been sold. The Morton Arboretum in Lisle, Il uses beet juice in their deicers. The beet juice additive has minimal environmental affects, and helps the salt stick where applied. With the addition of beet juice, the arboretum is using nine times less salt, and saving an estimated $14,000 in material costs (The Morton Arboretum, 2014). Another unconventional additive that has been used is cheese brine. Wisconsin has used a cheese brine in at least six counties in the state (Rodan and Sanburn, 2014).
Fu et al. (2012) looked at two beet molasses-based deicers in comparison with a salt brine deicer. When used as a prewetting material, there was no statistically significant difference between any of the chemicals. When used as an anti-icing material, the organic material performed 30% better.
|Category||Type||Lowest Practical Melting Pavement Temperature 1,2||Potential for corrosion impairment3||Environmental Impact3|
|Atmospheric Corrosion to Metals||Concrete Matrix||Concrete Reinforcing||Water Quality/Aquatic Live||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||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||-15°F||Low/moderate; Potential to initiate and accelerate corrosion due to elevated conductivity||Low; probably little or no effect||High: Organic content leading to oxygen demand||Low: Leads to reduced abrasives use|
|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|