Deicers are materials which either inhibit the formation or accumulation of ice on various surfaces. The chemistries of such products are different but they primarily function by lowering the freezing temperature of water. In physics, a common phenomenon is “the elevation of boiling point and depression of freeing point” when salts (and other materials) are dissolved in water. Deicers, when applied, either prior to or after a snow event, dissolve in the moisture (in snow), thus depressing the freezing temperatures of water. The use of deicers has been essential for climatic conditions where snow or frozen moisture on pavements may pose a traffic or pedestrian hazards. Even after snow removal, the pavements are treated with deicers to melt the residual ice.
For their selection, the following main criterion is considered.
- The deicing capability for the frequently encountered climatic conditions.
- The rate of the ice melting for the safety of pedestrian and vehicular traffic.
- The environmental consideration.
- The least degree of damage to the pavement.
In the following discussion we will highlight only the common types of deicing materials that are used on pavements and road surfaces.
1. Rock Salt– Known by other names, table salt, sodium chloride, rock salt is most widely used deicer. It is readily available, least expensive, and suitable for most climatic conditions. Its efficiency, however, is inferior to other materials on most of the criterion described in the foregoing section. It is slow, does not work well below +20°F (-7°C), and is damaging for plants and vegetation, and is corrosive to metals, like other chloride-based deicers.
2. Calcium Chloride (CaCl2) – As a deicer, calcium chloride is 13 times faster than rock Salt. It is six (6) times more expensive but melts up to eight (8) times more snow, pound for pound. The speed of snow melting is attributed to the heat generated (exothermic) when it combines with water to form the deicing solution with water. It Its lowest effective temperature, -25°F (-32°C), is far below than that of other common deicers. Highway studies have shown that calcium chloride/salt/abrasives mixture achieves faster bare pavement conditions in 85% of applications 30°F (-1°C). It has also been established that such deicers, with lower freezing temperatures, reduce pavement distress (cracks, potholes, etc.) due to lesser number of freeze thaw cycles, meaning less damaging than rock salt. Certain commercial variations based on calcium chloride claim to have marginal effects on grass and vegetation.
3. Magnesium Chloride (MgCl2) – Although the chemistries are similar, magnesium chloride, pound for pound, is only half as effective at similar to calcium chloride. It also generates heat (exothermic) but not as much calcium chloride. It has a lowest effective temperature of 0°F (-18°C).
4. Calcium Magnesium Acetate (CMA) – CMA is expensive and is typically sold in blends with rock salt and other filler. Its lowest effective temperature is +20°F (-7 C), similar to that of rock salt. The deicing function is not through formation of a brine solution with water, but not allowing the snow particles to stick together thus causing slippery surfaces. It is considered most environmentally friendly deicer.
Frequently Asked Questions
How do deicing materials affect the performance of sealcoating and crack sealers?
1. Effects on sealcoating:
a. Rock Salt will have the minimal effect on the sealcoating. Surface abrasion of the sealcoating may be an issue depending upon the frequency of salting and snow removal. More is disused later.
b. Calcium chloride may react with sealcoating due to the exothermic reaction between Calcium Chloride and water. It may soften and may become permanently imbedded in the sealcoating, thus rendering the sealcoating prone to re-emulsification under future rain events. Magnesium chloride is not as potent a deicer as Calcium Chloride, therefore, its effects are less sever but, similar.
2. Effect on Crack Fillers:
a. Hot pour crack fillers being composed of primarily, polymers, rubbers and asphalt, are not known to have been damaged by de-icing salts. There may be minimal surface damage, if any at all such crack filler.
b. Cold pour crack fillers, being composed of emulsified asphalt, fillers and rubbers may not be affected by rock salt but are liable to be attacked by calcium chloride or magnesium chloride for the reason given in the foregoing paragraphs.
c. This is more of a pre sealcoating issue. When large amounts of salts are used during a season the residue is left on the asphalt surface, in the cracks and pitted surface of the asphalt. It is very hard to remove with standard cleaning practices such as brooming and blowing. It really needs power washing before sealcoating and crack filling, otherwise the imbedded salt tries to bleed, seen as white streaks much later.
What may be the extent of damage to sealcoating and crack fillers at the end in spring, after winter deicing.
a. Rock salt- surface abrasion of the sealcoated surface may be a matter of concern, depending upon the frequency of salting and snow ploughing and traffic. Rock Salt in most cases is harsh and starts premature break down of the coating due to the sharp, angular edges, grinding into the coating as cars drive over the salt before it has melted or in the case of when the surface is pre salted on a dry surface before the snow comes down and wets the surface and the salt melts.
b. Calcium chloride, magnesium chloride and calcium magnesium acetate (CMA)- Overall minimal surface damage but erosion/reaction with concrete surfaces may be a matter of concern in areas where the salt may be unevenly used. CMA has the least degree of reactivity with concrete. Its mode of effectiveness is not through a chemical reaction but not allowing the snow particles to stick together thus causing slippery surfaces.
Which deicer type is better/safer-
a. Best for seal coated surfaces- In the order of preference; liquid calcium chloride, CMA and Rock Salt.
b. Effectiveness; Calcium chloride, CMA and rock salt.
c. Potassium Chloride and Urea are common ice melters that are often perceived as safe products to use around vegetation. Both need to be used at a slightly higher rate of application, with Urea melting to 15o F and Potassium Chloride melting to 12o F. Urea does not contain chlorides, so it is less corrosive and safer for use on concrete containing rebar and around steel structures. This is one of the preferred ice melters for airports.
Written by Girish C. Dubey and Brent Kilbarger