Calcium Chloride Programs

Many chemicals are used for freeze conditioning and to control dust on unpaved roads.  Two of the most frequently used options are calcium chloride and magnesium chloride.  Below is a deep dive into how the two materials compare in various applications.

 

Road Dust Control

Calcium chloride and magnesium chloride are both hygroscopic (moisture attracting) materials that draw moisture from the air to provide extended dust suppression.  Liquid magnesium chloride and liquid calcium chloride exhibit similar water attraction properties. The dust control performance of both CaCl2 and MgCl2 is based on their ability to keep road surfaces damp.

 

When applied to a gravel road, calcium chloride and magnesium chloride suppress dust by attracting moisture from the air, creating a solution that dampens the road surface. Once CaCl2 and MgCl2 are applied to a gravel road surface, the solution volume in the road surface changes as it seeks equilibrium with the moisture content of the air. If relative humidity is high, the solution volume grows. If conditions are dry, the opposite occurs. Calcium chloride remains liquid in hot, dry weather, extending dust control under conditions when magnesium chloride solidifies and provides little if any dust protection.

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Environment Canada has published best practices that recommend an application rate of 1.4 to 2.3 l/m2 of magnesium chloride to achieve the same dust suppression capability as calcium chloride applied at a rate of 0.9 to 1.6 l/m2. The USDA Forest Service found that a magnesium chloride application rate of 0.30 to 0.50 gal/yd2 was necessary to achieve the same dust suppression performance as 0.20 to 0.35 gal/yd2 of calcium chloride.

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Melting Ability

Freeze conditioning can be a convoluted space.  Many suppliers quote the lowest temperature at which their product melts ice in a laboratory (the eutectic point), rather than what is practical in the field.  While MgCl2 has a eutectic of -33C (-28F), its melting rate drops to a low level well before it reaches this temperature. CaCl2, with a eutectic point of -51C (-60F), still has substantial ice melting ability between -23 and-32C (-10 and -25F).

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This was clearly shown in a Midwest Research Institute study (based on FHWA, Strategic Highway Research Board test methods). The study found that at -7C (20F), CaCl2 flake melted 29% more ice after 10 minutes and 42% more ice after 30 minutes than did MgCl2 flake. At -15C (5F), the difference was 25% after 30 minutes.  The results were even more dramatic in a study by SGS Testing Services. At -18C (0 F), CaCl2 flake melted 40% more ice than MgCl2 flake 5 minutes after application. This increased to 75% after 30 minutes. At -1C (30F), CaCl2 was 50% better  thjan MagCl after 5 minutes and 132% better after 30 minutes.

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The ability for a product to penetrate frozen material is critical to performance.  The Midwest Research Institute study also evaluated ice penetration and found that at -7C (20F), CaCl2 has 22% more penetration after 10 minutes and 38% after 30 minutes than MgCl2. At -15C (5F), CaCl2 had penetrated 58% more ice than MagCl after 30 minutes.

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Corrosiveness

The Corrosion Data Survey published by the National Association of Corrosion Engineers indicates that MgCl2 is more than twice as corrosive to 304 stainless steel than CaCl2. The NACE survey also indicates that MgCl2 can be 10 times more corrosive to mild steel than CaCl2. 

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Environmental Impact

Although CaCl2 and MgCl2 are considered non-toxic, the Registry of Toxic Effects of Chemical Substances states that MgCl2 has nearly three times the toxicity of CaCl2 on a common measure of toxicity.  The Ministry of the Environment in British Columbia found that CaCl2 has significantly less toxicity than MgCl2 in bioassay tests on rainbow trout and the water flea daphnia. For instance, rainbow trout, which represent the high end of the food chain, were five times more sensitive to MgCl2 than to 35% CaCl2.

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Both materials are used as micronutrient sources in animal feeds. CaCl2 is also a common food ingredient and is “Generally Recognized as Safe” by the US Food and Drug Administration. It is found in such foods as beer, cheese, canned tomatoes, olives, cherries and pickles.

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Both materials are used in fertilizers. Beyond this, CaCl2 is sprayed on fruit trees and vegetables to provide calcium uptake. In fruit trees, for instance, this improves cold hardiness, reduces fruit disorders and boosts yields. And, an evaluation of how deicing salts affect spruce trees found that CaCl2 aids beneficial potassium uptake, while chloride levels increased with MgCl2.  After the first year of a two-year study on how deicers affect turf grass at Iowa State University, MgCl2 was found to be more detrimental than all other deicers except urea.