CALCIUM CHLORIDE VS. MAGNESIUM CHLORIDE
Performance on Snow and Ice
- Claim: Both materials effectively melt ice and snow to -32C (-25F)
FACT: Calcium chloride works well down to this temperature, while the melting action is impractically slow at this point. Melting temperature is a confusing area. 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).
- FACT: Magnesium chloride can clog equipment as temperature drops. The effectiveness of MgCl2 is often limited by the presence of magnesium sulphate as an impurity. Magnesium sulphate crystallizes between -18C (0 F) and -20.5C (5F) to cause sludge in tanks and clogging of spray nozzles and transfer umps. By contrast, a 32% CaCl2 solution, the most commonly used concentration in winter, does not form crystals within its working range (down to -29C or -20F).
- Claim: Magnesium Chloride is a more effective ice melter.
FACT: Calcium chloride actually melts more ice between -18C and -1C (0 F and 30F). 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 after 5 minutes and 132% better after 30 minutes.
FACT: Calcium Chloride penetrates ice faster than magnesium chloride.
The Midwest Research Institute study also evaluated ice penetration. This factor is critical because ice melters must punch through ice and packed snow to break their bond with the pavement so plows can remove them. The study 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 after 30 minutes.
FACT: Calcium chloride has a lower application rate.
Given their relative commercial strengths and active chemical purity, 50% to 100% more MgCl2 than CaCl2 is usually required to remove equal amounts of snow and ice. Liquid CaCl2 is applied at concentrations of 32% to 38%, while that for MgCl2 normally falls between 21% and 28%. Similarly, dry CaCl2 flake contains a minimum 83% active chemical versus dry MgCl2 which is at 48%. Conceptually, this means that two parts of CaCl2 does more work in less time than three parts of MgCl2.
- Claim: Magnesium Chloride is less damaging and has less impact on concrete.
FACT: Magnesium chloride is more detrimental to concrete.
MgCl2 suppliers claim less spalling than other deicers based on a test developed by SHRP. This method, which was designed to screen deicers quickly, does not correlate to the real world because it uses substandard, non air-entrained concrete and only 15 freeze-thaw cycles. The test sacrifices accuracy for speed. SHRP recognized this, and in the manual that discusses this laboratory test, it notes that “field testing is ultimately required to determine acceptable deicer performance and compatibility.”
More realistic testing was done by the Pittsburgh Testing Laboratory on air-entrained concrete (prepared according to ASTM C 672-91) over 500 freeze-thaw cycles. The data shows that CaCl2 has the least spalling of common deicers, including MgCl2. Spalling is measured on a scale of 0 to 5 (none to severe). A 4% solution of MgCl2 showed moderate scaling and had a 3.1 rating. The same concentration of CaCl2 had a 1.6 rating, or between very slight and slight to moderate scaling. This is borne out in American Concrete Institute’s guide to Durable Concrete, which says CaCl2 has a “negligible” effect on concrete while MgCl2 causes a slow deterioration of concrete surfaces. In addition, a study of concrete deterioration by deicing salts, including MgCl2 and CaCl2, at Iowa State University found that “magnesium chloride was the most destructive salt with severe deterioration produced under almost all of the experimental conditions.” Deterioration was judged by the degree of crumbling, fracturing and brownish discoloration.
FACT: Magnesium chloride is more corrosive to the metals found on roadways.
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. In addition, there are additives that provide even greater protection for concrete reinforcements, bridge decks, metal rebar in parking structures and metal highway components. These can reduce corrosion by more than 70% when compared to standard road salt.
- Claim: Magnesium is less toxic and has less impact on vegetation and the environment.
FACT: Magnesium chloride is more toxic.
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.
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.
FACT: If anything, Magnesium chloride is more harmful to vegetation.
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.
FACT: Magnesium chloride appears to be more harmful to the environment.
Chloride ions (not the element chlorine) are generally considered when looking at adverse effects on the environment. When the two materials are compared equally (on a dry weight basis that removes all water), MgCl2 has 74% chloride while CaCl2 has 64% chloride. When the two compounds are used in equal amounts, MgCl2 thus adds about 15% more chloride to the environment than CaCl2. Also, since MgCl2 is a less effective ice melter than CaCl2, MgCl2 adds even more chloride to the environment because more must be used to achieve the same degree of ice control as a given amount of CaCl2.
Tests with calcium chloride by Quebec’s Ministry of Environment found “no definite areas of environmental problems … subject to the use of good application practices”. In addition, CaCl2 is a clean, inorganic material that does not leave an oily or powdery residue after its use.
References to Reports/Studies
Handbook of Chemistry and Physics, Chemical Rubber Company.
McElroy, AD, CC Chappelow, G Cooper and JA Gail. “Melting and Penetration of Magnesium Chloride and Flake Calcium Chloride Deicers”. Transportation Research Board 75th Annual Meeting. Jan.1996
SGS Testing Services Data. Unpublished report, 1995.
Chappelow, CC, Ad McElroy and RR Blackburn, “Handbook of Test Methods for Evaluating Deicers”. Strategic Highway Research Program, 1992.
Pittsburgh Testing Laboratory, Unpublished report.
Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals. ASTM C 672-91.
Guide to Durable Concrete, American Concrete Institute, 201.2R-92.
Cody, Robert D, AM Cody, Pg Spry and GL Gan, “Concrete Deterioration by Deicing Salts: An Experimental Study”. Chiefly funded by the Iowa Dept. of Transportation, Project # HR-355.
NACE Corrosion Data Survey, Metals Section. Third Edition.
Corrtrol Services. Unpublished study.
Registry of Toxic Effects of Chemical Substances, Lewis RJ SR, Sax’s Dangerous Properties of Industrial Materials. Ninth edition, 1998.
Ministry of the Environment, Province of British Columbia, File: 10-3-3-20: 1990.
Rase, Thomas J, “Calcium Nutrition Affects Cold Hardiness, Yield, and Fruit Disorders of Apple and Pear Trees”. Journal of Plant Nutrition, 19(7), 1996.
Bogemans, J, L Neirincks and JM Stassart, “Effect of Deicing Chloride Salts on Ion Accumulation in Spruce: Plant and Soil, 113. 1989.
Letter from LT Hubbard, PE, Director of Municipal Liquid and Environmental Waste Branch, Environmental Protection Division, Quebec Ministry of the Environment to the Ministry of Transportation.
By Pollard Highway Products, Ltd. Copyright © 2012