Archive for Wednesday, January 12, 2011

Five Questions: Breaking the ice

Melting products can carry some risk

Ice-melting or de-icer products can be effective in the battle against Old Man Winter if used correctly. But if they are overused or misapplied, they can damage concrete as well as nearby plant materials, including lawns and shrubs.

Ice-melting or de-icer products can be effective in the battle against Old Man Winter if used correctly. But if they are overused or misapplied, they can damage concrete as well as nearby plant materials, including lawns and shrubs.

January 12, 2011

Kansas State University Research and Extension Service answers these questions about de-icers.

Q: What materials are used in ice-melting products?

A: There are five main materials that are used as chemical de-icers: calcium chloride, sodium chloride or salt, potassium chloride, urea and calcium magnesium acetate.

Q: What’s the most popular?

A: Calcium chloride is the traditional product that has been used most often. It is one of the most frequently used materials for road and highway de-icing, and it is effective. It will transform ice into a slippery, slimy surface. This product is effective to about minus 25 degrees. Plants are not likely to be harmed unless excessive amounts are used.

Q: What about salt?

A: Sodium chloride is the least expensive material available. It is effective to approximately 12 degrees but can damage soil, plants and metals.

Q: Is something similar to vinegar also being marketed as a de-icer?

A: Calcium magnesium acetate, or CMA, is a newer product that is made from dolomitic limestone and acetic acid, the main compound found in vinegar. CMA works differently than other materials in that it does not form brine like salts, but rather helps prevent snow particles from sticking to each other on the surface. It has little effect on plant growth or concrete surfaces. The product works best when temperatures remain about 20 degrees.

Q: Are any of these de-icers better than the other?

A: All of these products are acceptable for use. Limited use of any of these products should cause little damage. Problems occur when de-icers are used excessively and there is not adequate rainfall to wash or leach the material from the area.

Comments

sawman 3 years, 3 months ago

Just don't let anybody use magnesium chloride on your concrete.

How Magnesium Chloride Damages Concrete: One must have a fundamental knowledge of concrete in its hardened state. Concrete, when setting from a plastic to hardened condition, goes through a number of chemical reactions. Basically, hardened concrete consists of two major chemical compounds; calcium-silicate-hydrate and calcium hydroxide. Actually, the reaction products from cement hydration with water are very chemically complex, but for the purposes of this review, we will stick to the basics. When concrete is to be exposed to severe freezing, it is standard practice to entrain a system of microscopic air bubbles in concrete mixtures typically occupying a volume of 5-8%. The purpose of this air-void system is to provide space for the increased volume that water will occupy as it becomes ice. If one were to look at concrete under a microscope in the range of 3000X, this entrained air would look very much like a wasp nest. Magnesium chloride for deicing is effective in reducing the temperature at which water freezes. The problem begins as the magnesium chloride comes into contact with the now deiced concrete surface and remains contained in the melt water, and permeates into the concrete. While deicing salts containing sodium, potassium and calcium are chemically innocuous to concrete, this is not true of magnesium. The magnesium ions accumulate and react with the cementitious compound calcium- silicate-hydrate converting it to magnesium-silicate-hydrate (or a mineral called brucite), which is non-cementitious in nature. In other words, a fundamental major mineralogical product of solidified concrete has now been chemically altered (completely changed). Formation of magnesium-silicatehydrate breaks down the “glue” that binds aggregates together and concrete surfaces begin to deteriorate. The net effect is we now have a chemical and physical attack that concrete is not designed to withstand, nor be subjected to.

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