Breaking the ice
Using ice melting compounds to clear snow and ice from walks, drives, and entries near public buildings is virtually a universal practice today. Facility maintenance personnel learned long ago that to achieve safe surfaces in the shortest time with the least total cost, ice melters are a necessity. Understandably, whenever a product category gains such widespread acceptance, the market attracts a host of suppliers looking to capture a share. As a result, there are more than 100 brands of ice melters available today. Unfortunately, many of these products are packaged with no mention of their chemical composition. Others carry labeling which specifies contents but make erroneous or misleading claims about the products’ abilities. The result is considerable confusion about the benefits and limitations of such products.
Few Actual Materials
Although there are many dozen brands of ice melter, the list of materials in common use is much shorter. It includes the following compounds:
- Sodium Chloride (rock salt)
- Calcium Chloride
- Potassium Chloride
- Magnesium Chloride
- Sodium Acetate
- Calcium Magnesium Acetate
- Ammonium Nitrate
- Ammonium Sulfate
- Various blends of the above, with and without abrasives (such as sand, etc.)
Of the materials listed, rock salt and calcium chloride are most extensively used in applications around commercial, industrial, and institutional facilities. Rock salt, calcium chloride, potassium chloride, and magnesium chloride are naturally occurring salts. Urea, ammonium nitrate, and ammonium sulfate are synthetic materials which find their most common applications as fertilizers.
How Ice Melters Work
Generally, all ice melters work in the same way. They depress the freezing point of ice or snow and turn the mixture into a liquid or semi-liquid slush. Solid chemical salts bore through ice or snow and form a strong brine solution. This brine spreads under the ice or hard-packed snow and undercuts, breaking the bond to the surface. Once loose, the ice or snow is easily removed by mechanical means. Or, in many cases, users, apply the material in anticipation of ice or snow. This prevents the bond to the surface and melts the snow or ice as it comes in contact with the brine.
Fertilizer products work in much the same manner, though they do not form a brine. All are soluble in water and the resulting solution acts by depressing the freezing point of snow and ice.
Though common deicing materials work in the same way, they vary widely in performance. The determining factors are speed, quantity of material required, and duration of melting action. Environmental considerations are also important.
Comparing Temperature Ranges
The first measure of an ice melter’s effectiveness is the range of temperatures in which it can provide deicing action (in a reasonable time period). The “practical” lowest temperature limits for these materials is defined as effective within 15-20 minutes of application and is listed next to the material. When reviewing deicing materials on the basis of their effectiveness at practical temperatures, they rank as follows:
- Calcium Chloride (-25o F)
- Magnesium Chloride (5o F)
- Sodium Acetate (5o F)
- Calcium Magnesium Acetate (5oF)
- Potassium Chloride (12o F)
- Urea (15o F)
- Sodium Chloride (20-22o F)
- Various Blends (usually 20-22o F)
In order for an ice melter to be effective, it must go into solution quickly. It is the solution which penetrates the ice or snow to provide the undercutting, not the solid material. There are basic differences in how quickly different compounds turn into a deicing brine at low temperatures. Calcium chloride and magnesium chloride are liquids in their natural states and have an affinity for returning to a liquid. Plus, when solid forms of these compounds come into contact with water, they release heat. In practice, once calcium chloride and magnesium chloride touch ice or snow, they immediately pick up water to form a strong brine, emit heat to give added deicing effect, create more water, and form more brine. This process is repeated over and over.
Sodium Chloride and potassium chloride are both solids in their natural state. When they come into contact with moisture, they also will go into solution to form a strong brine. But, in doing so, they must absorb heat from the environment. Urea, ammonium nitrate, and ammonium sulfate also go into a solution (though not a brine) when they contact moisture, but also must absorb heat before the solution can be formed.
Another measure of ice melter effectiveness is the amount of material needed to accomplish the undercutting job. Perhaps the best way to compare materials is to look at the volume of ice they are able to melt pound-for-pound within normal temperature conditions over a reasonable time period. When reviewing materials based on amount, most users will choose calcium chloride first, followed by magnesium chloride and sodium chloride.
A final measure of performance for an ice melter is how long it will provide deicing action. Obviously, the longer the ice melter acts, the less often reapplication will be required. The natural state of the chemical has the greatest effect on how long an ice melter will last. Those which are naturally liquids – calcium chloride and magnesium chloride – continue as brines longer since they resist evaporation.
Beyond physical properties, the shape of ice melters is important. Research confirms that rounder particles have distinct performance advantages. Round particles contact a smaller surface area than flakes or irregularly shaped granules, so they’re more effective at boring vertically downward rather than horizontally. This results in faster penetration to the pavement and quicker disbondment.
Considerable emphasis has been placed on the environmental impact of ice melters and many studies have been conducted. Virtually all of these studies have concluded that, given the alternative of hazardous conditions, the benefits of ice melters far outweigh their potential disadvantages. However, these concerns should be addressed.
Residues. Of the materials under review, the only materials which have the potential for leaving a solid residue on internal flooring are those which naturally occur as a solid.
Effect On Vegetation. All materials under review have the potential to damage plant life. However, in the amounts recommended for grounds maintenance, the threat to grass, trees and shrubs is minimal. In fact, The Institute for Safety Analysis concluded in its major study, “Benefits and Costs in the Use of Salt to Deice Highways,” that: “There is no evidence that road salting produces permanent ecological effects. What salinity build-ups occur are due almost entirely to improper storage rather than application”.
Effect On Concrete. Many are concerned with deicers’ effects on concrete. Among the materials under review, only ammonium sulfate and ammonium nitrate will chemically attack concrete. The others do not chemically attack concrete, but can affect the freezing point of water. When the freezing point of water is depressed, the number of freeze-thaw cycles the water goes through can increase. And the expansion of freezing water (hydraulic pressure) can exceed the strength limits of the concrete. Spalling can be the result, but this is greatly minimized in good quality air-entrained concrete.
Judicious use of deicers will minimize concrete damage. Prompt removal of slush and residual deicer from concrete surfaces will further minimize the chance for damage.
An objective review of the performance capabilities of common ice melting compounds finds significant differences in their performance. As a result, firms should always make their purchasing decisions with full knowledge of exactly which compound(s) are in the products they choose.