Using the wrong ice melt can be very damaging to your concrete sidewalks and driveways. Although they look very solid, concrete is actually a porous material that absorbs water. In cold weather the snow or ice is a solid and does not penetrate into concrete. But, when ice melters are applied, the melting ice/snow is turned into a chemical/water mix and is absorbed by concrete.
Additionally rock salt is hygroscopic meaning it actually attracts more water to it. So when ice is melted by rock salt and changes into a salt/water mix, it enters the concrete with approximately 10% more water than would normally enter concrete. When temperatures fall low enough, having the extra water (additional hydraulic pressure) in concrete causes expansion problems when the freezing water exceeds the compression strength of the concrete. The built up pressure causes pitting by pushing off small pieces of the surface.
Using the proper ice melt will minimize the damage and prolong the life of your concrete. There are basically four main types of ice melters that are commercially available.
Rock Salt (25 degrees protection)
Potassium Chloride (15 degrees protection)
Magnesium Chloride (-13 degrees protection)
Calcium Chloride (-25 degrees protection)
In the Midwest, your best bet would be to use Calcium Chloride. Calcium Chloride pellets are a fast acting product that melts ice/snow, and resists re-freezing to a temperature of –25 degrees. This protection to lower temperatures reduces the frequency and damage potential of the freeze/thaw cycles.
What NOT To Use
The most damaging of all ice melters contain ammonium nitrate and/or ammonium sulfate. These chemicals attack concrete chemically and can cause great damage, therefore should never be used as ice melters. Please note that these chemicals are locally available and are actually still used by some snow removal companies.
Published by Kevin Dougherty, Accord Building Services – St. Louis Janitorial / Commercial Office Cleaning