The damage that usually is attributed to rock salt is a spalling of the surface of the concrete. This is more prevalent in new concrete and concrete that is poorly installed. Typically, there are two reasons for this. The first is that concrete is porous and absorbs water. This water freezes in the wintertime and the expansion causes the concrete to crack or spall. The increased introduction of water by melting ice by salts magnifies this problem. The other reason is related to chemical reactions that develop between de-icers and the concrete material or metal reinforcement within that can weaken and/or compound the freeze thaw issues naturally present.
Proper concrete installation reduces its ability to absorb water resulting in freeze thaw damage. This includes proper strength, placement, additives, and finishing. Exterior concrete should be air-entrained (tiny air bubbles); an additive that helps prevent freeze/thaw harm. Finishing can create a surface on the concrete that is weak if done incorrectly. For example if too much water is added during finishing it can spall much easier. If concrete is correctly installed and allowed to cure it typically can withstand more abuse by de-icers.
Conventional thinking is that rock salt (sodium chloride) is the worse de-icer for concrete on the market. Magnesium chloride is sometimes cited as one of the safest de-icer for concrete available. Interestingly in my own research of the subject I found a study by the Iowa State University that seems to run counterintuitive to this thinking. In part it found in testing reaction of de-icers on highway concrete the following:
“Samples were experimentally deteriorated using wet/dry, freeze/thaw, and continuous soak conditions in solutions of magnesium chloride, calcium chloride, sodium chloride [rock salt], magnesium acetate, magnesium nitrate, and distilled water in order to determine relative deterioration activities. Magnesium chloride was most destructive. Calcium chloride was next, and sodium chloride was relatively benign.”
This seems to suggest that the preferred de-icer of some may in fact be more harmful than rock salt. While I am not suggesting the use of rock salt you may not want to regard other forms of de-icers as entirely safe for concrete. Currently it appears that newest de-icer on the market, calcium magnesium acetate (CMA), may be the safest for concrete according to the most recent published information. However it has its own drawbacks. A certain chemical company had this to say:
“CMA is a dry formulation used as an ice melter on bridges, parking decks and airport runways. It does not attack rebar in reinforced concrete and is biodegradable, creating no problems in runoff water. It changes ice and snow into a oatmeal texture. This is not desirable for sidewalks, and it also may be cost-prohibitive, as it costs four to five times more than calcium chloride.”
The point is, as will all de-icers, they are designed to break up and loosen snow and ice so it can be mechanically removed. Instructions will typically say to remove excess de-icer, water, or slush. They are not designed to “burn-off” ice and snow.
If you follow the tips below you should not experience damage to your home’s concrete sidewalks and driveways.
- Never use de-icers on new concrete or concrete already showing signs of damage. Instead use sand for traction.
- If you must use a de-icer use calcium magnesium acetate (CMA) or another acetate product and follow the manufacturer’s instructions.
- CMA is rather expensive. If you need an economic solution you can use rock salt but remove it as soon as the ice can be loosened. However again, sand may provide a better solution.
- Never leave a de-icer on concrete to “burn off” the ice, snow, or water.
- Clean your drives and walks in the morning to allow the sun to help naturally de-ice the concrete.
- Never use a shovel or other metal tools to break up ice on concrete. This can cause mechanical damage to the surface.
We hope you winter is a safe one for you, your family and your home.
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