Do Chemical Deicers Harm Concrete?
24 January 2000
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That's a question many people ask every spring, after winter's
snow and ice have disappeared leaving sidewalks and paths cracked and
pitted. But it's a question that should be asked right now, because
the storm that just ended has homeowners and commercial building
maintenance people liberally spreading chemical deicers to clear away
snow and ice.
Most common chemical deicers do not chemically attack concrete,
according to research chemists at The Dow Chemical Company in Midland,
Michigan. But that's only half the story, these experts are quick to
point out. Concrete spalling is actually a result of pressure created
within the concrete by the repeated freezing and expansion of water,
followed by thawing and contraction of that same water, and then
freezing again. This damage is much more likely to occur in poor
quality concrete.
So the first key to minimizing concrete damage, the Dow
scientists say, is to remove as much of the partially melted snow and
ice as possible. By removing the slush with a plow or shovel, you're
not only making the surface safer for walking, you're also removing
much of the liquid that might refreeze if the temperature drops low
enough. It's the repeated freeze/thaw cycles that actually do the
damage to concrete.
The next key, the Dow chemists go on to say, is to minimize the
number of freeze/thaw cycles concrete is subjected to. In other words,
if snow and ice are melted by a deicer and the slush is removed, if
any remaining brine stays in the liquid form rather than refreezing
when the temperature drops, the concrete will be spared another hard
freeze, and thus the internal pressure that could be damaging.
This means selecting a deicer with the lowest practical
temperature limit. A deicer's practical temperature limit is the
lowest temperature at which sufficient deicing action occurs within a
reasonable amount of time. Snow and ice melted by a deicer with a low
practical temperature limit is much more likely to remain in the
liquid form despite a temperature drop. The following table shows the
lowest practical temperature for commonly used deicer materials.
Material Lowest Practical Temperature Calcium chloride -25 degrees Fahrenheit Magnesium chloride +5 degrees Fahrenheit Sodium chloride (salt) +20 degrees Fahrenheit Potassium chloride +25 degrees Fahrenheit Urea +25 degrees Fahrenheit 50/50 mixture, sodium chloride & potassium chloride +20 degrees Fahrenheit
Some deicing products claim to be effective at melting snow and ice down to a much lower temperature, the Dow chemists caution. This lower temperature, known as the eutectic temperature, applies only to controlled laboratory test conditions and is not really valid in actual snow and ice melting. One way to make sure the deicer you have chosen is effective at low temperatures is simply to look at the list of ingredients, which must be shown on the package. Compare the lowest practical temperature in the above table with the ingredients listed on the package, and you'll know at what temperature your deicer will refreeze, possibly damaging concrete, as the outdoor temperature drops.
Obviously, snow and ice melted by calcium chloride and deicers containing calcium chloride will remain in the liquid form longer when outdoor temperature dips to zero and below. Calcium chloride deicers currently available on retail shelves include PELADOW(R) from The Dow Chemical Company, DRIVEWAY HEAT(R) from Prestone Products Corporation, QUICK JOE(R) from Milazzo Industries, and SNO/MELT(R) from Standard Tar Products Company.
