Salt Ineffective in Extreme Cold

Posted at: 12/10/2013 8:35 PM
Updated at: 12/10/2013 8:50 PM

Snow.  Wind.  Cold temperatures.  That is not a good trio to have if you want pristine road conditions.  Roads were bad this morning.  Dozens of people found out the hard way.  This was a common sight across the area.

It wasn't much snow, less than 1/2" in all locations.  But there was some blowing snow due to gusty winds.  Also, temperatures were at a critical point, ranging from 0-10° while snow was falling.  Too low for road crews armed with Rock Salt to deice the road surface (or to deice your sidewalk at home).

Yes, there's a point where the temperature becomes too cold for deicing to be effective.  Rock Salt is the most common material used for deicing around our parts.  It's the least caustic to the environment, while being the most economical.  The salt works by lowering the freezing point of water.

The problem is, once temperatures drop to the 15 to 20° range, water will start to freeze faster than Sodium Chloride (NaCl), the component makeup of Rock Salt, can melt ice, thereby losing it's effectiveness.  Increasing the amounts applied does help to an extent but there does become a point where it's not economical to use.  The image below from the Iowa DoT helps explain salts ice melting effectiveness relative to temperature.

There are other products that can be used as a substitute at temperatures below 15° to about -20°, such as Calcium Chloride and Magnesium Chloride.  These materials melt ice faster at colder temperatures.

However, they are more caustic to the road bed compared to Rock Salt leading to faster road deterioration.  In addition, they are also more expensive.

So what can you take from all this?  The colder the temperatures, the harder it's going to be to keep roads, or even your sidewalk, free from ice.  The colder the temperature gets, the more care is needed in winter driving.

Just like last night, we have another round of snow moving through right now.  Again the wind will pick up to cause blowing snow as snow exits by sunrise tomorrow.  And air temperatures will be well below zero.   It's another setup for a bad morning of driving.

Storm Tracker 6 Chief Meteorologist
Chris Kuball