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Why sand and salt?

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Every time a snow storm comes around we talk about spreading sand and salt or pretreating the roads with a brine solution. Why do road crews do that? Why does it help?

It all has to do with the chemistry behind freezing… We all know that water freezes at 32°F. When salt is added to water the freezing point is lowered. For example, a 10% salt solution has a freezing point of about 20°F. A 20% salt solution has a freezing point of about 2°F.

If you have every touched snow or ice you know that it is wet. That is because, in most cases, there are liquid water molecules that have not yet frozen on the surface of the ice. When you spread salt on ice those liquid water molecules dissolve some of the salt, creating a saltwater solution called “brine.” The salt/water brine prevents the liquid water molecules from freezing. As the salt mixes with more water, more melting occurs.

So why sand? When temperatures are really cold there are very few liquid water molecules on the surface of the ice so adding salt would have little to no effect. The sand is added for traction as a temporary help until temperatures drop and the salt can mix in.

-Meteorologist Myles Henderson