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What do they use instead of salt on roads?

When it's snowy out, what do some states use to keep the roads from getting slippery and icy, besides salt?

1 Answer

To make winter roads passable, highway personnel usually must either apply chemical de-icers to melt ice and snow or spread sand to provide traction.

Clearing winter roads to the bare pavement usually requires de-icing chemicals. In Wisconsin the most common chemical is salt (sodium chloride) which usually comes from mined rock salt that has been crushed, screened, and treated with an anti-caking agent. De-icing salt is relatively light--just over one ton per cubic yard--and comes as a mixture of three-eighths inch granules to fine crystals.

Another commonly used chemical, calcium chloride, comes from natural brines. It comes dry in pellets or flakes, or in solutions of various concentrations.

Research continues on alternative de-icing chemicals. Calcium magnesium acetate (CMA) is being produced and has few of the negative environmental impacts associated with salt and calcium chloride. Additives to reduce chemicals' corrosive properties are also being used. Currently these alternative materials are more expensive, but can be useful in special situations.

De-icing chemicals work by lowering the freezing point of water. A 23.3% concentration of salt water freezes at -6o F and a 29.8% solution of calcium chloride freezes at -67o F. These low freezing points are what makes salt and calcium chloride useful.

Before a dry de-icing chemical can act it must dissolve into a brine solution. The necessary moisture can come from snow on the road surface or from water vapor in the air (humidity). Calcium chloride has the ability to attract moisture directly from the air.

Changing ice or snow into water requires heat from the air, the sun, the pavement, or traffic friction. Even when the pavement is below freezing, it holds some heat and can help melt snow and ice.

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