Salt: Spreading a Path of Destruction

ICE BREAKERS: A bucket of de-icing salt.  Photo by Lauren Klose.
ICE BREAKERS: A bucket of de-icing salt. Photo Credit: Lauren Klose.

NEW YORK CITY – With harsh winter weather approaching, New Yorkers are likely to deal with their fair share of snow and ice, as well as potholes – an auto driver’s nightmare. Potholes seem to appear magically with the snow and ice each year, but how?

Chemicals present in de-icing salts can speed up the deterioration of road surfaces, which then become more vulnerable to damage by plows as they remove snow and ice from the streets. Potholes can result. According to its website, the city’s Department of Sanitation operates 550 spreaders, which work on approximately 6,500 miles of streets to remove snow and ice.

Yaghoob Farnam, a research associate at Purdue University who has studied the effects of de-icing salt on concrete, said concrete shrinks and cracks when it ages. De-icing salts get in the cracks and joints, causing deterioration and making the cracks bigger over time. The end results: weaker concrete and pothole-riddled roadways.

Not all de-icing salts are the same or create an equal amount of damage. The four main types of salts used in the removal of ice and snow are sodium chloride, calcium chloride, potassium chloride and magnesium chloride.

Sodium chloride, better known as rock salt, causes the least amount of damage to concrete and other roadways, and it’s safer for the environment. However, this option does have a drawback in that it is ineffective at particularly low temperatures. For sodium chloride to work, it pulls heat in from the surrounding area, making its lowest effective temperature 20 degrees Fahrenheit, according to a report by Occidental Chemical Corporation. Potassium chloride is similar, as it can only melt ice and snow when the temperature is above 15 degrees Fahrenheit unless mixed with other potentially harmful chemicals.

The two most effective de-icing salts are calcium and magnesium chloride. Magnesium chloride can melt snow and ice even if the temperature reaches minus 13 degrees Fahrenheit.  However, their power comes with a price, as certain concentrations of calcium chloride can destroy roadways and sidewalks. These compounds also cause corrosion on vehicles. Just a tiny amount of chloride can accelerate existing corrosion, according to a study published in Road Management Journal.

“Calcium chloride and magnesium are really effective in melting ice and snow because they can decrease the freezing temperature enormously,” Farnam said.

There are ways to make de-icing more effective. The first is to apply a brine salt solution or introduce crystallized salt onto the pavement before snow or ice forms. It has also become more common to pre-wet the salt using liquid calcium chloride to dissolve the snow and ice faster.

When it comes to the decision as to which salt is used, it’s not based on which is more sustainable, Farnam said. The cost of the different types of de-icing salts plays a large factor in their popularity.

“Money defines what is going on,” he said.

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