Road salts, or de-icing salts, are the invisible, silent warriors that battle day in and day out, keeping snow and ice accumulation at bay, and the streets clear and safe for travel. These heroes all perform the same task- -lowering the melting temperature of ice.
"We go through over 160 yards of rock salt a year to keep the sidewalks and parking lots as safe as possible," said Chris Brindley, University of Wisconsin-Stevens Point Buildings and Grounds Supervisor.
However, there are side effects – collateral damage – from the raging battle between road salt and the freezing precipitation (like Godzilla battling aliens inevitably results in panic, helicopters crashing and buildings collapsing). These side effects include corrosion of motor vehicles and vehicle infrastructure damage, degradation of the roadside environment and unwanted salts in the drinking and irrigation water.
"For the academic and administration areas, we use bagged calcium chloride for entrances and rock salt for all other sidewalks and parking lots" Brindley said.
The campus has experimented with multiple de-icing salt alternatives including liquid and granular forms. However, many alternatives are considerably more expensive and/or result in side effects such as stained carpet. With current budgets as well as the goal of a safe campus, rock salt is the best alternative right now. "To be honest with you, safety of getting the students and faculty members to the buildings is my number one priority," Brindley said.
In the United States, every year $1.5 billion is spent on highway snow and ice control programs. About one-third of that is spent on chemical de-icers and application. Since 1970, an average of 10 million tons of road salt is applied by highway agencies each winter.
Trees and vegetation alongside roads can be impacted by road salts through road splash and spray onto plant surfaces and cause soil chemistry changes. Of trees within 100 feet of a highway, 5-10 percent exhibited signs of salt stress in several concerned states.
As sodium accumulates, it can lead to an increase in soil density (compaction), which decreases drainage, water retention and fertility. This can inhibit plant growth and stimulate erosion.
Groundwater De-icing salts can get into groundwater, adding unwanted salts, which can corrode plumbing. Approximately $10 million is spent annualy in the U.S. mitigating salt in water supplies.
Since the adoption of road salts in the 1960s, they have been the greatest contributor to premature bridge deck deterioration in the Midwest and Northeast, costing $125-325 million per year.
According to a 1991 Transportation Research Board special report 235—"Highway De-icing: Comparing salt and calcium magnesium acetate," "The chloride ions in salt (NaCl) disrupt natural protective films on metal surfaces and increase the conductivity of water, which induces and accelerates corrosion."
Automotive manufacturers have been working since the 1960s to reduce the incidence and severity of corrosion. Over the last decade, corrosion has been greatly reduced, but with added manufacturing costs of $1.9-3.9 billion per year.
In some extreme circumstances, fish and other stream life can be harmed by high, persistent chloride concentrations from road salts.
Too much salt in the soil makes it difficult for plants to get water, causing a physiological drought, where a plant may have water available but is unable to uptake the water.