How salt clears and ruins roads


Melting: The substance is a cheap and effective weapon against winter woes, but it has limits and drawbacks.

February 18, 2003|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

It is one of the most abundant substances on Earth, was once used as currency and costs politicians their jobs if there isn't enough.

Salt, the ubiquitous substance that helps clear our highways of snow, is mined in a half-dozen states from deposits formed when the oceans that covered the continent receded 500 million years ago, leaving behind the salt from the water.

Used by the Romans to pay soldiers, the compound known as sodium chloride has helped clear snow from the roads in New England since the 1940s and has been a necessary weapon in the nation's war on winter for 40 years.

Despite the damage it causes to concrete, pavement, sidewalks and waterways, we use 16 million tons of it on highways nationwide each year.

Each fall, the state of Maryland stocks 230,000 tons of salt - enough to fill about 30,000 dump trucks - transporting it by truck from ships unloaded at the port of Baltimore to salt domes and cavernous storage barns across the state.

It is a chemical people hate on their cars, but demand on their roads. And shortages can be politically devastating.

The late Michael A. Bilandic was defeated in his bid to be re-elected as mayor of Chicago in 1979 shortly after he failed to sufficiently salt the city's roads during a blizzard. Shortages of salt for Baltimore County's roads in early 1994 were largely seen as contributing to the defeat of County Executive Roger B. Hayden later that year.

There are alternatives for melting snow and ice. But salt - specifically sodium chloride - is the most widely used for three reasons: chemistry, cost and climate.

Most snow in the United States falls when the temperatures are between 25 and 32 degrees Fahrenheit, which makes salt an ideal compound for winter because it works until temperatures drop to minus 6 degrees, a level at which salt itself will freeze.

In places such as Alaska, Canada, and the Upper Midwest, where temperatures frequently dip to subzero levels, highway crews often lay off the use of salt altogether because the weather is too cold for it to work.

Crews in such frigid areas repeatedly plow to keep the roads as clear as possible of moisture and when a lot of snow accumulates, they sometimes spread sand and crushed stones, which cannot melt snow but will increase traction.

"When you get down to zero degrees, or 10 below zero, the best thing to do is just make sure the roads are as clear as possible," said Bruce Beltram of the Salt Institute, an agency that represents salt wholesalers and dealers.

Salt's effectiveness also depends on the amount of snow on the roads.

Accumulations of more than three inches make the snow too deep for salt to be effective, said Sandra Dobson, a spokeswoman for the State Highway Administration.

As with other major storms, Maryland highway crews stopped salting and focused on plowing during the height of this week's storm because so much snow fell so fast, she said.

But Dobson said that crews were applying salt yesterday to several major arteries in the Baltimore area because enough snow had been cleared to let the salt work.

"We're only salting when we get down to about 2 inches of snow on the road," Dobson said yesterday afternoon.

How salt works is a matter of simple chemistry: Salt enters the snow, absorbing the moisture from it, on contact, the way that a sponge or towel will absorb drops of water.

As the salt crystals mix with the snow and ice, the crystals go into solution and form a brine that has a lower freezing temperature than snow around it. This in turn, melts the snow around the brine, turning the snow to a salty solution that is less treacherous than the salt on the roadways.

The traditional salt used is compound of two chemicals: sodium and chloride, which is the same chemical mix found in table salt.

When temperatures dip down to salt's minus-6 freezing point, highway crews often switch to organic compounds, liquid treatments, such as a salt brine, or alternative forms of salt, which includes calcium chloride, which has a freezing temperature of minus 58 degrees.

Many alternatives are promoted as being more effective at colder temperatures and causing less environmental damage.

Cargill Salt, a Minnesota-based salt producer, has sold an organic compound to the cities of Minneapolis and Rochester - as well as Baltimore - that contains molasses.

"It doesn't bounce, scatter and end up in a ditch," said Michael Hoerle, a Cargill sales representative in Plymouth, Minn.

For the state's chilliest storms in Garrett County, the State Highway Administration uses Ice Ban M-50, an agricultural byproduct that has a freezing point of minus 36 degrees.

Not only are alternative salts and treatments more expensive, but they don't always work.

For years Maryland used magnesium chloride as a pretreatment for snow storms predicted to begin at rush hour. If spread on roads just before an expected storm, it would prevent the snow and ice from bonding with the road surface, Dobson said.

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