During the winter months in Wisconsin we often see road salt used so much that there is often a shortage! Most people from Wisconsin have know that we use salt on our road, and some even use it on their driveways, but few know what the road salt actually does and how it helps to melt ice. The melting process is not hard to understand, but few people take the time to learn what road salts are actually doing on our roads. Unlike sand, which is commonly used on roads during the winter, the ice actually helps to melt the ice and keep it in a liquid state.
The freezing point of water, the temperature just cold enough to make it freeze into ice, is 0 degrees Celsius. Dissolving salt in water makes the water harder to freeze. To get salt water to freeze you have to make it colder than 0 degrees.
Sand
Ice ball
Pressure dependence of water melting pointSo, salt lowers the freezing point of water. Many people also believe that adding salt to water will help it boil faster. This is the same concept, but only reversed.
When sand is used on roads in the winter, it is used purely for traction. Sand does not melt ice, or lower the freezing point, like salt does. Sand creates a rough surface to prevent tires from slipping and spinning on ice. When there is a salt shortage, sand is used as a replacement. Sand is not the favored road maintenance tool, but will work for a short period of time. Salt is always preferred over sand because it actually fixes and prevents a problem opposed to just covering it up for a small time frame.
There is also a technique to spreading salt on roads. If not done right, it can be wasted and not effective. As the weather and temperatures change so do the amount of salt needed on the roads. Salt has to spread in a correct amount otherwise it wont all dissolve and some will be wasted. This is the main cause of the shortages in some counties. Spreading salt does not sound like a difficult or challenging task, but the trucks that disperse salt are specially designed to dispense just the right amount at a certain time.
After a long winter like the one we just had, it is becoming increasingly important that we know what road salts are used for and how they are used. The process of melting ice with salt is simple and easy to understand. Salt not only helps melt ice, but also helps keep it melted. Once the ice is turned the water, the salt stays in the water and prevents it from freezing until it evaporates. Salt has been used for the purpose of melting ice for years and is still doing a fantastic job!BibliographyUS Department Of Transportation, comp. "Using Salt and Sand for Winter Road Maintenance." US Road Management Journals. 1 Dec. 1997. 9 May 2008 http://www.usroads.com/journals/p/rmj/9712/rm971202.htm.
"Why Do They Use Salt to Melt Ice on the Road in Winter?" Howstuffworks.com. 1 Apr. 2000. 5 May 1997 http://science.howstuffworks.com/question58.htm.
English: Salt Pile. A stockpile for road salt/grit...
English: Road to Lough Salt
Clach Tholl - geograph.org.uk - 1529866