What is Salt and How Does it Work?
Salt is a general term that refers to various types of chemical compounds. For example, sodium chloride (NaCl), calcium chloride (CaCl2), magnesium chloride (MgCl2), and potassium chloride (KCl) are all salts. The most common salt for application to parking lots and sidewalks in the winter is sodium chloride which is also known as rock salt or road salt.
Salt Lowers the Freezing Point of Water
Water freezes into ice at 32°F. Salt applied to ice disrupts or breaks apart the ice structure by lowering its freezing point. This means that ice can melt at a lower temperature. Therefore, adding salt to ice causes it to melt. Different deicers lower the freeze point to different temperatures. Rock salt works well down to about 15°F. Magnesium and Calcium chlorides will work in colder temperatures. The colder the temperature, the slower the melting occurs and the amount of salt required increases.
Salt Prevents or Breaks the Bond Between Ice and Pavement
Applying liquid salt (commonly called salt brine) directly to pavement before a winter storm creates a thin layer that prevents ice bonding to the pavement. This process is called anti-icing. By forming this barrier, it makes it easier for plows or shovels to remove snow and ice. This approach improves safety, saves time, and requires less salt. Applying salt after the site is plowed (deicing) helps to break the bond between any remaining ice and the pavement so it can be removed mechanically.
Salt Increases Melting Speed
The melting speed of rock salt increases as pavement temperatures rise. Rock salt is most efficient at melting snow and ice when pavement temperatures are greater than 15°F. As pavement temperatures warm up to 32°F or higher, melting will occur naturally by using the sun and pavement warmth. It is not practical to apply rock salt when pavement temperatures are colder than 15°F. Rock salt does not effectively melt ice at colder temperatures. Other salts such as magnesium or calcium chloride, often blended with sodium chloride, can be used when pavement temperatures are lower than 15°F because they have a lower freezing point. Abrasives such as sand can also be used in cold temperatures to provide traction.