Road salts - deicing salt
De-icing salt/ road salt
Common road salt consists of over 95% sodium chloride (NaCl)  in Germany (ingredients and composition may vary in different countries). Natural impurities may consist of up to a few percent of insoluble constituents (mainly clay) and other salts (e.g., gypsum or calcium chloride, antarcticite). Other additives such as anti-caking agents are possible. The expression wet salt refers to dry NaCl salt that has been humidified with CaCl2- or MgCl2- solution. Wet salt, unlike dry salt, adheres better to the road surface and has a better thawing effect.
A comparison of the salt concentration detected in fresh and old snow samples, shows that the contamination of snow quickly washes into the substrate. If salt is applied in the proximity of a vulnerable object, the salt penetrates the object and is partially washed out in the course of thawing and rain.
Every year vast amounts of salt are applied to keep roads clear from snow. These vary from year to year depending on the snow fall, e.g., in the years 1980-1990 between 170 000 to 800 000t were used on west German highways and main roads. Not included is the salt used on sidewalks, in towns and public places, etc. In the winter 2009/2010 these amounts must have been exceeded significantly, taking regional variations into account.
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