When winter strikes, the conscious driver prepares for increasing traction in case of icy and slippery roads. Some bring a sandbag and a shovel while others gear up with a set of snow chains. Still, others have automatic snow chains mounted on their vehicle, so there is no need at all for special preparation. All these drivers rely on mechanical principles for increasing traction. But, are there no other options? Let’s dive into the world of chemical de-icing of roads.
Ice may be good–but not on roadsIn many parts of the world, wintertime means freezing temperatures and icy roads. For saftey reasons and transportation efficiency roads need to be kept as dry as possible. A possible way to avoid icy roads would be to either make sure ice cannot build up, or remove it.
A road surface where ice cannot build up would be ideal. However, there is no such solution at reasonable environmental and financial cost. Chemical treatment of road surfaces to avoid ice build-up is reserved for airports or other critical infrastructural areas where icy road surfaces can have disastrous consequences.
Mechanically removing ice can be made by scraping but it takes quite a huge operation to scrape countless miles of winter roads. Even if snow is pushed making the road clear to drive, the ice will often remain. Furthermore, a fully effective scraping would result in excessive wear of the road surface at an increased cost for tax-payers or road owners.
Another way to remove ice is merely to melt it by use of heat, e.g., built-in heating in the paving. For obvious reasons, this is a too costly method for roads in general, so heated roads are rare and mostly found in city centres.
Scraping and heating will only work temporarily as the ice will build up again (unless there is built-in heating of the road). For more efficient and cost-effective de-icing we must look into chemistry.
For de-icing roads different chemicals that depress freezeing temperature of water can be used. Typically, these are inorganic salts or organic compounds.
Salt lowers the freezing temperature of water and makes the ice melt. How it works is explained in the blog post Surface Treatments. Typically, salt is cheap and convenient, and it can easily be spread as crystals or brine by spreading vehicles. But, there are flaws. As it is corrosive, it will make not only vehicles rust but also steel constructions and the rebar in concrete bridges. Furthermore, it also has an environmental impact since it can be harmful to both plants and animals in high concentrations.
Sodium chloride, i.e., ordinary rock salt, is an inexpensive option readily available in large quantities. This is the most common chemical de-icer. At most (depending on concentration) it is effective down to approximately −18 °C (0 °F). If the temperature is lower, it is not effective.
To further improve effectiveness other salts can be used, e.g., calcium chloride or magnesium chloride. Such salts may depress the freezing point of water to approximately −30 °C (-22 °F), partly due to an exothermic reaction where heat is produced. Such chlorides are often mixed into the sodium chloride to improve effectiveness.
Organic compoundsSince salts at high concentration may have environmental impact, organic compounds are increasingly used. Mixing the organic compound with a salt results in a product that is effective to temperatures down to −34 °C (−29 °F). A positive environmental effect is the lower overall rates of spreading per unit area.
Examples of organic compounds possible to use for de-icing are:
- Calcium magnesium acetate
- Potassium acetate
- Potassium formate
- Sodium formate
- Calcium formate
Even though the chemical names may sound scary to some, these organic compounds are relatively harmless and have less impact on the environment–and they are less corrosive.
Also, there are by-products from the agricultural industry, e.g., from sugar beet refining, that can be mixed with salt to improve efficiency and reduce environmental impact.
De-icing or not?Attitudes to chemical de-icing (e.g. by using salt) differ from country to country and region to region. The extent of using chemicals (if any) is a compromise between road safety, cost and environmental impact.
Even if roads are de-iced temperature may drop, and the road surface may suddenly be icy. With or without road de-icing, automatic snow chains is the safest and most convenient way always to be prepared for slippery roads–irrespective of the cause.