Snow Removal - Surface Treatments

Surface Treatments

The surface is treated primarily by snow removal. Roads are also treated by spreading various materials on the surface. These materials generally fall into two categories: chemical and inert. Chemical (including salt) distribution induces freezing-point depression, causing ice and snow to melt at a lower temperature. Chemical treatment can be applied as a preventive measure and/or after snowfall. Inert materials (i.e. sand, brash, slag) make the surface irregular to improve traction. Both types can be applied together, but the inert materials tend to lower traction once the snow and ice has melted.

Chemical treatment materials include:

• Sodium chloride (common table salt, NaCl)
• Calcium chloride (CaCl₂)
• Potassium chloride (KCl)
• Magnesium chloride (MgCl₂)
• Ammonium nitrate (NH₄NO₃)
• Ammonium sulfate
• Potassium acetate (CH₃COOK)
• Urea
• Propylene glycol (C₃H₈O₂)
• Calcium magnesium acetate (C₄H₆O₂Ca and C₄H₆O₂Mg)
• Sodium ferrocyanide (hydrous, Na₄Fe(CN)₆•10H₂O)
• Methyl alpha-D-glucopyranoside (C₇H₁₄O₆)

In the European Union, ca 98% of chemical treatment materials used in 2000 were sodium chloride in various forms. It is effective down to −5 °C, at the most −7 °C. For colder temperatures, calcium chloride (CaCl₂) is added to NaCl in some countries, but deployment is limited as it costs about 6 times as much as sodium chloride. Other substances were used rarely and experimentally. Alternative substances (urea, alcohols, glycols) are often used at airports. In recent years, Geomelt, a combination of salt brine and beet juice that is otherwise considered a waste product has been used for pretreatment.

Inert spreadings can be:

• sand
• brash, rubble etc.
• slag
• wood ash (for household use only)
• sawdust

The choice of treatment may include consideration of the effect on vegetation, pets and other animals, the local watershed, and effectiveness with regard to speed and temperature. Some chemicals can degrade concrete, metals, and other materials. The resulting meltwater and slush can cause frost heaving if it re-freezes, which can also damage pavement. Inert materials can damage vehicles and create dust.

As an example, in the Czech Republic during the winter season of 2000/2001, net material expenditure for road treatment was: 168 000 tonnes of salt (mostly NaCl), 348 000 tonnes of sand and crushed stone and 91 000 tonnes of other materials like slag. In Ireland, the annual expenditure of salt was 30 000 tonnes. Switzerland reports their annual expenditure as 600 grammes of salt to every square metre of roads on average.