Breaking the ice: An overview of de-icing and anti-icing techniques

For the vast majority of Americans and Canadians, the new decade began under several feet of snow, icy roads and difficult travel conditions. It’s a not-so-subtle reminder of the need to maintain open travel ways — roads and bridges, airport taxiways and runways — in frigid temperatures. Let’s take a look at various methods to break the ice — or prevent the ice — that can make winter travel less of a slippery proposition.

To de-ice or anti-ice?

Anti-icing is aimed at preventing ice from forming while de-icing is designed to remove ice after it begins to accumulate.

De-icing removes frozen contaminants: snow, ice, slush and frost that are already bonded or formed to a surface. Methods of de-icing include mechanical processes (scraping, pushing); heat application; use of dry or liquid chemicals that lower the freezing point of water; or a combination of these techniques.

De-icing fluids can be applied over thin ice or snow pack but are best used early in a storm at their full strength as an anti-icer. There is no need for them to be diluted or heated.

Dry chemicals are best applied at the beginning of a storm and directly over ice or snow-pack to break the bonding effect of the frozen precipitation to the pavement. Dry chemicals may be pre-wetted with brine or other liquids to help them stick to the paved surfaces and to start melting ice more quickly. Once the ice or snow-pack is loose after de-icing, mechanical means are usually recommended to remove it to prevent re-freezing or re-bonding as the de-icer is diluted by melting ice or snow.

The effectiveness of de-icers depends on surface temperature, application rate, the amount of moisture or water present, and the applied concentration. When choosing a de-icer, it is important to review the certification, the effectiveness and how the de-icer works. Also, consider where it will be used: Is there an environmental or corrosion concern? The non-chloride de-icers are safer.

Solid de-icers are generally applied after snow and ice have fallen and bonded to the surface. Solids penetrate through the accumulated pack to the pavement as the de-icer alters its form from solid to liquid. Some solids like anhydrous sodium acetate actually give off heat (exothermic reaction) as they dissolve.

Solid de-icers are available as either pellets or granules. Pelleted de-icers are harder, less dusty and tend to spread more evenly. Pellets and granules stick to the surface and have less bounce during application when applied on wet or light-snow-covered surfaces.

Liquid de-icers are generally used as “anti-icers.” The choice of the right chemical for anti-icing applications is dependent upon a number of factors, including the area’s climate, chemical availability as well as environmental concerns. A fundamental characteristic of anti-icing chemicals is the ability to reduce the freezing point when added to water.

Anti-icing on roadways prevents ice and snow from adhering to the pavement, thus allowing easier removal by mechanical methods (snowplows). Brine or wetted salt is usually applied shortly before a snowstorm arrives. If performed properly, anti-icing can significantly reduce the amount of salt required to clear snow from a roadway.

Generally, anti-icing techniques are more efficient than de-icing because less energy is needed — therefore, less chemical is used — to prevent a bond from forming than to break it. Anti-icing can be applied before a storm hits or early in the storm. Maintenance costs are lower, and there is a reduced environmental impact.

Unfortunately, anti-icing measures alone are not enough to keep the paths of commerce and education open. A balance of anti-icing and de-icing methods is necessary. Understanding when and how to apply the appropriate chemicals for greatest effect comes by observing and measuring the combination of environment, chemical, application and result. This scientific approach is evident every winter day as we drive to work or board a plane to take us to sunnier and warmer climes.

A primer to de-icing chemicals

SOURCE: De-ice or Anti-ice? What’s an Airport to Do? was presented at the 2009 NIGP Annual Forum by Tony Myhra, Cryotech Deicing Technology.