The most common anti-icing chemical is calcium magnesium acetate (CMA), which was first developed in the 1970's by Chevron. It works by preventing snow and ice particles from adhering to each other or to the road surface. Anti-icing chemicals can be applied on top of snow and ice like other deicers or 30 minutes to two hours before precipitation begins. They can also be blended with road salt as a corrosion inhibitor. The Federal Highway Administration (FHWA) began the Strategic Highway Research Program (SHRP) in 1987 to test the effectiveness of anti-icing techniques. The program was carried out in nine states during the winters of 1993-94 and 1994-95. Results definitively showed that anti-icing is an extremely effective and economical means of snow and ice control.
Three different forms of anti-icing chemicals can be used:
Liquids and solids that are prewetted in the truck's spreader are the preferred forms because they minimize caking and corrosion. Once the chemicals are applied, they work immediately to prevent sticking of the first snowflakes. Snow that accumulates is lighter and drier than the brine that salt creates, which results in improved traction. In addition, because bonding to the pavement does not occur, a snowplow can be used to easily scrape aside the dry snow. As a result, much less of the chemical, as compared to salt, needs to be applied. Also, abrasives such as sand are not needed to provide additional friction for vehicles, which greatly reduces cleanup costs.
CMA and other anti-icing chemicals are extremely safe and environmentally sound. They are no more corrosive or damaging to concrete than tap water. They have low toxicity and are high biodegradability. In addition, because animals are attracted to salted roads, the use of anti-icing chemicals greatly reduces deer-related accidents. Finally, CMA replenishes salt-damaged soils by replacing stripped magnesium and calcium.
The primary limitations associated with the use of
anti-icing agents is cost and predicting when precipitation will
begin. One ton of CMA costs $300-600 as opposed to $20-70 for
salt. However, when indirect costs such as pollution and
corrosion are factored in, CMA is much more economical.
Furthermore, detection of precipitation is made possible by
collecting data from the Roadway Weather Information System
(RWIS) and national and local weather forecasts. Pavement sensors
installed under roadways also report conditions such as
temperature and the amount of anti-icing chemicals present on the
pavement. The information gathered is then entered into databases
and modeling techniques are used to accurately predict the start
Calcium magnesium propionate is a potentially revolutionary deicing chemical which is produced from agriculture residues. It was first developed by civil engineer Alex Mathews in response to the high cost of calcium magnesium acetate. Relatively inexpensive and abundant substances such as wheat, straw, grain dust, starch, and cellulose can be used in the production of CMP. Research is also in progress, however, to use residue from water treatment plants. So far, it has been shown to be highly effective when used to coat sand. Benefits of CMP include minimal effects on the environment, excellent performance in colder temperatures, and low cost. Although it is still experimental, CMP is projected to be ready for road tests in two years.
Calcium chloride melts snow and ice eight times faster than salt, but without the corrosive effects. Once applied, it remains active for long periods of time and is effective down to -59 degrees F. It can be applied alone or used to wet salt to speed up melting. Calcium chloride wetted salt works in several ways. It breaks bonds between pavement and ice, attracts moisture and dissolves quickly to activate salt, and releases heat as it melts. The use of calcium chloride results in the need for 40% less deicing material, which ultimately saves time and money. Furthermore, unlike salt, it does not cause sediment problems in tanks and is easy to clean up.
Scraping and sanding was the preferred method of
snow and ice control prior to the shift to salt in the 1960's.
Although it does not facilitate the melting of snow and ice, sand
increases traction on road surfaces. It is less expensive than
chemical treatments and has fewer environmental side effects.
Scraping and sanding also reduces the severity of accidents on
snow-covered roads because drivers are forced to slow down and
use more caution.
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