| Work Book
Ice and Snow Control Strategies for 2002
Anti-icing holds the key spot in today’s ice and snow control
strategy
arsenal — it just costs less to prevent slick roads than to
deice them later.
by Ruth W.
Stidger, Editor-in-Chief
 Choosing the right anti-icer is the first step. One of the best tools
to help you do it is Wilfred A. Nixon and Anissa D. William’s A Guide
for Selecting Anti-icing Chemicals. The technical report, published by the
College of Engineering at the University of Iowa in Iowa City, was updated
late last year, giving extremely current information.
The report discusses various chemicals, their advantages and
disadvantages, and tells how to compile an overall score for any given
chemical. It then shows how to rank those chemicals for your own
applications and geographical location.
This evaluation helps agencies develop anti-icer specifications easily,
Nixon and Williams say.
Chemical properties
 The first choice is organics versus inorganics. Organic chemicals can
be designed more easily than inorganics — to reduce corrosion or give a
better freeze point. But, organics tend to be less stable than inorganics,
the report says, requiring more careful handling.
Nixon and Williams look only at liquid chemicals since these are most
commonly used in anti-icing.
Properties and factors that need to be evaluated include:
1. Freezing point depression.
2. Consistency.
3. Viscosity.
4. Specific gravity.
5. Environmental impact.
6. Stability.
7. Corrosion effects.
8. Handling criteria.
9. Conductivity.
10. Documentation availability.
11. Friction characteristics (when possible).
12. Recommended use levels (when possible).
13. Cost.
14. Availability.
15. Technical support/customer service.
Nixon and Williams recommend a four-level classification system, with
grades from A to D for each property. The accompanying figure shows the
proposed levels for each category.
Individual agencies should decide how important specific properties are
to their operation. In Canada, for example, the freezing point depression
property takes on more importance because of the cold weather, giving it a
greater weight than in an area with only light freezes. An accompanying
table shows a hypothetical weighting of categories.
A second table shows scores for hypothetical chemicals based on their
assigned weights.
RWIS
Anti-icing depends on road weather information systems for success.
RWIS improvements in recent years provide greater accuracy to those
using or considering the systems. Improvements include:
1. Better integration with other RWIS and Intelligent Transportation
System applications, sharing information over a wider geographical area
and improving accuracy and timing.
2. Better hardware. Technical advancements include use of automatic
fixed broadcast systems for specific locations such as bridge decks,
according to an AASHTO report.
3. Benefit/cost analysis, with input from several associations and task
force groups.
At the city level
Deicing and anti-icing need to offer new environmentally safe
technologies for winter maintenance, says Justin Segall in a recent
report.
Anti-icing and deicing have been combined effectively in Denver, Segall
says, eliminating the use of sand in the downtown area and decreasing PM10
emissions.
Segall cites magnesium chloride as the chemical of choice in Colorado,
due to its lower freezing point. However, calcium chloride offers the same
advantage and penetrates ice twice as well as road salt, Segall says.
Calcium magnesium acetate works well and is environmentally acceptable.
Its current cost limits use.
Ammonium combinations with an inhibitor reduces deicing-related
corrosion, but could threaten water quality, Segall says.
Natural products such as sugar beet carbohydrates and byproducts may
also affect water supplies by causing algae blooms and other problems.
More efficient chemical application can help. Equipment that places
chemicals or sand at zero velocity using a mechanical or air process lets
the material stick where it falls on the pavement rather than flying off
the road. Epoke and Tyler both make equipment using the technology, which
reduces material applied by 20 to 40% and lets the operator travel at 50
rather than 25 miles per hour common with traditional spreaders.
Prewetting sand with calcium chloride or magnesium chloride is a common
step. In Germany, Segall says, calcium chloride has been mixed with
asphalt to provide a permanent anti-icer in the road.
The Finnish National Road Administration uses winter maintenance
cutting-edge technology that removes compacted snow and ice leaving a
grooved surface to catch deicing brine or chemicals. The Olofsfors P-300
blade is one cutting-edge device used.
Reprinted from Better Roads Magazine
August 2002 |
