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An
in-depth overview of the various Ice Melt Compounds that are on
the market.
Ice
melt compounds (deicing compounds) are manufactured to break the
bond between ice/snow and pavement.
They are not designed to melt all the ice/snow from the
pavement. After the
bond has been broken, mechanical removal of the ice/snow should
be performed.
The
two most widely used ice melt compounds in use are CALCIUM
CHLORIDE and SODIUM CHLORIDE (rock salt.)
POTASSIUM CHLORIDE (another naturally occurring
material), and UREA (manufactured as a fertilizer) are also
used as deicers. These
four products and combinations of them account for virtually all
the deicers available to the general public.
Deicing
materials cannot melt ice and snow in their dry state (solid.)
These materials must first attract, or come into contact
with moisture to form a chemical/water solution called brine.
The brine dissolves through ice/snow to the pavement and then fans out under the ice/snow to break the bond with
the pavement. Even though ice and snow are merely frozen water,
moisture is not readily available at freezing temperatures.
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Calcium
Chloride
- Seems better able to attract and retain moisture directly
from its surroundings. Calcium Chloride pellets liberate heat in
an exothermic reaction. One pound of calcium chloride liberates
290 BTU's (British Thermal Units) as it dissolves.
Other deicers draw BTU's from the environment in an
endothermic reaction. Calcium
chloride has a practical melting temperature of
-25°F,
making it the deicing compound with the lowest melting point. I
t is a liquid in its natural state.
This enables it to maintain a brine for a longer period
of time.
Sodium
Chloride
- Is one of the most popular ice melt compounds since it is
fairly effective and relatively inexpensive. Most salt manufacturers claim a practical melting temperature
of 15°F.
It is used extensively by highway departments since heat
generated by the friction of automobiles on the pavement surface
greatly aids in the performance of the compound.
Sodium Chloride works by endothermic reactions (absorbs
heat from its environment) it draws 39 BTU's from water as it
goes into solution.
Potassium
Chloride and Urea
- Are primarily fertilizers and neither alone is a very good
deicer. They both have practical melting temperatures of +20°F
and work by endothermic reaction. Potassium Chloride requires
170 BTU's and Urea requires 106 BTU's from water as they go
into solution. Under
practical conditions, when temperatures drop much below
freezing, the rate of heat pick-up from the ice and snow slows
to a point where they are no longer effective as deicers.
Potassium
Chloride and Urea are solids in their natural state.
This means they give up moisture freely as they try to
return to this state from a brine solution.
This slows the deicing process. These products most often
are blended with other ice-melting salts to enhance their
deicing qualities. The
primary advantage of these two products is that they are
fertilizers, therefore, any runoff in melted areas will not harm
surrounding vegetation (unless used in excess).
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Effects
on Concrete
– None of the commonly available deicers attack concrete
chemically. Concrete can be destroyed when these products
depress the freezing point of water and affect the number of
freeze-thaw cycles. This
causes the concrete to spall.
Therefore, avoid over-application and, remove the slush
and residual deicer once the bond is broken, to prevent
refreezing.
Residue
- Sodium Chloride, Potassium Chloride and Urea dry to a white
powdery residue once they are tracked indoors.
This residue is unsightly, especially in high traffic
areas such as lobbies and corridors. Calcium Chloride however, does not leave a visible residue.
All deicing compound residue (regardless or whether it is
visible or not) should be removed from floors as quickly as
possible since it is high in alkalinity.
This high alkalinity will deteriorate floor finish.
Residue tracked areas should be damp mopped with a
Neutralizer solution to remove the high alkalinity conditions and
prevent finish deterioration.
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