CALCIUM CHLORIDE — WINTER DE-ICING
Chemical de-icing involves applying chemical agents such as sodium chloride (rock salt) and calcium
chloride to lower the freezing point below 0oc. By spreading suitable chemicals on the road it is
possible to:
Prevent frost, ice or layers of ice from forming
Melt existing snow, ice etc
Prevent snow adhering to the road surface
Rock salt (NaCl) has for many years been the main chemical agent used for de-icing in countries with
relatively mild winters. However, where winter conditions can be more extreme, calcium chloride (CaCl 2)
in liquid or solid form is used as the de-icing agent. Increasingly today, pre-wetted salt, a combination of
NaCl and CaCl2 liquid, is finding application.
CONDITIONS REQUIRED TO MELT SNOW AND ICE
Moisture for the salt to dissolve
Energy (heat) for the melting process
A salt concentration lower than the eutectic value
For all the above required elements CaCl2 is more beneficial than NaCl.
CaCl2 is considerably more hygroscopic than NaCl, absorbing moisture from the air and this factor in
conjunction with the exothermic reaction between CaCl2 and water results in a much more rapid snow/
ice melting rate.
The eutectic temperature for CaCl2 is –51.6oc compared to –21.1oc for NaCl which means that CaCl2
can be used at lower temperatures.
CALCIUM CHLORIDE — WINTER DE-ICING
ADVANTAGES OF CaCl2
Faster initial melting of ice
Remains active for longer, preventing re-occurrence of icing
Effective to much lower temperatures
Increases the effectiveness of NaCl
Savings can be made by reduction in materials
More effective at a wider range of humidity levels
PREWETTED SALT
By „prewetting‟ NaCl with a CaCl2 solution the advantageous properties of CaCl2 can be utilised to
improve the performance of NaCl. Prewetting of NaCl can principally be carried out in two ways (1)The
solution can be sprayed before spreading is started, ie. when loading the truck with salt. or alternatively,
(2) prewetting takes place during spreading, where the truck has demountable tanks containing the
CaCl2 solution which is sprayed onto the NaCl at the spreader plate.
Prewetting of NaCl overcomes one of its major drawbacks “bounce and scatter”, where the NaCl is
dispersed in all directions and only a fraction retained on the treated surface. Work undertaken in the
1970‟s showed that less than 50% of dry NaCl was actually retained in the centre of the road.
Salt Retrieved from Treated Road 24ft in Width
80
60
Dry
% 40
Prew et
20
0
Centre 1/3
Outer 2/3 Unretrieved
Calcium Chloride Solution for Prewetting
The addition rate is typically 1:3, CaCl2 : NaCl, and the CaCl2 solution strength may vary from 2030% dependent upon the prevailing temperature. The eutectic point for a 30% CaCl2 solution is
approximately –51oc, which means that this solution would be most advantageous for prewetting at
extremely low temperatures. In the UK a 20-25% CaCl2 solution would be more applicable.
ADVANTAGES OF CaCl2 FOR PREWETTING
Effective to lower temperatures
Improved road adhesion
Faster melting action
Better spreading pattern
Reduced quantity of salt (NaCl) required
Less frequent passes required
Cost savings on fuel
CALCIUM CHLORIDE — WINTER DE-ICING
DILUTION OF CALCIUM CHLORIDE SOLUTION
The following formula can be used for dilution calculations:
V = 100H (A-B)
B
Where V = Volumes of water to add to each 100 volumes of original CaCl2 solution
A = % CaCl2 in the original solution
B = % CaCl2 required in the final diluted solution
H = Specific Gravity of the original solution
Example:
To prepare a 20% CaCl2 solution from a 36% CaCl2 solution with a specific gravity
of 1.36
Substituting in the formula:
V = 100 x 1.360 (36-20)
20
= 108 volumes
Therefore 108 volumes of H2O added to 100 volumes of 36% CaCl2 solution will
result in 20% CaCl2 solution.
The above result may be expressed in gallons, cubic feet, cubic metres or any
other volume unit.
All information given is believed to be accurate. However, no representation or guarantee, express or implied, is made as to its
completeness, accuracy, fitness for a particular purpose or any other matter, including without limitation, that the practice or
application of any such information is free of patent infringement or other intellectual property misappropriation. All information
provided herein is intended for use by persons having the requisite experience, knowledge and skill. Tata Chemicals Europe
Limited shall not be responsible or liable for the use, application or implementation of the information provided.