Maintech offers guide to snow & ice control
01 February 2010
Following snow, or the freezing of surface water, ice will bond to concrete, asphalt and other substrates. Adding salt and other chemicals enables thawing by lowering the freezing point of water, thus creating brine which breaks that bond.
Following snow, or the freezing of surface water in sub-zero temperatures, ice will bond to concrete, asphalt and other substrates. Adding salt and other chemicals enables thawing by lowering the freezing point of water, thus creating brine, which breaks the bond between the ice layer and substrate making it easier to remove.Chemical Deicers
There are two types of chemical deicers:
1. The first being endothermic, those that take heat from their surroundings (i.e. sunshine or heat from surrounding air / pavement) to work, such as, rock salt (sodium chloride) which work best at temperatures around freezing and will only work down to a temperature of -6 to -9°C.
2. The second type is exothermic; these create heat when added to ice and snow, such as Calcium Chloride and work down to a temperature of -28 to -30°C.
Exothermic deicers tend to work faster as they generate heat, as opposed to endothermic which needs heat in order to work, although an endothermic deicer can use friction as a source of heat, which is why rock salt can work successfully on roads in moderately low temperatures.
Using Deicers.
All chemical deicers work best if deployed in advance of ice forming, it is no-good putting a chemical deicer on 30cm of snow and expecting it to melt the snow. It is better to use too little, rather than too much deicer. Too much rock salt will result in the brine turning back to crystal form and having no greater effect. Also, too much calcium chloride (which is hygroscopic i.e. draws moisture from its surroundings) will result in a greasy and slippery residue.
When deployed before the formation of ice, deicers can be used at a rate of 25-50g/m², whereas more than 20 times this amount will be needed to completely melt 10cm of ice on 1m² at temperatures of -5°C. It is never recommended to use deicers in these high quantities, in a situation of thick snow or ice, use 100-250g/ m², the brine that is produced will help break the bond between ice and substrate allowing faster removal by mechanical means. If the deicer cannot be deployed in advance of ice or snowfall, use as soon as possible i.e. as soon as the snow starts falling, to minimize the amount needed.
Detrimental effects of using deicers.
Concrete and Asphalt
There is still some debate about whether the salts damage concrete. There is general agreement that a chemical deicer should not be used on concrete less than a year old and that any cracks are sealed and chips repaired in the concrete before the onset of winter. The main cause of damage to substrates, such as concrete and asphalt, is due to increased freeze thaw cycles when deicers are used. This is when water gets into cracks and porous parts of concrete and asphalt then expands when it freezes, causing the breakdown of the substrate. This is very noticeable on road surfaces where rock salt has been used and the night time temperature dips below -6°C. The water melts during daylight hours and freezes again at night damaging the road surface where it has penetrated, causing potholes. The use of Calcium Chloride which will not freeze above -28°C will help prevent this type of damage.
Vegetation
Most damage appears to be caused where chemicals are applied in large quantities and it runs or is splashed by traffic onto gardens and lawns. Rock salt tends to cause the most damage to vegetation, more so than calcium chloride, however, excessive use of any deicer will be detrimental to vegetation.
Metals
Chemical deicers will cause corrosion to the metal parts of building, fences and railings. This can be reduced by good maintenance practices, including ‘washing down’ and using protective coatings. Care should also be taken when storing de-icing chemicals near metal objects.
Tracking
Rock salt will leave a white powdery residue that is unsightly and can cause damage to carpets and floor finishes when it is tracked inside and calcium chloride can leave an oily residue that can damage wax or urethane finishes on wood floors. To prevent tracking do not over use deicers, clear the area nearest to entrances regularly and use track mats inside entrances. Any tracked rock salt can be removed by vacuum cleaner or a mop, and calcium chloride can be cleared using a mop with a good detergent.
Other types of chemical deicer
Other than the calcium chloride we have already mentioned, there are also the following chemical options:
Potassium Chloride and Urea (endothermic)
These are common fertilizers, but in high concentrations are deadly for plants. They work down to -10 °C but both materials work more slowly that calcium chloride.
Magnesium Chloride (exothermic)
Its benefits are similar to calcium chloride. However, its main drawback is that it is only 48% active and therefore, needs to be applied at a higher rate than calcium chloride.
Sodium Acetate & CMA
These are dry formulations used on bridges, multi storey car parks and airport runways where reinforcing bars may be near the surface, as is not recommended to use chlorides in such places. Sodium Acetate is also biodegradable and creates no problems in ‘run off’ water. It works down to approximately -17°C and melts rapidly, similar to calcium chloride. Sodium Acetate & CMA are expensive; however, CMA is often used as a corrosion inhibitor and can be blended with rock salt and other deicing chemicals.
Potassium Acetate
This is a clear liquid that contains no chlorides and is therefore safer to use on structural steel and reinforced concrete. It can be corrosive and is often mixed with a corrosion inhibitor. It is effective down to approximately -27°C.
Alpha Methyl Glucoside (MG-104)
A corn by-product, this is usually combined with other ingredients. MG-104 provides a catalytic effect that speeds melting, helps other chemicals to work at lower temperatures, and assists in the extension of the freeze-thaw cycles to reduce surface damage.
What You Need to Consider
In ice and snow conditions, maintaining a safe environment, preventing slips and falls and keeping roads clear for access of people and materials, are the priorities of maintenance and facilities managers. An effective and fast acting deicer makes the removal of ice and snow easier, which saves both time and money.
Facility and maintenance managers often rate deicer qualities in the following order of importance:
1. Works fast
2. Does not harm concrete
3. Works at low temperatures
4. Prevents damage by extension of freeze thaw cycle
5. Non tracking
6. Safe for vegetation
The biggest cost of ice and snow clearance is labour, so effectiveness is essential. Conditions must be taken into account, with temperatures around freezing rock salt will work efficiently, whereas lower temperatures may call for calcium chloride because of its effectiveness and extension of the freeze thaw cycle, which will help prevent ongoing maintenance to substrates after the thaw.
The number one consideration is always to deploy deicer before snow and ice when possible.
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