ROCK SALT FOR WINTER MAINTENANCEROCK SALT has a, "dry" density of approx. 1.28 tonnes/cu.metre,
and
a "wet" density of approximately 1.44 tonnes per cubic metre.
These figures are a GUIDE, because the density will depend upon the source of the salt, the grading and the moisture content.
It is an extremely quick and easy test to find the actual moisture content and density of the the salt you have delivered or have in stockpiles if you require more accurate figures.
SALT HAS VERY LITTLE EFFECT IN MELTING SNOW AND ICE BELOW THE TEMPERATURE OF MINUS 9 DEGREES CENTIGRADE
You will get an improvement in grip for vehicle wheels when using rock salt below 9 degrees from the physical action of the gritty nature of the salt improving friction.
ROCK SALT is specified in :-
B.S.3247:1991:Salt for spreading on highways for winter maintenance.
Anybody dealing with winter maintenance and buying salt should have a copy of this standard, it covers such points as storing quality, moisture content and grading.
Just one item of note is that SALT FOR SPREADING ON HIGHWAYS shall have a maximum moisture content of 4%, any higher and you are buying water at salt prices.
If the grading of the rock salt is not correct, and just as important of a consistant grading, the rate of spread of the salt will alter, even though spreader settings and speed are the same.
The cost of sampling and testing the salt supplied to you is not expensive compared to the cost of the salt and can reveal "interesting" information.
THE SPREADING OF SALT, AND SALT SPREADERS
The British Standard for salt spreaders and their calibration is found in :-
BS 1622 : Spreaders for winter maintenance
This specification deals with the various classesof SALT SPREADER, the methods in which to test them for correct distribution of salt, and it setsdown the acceptable levels of result to permit the issue of a certificate for a SALT SPREADER.
RATES OF SPREAD OF ROAD SALT
The following rates are a GUIDE to salting, the actual rate will depend upon the road conditions, residual salinity, and severity of predicted weather conditions.
This table of SUGGESTED rates of spread is for impervious road surfaces, using rock salt specified to BS 3247.
Frost or ice after dry conditions.............................10 - 15 grammes/sq. metre
Frost or ice after rainfall/wet conditions................... 20 - 40
Snowfall..................................................... 20 - 40
POROUS SURFACES
It has been widely recognised that the rate of spread of salt on porous wearing/surface courses needs to be increased to give the same degree of protection against ice forming, in relation to the rate of spread needed on impervious road surfaces
SOURCES OF USEFUL INFORMATION
CSS Report No.5/14-1989 : Winter Maintenance Manual and Code of Practice
It may be a little out of date, but it is still an extremely useful source of information on most aspects relating to winter maintenance.
WET SALTING
There are systems now being employed using a finer grade of salt that has been pre-wetted to a uniform standard before it is spread on the road, it is more, quite damp, rather than wet.
I am not familiar with these systems but you ought to be aware of them.
There have been a number of articles in the engineering magazines that will provide more information, or you could get in touch with one of the organisations who are using the system.
There are a number of claims that this method has advantages over the more traditional way, such as :-