PREWETTING
Prewetting rock salt with calcium chloride enhances salt’s performance at any temperature. Liquid calcium chloride provides salt with the moisture it needs to form liquid brine and initiate melting action. Once melting begins, the bond between ice and pavement can be broken, which enables mechanical removal. LIQUIDOW™ Technical Grade Calcium Chloride Solution, at a concentration of 32% calcium chloride, is typically specified for prewetting applications.
Generally speaking, the LIQUIDOWTM solution should be applied at a rate of 6-10 gallons per ton (25-42 liters per metric tonne) of rock salt. This liquid prewetting rate can be optimized by local agencies based on experience and storm conditions. Agencies are then able to minimize prewetted salt applications based on conditions. For example, the Ontario Ministry of Transportation provides the following recommended application rate guidance for prewetted salt. 1
Variable Salt Application Rates with On-Board Pre-Wetting1
| Precipitation Type | Road Surface Temperature Range, oC (oF) |
| Warmer than -5oC (23oF) Kg/lane-km (Lbs/lane-mile) | -5oC (23oF) to -10oC (14oF) Kg/lane-km (Lbs/lane-mile) | Less than -10oC (14oF) to -18oC (-1 oF) Kg/lane-km (Lbs/lane-mile) |
| Frost | 25 (97) | 35 (136) | 35 (136) |
| Light Snow | 35 (136) | 50 (195) | 65 (253) |
| Heavy Snow | 65 (253) | 65 (253) | 85 (331) |
| Freezing Rain | 65 (253) | 85 (331) | 85 (331) |
1 Ontario Ministry of Transportation. Memorandum: Pilot Implementation of Best Practices for Pre-Wetting and Variable Salt Application Rates, 2001.
Prewetting Abrasives
Conventional abrasives can also benefit from prewetting treatment with calcium chloride. Sand and cinder particles prewetted with calcium chloride stay free-flowing and embed more securely in packed snow and ice, reducing losses from bounce and scatter to help ensure maximum traction improvement on pavement surfaces. Application rates for prewetting abrasives are typically lower than rates used to prewet rock salt depending on the composition of the materials. As with pre-wetting rock salt, the liquid application rate will vary based on local experience and storm conditions.
Prewetting Application Systems
Truck-Mounted Systems – These systems are now the most widely used for solid salt and abrasive applications. They may employ pre-wetting machinery as an integral part of the spreader design or as an addition to an existing dry material spreader. Many on-board liquid storage configurations are possible, including saddle tanks for hopper spreaders or off-bed tanks that feed dump bed systems. A bulletin published by the Wisconsin Transportation Information Center suggests that feeding the prewetting liquid at the auger results in better coverage of solid deicer compared to addition at the spinner.2 Other operators prefer addition at the spinner, asserting that this approach minimizes internal corrosion of major machinery.
Truckload Applicators – These include overhead spray systems that are placed over loaded trucks or over conveyor systems carrying salt to the truck.
Treated Salts or Stockpile Wetting – In this system, stockpiles of rock salt, abrasives or salt abrasive blends are treated with an enhanced or neat solution of LIQUIDOWTM calcium chloride. The liquid calcium chloride can be sprayed or pugmilled onto the salt as it is conveyed into the salt shed. Click here for a treated salt literature piece.
2Wisconsin Transportation Information Center, Wisconsin Transportation Bulletin No. 22, “Pre-Wetting and Anti-icing – Techniques for Winter Road Maintenance”, University of Wisconsin – Madison, 2005