Liquids were introduced to the snow and ice control program beginning in 2000 after tests confirmed that they improve the effectiveness of road salt and can result in an overall reduction in salt use. They are either applied directly to the pavement in advance of snowfall or are sprayed onto granular salt as it is spread during a storm. A requirement that liquids other than those made from rock salt include corrosion inhibiting additives was introduced when contractors expressed concern that the liquids might add to rusting of their vehicles. The requirement closely follows that of other industry groups such as the Pacific Northwest Snow fighters, specifying that they reduce corrosion levels substantially below that of rock salt solution under laboratory conditions. Since then contractors have requested exemptions from the corrosion inhibitor requirement in an effort to reduce costs.
MTO launched field tests in fall 2006 to provide guidance in setting cost-effective requirements for corrosion inhibitors. The tests will provide comparative data on corrosion levels occurring over a winter season on test coupons installed on trucks and roadside infrastructure in areas where different levels of inhibitor are used. The project was undertaken by MTO's Design and Contract Standards, Materials Engineering and Research Offices, Southwest Region and Eastern Region, with assistance from contractors Steed and Evans, and TWD Roads Management.
Corrosion coupons of specified steel and aluminum measuring 89.0 x 50.0 mm x 1.59 mm thick, were weighed, numbered and then suspended on threaded nylon rods. The rods were either bolted or wired to the frames of two combination plow-spreader trucks and one patrol vehicle (Figure 1), two steel guide rail posts, two signposts and an environmental control away from the highway in each test area. 560 coupons were installed in total.
The coupons are exposed to WRMLs with inhibitor levels of 0%, 50% and 70% less corrosive as compared to sodium chloride brine. The WRMLs include sodium chloride brine, magnesium chloride brine, and multi-chloride brine containing sodium, calcium and magnesium. The coupons are exposed to all winter maintenance and environmental conditions that naturally occur in each field area and will provide a practical evaluation of the effectiveness of the inhibitors.
The coupons will remain mounted for the full winter season. They will be retrieved and re-weighed in spring 2007 to determine the extent of corrosion occurring in each area and the optimal percentage of inhibitors to use in MTO contracts. Look to future issues of Road Talk for coverage of preliminary results.
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