Both magnesium and calcium chloride products are used extensively in the American West for dust control and deicing purposes. Unfortunately, it has also been observed that these products can be corrosive to vehicles traveling on the treated roads. This blog will briefly describe the acceleration of aqueous corrosion of metal…mainly the rusting of steel, caused by the use of chloride products for dust control.
So, what is meant by corrosion? Corrosion is a naturally occurring phenomenon and can be defined as the deterioration of a material by the chemical interaction with their environment. In terms of metals, corrosion can be thought of being nature’s way of reverting a material back to its natural state. For example, many metals naturally exist as ores which are compounds such as oxides, sulphides, and sulphates. These compounds represent the metals most thermodynamically stable state. Therefore, the metals extracted from these ores will have a natural tendency to oxidize and revert back to its natural state. For example, pure iron is rarely found in nature therefore before iron is smelted and made into steel, it is mined mainly in its oxide forms such as hematite or magnetite. Therefore rust (corrosion) is reverting the iron back to its natural state as iron oxides which it was to begin with.
So, what makes these salts so corrosive to metals in the right conditions when applied for dust control? Generally, for aqueous corrosion to occur, you need oxygen, water, and electrolytes…such as the chloride ions. Without electrolytes, corrosion will take a much longer since its acceleration requires an electrochemical reaction.
For dust control, both magnesium and calcium chloride are commonly applied in a concentrated liquid form. As a liquid form, the chlorides are dissolved in water and normally applied in its concentrated solution. Both of these chloride products are “salts” and therefore, the concentrated aqueous solution of both products is pretty much like concentrated saltwater and since saltwater is a better electrical conductor than freshwater, it promotes corrosion. In addition, these chloride compounds are hygroscopic which means that they attract moisture from the air (e.g., humidity). So, when a chloride solution is applied to an unpaved road, it is this attracted moisture that dampens the treated road aggregates and therefore wets the dust particles and helps keep them from blowing away. But it is also another reason why chlorides can be corrosive since this hygroscopic nature is an important aspect in regard to their corrosivity.
Fortunately, Earthbind® 100 is a viable alternative dust control product that is not considered to be corrosive. For more information regarding Earthbind®, be sure to give EnviRoad a call at 1.800.536.2650, and we’ll be happy to answer any questions you may have!