Held in place by rivets, this shoe cracked under the jacking force of rust buildup. Photo: Technology Maintenance Council of the American Trucking Association
Equipment operating on highways and streets that have been treated with deicing chemicals is susceptible to rust and corrosion as never before.
Roy Gambrell is maintenance director for Truck It, a small trucking company in Franklin, Ky., and a member of the board of directors of the Technology and Maintenance Council (TMC) of American Trucking Associations. When investigating brake shoe failures after only 18 months of over-the-road service, he noticed edge cracks that initially looked like heat damage. Eventually, the cracks deepened enough to decommission the trucks.
When Gambrell pulled his wheels, the cracks went clear across the brake shoes. He removed the shoes and found rust buildup as high as ¼ inch on the shoe tables. Rust forms an A-shaped wedge that literally jacks up the brake shoe. Held in place by rivets, the shoes crack under the jacking force of the rust, just as expanding ice can crack the steel hull of a ship.
And thus Gambrell became the first to formally identify “rust jacking.” When he brought the phenomenon to the attention of the TMC, the council discovered that premature rusting was destroying equipment at rates never seen before.
Damage isn't confined to brakes. Virtually any unprotected metal is affected—steel, iron, and aluminum alike. Paint protects metals, but if the integrity of the paint is broken by a scratch or a stone chip, a path is opened for rusting to start.Cause And Effect
The sudden increase in rust damage is directly traceable to the increase in the use of more aggressive snow removal and deicing chemicals.
In the old days, most states used rock salt (sodium chloride), sometimes mixed with sand or cinders for traction. In the late 1990s, state and local road and transportation departments started experimenting with more aggressive chemicals: calcium chloride and magnesium chloride, often in combination with each other or with rock salt; and with potassium acetate and calcium-magnesium acetate.
Before the advent of these chemicals, dump trucks with snow plows were stationed along roads in anticipation of forecasted snows. If and when the snow reached a predetermined depth, the trucks were dispatched to start plowing and spreading salt. It took fuel to idle the engines, and lots of overtime to keep the workers in position. The public objected to all those idling diesels.
Today, chemicals are spread in advance of snow or ice storms, often dissolved in water and sprayed on roads several hours before they may be needed. In theory, they dry to an even coat and start working after the snow falls. Trucks and personnel need not be present.
In the real world, liquid chlorides and acetates stay on the pavement only until they're kicked up by car and truck tires as spray. The spray permeates the air and deposits on all vehicles driving through these mists. Once the chemicals find a weakness, even in recesses as hidden as the crevices between the brake linings and their brake shoes, corrosion starts.