Corrosion

Road salts have a tremendous impact on motor vehicles and infrastructure. Since the widespread introduction of road salts following World War II, motor vehicles have suffered from severe corrosion effects. Corrosion damage to motor vehicles can be separated into three categories: functional, structural, and cosmetic. Functional and structural damage occurs when corrosion causes a loss of operating performance or structural integrity. Examples include perforation of body panels, corrosion of brake linings, floor panels, exhaust systems, fuel pipes, brake pipes, and deterioration of the frame and bumper support systems. Cosmetic corrosion affects only the appearance of the vehicle. This includes rust staining of painted body panels and discoloration and pitting of trim metals

Source: Cryotech Deicing Technology: www.ga.com/cryotech/CMA

Corrosion has also played an important part in the condition of the nation's highways over the past 20 years. The premature deterioration of concrete bridge decks is a major concern. The use of deicing salt is the primary reason for bridge decay. In the 1950's and 1960's, bridge decks were built using cast-in-place concrete heavily reinforced with steel bars. The upper steel bars were designed to be positioned approximately 2 in. below the concrete surface. When these decks began to crack, the chloride ions from the road salt penetrated through the pores and cracks, which led to the corrosion of the steel bars. Corrosion occurs in these concrete decks by means of macrocell corrosion. Macrocell corrosion occurs when large areas of the steel become corroding anodes, and other areas become non-corroding cathodes. The rebars act as an electrical pathway, conducting electrons from the anode to the cathode. The chloride ions and water molecules act as an electrolyte, completing the electrical circuit. This produces rust in place of the steel, causing the surrounding concrete to crack. The problem is further aggravated by freeze thaw cycles.

Source: Cryotech Deicing Technology: www.ga.com/cryotech/CMA

Various other components of the deck system including grid decks, joint devices, and drainage systems are also primarily made of steel. These require frequent maintenance because they are more exposed to the salt (greater contact time and surface area). Salt-laden snow, mud, sand, and other debris often sit on these supporting structures and cause more rapid corrosion.

Other fixtures and appurtenances affected by corrosion from deicing salts are signposts, light columns, circuitry in traffic signals, guard rails, wire fencing, retaining walls, noise barriers (as well as their concrete bases), snow and ice control equipment, parking garages, utility lines, pipelines, steel storage tanks, bronze statues, monuments, and copper roofing.

The severity and extent of damage depends largely on prevailing local conditions, such as the degree of salt use, the number of roadside objects, the presence of other corrosion factors, and emission concentrations of SO₂ and NO_X gases.

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