Experimental Deterioration of Highway Concrete by Chloride Deicing Salts

Experiments were performed on five Iowa highway concretes to determine their resistance to deterioration by chloride deicer salts. Four-inch cores were obtained from the highways, and small blocks cut from the cores were experimentally subjected to wet/dry, freeze/thaw, and continuous soak conditions. Experiments were also performed with magnesium acetate and magnesium nitrate. Deterioration of the highway concretes resulted in: (a) crumbling; and (b) facturing. Crumbling was often accompanied by brown discoloration. Severity and type of deterioration depended chiefly on deicer cation and experimetnal conditions. Magnesium chloride was most destructive. Calcium chloride was next, and sodium chloride was relatively benign except under freeze/thaw cycling in 0.75M NaCl, and high temperature wet/dry cycling. Magnesium acetate produced severe crumbling and moderate fracturing, and magnesium nitrate caused moderate deterioration by crumbling. The major cause of deterioration by magnesium chloride was formation of non-cementitious magnesium silicate hydrates. (A)