http://worldcat.org/entity/work/id/3827240

Salt action on concrete

Serious deterioration of concrete bridges by deicing salts is generally ascribed to depassivation and corrosion of reinforcing steel, as growth of its corrosion products causes spalling. Here, simple evaporative tests simulated the salt weathering that slowly crumbles rocks in nature, where crystals growing from pore water fed from below stress the matrix just as do ice crystals in frost heaving soil. Like needle ice (surface frost action in soil) the salt columns exuded from concrete also lifted tiny particles, signifying crumbling. Microcracks developed in 1-3 years of after-test dry storage. In a four-month simpler repeat test with salt, such cracks developed in all six concretes tested (five dolomitic, one siliceous). The siliceous one developed eye-visible cracks in three-year storage and a visible stone chip in the short repeat test, both with sodium chloride. The siliceous concrete also cracked badly within one week with strong calcium chloride and deteriorated completely in three-year storage. It also cracked badly with dilute calcium chloride or calcium nitrate exudation in tests with seawater may signify internal reaction plugging pores with insoluble magnesium hydroxide. This suggests a hypothetical means of control by addition of Mg++ to deicers or concrete. Present results suggest that neither corrosion of steel nor the C1- ion are requisite in salt action on concrete but that salt-caused microcracks may facilitate access of salt for cracking and also of carbon dioxide, water and salt for ultimate corrosion effects.

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