Sulfate Attack

Sulfate attack is a widespread form of chemical attack on concrete. Sulfates are often present in groundwater, soil, and seawater. Local high concentrations of sulfates may be associated with industrial wastes. The major cause of expansion is the conversion of monosulfate phases into ettringite phases. This is accompanied by a large increase in solid volume. The volume increase and the needle-like shape of ettringite crystals are responsible for creating internal stresses that cause cracking.

Good example of paste expansion. Notice the unique crack pattern. (approx. 1mm full width) [Credit: Paul Stutzman, NIST]

Another BEI of polished section showing damage. [Credit: Paul Stutzman, NIST]