Sulfate attack
Deterioration caused by sulfates in soil or groundwater reacting with hardened cement paste, producing expansion, cracking, and progressive softening.
What does sulfate attack mean?
Sulfate-rich soils are common in parts of the western United States, and concrete in contact with them requires specific protection. The defenses are cements formulated for sulfate resistance, supplementary cementitious materials that reduce the vulnerable compounds, and above all a low water-cement ratio that keeps sulfates from getting in. Damage typically appears first at the ground line on foundations and slabs.
In practice
A soils report noting sulfate content is what drives a cement type change on a foundation, and ignoring it produces failures within a decade.