Sulfate attack [SO4] on concrete is a common occurrence with compromising effects. Sulfates are present in various sources often in contact with concrete, i.e. the gypsum in cement, in fly ash additives, acid rain, ground water runoff, seawater, clay, sewage, and industrial waste. As most sulfates are soluble in water, there is high probability of sulfate exposure in concrete’s lifespan. [a]

Sulfate exposure causes an expansive ettringite crystallization. The increase in volume causes both superficial  and interior cracking, which could compromise the structural integrity of the concrete. [b] Cracking is most likely to occur near the surface where water exposure is more common, which often results in spalling and crumbling of the exterior. Occupants would also be alarmed, as the surface under attack becomes covered in the white reaction product. As seen in Figures 1 & 3, building foundations exposed to ground water runoff commonly suffer sulfate attack.

Prevention methods mainly aim to decrease the porosity of the concrete exposed. Lower water/cement ratios produce less permeable concrete. Other chemical additives increase strength and thus resistance to cracking. [c]