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Sulfate attack typically happens to ground floor slabs in contact with soils containing a source of sulfates. [2] Sulfates dissolved by ground moisture migrate into the concrete of the slab where they react with different mineral phases of the hardened cement paste. The attack arises from soils containing SO 2−
A less common, but very severe, form of ESA is the thaumasitic form of sulfate attack (TSA) when concrete is exposed to an external source of sulfate in the concomitant presence of carbonate, HCO − 3 ions, or CO 2. [24] It preferentially occurs in clay formations exposed to air oxygen by excavation works and in which pyrite has been oxidized.
Sulfates in solution in contact with concrete can cause chemical changes to the cement, which can cause significant microstructural effects leading to the weakening of the cement binder (chemical sulfate attack). Sulfate solutions can also cause damage to porous cementitious materials through crystallization and recrystallization (salt attack). [7]
Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically oxidized in the presence of moisture to form sulfuric acid.
heat release, which can cause spontaneous overheating in large masses of concrete. Where necessary, tricalcium aluminate levels are reduced to control this effect. sulfate attack, in which sulfate solutions to which the concrete is exposed react with the AFm phases to form ettringite. This reaction is expansive, and can disrupt mature concrete.
GGBS cement is routinely specified in concrete to provide protection against both sulfate attack and chloride attack. GGBS has now effectively replaced sulfate-resisting Portland cement (SRPC) on the market for sulfate resistance because of its superior performance and greatly reduced cost compared to SRPC.
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Sulfate attacks, an hat appellation covering different concrete degradation mechanisms: Delayed ettringite formation (DEF), also known as internal sulfate attack (ISA) when the temperature of fresh concrete exceeds 65 °C during its setting and hardening; External sulfate attack (ESA), and; Thaumasite form of sulfate attack (TSA).