Sulphate attack on concrete causes:
Choose the correct answer
Concrete to shrink and become stronger
Expansive reaction (ettringite and gypsum formation) causing cracking and disintegration of concrete
Only surface discolouration
Increase in pH only
Correct Answer
B. Expansive reaction (ettringite and gypsum formation) causing cracking and disintegration of concrete
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Sulphate attack: SO4²⁻ ions (from soil, groundwater, industrial effluent) react with: C3A + gypsum → ettringite (expansive, disrupts concrete); also C-S-H attacked by MgSO4. Expansion and cracking result. Prevention: sulphate-resistant cement (low C3A), dense low-permeability concrete, w/c < 0.45, surface protection. External sulphate attack is most common.
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