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Per §8.3.1, which sulphate's action on hydrated cement is described as the most severe because it decomposes the calcium silicate hydrates completely?
A{'text': 'Sodium sulphate (Na2SO4)', 'label': 'A'}
B{'text': 'Potassium sulphate (K2SO4)', 'label': 'B'}
C{'text': 'Ammonium sulphate ((NH4)2SO4)', 'label': 'C'}
D{'text': 'Magnesium sulphate (MgSO4)', 'label': 'D'}
Answer & Solution
Correct answer: D. {'text': 'Magnesium sulphate (MgSO4)', 'label': 'D'}
1. §8.3.1(b) reads: 'Magnesium sulphate has much more active action as it reacts not only with calcium hydroxide and hydrated calcium aluminates… but also decomposes the hydrated calcium silicates completely.'
2. The reaction produces calcium sulphate (gypsum), magnesium hydroxide and free silica — the loss of CSH is what makes MgSO4 the worst attack.
_Source: IGNOU ET-522 Block-2 Unit-8 Durability of Concrete, §8.3.1(b), p. 67_
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