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Per §8.3.1 (Methods of Controlling Sulphate Attack), addition of pozzolana to cement helps because it:
A{'text': 'Helps remove Ca(OH)2, raising the imperviousness of concrete', 'label': 'A'}
B{'text': 'Increases the C3A content of the Portland cement clinker', 'label': 'B'}
C{'text': 'Causes a flash setting that seals capillaries at very early age', 'label': 'C'}
D{'text': 'Increases alkali content that drives further alkali-aggregate reaction', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Helps remove Ca(OH)2, raising the imperviousness of concrete', 'label': 'A'}
1. §8.3.1(iii)(c): 'Improved resistance to sulphate attack is obtained by addition of pozzolonas to cement. This helps in removing Ca(OH)2 and thus increasing imperviousness of concrete.'
2. Less calcium hydroxide means less raw material for the gypsum-and-calcium-sulphoaluminate reactions.
_Source: IGNOU ET-522 Block-2 Unit-8 Durability of Concrete, §8.3.1(iii)(c), p. 68_
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