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Per Table 8.3, for plain concrete in 'severe' exposure the source recommends a minimum cement content of:
A{'text': '220 kg/m³ and w/c not greater than 0.7', 'label': 'A'}
B{'text': '250 kg/m³ and w/c not greater than 0.6', 'label': 'B'}
C{'text': '310 kg/m³ and w/c not greater than 0.5', 'label': 'C'}
D{'text': '500 kg/m³ and w/c not greater than 0.3', 'label': 'D'}
Answer & Solution
Correct answer: C. {'text': '310 kg/m³ and w/c not greater than 0.5', 'label': 'C'}
1. Table 8.3 lists for severe exposure (e.g. sea water, alternate wetting/drying, freezing while wet, heavy condensation / corrosive fumes): plain concrete needs 310 kg/m³ and w/c ≤ 0.5; reinforced concrete needs 360 kg/m³ and w/c ≤ 0.45.
2. Milder exposures relax both cement-content and w/c requirements.
_Source: IGNOU ET-522 Block-2 Unit-8 Durability of Concrete, Table 8.3, §8.3.3, p. 70_
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