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Per §8.10, the rate of carbonation of concrete is highest at relative humidity in approximately what range?
A{'text': 'Below 30 percent humidity', 'label': 'A'}
B{'text': '40 to 75 percent humidity', 'label': 'B'}
C{'text': 'Always over 95 percent humidity', 'label': 'C'}
D{'text': 'Independent of humidity', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': '40 to 75 percent humidity', 'label': 'B'}
1. The carbonation diagram in §8.10 lists rate-of-carbonation against relative humidity: less than 30% = low, 40 to 75% = high, more than 75% = low.
2. At very low RH there is no water for the reaction; at very high RH the pores stay water-filled and CO2 cannot diffuse — both slow the reaction.
_Source: IGNOU ET-522 Block-2 Unit-8 Durability of Concrete, §8.10 carbonation diagram, p. 79_
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