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Per §8.3.2, in marine structures the MOST severe attack by sea water on concrete is observed:
A{'text': 'Below the low-water level (continuous immersion)', 'label': 'A'}
B{'text': 'Just above the high-water level (alternate wetting / drying)', 'label': 'B'}
C{'text': 'Only on freshly cast formwork', 'label': 'C'}
D{'text': 'Only at depths of more than 30 metres below the sea bed', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': 'Just above the high-water level (alternate wetting / drying)', 'label': 'B'}
1. §8.3.2(b)(i): 'most severe attack in sea water occurs just above the level of high water.'
2. The same paragraph clarifies that the area below the low-water level (continuously immersed) is the LEAST affected, and that the spray-zone crystallization of salts is the dominant mechanism.
_Source: IGNOU ET-522 Block-2 Unit-8 Durability of Concrete, §8.3.2, p. 69_
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