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Per §8.10, the carbonation of concrete is associated with which pH outcome that drives reinforcement corrosion?
A{'text': 'pH actually rises further from above 12.6 to about 14, intensifying passivation', 'label': 'A'}
B{'text': 'pH stays steady at 7, neither corroding nor passivating the steel further', 'label': 'B'}
C{'text': "pH drops from above 12.6 toward 8, removing the steel's passivating layer", 'label': 'C'}
D{'text': "pH first rises to 16 and then settles at about 11 over the structure's life", 'label': 'D'}
Answer & Solution
Correct answer: C. {'text': "pH drops from above 12.6 toward 8, removing the steel's passivating layer", 'label': 'C'}
1. §8.14 reads: 'Environmental influences and carbon dioxide in particular, will reduce the concrete's pH-value (carbonation) and thus remove the passivating effect, in conjunction with existing humidity, the result is corrosion of the reinforcement.'
2. The carbonation diagram shows the pH-scale moving from alkaline 12 down through 8 (carbonated zone) into the acidic range.
_Source: IGNOU ET-522 Block-2 Unit-8 Durability of Concrete, §8.10, p. 78-79_
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