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Per §4.14, steel embedded in fresh / hardened concrete is protected from corrosion mainly because cement hydration causes the pore solution to maintain a pH of:
A{'text': 'Above 12.6 (highly alkaline)', 'label': 'A'}
B{'text': 'About 6.5 to 7 (neutral)', 'label': 'B'}
C{'text': 'About 9 (mildly alkaline)', 'label': 'C'}
D{'text': 'About 3 to 4 (acidic)', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Above 12.6 (highly alkaline)', 'label': 'A'}
1. §4.14 reads: 'It is recognised that steel embedded in heavily alkaline medium with pH-values from 9 upwards will not rust.' It then adds: 'the chemical reaction between cement and water in the concrete causes calcium-hydroxide to be formed as a by product alongwith gel. This ensures the concrete to be alkaline producing a pH value of more than 12.6 which renders the steel surface passive.'
2. Sodium benzoate (2 percent in mixing water) and sodium nitrate may be added as further inhibitors.
_Source: IGNOU ET-522 Block-1 Unit-4 Admixtures, §4.14, p. 55_
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