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Per §4.1, admixtures used in concrete are best defined as:
A{'text': 'Chemicals added in EXCESS of the basic ingredients to modify properties of the concrete', 'label': 'A'}
B{'text': 'Direct chemical replacements for the basic Portland cement component in the mix', 'label': 'B'}
C{'text': 'Heat-treated derivatives of the coarse aggregate phase reused in the same concrete mix', 'label': 'C'}
D{'text': 'Bonding agents used only after curing is complete to join hardened concrete to new pours', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Chemicals added in EXCESS of the basic ingredients to modify properties of the concrete', 'label': 'A'}
1. §4.1 opens: 'Admixtures are the chemicals which are used in excess of the basic ingredients of concrete i.e. cement, water, fine aggregate and coarse aggregate.'
2. They are added during or before mixing to modify properties of fresh or hardened concrete — not as cement replacements and not after curing.
_Source: IGNOU ET-522 Block-1 Unit-4 Admixtures, §4.1, p. 45_
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