Per §7.2 ('Age of Concrete'), the 28-day strength of normal concrete t…

Question

Per §7.2 ('Age of Concrete'), the 28-day strength of normal concrete typically represents what fraction of the strength still being gained?

Accepted Answer

A. {'text': 'About 80 percent of ultimate strength', 'label': 'A'}

1. §7.2 (Age of Concrete) reads: 'completing about 80 per cent of strength gaining in 28 days. However, concrete goes on gaining strength after 28 days but as it attains about 80 percent of it ultimate in 28 days it was customary to assume 28 days strength as full strength of concrete.'
2. IS 456-78 (Table 7.1) provides age factors of 1.0, 1.10, 1.15 and 1.20 for ages of 1, 3, 6 and 12 months.
_Source: IGNOU ET-522 Block-2 Unit-7 Strength of Concrete, §7.2 and Table 7.1, p. 48_

Answer

{'text': 'About 50 percent of ultimate strength', 'label': 'B'}

Answer

{'text': 'About 20 percent of ultimate strength', 'label': 'C'}

Answer

{'text': 'Effectively 100 percent of ultimate strength', 'label': 'D'}