alleryStart learning →Per §10.4 and IS 456-78, the minimum sample size to determine the standard deviation σ for concrete is:
AAt least 10 test results
BAt least 30 test results
CAt least 20 test results
DAt least 100 test results
Answer & Solution
Correct answer: B. At least 30 test results
1. §10.4: 'For determination of σ at least 30 samples are to be taken as per IS 456 - 78.'
2. The same section caps the coefficient of variation V = (σ/μ) × 100 at 15 percent for acceptable concrete production.
_Source: IGNOU ET-522 Block-3 Unit-10 Concrete Mix Design, §10.4, p. 8_
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