alleryStart learning →Per Table 10.3, the suggested standard deviation σ for M 20 grade concrete with 'GOOD' degree of control is:
A2.3 N/mm-square
B4.6 N/mm-square
C3.6 N/mm-square
D5.6 N/mm-square
Answer & Solution
Correct answer: B. 4.6 N/mm-square
1. Table 10.3 lists σ for M 20: Very Good = 3.6, Good = 4.6, Fair = 5.6 N/mm².
2. 'Good' control implies weigh-batching, periodic tests, controlled water and intermittent supervision per Table 10.4.
_Source: IGNOU ET-522 Block-3 Unit-10 Concrete Mix Design, Table 10.3, §10.8 Step 1, p. 15_
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