According to IS 456-2000, in the method of design mix concrete for an RCC structure, what will be the target mean strength of concrete if the mean characteristic strength is 35MPa with a standard deviation of 6 N/mm2?

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HPCL Engineer (Civil) 04 Nov 2022 Official Paper
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  1. 44.9 MPa
  2. 35 MPa
  3. 35.77 MPa
  4. 25 MPa

Answer (Detailed Solution Below)

Option 1 : 44.9 MPa
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Detailed Solution

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Concept:

The correct expression as per IS 456: 2000 to find Target mean strength is:

fcm = fck + (1.65 × σ)

fcm = Target mean strength

fck = Characteristic strength

σ = Standard deviation

1.65 is generally a risk factor

Calculations:

fck = 35 N/mm2

σ = 6 N/mm2

Target mean strength is:

fcm = fck + (1.65 × σ)

fcm = 35 + (1.65 × 6)

fcm = 44.9 N/mm2

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