Civil war Day 23 PWD-RCC INTRO.

The minimum cube strength of concrete used for a pre-stressed member, is ________

• 350 kg/cm2
• 100 kg/cm2
• 150 kg/cm2
• 50 kg/cm2

Answer explanation

Prestressed concrete needs high strength; minimum ≈ 350 kg/cm².

Mild steel have a yield point of ....... MPa

• 140
• 230
• 250
• 480

Answer explanation

Mild steel (Fe 250) has yield strength ≈ 250 MPa.

pH value of water used for concrete shall not be

• Less than 6
• 6
• Less than 7
• More than 7

Answer explanation

IS 456 specifies pH ≥ 6.

Short Term Modulus of Elasticity of concrete is

• more than long Term Modulus of Elasticity of concrete
• less than long Term Modulus of Elasticity of concrete
• equal to long Term Modulus of Elasticity of concrete
• none of these

Answer explanation

Short-term modulus is higher; long-term is reduced by creep.

As cement content increases, creep

• increases
• decreases
• first increase then decrease
• first decrease then increase

Answer explanation

Higher cement → lower w/c ratio → lower creep.

The relation between modulus of rupture fcr, splitting tensile strength fcs and direct tensile strength fct is given by

• fcr = fcs = fct
• fcr < fcs < fct
• fcr > fcs > fct
• fcs > fcr > fct

Answer explanation

Flexural > splitting > direct tensile strength.

Flexural Strength of concrete with characteristic strength fck is given by

• 5000 √fck
• 0.3 √fck
• 3.13 √fck
• 0.7 √fck

Answer explanation

According to IS 456: fcr = 0.7√fck.

If characteristic compressive strength at 28 days is 40 N/mm2 and the standard deviation is 5 N/mm2, the target strength at 28days for concrete mix proportioning

• 40 N/mm2
• 45 N/mm2
• 43.25 N/mm2
• 48.25 N/mm2

Answer explanation

fck + 1.65s = 40 + 8.25 = 48.25 N/mm².

Modulus of rupture is a measure of

• the tensile strength of concrete
• the compressive strength of concrete
• the shear strength of concrete
• none of these

Answer explanation

Modulus of rupture = flexural tensile strength.

Ductility factor is the ratio between :

• Elastic modulus x stress
• Elastic modulus x yield strain
• failure strain to yield strain
• Yield strain to failure strain

Answer explanation

μ = Ultimate strain / Yield strain.