Some question and answers those who are appearing for interview

archdevil

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Sep 21, 2017
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CONCRETE TECHNOLOGY - GENERAL QUESTIONS
ASKED IN COMPETITIVE EXAMS

To determine the modulus of rupture, the size of test specimen used is
a) 150 x150 x500 mm
b) 100 x100 x700 mm
c) 150 x150 x700 mm
d) 100 x100 x500 mm
Ans: c

The property of fresh concrete, in which the water in the mix tends to rise to the surface while placing and compacting, is called
a) segregation
b) bleeding
c) bulking
d) creep
Ans: b

Select the incorrect statement
a) Lean mixes bleed more as compared to rich ones.
b) Bleeding can be minimized by adding pozzuolana finer aggregate.
c) Bleeding can be increased by addition 'of calcium chloride.
d) none of the above
Ans: d

The property of the ingredients to separate from each other while placing the concrete is called
a) segregation
b) compaction
c) shrinkage
d) bulking
Ans: a

Workability of concrete is directly proportional to
a) aggregate cement ratio
b) time of transit
c) grading of the aggregate
d) all of above
Ans: c

Workability of concrete is inversely pro¬portional to
a) time of transit
b) water-cement ratio
c) the air in the mix
d) size of aggregate
Ans: a

Approximate value of shrinkage strain in concrete, is
a) 0.003
b) 0.0003
c) 0.00003
d) 0.03
Ans: b

Air entrainment in the concrete increases
a) workability
b) strength
c) the effects of temperature variations
d) the unit weight
Ans: a

The relation between modulus of rupture fcr, splitting strength fcs and direct tensile strength fcl is given by
a) tcr -rcs = tct
b) fcr>fcs>fc.
C) fcr
d) fc5>fcr>fC.
Ans: b

The approximate value of the ratio between direct tensile strength and flexural strength is
a) 0.33
b) 0.5
c) 0.75
d) 1.0
Ans: b

Strength of concrete increases with
a) increase in water-cement ratio
b) increase in fineness of cement
c) decrease in curing time
d) decrease in size of aggregate
Ans: b

The relation between modulus of rupture and characteristic strength of concrete fck is given by
a) fcr=0.35Vf7
b) fcr=0.57f7
c) fcr=0.7Vf7
d) fcr=1.2Vf7
where fcr and fck are in N/mm2'
Ans: c

The compressive strength of 100 mm cube as compared to 150 mm cube is always
a) less
b) more
c) equal
d) none of the above
Ans: b

According to IS : 456 -1978, the modulus of elasticity of concrete Ec (in N/mm2) can be taken as
a) Ec = = 5700
b) Ec = = 570
c) Ec = = 5700fck
d) Ec = where fck N/mm2 = 700 is the characteristic strength in
Ans: a

Increase in the moisture content in con-crete
a) reduces the strength
b) increases the strength
c) does not change the strength
d) all of the above
Ans: a

As compared to ordinary portland cement, use of pozzuolanic cement
a) reduces workability
b) increases bleeding
c) increases shrinkage
d) increases strength
Ans: c

Admixtures which cause early setting, and hardening of concrete are called
a) workability admixtures
b) accelerators
c) retarders
d) air entraining agents
Ans: b

The most commonly used admixture which prolongs the setting and hardening time is
a) gypsum
b) calcium chloride
c) sodium silicate
d) all of the above
Ans: a

The percentage of voids in cement is approximately
a) 25%
b) 40%
c) 60%
d) 80%
Ans: b

The strength of concrete after one year as compared to 28 days strength is about
a) 10 to 15% more
b) 15 to 20% more
c) 20 to 25% more
d) 25 to 50% more
Ans: c

As compared to ordinary portland cement, high alumina cement has
a) higher initial setting time but lower final setting time
b) lower initial setting time but higher final setting time
c) higher initial and final setting times
d) lower initial and final setting times
Ans: a

Modulus of rupture of concrete is a measure of
a) flexural tensile strength
b) direct tensile strength
c) compressive strength
d) split tensile strength
Ans: a

In order to obtain the best workability of concrete, the preferred shape of aggregate is
a) rounded
b) elongated
c) angular
d) all of the above
Ans: a

Bulking of sand is maximum if moisture content is about
a) 2 %
b) 4%
c) 6%
d) 10%
Ans: b

Finer grinding of cement
a) affects only the early development of strength
b) affects only the ultimate strength
c) both (a) and (b)
d) does not affect the strength
Ans: a

Poisson's ratio for concrete
a) remains constant
b) increases with richer mixes
c) decreases with richer mixes
d) none of the above
Ans: b

1% of voids in a concrete mix would reduce its strength by about
a) 5%
b) 10 %
c) 15%
d) 20%
Ans: a

The fineness modulus of fine aggregate is in the range of
a) 2.0 to 3.5
b) 3.5 to 5.0
c) 5.0 to 7.0
d) 6.0 to 8.5
Ans: a

The factor of safety for
a) steel and concrete are same
b) steel is lower than that for concrete
c) steel is higher than that for concrete
d) none of the above
Ans: b


For a reinforced concrete section, the shape of shear stress diagram is
a) wholly parabolic
b) wholly rectangular
c) parabolic above neutral axis and rectangular below neutral axis
d) rectangular above neutral axis and parabolic below neutral axis
Ans: c

Diagonal tension in a beam
a) is maximum at neutral axis
b) decreases below the neutral axis and increases above the neutral axis
c) increases below the neutral axis and decreases above the neutral axis
d) remains same
Ans: c

If a beam fails in bond, then its bond strength can be increased most economi-cally by
a) increasing the depth of beam
b) using thinner bars but more in number
c) using thicker bars but less in number
d) providing vertical stirrups
Ans: b

If nominal shear stress tv exceeds the design shear strength of concrete xc, the nominal shear reinforcement as per IS : 456-1978 shall be provided for carrying a shear stress equal to
a) xv
b) xc
c) xv - TC
d) Tv + Tc
Ans: c

If the depth of actual neutral axis in a beam is more than the depth of critical neutral axis, then the beam is called
a) balanced beam
b) under-reinforced beam
c) over-reinforced beam
d) none of the above
Ans: c

If the depth of neutral axis for a singly reinforced rectangular section is represented by kd in working stress design, then the value of k for balanced section
a) depends on as, only
b) depends on aCbC only
c) depends on both crst and acbc
d) is independant of both ast and acbc where d is the effective depth, ast is per-missible
stress in steel in tension and ocbc is permissible stress in concrete in bend¬ing compression.
Ans: a

If the permissible stress in steel in tension is 140 N/mm2, then the depth of neutral axis for a singly reinforced rectangular balanced section will be
a) 0.35 d
b) 0.40 d
c) 0.45 d
d) dependent on grade of concrete also
Ans: b

Modulus of elasticity of steel as per IS : 456-1978 shall be taken as
a) 20 kN/cm2
b) 200 kN/cm2
c) 200kN/mm2
d) 2xl06N/cm2
Ans: c

Minimum grade of concrete to be used in reinforced concrete as per IS:456-1978 is
a) M15
b) M20
c) M 10
d) M25
Ans: a

For concreting of heavily reinforced sections without vibration, the workability of concrete expressed as compacting factor should be
a) 0.75-0.80
b) 0.80-0.85
c) 0.85 - 0.92
d) above 0.92
Ans: d

Maximum quantity of water needed per 50 kg of cement for M 15 grade of concrete is
a) 28 litres
b) 30 litres
c) 32 litres
d) 34 litres
Ans: c

In case of hand mixing of concrete, the extra cement to be added is
a) 5%
b) 10%
c) 15%
d) 20%
Ans: b

For walls, columns and vertical faces of all structural members, the form work is generally removed after
a) 24 to 48 hours
b) 3 days
c) 7 days
d) 14 days
Ans: a

The individual variation between test strength of sample should not be more than
a) ±5% of average
b) ± 10% of average
c) ± 15% of average
d) ±20% of average
Ans: c

For a cantilever of effective depth of 0.5m, the maximum span to satisfy vertical deflection limit is
a) 3.5 m
b) 4 m
c) 4.5 m
d) 5 m
Ans: a

For a simply supported beam of span 15m, the minimum effective depth to satisfy the vertical deflection limits should be
a) 600 mm
b) 750 mm
c) 900 mm
d) more than 1 m
Ans: b

For a continuous slab of 3 m x 3.5 m size, the minimum overall depth of slab to satisfy vertical deflection limits is
a) 50 mm
b) 75 mm
c) 100 mm
d) 120 mm
Ans: b

According to IS : 456-1978, the fiexural strength of concrete is
a) directly proportional to compressive strength
b) inversely proportional to compressive strength
c) directly proportional to square root of compressive strength
d) inversely proportional to square root of compressive strength
Ans: c

According to IS : 456-1978, the cblumn or the strut is the member whose effective length is greater than
a) the least lateral dimension
b) 2 times the least lateral dimension
c) 3 times the least lateral dimension
d) 4 times the least lateral dimension
Ans: c

According to IS : 456- 1978, minimum slenderness ratio for a short column is
a) less than 12
b) less than 18
c) between 18 and 24
d) more than 24
Ans: a

Lap length in compression shall not be less than
a) 15 4>
b) 20 <}>
c) 24 (j)
d) 30 (j)
where (j) is diameter of bar
Ans: c

The minimum cover in a slab should neither be less than the diameter of bar nor less than
a) 10 mm
b) 15 mm
c) 25 mm
d) 13 mm
Ans: b