Admixtures which cause early setting and hardening of concrete are called
Workability admixtures
Accelerators
Retarders
Air entraining agents
Correct Answer :
B. Accelerators
Related Questions
Admixtures which cause early setting and hardening of concrete are called
Workability admixtures
Accelerators
Retarders
Air entraining agents
The most commonly used admixture which prolongs the setting and hardening time is
Gypsum
Calcium chloride
Sodium silicate
All of the above
Segregation is responsible for
Honey-combed concrete
Porous layers in concrete
Surface scaling in concrete
All the above
For an ordinary Portland cement
Residual does not exceed 10% when sieved through IS Sieve No. 9
Soundness varies from 5 to 10 mm
Initial setting time is not less than 30 minutes
Compressive stress after 7 days, is not less than 175 kg/cm2
For the construction of cement concrete dams, the maximum permissible size of the aggregates, is
40 mm
50 mm
60 mm
70 mm
If fineness modulus of sand is 2.5, it is graded as
Very fine sand
Fine sand
Medium sand
Coarse sand
The main reinforcement in the heel of a T-shaped R.C. retaining wall is provided on
Top face perpendicular to wall
Bottom face perpendicular to wall
Both top and bottom faces perpendicular to wall
None of the above
Horizontal construction joints in concrete walls are generally provided at
Soffit level
Window sill level
Floor level
All the above
Water required per bag of cement, is
7 kg
14 kg
21 kg
35 kg
The slab is designed as one way if the ratio of long span to short span is
Less than 1
Between 1 and 1.5
Between 1.5 and 2
Greater than 2
The datum temperature for maturity by Plowman, is
23°C
0°
- 5.6°C
- 11.7°C
Bulking of sand is maximum if moisture content is about
2 %
4 %
6 %
10 %
Separation of coarse aggregates from mortar during transportation, is known
Bleeding
Creeping
Segregation
Shrinkage
Pick up the correct statement from the following:
A highly absorptive aggregate reduces the workability of concrete considerably
The specific gravity of aggregate is important for the determination of the moisture content
The absorption and porosity of an aggregate influence the property of the concrete
All the above
The grade of concrete not recommended by I.S. : 456, is
M 100
M 200
M 300
M 500
The strength and quality of concrete, depend upon:
Grading of aggregates
Surface area of aggregates
Shape of aggregates
All the above
Air entrainment in the concrete increases
Workability
Strength
The effects of temperature variations
The unit weight
The minimum percentage of chemical ingredient of cement is that of
Magnesium oxide
Iron oxide
Alumina
Lime
Pozzolanic properties exist in
Shales
Fly ash
Pumicite
All the above
Cement used for normal concrete construction, is obtained by burning a mixture of
Siliceous and argillaceous materials
Argillaceous and calcareous materials
Siliceous and calcareous materials
Siliceous, argillaceous and calcareous materials
Finer grinding of cement
Affects only the early development of strength
Affects only the ultimate strength
Both (A) and (B)
Does not affect the strength
To obtain a very high strength concrete, use very fine grained
Granite
Magnetite
Barite
Volcanic scoria
Sands of zone I are:
Course
Medium
Medium to fine
Fine
If X, Y and Z are the fineness modulli of coarse, fine and combined aggregates, the percentage (P) of fine aggregates to combined aggregates, is
P = [(Z - X)/(Z - Y)] × 100
P = [(X - Z)/(Z - Y)] × 100
P = [(X - Z)/(Z + Y)] × 100
P = [(Z + X)/(Z - Y)] × 100
For preparing a test-specimen, it is necessary
To mix cement and fine aggregate by dry hand
To mix coarse aggregates
To mix water to the cement, fine aggregates and coarse aggregates
All the above
In case of hand mixing of concrete, the extra cement to be added is
5 %
10 %
15 %
20 %
Shrinkage of concrete depends upon
(i) Humidity of atmosphere
(ii) Passage of time
(iii) Stress The correct answer is
(i) and (ii)
(ii) and (iii)
Only (iii)
All (i), (ii) and (iii)
Maximum distance between expansion joints in structures as per IS: 456 1978 is
20 m
30 m
45 m
60 m
In pre-stressed concrete
Forces of tension and compression change but lever arm remains unchanged
Forces of tension and compressions remain unchanged but lever arm changes with the moment
Both forces of tension and compression as well as lever arm change
Both forces of tension and compression as well as lever arm remain unchanged
Particles of 0.002 mm size are that of
Clay
Sand
Gravel
None of these