The impurity of mixing water which affects the setting time and strength of concrete, is
Sodium sulphates
Sodium chlorides
Sodium carbonates and bicarbonates
Calcium bicarbonates
Correct Answer :
C. Sodium carbonates and bicarbonates
Related Questions
Slump test of concrete is a measure of its
Consistency
Compressive strength
Tensile strength
Impact value
If the size of panel in a flat slab is 6 m × 6 m, then as per Indian Standard Code, the widths of column strip and middle strip are
3.0 m and 1.5 m
1.5 m and 3.0 m
3.0 m and 3.0 m
1.5 m and 1.5 m
For a reinforced concrete section, the shape of shear stress diagram is
Wholly parabolic
Wholly rectangular
Parabolic above neutral axis and rectangular below neutral axis
Rectangular above neutral axis and parabolic below neutral axis
High carbon content in the steel causes
Decrease in tensile strength but increase in ductility
Increase in tensile strength but decrease in ductility
Decrease in both tensile strength and ductility
Increase in both tensile strength and ductility
Pick up the correct statement from the following:
Segregation is necessary for a workable concrete
Consistency does not affect the workability of concrete
If the concrete mix is dry, the slump is maximum
None of these
The 28 days cube strength of mass concrete using aggregates of maximum size 5 cm for gravity dams should be
Between 150 to 300 kg/cm2
Between 350 to 600 kg/cm2
Between 150 to 500 kg/cm2
Below 200 kg/cm2
A continuous beam is deemed to be a deep beam when the ratio of effective span to overall depth (1/D) is less than
1.5
2.0
2.5
3.0
Minimum pitch of transverse reinforcement in a column is
The least lateral dimension of the member
Sixteen times the smallest diameter of longitudinal reinforcement bar to be tied
Forty-eight times the diameter of transverse reinforcement
Lesser of the above three values
The size of fine aggregates does not exceed
2.75 mm
3.00 mm
3.75 mm
4.75 mm
Workability of concrete is measured by
Vicat apparatus test
Slump test
Minimum void method
Talbot Richard test
The factor of safety for
Steel and concrete are same
Steel is lower than that for concrete
Steel is higher than that for concrete
None of the above
The grade of concrete not recommended by I.S. : 456, is
M 100
M 200
M 300
M 500
The entrained air in concrete
Increases workability
Decreases workability
Decreases resistance to weathering
Increases strength
The depth of footing for an isolated column is governed by (i) Maximum bending moment (ii) Shear force (iii) Punching shear The correct answer is
Only (i)
(i) and (ii)
(i) and (iii)
All (i), (ii) and (iii)
Horizontal construction joints in concrete walls are generally provided at
Soffit level
Window sill level
Floor level
All the above
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
Select the incorrect statement
The loss of pre-stress is more in pre-tensioning system than in posttensioning system.
Pre-tensioning system has greater certainty about its durability.
For heavy loads and large spans in buildings or bridges, posttensioning system is cheaper than pre-tensioning system
None of the above
The cement whose strength is a little lower than the ordinary cement during the first three months but attains afterwards the same strength, is known as
Low-heat Portland cement
Rapid hardening Portland cement
Portland blast slag cement
Portland pozzolana cement
The relation between modulus of rupture fcr, splitting strength fcs and direct tensile strength fcl is given by
fcr - fcs = fcl
fcr > fcs > fcl
fcr < fcs < fcl
fcs > fcr > fcl
Stress strain curve of high tensile steel
Has a definite yield point
Does not show definite yield point but yield point is defined by 0.1% proof stress
Does not show definite yield point but yield point is defined by 0.2% proof stress
Does not show definite yield point but yield point is defined by 2% proof stress,
Pick up the correct statement from the following:
The free water is the amount of water added while mixing and the amount of water held on the surface of the aggregates prior to mixing
The total water is the free water and the amount actually absorbed by the aggregates
Neither (a) nor (b)
Both (a) and (b)
How long will it take for the concrete to achieve 100% of its strength?
7 days
14 days
21 days
28 days
Curing
Reduces the shrinkage of concrete
Preserves the properties of concrete
Prevents the loss of water by evaporation
All of the above
To prevent segregation, the maximum height for placing concrete, is
100 cm
125 cm
150 cm
200 cm
Workability of concrete is directly proportional to
Aggregate cement ratio
Time of transit
Grading of the aggregate
All of above
The condition not applicable to water cement ratio law, is
Internal moisture conditions on hydration continue till complete strength is gained
Concrete specimens may be tested at any temperature
Concrete specimens need be of same age
Concrete specimens need be of same size
Addition of pozzolana to ordinary port land cement, causes
Decrease in early strength
Reduction in chemical action with sulphates
Increase in shrinkage
All the above
Efflorescence in cement is caused due to an excess of
Alumina
Iron oxide
Silica
Alkalis
In a ring beam subjected to uniformly distributed load (i) Shear force at mid span is zero (ii) Shear force at mid span is maximum (iii) Torsion at mid span is zero (iv) Torsion at mid span is maximum The correct answer is
(i) and (iii)
(i) and (iv)
(ii) and (iii)
(ii) and (iv)
If a beam fails in bond, then its bond strength can be increased most economically by
Increasing the depth of beam
Using thinner bars but more in number
Using thicker bars but less in number
Providing vertical stirrups