126. Pick up the correct statement from the following:
a) the concrete gains strength due to hydration of cement
b) the concrete cured at a temperature below 23°C, gains strength up to 28 days
c) the concrete does not set at freezing point
d) the strength of concrete increases with its age
e) all of the above
127. At freezing point of water, concrete
a) sets freely
b) sets slowly
c) sets rapidly
d) does not set
128. The datum temperature for maturity by Plowman, is
a) 23°C
b) 0°C
c)-5.6°C
d)-11.7°C
129.I.S.I. has specified the full strength of concrete after
a) 7 days
b) 14 days
c) 21 days
d) 28 days
130. The strength of concrete is directly proportional to
a) cement water ratio
b) water cement ratio
c) sand cement ratio
d) water aggregate ratio
131. The approximate ratio of strength of cement concrete at 3 months to that of 28 days of curing
a) 1.0
b) 1.15
c) 1.20
d) 1.30
132. The percentage of compressive strength of concrete at 7 days to that of 28 days
a) 40%
b) 65%
c) 100%
d) 115%
133. The approximate ratio of direct tensile strength to direct compressive strength test of concrete
a) 0.65
b) 0.40
c) 0.15
d) 0.10
134. Gypsum is added for
a) colour
b) strength
c) controlling setting time
d) none of these
135. High increase in temperature
a) increases the strength of concrete
b) decreases the strength of concrete
c) has no effect on the strength of concrete
d) none of these
136. Segregation is responsible for
a) honey-combed concrete
b) porous layers in concrete
c) surface scaling in concrete
d) sand streaks in concrete
e) all of the above
137. Separation of coarse aggregates from cement concrete during transportation, is known
a) bleeding
b) creeping
c) segregation
d) shrinkage
138. Separation of water or water sand cement from a freshly mixed concrete, is known
a) bleeding
b) creeping
c) segregation
d) shrinkage
139. The specific surface of cement is expressed in
a) mm²
b) mm/g
c) g/mm²
d) mm²/g mm
140. A setting of cement or concrete which occurs suddenly while being mixed and placed and prevents further working of the materials is called
a) quick set
b) flash set
c) initial setting
d) knocking
141. Adding a thin layer of cement mortar to the surface of concrete
is known as
a) punning
b) admixing
c) rodding
d) rendering
142. The breaking up and remixing of concrete that has layers to set is called
a) resetting
b) double setting
c) knocking
d) time setting
143. A concrete mix that causes difficulty in obtaining a smooth or good contact with forms which may be due to excess of middle sized particles or a deficiency of lime materials is called
a) uneven mix
b) harsh mix
c) heterogeneous
d) none of the above
144. A watery scum that is formed on top of concrete due to excessive water or excessive use of trowel or float is called
a) laitance
b) flashing
c) punning
d) water facing
145. For protection from frost, concrete should be
a) dense
b) free from cracks
c)adhesion between mortar and aggregate should be perfect
d) all of the above
146. The lower water cement ratio in concrete, introduces
a) smaller creep and shrinkage
b) greater density and smaller permeability
c) improved frost resistance
d) greater wear resistance and improved bond strength
e) all of the above
147. The entrained air in concrete
a) increases workability
b) decrease workability
c) decrease resistance to weathering
d) increase strength
148. The concrete mix which causes difficulty in obtaining a smooth finish, is known to possess
a) segregation
b) internal friction
c) hardness
d) bleeding
149. The factor which affects workability, is
a) water content and its temperature
b) shape and size of the aggregates
c) grading and surface textures of the aggregates
d) air entraining agents
e) all of the above
150. Pick up the correct statement from the following:
a) an increase in water content must be accompanied by an increase in cement content
b) angular and rough aggregates reduce the workability of the concrete
c) large size aggregates increase the workability due to lesser surface area
d) the slump of the concrete mix decreases due to an increase in temperature
e) all of the above
