Concrete Technology (141-160)

Updated: Apr 29, 2020

141.

a) The loss of prestress is more in pretension ing system than in post

tensioning system.

b) Pretensioning system has greater certainty about its durability.

c) For heavy loads and large spans in buildings or bridges, post-tensioning

system is cheaper than pretensioning system


142. Which of the following losses of prestress occurs only in pretensioning and not in post-tensioning ? elastic shortening of concrete




143. Prestress loss due to friction occurs only in post-tensioned beams


144. The coefficient of shrinkage for high grade concrete for pretensioned work is

3 x 10⁻⁴

145. Which of the following has high tensile strength ? cold drawn wires

146. High carbon content in the steel causes increase in tensile strength but

decrease in ductility


147. Stress strain curve of high tensile steel does not show definite yield point but

yield point is defined by 0.2% proof stress

148. Elastic modulus of high tensile steel is nearly the same as that of mild steel

149. Cube strength of controlled concrete to be used for pretensioned and post-tensioned work respectively should not be less than 42 MPa and 35 MPa

150. Ultimate strength of cold drawn high steel wires decreases with increase in diameter of bar

151. Prestressing losses in post-tensioned and pre-tensioned beams are respectively 15% and 20%

152. In concrete, use of angular crushed aggregate in place of natural rounded

gravel affects flexural tensile strength

153. Ratio of compressive strength to tensile strength of concrete increases with age


154. According to Indian Standards, the grading of fine aggregates is divided into

four zones

155. Assertion A : Lightweight concrete exhibits higher shrinkage than normal weight concrete.

Reason R : Modulus of elasticity of light weight concrete is lower, than that of

normal weight concrete.

Both A and R are true and R is the correct explanation of A


156. Endurance limit of mild steel is approximately equal to Endurance limit is defined as the maximum value of the ratio of maximum stress to short time static strength, below which no failure occurs 0.5

157. With the increase in rate of loading during testing, compressive strength of concrete increases

158. For a given aggregate content, increasing the water-cement ratio in concrete

increases shrinkage

159.Assertion A : The net loss of strength due to air entrapment of a richer mix is higher than that of a leaner mix.

Reason R : Effect of air entrainment on improving workability is smaller in richer

mix than in a leaner mix. Select your answer based on the coding system given

below

Both A and R are true and R is the correct explanation of A


160. The bond strength between steel reinforcement and concrete is affected by

i) steel properties

ii) concrete properties

iii) shrinkage of concrete

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