Civil engineer objective questions – Concrete Technology (Section-14)

326. If the average compressive strength is 4000 kg / cm² and standard deviation is 500 , the co – efficient of variation is

a ) 10 %

b ) 12.5 %

c ) 15 %

d ) 18.5 %

327. The risk of segregation is more for

a ) water mix

b ) larger proportion of maximum size

c ) coarser grading

d ) all of the above

 328. The process by which fresh cement concrete is compacted to remove the air bubbles is known as

a ) compaction

b) wetting

c ) placing

d) consolidation

329. Maturity of concrete means

a ) oldness of concrete

b ) strength of concrete

c ) sum of product of temperature & time

d ) none of the above

330. Gypsum is used as admixture in concrete to increase the property of concrete

a ) accelerator

b ) retarder

c ) water proofer

d ) none of the above

331. Calcium chloride is used as admixture in concret e to increase the property , of concrete

a ) accelerator

b) retarder

c ) water proofer

d ) none of the above

332. Calcium chloride as an recommended for use with

a ) ordinary portland cement

b) high alumina cement

c ) rapid hardening cement

d) none of the above

333. To improve the certain properties of concrete , admixture is used in concrete at the time of

a) grading of cement

b ) mixing of concrete

c) after pouring of concrete

d) none of the above

334. An admixture

a ) is a basic ingredient of concrete

b ) offers improvement not economically attained by adjusting mix proportions

c ) is a substitute for good concreting practice

d ) is beneficial to the properties of concrete when used in large quantities

335. An admixture could be used to

a ) accelerate initial setting of concrete

b ) increase strength of concrete

c ) improve workability

d ) all of the above

336. An accelerator shortens all of the following except

a ) setting time

b ) period of curing

c ) strength of concrete

d ) period of removal of formwork

337. Addition of retarder to concrete decreases all of the following except

a ) rate of hydration

b ) water – cement ratio

c ) workability and compressive strength

d ) rate of development of strength

338. Pick up the incorrect statement from the following :

a ) admixtures accelerate hydration

b ) admixtures make concrete water proof

c ) admixtures make concrete acid proof

d ) admixtures give high strength

e ) none of the above

339. Gel space ratio is defined as the ratio of

a ) volume of hydrated cement to the sum of volume of hydrated cement and capillary pores

b ) the sum of volume of hydrated ceme nt and capillary pores to volume of hydrated cement

c ) both (a ) and (b ) of above

d ) none of the above

340. Find the gel space ratio of concrete with following data : cement = 50 kg , Weight of water = 20 kg

a ) 0.85

b ) 0.91

c ) 0.96

d ) 0.99

341. The minimum grade of high strength concrete is

a ) M25

b ) M40

c ) M50

d ) M60

342. The type of aggregates not suitable for high strength concrete and for pavements subjected to tension , is

a ) rounded aggregate

b ) irregular aggregate

c ) angular aggregate

d ) flaky aggregate

343. The aggregate used for high strength concrete is

a ) round aggregate

b ) irregular aggregate

c ) angular aggregate

d ) all of the above

344. To obtain a very high strength concrete , use very fine grained

a ) granite

b ) magnetite

c ) barite

d ) pumice

345. Prestress is imparted to concrete by bearing in

a ) pre tensioning

b ) post tensioning

c ) both ( a ) and ( b ) of above

d ) none of the above

346. The minimum grade of concrete for pre – tensioned member is

a ) M15

b ) M20

c ) M25

d ) M40

347. The mix proportion of cement mortar to be used in the joints in the precast prestressed member is

a ) 1 : 1

b) 1:1.5

c ) 1 : 2

d) 1:2.5

348. The diameter of high tensile steel tendons used is

a ) 3 mm to 5 mm

b ) 5 mm to 8 mm

c ) 6 mm to 9 mm

d ) 8 mm to 12 mm

349. The minimum clear spacing for single wires used in pre tension system is

a ) 2 times the diameter of the wire and max . size of aggregate whichever is greater.

b ) 3 times the diameter of the wire and max . size of aggregate whichever is greater

c ) 2 times the diameter of the wire and 1.5 times max . size of aggregate whichever is greater

d ) 3 times the diameter of the wire and 1.5 times max . size of aggregate whichever is greater

350. The minimum clear spacing of non – grouped cables or large bars shall be

a ) 40 mm

b ) maximum size of cable or bar

c ) 5 mm plus maximum size of aggregate

d ) greater of ( a ) , ( b ) and ( c ) of above