Concrete Technology (181-200)

Updated: Apr 29, 2020

181. According to Indian Standards, the limit of loss on ignition for ordinary portland cement is 5%


182. For a constant water-cement ratio, decrease in aggregate-cement ratio causes increase in workability




183. Assertion A : Workability of fresh concrete increases with time.

Reason R : There is a loss of moisture in concrete with time

A is false but R is true.

184. Workability of concrete increases by

i) increasing the water content

ii) increasing the temperature

185. Which of the following workability tests is most suitable for concrete of very low workability ? Vee-Bee test

186. The value of Vee-Bee time for low workability as per Indian Standards is

prescribed as 5 - 1 0 seconds


187. If the compacting factor of a concrete is 0.90, then the workability according to Indian Standards is medium

188.

a) Higher temperature reduces work ability

b) Segregation can be reduced by use of air entrainment

c) Bleeding is increased by use of air entrainment

189. According to Indian Standards, the increase in compressive strength of high

alumina cement concrete at 6 months, beyond 28 days compressive strength, is

zero

190. For a satisfactory workable concrete with a constant water-cement ratio, increase in aggregate cement ratio increases the strength of concrete

191. Minimum water-cement ratio required for full hydration of cement is 0.36

192. The presence of entrained air in concrete results in

i) reducing bleeding

ii) lowering density of concrete

iii) decreasing strength at all ages

193. The Indian Standards recommend the use of calcium chloride as accelerating

admixture in plain and reinforced concrete works only


194. Calcium chloride as accclearating admixture is not recommended for use with high alumina cement

195. Reduction in the quantity of mixing water which is possible by the use of plasticizers and admixtures varies from 5% to 15%

196. Assertion A : Retarders are useful when concreting is done in hot weather.

Reason R : In hot weather normal setting time of concrete is reduced due to

higher temperature gms, then the water absorption of sand is

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

197. Addition of sugar in concrete (about 0.05% of weight of cement) results in

increasing the setting time by about 4 hours

198. In concrete mix design, allowance for bulking of sand is necessary in case of

volume batching only

199. In concrete mix design, allowance for surface water carried by aggregate is

necessary in case of

a) volume batching only

b) weight batching only

200. Which of the following types of concrete mixers is most commonly used in precast concrete factories ?

pan type mixer

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