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