Concrete Technology (General Engineering) (SSC JE)

Total Questions: 53

31. According to IS 456, nominal mix concrete can be used upto which of the following grade [RRB S.S.E. (Secunderabad) 02.09.2015 (Shift-I)]

Correct Answer: (c) 20
Solution:

32. The batching tolerance for cement as per IS 456 is [RRB S.S.E. (Secunderabad) 02.09.2015 (Shift-I)]

Correct Answer: (c) ± 2%
Solution:

The batching tolerance for cement as per IS : 456 is ± 2%.

The accuracy of the measuring equipment shall be with in ±3% of the quantity of aggregate; admixtures and water.

33. Which one of the following does not react with concrete- [RRB JE 28.08.2015 (Shift-III) ]

Correct Answer: (d) Alcohol
Solution:

Alcohol does not react with concrete due to this is non acidic and non corrosive, there is no present of minerals in cement and aggregates. So, generally we can say that alcohol can used safely in concrete.

34. The rapid development of rigidity in a freshly mixed Portland cement paste, mortar, or concrete, usually happens with evolution of considerable heat. This rigidity cannot be dispelled, nor can the plasticity be regained, by further mixing without addition of water. This is called as [RRB S.S.E. 02.09.2015 (Shift-II) ]

Correct Answer: (b) Flash set
Solution:

The rapid development of rigidity in a freshly mixed Portland cement paste, mortar, or concrete, usually happens with evolution of considerable heat. This rigidity cannot be dispelled, nor can the plasticity be regained, by further mixing without addition of water. This is called as flash set.

35. Bleeding of concrete is said to occur when– [RRB JE 29.08.2015 (Shift-I) ]

Correct Answer: (c) Cement paste rises to the surface of concrete
Solution:

Bleeding of concrete is said to occur when cement paste rises to the surface of concrete and forming a thin layer on top of the concrete.

Reasons–
1. Insufficient compaction
2. Poorly graded aggregate |
3. Laceration (cuts)
4. Crushing injuries

36. Grading of aggregate in a concrete mix is necessary to achieve– [RRB JE 29.08.2015 (Shift-II)]

Correct Answer: (c) Reduction in voids
Solution:

Grading of aggregate in a concrete mix is necessary to achieved reduction in voids. For a good gradation of aggregate which have minimum void and sample paste generally fill the voids in the aggregate.

The paste requirement is the factor controlling the lost, since cement is the most expensive component.

37. The recommended slump for pumped concrete is : [RRB S.S.E. 03.09.2015 (Shift-I)]

Correct Answer: (d) 4-6 inches
Solution:

Slump test used to find workability of concrete slump value for pumped concrete work is 4 to 6 inches.

• If coarse aggregate of size greater than 38mm are used, then slump test is not conducted. For low water content mix slump value is zero.

38. According to IS 516, what is the minimum number of specimen to be tested for estimating the compressive strength [RRB S.S.E. 03.09.2015 (Shift-III)]

Correct Answer: (b) 3
Solution:

39. In general, the coefficient of thermal expansion of concrete does not depend on which of the following factors [RRB S.S.E. 03.09.2015 (Shift-III) ]

Correct Answer: (d) The quality of water
Solution:

Physical properties of concrete such as thermal expansion, etc depends upon type and quantity of cement. Physical properties do not depend upon quality of water.

40. Which of the following is not a non-destructive test used for concrete? [RRB S.S.E. 03.09.2015 (Shift-III]

Correct Answer: (d) Direct tensile test
Solution:

Tests of concrete in which the specimen are not destroyed are known as non-destructive tests. Nondestructive test are –

(i) Rebound hammer→ To find compressive strength of concrete.
(ii) Pull off test→ To find compressive strength
(iii) Ultrasonic test→ To check quality of concrete and aggregates.

Direct tensile test is a destructive test on small specimens to find tensile strength. Direct tensile strength of concrete is difficult to determine, recourse is often taken to the determination of flexural strength or the splitting tensile strength and computing the direct tensile.