This set of Basic Civil Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Properties of Concrete”.
1. Properties of concrete can broadly be divided into:
Explanation: Based on the state of concrete, its properties vary. Concrete in the fresh state has different properties than concrete in a hardened state.
2. The accumulation of water on the outer surface of the concrete is:
Explanation: Bleeding can be good as well as bad for fresh concrete. Sometimes due to improper mixing, the water forms a thin layer on the outer surface, by oozing out through voids.
3. Which of the below property of aggregates is not desirable?
a) Smooth texture
b) Well graded
c) Angular shape
d) Smaller size
Explanation: Aggregates should provide space for cement paste so as to lubricate the area. The parameters like texture, size, shape, grading are to be considered. Larger size, cubical, round and rough textured aggregates are preferred.
4. How does the strength of concrete differ with age of concrete?
c) No effect
d) Increases, then decreases
Explanation: It increases with increase in age. The strength measured after days, months and years shows an increase. It takes 28 days for concrete to attain full strength. However, it continues to attain strength even after 28 days.
5. Impermeability is a property of fresh concrete.
Explanation: Fresh concrete cannot be judged as impermeable. After it hardens and forms a structure, it may be impervious or pervious. Ideally, it should be impermeable.
6. Permanent dimension changes due to loading is termed as:
Explanation: Concrete shrinks with age. The changes in dimension are called creep. It is determined using creep coefficient which is the ratio of ultimate creep strain to elastic strain at the age of loading.
7. Which admixture is used to improve workability?
Explanation: Plasticizers help to increase the workability of concrete without altering the water-cement ratio. It is very helpful as it provides the required workability, at the same time does not compromise on strength.
8. Workability reduces with time.
Explanation: The rate of evaporation of water from concrete mix increases as time increases. Loss of water leads to less workability.
9. Bleeding is good to an extent if it occurs when concrete is:
Explanation: While the concrete is still plastic, the accumulated water due to bleeding can be used to mix concrete again and improve workability. It also benefits by further reducing water-cement ratio.
10. M15 concrete is used for:
d) Mass concreting works
Explanation: M10 is used for Mass concrete works, dams, etc. M20 is used for R.C.C. structures. M15 can be used for ground floor construction also.
11. In design of R.C.C. structures, the tensile strength of concrete is taken as:
Explanation: Since concrete does not take up tensile loads, it is taken as zero. But IS 456-2000 recommends the tensile strength to be calculated using Ft = 0.7√fck N/mm2.
12. Higher the cement content,
a) Higher aggregates
b) Lower workability
c) Higher strength
d) Lower strength
Explanation: Higher the cement content i.e. lower the aggregate cement ratio, higher is the strength. It improves workability also.
Sanfoundry Global Education & Learning Series – Basic Civil Engineering.
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