This set of Basic Civil Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Composition of Concrete”.
1. How many components are mainly used to prepare concrete?
Explanation: Concrete is prepared by mixing cement, fine aggregate, coarse aggregate with water. It is a thick paste and hence has high bulk density.
2. Which of the below is the most common alternative to cement in concrete?
b) Fly ash
Explanation: Asphalt is the highly cementitious material. It possesses almost all qualities of cement and is widely used as an alternative to cement.
3. What is the ideal water-cement ratio to be used while hand mixing?
Explanation: Ideal water cement ratio for general works is 0.45. During machine mixing, it can be in the range of 0.4-0.5. Hand mixing is done by labourers and maximum 0.6 can be allowed.
4. Which IS code gives details regarding water to be used in concrete?
a) IS 456
b) IS 383
c) IS 565
d) IS 3012
Explanation: Normally, potable water is to be used for preparing concrete. In the case where potable water is not available, a certain amount of impurities are permissible in the water to be used. Those are given in Table in IS 456.
5. How many types of chemical admixture are there?
Explanation: Admixtures are compounds added to concrete to attain specific properties. The chemical admixtures are added in small amounts. The 4 types are accelerators, retarders, plasticizers and air entraining agents.
6. Retarders are used for:
a) Construction of high rise building
b) Repair works
c) Cold weather conditions
d) Grouting deep oil wells
Explanation: Retarders are used to slow down the initial rate of hydration and extend the initial setting time. It is therefore used to grout deep oil wells, transport RMC (Ready Made Concrete) and avoid cold joints. Accelerator is used for first 3 options.
7. _________ is added to make white concrete.
a) Fly ash
c) Rise husk
Explanation: Fly ash, Rise husk are dark in colour. Metakaolin is usually bright white in colour and is the preferred choice for architectural concrete where appearance is important.
8. As water cement ratio increases, ________ also increases.
a) Compressive strength
b) Tensile strength
Explanation: More water improves the workability of a mix, but compromises on the strength requirements. Hence, ideal w/c ratio of 0.45 is to be used.
9. Which of the below is an example of plasticizer?
a) Hydroxylated carboxylic acid
Explanation: Fluoro-silicate is an accelerator. Gypsum is a retarder and surkhi is a type of mineral admixture.
10. Which component of concrete gives it desired compressive strength?
Explanation: Aggregates used are sand, gravel or crushed stones. These have high compressive strength. Concrete is strong in compression and weak in tension due to this reason.
11. What is the ratio of the component in grade M20 concrete?
Explanation: Concrete is graded into many types as per IS 456-2000. M stands for mix and the number, say, 20 is a compressive strength after 28 days in N/mm2. Generally, M20 grade is used. The ratio of cement: fine: coarse aggregate for M20 is 1:1.5:3. For M10 it is 1:3:6, M15 it is 1:2:4 and M25 it is 1:1:2.
Sanfoundry Global Education & Learning Series – Basic Civil Engineering.
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