1. Which component of concrete gives it desired compressive strength?
a) Water
b) Cement
c) Aggregates
d) Admixture
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.
2. What is the ratio of the component in grade M20 concrete
a) 1:3:6
b) 1:1.5:3
c) 1:1:2
d) 1:2:4
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.
3. Which process comes after batching in manufacture process?
a) Transportation
b) Placing
c) Mixing
d) Compacting
Explanation: Batching involves measuring the amount of raw materials required for the manufacture of concrete. The next step is to mix all these ingredients together.
4. Ready mix plant and central mix plant differ in:?
a) Transportation
b) Setting time
c) Properties
d) Water addition
Explanation: In ready mix plants, all the other ingredients are mixed, except water. While in central mix plants, water is also mixed along with other ingredients.
5. How many methods of batching are there?
a) 2
b) 3
c) 5
d) 6
Explanation: There are 2 types of batching – weigh and volume batching. In volume batching, volumetric measure of materials is taken (1 bag cement-35 litre). In weigh batching, measurement is in terms of weight (1 bag cement-50 kg).
6. What is the maximum height through which concrete can be poured
a) 0.1-0.6 m
b) 0.8-1 m
c) 0.5 m
d) 2 m
Explanation: Concrete consists of coarse aggregates. If it is placed or poured from a height above 1 m, segregation of coarse aggregate will take place, leading to improper distribution. It affects the strength parameter.
7. How many types of machine mixers are available?
a) 2
b) 5
c) 6
d) 3
Explanation: Based on the technique of discharging mixed concrete, there are 3 types of mixers available. They are tilting type, non-tilting type and pan type mixers.
8. In small works, concrete is transported using:
a) Conveyer belts
b) Pumps
c) Pans
d) Buckets
Explanation: In small works, less quantity of concrete is required. So, workers carry it in a pan atop their heads. Conveyer belts and pumps are used for large construction works.
9. Compacting is done to:
a) Place concrete on flat surface
b) Remove air bubbles
c) Place concrete on sloping surface
d) Introduce air bubbles
Explanation: While mixing of concrete, sometimes air gets trapped in it in the form of bubbles. These have to be removed to ensure strength parameters are met with.
10. Concrete is generally placed on a:
a) Form work
b) Stand
c) Mould
d) Platform
Explanation: Form work is a mould in which concrete is poured and allowed to set. It should be properly oiled and cleaned before pouring concrete. It can be used to cast beams, slabs, columns, etc.