1. Which is the best method for curing flat surfaces?
a) Spraying water
b) Placing wet gunny bags
c) Applying curing compounds
d) Stagnating water
Explanation: Curing is the process of maintaining moisture in freshly laid concrete to strengthen it. For flat surfaces like floors and slabs, ponding or stagnating water is the best method. Temporary bund can be made with mortar and filled with water to cure.
2. Excess vibration during compacting can lead to:
a) Bleeding
b) Segregation
c) High strength
d) Air bubbles
Explanation: Over vibration may lead to a problem called segregation. The coarse aggregate is separated from the cement matrix. This leads to low strength.
3. Steam curing is adopted for
a) Precast structures
b) Columns
c) Beams
d) Walls
Explanation: The precast structures are placed in enclosed chambers. Then the steam is pumped into the chamber. It accelerates the hydration of concrete and it is left for the curing period.
4. A gap of 0.3m is to maintained between cement bag and wall, while storing cement.
a) True
b) false
Explanation: The storage of cement is important. It should not be placed too close to the wall or other cement bags to avoid air circulation around bags. It may dampen the cement and make it useless.
5. Tensile strength is found out using:
a) CTM
b) Gradual tensile test
c) Split tensile test
d) Radial tensile test
Explanation: In addition to using characteristic strength fck to determine tensile strength, split tensile test can also be used. It is performed using a UTM.
6. Flexure strength is determined as:
a) Modulus of rigidity
b) Modulus of rupture
c) Modulus of plasticity
d) Modulus of elasticity
Explanation: Flexure strength of concrete is defined as the tensile strength of extreme fibre of plain concrete beam. It is determined in terms of modulus of rupture.
7. Compaction factor for a heavily reinforced section with vibration is:
a) <0.75
b) 0.75-0.85
c) 0.85-0.92
d) >0.92
Explanation: Compaction factor test is conducted to determine the compaction factor. It has different values required for different purposes. To concrete a heavily reinforced section with vibration it is 0.85-0.92.
8. The result of Vee-Bee test is expressed in terms of:
a) s
b) m
c) N/mm2
d) kg
Explanation: The time is tested is Vee-Bee test. Time required to complete remoulding of concrete when subjected to the vibration is measured. It is then expressed in seconds.
9. The size of a commonly used specimen for compression test is:
a) 50×30 mm
b) 150x150x150 mm
c) 150x50x50 mm
d) 150×150 mm
Explanation: The commonly used specimen to test compressive strength is a cube. It has 3 dimensions-length, width and height. These cubes are cast in moulds of size 150x150x150mm.
10. Concrete is filled in how many layers in slump cone in slump test.
a) 3
b) 2
c) 6
d) 4
Explanation: The fresh concrete is filled in slump cone in 4 layers. Each layer is tamped 25 times with a 16mm pointed rod. The specifications are given in IS 1199.