# Pavement Design Questions and Answers – Concrete Materials for Pavements – 1

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This set of Pavement Design Multiple Choice Questions & Answers (MCQs) focuses on “Concrete Materials for Pavements – 1”.

1. What is the minimum grade of concrete to be used in pavements?
a) M30
b) M40
c) M20
d) M50

Explanation: According to the standards, the minimum grade of concrete to be used for pavement construction is M40. It must be capable of withstanding the heavy wheel loads that are coming on top of it.

2. If OPC is used, then it should be done so in accordance with which code?
a) IS 456
b) IS 1489
c) IS 455
d) IS 269

Explanation: If OPC i.e. ordinary Portland cement is used, then the guidelines in IS 269 have to be followed. For Portland slag cement, IS 455 can be made use of. IS 1489 is used for Portland pozzolana cement and IS 456 is used for concrete design.

3. As per the classification of Portland cement according to properties, what does Type-III indicate?
a) High sulphate resistance
b) Normal concrete
c) High early strength
d) Low heat of hydration

Explanation: Based on the ASTM code, there are five types of Portland cement based on properties. Type-I indicates normal concrete, Type-II indicates moderate sulphate resistance, Type-III indicates high early strength, Type-IV indicates low heat of hydration and Type-V indicates high sulphate resistance.
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4. What is the formula for determining the modulus of elasticity of concrete as per ACI?
a) E=4500$$\sqrt{f_{ck}}$$
b) E=5500$$\sqrt{f_{ck}}$$
c) E=4700$$\sqrt{f_{ck}}$$
d) E=5000$$\sqrt{f_{ck}}$$

Explanation: E=5000$$\sqrt{f_{ck}}$$ is the formula as per ACI (American Concrete Institute) 318-14 for normal weight concrete. E=4500$$\sqrt{f_{ck}}$$ is according to Canadian Standard Association and E=5000$$\sqrt{f_{ck}}$$ is as per Indian Standard code.

5. What does PQC stand for?
a) Pavement Quality Control
b) Pavement Quality Cement
c) Pavement Quality Construction
d) Pavement Quality Concrete

Explanation: PQC is pavement quality concrete that is been used widely for concrete pavement construction. It is of high strength and long life of around 30 years. The PQC can be used for the construction of highways, expressways and runways.

6. What is the maximum size of coarse aggregates to be used in PQC?
a) 25 mm
b) 40 mm
c) 10 mm
d) 12.5 mm

Explanation: The coarse aggregates to be used in PQC should be crushed aggregates and they must be complying with IS 383. As per MORTH, the maximum size of coarse aggregate permitted is 25 mm.

7. ______ test is used to control the workability of the mix.
a) Ball penetration
b) Slump
c) Consistency
d) Vee Bee

Explanation: Slump test is the one generally employed to find the workability of the concrete mix. The ball penetration test is performed on a fresh concrete mix and it is considered an alternative to the slump test. Consistency and Vee Bee tests are conducted in the laboratory and are generally not employed to test the workability of the mix for pavement design.

8. Which of the below options represents the correct sequence of the stages in the hydration of cement?
a) Mixing, hardening, dormancy, cooling, densification
b) Mixing, dormancy, cooling, densification, hardening
c) Mixing, dormancy, hardening, cooling, densification
d) Mixing, hardening, cooling, densification, dormancy

Explanation: There are 5 different stages in the hydration process of cement. The stages in the sequential order are mixing, dormancy, hardening, cooling and densification. The stages are arranged in increasing order of the time taken for the completion of the stage.

9. What will be the compressive strength of a 150 mm concrete cylinder if the failure load is 500 kN?
a) 0.2829 N/mm2
b) 0.02829 N/mm2
c) 0.02829×10-3 N/mm2
d) 28.29 N/mm2

Explanation: The equation to compute the compressive strength of cement is given by $$f_C=\frac{P}{{\frac{π}{4}} D^2}$$ .
Where P is the failure load (kN)
D is the diameter of the sample (mm)
$$f_C=\frac{P}{{\frac{π}{4}} D^2}=\frac{500}{{\frac{π}{4}} 150^2} =0.02829 kN/mm^2≈28.29 N/mm^2$$

10. The cracks developed in the concrete pavement due to the freezing and thawing cycle of the aggregates is called S-cracking.
a) True
b) False

Explanation: The aggregates get deformed when subjected to alternate freezing and thawing cycles. This causes the development of cracks in the concrete pavement. These cracks are referred to as D-cracking or durability cracking.

11. The volume of concrete increases when attacked by sulphate.
a) True
b) False

Explanation: Sulphate attack is due to the reaction of sulphates with free calcium hydroxides and aluminates present in the mix. These tend to form crystals and insoluble compounds; hence the volume of concrete increases and it is prone to cracking.

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