Cement – #Building Materials

Cement 

1. Introduction

Cement is a fine powder obtained by grinding a mixture of limestone and clay, which when mixed with water forms a paste that sets and hardens, binding other materials together.

👉 In simple words: Cement is a binding material used to make mortar and concrete.

2. Core Concepts
3. Raw Materials of Cement

Main raw materials:

Material	Function
Limestone	Provides calcium
Clay	Provides silica & alumina
Gypsum	Controls setting time

1. Manufacturing Process of Cement

This is a very important exam topic.

Step 1: Crushing and Grinding

• Limestone and clay are crushed
• Ground to fine powder

Step 2: Mixing of Raw Materials

Two methods:

• Wet process
• Dry process (most common)

Step 3: Burning in Rotary Kiln

• Temperature: 1400°C – 1500°C
• Forms hard nodules called clinker

Step 4: Grinding of Clinker

• Clinker is ground with 3–5% gypsum
• Produces Portland cement

1. Composition of Cement

Compound	Function
Lime (CaO)	Strength
Silica (SiO₂)	Hardness
Alumina (Al₂O₃)	Quick setting
Iron oxide (Fe₂O₃)	Colour & strength
Gypsum	Controls setting

1. Types of Cement

Type	Use
Ordinary Portland Cement (OPC)	General construction
Portland Pozzolana Cement (PPC)	Mass concrete
Rapid Hardening Cement	Road works
Low Heat Cement	Dams
Sulphate Resisting Cement	Marine works

1. Properties of Cement

Property	Purpose
Setting time	Workability
Soundness	Volume stability
Strength	Load carrying
Fineness	Rate of hydration

1. Uses of Cement

• Making concrete
• Masonry mortar
• Plastering
• RCC works

3. Step-by-Step Practical Examples

Example 1: Choosing Cement for Dam Construction

Problem:
Which cement is suitable for a dam?

Step 1: Identify requirement

Dam produces large heat.

Step 2: Match cement type

Low heat cement produces less heat.

➡ Answer: Low Heat Cement

Example 2: Function of Gypsum in Cement

Question:
Why is gypsum added to cement?

Step 1: Observe property

Without gypsum, cement sets too quickly.

Step 2: Identify role

Gypsum controls setting time.

➡ Gypsum prevents flash setting

4. Description of Diagram (Manufacture of Cement)

A flow diagram:

Limestone + Clay → Crushing → Grinding → Mixing → Rotary Kiln (Clinker) → Grinding with Gypsum → Cement

Each step in a rectangular box connected by arrows.

This diagram helps remember manufacturing steps in order.

5. Exam Focus: Must-Know Points ⭐

• Cement is a binding material that sets with water.
• Clinker is formed in a rotary kiln at 1400°C – 1500°C.
• Gypsum controls setting time of cement.
• OPC is used for general construction.
• Low heat cement is used for dams.

6. Multiple Choice Questions (MCQs)
7. Cement mainly acts as a:
8. Aggregate
   B. Binding material
   C. Filler
   D. Reinforcement

Answer: B

Explanation: Cement binds sand and aggregates.

2. Main raw material of cement is:
3. Sand
   B. Limestone
   C. Gypsum
   D. Clay

Answer: B

Explanation: Limestone provides calcium.

3. Which material controls setting time of cement?
4. Clay
   B. Silica
   C. Gypsum
   D. Iron oxide

Answer: C

Explanation: Gypsum prevents quick setting.

4. Temperature in rotary kiln is about:
5. 500°C
   B. 900°C
   C. 1200°C
   D. 1450°C

Answer: D

Explanation: Clinker forms at 1400–1500°C.

5. Clinker is obtained in:
6. Crusher
   B. Grinder
   C. Rotary kiln
   D. Mixer

Answer: C

Explanation: Burning in kiln forms clinker.

6. Cement used for marine works is:
7. OPC
   B. PPC
   C. Rapid hardening
   D. Sulphate resisting

Answer: D

Explanation: Resists sulphate attack.

7. Cement used for road repair works is:
8. OPC
   B. Rapid hardening
   C. Low heat
   D. PPC

Answer: B

Explanation: Gains strength quickly.

8. Which cement is used for mass concrete works?
9. PPC
   B. OPC
   C. Rapid hardening
   D. White cement

Answer: A

Explanation: PPC produces less heat.

9. Fineness of cement mainly affects:
10. Colour
    B. Strength gain
    C. Weight
    D. Soundness

Answer: B

Explanation: Finer cement hydrates faster.

10. Soundness test checks:
11. Strength
    B. Setting time
    C. Volume stability
    D. Colour

Answer: C

Explanation: Prevents expansion after setting.

11. Alumina in cement causes:
12. Slow setting
    B. Quick setting
    C. No effect
    D. Colour change

Answer: B

Explanation: Alumina speeds up setting.

12. Iron oxide gives cement:
13. Strength only
    B. Colour only
    C. Strength and colour
    D. Hardness only

Answer: C

Explanation: Fe₂O₃ improves strength and colour.

13. Low heat cement is used for:
14. Bridges
    B. Dams
    C. Roads
    D. Buildings

Answer: B

Explanation: Reduces thermal cracks.

14. Cement mixed with sand and water is called:
15. Concrete
    B. Mortar
    C. Paste
    D. Grout

Answer: B

Explanation: Mortar = cement + sand + water.

15. Which cement is used for decorative works?
16. White cement
    B. OPC
    C. PPC
    D. SRC

Answer: A

Explanation: White cement is used for finish.

16. Rapid hardening cement is obtained by:
17. Adding lime
    B. Adding gypsum
    C. Finer grinding
    D. Adding sand

Answer: C

Explanation: Finer grinding increases hydration rate.

17. Main function of silica in cement is:
18. Colour
    B. Strength
    C. Setting control
    D. Expansion

Answer: B

Explanation: Silica increases strength.

18. Cement stored for long time becomes:
19. Stronger
    B. Lighter
    C. Lumpy
    D. Coloured

Answer: C

Explanation: Moisture causes lump formation.

19. OPC stands for:
20. Ordinary Portland Cement
    B. Original Portland Cement
    C. Ordinary Pozzolana Cement
    D. Open Portland Cement

Answer: A

Explanation: OPC is general-purpose cement.

20. Which test checks early setting of cement?
21. Soundness test
    B. Setting time test
    C. Fineness test
    D. Strength test

Answer: B

Explanation: Setting time test measures initial and final set.