---
title: "Constituents of brick earth and functions"
subject: "Civil Engineering Materials"
chapter: 3
key: "semester_3/civil_engineering_materials:constituents-brick-earth-functions"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/constituents-brick-earth-functions
site: BCT Engineering
---

# Constituents of brick earth and functions

Civil Engineering Materials · Chapter 3: Clay Products

- Asked in: 2081 Bhadra, 3 marks; 2081 Chaitra (new course), 3 marks; 2081 Kartik (new course), 2 marks; 2076 Chaitra, 2 marks; 2069 Chaitra, 4 marks; 2072 Chaitra, 2 marks; 2068 Chaitra, 1 marks; 2070 Chaitra (old course), 3 marks; 2066 Shrawan (old course), 3 marks (asked 9 times)
- Video: [composition of bricks| Function of constituents of Bricks | Proportion of ingredients of bricks](https://www.youtube.com/watch?v=nRZtbqRj5sA) — Civillogy (Study of Civil Engineering)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/constituents-brick-earth-functions
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-3

## Question

Write about the essential constituents of good brick earth with their percentage composition and function (role in manufacturing and property of bricks).

## Short answer

Good brick earth contains 50–60% silica to prevent shrinkage and give durability, 20–30% alumina for plasticity, 5–10% lime as flux, and 5–6% iron oxide for red colour and strength. Excesses cause brittleness, cracks, or melting.

## Answer

Good brick earth is mainly clay with the following constituents.

| Constituent | Percentage | Function |
|---|---|---|
| Silica (sand) | 50-60% | Prevents shrinkage, warping and cracking; gives shape, durability and hardness; excess makes bricks brittle |
| Alumina (clay) | 20-30% | Gives plasticity for moulding; excess causes shrinkage and cracks on drying |
| Lime | 5-10% | Acts as a flux, binds the particles at kiln temperature; excess melts the brick and distorts shape |
| Iron oxide | 5-6% | Acts as a flux, gives the red colour on burning, adds strength; excess turns bricks dark blue-black |
| Magnesia | less than 1% | Gives yellow tint and reduces shrinkage; excess decays the brick |

Silica gives the skeleton, alumina the plasticity, and lime and iron oxide fuse the particles into a strong mass during burning.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the function of silica in brick earth?
   A. Gives plasticity
   B. Prevents shrinkage, warping and cracking, gives hardness
   C. Acts as flux giving red colour
   D. Causes decay of brick
   Answer: B. Silica forms the skeleton; excess makes bricks brittle. (Key point: Silica)

2. Alumina in brick earth (20-30%) gives:
   A. Red colour
   B. Fusibility
   C. Plasticity for moulding
   D. Hardness against scratching
   Answer: C. Alumina makes clay plastic; excess causes shrinkage and cracks. (Key point: Alumina)

3. Iron oxide in brick earth:
   A. Prevents shrinkage
   B. Gives yellow tint
   C. Gives plasticity
   D. Acts as flux and gives red colour on burning
   Answer: D. Excess turns the brick dark blue-black. (Key point: Iron oxide)

4. Excess lime in brick earth causes:
   A. Melting of the brick and loss of shape
   B. Increased plasticity
   C. Brittleness
   D. Yellow tint
   Answer: A. Lime is a flux; too much melts and distorts the brick. (Key point: Excess lime)

## Related in Civil Engineering Materials

- [Characteristics of good brick earth](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acharacteristics-good-brick-earth) — Civil Engineering Materials, chapter 3
- [Manufacturing process of bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Amanufacturing-process-of-bricks) — Civil Engineering Materials, chapter 3, asked 4×
- [Characteristics of good bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acharacteristics-good-bricks) — Civil Engineering Materials, chapter 3, asked 4×
- [Harmful ingredients in brick earth](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aharmful-ingredients-brick-earth) — Civil Engineering Materials, chapter 3, asked 3×
- [Preparation of clay for bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aclay-preparation-for-bricks) — Civil Engineering Materials, chapter 3
- [Efflorescence in bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aefflorescence-in-brick) — Civil Engineering Materials, chapter 3, asked 2×

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- [Test for property; state and path function](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Athermodynamic-property-test-state-path) — Fundamental of Thermodynamics & Heat Transfer, chapter 1
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