---
title: "Why composite materials are used"
subject: "Civil Engineering Materials"
chapter: 10
key: "semester_3/civil_engineering_materials:composite-materials-why-used"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/composite-materials-why-used
site: BCT Engineering
---

# Why composite materials are used

Civil Engineering Materials · Chapter 10: Asphalt, Bitumen, Tar and Miscellaneous Materials

- Asked in: 2073 Shrawan, 3 marks; 2069 Chaitra (asked 2 times)
- Video: [Understanding Composite Materials: Advantages and Disadvantages](https://www.youtube.com/watch?v=h6vjd5dXOjA) — AI POWERED LEARNING 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/composite-materials-why-used
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-10

## Question

Why is the use of composite materials so high (predominant compared with conventional natural building materials)?

## Short answer

Composites combine matrix and reinforcement to give high strength-to-weight ratio, tailored properties, corrosion resistance, and combined advantages (e.g., RCC). They provide uniform quality, low maintenance, and replace scarce natural materials, though initial cost can be higher.

## Answer

A **composite material** is made by combining two or more different materials (a matrix and a reinforcement) so that the product has better properties than any of the components. Examples: reinforced concrete, FRP, GRP, plywood, fibre cement, steel-concrete composite.

#### Reasons for their predominant use

1. **High strength-to-weight ratio:** Fibres (glass, carbon) in resin give strength like steel at a fraction of the weight.
2. **Tailor-made properties:** Fibres, matrix and layout can be chosen to give the needed strength, stiffness or insulation.
3. **Durability:** They do not rust or rot, and resist chemicals and weather better than steel and timber.
4. **Combines advantages:** Concrete resists compression and steel resists tension in RCC.
5. **Easily moulded:** Complex shapes and large components are made by moulding and cast-in-place.
6. **Low maintenance and long life.**
7. **Natural materials are scarce:** Good timber and stone are limited, expensive and uneven in quality, whereas composites are uniform and consistent.
8. **Better thermal, acoustic and fire performance** in several kinds (e.g. sandwich panels).

**Limit:** They may cost more at first, and some (FRP) cannot be easily recycled or repaired.

## Check yourself

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

1. A composite combines what?
   A. Two or more materials as matrix and reinforcement for better properties
   B. Only metals
   C. Only natural materials
   D. Two identical materials
   Answer: A. Properties are better than any single component. (Key point: Definition)

2. In RCC the roles are what?
   A. Concrete resists tension, steel compression
   B. Concrete resists compression, steel tension
   C. Both compression
   D. Both tension
   Answer: B. Concrete in compression, steel in tension. (Key point: RCC)

3. Fibres in resin give what?
   A. Steel-like strength at a fraction of the weight
   B. Low strength
   C. High density
   D. Rust
   Answer: A. High strength-to-weight ratio. (Key point: Strength-to-weight)

4. A limitation of FRP is what?
   A. Rusts
   B. Cannot be easily recycled or repaired
   C. Rots
   D. Heavy
   Answer: B. Some cannot be easily recycled or repaired, and cost may be higher. (Key point: Limit)

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