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A composite material consists of two or more materials with different properties. They are combined to produce a material with improved properties. Most composite materials have two components:

• the reinforcement
• the matrix, which binds the reinforcement together

The table shows some examples of composite materials:

It is often possible to separate the reinforcement from the matrix by physical processes. For example, reinforced concrete can be broken up using machinery. This is one stage in recycling the components of reinforced concrete.

Fibre glass and carbon fibre reinforced polymer (CFRP)

The fibres in these composite materials have a low density. They are strong in tension, so they are not easily stretched, but they are flexible. The polymer resin which binds the fibres together is not strong but it is stiff. The composite materials show a combination of these properties. They are strong, stiff and lightweight.

Chipboard

Wood itself is a natural composite material. It consists of a reinforcement of cellulose fibres bonded together by a matrix of lignin. The fibres are aligned alongside each other, so wood is stronger in one direction than it is in the other. Chipboard contains randomly arranged wood chips bonded together by a glue, so it is strong in all directions.

Reinforced concrete

The properties of concrete can be improved by reinforcing it with steel rods or mesh. The compressive strength of concrete is higher than its tensile strength, but the tensile strength of steel is higher than its compressive strength. The combination of the two materials that is strong in tension and in compression. This allows reinforced concrete to be strong and slightly flexible, which is important when constructing large buildings and structures.

A comparison of different materials

Different materials have different properties but they may also have some properties in common. The table summarises some of the typical properties of glass and clay ceramics, metals, plastics and composites.