Composites are combinations of two more separate materials on a microscopic level, in a controlled manner to give desired properties. The properties of a composite will be different from those of the constituents in isolation.
When two materials are combined together to form a composite, one of the materials will be in “Reinforcing phase” and the other material will be in “Matrix phase”. Typically, reinforcing material in the form of fibres, sheets or particles are strong with low densities while the matrix is usually a ductile or tough material.
Eg.: Glass -> Reinforcing material
Polyester -> Matrix material
Glass + Polyester -> GRP (Glass fibre reinforced plastic)
Composites can be broadly classified in to two groups. They are,
1. Natural composites
2. Man-made composites
Several natural materials can be grouped under natural composites.
Eg.: Bone, Wood etc.,
Man-made composites are produced by combining two or more materials in definite proportions under controlled conditions.
1. Mud mixed straw to produce stronger mud mortar and bricks.
3. Concrete and RCC
4. Plywood, Chipboards, Decorative laminates
5. Asbestos Cement Sheets
6. Reinforced Glass
7. Fibre Reinforced Plastic (FRP)
8. Carbon Composites
Properties of Composites
1. Composites posses excellent strength and stiffness
2. They are very light materials
3. They possess high resistance to corrosion, chemicals and other weathering agents.
4. They can be moulded to any shape and size with required mechanical properties in different directions.
Disadvantages of composites
1. High production cost
2. Difficult to repair
3. Susceptible to damage
Uses of composite materials
1. Extensively used in space technology and production of commercial air-planes.
2. Used in the production of sport goods.
3. Used for general industrial and engineering structures
4. Used in high speed and fuel efficient transport vehicles
Applications in the field of Civil Engineering
Composites are extensively used in the field of Civil Engineering. Ferro-cement is a good example for composite. R.C.C. and P.S.C. (Pre-stressed Cement Concrete) are composites that are widely used for structural components. Even concrete can be considered as a composite. Block boards, Batten boards, and Chip boards which are composites are used in light construction works such as doors, windows, furniture and cabinets. Asbestos Cement Sheets are used as roofing material. Reinforced glass is used for sky-lights and door and window panelling.