Composites

Objectives To understand what a composite is. To understand the benefits of using composites. To know some examples of composites.

Composite materials A complex material made of two or more separate substances.

MDF Medium density fibre board. Compressed wood and fibre particles stuck with glue. Strong, light and doesn’t splinter easily.

Carbon fibre Improves strength Reduces weight

Fibre glass – Glass reinforced plastic Improves strength Reduces weight

Reinforced concrete Metal is inside the concerte.

Reinforced concrete Then the concrete is added in stages. Improves the strength.

Make your own re-inforced concrete Wear gloves to protect your hands and goggles over your eyes. Take care not to breathe in any cement powder. Lightly smear the inside of the mould with vaseline. Using a beaker measure out three cans of gravel, two cans of sand and one can of cement powder. Mix these materials together in a bowl. Stir in a little water. The mixture should be quite stiff. Add more water if necessary. Pour some of the concrete into the mould until it is about half full. Use wire cutters to cut two lengths of wire which can fit into the mould. Place these wires on the wet concrete. Add more concrete to the mould. It should be level with the top of the wood. Tap the concrete with a piece of wood to push out any air bubbles. Leave the reinforced concrete to harden. When it is hard remove the wooden mould.

Concrete Use scissors to remove the top and bottom sections from the cardboard fruit juice containers. Make some concrete. Use the same method as before. Smear the insides of both cardboard containers with vaseline. Pour concrete into each container. Cut some short lengths of wire and place them vertically in the concrete. Add more concrete until the containers are full. Leave to harden. Remove the reinforced concrete from the containers.

How could you test these concretes? Devise a method to test the properties of the two samples of concrete. Which material is the strongest? What might you use re-inforced concrete for and why not just concrete?