Foamed bitumen (also known as foamed asphalt or expanded asphalt) is a mixture of air, water and bitumen. When injected with a small quantity of cold water, the hot bitumen expands explosively to about fifteen times its original volume and forms a fine mist or foam. In this foamed state, the bitumen has a very large surface area and an extremely low viscosity. The bitumen is then used to coat cold aggregates and produce asphalt. This material can be successfully utilised in the binder and base/road base layers and can incorporate a wide range of `secondary' recycled aggregate.