Tunnels, breakwaters, house building - we come across concrete almost everywhere. The basic concept is simple - cement made from limestone and clay and sand, gravel and finally water. But how these are mixed is important. How heavy or light, pressure-resistant or heat-insulating should the concrete be? Is the emphasis on load bearing capacity or safety, thermal insulation, moisture protection, fire prevention or sound insulation? Great Inventions explores this fascinating building material, said to have been used by the Egyptians more than 5000 years ago in the construction of their pyramids.