Concrete is one of the oldest building materials in the history of man, dating back as far as 5600 BC. This man-made product consists of cement, other materials like ash or slag, a coarse aggregate like limestone, gravel or granite and a fine aggregate like sand and water. When mixed together these materials harden to form a very durable and very strong material that is commonly used for construction. Concrete is a great choice for construction because of the long life cycle, it is fire retardant, and thermal properties making concrete one of the most energy efficient building materials available. Concrete constructed buildings have a long life with minimal maintenance thus requiring less new construction. Unlike natural building materials, when the life of an old building come to an end, the concrete can be crushed, recycled and reused.