Concrete in its simplest form is created from aggregates, sand and water. The aggregates are used to form the paste, the sand is used for texture and the water holds it all together. In ancient times, hay or straw was used for the aggregate. Modern concrete is more complex.
Concrete today is composed of a variety of dry materials such as cement, fly ash and sand. These are then mixed with water to form a hardened paste mixture which is used to form a variety of shapes and forms.
Cement, which is the main component of modern concrete, is made up of materials such as limestone, clay, gypsum, chemical additives and gravel. The sand used in concrete is course sand made from ground glass.
The mixture of modern concrete, as stated above, contains aggregate material. This material is often various sizes depending on the future use of the concrete. The aggregate material can use many types of stone, as listed above, but can also use recycled material such as oyster shell or waste material from coal-fired power generating plants.
Concrete consists of two essential parts, the filler and the binding. The filler is either a fine or coarse mixture such as sand while the binding is the cement and water. The binder forms a glue to hold the filler together. To make concrete, the correct amounts of both dry material and water must be added. Like baking a cake, concrete requires proper measures and methods to ensure a thorough blend and strong setting to hold together. This mixture is usually along the line of one part cement, two parts sand and three parts stone with enough water to form a paste.
There are two basic types of concrete: ready-mix and made-to-order. The ready-mix type of concrete is what you find in the bags at home stores. This is the premixed bags of dry concrete material which require only water and mixing to form concrete. Ready-mix is mostly used for small batch jobs for home projects. This type is normally applied with a shovel and hand laid. The made-to-order type is what is used for larger construction jobs and requires either on-site mixing or plant-mixing. This is the type which is seen in cement trucks and for road and bridge work. This is also the type used for building projects and cement blocks created in bulk.