Precast concrete

Precast concrete is a construction product produced by casting concrete in a reusable mold or 'form' which is then cured in a controlled environment, transported to the construction site and lifted into place ('tilt up'). In contrast, standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast concrete using a fine aggregate in the mixture, so the final product approaches the appearance of naturally occurring rock or stone. More recently expanded polystyrene is being used as the cores to precast wall panels. This is lightweight and has better thermal insulation. Precast is used within exterior and interior walls. By producing precast concrete in a controlled environment (typically referred to as a precast plant), the precast concrete is afforded the opportunity to properly cure and be closely monitored by plant employees. Using a precast concrete system offers many potential advantages over onsite casting. Precast concrete production can be performed on ground level, which helps with safety throughout a project. There is greater control over material quality and workmanship in a precast plant compared to a construction site. The forms used in a precast plant can be reused hundreds to thousands of times before they have to be replaced, often making it cheaper than onsite casting when looking at the cost per unit of formwork. There are many different types of precast concrete forming systems for architectural applications, differing in size, function, and cost. Precast architectural panels are also used to clad all or part of a building facades or free-standing walls used for landscaping, soundproofing, and security walls, and some can be prestressed concrete structural elements. Stormwater drainage, water and sewage pipes, and tunnels make use of precast concrete units. To complete the look of the four precast wall panel types — sandwich, plastered sandwich, inner layer and cladding panels — many surface finishes are available. Standard cement is white or grey, though different colors can be added with pigments or paints. The color and size of aggregate can also affect the appearance and texture of concrete surfaces. The shape and surface of the precast concrete molds have an effect on the look: The mold can be made of timber, steel, plastic, rubber or fiberglass, each material giving a unique finish. Ancient Roman builders made use of concrete and soon poured the material into moulds to build their complex network of aqueducts, culverts, and tunnels. Modern uses for pre-cast technology include a variety of architectural and structural applications — including individual parts, or even entire building systems. In the modern world, precast panelled buildings were pioneered in Liverpool, England, in 1905. The process was invented by city engineer John Alexander Brodie, a creative genius who also invented the idea of the football goal net. The tram stables at Walton in Liverpool followed in 1906. The idea was not taken up extensively in Britain. However, it was adopted all over the world, particularly in Eastern Europe and Scandinavia.