Precast concrete

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Precast concrete is an ancient type of construction material made with concrete cast in a reusable mold or "form" and cured in a controlled environment, then transported to the construction site and lifted into place. In contrast, standard concrete is poured-in-place in large forms and cured on site. Precast "stone" is distinguished from precast concrete by using a fine aggregate in the mixture so the final product approaches the appearance of naturally occurring rock or stone.

Ancient Roman builders made use of concrete and soon poured the material into molds to build their complex network of aqueducts, culverts and tunnels. Modern uses for precast technology include a variety of architectural applications including free-standing walls used for landscaping, soundproofing and security walls. Precast architectural panels are also used to clad all or part of a building facade. Stormwater drainage, water and sewage pipes and tunnels make use of precast concrete units. The advantages of using precast concrete is the increased quality of the material, when formed in controlled conditions, and the reduced cost of constructing large forms used with poured-in-place concrete.

There are many different types of precast concrete forming systems for architectural applications -differing in size, function and cost. For example, a wall form can be bought for $5,000 and will make about 5 feet of wall per day, while another form will cost significantly more, but can make up to 100 feet per day.

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Girling Concrete (defunct) Precast concreting is preferred - In adverse weather conditions , such as extremely high or low temperatures , that would not permit the sitecasting of concrete - When high control on the quality of materials or workmanship is required - If pretensioning of steel is needed for a greater structural efficiency ie longer spans, lesser depths , lower weights when compared to site cast elements. - if there is requirement of permanent forms made of steel , concrete , glass-fibre-reinforced plastic or wood panels. - If the surface has to be smooth with excellent surface properties - Due to cost considerations . Usually the formwork per unit cost of precast elements are less since the forms can be reused for hundreds or thousands of times more - When the construction has to be accelerated . Erection is faster than that of site concrete because there is now form work to be erected and stripped and little or no waiting for concrete to cure