chapter  1
19 Pages

What is precast concrete

ByKim S. Elliott

What makes precast concrete different from other forms of concrete construction? Whether concrete is precast, that is statically reinforced or pretensioned (prestressed), is not always apparent. It is only when we consider the role concrete will play in developing structural characteristics that its precast nature becomes significant. The most obvious definition for precast concrete is that it is concrete which has been prepared for casting, cast and cured in a location which is not its final destination. The distance travelled from the casting site may only be a few metres, where on-site precasting methods are used to avoid expensive haulage (or VAT in some countries), or may be thousands of kilometres, in the case of high-value-added products where manufacturing and haulage costs are low. The grit basted architectural precast concrete in Figure 1.1 was manufactured 600 km from the site, whereas the precast concrete columns, beams and walls shown in Figure 1.2a and b travelled less than 60 m; wall panels have been stack-cast in layers between sheets of polythene adjacent to the final building. Architectural-structural precast concrete frame at Scottish Office, Leith, United Kingdom. (Courtesy of Trent Concrete Ltd., Leith, UK.) (a) Site cast using stack casting between sheets of polythene. (b) Completed structure of mould cast columns and beams and stack cast walls.