Traditional Insitu applications, on the other hand, are poured into site-specific moulds and cured on the spot. This old mode of production raises a number of quality control and safety concerns.
In ordinary reinforced concrete, stresses are carried by the steel reinforcement, whereas prestressed concrete supports the load by induced stresses throughout the entire structural element. This makes it more resistant to shock and vibration than ordinary concrete, and able to form long, thin structures with much smaller sectional areas to support equivalent loads.
Prestressed concrete was patented by San Francisco engineer P.H Jackson in 1886, but it was not widely used as a building material until 50 years later, when a shortage of steel, combined with technological advancements, made prestressed concrete the preferred material for postwar reconstruction in Europe.
Floor beams, piles, and railway sleepers, as well as constructions like bridges, water tanks, roofs, and runways, are increasingly often made with it. Precast concrete is not required for most columns and walls, but it can be utilized cost-effectively for tall columns and high retaining walls with severe bending loads.
Advantages of precast concrete:
- All precast components are manufactured off-site in an enclosed casting environment, avoiding delays due to inclement weather conditions.
- Extremely structurally efficient – Precast is designed and supplied to exact build fit and specification, accelerating the build process.
- Precast components allow immediate site and finishing access following installation, providing a solid footing reducing delays for follow on trades.
- Components can be delivered to site as required in the build process ensuring that on-site storage is not an issue when space is at a premium.
- Quicker and safer than in situ mould construction and pouring.
- Can be constructed in to most shapes.
As a general rule, traditional reinforced concrete is the most economic method for a span of up to 6 m. Prestressed concrete is more economical when spans are over 9 m. Between 6 and 9 m, the two options must be considered according to the particular requirements as to which is the most suitable option.