Basic information on Precast concrete products

Dear friends,

Being in the precast industry for over 20 years, I'd like to share some general things about precast construction in a simple way so that all can comprehend.

1) Conventional construction vs Precast construction

In conventional construction all the concrete members are cast at site while in precast construction, the concrete members are cast in the factory, transported to site in trailers and erected at site by means of a mobile crane or a tower crane.

Conventional construction is relatively a slower process as it involves several activities which hold the subsequent activities while precast construction is relatively faster as the concrete members could be designed, produced and kept ready - hand in hand with the site preparation.

Conventional construction is way economical when compared to precast construction. Even though precast construction is expensive, it is preferred in Gulf countries and Scandinavian countries as the project duration is reduced significantly.

2) Precast Concrete Products

Precast concrete elements in a building are columns, beams, slabs (hollowcore slab/single T slab/double T slab, solid slab etc.), load bearing wall panels, partition wall panels, cladding panels, insulated sandwich panels, drops, parapets, cable trenches and covers etc. (you can see a glimpse of these elements in Google images).

In precast boundary walls, the components are precast footings, precast columns, Boundary wall panels.

In bridges and metro rails, the components are heavy columns, beams, viaducts etc.

In industrial projects, components like precast columns and beams are used in structures like pipe racks.

3) Combination of conventional and precast construction

In skyscrapers and multistroried buildings a combination of precast and conventional construction is adopted.

(ie) Raft foundation, colums and beams are cast-in-situ while the slabs, cladding panels are in precast.(columns and beams may also be pre-engineered steel )

4) Production of precast

Precast factory has a huge production area and stockyard. Production area comprises of steel tables, moulds, pre-tensioning facility, steel yard, fabrication workshop, over head cranes, batching plants, concrete shuttles etc. After de-moulding the precast elements are shifted to stockyard where curing is done. Minor repairing and cosmetic repairs are done at the stockyard. Then the elements are loaded on the trailers and transported to site for installation.

5) Erection of Precast elements

When the precast elements reach the site, erection of the same is carried out in accordance with the Method statement and the lifting plan. Many mechanical connections, wet connections, temporary propping, grouting etc. are involved.

Conclusion : In India precast construction came into existence late when compared to other countries. But it is becoming more and more popular. Noida, for example, is full of precast projects. Even in bridges and Metro, companies like L&T have done great jobs.In an expansion of cities, precast is the best option. Within the city it is practically difficult as the roads and streets are two narrow to accommodate cranes and trailers.