Need: Timely execution of projects has always been a challenge in India. With large
scale movement of construction workers back to their native because of ongoing
pandemic, availability of right skill manpower shall be a big challenge at least in
the near future. The restrictions on interstate movement, limited available
transport options, focus of the government on development of local development
is expected to further limit availability of workers at construction sites. Even with
available manpower, physical distancing requirements shall further pose a
con straint on productivity and work progress. This new normal has necessiated
some rethink on our approach to project execution.
One of the methods to achieve this objective is use of Precast construction. Precast
concrete is an alternative to cast-in-situ concrete. While cast-in-situ concrete
is cast in its actual location, precast concrete is cast at another location, either
at the building site or in a factory, and is then lifted to its final resting place and
fixed securely. This means that unlike cast-in-situ construction, which is monolithic
or continuous, precast concrete buildings are made of separate pieces that are
bolted or connected together.
Long used for infrastructure and pavement construction, the technique is more
affordable and is now gaining acceptance in the building industry. It requires
meticulous planning and detailing as well as a greater eye for quality and precision.
Manufactured at shop or factory using pre-assembled forms and rebar/wire mesh
reinforcement; after casting and curing, these components can be shipped direct
to job site and are ready for installation.
Precasting is great for producing large numbers of identical components. As an
example, if we are building an affordable housing project with 3,000 identical
apartments, precasting can be extensively used to produce wall slabs and floor
slabs for all the apartments, even columns and beams and then lift them into place
and connect them.
Since the precasting of elements is done in a purpose-built precasting yard or
factory, it makes construction easier for the following reasons:
- The construction is done on the ground rather than at a height
- It can be done inside a climate-controlled structure, eliminating problems of
rain, dust, cold, or heat - Specialized formwork (moulds) can be built for doing many repetitions of the
same component - Specialized equipment can be used to make, move, and pour the liquid concrete
- Curing of the concrete can be done in a controlled environment
This also means that the quality of precast components can be very high. Since
the components can be made beforehand, construction can be very quick. In cast-
in-situ construction, engineers have to build each set of components after the
previous set has finished, which does take time, as concrete generally takes 28
days to reach its full strength.