Precast Concrete Members

Many of the components of a building are prefabricated. This means that they are made in advance at any time and place, and can be used for any building. The most common examples are the various sorts of blocks, i/lywood, roofing sheets etc.

In the same way, many reinforced concrete members of the structure can be made well in advance so that they are ready to be used as the construction proceeds and they are needed. These are referred to as "precast" members, as opposed to the "east-in-situ" members.

Generally speaking, prefabricated construction is divided into two classes with regard to buildings:

• a - Prefabricated units produced in a factory and transported to the building site
• b - Units produced by the contractor in a yard next to the building site.

Since Rural Building is understood to be conventional building and not factory production, the first method does not apply to us.

It is becoming more and more common however for the contractor to prefabricate members near the building site, although the possibilities of this method are limited to small-scale applications.

In Rural Building the most frequently made precast concrete members are:

REINFORCED CONCRETE LINTELS:

These cannot exceed 1,5 m in their length, as otherwise they will be too heavy and impossible to set in place without using a lifting device.

REINFORCED CONCRETE POSTS:

For fencing purposes (Fig. 1).

REINFORCED CONCRETE PILLARS:

These should not be too heavy to be set up under rural conditions.

CONCRETE COPINGS OR CAPPINGS:

These are of various shapes, with or without reinforcement (Fig. 2).

REINFORCED CONCRETE SLABS:

Of limited size and thickness, used to cover manholes or to serve as draining boards in kitchens, etc.

PLANNING THE WORK

All the plans and if possible, detailed drawings must be available before you start to make precast concrete members. Careful planning, supervision and performance are all necessary in order to obtain the desired product.

SAVING TIME:

As soon as the required materials are available, a group of the workers can start production of precast concrete members. The earlier they begin the better, because the concrete needs to be cured for some time before it is used in the building. By the time the precast member, for example a lintel, is needed the curing process will be complete and the lintel can simply be set into place.

In contrast to the cast-in-situ method, this method allows construction to proceed without delays caused by waiting for concrete to harden; and without being hindered by shuttering and strutting. in this way the total construction time is shortened.

This time-saving can become very important, for example if the wet season is approaching and the building has to be done before that time.

SAVING MATERIALS:

Since precast concrete members can simply be made on levelled ground, there is no need for poles and braces or other strutting to hold up the shuttering. Curing is also made much easier.

In addition, the same formwork can be used repeatedly if several members of the same size and shape have to be made.

If there is no proper storage space for the cement on a job, it is better to precast as many members as possible; thereby using up the cement before it gets spoiled.

NOTE: The more time, materials and money you save, the happier your client will be. Not only that, but your reputation as a Rural Builder will grow in the eyes of the people around you and be appreciated in the society.