Types of Precast Concrete Units

Stated below are the different types of precast concrete units:

Hollow Concrete Blocks

This type of precast concrete unit is manufactured in different shapes and sizes. The blocks of concrete are molded in a machine. The standard size of blocks which are used for different works are stated below:

1. Hollow concrete blocks - 39 cm x 19 cm x 30 cm.
2. Hollow building tiles - 39 cm x 19 cm x 20 cm.
3. Hollow concrete blocks for partition walls - 39 cm x 19 cm x 10 cm.

5cm or more is maintained as the face thickness of the blocks.

For the construction of walls and columns the standard hollow blocks are used. The overall length and height of the walls must remain fixed to ensure maximum economy during construction and also to make full use of the full and half-length blocks.

To decide on the height of the door and window openings the availability of the size of hollow blocks must be considered.

For corners, sills, lintels, and jambs, wall closures, piers between the doors and windows, etc. specially shaped blocked are produced.

Lintel units

For windows, door openings, and passage openings prefabricated RCC lintels can be used. By using precast lintels the speed of construction indirectly increases as the curing process is eliminated.

This type is preferred for small spaces up to 2meters, usually cast in wooden molds and are cured prior to the usage.

It must be made sure that the marked face of the lintel is kept on the top or upper side while laying down the precast lintel case.

The top of all precast lintels is painted with tar or paint so that they can be distinguished from the bottom part. This is important and if the position of the reinforcement is wrong it can lead to structural failure.

Door and Window Frames

Prefabrication of doors and windows can take place. Through the frames of the doors or windows steel bars of about 4-40mm in diameter are run through.

For fixing hinges suitable hardwood blocks can be used. The concrete is made to vibrate using a table vibrator and it is then poured into the mold which ensures durability of the mix.

Roofing and flooring elements

For roofing and flooring prefabricated reinforced concrete are used instead of wooden battens. Precast reinforced and prestressed concrete trusses might be used for the sloping roof.

For the roofing and flooring of flat roofs plain precast concrete tiles are used.

Precast Shell Units

Plain or lightly reinforced concrete can be used in form of precast shell roofing for which a suitable frame must be made so as to cast the shell unit.

Sunshade Unit

With 75mm at the cantilever and tapered upwards to the depth of lintel sunshades are made. They come monolithic along with lintel.

On an average the projection will be 60-90cm. 8mm rods can be used as the main rods for the cantilever of the sunshade with a 10cm centers with 8mm distributors at 15cm centers.