When concrete is poured off-site and then transported to the permanent location of the building structure, it is called precast concrete.
The term precast concrete is applied to a variety of individual concrete members, which are cast in different forms before being placed in the structure.
Here we will learn aobut precast concrete, types of precast concrete & much more.
Introduction to precast concrete:
Precast members are made on construction sites or in casting yards located at some distance or in precast factories, then transported to the site.
After transported to the site they held in position by cranes or other equipment if they are heavy like beam or slab units.
The simplest form is hollow and solid concrete blocks used to construct external and internal load bearing or non load bearing walls, composite walls.
Types of precast concrete:
There are two main classes of beams:
- Internal Beam: Wherever floor loading is nearly symmetrical
- External beam: wherever floor loading is predominantly symmetric.
2.Precast floor slabs:
The main varieties of slabs working described the frames are:
- Hollow-core block.
- Double Tee Block.
4.Precast concrete walls:
Prefabricated concrete walls serve as a stabilizer, stairs and shafts are carried in the form of walls or boxes.
The walls are also classified as Infill or Cantilever.
- The walls of the infill consider as composite action embodied with beam and column frames.
- The cantilever walls or boxes act as deep beams that tilt the frame.
Three options for the stairs formed are achievable:
- A single formed unit consisting of all flights and landings.
- Parts of flights and landings are made in one piece.
For precast concrete structures of five stories or less, each column can be continuous for the total height of the building.
The main varieties of pillars formed are:
- Edge column: They are symmetric in one direction.
- Inner Column: They are symmetric fully directions.
- Corner column: They are not symmetrical.
Precast concrete manufacturing process:
Pre-casting can be done in the following steps:
- Procurement of concrete material.
- Storage and handling.
- Batching of concrete components.
- Laying of concrete in required formwork with or without reinforcement as per design.
- Concrete compaction.
- Curing of concrete.
- Finishing for concrete.
- Transporting the inserted member on site.
Precast concrete advantages and disadvantages:
- These members have very high erection speed.
- They have good quality control.
- The entire building may have precast walls, floors, beams, etc.
- They are fast construction on the site.
- High quality is due to managed situations within the manufacturing unit.
- Precast is well-executed which may reduce the dimensions and number of structural members.
- They are very heavy members.
- It provides camber in beam and slab.
- The very low margin for error.
- The connection could also be difficult.
- Slightly restricted constructing design flexibility.
- Panel size is restricted, this concrete cannot be used for two-way structural techniques.
- The economics of scale demand regular-sized buildings.
- The need for repetition of types will affect the design of the building.
- Joints between panels are sometimes costly and complicated.
- On-site panel application requires skilled workmanship.
- Cranes are required to raise the panels.
Uses of precast concrete:
- For casting various building elements such as beams, columns, slabs, water tanks etc.
- For the manufacture of compound poles, electric poles, ornamental structures.
- Construction of R.C.C. Pipes, bridge girders, bridge piers, concrete piles.