It is of reinforcing concrete, masonry, and other structural elements. Post-Tensioning is a method of prestressing. Prestressed concrete or masonry has internal stresses (forces) induced into it during the construction phase for the purpose of counteracting the anticipated external loads that it will encounter during its lifecycle.
There are two methods of prestressing. One is called pre-tensioning. This method consists of stressing the reinforcing inside of large steel buttresses, and then casting the concrete around the reinforcing. This method can only be done at a precast manufacturing facility and requires the completed prestressed concrete members to be trucked out to the job site and then assembled.
The other method of prestressing is called post-tensioning. Instead of stressing the reinforcing inside of large steel buttresses at a manufacturing plant, the reinforcing is simply installed on the job site after the contractor forms up the slabs or constructs the walls.
The reinforcing steel is housed in a sheathing or duct that prevents the steel from bonding to the concrete so that it can be stressed after the concrete cures (hardens). Using the post-tensioning method of prestressing enables a builder to get all the advantages of prestressed concrete or masonry (described below) while still enabling the freedom to construct the member (slab, wall, column, etc,) on the job site.
Roof/intermediate floor is constructed to span between supports such as walls and columns. It is structurally designed to safely carry the ‘dead load’ of its own weight (including finishing layers above it) and any additional ‘live load’ imposed by human activity.
The most common technique for constructing the roof/ floor in India is by casting a Reinforced Cement Concrete (RCC) slab. Reinforced Cement Concrete, as it is practiced today, has been in use since 1867. RCC slab is a monolithic element which consists of cement concrete which encases within itself a matrix of steel rods called ‘reinforcement’.It uses the unique property of concrete to quickly harden into a rigid mass after being laid in different forms and thicknesses.
However, concrete, which is most efficient in resisting compressive loads, is very poor in resisting tension which develops when it bends. So, the performance of concrete is further enhanced by placing reinforcement rods in the concrete which allows the concrete to resist the bending which would result in a thin RCC slab spanning between two supports. RCC scan either be cast-in-situ by pouring concrete on shuttering or it can be pre-cast where smaller sized slab components are first made and then transported and installed at the site to create the floor/roof.
The biggest advantage of RCC slab is that the basic raw materials needed for its construction – cement, sand, steel and aggregates – and skilled masons for casting the slab are easily available everywhere. However, because RCC has become such a commonly practiced technology, basic quality control guidelines for a good quality and durable RCC slab are often ignored in practice, especially in rural areas, where it has not been traditionally practiced.
Now this video will demonstrate how post tension method apply on construction of RCC slab.