Concrete is supposed to be a very strong material. However, when longer concrete slabs for a huge cantilever or say for a bridge are required, it is not resistant to breakdown. Large spans are also preferred in commercial building, offices etc. to make them more workable. To achieve this, the concrete slab is tensioned with a process called pre-stressing and the concrete slab which comes out of this is known as post tension slab or PT Slab as is commonly referred to.
Pre-stressing of the concrete is done through either pre tensioning or post tensioning. In pre tensioning, tendons are tensioned before the concrete is placed. In post tensioning, tendons are tensioned after the concrete is hardened. In pre tensioning, the transfer of pre stress is accomplished in one operation and within a short period. In post tensioning, the transfer is gradual, the pre stress in the tendons being transferred to concrete one by one. However, in both, there is no external load on the member, except its weight.
The post tension slab is one of the most useful construction technologies for modern architecture. One cannot think to make long bridges, efficient skyscrapers without using it. It has many advantages.
- Post tensioned construction technology eliminates or reduces the size of beams thereby resulting in more headroom.
- The thin sections lead to reduction of quantity of concrete and steel.
- Stronger structures are constructed at reduced cost of construction.
- Reduction of dead load of the building.
- Resulting in large column free spaces thereby having more flexibility for creativity and more usable area.
- It is very strong and durable as it is a strong substitute of normal concrete.
- As mentioned earlier, it results in more floor to floor height.
- Chances of corrosion are less.
- Construction is speedy.
- Good quality of construction.
However, this technology has few disadvantages.
- Quality of material used has to be ensured. Since there are a number of tendons and wires spread inside, there are chances of corrosion.
- Skilled labour is required for its construction. If due care is not taken during construction, it may lead to a mishap.
Given so many advantages, needless to say, eventually, this construction technology is going to replace traditional RCC construction in India.
Dr. Sonia Mehta