[Er.Amit Mathur]

Concrete in which there has been introduced internal stresses of such magnitude and distribution that the stresses resulting from given external loadings are counteracted to a desired degree. In reinforced concrete members the prestress is commonly introduced by tensioning the steel reinforcement.



This internal stress is induced into the member by either of the following prestressing methods:
Pre-Tensioning : Apply prestress to steel strands before casting concrete;
Post-Tensioning : Apply prestress to steel tendons after casting concrete

http://frontdesk.co.in/prestress.html

[Er.Amit Mathur]

Prestressed post tensioning concrete can create larger bigger span in lesser depth of beam and slab.
Typical span to slab depth ratios are :
In RCC 1 : 28
In PT 1 : 45