Post-tension is a method of reinforcing (strengthening)concrete or other materials with high-strength steel strands but to fully appreciate the benefits of post-tension ,it is helpful to know a little bit about concrete . Concrete is very strong in compression but weak in tension, it will crack when forces act to pull it apart ,in conventional concrete construction, if a load such as cars in a parking garage is applied to a slab or beam ,the beam will tend to deflect or sag so, this deflection will cause the bottom of the elongate slightly .even a slight elongation is usually enough to cause cracking .steel reinforcing bars (‘rebar’)are typical embedded in the concrete as tensile reinforcement to limit the crack widths .rebar is what is called ”passive” reinforcement however; it does not carry any force until the concrete has already deflected enough to cracks But, post-tensioning tendons, on the other hand, are considered ‘active’ reinforcing .because it is pre-stressed , the steel is effective as reinforcement even thought the concrete may not be cracked. Post-tensioned structures can be designed to have minimal deflection and cracking, even under full load.