The post tensioning slabs for the building indutry have been used with success in many countries since the 70 ,s. As the contruction industry moves in to the 21st century, so the need for ever more efficient structural form continues to grow. Nowadays, the cast in situ construction of slabs using post tension systems is an alternative that should be seriously considered. The increasing cost of materials, construction equipments, labor and transport demands the maximum optimization of resources. It also involves the use of high quality techniques, saves materials costs and is fast in execution. The post tensioning method lightens the structure, allows the reduction of the slab thickness and allows releasing the formwork in record time and it even guaranties a higher durability.