Fundamentals of Post-Tensioning Construction
Construction of post-tensioned slabs on grade is equivalent to applying reinforcing steel, with the exception of the tensioning step.
The placing of cables is done according to the suggestions provided by the engineer and managed to run through the center of the slab. For residential construction, tendons at 48 inches on center are mostly found.
There are huge amount of steel for commercial foundations. Tendons are routed around obstructions without difficulty.
A residential post-tensioned concrete slab will generally be available as 8 inches thick and made of 3000 psi concrete. Once the concrete has attained strength to 2000 psi, normally within the 3 to 10 days suggested by PTI, the tendons are stressed.
Tendons belong to seven high-strength steel wires which are cut jointly and arranged inside a plastic duct. At each end a PT anchor is situated and these are positioned in pockets which are implanted into the slab edge. If the strands are stressed, the wires will also stretch—about 4 inches for a 50 foot strand—to employ 33,000 pounds of load.
Stressing should only be performed with skilled workers. Once the stressing is completed, the tendon is cut off and the pocket in which the anchors are positioned is filled with grout to get rid of corrosion.
Larger structural concrete members are also post-tensioned, particularly in bridges and floors and beams in parking structures. The method is very user-friendly as compared to that utilized for slabs, apart from a bigger scale. The tendons will be "draped" frequently in order that they are low at the center of a beam and high at the supports—this settles the steel at the point of highest tension to retain the concrete kept together firmly.
By applying structural members the duct is frequently grouted entirely following stressing to tie the strand to the concrete along its complete length—these are known as bonded tendons. Unbonded tendons are mainly found in residential slabs and can freely move inside the duct and are safeguarded against corrosion with grease.
PT tendon placement and stressing is generally performed by companies with certified workers who have good skills in this work.
The benefits of PT that there is no cracking (or minimum very narrow cracks) and it has capacity to span additionally. PT slabs on ground can be arranged and stamped similar to any other concrete slab. Surfaces are stained or coated. It should be kept in mind that no cutting or drilling should be done to post-tensioned concrete slabs, because once a tendon is cut, it becomes complicated to repair. Many post-tensioned slabs are stamped to notify the owner and any renovation contractors to make sure that the slab is post tensioned.