What is a post tension slab on grade?
Structural concrete requires two important ingredients: the concrete and the reinforcing steel. Post-tensioning takes the strengths of these components and combines them to produce a more effective and economical structural system than conventionally reinforced concrete. Concrete is a relatively inexpensive building material that is readily available, environmentally friendly, easily formed into any shape and is very strong in compression. However, concrete is relatively weak in tension. For this reason, you often see cracks in concrete. Steel has very high tensile strength and is an excellent material to use when tensile stresses are involved. Builders for many centuries combined concrete and steel to take advantage of the strengths of these two materials by using “reinforced concrete”. However, conventional rebar steel in concrete is passive reinforcement which remains inactive until stresses develop, movement occurs, and cracks form. The deformations on the rebar surface then engages with the concrete to hold the cracks together. Post-tensioning of the steel takes this combination of materials a step further by pre-stressing the steel in the concrete to place the concrete in pre-compression. The prestressed steel will typically increase the tensile strength by approximately two times that of the non-prestressed concrete. This allows for greater strength and stiffness with less materials, thus much better efficiency and economy.
Post-tension steel tendons have an ultimate tensile strength of 270,000 pounds per square inch (PSI) compared to mild rebar steel with a typical tensile strength of 60,000 pounds per square inch. Post-tension tendons are fabricated to the proper lengths and delivered to the site where they are simply uncoiled and placed in the forms prior to concrete placement. Post-tension reinforcement is installed must faster than rebar steel which reduces construction time and cost. In short, post-tension concrete construction gives you more strength per dollar than conventionally reinforced concrete and when properly designed and constructed, less cracks.
Post-tension steel tendons have an ultimate tensile strength of 270,000 pounds per square inch (PSI) compared to mild rebar steel with a typical tensile strength of 60,000 pounds per square inch. Post-tension tendons are fabricated to the proper lengths and delivered to the site where they are simply uncoiled and placed in the forms prior to concrete placement. Post-tension reinforcement is installed must faster than rebar steel which reduces construction time and cost. In short, post-tension concrete construction gives you more strength per dollar than conventionally reinforced concrete and when properly designed and constructed, less cracks.
how we do it
tendon fabrication
Post Tension Technologies, LLC. operates a Post Tension Institute (PTI) certified tendon fabrication facility in Montgomery, Alabama. All tendons are custom fabricated in the shop for each project, sorted, coiled, and delivered to the site allowing for quick and efficient field installation. Tendons are installed much faster than rebar which reduces construction time and cost.
tendon layout
Tendons are installed with a "dead end" that remains embeded in the concrete slab and a "live end" that projects through the form. Once the concrete has reached certain cure requirements, the live end of the tendon is stressed with a hydraulic jack.
tendon stressing
Tendons are stressed by certified PTI installers, verified with elongation measurements, and reviewed by the engineer of record of the slab.
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tendon installation
After fabrication and delivery, tendons are installed per engineered drawings. Because of the efficiency of post-tension slabs, there is generally much less reinforcement required allowing for quicker installation and easier coordination between plumbing and electrical utilities.
concrete casting
Once the tendons are in place, concrete is cast and finished in the same way as conventionally reinforced concrete construction.
tendon cappingOnce the tendons have been stressed and verified the tendons are trimmed and the live ends are sealed with grout.
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