Post-tensioning applications combine the high compressive characteristics of concrete with the tensile strength of steel to increase overall strength and durability. Concrete is very strong in compressive strength (resistance to crushing forces) and relatively weak in tensile strength (forces that pull an element apart), while steel is very strong in tension. Since the framing members in a building must resist loads through a combination of both compression and tension, concrete framing is reinforced with steel. Using the reinforcing steel to "squeeze the concrete together", or place it in compression, increases the tensile strength of the concrete itself (making the concrete slab or masonry wall stiffer). Increasing the tensile strength allows a designer to specify longer spans with thinner concrete sections.

In a post tension concrete system, high-strength steel tendons, in combination with reinforcing steel bars, are embedded and anchored in the concrete. When the concrete has acquired adequate strength, usually within three days after placement, the tendons are tensioned, (stretched, like rubber bands) imposing a compression force on the concrete. These tendons remain stressed throughout the life of the structure, counterbalancing future tension loads.

Designers and engineers typically choose post-tensioned concrete because of low material costs and availability, flexible column spacing and structural depth, and demanding construction schedules. This concrete system is also an efficient choice for reduced sound and vibration. Post-tensioned concrete is used most often for moderate to long spans with moderate floor loads, as seen in parking and residential buildings. In these situations, post-tensioned concrete framing may result in shallower depths than steel framing.

The rate of construction can generally be increased with post tensioned concrete buildings due to the quick strengthening properties of the material. Form work in relatively simple successive floors can be built within a week of concrete placement.

Prairie designs mixes with early high-strength characteristics (3,000 psi in 44 hours) that can be placed 12 months a year.

Information from the Post Tensioning Institute and the Seattle Daily Journal of Commerce .