What is the strength percentage of concrete achieved before jacking in post-tensioning?

In post-tensioning, concrete must reach a certain strength before the tendons are stressed or "jacked." The typical industry standard is that concrete should achieve approximately 75% of its specified compressive strength before jacking. This percentage ensures that the concrete can adequately handle the forces applied during the post-tensioning process without risking damage or failure.

Achieving this strength allows for effective tensioning of the cables while providing the necessary support to the concrete structure. It also helps in reducing the likelihood of cracking and ensures that the structural integrity is maintained as the pre-stressed tendons are tightened. Therefore, the selection of 75% reflects an important balance between safety and performance in post-tensioned concrete design.