Post-tension concrete is a structural system that introduces internal forces into a concrete slab to improve its performance and strength.
According to the provided reference, the mechanism in post-tensioned slabs involves steel cables and the drying process of the concrete.
Here's a breakdown of how it works based on the reference:
The Post-Tensioning Process
- Cable Placement: In post-tensioned slabs, steel cables, also known as tendons, are integrated into the structure. These cables are typically run crisscrossed throughout the center of the concrete slab.
- Timing of Placement: The reference states that these tendons are placed after the concrete has already hardened.
- The Key Action: A critical step described is what happens as the poured concrete dries. As the poured concrete dries, the post-tensioned cables stretch and tighten, which applies a significant force to the concrete slab.
- Application of Force: This stretching and tightening of the cables exerts an inward force on the concrete.
Why This Force is Applied
Applying this significant force puts the concrete into a state of compression. Concrete is very strong under compression but weaker under tension (pulling forces). Structures, especially slabs spanning large areas, experience tension from loads and their own weight.
By introducing compression through post-tensioning, the concrete slab is better able to resist the tensile stresses that would otherwise cause cracks or excessive bending. This allows for:
- Longer spans between supports
- Thinner slabs
- Reduced cracking
- Improved load-bearing capacity
In essence, post-tensioning uses stretched steel cables to actively compress the concrete, counteracting the forces that would pull it apart.
