Can a Post-Tension Slab be Repaired?

by Tendon, on Jan 12, 2023 7:00:00 AM

Post-tensioning is among the most effective ways to strengthen concrete slabs, but it’s not perfect. Over time, even the most expertly engineered concrete slabs may require post-tension cable repair.

It’s a fact that the structural integrity of any concrete structure can degrade with extreme age and in poor conditions, but can a post-tension slab be repaired? Absolutely. It just has to be done right.

Repairing post-tension cables is an exact science that requires a true expert touch. Read on to learn more about this topic, and contact the experts at Tendon Systems for all of your concrete reinforcement needs.

When Is Post-Tension Cable Repair Necessary?

Because post-tension cables are embedded in concrete slabs, it can be difficult to tell whether a slab actually requires cable repair or replacement. Fortunately, there are a few telltale signs of distress that can alert you to the fact that you need post-tension cable repair.

Here are some signs to look for:

  • Rust staining
  • Tendons protruding from the slab
  • Crack patterns in the slab (concrete spalling)
  • White- or gray-tinted salt deposits anywhere on the slab
  • Deflection

These are all signs that may be visible on the outer surfaces of a concrete slab or structure. A concrete construction expert can take a closer look inside the slab by testing for corrosive chemicals, excavating grout pockets, penetration testing and testing for moisture inside the slab.

Causes of Post-Tension Cable Distress

You may also get a sense of whether you need post-tension cable repair by assessing the conditions the slab in question has been subjected to. Cables can become distressed under a variety of conditions, but this distress typically leads to one of two outcomes: cable corrosion or cable rupture.

Cable Corrosion

When a slab is reinforced with cables, it could have small voids along the length of the cables. For unbonded post tension, there shouldn’t be any voids if encapsulation is done correctly. However, older unbonded systems may not be encapsulated. When that is the case, water and salt intrusion is a major factor for cable distress.

Cable Rupture

Even for perfectly engineered post-tension slabs, post-tension cable repair can become necessary due to cable rupture. This is typically not a random event. Unfortunately, cable rupture is usually the result of improper work being done to the structure or slab.

For example, concrete coring without proper ground-penetrating radar (GPR) scanning can cause workers to cut into post-tension cables, leading to rupture.

However, cable rupture can also occur when a cable is damaged before installation or remains in a corroded state for a long time. In any case, cable rupture represents a serious threat to the integrity of the slab and requires expert attention.

Post-Tension Cable Repair, Replacement and Modification

To repair a post-tension cable, an expert team often must re-couple the portions of a ruptured tendon or make repairs to cable anchors. Sometimes, however, a cable is so deteriorated that it has to be replaced entirely. Post-tension cable replacement is a more in-depth process, but it is possible in many concrete slabs.

In other scenarios, repair or replacement might only be necessary because a building’s owner wants to make modifications. For example, if the owner of a building wants to add to the structure, and the addition requires creating a large opening in a post-tension slab, post-tension cable modification may become the name of the game. 

Modifying post-tension cables can allow for construction changes on a given slab while maintaining the slab’s strength. This might involve de-stressing existing cables to allow for removal and then reconfiguring cable placement in the modified slab.

Alternatives to Cable Repair for Structural Strengthening

Ultimately, safety must be the first priority when you’re dealing with a post-tension slab. Post-tension cable repair is often necessary to maintain safety, but in some cases, you can achieve the required level of reinforcement through other means. 

One of those means is called fiber-reinforced polymers (FRP). These sheets of strong fibers woven together are applied to the exterior of a concrete slab to add strength and stability. Fibers can be made of fiberglass, steel wire or carbon. Carbon fibers are the strongest, making them the solution of choice for many concrete applications. 

A concrete reinforcement expert can help you determine whether your situation calls for cable repair, FRP or both.

The Leading Post-Tension Slab Repair Experts

The expert field service technicians at Tendon Systems provide world-class post-tension cable repair and related services quickly and efficiently. We have been doing this for years, and we are proud to bring an expert touch to such an important field.

Post-tension slabs can be repaired, and our team is the one that can do it right. Ready to work with us? Give us a call at 678-835-1100 or contact us online to get started.