1. First a shoring system is designed to adequately support the area under repair, and the tendon anchors are located using original design drawings.

2. After locating the anchor, the concrete patch over it is removed and the button-heads are inspected for damage.

3. If damage is found, the tendons are detensioned and the concrete is removed behind the anchor until undamaged tendon wire is found. (In most cases this is 10" to 12" of concrete, but can be as much as 3' to 4' feet).

4. If the damaged area is 10 to 12 inches, a new bearing plate is set in high density concrete, (9,000 to 10,000 psi compressive strength vs 4,000 psi for conventional concrete). High density concrete is used because of its resistance to cracking and thus water penetration

5. A new stressing head is attached to the wire and the tendons are stressed to the required force using a hydraulic jack.

6. Once the required force has been reached, steel shims are inserted to "lock off" the force and the jack is removed.

7. If the damage extends 3 to 4 feet, the damaged tendons are cut square, and new material is spliced in to bring them back to the location of the original anchor.

8.This is accomplished by locating good wire and buttonheading on a stressing head. The buttonheads are cold-formed after the wire is passed through  a machined anchorage fixture. This results in a no-slip anchorage and eliminates potential seating losses common in friction-grip anchors.

9. A similar anchorage is attached to a new section of wire and the anchorages joined by a coupler (seen below). This allows a new bearing plate to be cast in the original location and the tendon stressed as before.

10. For areas of damaged wire in the middle of a tendon where the end anchorages are still accessible, two couplers can be used to replace the section of corroded wire.

In the photograph to the right the tendon rises over a beam and is near the surface.

Where the tendon is mid-span and near the bottom of the slab, new wires are welded to the section of wire to be removed. As the wires are pulled out of the slab the new wires are drawn through the existing void thus maintaining the designed profile.

11. Tendons who's ends are now inaccessible, either by additional construction, walls or decorative cladding, that suffer deterioration can be repaired at the location of the damage by using a "Y splice".

12. As before the damaged area is removed to reveal good wire whereupon  a series of four plates are buttonheaded onto the wire and connected.

In the photograph to the left, the bottom splice has been tensioned and the top splice is awaiting completion.

13. The tendons are adjusted to the required anchoring forces, which compensate for any relaxation of tensioning that may occur.

14.The anchor and exposed tendons are epoxy-coated to deter corrosion. Conventional concrete is placed in the pocket around the anchor.

15. Above the anchor pocket, the concrete is coated with a urethane traffic-bearing coating to help keep moisture from penetrating to the anchors.

These type of repairs, and many other types, can be adapted to individual requirements and different locations based upon the customers needs. With proper maintenance, a repaired facility should withstand normal usage for another 20 to 30 years.