The complexity of post-tensioning repairs requires a contractor that specializes in, and is familiar with, all elements of post-tensioning systems. STRUCTURAL has been repairing post-tensioned structures since 1976 and is the only contractor with the in-house expertise of VSL Post-Tensioning Systems.
Corrosion of unbonded tendons is common for post-tensioned structures exposed to aggressive environments. Insufficient cover over the tendons and lack of corrosion protection at anchorages combined with exposure to chlorides through deicing materials and coastal air lead to the corrosion of post-tensioning systems.
Barrier cables used in parking garages are similar to post-tension cables in concrete slabs and are subject to the similar deterioration mechanisms. In some cases the failures occur more quickly since the cables are directly exposed to the elements and do not have the added protection provided by concrete cover. Replacing barrier cables and anchors requires the same expertise as repairing post-tensioning tendons.
Repairs to post-tensioning systems fall into two categories:
1) Structural Repairs
These repairs address system failures. Signs of structural post-tensioning system distress disclosed in the inspection can include the following and will require immediate repairs to restore strength and integrity to the structure:
2) Preventative Maintenance:
- Broken strands which can be seen coming out of the structure
- End anchorage which has lifted out of the concrete
- Cracking concrete which is running parallel to the strands
- Excessive deflections
- Punching shear cracks in slabs
- Diagonal shear / flexure cracks in beams and joists
Regular inspection of strand systems for signs of distress is one of the best ways for a building owner to prevent costly repairs. Items to be considered in the inspection of post-tensioned structures:
- Appropriate concrete cover over strands exposed to aggressive environments
- Condition of protective grease and sheathing
- Cracking near strands (P-T systems are designed to reduce or eliminate cracking, so any excess cracking may indicate a problem)
- Condition of concrete at anchorage pockets
- Rust staining on the concrete near strands
- Grease staining on slab soffits