PT Anchorage End Pocket Repairs
The concrete patching of a post-tensioning anchorage primarily performs two basic functions:
- Fire rating of the anchorage
- Durability of the anchorage
The most common problems we see in day to day construction of PT end pockets relate to the cover of the cut strand and the quality of the dry pack material.
Using conventional abrasive disc cutters, getting much better than an average of 20mm to 25mm cover to cut strands in a typical void former recess is difficult. This is why the quality of the dry-pack concrete repair material, as well as the application of the material, is so important.
The quality of the tendon grout is also critical in encapsulating the internal anchorage void during the tendon grouting process.
Unfortunately, you will often see PT pockets with very low levels of cover to the strand, to the point where you can almost make out the individual strands visually. Over the years, there has also been very limited quality control on the products being applied as the dry pack material; in many cases, it was purely a prebagged sand/cement where the cementitious content could typically be very low.
Before specifying the concrete repair remedial solution, it is important to thoroughly inspect the anchorage zone to determine the scope of the work required. Still, it is very important to remember that the anchorage zone is a very highly stressed area, even in the grouted condition, meaning a thorough understanding of PT anchorage systems is necessary before undertaking any work in the vicinity of the anchorage.
The inspection should include the following as a minimum:
- Corrosion level on the strand and anchorage components
- The level of cover to the strand ends
- Evidence of PT grout around the wedges and in between the wires of the strand
- Minimum cover levels to the top of the slab and the soffit, particularly around façade fixings/rebates
- Minimum spacing requirements between anchorages
- Visible cracking in the anchorage zone, if any
- Visible reinforcement, if any
- Any post-pour fixings or other alterations
Concrete repair procedures are determined on a case-by-case basis following the above inspection and reflecting the environmental conditions in which the anchorage is located.
Subject to the above, as a minimum, Slabtec typically adopts an R4 class high-build concrete repair mortar as a part of an overall repair system, including a bonding bridge with an anti-corrosion primer, the high-build mortar itself and a levelling/finishing mortar where required.
In areas subject to severe durability conditions, further considerations may be necessary.