Cutting Existing Damaged PT Tendon Tails

plausibly_civil · Jan 9, 2025

I am working on an existing building with three levels of elevated PT slabs. The building was built circa 2000 using unbonded PT tendons. The contractor is currently completing the strip portion of a full strip & reclad and discovered some PT tendons that appear to have never been cut or at least not capped during construction. The OSB sheathing at the third level was cut around the tendons and the tendons were butted up to/encapsulated in the exterior stucco. Has anyone seen a situation like this before? I was thinking about having them shear cut, cap, and grout the tendons for water protection after I was informed over the phone of the situation. However the damage looks more significant now that I have photos. The structure has performed fine for the last 25 years and the planned repairs to this building are mainly architectural, not due to structural distress. I'm wondering if we can arrest the damage at its current state without an intrusive repair and essentially abandon the tendons after cutting, cleaning, capping, and grouting. I worry about getting a good seal with the cap/grout given the damage to some of the wedge anchors, as well as the fact that there doesn't really appear to be a pocket to cap and grout.

Normally I have had tendons cut within 72 hours of the pour, followed by grease capping and grouting within a day. Are there any unintended consequences of cutting and capping the existing tendons now? Any thoughts to avoid an intrusive repair? My PT repair experience in the past has been all in new construction during CA. See attached photos for reference where the holes in the OSB are marked in red.

Ingenuity · Jan 9, 2025

Something seems dimensionally amiss here.

Did the slab edge get constructed incorrectly, such that it had to be 'chipped' back because there is no PT pocket and the OSB sheathing is hard against the PT stressing anchors.

Do you have a photo of a length of slab edge AFTER the OSB sheathing was removed to check the slab edge between PT anchors?

There is a significant strand tail remaining to the tendons - if this was my project I would be doing a few (min 10% sampling) lift-off tests to check the tendons before closing it up with greased end caps, sheathing etc.

Ingenuity · Jan 9, 2025

I will add that current PT systems (fully encapsulated PT anchorages and end caps) work well as a system, but to adapt an encapsulated end cap to an UNencapsulated anchorages is difficult - there is nothing to grip/bond to.

Back in the day (late 90's/early 2000's) a company called TIGER INDUSTRIES developed a greased end cap that did fit over a trimmed strand tail via a snap ring. Unfortunately they are no longer manufactured (although I still have several thousand that I use on PT repair projects).

If a greased end-cap cannot be made to work, I would be steel wire cleaning the exposed anchorage, wedge face and strand tail and apply two coats of epoxy before a cementitious patch.

plausibly_civil · Jan 9, 2025

Something seems dimensionally amiss here.

Agreed, it's a bit of a head scratcher.

Did the slab edge get constructed incorrectly, such that it had to be 'chipped' back because there is no PT pocket and the OSB sheathing is hard against the PT stressing anchors.

Do you have a photo of a length of slab edge AFTER the OSB sheathing was removed to check the slab edge between PT anchors?

I haven't seen this situation at the other, lower level slab edges which leads me to believe that they hopefully only screwed up this level (or elevation). The chipping back is an interesting observation. The contractor is pulling off OSB today so I should be able to get some better observations and photos later today.

if this was my project I would be doing a few (min 10% sampling) lift-off tests to check the tendons before closing it up with greased end caps, sheathing etc.

Testing does seem like a good first step in this case. Looks like I'll be reaching out to a PT sub soon.

plausibly_civil · Feb 4, 2025

Sorry for taking a while to get back to this thread, but I was able to get some additional observations of the tendons. It seems like they had an issue for the formwork pushing out during the concrete pour or something similar and the contractor decided to cover it up. No idea how this got past inspection.

The photos below show a group of uncovered tendons with no grout pockets. Some of the tendon groups at this bushed back edge had grout pockets but the tendon tails still poked through. I attached a photo of the tendons in their existing state and after brushing bright with a wire wheel. As you can see the tendon anchor is basically flush with the slab edge at this location. I also attached a photo of the slab edge transition from where the slab edge was bushed back to smooth.

There were no grease caps at any of the anchors, including other areas where we chipped out typical grout pockets. Corrosion did not appear to significantly reduce the tendon section and didn't appear to propagate through the wedges from what I could see. I could still see the teeth of the wedges after brushing bright which is a good sign. I'm thinking the path forward right now is to coat with epoxy and encapsulate without grout pockets somehow where they aren't possible, maybe with a embedded stainless steel box around the anchors. There really isn't a lot of space to work with here considering how far the tendons poke out into the wall assembly. Even cutting them down to 3/4" that's still 3/4" into the wall assembly which makes this whole situation tricky. Any other thoughts would be appreciated!

Ingenuity · Feb 4, 2025

Are only three PT anchorages applicable here or is it over a significant slab edge with more anchorages in play?

If only three anchorages: I would carefully chip the slab edge to remove the existing grease/wire brush marks to the concrete, trim the existing tails using an abrasive grinder to remove the previous O/A dross, coat the exposed tails and anchorage with 2 coats of epoxy, then upon cure of the epoxy, coat the entire slab edge in proximity to the anchorages with an elastomeric coating. I personally would not install a stainless steel cover/box over the anchors.

If more than 3 anchorages make up this error: I would consider some lift off testing given there appears to be adequate strand tail for such testing. If lift off tests results are say 25 kips with no consequences, then treat the anchors and concrete as suggested above.

Good luck.

plausibly_civil · Feb 4, 2025

There are (7) tendon groups with (3) anchorages each that are affected, so (21) total anchorages. The original design is a banded/distributed two-way flat plate and these anchorages are all in the distributed direction. I appreciate the insight and I'll look into the elastomeric coating for the final repair. Fortunately, we already have a waterproofing specialist/architect on the project since this is a full strip and reclad. I think some lift-off tests at the longer tails would be beneficial to determine that the damage is limited to the exposed tails. Again thanks for the responses!

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