Basic Equipment and Training Needed for a Contractor to do Post-Tension Restoration Work 1

[KootK]

Disclaimer: this is one of those threads where I'm too lazy and time pressed to do my own research. If you're not down with helping out on that basis, do abstain.

I've got a restoration contractor friend that wants to jump into PT restoration work as it pertains to general concrete restoration. Canada, mostly slabs, lots of slab edge rebuilding. He's got a project that he needs to bid on this week. Before he does, he wants to get some kind of handle on:

1) The core procedures that he'll have to figure out how to execute (distressing, splicing etc).

2) The basic equipment that will be required.

3) The basic training that will be required and the options for acquiring it (PTI etc).

I've been asked to help with with this and it represents an opportunity that I've been longing for. So if I can be impressively helpful -- and helpful this week -- there may be real value in it for me. I know my way around new built PT and am not a complete noob on the restoration side. That said, I know that we've got some PT reno rock-stars here who could save me some time and improve my odds of knocking this out of the park.

So... recommendations? I've got the publication below on order which I think will be a good start. Of course, the chances of my doing much more than thumbing through it this week are pretty remote.

 

[Canuck65]

Kootk,

Not sure if this is what you are looking for, but here goes ... From a few years back I had some experience with post-tensioned rehabilitation. In the projects I have worked on they have been unbounded and involved total replacement of the tendons. This is just a quick summary, I will likely need to think it through a bit more for a more complete list.

1. Someone needs to mark out the location of all the PT tendons at high points using a covermeter. Paint marks at each high point along the length. Often done by the consultant or testing company. Need to differentiate between mild steel and tendons.
2. Sometimes a good idea to also mark out the mild steel that may conflict/overlap with PT tendon locations.
3. Install shoring, if necessary, or have staged replacement, i.e. every third set of tendons, complete the project in three cycles.
4. Install protection/hoarding/sandbagging, etc.... Generally we only had the contractors plywood and sandbag the original anchorage locations, it was not necessary along the length of the tendons.
5. Clear all persons from above and below the path of any tendons being distressed.
6. Time to get out the quick cut concrete saw. Choose a high point, start sawing perpendicular to the tendon, wait for the sparks to start, then you will eventually hear the tendon strands popping. These locations need to be chosen carefully by someone who understands how many tendons may be in a bundle, and if all the tendons are full length, some might stop short, etc... All in all, the process takes about 2 minutes to distress a set of tendons. Double check all the strands are cut. Note, where barrels can be accessed, sometimes they will destress by torching the barrel and wedges.
7. Very carefully jackhammer out any tendon anchorage locations. Someone needs to be sure, usually via the paint marks, that the workers are not jackhammering into live anchor locations. Not difficult, but very important for safety. Also jackhammer out the distressing locations so that you can repair the sheathing. Any regular type concrete delaminations can be dealt with at this time (within the destressed area).
8. Pull old tendons out, usually via some pullies and a forklift.
9. Use a button wire with various rags, etc... to clean old grease and any moisture from within the existing sheaths. Essentially insert button wire and pull back through a few times. Perhaps there is a better way now, not sure.
10. Rebuild concrete bulkheads, with additional reinforcement added. Excellent concrete repair and bonding techniques required. Also, make sure the new bulkheads are plumb.
11. Feed button wire through sheathing and weld end of new tendon to button wire. Pull tendon through with application of as much grease as possible. Use the forklift and pulley system. If any tight spots are encountered, they are located and jackhammered out.
12. Install all the dead end anchors, trim and cap.
13. Pour all dead end anchors.
14. Once concrete reaches strength (silica fume aids in turnaround time), the live ends can then be stressed, trimmed and capped.
15. Final pours of bulkheads to encapsulate the live stressing ends.

Most of the equipment needed will be available to a general restoration contractor except for the hydraulic stressing jacks perhaps. On a typical Canadian pt restoration project that I have been involved with, we would have a general contractor that was experienced in regular concrete restoration doing most of the work, with the specialty pt subcontractor bringing the tendons to site, pulling the old ones out, putting the new ones in, stressing and capping. All the destressing work and concrete restoration would be done by the general.

 

[KootK]

@Canuck65: your response was a huge help. Thanks for the effort.

 

[Ingenuity]

I will preface the following by saying that PT repairs are a tough gig - very hard work, dangerous work for the unskilled, often variable work scope, clients who can be very demanding (what else is new?), and requires a crew with patience and with abilities to think outside the box.

...and workers compensation insurance rates for contractors involved with PT repair scope can be significantly higher in some markets.

In my market (and most typical in the US - and certainly in So-Califonia after speaking with colleagues) the traditional PT crews who install PT to suspended slabs to new buildings typically are not so good at PT repairs, IMO. They are ironworkers who know little about concrete, and even less about deteriorated and damaged concrete and associated repairs. When such crews are engaged on a PT repair project they require another sub (concrete/mason sub) to do the chipping/cutting (and some of those subs have little understanding of concrete chipping with PT tendons), then the PT crew returns and does the tendon work, then the concrete sub returns to patch etc. Very inefficient, and I have seen several personnel accidents happen with this model.

Preferable for the concrete repair contractor to have in-house EXPERIENCED PT repair capabilities.

What I did several years ago was set up a selection of standard in-house details of tendon repair types (like Type A, Type B repairs etc) that we can pass to the field so at each tendon, at each end, or intermediate location, we know whether it will be a splice repair, a center-stressing ("dogbone") repair), double-end stressed, abandoned, relocated anchorage etc etc - basically covering most of the possible options, so that things can be mixed-and-matched to suite the site details, access availability, and degree of damage/distress. Even with most of the variables covered/detailed there is always a wild card that requires special consideration.

De-stressing can take many forms: down-and-dirty angle grinder to sever strands where access permits, to more complicated situations where you have to chip out the anchorage (on the slab edge side) and let is 'self-demolish' - takes some getting used to!

Strand removal and replacement can often be challenging. Paper-wrapped systems can be especially frustrating, and time-consuming.

Sheath repairs can be a real pain - clients expect that PT repairs will last forever - and to that end, many many PT repairs do not go far enough to ensure that the best possible durability is built into the tendon repair - especially at breaches in the sheath, and protection to splicing hardware.

Multi-monostrand tendon bands repairs can be troublesome - especially if one or two 'internal' tendons to a group of say five has been damaged - how to best accommodate splicing hardware, and not screw up adjacent un-damaged tendons, nor interfere with other repaired tendon hardware.

Technical resources are a bit lacking on this subject. The PTI Guide to Evaluation is an ok reference, but more for the front-end of the proposed repairs, where the EoR will use to try and establish the severity of damage to the tendons, and the probable scope of repairs. What I did about 25 years ago was search ACI's Concrete International and ICRI's Concrete Repair Bulletin and photocopy (before digital PDF files) case studies articles on PT repair projects, then read/collected/stored them, and continue to regularly update my 'portfolio' of PT repair case studies. You can learn a bunch from those case studies. I also attended the ICRI conventions and listened to presentations on the subject. But the regular attendance at conventions can be a huge time commitment...and invariable it is just a marketing presentation by the speaker, and not the technical content I expected.

With regards to training, 99% of it comes from field experience - takes time to get it, but nothing beats it. I came from the design office, designing several million SF of PT, then, after working for a large PT contractor, transitioned into PT repairs - so, IMO, it helps having the technical/theoretical why and where-fores, but damn, an experienced practical field guy/crew will run rings around the technical/theory.

For 2019, PTI has a new field certification entitled LEVEL 3 UNBONDED PT REPAIR REHABILITATION & STRENGTHENING - first session begins this June. I am not a particular fan of the PTI Certifications for this scope of work - you can attend the class room sessions and achieve an 80% pass and you are - in theory - good to go - when in reality PT repair scope is very hand-on practical. But here is the link to the course: Link

As far as equipment, here is a short list of the specialty equipment required (over and above the usual concrete restoration equipment like chipping hammers, grinders, air compressors etc):

1. 8" stroke and long-stroke monostrand rams;
2. hydraulic pumps and gauges;
3. oxy-acetylene brazing equipment;
4. short-stressing gear;
5. de-stressing bridges
6. double-end joiners;
7. reusable splice chucks;
8. HDPE welding machine (optional, but superior for sheath repairs);
9. grease pumps and injectors
10.3/8" strand with associated grippers for rams;
11. strand pushers/pullers;
12. GPR subsurface radar/scanner.
​

I would recommend that your restoration contractor friend do some research on the availability of PT hardware/equipment suppliers in their market locale. In the US, companies like PRECISION HAYES (now combined with GTI) have a bunch of specialized tools that assist the PT repair contractor, and with their manufacturing expertise they can often fabricate custom equipment to your requirements.


Good luck to you and your friend on the endeavor.

 

[KootK]

I just wanted to thank you for your contribution on this Ingenuity. I was hoping that you'd surface for this one and your comments were a huge help.