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Tilt Up Concrete Repair Using Shotcrete
2

Tilt Up Concrete Repair Using Shotcrete

Tilt Up Concrete Repair Using Shotcrete

(OP)
I am working on a job currently where chlorides have deteriorated a tilt up panel excessively.  Cracks have developed along the reinforcing lines both vertically and horizontally and extend to the reinforcing which is located in the center of the 5.75" thick panel.  There is also excessive spalling on the exterior face of the wall.  The wall has deflected out of plane roughly 3".  The wall supports roof joists which span 32'.  

I am looking at several options and one involves shoring the roof and removing the deteriorated concrete from the exterior face and then adding shotcrete to increase the section of the wall.  Has anyone ever done something similar?

I am worried about the pressure of the shotcrete and the necessity of shoring the panel while adding shotcrete.   

RE: Tilt Up Concrete Repair Using Shotcrete

I'm assuming there are corrosion stains on the wall and it is assumed that the rebar is corroded which you have determined is causing the concrete cracking and spalling?

Oh wait, the wall has deflected out of plane 3"?? I think you need to have this shored up immediately until you come up with a solution. How tall is the wall?

Sounds like a major problem and complete removal and replacement may be necessary. But that is based on very limited info.

RE: Tilt Up Concrete Repair Using Shotcrete

Why that particular panel and no others?

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
The wall has undergone long term deflection as the building was built circa 1970's.  We had cores taken and petrographic analysis performed.  The wall is 22'.  Complete tear down is obviously an option, but a last option.   

RE: Tilt Up Concrete Repair Using Shotcrete

With the conviction of pretty complete ignorance of the situation, I would explore the removal and replacement of the panel option. In the long run, you're going to be happier than trying to patch and repair a tilt up panel. Besides, I don't think replacement will be all that expensive.

RE: Tilt Up Concrete Repair Using Shotcrete

Has this panel been at the source of a fire in the past?

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Tilt Up Concrete Repair Using Shotcrete

Agree with A2...shore the structure NOW!!

I have done structural repairs with shotcrete before....it's difficult to get it done correctly and will still be a patch in the end.  The pressure of the shotcrete is not the issue..that can be handled.  It is the bond of the shotcrete and the integrity of the repair behind the  existing rebar and the additional rebar.  There are plenty of shotcrete pool builders out there...but few who can do good structural shotcrete.

Same question as Mike...why only this panel and is there something unique about this panel as compared to the others?  As Mike noted, fire is a possibility as it would increase the carbonation depth and allow penetration of chlorides...but what is the source of the chlorides?  If in the mix...all the panels will be affected...eventually.  If external, then why only this panel..drainage? Exposure?

Seems a bit odd for a single panel to be so adversely affected.  I would shore the existing issue, then investigate further before doing repairs.

 

RE: Tilt Up Concrete Repair Using Shotcrete

Often shotcreting makes the appearance worse...

Dik

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
The building is a warehouse and the panel is along the rear.  Every other panel is cracked to some extent.  This panel is simply the worst by far.  

The deflection of this panel is puzzling to me because the eccentricity of the roof load should act against the deflection (wall deflects inward and joists are anchored to inside face of panel).  There are large horizontal cracks at the location of maximum deflection.  There are also pick points at this location.  It is possible that the panel was not picked properly and these are stress cracks that weakened the section.  As far as the excessive cracks along the exterior, I'm not sure why this is worse than the others.  Moisture has a direct path in to the cracks as the roof sheet drains to the back, but not sure why this specific panel is that much worse.  

There has never been a fire and carbonation is not the cause of the cracks...the petrographic analysis found chlorides in the amount of 14% which is extremely high and it can be assumed pretty confidently that accelerators were used.  As I mentioned above, every other panel is showing signs of cracking.  The panels in between are uncracked.  There were two different mixes used.  Each panel is about 9 cubic yards which is about what a concrete truck can hold and it appears that every other truck had a different mix.  There were no chlorides found in the good panels.    

Ron - I'm interested in the structural repairs that you have done with shotcrete.  Have you repaired tilt-up panels?  I really have been able to find nothing on tilt-up panel walls specifically.  Most uses I've found are on retaining walls and bridge abutments which are much different than this.  

Trust me, I would rather take the wall down and have them build back masonry, but that's not the best option for the building owner, so I'm trying to find a better solution.

RE: Tilt Up Concrete Repair Using Shotcrete

I've seen all I need to see. If its my seal, they are getting new wall panels or CMU. It won't be the first or last time to disappoint an owner. Older buildings are buyer beware, and they rarely hire us to review a building before buying it...

I suppose anything IS repairable, but I'll follow this post with interest to see if any really good repair is going to be more economical than replacement.

RE: Tilt Up Concrete Repair Using Shotcrete

One method that hasnt been mentioned is the possibility of placing a column on the inside to take the loads.

Could this cracking be the result of a vehicle impact from the outside?

Anyway, I wouldnt be happy with shotcrete for this one.

 

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
That was another option - support the roof with steel and let the wall be self supporting.  The problem is that the wall will continue to deteriorate unless the delaminated concrete is removed and replaced and sealed to keep out moisture.  Basically, the entire face of the exterior wall would need to be repaired.

I'm going to recommend total replacement.  I agree - it is the best option.   

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
vehicular damage is impossible due to the location of the panel

RE: Tilt Up Concrete Repair Using Shotcrete

Then it must be associated with the mix of that particular panel - perhaps misbatched at the plant.  The panel is only 6 to 8 yards in volume from what I can gather - a single batch for one truck.

The panel needs to be immediaqtely shored and replaced.  No question.  Tis time with the right mix.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Tilt Up Concrete Repair Using Shotcrete

The panels with excessive chlorides can't be saved.  Time to bite the bullet.

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
hokie66,

I am pretty sure that the rest of the panels also have chlorides, but the deterioration is not as severe.  Our recommendation to them on that is to repair cracks and spalling and provide an elastomeric paint coating.      

RE: Tilt Up Concrete Repair Using Shotcrete

sponcyv...If the chlorides are in the mix and not environmental, deterioration will continue even if you coat with elastomeric coating.

You stated that the petrography showed chlorides.  A petrographic examination typically does not quantitatively characterize chlorides..only the result of their actions.  Even then, chlorides don't affect the concrete, just the rebar.

Chlorides are determined two ways...acid soluble and water soluble.  The results obtained in the water soluble chlorides test are more relevant and indicative for rebar corrosion.

I don't know of any environmental condition that would induce chlorides in a vertical application.  It's common in parking garages, bridge decks and pavements, but not in buildings unless in the mix.  With levels you noted, it appears to be a mix issue.  As Mike noted, it could be isolated but with the cracking you noticed, it is likely pervasive.  I would sample and test a few more areas.  This could be a construction defect for which there might be legal recourse to the owner...if so, that would soften the blow of the repairs.  This possibility should be explored.  

Attached is a sampling procedure for chlorides sampling to prevent contamination and to prevent having to take cores.

  

RE: Tilt Up Concrete Repair Using Shotcrete

There seems to be a great deal of focus on the concrete for obvious reason, but I am curious about the rebar condition?

Brad

RE: Tilt Up Concrete Repair Using Shotcrete

Brad...from the descriptions of cracking and spalling, the rebar is exfoliating and expanding..so condition not so good!

RE: Tilt Up Concrete Repair Using Shotcrete

That is what I was guessing, but the focus seems to be putting something over without discussing the issues of new rebar.

RE: Tilt Up Concrete Repair Using Shotcrete

I would shore this immediately.

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
Water soluble chloride testing was performed on powder samples.  The tests do indicate that chlorides were in the mix leading to the likelihood that chloride accelerators were used.  

This building is 40 years old and has changed hands multiple times making it very difficult to go after legal recourse.

Yes, the rebar is corroded and is the source of the cracking.  

I'm not worried about shoring the roof immediately as many are in this forum however.  

I do appreciate everyones input and this forum is really great!

RE: Tilt Up Concrete Repair Using Shotcrete

Not to be pushy- its your call, you've been to the site, all we have seen is a couple of pictures. But with 3" out of plane lateral deflection, and all of the other indications of distress, why wouldn't you shore and brace this panel and the roof?

RE: Tilt Up Concrete Repair Using Shotcrete

(OP)
I understand where you are coming from and it is the safe thing to do being that I've been to the site and I've seen it and making them shore would cover myself.  I also know the wall didn't experience this deflection overnight.  In fact, the wall has been standing for 40 years and I have a strong opinion that the deflection was caused by stress in the panel during erection.  When tilt wall panels have been tested under combined axial and lateral loads, the deflections before failure have been extremely high (10" and more).  That being said, I also understand that the concrete mixes were good and they were tested in a controlled environment.  This wall is not carrying much load.  It is my strong opinion that this wall will not collapse outside of an extreme event.  I try to see things through the owner's eyes and be practical.  Just because I've been to the site does not mean the wall is going to fall in the next week before construction begins.          

RE: Tilt Up Concrete Repair Using Shotcrete

I had a long drive today and your problem popped into my head. I racked my brain as to why the panel would deflect inward and not outward as you said, based on the roof connection being eccentric and causing a moment that in theory would produce outward panel deflection. I know its only a theoretical discussion. Maybe it was cast poorly with a small concave, or lifted too early or incorrectly?..

That's interesting about that testing, 10" for how tall of a panel? That's amazing. But that is with intact and developed rebar. I would worry with the amount of corrosion you have that your rebar bond to the concrete and your loss of steel section may leave your panel with very little tensile strength.

Steel pipes and jacks are cheap and fast, can I talk you into at least shoring up the steel joists? The panels then only have to support their own weight.

I do a lot of forensics, this one is very interesting. I am saving that pic to my library. Keep us updated with another post and a couple more pics if you want. Most tile panel issues I have dealt with involve construction problems like improper or inadequate bracing, misplaced connections, etc...

RE: Tilt Up Concrete Repair Using Shotcrete

A prop is cheap insurance.

If this panel fails and falls on someone before you come up with a solution then you may struggle to get a decent job again. Do not succumb to pressure from the client to do otherwise.

You must never forget that you have a legal duty of care.

RE: Tilt Up Concrete Repair Using Shotcrete

Sponcyv:
Can I hijack your thread for a moment?  I see two people right here that I want to talk to, and then I've got bigger fish to fry this evening.  How did your Hertz stress problem turn out, let me know, I really am interested in what you finally did.

This tilt-up wall is certainly an interesting problem, and I will follow it to see what you do.  Do what's right and safe; of course you have to be practical and do what's best for the client, but you shouldn't stick your neck out a mile to save him a few bucks or put your company in a dangerous position to do that either.

A2mfk:
I believe you and Slick chided me some time back for not posting sketches of my own ideas, when I harp on that so much.  That OP was something about proper location of a light single web stiffener, under two heavy lifting lugs, on a light WF; a complicated little lifting beam problem, which I thought was way over detailed.  Then you got after me again the other day for not knowing how to post an attachment, and more or less suggested I should go back to 4th grade, or at least get help from there, in a nice way of course.  WELL!  Look what I think I can do......   we'll see.  Talk about teaching an old dog new tricks.

RE: Tilt Up Concrete Repair Using Shotcrete

I was so damn excited to see if the scan would work, that I forgot something I intended to add....
Thanks to you too, BA for some direction, even if you're older than 10.

MERRY CHRISTMAS to all, and to all a good night.

Dick

RE: Tilt Up Concrete Repair Using Shotcrete

dhengr- You see, I knew you could do it! Nice self portrait!

RE: Tilt Up Concrete Repair Using Shotcrete

Would there be a temperature differential between the inside and outside of the building that caused the wall panel to deflect inwards.

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