Tilt Up Concrete Repair Using Shotcrete 2

[sponcyv]

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.

 

[a2mfk]

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.

 

[msquared48]

Why that particular panel and no others?

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

 

[sponcyv]

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.

 

[JedClampett]

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.

 

[msquared48]

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

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

 

[Ron]

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.

 

[dik]

Often shotcreting makes the appearance worse...

Dik

 

[sponcyv]

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.

 

[sponcyv]

a picture of the deflection

 

[a2mfk]

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.

 

[csd72]

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.

 

[sponcyv]

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.

 

[sponcyv]

vehicular damage is impossible due to the location of the panel

 

[msquared48]

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

 

[hokie66]

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

 

[sponcyv]

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.

 

[Ron]

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.

 

[Brad805]

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

Brad

 

[Ron]

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