Underside repair of 30" thick concrete slab in old winery

[Jc67roch]

I have a condition in an old winery where the 30" thick slab is failing. The construction dates from 1872. The slab supports large tanks and vessels. The slab is essentially falling away from below. There is very minimal (1 per slab bay) reinforcing bars. Wondering if anyone has a creative way to support or repair the slab from below? My thoughts are to clean and shotcrete from below, or full demolition and replacement - either with precast plank or new cast-in-place slab. See photo attached. Note, it appears the slab may have been placed in two separate lifts.

 

[JedClampett]

Before you repair it, you need to figure out what is causing it. Do the tanks above the slab leak nasty chemicals? Then they need to be repaired. Or it's possible it's just old.
There appears to be steel beams embedded in the concrete. Are they the structural supports? What kind of shape are they in?
You're on the right track for the fix with shotcrete or some troweled on repair mortar. But I'd figure out the existing system and the problems before I did anything else.

 

[dik]

Jed summed it up in the first paragraph... you need to determine if moisture is getting beneath the slab... has the concrete deteriorated? maybe not Portland cement in 1872... if moisture is the problem, stop the source of moisture and then if needed, you can pressure grout the area under the slab.

 

[TLHS]

Be careful and take a look at your code. This is a very old structure and you're going to have problems figuring out capacities of the existing. If you start adding significant amounts of material you may end up opening up the entire structure for review and verification, or at least your entire load path to the ground as well as all the loads working on it.

 

[dhengr]

I agree with all the above. Is it possible that the lower, lighter, layer is a prior underside repair attempt? Note unlike what you are suggesting you might do.

 

[shobroco]

Are you sure about the age? A suspended concrete slab would have been pretty cutting edge in 1872, especially with reinforcing. 30 years later innovative structures were being built of monolithic unreinforced concrete, so I'd question the date. Hot-rolled wide-flange sections of that age would also be pretty surprising. It appears as though there are broken wine bottles in the surface of the concrete where it has spalled; it certainly looks like they were placed on top of an existing slab when they were cast in place. I think your original slab of undetermined age was later capped with another slab, and the mass of concrete has worked by dumb luck for years. The original slab is now falling away. I wouldn't trust any of it if there is much load on it.

 

[cvg]

http://www.auburn.edu/academic/architecture/bsc/classes/bsc314/timeline/timeline.htm

If built in 1872, this would have been one of the first reinforced concrete stuctures in existence.

 

[paddingtongreen]

"If built in 1872, this would have been one of the first reinforced concrete stuctures in existence."

Add, "in the modern era." to the above quotation to make it truthful. Types of concrete have been reinforced with bamboo for a very long time.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[msquared48]

I wonder if the structural depth is 30"? Seems more like 4 to 6" with some kind of architectural infill over it?

Could also be a primitive form of a sandwich panel, concrete top and bottom with a lighter infill material?

All the steel looks rusted, so I question the humidity/leaks/chemicals causing it. Needs to be addressed and solved before any repairs as mentioned above.

Welding a rebar grid to the bottom and shotcreeting could work if the co0ncrete mass is viable. Any cylinder core tests done?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Jc67roch]

Thank you all. The thickness of slab is per the Owner. However, I confirmed the spalled areas are 14 to 16 inches deep (photos are deceptive). And it does appear to be laminated or at least two layers of concrete. No cores have been taken as yet - I am proposing on the design project. The steel beams are corroded and flaking, but there is suprisingly little section loss. However, detailed measurements will be part of my proposal. We have no information on the actual date of the concrete construction, only that the building was constructed in 1872 - so an original floor system may have been replaced at some point. Based on the current tanks located above, it seems I might be looking at floor loads on the order of 400 psf. Yikes!

 

[MikeHalloran]

Speaking of nasty chemicals, wineries get hosed down regularly, with whatever is allowed for sanitizing, and the spilled wine turns to vinegar.



Mike Halloran
Pembroke Pines, FL, USA

 

[dik]

flaking? if built up from rolled sections... you might want to check for wrought iron... given the time period.

Dik

 

[bookowski]

Agree with the others - if that slab is from 1872 it would be one of the earliest in the US. What does the rebar look like - is it deformed? At that age I'd expect square bars unless they are actually tie rods and it's a flat arch system. It's hard to tell in the picture but those beams look like rolled steel? Sounds like the date might be off. Do you know the size and material of the beams - it's probably going to be in the 30ksi range, do they work by calculation including the dead load of a 30in slab? Just wondering if adding even more dead load is even an option. It seems like removal/replacement might be the best option.

 

[EngineerofSteel]

You might want to get a history of operations in the wharehouse above. When did the current tanks enter operations? It may be possible that loads greater than the design have entered.

Meaning, if the steel beams are deflecting more, this will easily increase stresses in the tension edge of the concrete- creating microcracks and eventually leading to spall.

I think the suggestion to remove the spalling material is a good one. It removes an apparent dead load with no benefit to overall capacity of the floor system.

If overloading is contributing to the issue, deflection of the steel should be measurable.

I'm guessing the area beneath the slab is used for wine storage, in which case they likely maintain 40 or 50% humidity. If so, you may want to propose a solution that will protect the underside from future moisture damage.

 

[MiketheEngineer]

Yes - to all above.

Have you considered mud-jacking - a relatively cheap solution to many of these types of problems. Just find a guy who has been doing it about 30 years to guide you..