concrete attack 4

[ukengineer58]

hi i am inspecting a suspended slab which has some serious degradation. the bottom steel has lost all concrete in large areas. that is to say the bars are hanging with concrete cover loss and loss behind the bars. is this repairable. im not even sure what's keeping in in place.

 

[msquared48]

May be repairable, depending on how much steel area is still there and the quality of the surrounding concrete. Can you post any photos?

Another consideration would be to make sure that whatever is causing the deterioration is repaired prior to any restoration work.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

Mike is right. It depends. But even if it is repairable, whether or not it is practical to do so will be dictated by whether or not it is more economical to repair or replace.

 

[Ron]

agree with Mike and hokie...need to determine cause before you select fix. Post photos

 

[dik]

Parking garage?

Dik

 

[ukengineer58]

im afraid i cannot post photos as the client will not allow use of photos. its an effluent plant the cause is hydrogen sulphate gas. this will still be present afterwards due to the nature of the process and design of the structure. there is a kit room above. it would be impractical to replace the slab the whole structure would go. i would say up to fifty percent of the underside is in this condition. we do not have existing rc drawings to see original bar sizes.

 

[msquared48]

Hydrogren Sulfate, or Hydrogen Sulfide?

Sounds like whatever repair is made, you need to protect the underside of the concrete after it is completed, otherwise it is just a matter of time until it happens again.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[rowingengineer]

personally I would look at propping the existing slab, removing all the concrete that is suspect. then look at replacing the reo with an frp system. This system would either be in the form of strips or beams.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[ukengineer58]

fry not an option i don't think. oh its also a confined space, in the legal and literal sense

 

[JedClampett]

I've had this happen several times. The cadillac way to repair it is to remove the whole slab and recast it with Ameron's T-Lock liner. It's pretty easy to line the bottom of a slab (walls and tops of slabs are another matter)and the protection is very good. Maybe if you present it as the most permanent fix, they can figure a place to temporarily put the equipment above.
Or you can thicken the bottom of the slab by 4 or 6 inches. Add the reinfocing in the space. Build falsework and pour from above using access holes cut in the slab above. You can line the formwork with T-Lock. It's tricky, because you're working blind.
The second best fix is to do your structural repairs (replace reinforcing, trowel on repair material, or shotcrete or whatever)from below and line it with a high quality coating done by a qualified applicator (harder to find than it seems). We like Sauereisen's systems, but everyone (Plasite, etc.) has a system and most of them will work for a while. There are PVC liner systems that can be retrofit, but applying it to the underside of a slab seems very difficult.
Whatever you do, carry the lining down the wall. Once the gas is resisted by the liner, it moves on to the next weak link, which will be the walls.

 

[hokie66]

ukengineer,
Listen to Jed. He has experience in sewage treatment plants, while most of us don't. Whatever you do, the chamber has to be taken out of service for the repairs. As well, there may be modifications required in the process to lessen the problem of H2S and H2SO4.

 

[dik]

H2SO4 is Sulphuric Acid... likely Hydrogen Sulphide...

 

[hokie66]

dik,
My chemistry is not too sharp, but I think both hydrogen sulfide and sulfuric acid are involved.

 

[rowingengineer]

yes agree with Hokie, Jed has a lot of experience in this field

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[ukengineer58]

i have asked for some testing of concrete where it remains. compesive, carbonation and petrographic analysis. the client us resisting petrographic analysis and reckons we can get what we need without it. i disagree what do you think? i want to ensure wearer removing any problems.

 

[dicksewerrat]

If you don't get all the bad concrete out and just cover it up, the corrosion will continue until you get colllapse. There is an outfit in Iowa that has a sulfide resistant spray on cementitious material. I think it is AP/ M Permaform. search 'permaform' They also know about as much as anyone else in the US about sewage attacks on concrete.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com