Spalling caused by insufficient concrete cover
Spalling caused by insufficient concrete cover
(OP)
Anyone have any insight of the correct method of concrete restoration for the following scenario:
A reinforced concrete tank, about 40 years old, has several areas experiencing spalling. The owner wants to address this problem becasue the spalling has become so prevalent, that it is now a hazard to walk near the tank as you never know when another piece of concrete will be falling off. After examining the tank, the spalling is occuring in multiple locations where the circumfrential hoop steel was incorrectly placed during original construction. There are many areas where there is on;y 1/2" to 3/4" concrete cover over the hoop bars.
What would be the repair strategy here? I understand that typically in concrete restoration, you want to saw cut perimeters of unsound areas of concrete so that the repair material has a minimum 1" thickenss (avoiding feathered edges). I would assume that to have a long lasting repair, the thickness of cocnrete cover will need to increase in these areas where minimal concrete cover was provided at original construction. But in 'building up' the thickness with repair material...how could you avoid a feathered edge conditon with the repair material???
Maybe my approach isn't even the best one for this type of problem. I'm open to totally new strategies if anybody has suggestions. Thanks!
A reinforced concrete tank, about 40 years old, has several areas experiencing spalling. The owner wants to address this problem becasue the spalling has become so prevalent, that it is now a hazard to walk near the tank as you never know when another piece of concrete will be falling off. After examining the tank, the spalling is occuring in multiple locations where the circumfrential hoop steel was incorrectly placed during original construction. There are many areas where there is on;y 1/2" to 3/4" concrete cover over the hoop bars.
What would be the repair strategy here? I understand that typically in concrete restoration, you want to saw cut perimeters of unsound areas of concrete so that the repair material has a minimum 1" thickenss (avoiding feathered edges). I would assume that to have a long lasting repair, the thickness of cocnrete cover will need to increase in these areas where minimal concrete cover was provided at original construction. But in 'building up' the thickness with repair material...how could you avoid a feathered edge conditon with the repair material???
Maybe my approach isn't even the best one for this type of problem. I'm open to totally new strategies if anybody has suggestions. Thanks!
Talk To Other Members
RE: Spalling caused by insufficient concrete cover
You might consider a shotcrete repair if there are large areas. You could then use the existing tank as the inside form and reinforce as necessary within the shotcrete.
RE: Spalling caused by insufficient concrete cover
A more expensive alternate is to wrap the tank with prestressing tendons and then shotcrete. This will assure that the spalled material is held in place.
RE: Spalling caused by insufficient concrete cover
The contractor the owner first engaged about repairs wants to address only the superfical after effect of the problem - they propose chipping away unsound concrete and patching back in with shotcrete and polymer concretes. I have consulted with the owner that this repair doesn't address the root of problem and would likely be a repair that last a few years.
I guess the 1-1/2" shotcrete external liner would be a solution. The owner may poo a brick when we talk costs on that repair strategy. Any other ideas out there?
The areas where the insufficent concrete cover exists is in small isolated areas around the perimeter. But there are a lot of these small isoated areas and they are pretty eveny distributed everywhere...if this makes any sense.
RE: Spalling caused by insufficient concrete cover
It's a matter of checking if the existing rebar is OK and if so, cleaning the surface to accept a patch... a couple of good products have been mentioned. The quality of the existing concrete should be determined also prior to patching...
Dik
RE: Spalling caused by insufficient concrete cover
If you were going to create "blisters" or "build up" you avoid feathered edges by maintaining a constant overlay thickness. However, it looks ugly. If you're ever in Queens look at the piers for the Long Island Expressway/Van Wyck Expressway and the bridges over the LIE to the east of there, you'll see what I mean.
We avoided the blister problem on one project by painting the bars; don't recall the product but it was made by Fosroc, that was 20 years ago.
RE: Spalling caused by insufficient concrete cover
So the 'blisters' you are describing, bridgebusters....I assume that means that at the perimeter of the build up area, you will literally have a 1-1/2" (or whatever thickness of material you are adding) step down to the original material at the patches. Correct?
If we went the route of a full 1-1/2" exterior liner around the entire perimeter...Would you recommend placing reinforcing (WWF) in the new 1-1/2 shotcrete liner?
Thanks!
RE: Spalling caused by insufficient concrete cover