Spalled concrete repair details

[DBuker]

I'm looking for a source for generic spalled concrete repair details. At a former firm I remember a reference manual that had some isometric drawings showing how to remove the concrete around the corroded bar and how to clean the bar up and patch it. It also gave recommendations for the repair specs. Does ACI 546 have those details or is it one of the ICRI documents?

A little background:
A client has a project that consists of re-roofing a 13 story concrete building that was built circa 1950. The old roof membrane has leaked like a sieve and at the beginning of the project they found one location where the rebar had corroded and caused the bottom of the slab to spall. I recommended that I do a full survey of the underside of the slab to determine if the spalling is a systemic problem or an isolated one. During my investigation I found 4 separate locations where a single longitudinal bar had corroded and caused spalling. In one case it was clearly caused by a plumbing vent that was installed directly against a bar and was not kept water tight and in another it appeared to be that the bar had too little cover (fell off chair during construction maybe). I assume that in the remaining two the cause was water infiltration, possibly the water got into the slab via a shrinkage crack and over the last 65 years it has grown to the current problem. Besides these 4 locations the slab appears to be in good shape.

In conclusion, I need to develop a repair spec with some generic details and I'm looking for the appropriate reference manual.

Sorry if this question has already been asked and answered, I searched and didn't find a good answer to my specific question.

Thanks in advance,
Daniel

 

[bridgebuster]

The Corp of Engineers has three manuals (that I know of) :UFC 3-270-04, 15 March 2001; UFC 3-270-03, 15 March 2001; and EM 1110-2-2002; 30 June 1995.


Attached is an ACI pamphlet. I also post a PennDoT standard sheet. I have drawings from a various bridge projects, if you need more let me know.

 

[bridgebuster]

PennDOT standard sheet.

 

[DBuker]

Thanks for the input bridgebuster.

I ended up purchasing a copy of ICRI 310.1R-2008. It gives a fairly simplified overview of concrete repair along with recommendations about clearance distances between concrete and damaged rebar during repair. I'm also using ACI 546r-96, which has much more depth on the subject. I may purchase the updated copy of ACI 546 if it seems necessary.

Has anyone had any luck with removing spalled concrete and cleaning the rust off of rebar in a way that doesn't require hydrodemolition or sandblasting. Unfortunately in my case the damaged concrete is immediately above some very high-end condos and I'm afraid that the owners won't accept the cost associated with the repair.

 

[Bagman2524]

I've fount Concrete Repair and Maintenance Ilustrated by Emmons to be useful in the past.

http://books.google.com/books?id=DfRRAAAAMAAJ&source=gbs_similarbooks

 

[hokie66]

DBuker,
Because the situation as you described it doesn't sound severe and the slab is in generally good condition, it may be appropriate in your case to just use hand tools to remove the spalled concrete, sand off the rust, and patch with a concrete repair mortar. This assumes that a new membrane, including flashing of penetrations, will solve any future water intrusion issues.

 

[DBuker]

Hokie66,
I was wondering about that. The scope of work is to re-roof the building. That should stop any future water infiltration, at least until the roof membrane fails sometime way into the future. My concern is that the bar is rusted on all sides and by only cleaning the exposed side it may not be fully bonded to the concrete in the slab.

I still need to do some investigation into the as-built slab capacity vs. the demand. From what I can tell, the roof slab should have some extra capacity based on a comparison of the design loads and the actual roof assembly. It's possible that I'll find that removing a single longitudinal bar is acceptable, in which case it may be plausible to do nothing at all. Although, I can't imagine that I would actually recommend that.

As an alternative, I've wondered about laying a channel (or plate) flat on the underside of the slab and bolting it to the slab with epoxy anchors as a way to "replace" the corroded rebar. It seems like it wouldn't really work as intended but maybe that would be an option? Has anyone done a repair like that with any success?