Full depth slab replacement for concrete balcony?
Full depth slab replacement for concrete balcony?
(OP)
Surprisingly, I could not find this issue on any other threads:
I’m developing a repair spec/drawing for a job involving deteriorated concrete balconies. This job is the typical removal and replacement of the embedded handrail post. The concrete balconies are about 50 years old.
The existing embedded handrail posts are severely corroded, and are cracking the surrounding concrete. There is no other deterioration of the concrete due to carbonation, or corrosion of embedded steel. The slab thickness is approximately 4.5”, the rebar is positioned in an approximate 9”x9” grid. The bar is probably #4 or #5 at about mid-depth of slab.
We are looking at requiring a full depth removal of about a 1’ square surrounding the existing post embedments. My concern is regarding the structural capacity of the newly placed concrete patch. Is there typically adequate bond between existing and old concrete, or is a epoxy bonding agent typically spec’d. Should we “dowel” into the old concrete with epoxy rebar? Or can I just assume that the newly placed concrete will act monolithically with the old concrete? Any help would be great!!!
I’m developing a repair spec/drawing for a job involving deteriorated concrete balconies. This job is the typical removal and replacement of the embedded handrail post. The concrete balconies are about 50 years old.
The existing embedded handrail posts are severely corroded, and are cracking the surrounding concrete. There is no other deterioration of the concrete due to carbonation, or corrosion of embedded steel. The slab thickness is approximately 4.5”, the rebar is positioned in an approximate 9”x9” grid. The bar is probably #4 or #5 at about mid-depth of slab.
We are looking at requiring a full depth removal of about a 1’ square surrounding the existing post embedments. My concern is regarding the structural capacity of the newly placed concrete patch. Is there typically adequate bond between existing and old concrete, or is a epoxy bonding agent typically spec’d. Should we “dowel” into the old concrete with epoxy rebar? Or can I just assume that the newly placed concrete will act monolithically with the old concrete? Any help would be great!!!





RE: Full depth slab replacement for concrete balcony?
RE: Full depth slab replacement for concrete balcony?
By re-filling the opening with concrete, and leaving the original slab rebar in place, you would at least have one bar crossing the cold joint interface in each direction. This probably would be enough to ensure a good shear-friction capacity (ACI 11.7).
Doweling into 4.5" of concrete is tough to do too, but can be done with care.
Alternatives:
1. Patch back the bad concrete (12x12) but do not rely on it. Instead use steel plating or other shapes to more positively attach to the main body of the balcony slab...possibly plates on top and bottom with through-bolts.
2. Patch back the bad concrete (12x12) and use some other means to provide the lateral stability of the top rail - by possibly creating a rail to span from adjacent walls (if any?) and not rely on a vertical cantilever action to resist the guardrail forces.
RE: Full depth slab replacement for concrete balcony?
Why not core an oversize hole, then set new handrails in an epoxy grout?
Also, be sure to check what you're doing to the waterproofing on the balcony when you cut into it....assuming there is waterproofing.
RE: Full depth slab replacement for concrete balcony?
JAE -> I would prefer not to have steel plates do to aesthetic reasons. I’m anchoring into an adjacent wall instead of installing posts at some locations. However, most locations require a post to be connected to the concrete deck of the balcony.
Ron -> I thought about core drilling the embedment, but there are numerous locations where the corrosion from the existing embedment caused spalling on the underside of the deck. There is probably about a 6” diameter area around the embedment where the concrete is unsound.
We are installing new waterproofing after the repair of damaged concrete.
Is there typically adequate bond between existing and old concrete, or is a epoxy bonding agent typically spec’d. Should I “dowel” into the old concrete with epoxy rebar? Or can I just assume that the newly placed concrete will act monolithically with the old concrete?
RE: Full depth slab replacement for concrete balcony?
I've also seen cases where a bonding agent was used but the concrete broke free, seemingly indicating that the bonding agent acted more as a de-bonding agent....probably due to poor workmanship.
I would think that any doweling, roughened surface, etc. to develop a mechanical anchorage would be preferable and more dependable than depending on raw bond.
RE: Full depth slab replacement for concrete balcony?
One method you can use in demolition is to score the top and bottom surfaces by sawing, then use a demolition hammer to remove the outboard concrete, leaving the rebar intact. Then if you clean the exposed surface of the concrete, apply a good bonding agent, and utilize the existing rebar, you should get by with only minimal doweling.
Be careful with only wall attachment of the rails. You'll have to meet a lateral and vertical load requirement by code.
RE: Full depth slab replacement for concrete balcony?
RE: Full depth slab replacement for concrete balcony?
RE: Full depth slab replacement for concrete balcony?
I would suggest doweling and roughing surfaces.
RE: Full depth slab replacement for concrete balcony?
Either way, I think I would rig something up to load test a few posts just to be sure. Your building code should have the required loads.