Waffle Slab Repair
Waffle Slab Repair
(OP)
Was it customary to reinforce the 2.5" slab in a waffle slab system with mesh?
How can we place a new slab so that shear is transferred across the cold joint that will be created between the new and old concrete? Would the attached be satisfactory?
Anyone ever repaired a waffle slab?
How can we place a new slab so that shear is transferred across the cold joint that will be created between the new and old concrete? Would the attached be satisfactory?
Anyone ever repaired a waffle slab?






RE: Waffle Slab Repair
What is structurally wrong with the slab that you have to repair it now?
Mike McCann, PE, SE (WA)
RE: Waffle Slab Repair
It is a below grade parking garage built > 50 years ago. The corrosive deicing chemical got to the top and bottom bars in the waffle slab and they corroded (most likely failure to replace the membrane waterproofing system after it had exceeded its expected life, but also possibly was used for some years before the membrane was installed), the expansive corrosion products caused delamination of the concrete. The top bars extend into the 2½" slab of the waffle system and caused it to delaminate.
Any comment on my preliminary repair detail for the slab?
I will prepare several details for diffferent conditions that will be encountered, but the one I posted would start me off.
RE: Waffle Slab Repair
RE: Waffle Slab Repair
RE: Waffle Slab Repair
RE: Waffle Slab Repair
I have completed several repairs to waffle slabs in the past. All the ones I have dealt with have mesh in the top. Some guidance from past experience:
1. If the repair includes adjacent units, also remove the top of the rib and incorporate that into your repair patch. Good patch geometry and clearance around rebar in top or bottom of ribs is important.
2. I would extend the edge of your repair detail and form a 1" key over the rib at the perimeter of the thin slab areas.
3. Ask around, we were lucky on two projects to have found spare waffle slab forms in a storage room. Made the forming of the repair areas very easy. Some contractors may also have some stockpiled.
4. Don't forget to specify vertical sawcuts around the perimeter of the repair patch area at the top of slab, to prevent feather edging.
5. Bonding agent, waterproofing membrane, etc ....
RE: Waffle Slab Repair
Thanks for all the good points. Much appreciated.
One of the problems on this job is very tiny (3 mm) side cover to bottom bars in some locations. So we think a wood form would be better than the metal form in our particular case, so that we can form a wider rib and achieve better side cover. This was perhaps not an issue in your project. Our job has #7 bottom bars, fitted into a 5" wide rib...not the best situation.
The contractor says that if we are going to take the slab out where it runs over the beam, we should take out the whole rib depth too. Seems like wise counsel because I cannot reliably make the new slab and old rib act together (too narrow to install significant mechanical fasteners), and in any event it will be more trouble to try to retain the old rib below the slab than to just remove it at the same time as the 2.5" slab is removed.
RE: Waffle Slab Repair
My real concern is that the replacement rib will not have adequate shear connection with the intersecting ribs for high point loads.
RE: Waffle Slab Repair
RE: Waffle Slab Repair