Large scale concrete repair

[mfstructural]

I may be getting involved in a project where there is extensive deterioration of the concrete and rebars in a 10" conc slab. Approximately 500 localized areas of 1 to 5 square foot repairs. The depths of the repairs will likely vary and be up to 2 to 3" at some areas. In the past we've specified to remove the loose concrete clean bars and add bars as necessary if section loss of the existing bars requires it. Then either perform a trowel patch or a patch where plywood is installed on the underside of the slab and patch mix pumped into the void and vibrated. For such a large scale of repairs I'm wondering if anyone has any other techniques that can simplify the process or make it more cost effective but still meet the same repair standard.

Thanks

 

[Enable]

I would not consider this a large scale repair unless your slab is quite small and these repairs are close together. In which case, you should combine them. Doing topside soffit repairs on 1ft2 is generally a waste of money (and serves mostly just to reduce risk of falling concrete debris, rather than restore slab capacity).

Can you provide a plan view of the slab with the identified repair areas superimposed?



EDIT - Just realized that since you mentioned pumping that you may be discussing soffit repairs (erroneous inference on my part about topside, not enough coffee this morning I guess, my bad!). Can you confirm that's the case? Still would like to see areas superimposed on a plan. Generally, we try to avoid minor soffit repairs all over the place and opt for through-slab (if you have access to the top of the slab).

 

[lexpatrie]

The Morabito drawings for Champlain Towers South shows their repair approach, (up to you on how much confidence you have in thst sort of repair) and there's what, ACI 562?

The shear friction provisions require surface prep and roughening and removing any laitance with a wire brush, that makes sense to me.

 

[Ingenuity]

1. Overhead spall repair via form-and-pump

2. Overhead spall repair via hand troweling

3. Overhead spall repair via pre-placed aggregate

4. Overhead spall repair via shotcrete

The most common would be techniques 1 and 2. I have a preference for 'form-and-pump' because of the superior bond to the substrate (if done correctly) but the setup and equipment is not justified for small areas, IMO.

ACI has Repair Application Procedures (RAP) on their website that addresses all techniques. https://www.concrete.org/topicsinconcrete/topicdetail.aspx?search=rap

 

[dik]

The Morabito drawings for Champlain Towers South shows their repair approach, (up to you on how much confidence you have in thst sort of repair) and there's what, ACI 562

If they're the ones I've seen, they show 3/4" concrete cover for a parkade structure; that was common 50 years ago or so... I immediately started shaking the sawdust from between my ears.

 

[structuralrepair937]

Current restoration project. Includes floor,soffit and wall repairs a varying depths. Slab thickness varies from 8" to 11".
Soffit= smaller shallow patches. Demo from below with 32# chipping hammers to sound concrete. 1/2" to 3/4" above bar where exposed. 1/4"x 3" ss. Raw spike installed where rebar is not exposed. Epoxy bond coat applied and patched back with trowel grade V.O. material.

Floor repairs= Demo to sound concrete or 3/4" past top run of bar. 2 independent coats of epoxy on bar. Ssd before pouring with sika 1000. Scrub coat ahead of pour. Vibrate and mag finish.

 

[dik]

The Morabito drawings for Champlain Towers South shows their repair approach

They also had 3/4" concrete cover in a marine environment; I'd look elsewhere for repair information.

 

[BridgeSmith]

I suggest looking into hydrodemolition for removal, and repairing with an overlay of latex modified or silica fume modified concrete. May not be suitable, depending on how concentrated the repair areas are. Chipping and repairing with the latex or silica fume concrete is also an option worth considering.