How to repair concrete spalling?

[trentdi]

My pool coping ledge is suffering from some concrete cancer - the rebar has rust on it and has caused the
concrete to crack and spall. One corner has a crack from top to bottom, so I think I will have to saw the
corner off and reform (drilling in some cement anchor screws as needed), keeping the rebar in place.

For the parts where the rebar is already exposed, I was going to pack in new concrete similar to this video:
https://www.youtube.com/watch?v=eVofsam9Sww. I've already gone through some areas with a concrete saw and
chisel to neaten things up and get rid of loose concrete.

For the area where there is just a crack, in some places I've already sawed an incision all the way to the
rebar in order to confirm that the rebar is rusted. Also I was thinking that the incision will allow me to
pack in new concrete like for the other sections. But now I'm not sure if sawing into the concrete along the
crack is a good idea. Where I have already sawed to the rebar, I've found that yes the rebar is rusted (so
this is the reason why the concrete has cracked there), but I'm wondering if I'm actually making things
harder/worse by sawing into concrete that's in decent shape (it's not drummy - just cracked).

- For the areas that are already quite exposed, is repacking with new concrete the way to go? Does it matter
if I can't force the concrete into all the cavities? Should I follow up after packing the new concrete by
injecting some crack filler just to make sure there aren't any cavities left? My concern is that by leaving
cavities I'm going to end up with rust problems again.

- Is injecting crack filler DIY possible?
- Should I go with my original plan of cutting along the crack to expose the rebar, and then pack in
concrete? Or I should I just leave the crack and inject some crack filler?
- Any recommendations on concrete/primer I should be using?

There is a section where the edge is drummy, and with this section there's also a small crack on the top of
the coping, so I'd say this area is particularly weak. But I'm not too concerned about the structural
integrity since no one is walking along this - I'm mainly concerned about stopping the concrete cancer and
rust from travelling towards the inside of the pool.

I am planing on re-sealing then repaving over the current coping, so this will hopefully stop moisture getting
into this part of the concrete.

Hoping that someone more knowledgeable with me can opine on the above - am I missing anything i should be
doing? Any advice or things to watch out for?

The damage - that corner is a bit loose and I think needs to come off

Crack that I've sawed out showing the crack going to the rebar

Particularly drummy section - here there's a crack also on the topside of the coping

section with just a crack - should I saw this out and pack in with concrete?

[MitchellMc]

Welcome to the Bunnings Workshop community @trentdi. It's terrific to have you join us, and many thanks for your question about repairing concrete.

Besides improving the aesthetics from underneath, I'm unsure how effective your approach will be. Simply packing over the rusted rebar will only cover it up; I can't see it halting any progress of concrete cancer and rust travelling towards the pool or improving the structural integrity.

The issue seems to be isolated on the edge of the counter-levered section and right where that rebar has been laid. I suspect the appropriate way to tackle this issue would be to cut the entire edge off completely, including the rusted rebar. A series of holes would be drilled perpendicular to the edge of the concrete and rebar chemically anchored into them. Additional rebar would be installed along with formwork and the edge repoured. This would obviously be a whole heap of work.

I think this is a case of there being appropriate and permanent solutions, but they might not be viable due to the cost and work involved. You could potentially drill through the edge of the degraded coping and into the solid material behind the rusted reo-bar. You could then insert and glue in reo-bar to provide structural support for the failing edge.

Please let me know if you have any questions.

Mitchell
 

[MitchellMc]

Hi again @trentdi,

I thought I'd add a note that although this appears just to be damage around the edge of the counter-levered section, it is the area that the balustrade is attached to. I reckon it might be a good idea to have it assessed by a structural engineer who will also be able to provide guidance on acceptable repair options. It's better to be on the safe side as there is a considerable elevation height.

Mitchell

[Dave-1]

Good afternoon @trentdi 

I was going to offer you some ideas on how to fix the issue but that first pic when I went back and had a second look. It looks like a long crack to the piller?

As @MitchellMc suggests Id still err on the side of caution and get a structual engineer to have a look .

I have repaired my balcony that had cracked and blown out from the same type of steel posts that you have above the pebblecrete. 

Concrete Patio repair is the project but it really only delt with spots of cracking not the length. 

I still havnt finished the railing, just saving some $$$ to buy the bits I want. and the repairs seem to be holding up well.

Dave

[trentdi]

Hey Mitchell - thanks so much for replying!

Regarding your point in whether my approach will be effective, I thought one purpose of fixing spalling concrete like this was to effectively re-encase the rebar. The rebar is rusting because air and water is reaching it, and by packing in concrete we are going part of the way of eliminating this (I'm also going to waterproof the top and underneath to stop water from getting into the concrete). This was the reason why I was asking whether I should also be injecting filler into the cracks (to eliminate any remaining air pockets). And we want to to halt the rebar rusting because rusting rebar weakens and cracks the concrete. As you said, I don't expect this to really improve the structural integrity, but I'm ok with this as the cracks are only on the edge, and this part isn't trafficked by people since the pool fence keeps people away from the edge. My main concern is the potential for rust travelling at right angles to the length of the pool towards the pool walls (and weakening the pool walls, which will then create structural issues with the part of the pool holding water - something I want to avoid!), but I don't think this is happening since the concrete looks solid near the pool walls (no sign of cracks or spalling).

Is there a reason why you think the existing rebar needs to be cut off and discarded? There's a fair bit of rust on the surface, but the rebar feels solid and it's pretty thick (maybe 1cm). The videos I've seen of people fixing spalling concrete advise that the surface rust be removed (usually with a wire brush), and the rebar only to be removed if it's rusted through.

I was thinking of cutting off the drummy parts of the edge, reinstalling additional rebar, and reforming. But I was thinking that this would only be needed for the particularly bad section (1st and 3rd photo).

My last comment is on having an engineer come and assess. I did have a civil engineer come and assess the structural integrity of the pool (there are a few cracks in it). He did see the section of the coping we're discussing, and said that it needed fixing - I think mainly to prevent further damage since he didn't say that the structural integrity was compromised.

Thanks again!

[trentdi]

Thanks Dave - seeing what you've done has given me a much better idea of what the sort of work that I'll need to do. I especially liked your pictures on your formwork, and buying a laminate board is an awesome idea.

Agree that it's a bit of a concern that the crack goes all the way down the length of the pool, but the civil engineer that came around wasn't particularly alarmed, although he did say that it needed fixing (see my response to Mitchell's post). One saving grace is that people aren't really standing on this part, since the pool fence keeps them away from the edge.

[MitchellMc]

Hi @trentdi,

You have structural cracks through an elevated slab that has a handrail on it; it's effectively a balcony. There is potential that the entire edge give way and take the railing with it. This could cause a serious injury if someone were leaning on the rail at the time. Patching over the heavily degraded rebar, in my opinion, is not going to inhibit further degradation of the rebar. Patching over and sealing the degraded rebar might be an appropriate approach on a ground-level slab, but certainly not on a balcony. The area needs to be assessed and structural solutions employed to resolve the issue.

Mitchell