Concrete Experts please chime in

[rdalley]

I have several big chuncks coming off my relatively new concrete. The broken slab is my 24x24 garage, just outside the door. Its a north facing garage so ice, snow etc gets piled up against the door and right on the joint where these are breaking in the winter. What product/technique if any can I use to fill these in and repair them?

They start off looking like feathery cracks and then just chunk off. Im open to all input and suggestions.

 

[zporta]

Too me it looks like the driveway was tied in with rebar and the dowels weren't drilled low enough in the garage slab. After a few freeze/thaws and the movement of the drive way the garage lip cracked due to such a thin amount of concrete b/w the steel and top of the slab.

I have seen this happen a few times and I alway make sure to drill the bottom 1/3 of existing concrete when I dowel it

 

[rdalley]

I hadn't thought about that. I honestly cant remember if they pinned the slabs together or not. Any ideas on what product to use to fill it in?

 

[zporta]

I would personally saw cut the concrete around the pop marks, remove all the concrete and cut out the rebar and replace with new concrete. If not an it is the rebar causing the issue any patch is going to fail over a short period of time.

 

[LegacyIndustrial]

Epoxy repair patch and broadcast sand into it when done. Most cementious products will not do well in this application.

 

[rdalley]

Epoxy repair patch and broadcast sand into it when done. Most cementious products will not do well in this application.

Thanks. Do I mix the sand with the epoxy patch? Sorry, I am completely dumb to concrete, etc.

 

[Edger]

I am no expert when it comes to snow and concrete, however this is common enough when there is an edge problem. I have seen it caused by rusting of rebar used for pinning. The expanding rust causes it, but your problem does not look like that.

It looks more like problems caused by expansion rather than shrinkage where two slabs push together and break away the top. What puzzles me here is that you have expansion board in the joint, very stiff so it does not help much, but I would have thought enough to stop the problem.

Last possibility is that the concrete at the edge was not finished properly. Sometimes the concreter concentrates his efforts on the main areas and if he has taken a little too much concrete away without filling right up against the formwork he can then push some concrete into the gaps when troweling off which just fills them with slightly cured concrete rather than becomes a part of the concrete mix. Being on the edge it looks good from the top but any weight on the edge causes it to crack away. Ice would do the rest I guess.

Just some thoughts.

 

[rdalley]

would it be worth it to tear out the expansion board, repair the damage and then fill the joint with something that is more forgiving to expansion between the slabs?

 

[zporta]

I really do think it's the expansion board. I have done 50+ concrete driveways without issue. The dowel was placed too high in the concrete weakening the upper part of the lip. When under stress concrete will find the weakest area to crack.

You can see the weakest areas.

I would say if one small 2-3" area it could be improper edging techniques, but not **** a large area and popping so deep

 

[rdalley]

zporta, thanks for the info, now how do I repair it? Should I cut down through the rebar pins and then patch it or will not having the slabs pinned together lead to more serious problems later?

 

[zporta]

The pinning is going to stop the driveway from raising or settling in the future. But in two or three areas I think you would be fine to cut the concrete out cut the rebar and re pour. If you have the necessary tools it would be smart to add one piece of rebar on each side of the patch area to keep the garage slab locked in with the patch. Make sure of you do this to drill your holes low!