Shrinkage cracks? photo
Shrinkage cracks? photo
(OP)
Hi,
This photo shows a repair in a carpark slab on ground. Apparently a water hydrant line failed under this point so the builder saw cut a hole, fixed the pipe and did this repair.
You can see there are radiating cracks out from the hole. I am assuming this is due to a release of shrinkage tension in the mesh when the hole was cut out of it, however would like your expert opinions!
I don't have details of the original leak and symptoms.
This photo shows a repair in a carpark slab on ground. Apparently a water hydrant line failed under this point so the builder saw cut a hole, fixed the pipe and did this repair.
You can see there are radiating cracks out from the hole. I am assuming this is due to a release of shrinkage tension in the mesh when the hole was cut out of it, however would like your expert opinions!
I don't have details of the original leak and symptoms.






RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
In any case, stuff happens in construction, so the owner will have to accept that a repair was necessary and there's not much that can be done, short of fully removing the slab from joint-to-joint.
RE: Shrinkage cracks? photo
My job is just to give a cause of the cracks - I assume the developer is looking for something to sting the builder with. I believe the cracks are an inevitable result of having to cut a hole in the slab (mesh is cut so can no longer hold the shrinkage tension) and not the builder's fault. The only way of fixing is to replace the whole panel between joints.
RE: Shrinkage cracks? photo
Ron, this would also fit your hypothesis that the cracks were there before the cut, probably radiating ouward from the original pentration of the hydrant through the slab.
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
Is it possible that the contractor lifted the soils upwards as the hydrant was yanked out of the ground, causing the slab to rise during the demo?
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
Is it possible that the hydrant line failure was catastophic and caused uplift, or was it just a slow leak?
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
RE: Shrinkage cracks? photo
I agree if the developer does not like the look of the repair, then joint-to-joint replacement is the option.
There's no evidence of anything other than shrinkage being the mechanism. If heaving or uplift, there would be faulting at the cracks. The only thing that puzzles me is that there is only one true reentrant corner crack showing..perhaps I just can't see them in the photo.
RE: Shrinkage cracks? photo
This is a puzzle.
RE: Shrinkage cracks? photo
When the hole was sawn in the slab, the entire slab was in tension due to the ground restraining the soffit of the slab. If we assume that the tension stress across a given section is uniform, and then we remove part of the section, the force taken by this removed part has to redistribute into the remaining slab. The cut edge adjacent to the removed part thus tries to take the force, resulting in cracking of the concrete until the force redistributes to the steel.
While cracks often propagate from reeentrant corners because of the stress riser effect, they can start at other places also.
RE: Shrinkage cracks? photo
The concrete shrinks during curing, the minimum, "shrinkage reinforcing" makes sure that many fine cracks appear instead of fewer, wider cracks. When the piece is removed, the restraint provided by the rebar is gone and the local cracks open up, especially at the corners where the release is in both directions.
When making repairs or modifications to slabs where appearance is important, I usually specify core boring the corners first and then cutting the straight edges. It's not perfect but it helps.
Timing has a lot to do with the outcome of a rain dance.
RE: Shrinkage cracks? photo
I found out that the repair happened 3 days after pouring of the slab. I'm not sure how the location of the water leak was evident however - the parties involved are still not talking to each other!
RE: Shrinkage cracks? photo
LOL
Michael.
Timing has a lot to do with the outcome of a rain dance.