Slab cracking matches WWM 1

[JAV72]

Hey folks. Has anyone seen this before? Any idea of potential causes?
2nd floor slab, 2.5" NW concrete topping over 9/16" deck over bar joists at 24" max.
Exhibits through much of the slab (to lesser extent in some areas).
Photos show the mesh chaired, tied and in the proper location...of course those could have been selectively chosen.
Some portions poured in sun others in shade, fair weather, temps in low to mid 80's.
Thanks

 

[jayrod12]

So much for crack prevention.

perhaps the chairs were too tall? or the concrete wasn't poured the whole thickness.

 

[KootK]

That looks like plastic settlement cracking to me: Link.

The slab system is quite thin. What was the design cover on the WWM?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JAV72]

KootK: Thanks for the link. 3/4" cover minimum. We've spec'd this type of slab hundreds of times without trouble. I wonder if vibration would prevent plastic settlement? The mix designs were fine, perhaps they added a boat-load of water.

 

[dcarr82775]

I have seen things like that when the reinf to too close to the top.

 

[manstrom]

They didn't drop the mesh into wet concrete? I've seen people do that before.

 

[hokie66]

KootK is correct. Cracking which mirrors the reinforcement is invariably plastic settlement cracking. But in such a thin slab, the remedy of revibration was not available. Perhaps your contractor was too diligent in keeping the top cover. It would be better to put the mesh in the centre of the slab.