Spalling Concrete

[Haqyusof]

hi im from Malaysia and im new in this group. Hope you guys can help me.
My issue is spalling concrete occurred on the ceiling slab (600mm x 600mm x 60mm in depth). the reinforcement bar is not corroded and no sign of water ingression. Above the defective concrete is ramp area and open air . the concrete cover is 50mm+
What is the cause of the spalling concrete.?

 

[hokie66]

It would be very unusual to have that type driveway finish in the suspended slab itself. That is very likely a topping, and as such its cracks would tell you little about the underlying slab.

 

[JAE]

Does this place freeze in winter? Could some water have penetrated into the concrete and froze near the bottom of the slab, popping off the concrete?
Just winging another idea out there.

 

[r13]

hokie66 are correct, as we see in the photo is the topping material. As the driveway is slopped, I believe there is another support structure below, but couldn't tell if the roof in concern is part of the driveway supporting structure or not. Why not to remove the remaining loose concrete to see whether there is indication of defect. Look at the first and second photos, it looks like something behind the concrete was expended forcefully, that causing huge/deep spider web type cracks, and finally the fall of the big chunk of concrete along the edge.

 

[bridgebuster]

In the absence of any other information, I would chalk it up as a construction defect - yes, I know, typical engineer, blame it on the contractor. On the one hand, it looks like a typical freeze-thaw blowout but the OP said he is from Malaysia (assuming the photo was taken in Malaysia) freeze-thaw isn't a possibility. Also, the surface photo doesn't show any impact damage. OP didn't state if the problem is widespread; I assume it's localized. In the underside photo, there's a small fracture; that's why I think there could have been a void when the slab was placed; over time it just gave out; 3T truck isn't much but over 10 years it could add up. 50+ mm of cover isn't excessive (thanks for pointing that out hokie. I was more focused on the NFL pregame show than on spalling) but if there was a void, the additional weight could matter.

 

[JAE]

One last thought - I have seen similar spalling when an anchor was installed too shallow and the load pulled off the concrete cover like what is seen in the photos.
Not sure if a previous hanger was installed to cause this - just another idea.