Slab cracking - opinions requested 1

[Naggud]

Hi all,

See attached for photos of a cracked slab. It was poured about 6 months ago.

The floor was grinded recently ahead of the floor finish being applied.

The slab is elevated, and supported on a metal deck (trapezoidal deck), there is a mesh in the top of the slab for cracking but the tensile capacity is coming from the interaction between the concrete and the metal deck. We have used this type of slab on many similar projects with no issues.

Interested to get your thoughts on whether these are structural cracks or just shrinkage.

Thanks in advance.

 

[jhnblgr]

Construction loads were not accounted for in the design. The concrete set and cracked during finishing and cream was worked into the cracks to hide them. See this every time metal joists are used.

 

[ANE91]

Respectfully, you’re going to get every answer under the sun. Two photos do not beget a diagnosis.

Do you have batch tickets? What were the weather conditions at time of placement? Have you mapped the distribution, size, and extent of cracking, as related to the span direction of the slab and any joints? This could be due to one or more of a dozen different things. Cracks due to “just shrinkage” can absolutely be a structural (durability) issue, situationally. Free opinions on the internet are worth about what you pay for.

Moreover, are the cracks actually an issue for your desired finish? If so, consider applying methylmethacrylate in advance.

the tensile capacity is coming from the interaction between the concrete and the metal deck.

I assume you mean flexural capacity, as in a composite floor. If you’re the contractor, then tell us what your spec’d finish is, and maybe we can help.

 

[FootNMouth]

Appears to be some delamination of the concrete as well, what was the specified and tested air content in the mix?