Repairing COncrete Cracks

[CScottFlanagan]

We poured a 6" thick concrete slab, reinforced with 6x6-W2.0xW2.0 wire mesh. The contraction joints were sawn at 15' x 20' centers. (Let's leave the debate over proper joint spacing for another day!)
I now have some very narrow cracks running in the middle of the 20' bays. The cracks are so thing that you can't get a knife inserted. The owner objects to the cracks.
The floor is loaded at a maximum of 400 psf, and this in only a small area. The remainder of the floor is light storage (150 psf) and foot traffic.
I have been advised to leave the cracks alone, or use "injectable resin" in the narrow cracks. Grooving and epoxying will only make the cracks look worse by being more visible.
Any recommendations on repair of these cracks? Any publications available that I can show to the owner to support our recommendations?

 

[RiBeneke]

Is the wire mesh continuous through the sawn joints ?
Presumably this is a slab on grade.
Presumably there are no corrosive influences on the slab surface.
How long ago was the concrete poured, and has it now dried on the surface ?
Is there no vehicular traffic servicing the storage area ?

I would recommend to leave the cracks alone.
Most concrete design codes allow for some cracking.

 

[CScottFlanagan]

The wire mesh is continuous through the cracks.
It is a slab on grage (SOG).
No corrosion is involved.
The slab was poured in Mid-July (ambient temperature approximately 90 deg F.) The cracks were not noticed until mid-October (ambient temperature at mid-60's).
There has been some forklift traffic on the slab, but nothing heavy. 5,000 capacity maximum. And the cracks also occure in areas of the cloor where the forklifts have not been on.

Do you have any specific references to allowable cracks? Does ACI have a standard?

 

[RiBeneke]

By this time over 90% of the curing and drying shrinkage should have taken place, and I do not think there is s serious problem. You just have to prove it to the client. I am based in South Africa, and do not have ACI documents, so cannot help you with this. Maybe you will get a quicker answer from someone in USA if you repost the question on the 'Concrete Engineering general discussion' forum or "Engineering structural other topics' forum - they are more active.

 

[dik]

I suspect the problem is with the mix proportions and/or curing (for another day, sawcut spacing isn't likely the cause, although the timing can be a bit of a problem). If it is necessary to seal the cracks, this can be done with any number of injection materials, bearing in mind, that these will make the cracking more noticeable. Unless you have a concentrated load in vicinity of the shrinkage crack, or in the corner where two cracks intersect, you likely don't have a problem.