Cracks in a reinforced concrete SOG
Cracks in a reinforced concrete SOG
(OP)
We Pumped a SOG basement level 85' x 70' (slab was enclosed)Im sure during the set time it was hot in the basement and there was no air movement. the slab was a 6" slab #4 @12" EW 3"from top. control joints cut in 20'x20' panels at the column block outs 1" deep 1/4" wide cut in right after set up same day. curing compound used. The problem is that we have a number of cracks through out the floor more than can be expected. going in all directions. We are being told that are control joints are to far apart and the cuts are to small. I don't see that being the answer to the cracks. Is there any other reason or is that the reason for the cracks.





RE: Cracks in a reinforced concrete SOG
If sawcutting started about 8 hours after finishing, it was likely sawcut at the right time. If you pumped it and didn't use a superplasticizer, the slump may have been too high. For slabs, I usually use a 3" slump or equivalent with a plasticizer. Also for a 6" slab, I would normally sawcut it 1-1/2" to 2" deep. The 20'x20' panels seem about right; I've done many slabs of this thickness and panel spacing.
Unless the subgrade was 'really' bad, it's likely too early for it to be a settlement problem.
RE: Cracks in a reinforced concrete SOG
Carl Bauer
www.bauerconsultbotswana.com
RE: Cracks in a reinforced concrete SOG
RE: Cracks in a reinforced concrete SOG
As dik said, would be interested in the pattern of cracking. Closely spaced, shallow cracks or crazing at the surface indicate too much water in the mix or fast bleed rate. Short, discontinuous cracks that ultimately connected by shrinkage are indicative of plastic shrinkage that occurred early in the curing stage, so sawcuts would have no effect on them. They are caused when the evaporation rate of the surface moisture in the concrete exceeds the bleed rate of the mix water.
Give us a little more info as dik requested.
RE: Cracks in a reinforced concrete SOG
I usually use 1-1/2" to 2" conc cover to rebar (depends on sawcut depth) and for general developer use (inexpensive), caulk the sawcuts with a medium firm caulking material to support the edges of the slab at the cut.
The #4@12 are heavier than normal. The 12" spacing might make it difficult to walk 'through'; any chance these are located at the bottom of the slab, on top of the base? It's easier to walk on them, then... <G>.