sdkubota
Platinum Member
Leave them alone.
Cracks in new concrete?
- Thread starter OutbackL130
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Leave them alone.
EddieWalker
Epic Contributor
Nothing you can do to fix them. Hopefully you used rebar. The rebar will hold the concrete together and level.
They are caused from drying to fast and probably too wet a mix.
It's too soon for it to be related to compaction. If there are compaction issues, that will happen over time. The most obvious clue is that the slab will change heights at the crack.
Cutting expansion joints into concrete just makes it weaker where it's cut and just about guarantees that it will crack. The crack is usually less obvious because it's in the cut. It's not something I recommend, but for some reason, a lot of people seem to like them.
Concrete expands and contracts when it's hot or cold. This movement also causes cracking. This is why on big slabs, you pour it in sections with something between each section to absorb that movement. This is also why you pour a house slab and all your porches separately. Some places also pour garages separate from the house due to the difference in temperature inside the house to outside. You never need to worry about expansion inside a cooled and heated house because the concrete temperature is constant enough to not move to a noticeable degree. It will still crack over time, but if everything is done right, it wont cause any issues.
All concrete cracks.
Eddie
They are caused from drying to fast and probably too wet a mix.
It's too soon for it to be related to compaction. If there are compaction issues, that will happen over time. The most obvious clue is that the slab will change heights at the crack.
Cutting expansion joints into concrete just makes it weaker where it's cut and just about guarantees that it will crack. The crack is usually less obvious because it's in the cut. It's not something I recommend, but for some reason, a lot of people seem to like them.
Concrete expands and contracts when it's hot or cold. This movement also causes cracking. This is why on big slabs, you pour it in sections with something between each section to absorb that movement. This is also why you pour a house slab and all your porches separately. Some places also pour garages separate from the house due to the difference in temperature inside the house to outside. You never need to worry about expansion inside a cooled and heated house because the concrete temperature is constant enough to not move to a noticeable degree. It will still crack over time, but if everything is done right, it wont cause any issues.
All concrete cracks.
Eddie
KWentling
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"All concrete cracks" And that's why you do the control joints, so you don't have random cracks. I can't see it that it makes in any weaker. I'm a big believer in rebar, too.
Kim
Kim
OP
OutbackL130
Silver Member
The slab that cracked I know has rebar. The other two slabs are fiber reinforced and I'm not sure they used rebar in them.
dave1949
Super Star Member
The cracks are likely more cosmetic than any real problem, especially since you know there is rebar installed.
If this is not going to be a heated building, and there is a possibility of freezing along with moisture/drips on the floor, I would seal the cracks with caulking. Chickamauga does seem warm for that possibility, just a thought.
If this is not going to be a heated building, and there is a possibility of freezing along with moisture/drips on the floor, I would seal the cracks with caulking. Chickamauga does seem warm for that possibility, just a thought.
OP
OutbackL130
Silver Member
Just curious would the cracks have formed due to not keeping the concrete wet while it cured? I asked about the need to water it before they poured but they said nobody does that anymore with the new chemicals.
don45640
Gold Member
The fiber prevents the shrinkage cracking pretty well,which is nice from a contractor's point of view,who doesn't want the customer to have a cracked,brand new slab before he gets his saw-joints cut. I used to use a half-dose of fiber in hot weather,and I conditioned the slab with a trowel machine by using float blades and NOT just combination blades.
A coupla passes with float blades levels the floor,and really helps diminish the likelihood of precracking,even in hot weather.
Something noone has mentioned specifically is that concrete cannot be old and give good results. don-ohio
^)
A coupla passes with float blades levels the floor,and really helps diminish the likelihood of precracking,even in hot weather.
Something noone has mentioned specifically is that concrete cannot be old and give good results. don-ohio
^)slow wrench
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The cracks in the pictures look very wide for a concrete slab with rebar in it.Rebar needs to be held up off the ground with dobbies or pulled up into the center of the slab, with a hook, as they pour,otherwise its worthless.
OP
OutbackL130
Silver Member
Is it important for slabs my size to have expansion joints cut in? None of mine do. The original building is a 24 x 30 built about 30 years ago. The concrete is in fairly nice shape with minor cracking. This year we did a 18 x 20 addition to the front of the building, and then a 20 x 25 addition out the back(which is the slab that has cracked). Then there is a seperate 18 x 20 building as well.
The concrete people are supposed to come this week to pour another slab 20 x 25 adding onto the other 20 x 25 so that I can put up a 20 x 50 building.
The concrete people are supposed to come this week to pour another slab 20 x 25 adding onto the other 20 x 25 so that I can put up a 20 x 50 building.
SPIKER
Elite Member
Looks to me like the slab dried (water left it) too fast, this can also cause weak concrete. Keeping it moist for proper hydration would have helped it back when. Nothing can be done to fix it short of jackhammer out the cracks and use a patch or total replacement. Will it weaken the slab? maybe some is it worth replacing or fixing, that is your call but probably not required in a pole building.. On those wider cracks almost look like settling cracks to me due to the width fo them, is there any offset up/down on the slab?
As for Cutting it also not required it just makes the concrete crack in straight line in the crack that is usually wider and more of an eyesore than a natural crooked fracture in uncut concrete. They (cut lines) also are harder to roll a creeper over them and are more likely to trap larger amounts of dirt & bugs...
Mark
As for Cutting it also not required it just makes the concrete crack in straight line in the crack that is usually wider and more of an eyesore than a natural crooked fracture in uncut concrete. They (cut lines) also are harder to roll a creeper over them and are more likely to trap larger amounts of dirt & bugs...
Mark
