New concrete floor crack timeline?

[Snip]

Pole barn floor )40x66, 5" thick, 4k psi)was poured and smooth finished last friday then saw cut in aprox 10x10 squares. The shop has a 12x12 and a 10x10 R.O. for doors, not installed yet. The temp at pour time was around 50* and around 40* first night. The finisher did add calcium to each load. Around the same on Saturday. Sunday night it cooled off. Monday and Tuesday highs were above freezing but lows were around 20. So far I can see where the concrete has loosened its grip (shrunk slightly) around the perimeter boards but so far no cracks anywhere. Tomorrow it will be a week old. Generaly speaking what is the window of time to see cracks if I am going to see any?

 

[ConCretin]

I'd say you are probably in the clear now when it comes to cracks you can see. In a floor that size you probably have plenty of cracks but they are concealed in the bottom of your control joints.

 

[Snip]

Thank you, That is very reassuring to hear. I have tried to read as much here as I could to understand what I wanted and how to convey that to the concrete contractor. When asking around with different contractors for who they would use for a project like mine several names came up, his more than the others. I even had folks from batch plant recommend him.
When bidding it I called 5 of the names I was given, 3 showed up, one of them wanted to do it in 2 pours but later backed out due to the size but recommend either of the other two.
With some of the horror stories I had read on here I was nervous as s#*t pulling the trigger.
I did have him apply a sealer/curring product (Super Seal-25) that was used and recommended by him and the batch plant after finishing. He was so reasonable on the additional labor i saw no need to deal with it my self.
Thank you and all that contribute to this forum.

 

[Jking24]

I have a 40x60 3500psi 1/2" rebar 16" on center 5" thick no relief cuts or expansion joints i have two light cracks that start and stop within the slab one is about 5' long the other is maybe 10'. They both showed up within the first week. We suspect their spots where a ziptie nasty have gotten broken or slid around during the poor and the radiant heat tubing may be a little shallow in this spots

 

[ConCretin]

I have a 40x60 3500psi 1/2" rebar 16" on center 5" thick no relief cuts or expansion joints i have two light cracks that start and stop within the slab one is about 5' long the other is maybe 10'. They both showed up within the first week. We suspect their spots where a ziptie nasty have gotten broken or slid around during the poor and the radiant heat tubing may be a little shallow in this spots

The overwhelming majority of cracks in new concrete slabs are caused by shrinkage and I suspect this is the case here. You must have done some things right to only have two in a slab that size. Well done.

Most people prefer to hide shrinkage cracks in the bottom of control joints but if an occasional random crack won't bother you, there's nothing wrong with just going without. This is particularly true when steel reinforcing is used that will keep the cracks tight.

 

[jkeyser14]

Pole barn floor )40x66, 5" thick, 4k psi)was poured and smooth finished last friday then saw cut in aprox 10x10 squares. The shop has a 12x12 and a 10x10 R.O. for doors, not installed yet. The temp at pour time was around 50* and around 40* first night. The finisher did add calcium to each load. Around the same on Saturday. Sunday night it cooled off. Monday and Tuesday highs were above freezing but lows were around 20. So far I can see where the concrete has loosened its grip (shrunk slightly) around the perimeter boards but so far no cracks anywhere. Tomorrow it will be a week old. Generaly speaking what is the window of time to see cracks if I am going to see any?

95% of the shrinkage cracks develop in the first year.

 

[Jking24]

The overwhelming majority of cracks in new concrete slabs are caused by shrinkage and I suspect this is the case here. You must have done some things right to only have two in a slab that size. Well done.

Most people prefer to hide shrinkage cracks in the bottom of control joints but if an occasional random crack won't bother you, there's nothing wrong with just going without. This is particularly true when steel reinforcing is used that will keep the cracks tight.

Yes and the theory behind mine was i can't count how many cracks I've seen right next to or right through a control joint. We roll alot of things around in my shop. So it was decide to keep it a smooth as possible and let it be. I have no regrets. I hate getting hung up on a joint lol. I am no engineer but i beleive the reason for my success comes from the subgrade great attention was put into leveling and compacting the stone before the foam was laid then the vapor barrier, this coupled with the fact that the slab is truly floating created a pad that is very uniform and not overly mechanically bound to the sublayer allowing the pad to move/ shrink more consistently minimizing cracking to the two spots listed

 

[ConCretin]

Yes and the theory behind mine was i can't count how many cracks I've seen right next to or right through a control joint. We roll alot of things around in my shop. So it was decide to keep it a smooth as possible and let it be. I have no regrets. I hate getting hung up on a joint lol. I am no engineer but i beleive the reason for my success comes from the subgrade great attention was put into leveling and compacting the stone before the foam was laid then the vapor barrier, this coupled with the fact that the slab is truly floating created a pad that is very uniform and not overly mechanically bound to the sublayer allowing the pad to move/ shrink more consistently minimizing cracking to the two spots listed

You clearly have an good understanding of how a concrete slab works. A flat sub-grade covered by a vapor barrier does allow a slab to contract with minimal resistance rather than cracking. I suspect you also kept your slumps low?

I've been doing concrete for a long time and am accustomed to people freaking out about a crack in their concrete. Control joints just hide the crack and make everyone feel better. If you think about it, your approach makes a lot of sense.