Construction joint or pour separate pads with isolation joint?

[Kom3]

Hi, I have two new pads. One very large 100'x25' and one smaller square shape pad about 15'x15'. Both are 18" thick. The way they are oriented (see below), I am sure they would crack along their connected edge if they were poured together. Should I pour them as separate pads? I planned for it to be separate pads but it was brought up that it would cost a bit more construction wise. Is there a structural reason to justify the additional construction cost? Is there any issues if I go with a construction joint and it does end up cracking there?

Regards.

 

[AskTooMuch]

If you plan on pouring separate why do you worry if it crack at the joint if poured together?

Yes, it will cost extra for concrete truck to come back and workers to do their work again for that small pour.

Maybe put contraction joint instead so "crack" looks clean.

 

[Lomarandil]

First off, as I understand the terminology, a construction joint would be the same thing as pouring two pads.

If these are out of sight, and there arent significant water-intrusion concerns, I'd be ok with pouring them together with a deep joint between the two.

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just call me Lo.

 

[phamENG]

As Lo said, a construction joint is a joint placed for ease of construction - they stop the pour with an edge formed to receive the next pour or they have dowels in it (or dowel baskets, or plate pockets, or any of the other fancy load sharing joint devices). So a construction joint is two separate pours.

A crack control joint is a joint that is either formed or cut into a slab after it has been poured. You get the schedule benefits of a single pour with the crack control benefits of the construction joint - if it's done properly. If it is cut too late or too shallow or there's too much reinforcing through the joint, the crack may not occur within the joint.

But I wonder if this question is moot. You're not mentioning any control joints in your long, slender slab (aspect ratio of 4:1), so this is either heavily reinforced such that cracking isn't actually an issue or you need to look at it there, too. I prefer aspect ratios of 1:1 for slabs on grade, but will go up to 1.5:1 without worrying too much so long as the overall spacing is in the 24t-30t range. Greater than that and I start increasing reinforcing to control cracks.