slab isolation joint - 1/2" typ? 1

[HeavyCivil]

What is the width of a typical isolation joint for a concrete slab on grade? As in the type that would interface between a column footing and slab, a generator pad, or around the perimeter of a 'floating' slab?

I have used 1/2" in sidewalks I've poured but have limited experience pouring (or designing) slabs.

 

[SlideRuleEra]

For industrial applications, isolation joint thickness depends on the use of the slab. If vibration is expected (say an equipment foundation) then an inch and half, or so may be wise. For typical slabs that provide general access, perhaps 3/4".

Note that the "oversized" joints for equipment foundations are not needed for normal operation. The extra clearance is for the day when the equipment "fails" and vibration becomes excessive. Then the extra space is to help limit any structural damage to the foundation itself.

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[structuresguy]

We use 1/2" iso joints as our typical joint width for all commercial slabs. This would apply at wall/slab interface, around columns, around equipment pads, etc...

The only time I have used larger joints was for airport apron slabs outside a hangar I designed. There, the joints followed standard FAA requirements, which used something like a 1.25" wide premolded rubber joint filler.

If you had large expanse of slab, you could calculate expansion/contraction with thermal changes, along with any shrinkage anticipated after the joint is finihsed. This would then tell you how much movement you need in your joints. Then, you could see if your joint filler (caulking) could take that range of movement. If you found that you need +/- 1/8", well, a 1/2" wide joint with caulking capable of moving +/-25% would work.

 

[Ron]

1/2" is plenty for your application. Keep in mind that the concrete will likely never get larger than when it was placed, so your joint will widen, not get narrower.

 

[cap4000]

Large increase in tempertures can lead to concrete expansion even while pouring it from the heat of hydration. Thermal Expansion Coefficient is taken as 6x10-6/degree F.

 

[Ron]

cap4000...concrete expansion RARELY exceeds shrinkage. Usually if expansion is an issue it occurs in long, narrow sections with impacted joints.

 

[rowingengineer]

Don't forget sealants, always take a look at the sealant spec, they can have some requirements (ie depth to thickness and min width). Sealants server many purpose in slab design, they server to stop water entering the sub base and stop dirt from entering the joint. The dirt entering the joint will cause the joint to widen when trucks drive over the area. Thus the sealant is important.

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[rowingengineer]

sorry for the poor english in the last post, didn't proof read.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it