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Concrete Slab expansion joint

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Kevin Gilmour

Kevin Gilmour

Structural
Nov 5, 2022
1
Morning everyone, looking for a bit of advice please.
I’m about to pour a raised (around 400mm high) concrete slab for a patio which is getting tiled with porcelain tiles 600mm x 900mm. The slab is just under 6m by 4m and 6” thick. However all around the edge of the slab will be a box section of the concrete reinforced with rebar and the whole slab will have mesh rebar reinforced. With this size of slab, and the rebar and porcelain tiles, should I put an expansion joint in at all ? The patio is south facing so does get full sun all day in summer.
Thanks in advance for any advice, Kevin.
 
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Yes, I would probably divide that slab with a shrinkage joint down the middle to get to 3x4m panels. I'd also prefer that the slab and box section are poured separately with a bond breaker in between to prevent the deeper beam section from causing additional slab shrinkage restraint. Depending on your locale and subgrade, those could be a tooled/cut joint, or a joint with some sort of dowel to prevent vertical heave that would telegraph through your tile.
 
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When you say "around the edge of the slab", is that a footing under the edge, or around the perimeter outside of the slab, confining it?


Rod Smith, P.E., The artist formerly known as HotRod10
 
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Match your control joints to the tile dimensions, and make sure the joints are sawcut at the proper time.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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OP is asking about EXPANSION joints, not control joints. No expansion joint needed.
 
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I use the term control joint, since the concrete may shrink and, if done properly, they regulate where the cracks will likely form if they do. Expansion joints are something else. Other than minor shrinkage, there will not likely be much movement with this slab. By locating the joint at a tile edge, if the slab cracks, the crack will likely telegraph into a mortar joint of the tile.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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