Residential slab/footing shrinkage reinforcement 1

MrJB said:

Gut feel is that we need to up the slab reo rate to be about 1% in the long direction yet does anyone have a more scientific approach?

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Absolutely, the U.S. Federal Highway Administration (FHWA) "Continuously Reinforced Concrete Pavement Manual", 0.7% minimum. Continuous reinforcement does not prevent cracks, it's just that cracks are so small and closely spaced they can't be seen or cause "trouble".

I started applying this technique to some of our industrial slabs (not highways), about 40 years ago, it works well.

I’ve had success at 0.5% in jointless slabs. My go-to reference is the control joint spacing vs reinforcement ratio table in ACI-350.

There's a price to pay for not having joints. I generally use about 0.8%.

You have to take care that there are no obstructions that can restrain the slab and make allowance for them... eg. reentrant corners, footing/pile caps or piers, etc. I generally place the reinforcing with about 1-1/2" conc cover for sawcutting. That's near the top, but that's where the cracks form. If not sawcut, then maybe 1" cover. Not sawcut, I'd still use 1-1/2" cover. You have to make sure your base materials are uniform and well compacted (true with any slab, but for one without sawcuts, maybe a little more critical).

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

-Dik

Excellent publication SRE... incredibly detailed. I was surprised that epoxy bars were still referenced.

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

-Dik

The default waffle slabs are around 0.25%, which is closer to minimum reinforcement.

We do a lot of waffle slabs in the 30-40m range, with around 0.4% in total. Bars at 100 cts (eg SL81 mesh).

1% would be pretty heavy. Almost twice as much as AS3600’s “strong” crack control.