Slab on Grade (Edge)

[slickdeals]

What's your typical detail for the following situations?

1. When a slab on grade terminates against an interior/exterior CMU or concrete wall? Do you have a thickened (turn down) edge or without it? Seems like it would be more work to first grade and compact and then excavate for a downturned edge.

2. When a slab on grade terminates around a concrete column - we typically do a turndown if the footing is 12" below finish grade. Else, my preference is not to do a turndown.

Are there any industry-recommended details for reference? Are there any lessons learned from doing it either way?

Seems like different consultants do it differently.

 

[spieng89]

OP,

1. Unless poor soil conditions, typically I detail expansion joint/isolation material between the slab and wall with no turn down edge. If poor soils and shallow frost depth, I'll incorporate the slab edge into the footing design.

2. I do the same

 

[Leftwow]

Bump

I am interested in this discussion.

 

[jdgengineer]

We typically show a thickened slab edge. It's my understanding that ACI 360 recommends it to reduce slab edge curling as the added weight helps hold the slab down and slow down the surface shrinkage due to the extra volume of concrete at the downturned edge.

 

[dik]

Many references, for pavement, will recommend the edge be thickened to 1/3 greater than the pavement thickness. This goes back on a 1:10 slope to minimise and drag by the slab as it shrinks. This accounts for the loss of stiffness in not having an adjacent concrete slab.

Dik

 

[hokie66]

For interior conditions, as I think the OP means, I see no need for thickenings adjacent to walls or columns. The thickenings act to restrain the slab, thus increasing direct tension shrinkage cracking.

 

[dik]

Hokie:
When a slab terminates against an interior or exterior wall (concrete or masonry), ie. it is not continuous, I usually thicken the slab as noted and for the reason noted, if there is a chance the slab will see loading.

Dik

 

[slickdeals]

@dik, @jdengineer
Found this article on ACI's website that talks about the thickened edge. The author's opinion is that it doesn't do much to prevent curling.

https://www.concrete.org/publications/internationalconcreteabstractsportal.aspx?m=details&ID=11740

Agree that there's no benefit for Item No. 2 of my OP. For Item #1, seems like there's differing opinions. Seems like a lot of additional work and cost for not too much benefit.

 

[TLHS]

I've seen all sorts of flat, unthickened, slabs that look fine after decades. They tend to be reinforced slabs for industrial loading though. I'll put a thickened edge around the perimeter because the ACI slab design document recommends it, but I don't worry about it at detailing locations where it would be awkward.

 

[dik]

Has nothing to do with curling... where a slab abuts another but still has an aggregate vertical restriant, the added thickness compensates for the restraint offered by the adjacent concrete.

Dik