Saw cutting a mesh-reinforced concrete surface bed?

[BST-98]

Good day, All

I would like to ask your thoughts on saw-cutting a concrete surface bed with mesh in it. Let's say 150thk concrete with Y10s @ 200 mesh (50mm cover from top) with general expansion joints that are provided at roughly 40m - 45m intervals for argument sake.

In my opinion and projects that I've done, I've never specified saw cuts when a decent-sized mesh is applied as I feel the mesh assists with crack control already. This being said I haven't experienced cracking on these projects. But the same can be said for saw cuts on a mesh surface bed as well.

I would like to know your point of view and which is best practice.

Thanks

 

[jayrod12]

We always sawcut slabs-on-grade except in extremely rare cases. And in those cases, we're providing something like 0.5% Ag as the steel to mitigate the size and randomness of the cracking.

We also specify that the contractor needs to layout the sawcuts before the pours, and cut half of the bars crossing each sawcut. Sawcut depth to be tailored not to cut the remaining bars across the joint.

On a 150 thick slab we'd be looking at maximum 3.6m o/c spacing for the sawcuts to mitigate the chances of randomized cracking.

Lastly, the sawcuts must be performed within 24 hours of pouring, essentially as soon as the slab has set up enough to allow the worker and saw without damaging the surface. If they wait until after the slab is fully set up, it's too late. The cracks have already formed wherever they're going to at that point and it's just a matter of time before they widen.

 

[Just Some Nerd]

Standard here is pretty close to what jayrod has described. Slab thicknesses and spacing of saw-cut joints may very (usually more like 120 slabs with 4m spacings) but the rest of the process is the same

From my experience, slabs sitting on the ground are notoriously crack-prone and you're better off controlling where those cracks form

 

[HTURKAK]

ACI 302.1R is a good reference for the slab on grade construction and the recommended spacing for saw cut control joints are 48 t. If thk 150 mm, spacing should be around 7200 mm.

 

[dik]

The most important thing about sawcutting is the timing... it should be done 4 to 6 hours after finishing (no ravelling of aggregate). 24 hours is too long. You can sawcut earlier if you use a Sofcut saw that helps prevent ravelling.

 

[dik]

We also specify that the contractor needs to layout the sawcuts before the pours, and cut half of the bars crossing each sawcut. Sawcut depth to be tailored not to cut the remaining bars across the joint.

For a 6" slab, I usually use 2" concrete cover and sawcut 1-1/2" deep.

 

[dik]

I've never specified saw cuts when a decent-sized mesh is applied

I don't like using mesh; if used it should be sawcut like normal rebar. Also if used it should be in flat sheets, not rolled and should be chaired like normal rebar.