Saw cuts in suspended slab?

[Tim M]

Tomorrow they are pouring the suspended slab of my garage basement project. I am using 4000 psi concrete with fiber, wwf sheets and #3 rebar 16 oc over 18 gauge galvanized decking on W18x46 I beams < 6' spacing.

My concrete guy says no relief cuts. I guess because this slab needs to be watertight to protect the shop below. I'd think relief cuts with some good expanding crack filler might be better.

Thoughts?

Thanks in advance,
Tim

 

[jmh21586]

Since its a suspended slab on a stable foundation there shouldn't be any movement at all. So why the need for relief cuts?? Usually those cuts are meant to control cracking due to slab movement when poured over dirt. Setteling, freeze thaw cycles, etc. Probably wouldn't have any of those issues on a suspended slab.

Just my poinion though. I'm no expert.

 

[rasit]

You didn't mention how large or thick the slab is. Besides movement concrete will crack due to shrinkage but your mix with added fiber should help as long as the slab isn't not big. No guarentees here. I would rather caulk a straight crack as opposed to random one. just my 2 cents........

 

[Tim M]

Slab is 26'x42'. At the back it will be 7" thick tapering to 5" at the front.

 

[Torque1st]

The Engineer that designed the slab should be consulted. If you modify the slab after the plans were stamped the inspector may decide you need to do it all over again per print.

 

[blkhonda1991]

what ever the engineer put on the drawings is what should be done.

 

[rasit]

Tim M, How did the pour go? What did you end up doing?
As previously stated there are no guarantees here. Asked both the engineer and the contractor if they will cover any costs associated with any cracks that develop within one year and let me know what their answer is. I've seen reinforced concrete walls that were 30" thick with triple mats of #8 bar, twelve inches on center develop shrinkage cracks in a water treatment plant that I worked in. Only solution at that point was to repair the crack with some type of epoxy, sealant/caulk that was pumped in under pressure. By the way, the engineers on the job that designed it, said they would not pay for any of the costs under a change order because it was not an engineering flaw, they attributed it to the natural characteristics of concrete shrinkage. Shrinkage can be minimized by wet curing for the first week, like they do on bridge decks.

 

[Tim M]

Just got back in from spraying the slab. They did some very nice work.

With very little nudging I talked my concrete guy into doing the cuts. We've got cool rainy weather for the next few days. Cracks be damned!

BTW the saw cuts do not affect the structure from an engineering standpoint at all. It is purely cosmetic attempt to control where it cracks. The engineer made no mention of it.

I will post pictures soon.

Tim

 

[Torque1st]

ASK the Engineer!!!

 

[cream 46 sedan]

As a concrete contractor a good rule of thumb is 12'x12' squares or as close as you can get to that. All concrete comes with two guarantees it will get hard and it will crack.

 

[kwb]

BTW the saw cuts do not affect the structure from an engineering standpoint at all. It is purely cosmetic attempt to control where it cracks. The engineer made no mention of it.

If he (engineer) didn't mention of it how do you know the saw cuts do not affect the structure from an engineering standpoint?

Small cracks and crazing are nothing more than appearance items and being suspended you will not have ground heaving to shift the surface so why are you so gung-ho to cut (and make engineering judgements) without consulting with the guy you paid to design/spec the floor. The answer should be free, quick and painless. If you guessed wrong and cut the slab it won't be free, quick or painless.

 

[mad57]

as a concrete contractor a good rule of thumb is 12'x12' squares or as close as you can get to that. All concrete comes with two guarantees it will get hard and it will crack.

so true ...cuts wont hurt go for it if you want.

 

[rasit]

Quote:
Originally Posted by KWB

If he (engineer) didn't mention of it how do you know the saw cuts do not affect the structure from an engineering standpoint?
If you guessed wrong and cut the slab it won't be free, quick or painless.

Jeez, how deep do you think control joints are cut? All you are really doing is scoring the concrete about a half inch deep. This will provide the point of least resistence for the required relief due to shrinkage and/or movement.

CAUTION!!! If your saw has a 12" or larger diamond blade and you plunge it into the concrete, or, if as you are cutting you see sparks flying because you are cutting through rebar, wire mesh, I-beams, deck pans etc., you probably have cut too deep and should have consulted an engineer before you got started.