Maximum size/length of one concrete pour for elevated slab 3

[aquacata]

I have an elevated 6" thick concrete slab being supported by concrete walls at perimeter and concrete beams and columns at interior. The footprint of the slab is overall 100' x 120'. I wonder if the whole slab can be poured one time. Do I need a control joint for this size of slab? Thank you very much for your input.

 

[msquared48]

Why don't you put in a detail for a control joint, and state in the detail "if needed". Leave it up to the contractor. You are talking 37 ten yard trucks here, at least, and an unknown number of pumpers and spreaders and finishers.

You cannot and should not predict what equipment or personnel he will have. That's his bag and it affects his bid.

Mike McCann
MMC Engineering

 

[aquacata]

Actually It is the contractor who wanted to do one pour. But I am not sure if one pour for the 100'x124' size will cause cracks or not, you know, due to the shrinkage. How do you think? Thanks a lot!

 

[msquared48]

You are talking two things here, cold pour joints and construction joints.

If the slab can be done in one single pour, there will be no cold joints, but it will have construction joints (sawed, zip strip, etc.)

If it cannot be done in one pour, it will have at least one cold joint, but will also have construction joints.

Depending on the slab layout, the area between construction joints should be limited to 400 to 600 square feet or so. Cold joints are placed at the end of a day's pour.

Mike McCann
MMC Engineering

 

[msquared48]

Sorry, I saw the word "elevated", and I have to qualify my previous post. That would apply to slabs-on-grade.

For elevated slabs, I rarely spec any construction joints and leave the cold joint placement to the contractor unless noted otherwise on the plans.

Is that muddy enough for you?

Mike McCann
MMC Engineering

 

[hokie66]

The original question was about control joints in a suspended slab. For a 100' x 120' slab, movement joints would not be required, and in most instances, construction joints would be unnecessary. This is a typical size for a single day's placement, usually controlled more by the finishing and curing operations than by the supply and placement.

Shrinkage cracking due to restraint by the perimeter walls is another issue. These walls will heavily restrain the slab, and cracking will be inevitable. The amount of crack control reinforcement required to control the width of the cracks depends on the useage of the slab.