Concrete Slab on Grade Adjacent Pours

[SperlingPE]

I have a large industrial floor that is being poured with several different pours. I have asked for 7 days minimum between adjacent pours. Contractor wants to cut this to 3 days.
Slab will be in an unconditioned warehouse type building [some heat in the winter].
So slab is subject to temperature changes from summer to winter.

We are trying to keep the construction joints tight, knowing that they will be moving with the temperature changes.


What amount of time would you consider?

 

[Ron]

SperlingPE...very little shrinkage will have been developed overall in three days; however, you are somewhat chasing your tail trying to fine tune drying shrinkage against thermal fluctuation. Both issues can be mitigate a lot by having closely spaced joints.

 

[hokie66]

Keep in mind that shrinkage occurs in all directions. Delaying subsequent pours may make the width of joints slightly less wide, if that is important, although I don't know why it would be. But shrinkage parallel to the joint means that the first slab will likely provide greater restraint to the second slab's shrinkage (if this is not addressed by special dowels), thus increasing the possibility of cracking perpendicular to the joint.

 

[SperlingPE]

thanks for the replies.
You are all bringing up issues that we talk about every time we have one of these projects.
Generally, we find that there are too many variables to come up with the absolute correct solution.
Time of year of pour
conditioned or un-conditioned building
rack locations
equipment traffic
docks
bollards
pallet storage
special racking - wire guided pick modules
mezzanine columns that are off of the main column lines
storm pipes from the roof adjacent to columns
flat work sub contractor experience
mix design
sub-grade
base course
I could go on.

 

[KootK]

Depending on your layout, the contractor could pour the slab in a checker board fashion in order to speed things up and still meet your seven day requirement. Perhaps this is already being done.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[hokie66]

SperlingPE,
All those issues are leading to the attractiveness of "jointless" floors. Warehouses (and big box retail) where I am are being built with joints at about 30 metre centres. I haven't been personally involved in any of these projects, but know they use low shrinkage mixes, and steel fibres. I think that eventually, standards for routine use will be developed which eliminate many of the joints, as joints are the biggest problem in warehouses.

 

[SperlingPE]

KootK
The floor is being poured checkerboard and staggered.
This is for the most part keeping adjacent pours 7 days apart.
There are going to be some later on that will be 3-4 days apart
GC's schedule is pushing the faster pours.

Hokie66
I don't disagree that joints are always an issue.
We have looked into shrinkage compensating cement mixes.
We have looked into fiber reinforcing.
We always spread joints out as far as possible.

SC cement has a large upfront cost.
Spreading joints apart as far as possible is always a priority with warehouse floors.
There are always things that get in the way of this; mezzanine columns, mechanical pipes, bollards.

thanks for all the replies

 

[KootK]

I've gotten myself into a bit of trouble in the past trying to exert too much control over SC concrete mixes. SOG finishers often seem to be very particular about the mix designs that go into slabs that they have to work with, particularly when the tolerances are demanding. I've switched to specifying shrinkage performance characteristics.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.