Crack Control (Shrinkage) Joints and Isiolation Joints in Slab on Grade

[Signious]

Hello, quick question that (hopefully) has an easy answer:

I am finishing my details for a small (38' x 20') slab on grade for a community garbage collection site.

6.5" thick slab, 15M @ 6" o/c designed for 110psi contact pressure per tire from a tandem axle garbage collector (85,000 max GVW) @ 2 load cycles per day, and regular traffic at continuous loading, 30yr shelf life.

The area is broken into (5) 6'-10" x 10'-0" 'bays' for the various garbage bins (see attached), with traffic bollards separating them. Normally I would detail a diamond shaped isolation joint around the bollards (see detail 'a' attached) with the intersections meeting at crack control joints.

In this case the crack control joints would end up being spaced significantly closer (~50%) than I would normally. Do you foresee problems occurring using a 1-1/4" saw cut joint at tighter than normal spacing?

I don't see the point in isolating the bollard without meeting at crack control joints as it would cause surface cracks eventually (see detail 'b' of attached)

Thanks!

 

[Ron]

As long as the joint saw cuts are made the same day as placement of the concrete, it is not a big deal. I would increase the depth of cut to 1-1/2". Also, your pattern of 7'x10' is marginal on the aspect ratio of the slab section. The closer you can get to square sections, the better.

 

[hokie66]

What is the point of the sawn joints in a slab of this type? Is it just so that your cracks will be straight rather than crooked? The sawn joints will require maintenance to prevent accumulation of debris which will tend to push the sections apart.

 

[Signious]

I spec the saw cuts to be sealed to prevent water flow to below and packed with a low shrinkage, non bonding material to flush to avoid any crap buildup in them.

Just to keep the cracks to the bottom of the saw cuts, as opposed to visual surface cracks. I would normally go closer to 1-1/2" but that is getting too close to my bar for my own comfort (1-3/4" cover from top of slab)

 

[XR250]

I assume 15m is around a #5 bar 2 6" o.C. (each way ?)
I can't imagine needing more than 1 control joint to split that slab in half

 

[Ron]

For traffic slabs like this I specify a semi-rigid epoxy joint sealer. W.R. Meadows Co. Is the one I use.