# Re-inforced Concrete slab, help with layout of rebar and expansion joint..



## Little (Jul 22, 2006)

I can't believe after being in this business for 12 years I've yet to pour a very long re-inforced concrete slab. I have some question regarding the placement of the expansion joints. 

40ft x 15ft dumpster pad, 8" thick with double mat of #4 rebar 16" OC Each way. They want one expansion joint down the middle at 20ft. How do I install the expansion joint with the rebar going through? Should i actually be making two seperate pads with a separation of the rebar mat in btw each? 

I also have to do another pad 40ft long x 6.5ft wide, 12" thick with dbl mat of #5 bar with the same thing, @ 20ft install expansion joint. This pad is the entrance pad to a wash bay bldg for commercial vehicles and is attached the new bldg with dowels out of the floor slab. 

I feel stupid right now :bangin:


----------



## Tinstaafl (Jan 6, 2008)

I should just keep my mouth shut rather than _proving_ my ignorance, but wouldn't it make sense to have the rebar span the joint so that the two sections can't shift in relation to each other?


----------



## CommercialSuper (Mar 30, 2012)

Little said:


> 40ft x 15ft dumpster pad, 8" thick with double mat of #4 rebar 16" OC Each way. They want one expansion joint down the middle at 20ft. How do I install the expansion joint with the rebar going through? Should i actually be making two seperate pads with a separation of the rebar mat in btw each?


Do they want a true expansion joint or a control joint? If it's expansion then yes, it will seem to be 2 separate pads - NO rebar connecting. (possibly some slick dowels to help prevent heaving) I've seen this done by pouring half, tacking up the expansion joint material to the newly poured edge, and then pouring the second half. - The advantage here is you can build the forms square and ensure your expansion joint wont get sloppy compared to below... 


Or you pour it all at once and 'wet set' the expansion joint. This is doable, but you want to make sure it doesnt get wavey. Either way, the rebar is split into 2 pads. Can't really do slick dowels with this method. Not easily anyhow. 



> I also have to do another pad 40ft long x 6.5ft wide, 12" thick with dbl mat of #5 bar with the same thing, @ 20ft install expansion joint. This pad is the entrance pad to a wash bay bldg for commercial vehicles and is attached the new bldg with dowels out of the floor slab.


Same premise as above. My question is what are you doing at the areas where you attach to the building? Are you installing expansion joint there as well, or a bond breaker at a minimum. Are the dowels coming out of the building rebar or slick dowels? What kind of compaction are you looking at 3000 psf? 


Depending on what the soils look like, it doesnt make a lot of sence to me to install expansion joints that close to each other. I figure it instead would be a sawcut control joint, especially with the double mats. They obviously don't want it to move. If it is supposed to be expansion- ask about doweling them together. 


As far as doweling with an expansion joint... I'd form one half of the pad. Install expansion joint on the inside of the form edge. Drill through the forms and through the expansion joint to install slick dowels. Pour slab in form. Wreck form without pulling out dowels. Use edge of expansion joint (against newly poured slab) as form and pour dowels into second half. 

With the greased slick dowel it allows for horizontal expansion/shrinkage/movement, but restricts vertical/heaving. 




> I feel stupid right now :bangin:


Don't. I work with people who do this kind of thing every day and still manage to screw it up on a regular basis, and on top of that, I'm sure someone will come along and tell me a different/better way to do it than I've described above.


----------



## Little (Jul 22, 2006)

At the building I will separate the pad from the bldg with expansion joint. The bldg mason is installing the dowels, I do not know what kind of dowels he is doing yet. Maybe i'll just give him a shout and get his recommendation


----------



## PPRI (Oct 9, 2010)

For a single pour: Green treat 1x8 at the 20 foot mark. Nail parting stop on top of the 1x. String this straight and use wood stakes to hold the 1x. Set the stakes 4 inches below the top. Pour both sides like you normally would. After the pour you pull off the parting stop and you have a urethane joint. If you need a true expansion for the dowels just drill through and use greased slick dowels or you can cut pieces of tubing and slide them over the ends of the bar to allow an air space for expansion. The bar from one half will not be tied to the bar from the other half.


----------



## ScipioAfricanus (Sep 13, 2008)

Little said:


> At the building I will separate the pad from the bldg with expansion joint. The bldg mason is installing the dowels, I do not know what kind of dowels he is doing yet. Maybe i'll just give him a shout and get his recommendation


What is the purpose of using expansion joint material at the union of the new to the existing slab?

You are doweling into the existing slab right?
Andy.


----------



## PPRI (Oct 9, 2010)

Chances are the building slab is conditioned and sitting on a footing or foundation. It's not going to move much if at all. The exterior slab is going to move up and down while pivoting on the dowels. By using expansion joint at that union it is possible to keep the slabs from sloughing their top surfaces from binding.


----------

