Rebar in a divided slab

[sive]

I am in the process of pouring a 24'x22' driveway slab. I have it divided into 16 - 6' x 5 1/2' sections. I am mixing the material and hope the soft redwood acts as a good joint for expansion. I plan to run 20 foot 1/2" rebar at 12" intervals north to south and 2 foot intervals east to west. My plan is to drill holes through the 2 x 6 redwood I am using for the permanent forms with the exception of the perimeter boards. I have read in several locations that the rebar must touch the outer forms when pouring a slab. However, this is without mention of the inner 2 x 6's that I will be using and drilling through to run the rebar. I realize you don't want the metal too close to the outer edge where forms are usually removed. My question is: Will there be a problem down the road by running the rebar through the wood dividers thus making both part of the permanent slab?

MS

[Rich]

The one problem I see with running the rebar through the redwood is when you need to replace the redwood - which you will need to replace.. probably sooner than you think.
Why are you using redwood? Why not just tool some control joints in?

[mjpliv]

The rule of thumb for rebar is 3/4" from the concrete surface above grade and 1-1/2" from the concrete surface below grade and in corrosive environments.

Rich is correct - tool your control joints after the concrete "stiffens" enough to walk on or cut them with a concrete saw a few days after pouring.

If you haven't bought the rebar yet I would suggest 5/8" bar at 12"-14" OC in both direstions. The 1/2" is a little light for traffic loads.

[sive]

Hmmmm.... I can take the rebar back for a larger size. As for the use of redwood and lack of control joints. I am mixing and pouring my own with the aid of a 12 year old. Hence the smaller workable sections. This is a dry climate. Less than 11 inches per year.

Again, my initial question had to do with why we are warned to keep the rebar 2-3 inches away from the forms. And would this also apply to wood being used as permanent forms inside the perimeter?

MS

[mjpliv]

I have no idea why you were warned unless they seem to think that you would experience rust staining. With the rebar installed 1-2 inches from the bottom of the slab where it belongs and 1-2" from the edges then you should be fine.

[RobBase]

sive, the rule of thumb for concrete that will be below ground (I'm assuming that the slab edges will later be backfilled so that the top of slab and top of grass/landscaping are equal) is to keep steel reinforcing 3" from the inside of the forms. The reasoning is that ground water can saturate through the concrete, reach the rebar and rust/corrode it.

I've seen redwood divided slabs here in MD with it's somewhat wet climate that have lasted for 10+ years.

If I was you and to make it a little easier on yourself here's a suggestion........

Take some of your rebar and cut it into 16" pieces. You can figure out how many you'll need after you hear me out....you will need far less than what you already have. Then buy some wire mesh and cut it into squares that will fit inside your "slab panels." Before you pour a panel, drill 3 holes through each side of your redwood dividers and stick the rebar dowels halfway through. Now pour your concrete and after it's all floated off, check your dowels and make them level and square with the forms.
Next day, before you pour a panel adjacent to the one you poured earlier, take some building felt and duct tape and wrap it around the rebar projecting out so the felt becomes like a sleeve which slides back and forth on the rebar. Now pour this panel.

The rebar dowels will allow some expansion/contraction without allowing any of the panels to move up or down against each other.

P.S. Make sure you lift the wire mesh up halfway of the depth of the slab as you pour.

[sive]

Now that is what I was looking for! I got my answer and then some.

Thanks,

M.Sive