Filling in concrete slabs

OK after doing some major plumbing work, I have now four bathrooms and one kitchen with holes of varying sizes to fill back with concrete.
The largest hole is 7' wide x 5' long by 4" thick, the smallest one is about a 12"x12"x4".
I will be doing termite sprays, moisture barriers, and rebar ties for all the big holes and throw in some wire meshes as well.
Now the problem is how to get the concrete into those holes.
Obviously the fastest way is to measure them off and calculate the yardage and order the concrete to be delivered and wheel it in and fill them all in one shot...but this makes me very uneasy.
I remember last time I did this, the concrete truck was very close to my driveway, it spills all sorts of concrete into my driveway and stairway as well as fence, took me a long time to clean them off. As the wheel barrow fills up and gets wheeled to the individual rooms, they also spill and drip and made a mess, and finally I don't think I can handle filling of 9 holes in 5 rooms and smooth them fast enough...
I prefer to take it one room at a time and if I mess up I learn from my mistake as I move forward.
So I think I will mix my own and pour at my own pace. I will need to rent a concrete mixer (or may be cheaper to buy one if I have to rent for an entire week).
question is for the large hole - 5'x7'x4" thick, I might have to mix several times. So is it ok if I say divide it up, put may be a sheet of plywood in between and pour in sections, do one, wait for it to dry in a day, and pour another section...is that ok? I know this is probably not as strong as one continuous pour in one single step but I don't think I can do enough fast enough.
Would appreciate any thoughts and comments on what's the best way to attack this.
Thanks,
MC
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wrote:

The big hole is about 20 bags of concrete. That is a lot to mix if you don't have help. 3 people can do it but they will stay busy. One running the mixer, one wheeling and one placing the mud. You are already going to have a cold joint on the edges I would try to avoid another seam if you can. "Stick and dowel" the slab with rebar. Drill holes into the existing slab, epoxy the rebar in from both sides and lap it about 24" for #4 (1/2" rebar) or 18" for #3 (3/6") and tie it with wire. A 12x12 grid is probably more than you need. 18x18 or even 24x24 should stablize it You probably don't need anything in the small holes.
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wrote:

In the time you have spent worrying and writing about it, you could have already have finished it.
Put your vapor barrier down and start the mixer and get busy. Each time you dump a load, mix it in with the last load you dumped. It won't dry and harden in the 30 minutes it takes to mix up another batch, so you just keep mixing, dumping and stirring it in.
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Here in the Phoenix area, there are places where you can order small batches of concrete in a dump-it-yourself trailer. Might work for you if you or a friend have a truck with a hitch. Sounds a lot easier than mixing the 20 bags that another poster estimated by yourself.
Jerry
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You could also pump it in.

Small mixers are cheap now, look at the Husky at Home Depot for around $260. I've done 20 yards so far with that Husky.

You should able to do 5x7 in one pour, I've done 10x10 on a mixer with just the wife and me. I have the mixer next to the form to dump the mix. Your advantage is that its indoors and more time to work with before the concrete sets up. How are you transporting all that concrete without screwing up the interior of the house as wheelbarrows don't turn well in tight hallways.

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Google "Yard at a Time" concrete

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