Cement

[rusty]

John, Non reinforced concrete poured on grade is only as good as the subgrade it is poured on. You have a couple of problems, One the imported fill and two the ground water. If the fill has been there for a while and is performing Ok then all you have to do is tear it up 12 inches down and compact it back in 6 inch lifts. Add enough water to make it bind together. If you don't get pumping of water up through the fill while conpacting you are good to go. When done compacting do a roll test the check the compaction. This can be done by driving your bus on it to see if there is any soft spots.
The concrete mix I would use is a 4000 # mix.The mix should have somewhere around 600# of cement in it. You can subsitute 15 or 20% of the cement with flyash. Air content of between 5 and 8 %, and it can have a water reducing add mixture to help the water cement ratio. Flyash is fine. It will get its strength a little slower but will get stronger in the long run. A 4 inch slump is fine. We pour bridge decks with a 4 inch slump all day long. You will get a better job than trying to pour to dry. If you pour to dry you will need to vibrate and possibly use a machine.
I would pour 6 inches thick if the subgrade is OK. Fibremesh is a good add to the mix ( 1 1/2 poundls per c.y. ). If you don't use fibremesh than use #4 rebar 12 inches on center both ways bricked up to the center of the slab.
When you pour don't over work the slab. Screed it, bull float it. Fresno it, broom it , and cure it. There are two kinds of concrete, concrete that is cracked and concrete that is going to crack. Help it crack by tooling joints or sawing joints 12 feet centers max. I prefer to saw joints it makes for a smoother slab. Then caulk the joints with a good caulk you can get at Home Depot.
You will not have to wait 30 days to use the slab. With the above mix you will get 80% strength in one week and can use the slab in two weeks.
You can ask the redi mix company for test results of the mix to see how it will preform.
If you subgrade is not Ok you can use a structural slab. 10 or 12 inches thick with two layers of # 5 rebar 12 inches on center both ways. Use the same mix as above ith out the fibremesh.

If you need more call me 303-591-0372

Good Luck Wayne

[robertglines1]

Lots of floating roads around like Wayne said:actually anchored off with cables to hold in place with dead men. We are explaining extreme circumstances. Your local guy will treat you rite just ask for refrences and look at some work at least a year old.   Bob.  The little knowledge you have will keep him on his toes.

[luvrbus]

Looks like Co has different specs for bridges Wayne I looked at Ok and Tex, Tex will allow flyash for paving not on bridge decks same as AZ on the slump 2 in max chilled water over 95 degrees.
That is hard to think of 600 lbs of cement in 4000 lb concrete the rock must be getting real soft there now, I could get a 28 day break over 4000# using 400 lbs of cement with 1 1/2 inch river rock in Houston 
City of Tulsa no flyash 2 in slump for all concrete paving and bridge decks.
I am trying to find the specs for the Jefferson County Jail on what the mix was on the 8000 lb that stuff was nasty in July .  
Lol what did you guys use for concrete from Limon to Denver that was the worst section of interstate in the nation.Flyash maybe a thing of the past if the chief in DC gets his way and closes all the coal fired plants  


Call me I have all officers in place now for the club  OT

good luck

[chev49]

Too bad you aren't out in the country like us up here, we would fix you right up with the equipment  and steve would do the concrete. He last did the rural fire station concrete where the full water trucks are parked all the time. That job took some extra time because of the big floor drains that went to the ditch. (Haha.. try that in town    ) I mostly watched.. cept for doing some excavation with one of the old 331 bobcats in the front of the building.