Joints required for concrete slab? 2

[langeng]

I am a civil engineer and have recently received a contractors submittal for a slab on grade, which I am concerned about and would like some input.
The slab is: 120' long X 40' wide with 1' X 1' grade beams every 20' across the width and also down the center running lengthways of the slab. It also has 18" wide X 24" deep grade beam around perimeter. It is 6" thick and contains #3 bars @ 16" O.C. both ways. he is proposing the use of normal weight 3000 psi concrete with no joints being cut.
My question is, won't the concrete crack excesively without the use of control joints. I have designed plenty of pavement but not many slabs so I am a bit green in this area.
I appreciate any input.

 

[dik]

Sawcut timing is also critical... it should be sawcut within about 6 to 8 hours after finishing or earlier with a sofcut saw.

Dik

 

[dik]

If you're looking at increasing the steel, then rather than shorten the spacing, increase the bar size to #4? 16" centres is easier to step through for placing the concrete and less likely to bend. Rebar should be 1-1/2" to 2" from the top. There are also fewer bars to place at the greater spacing. Determining a sawcut distance, timing and using a proper spec for the concrete is of utmost importance.

Dik

 

[langeng]

Thanks guys your advise is much appreciated.