Concrete thickness for gravel driveway entrance

[Macinnis]

At 4000 psi...how much stronger is a 4” slab vs 5”?

Just saw this from what looked like a reputable site...pretty amazing to me:

How thick should a concrete driveway be?
A minimum of 4 inches is recommended. Keep in mind that the 2 x 4's often used to form driveways are only 3 inches wide, so the ground inside the 2 x 4 forming needs to be removed at least an inch below the bottom of the form. Thickness is the major factor (even more than the strength of the concrete) in determining the driveway structural capacity. In other words, thickening your concrete slab carries more load. Increasing your driveway's thickness from 4 inches to 5 inches will add 20% to your concrete cost, but the additional inch of concrete will add almost 50% to the load -carrying capacity of your driveway. If the driveway will be used by both cars and light trucks or SUVs, then a 4" thickness should be adequate. If garbage trucks or other heavy vehicles will be traveling on the slab 5 or more inches may be necessary.

 

[Hay Dude]

Just saw this from what looked like a reputable site...pretty amazing to me:

How thick should a concrete driveway be?
A minimum of 4 inches is recommended. Keep in mind that the 2 x 4's often used to form driveways are only 3 inches wide, so the ground inside the 2 x 4 forming needs to be removed at least an inch below the bottom of the form. Thickness is the major factor (even more than the strength of the concrete) in determining the driveway structural capacity. In other words, thickening your concrete slab carries more load. Increasing your driveway's thickness from 4 inches to 5 inches will add 20% to your concrete cost, but the additional inch of concrete will add almost 50% to the load -carrying capacity of your driveway. If the driveway will be used by both cars and light trucks or SUVs, then a 4" thickness should be adequate. If garbage trucks or other heavy vehicles will be traveling on the slab 5 or more inches may be necessary.

You should be commended by looking at it this way. 4” is the MINIMUM thickness.
What other things do we do in life to the bare minimum and expect lasting results?

 

[Captain Dirty]

Well the nice thing about 5 1/2" is that it is a 2x6 in height for a form.
To get a full six inch you would need different forms.

2 x 4, 6, 8 are 1-1/2" x 3-1/2", 5-1/2", 7-1/2". Rather than trying to suspend 2 x 6 form boards, I would use 2 x 8s and dig about 1' around the inside of the perimeter down to 7-1/2". The thicker edges will strengthen the slab where it needs it most.

 

[rademamj1]

Need to know subgrade to properly design concrete. With unknown subgrade I would use 6 as minimum
For strength ,rebar or wire should be near bottom of slab. Middle is wrong spot
As Eddie Said excess water is bad for slab durability

Streetcar: Middle of the slab is the correct position for rebar, for maximum strength of the concrete slab. This is repeatedly supported by numerous laboratory, industry studies and concrete field tests. Right now Texas DOT is overhauling and widening I-35, and specs call for 42" packed base, 12" asphalt and 12" concrete with 1" rebar placed mid-depth or 6" above asphalt. Texas believes this Interstate to have a 45 year life. I might add, for many years it was considered best practice to place rebar in upper 1/3 of the concrete, but surprisingly, industry studies show even greater strength is gained with rebar at mid-depth.

Placing rebar on the ground, basically makes it real quick and easy to lay down, but there is limited structural support during the life of the concrete pour.

 

[hslogger]

Often the corner will fail when some heavy truck hits it. I asked my concrete man about it when I hired him to pour a new apron and aproach to a garage I jacked up and rebuilt. He dug the corners out DEEEPER in addition to the fiber and metal. It has proved to be a winner for us.

 

[kwbretired]

I was thinking the rebar or 6 x 6 wire mesh was put in concrete not so much for strength but to hold the concrete together when it cracks.

 

[Hay Dude]

Often the corner will fail when some heavy truck hits it. I asked my concrete man about it when I hired him to pour a new apron and aproach to a garage I jacked up and rebuilt. He dug the corners out DEEEPER in addition to the fiber and metal. It has proved to be a winner for us.

Ive been called a toothless amateur, but have poured miles of concrete. If I was doing the job for the OP, I would dig mini footings around the perimeter-maybe 6-12 inches deeper than slab. That way the edges, which can break or crack, are thicker and better absorb the weight and shock of a heavy truck tire on the initial hit to the edge of the slab. Take your rebar an bend the tips down 90 degrees into the mini footings. Id do rebar in a 2 foot by 2 foot grid and throw WWF on it. Pour slab 6 and footings another 6 deep by 1 foot wide give or take.
I have done this with great success on large concrete slabs for farmers and equipment owners outside of the pole barns we build.

 

[Streetcar]

Do you have any links for these studies. Rebar in top or middle works for crack control but strength is gained by placing rebar in bottom of the slab

Streetcar: Middle of the slab is the correct position for rebar, for maximum strength of the concrete slab. This is repeatedly supported by numerous laboratory, industry studies and concrete field tests. Right now Texas DOT is overhauling and widening I-35, and specs call for 42" packed base, 12" asphalt and 12" concrete with 1" rebar placed mid-depth or 6" above asphalt. Texas believes this Interstate to have a 45 year life. I might add, for many years it was considered best practice to place rebar in upper 1/3 of the concrete, but surprisingly, industry studies show even greater strength is gained with rebar at mid-depth.

Placing rebar on the ground, basically makes it real quick and easy to lay down, but there is limited structural support during the life of the concrete pour.

 

[lilranch2001]

Correct Position for Slab Rebar| Concrete Construction Magazine

This was the first hit I got on a quick search

 

[Streetcar]

Link confirms what I said rebar at top or middle for crack control, bottom for strength of slab

Correct Position for Slab Rebar| Concrete Construction Magazine

This was the first hit I got on a quick search