concrete slab question

[joeu235]

I'm about to have a 20 x 25 slab put in to use as a parking spot and patio. soil type is black land clay. I got two quotes. One contractor wants to to pour a 4 inch thick slab with #5 reinforced exterior beams and #3 12" spaced rebar in the field. The other contract wants to just pour a 5" slab with #3 12" spaced rebar. The first quote is x2 the second.

Any educated opinions on whether the beams are needed for my soil type?

 

[ustmd]

Howdy neighbor,

I am over near Manor and Elgin.

You want the first guy, unless you want cracks in our black land clay soil.

I have had 4 engineered slabs done. I am the only one of my neighbors who has NOT had any foundation issues in any of my slabs. All of my slabs were closer to design of the first than the second.

Good luck

 

[ustmd]

Here is a picture of the rebar and perimeter beam they spec'd for a covered porch on my house-30 x 17

 

[Streetcar]

I would go with design,#2.
Thicker concrete will help more than edge beam

 

[RNeumann]

The thickened edge is far less important than the imported material beneath the slab and other prep. Another factor is the quality for the concrete. Another is the finish and joints.

My only question would be in relation to the frost level and slope- those are two reasons to thicken the slab around the edge. From your post it doesn’t sound like anything you are putting on the slab would require the thickened edge.

It sounds like both want to do a good job and it’s the details that may reveal if the one person is worth twice as much.

 

[joeu235]

My only question would be in relation to the frost level and slope- those are two reasons to thicken the slab around the edge. From your post it doesn稚 sound like anything you are putting on the slab would require the thickened edge.

It sounds like both want to do a good job and itç—´ the details that may reveal if the one person is worth twice as much.

Luckily the frost level is 0" here, and maybe slopes 2 inches where I want the slab to go.

Below is a picture of the slab under my shop. This slab will be right next to it. The shop slab has 3' deep beams with #5 rebar. Just don't think a parking slab needs to be this beefy, but definitely want it to last.

 

[Diggin It]

If you're not building a living space on it, does it really matter?

My driveway is 2" blacktop, no rebar or foundation.

.

 

[RNeumann]

Luckily the frost level is 0" here, and maybe slopes 2 inches where I want the slab to go.

Below is a picture of the slab under my shop. This slab will be right next to it. The shop slab has 3' deep beams with #5 rebar. Just don't think a parking slab needs to be this beefy, but definitely want it to last.

View attachment 602621

With no slope, no frost and no need for footings (heavy point load on the slab) I don’t see a need to spend twice as much for a thickened edge. If you have good prep, the specified rebar, decent concrete and proper control joints a 4-5” slab should work just fine.

 

[Tractor Seabee]

For a slab on grade; what is under it is more important than what's in it. I am not famaliar with your type subgrade material. A 6" layer of 3/4 minus crusher run gravel base will always help stabilize. If an unstable sub-grade is not economical to correct then you need the structural slab with re-bar. Slab thickness and re-bar design are matched to the static and dynamic loading downward. For admin type vehicle parking quote #2 appears more than adequate unless building on mud. For size of the slab it will need to be divided in four sections with control joints sawed in right after slab is finished (not the next day). I have done saw cutting in the dark many times.

Ron

Ron

 

[texas42]

In Texas, we have very expansive clays with severe linear expansion between dry and wet.
These clays when saturated are very muddy and sticky, but when they dry out become rock hard.
In addition, when they dry out they shrink and crack open - 1/2 to 3/4 inches.
That's why most engineered slabs have reinforced beams every so often.
Without proper reinforcements the shrinking and expanding clay will destroy a simple slab on grade.