Pouring Concrete On Gravel Driveway

72chevy4x4

that about sums it up-can I do it? The gravel driveway has been around for many years and is very firm-there is a little dirt in it, but not much. can a 4" pour be placed on top and not have any issues b/c of the substrate?

When you guys pour footers and basements, is crush and run used, or pea gravel or something like a 3/4" gravel?

Same Old

Footers go right on the ground, no base.
Check to see how deep your existing gravel base is. If you have 4inch you will be allright for a light duty residential driveway. Depending on soils and width I'd go either a full 4" (not 3.5") or 5"
Don't waste your time with mesh, just put down a 3' x 3' grid of #4 bar. and control cut every 10' You'll have a gorgeous driveway for a long time.

And if you live in a freezing climate spend a couple bucks extra for an all granite aggregate to eliminate those popouts.

I'd use a 4000psi 3/4 granite ag mix with air.

concretemasonry

Make your cuts (1 1/2" deep) much later the same day or early the next. Let the concrete crack at the cut and them caulk with the most expensive appropriate caulk you can buy (it is important).

For cold weather, never less than 4000 psi (some producrers will not deliver less to a driveway). Definitely use air enstrained concrete for durability.

I prefer to see wire mesh in the slab. If you spread out rebars, mesh will help with the microcracking between bars. My choice is wire mesh (6x6) and fibermesh, but if I had only one choice, it would be wire. - Personal opinion. The joints are absolutely necessary!!

__________________
Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

house bldr

You can pour directly over the gravel but I would recommend a thin layer of sand if possible to cover the dirt you referred to.Wet it slightly before you pour, dirt tends to suck the moisture out of the concrete quickly causing a fast set, weak concrete problem.

Same Old

Oops I forgot to say add microfibers instead of the mesh. It really is far superior to wire mesh to control early set shirinkage cracking.
I know you older guys like the mesh but study after study declares fibers the winner here, and there's no labor and the materials are cheaper. The current fibers are completely invisible too.

I push the bar because a lot of guys think the mesh is a reinforcement, when it isn't. It's job is done in the first week. It only helps control shrinkage. It will NOT prevent cracks from opening up . I've seen plenty of sheared mesh at cracks. Bar is relatively cheap, use a lot of it and you'll have some long lasting slabes in nearly any situation.

Definitely get on your control cuts as soon as possible.

Sucking moisture from the bottom of the slab is exactly what sand is there to do. Not suck so much I guess, but it provides a place for excess bleed water to migrate out the bottom of the slab to keep even with the top. This reduces slab curl. I like my base sprayed down damp. Not wet as that will increase the set time too much. But no so dry that it is sucking water out of the mud. Did that last paragraph confuse? Sorry.

cleveman

sounds fine. maybe dig a trench on either side and put some rebar in the trench, say a 1x1' trench. Put some rebar or fibre in the field and some plastic underneath. Slope down to the trench if you like and pour everything at once. This is what is known as a neolitic pour.