On Fri, 27 Apr 2012 00:05:55 -0600, Tony Hwang
wrote:



Pat wrote:
A fairly simple job. However, someone told me I must put dravel under
it first. Is this gravel really needed? If it is, why? After all, I
already have the rock base, which is very solid, and rock is like
gravel. It's just that dirt has filled in around the rock so it just
looks like dirt now.


You say nothing about your climate or location. Do you have freeze thaw
cycles? Gravel base helps keep the water away from the concrete. Do you
have seasons? Dry, wet cycles? Soil expands when it gets wet and shrinks
when it dries. Rock helps isolate the concrete from soil movement. When
the soil is wet its load carrying capacity is diminished. Concrete corners
may not have good support and break. Generally rock under concrete is
essential. Especially under driveways where there is loading from vehicles.

A thin layer of sand under the concrete allows up to 10 feet between joints.
The joints control where the concrete cracks. If the joints are too far
apart then a crack forms before the joint is reached. The sand allows a
little slippage so the joints can be stretched a little.

I figure 2.7 yards.



And no rebar?


I like the idea of rebar (or even mesh) in residential driveways but
I've yet to see it in the dozen or so driveways under construction
I've come across on Long Island or in Houston. All were poured on
just sand without any gravel. Personally I like the idea of sand,
gravel and rebar but that's not what I've seen so far. Of course one
reason is probably to keep costs down.