Preparing for a concrete slab

[numbah9]

A buddy of mine is a concrete contractor and he came by yesterday. He wants to do a 20'x20' slab, 6" deep with 12" honches, #4 rebar 24" O.C. at about 3500psi and 5% air.

Now I just need the city to give me permission..

[numbah9]

What determines when I should or shouldn't put in a frost wall? I had an excavator give me a quote to knock down my 2 garages and haul the stuff away and he said I should do a 4' frost wall. His basis for this was that the soil wasn't good enough to withstand the frost heaves.

How do I know whether this is something I need to do or not? He's the first excavator I've talked to about it. My concrete guy didn't think it was necessary, so I'm not sure who to trust. The garage will probably never be heated.

I don't believe code here requires a frost wall. I suppose it's preferable, but it's considerably more work and considerably more concrete. Should I find a geologist to check the soil?

[numbah9]

Originally Posted by dcs Inc

Yes. the biggest thing is to make sure it is compacted well. The best type of granular fill is crushed stone with a graduated size of 1.5" to fines. This compacts real well. Don't do the pea gravel, that invites moisture. Sand is tough to keep in place and moves around a lot when placing concrete making an uneven sub surface. gene

Gene, what do you think you would pick out of this list of fill: http://www.gsgravel.com/zones/view/2