Pouring concrete without sand or gravel?

Hamilton, TX guy's Avatar (by Gravatar) by Hamilton, TX guy in  Masonry » Concrete 

Built my own home, but neglected to consider wind driven rain coming in the front/side doors. So I cannot put my wood flooring in until I keep the water out. Two storm doors are out of the question. I should have covered both doors: complete oversight on my part. So . . . I need to pour an 8 foot slab (40 feet long) for the front of the house (front porch). I need to pour a 12 foot slab (30 feet long) for the carport that will be at my side door. I do not want to add 4 inches of sand and then 4 inches of concrete because my Hardie Board siding starts on top of beautiful rock siding made of native rock. This rock work is about 24 inches high and goes all the way around the house. This rock work includes two stet up door entrances to my pier & beam house. I have dug down the necessary 4 inches for the concrete, but do not want to dig further: should it cause problem with my rocking (that extends only 24 inches up). I also have the rock stepping to consider at both doors.

The reason that I BELIEVE I can go without the sand is that the entire acre lot has a 4 inch solid rock formation running through it (just 10 inches deep). This rock formation (and the soil) slopes gradually down toward the road from the front of the house, so I intend to jack-hammer through it in several places, then dig 24 inches deeper to the next rock formation, and run rebar down into the holes to keep the slab from gradually sliding away from the house. I will jack-hammer one hole below every support that I will use to hold up the front porch and carport. BTW, storm doors are out of the question because I would have to tear out rocks and rework the entrances. Also, both doors really should be covered . . . I know that now. (Building things is a learning curve!)

So, there are the details. I live in Central Texas where it is very dry. We do get some very strong rains, on occasion, but everything dries up in a week or two (at the most). Can I go without a sand or rock substrate below the concrete slabs???? Honestly, I live way out in the country; I can live with a few hairline cracks. A few. I just do not want a huge problem cropping up that I failed to consider . . . again. Thank you all, very much!

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I'd say yeah, try it with the carport slab first...since that'll be the biggest test loading. I have 100-year old concrete for a parking pad that's just 2-inches thick sitting on dirt, in the Northeastern U.S. It's not legal by today's practices and has some cracks at just one corner since it wasn't even reinforced. But, it's not going anywhere and the largest and fully loaded SUV's haven't even made any new cracks.

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