I'm wanting to put a 20 foot concrete pad in front of my garage. Right now, the garage floor is concrete, but the driveway in front is just dirt. However, under that dirt, there is a bed of 2" to 3" rock, which I put there about 6 years ago. What I want to do is just make forms and have a just have a few yards of concrete delivered, to trowel myself. The base dirt is well packed and solid from years of driving on it.
To add gravel, I will have to disturb this well packed dirt with the rock underneath. (or the drive will be higher than the garage floor). Not only will this disturb the well packed base, but will double the cost of this job, because of the cost of the gravel, and the cost to rent some sort of machinery to dig up this dirt and rock base, since I already tried a shovel and with that rock base, the shovel wont even go in the ground unless it's after a rain when it's muddy, and even then the rock base could not be dug up with just a shovel.
My plan was to simply make forms, remove the small wooden ramp I made at the front edge of the concrete garage floor (I left the dirt about 4 inches lower than the garage floor intending to pour concrete, but made that ramp out of stacked 2x8's to drive in and out of the garage). Add a few bricks with some rebar on top, And pour/finish the concrete. 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.
One other thing. For a 20 foot long by 12 foot wide strip of concrete, how many joints should I cut in the concrete? I'm thinking just one, so each section is 10ft. I plan to place one of those black fiber strips where it meets the garage slab. I'll probably just trowel the joint in the middle, to avoid having to rent a concrete saw.
Finally, did I figure this correctly?
20 X 12 = 240 sq ft. At 4 inches think, I estimated that I need roughly 3 cubic yards of concrete. (Actually 2.96 cu yd). Is this right? (I'm not the best at math).Thanks