Concrete Slab Repair on Garage with No Foundation
I have a 12'x20' garage with an off-center door. I am in the process of widening the door to 9' and repairing the cracked, uneven floor under the garage door. My plan was to remove part of the slab and repour so the new door would sit on a nice level surface.
I thought the garage had a foundation, but after I started jackhammer today, I realized I was wrong!
As of right now, I removed the concrete up to the major crack (photo to be posted in next reply) inside the garage. I also removed about two feet of the concrete skirt outside the garage to provide room for wooden forms.
I'm trying to pour a new slab and join it to the old slab but I'm not sure how to support the new slab since there is no foundation. My father's car will be stored in the garage but it will only be driven a couple times per week. When parked, the car will not be sitting on the new slab. I live in southern New York. The garage is not heated. The old slab is about 4"-6" thick in the middle and about 12" thick around the perimeter.
I've read other posts on this site that said drilling rebar approx. 4" into the old concrete, extending the rebar into the new slab, and connecting the rebar with wire mesh will help keep the slabs together.
But what can I do to prevent the new slab from sinking since there is no foundation?
Will bagged concrete mix be strong enough or should I bring a small truck in to pour a stronger mix?