I'm planning to pour a pad into an existing open carport / garage area that has mid-span supports resting on poured piers and a foundation wall going around the outside. I'm planning on digging down about 10-12", laying gravel and compacting, laying sand and compacting, then add a vapor barrier and metal mesh / rebar.
Is there anything I need to think about when pouring the new slab up to the edges of the foundation and around the piers? do I need to wrap the slab edges with foam insulation to give an expansion joint / allow them to slip past each other when settling occurs or is there a better solution?
The piers / foundation have been in place for at least 40 years. The slab would just be adding a new surface in the garage area.
EDIT: there will eventually be living space above the garage. I was sort of assuming I'd want the vapor barrier due to this. The space is approx 30' wide by 20' deep, and there's three garage slots, with posts supporting the joists above between each slot.
Best Answer
I assume the pier is above the finished floor. You are correct in thinking to provide the full depth expansion joint around the pier, as well as around the perimeter of the slab that will be poured against existing concrete.
If the garage area is large, in addition to the expansion joint, it is recommended to have a control joint at an approximate 10'-15' interval in each direction to minimize the potential for random crack. The control joint (1/8"-1/4" wide x 1" depth) shall be made by saw-cut within 24 hours of concrete placement. Around the pier, the diamond-shaped control joint is recommended to avoid diagonal cracks at the reentrant corners of the slab.
The last recommendation is the fresh concrete shall have at least 5% of entrained air to improve its durability against weathering, especially in the cold regions.