Concrete – How many bags of concrete do I need

From the description and photograph, it appears that the crack is the natural result of the sort of stresses one would expect at a location with:

• Drastic change in slab width to extend the slab through the door opening.

• Drastic change in thermal stress where the slab transitions from interior temperatures to exterior temperatures.

• Drastic change in slab stiffness. Dynamic vehicle loads are applied sequentially from the rigidly supported portion directly above the wall below to the spanning portion where they create deflection in the supporting structure.

All of which is to say that repairing the joint does not mean filling it in. There will always be a joint there. Instead, repairing the joint probably consists of keeping water out using backer rod and a flexible traffic sealant rated for wide joints...and perhaps a metal joint cover.

There's no magic in a can that it going to defy the laws of physics or change the internal stresses of a concrete slab under dynamic vehicular loads. Any repair needs to be premised on acceptance that there will be a joint across the opening where the slab narrows.

Depending on the percentage of the portions in the mix , a fully cured slab of concrete should have a compressive strength of between 2200-5000 psi. So depending on what the slab needs to support will determine the thickness and configuration of the concrete. A standard residential driveway is commonly 4-6 inches thick concrete with re-enforced steel bars. A residential garage normally is constructed on a 4 inch mono-lithic re-barred slab. These are just generalizations and you should consider all extenuating factors for your project for your region.