Grounding Rod for Residential application
This is a ufer ground or a concrete encased electrode. There should be a listed connector that connects to the rebar. To repair this wire brush the rebar and get the correct size clamp for the rebar size, tighten the clamp to the rebar then attach the copper to the clamp at the screw. These clamps are usually brass with a stainless screw, the rebar will get rusty but a ufer ground is the best method for grounding due to the large foundation area that is in contact with earth. If you want you can add a driven rod right next to the rebar it sounds like the wire may be long enough but a clamp to the rod will also be needed. Even though the rebar is rusty this is a superior grounding method so clean it up and use it even if you decide to add a driven rod.