are you working to a certain code?

The code of construction to be used for performance qualification (or any qualification for that matter) should be stated in contract documents. In lieu of that, that code which you believe best represents the standards necessary to ensure the viability of the welds you produce, should be the one you choose. Since it is a concrete reinforcing application AWS D1.4 would be a good place to start.
However, I would start with a Request for Information (RFI) to your client to see if they haven't just overlooked stating the code of construction in the contract documents explicitly, since to my knowledge D1.4 doesn't exactly suit your application. If the client is leaving it up to you, you need to be sure you can defend your decision litigously.
Municipal and county or state jurisdictions will often dictate the code to be used for qualification. Make sure you don't have a requirement in jurisdictional codes you must comply with.