Joining Windows domain requires 2 different steps:
- the very first time your workstation or server joins the domain
- once you have successfully join target domain, you can authenticate against this domain and connect to it.
As explained by Microsoft, first step does require to use local Admin account
Based on this, what do you mean when you say that it requires admin account?
- admin account to join first time
- your domain account to open session on this server must be also "domain account"?