I see no reason why Allen Browne's function should not work in Access 2013. It's available at:
http://allenbrowne.com/func-concat.html
You'll also find an alternative GetList function, using the highly efficient GetString method of the ADO recordset object in Concat.zip in my public databases folder at:
https://onedrive.live.com/?cid=44CC60D7FEA42912&id=44CC60D7FEA42912!169
Note that if you are using an earlier version of Access you might find that the colour of some form objects such as buttons shows incorrectly and you will need to amend the form design accordingly.
If you have difficulty opening the link copy its text (NB, not the link location) and paste it into your browser's address bar.
This little demo file illustrates the use of the function by means of a report, using Northwind data.