It looks like he is wearing a suit with a patriotic sash overtop, such as the one on this website I have attached . Many Civil War sodiers were in different organizations, such as the Patriotic Order Sons of America, that had different ribbons and things for their members. If you can research different Civil War patriotic honor organizations, you may find an exact match to your Great-Great Grandfathers photograph! Good Luck, I hope this helps :)

http://www.cowanauctions.com/auctions/item.aspx?ItemId=10732