  In this work, we apply the idea of composite matrices arising from group
rings to derive a number of different techniques for constructing self-dual
codes over finite commutative Frobenius rings. By applying these techniques
over different alphabets, we construct best known singly-even binary self-dual
codes of lengths 80, 84 and 96 as well as doubly-even binary self-dual codes of
length 96 that were not known in the literature before.
