Let $C$ be the standard Cantor middle-third set. As a consequence of the Baire category theorem, there are numbers $r$ such that $C+r$ consists solely of irrational numbers, see here.

What would be an explicit example of a number $r$ with this property?

Short of an explicit example, are there any references addressing this question?

A natural approach would be to see that all irrationals in $C$ are transcendental, so it would suffice to take $r=\sqrt2$. But this is open, see here.

Many thanks for the answers. (It would be interesting to know whether $\sqrt2$ works.)