Side edging for hexagonal stone pavers? Concrete ok?
Expansion isn't really a concern. Finishing the edge is. You can't just screed the slab to the pavers and expect a good outcome. You'd have to edge the slab along each angle of the pavers' shape to eliminate the sharp corner. You can imagine how tedious that would be.

Also, you'll have staining on the surface of your pavers unless you protect them somehow or acid wash it later.

Like JPhi1618 said, halving pavers to create a straight line is the usual approach. A 7" angle grinder with a serrated diamond blade works well, or rent a wet saw.