I have seen plenty of details for construction joints, retaining wall bases etc. which shows a shear key with reinforcing running through it.
It appears that using shear friction (even on a smooth formed surface), you would get considerably more capacity than the shear key.
However, the mechanics of dowel action require some surface roughness, but has testing been done on dowel action in perfectly smooth surfaces?
What are the reasons for providing one even if it is not as effective as the reinforcing bars passing through the joint.
My question becomes more pertinent when trying to frame a concrete beam/slab into an existing concrete structure. The effort for roughening/installing shear keys are quite significant.