How do I clean reclaimed wood from construction?
You could try X'Crete which is advertized as suited to removing concrete from forms.  It dissolves the concrete into a slush you can rinse away.  There's probably other similar products.

Or a more hard-core approach would be to use Muriatic Acid; apparently that's what masons use to clean their stuff.  Downside being it's dangerous.

A more tool-oriented approach would be a belt sander with a low grit paper.  Belt sander don't care.