Someone mentioned expanding epoxy to me recently. I didn't ask for a brand
name or type. Does this sound familiar to anyone?

They drill holes into the concrete, perpendicular to the crack. Next them
hammer in plastic feeder tubes into the holes. In the exposed end of the
tube they screw in a fitting similar to what you'd find on a ball joint.
Finally they mix the epoxy and pump in through the fitting into the tube
until is starts coming out of the crack. The epoxy also expands as it sets -
at least it did with our foundation.