100VAC between concrete floor and outlet ground
I don't have enough rep to leave a comment, so let me say this.
Your Fluke may be reading a phantom voltage, but this is unlikely because you actually felt a shock.  What may have happened is that the grounding rod became disconnected from the bonding screw in your mains electrical panel and now the system is ungrounded.  This can happen for several reasons that I've seen.  A plumber installing plastic lines and the earth ground getting disconnected.  Sometimes a lawn-mower can hit the grounding rod and disconnect the copper wire.
Basically, the general concept of grounding is that everything in your house should be at ground potential.  At my workplace, the building has heavy-duty copper-cable embedded in the concrete around the steel columns connecting the columns to the concrete and earth.  Without doing this, it is possible for voltages to exist between different locations on the floor.  Copper allows a low impedance path for the current to flow so everything is at equal potential.
Try connecting a small load between the ground wire of your receptacle and the cement.  Like an inductor-style voltage tester or an incandescent flashlight bulb.  I've done this in my own house and got an LED to light up where there should not be any voltage at all.  Figure out a way to do this SAFELY.  The reason for small voltages to exist is because of naturally occurring voltage differences in the soil, but something like you are experiencing is likely due to a failed grounding system in your house.