Muhleman developed a concrete powder bed 3d printer that uses hacked Shapeoko CNC router mechanism.
It uses sand and cement mixture and a liquid soil hardener called polypavement as binding agent. Powder bed is loaded manually :-) but a mechanism could be developed in the futre.
Printed objects are rough but the concept is interesting for artistic purposes and concrete furniture where you can get more complex organic forms.
Full construction guide with plans and operational instructions can be found at:
Here is a video of it in action: