To convert concrete powder into concrete, simply insert a single piece of concrete powder into the first slot of a water tank. The water tank will harden the concrete, emptying 1/3 of a bucket from the tank. Cement mixers work with all types of concrete powder.
A Water Tank Converting Concrete Powder to Concrete
Technical Details
Water Tanks are processed every 0.8 seconds, 16 game ticks, or 8 redstone ticks, meaning concrete can be converted at a maximum rate of 1.25 concrete per second per tank. When switching from converting concrete to filling the water tank, the tank must be empty for one processing cycle.