To provide a method for managing a ready-mixed concrete sludge capable of sensing an excess or an insufficiency of a setting retarder added to a sludge water and immediately dealing with it in a method for not discharging a waste from a factory by reusing the sludge water obtained by cleaning an apparatus in which a ready-mixed concrete is adhered with water containing the retarder and then removing the aggregate, as a part of a kneaded water of a cement after next day or the following day.

In the method for reusing the sludge water obtained by cleaning an apparatus in which a ready mixed concrete is adhered with water containing the retarder and then removing the aggregate, as a part of a kneaded water of a cement after next day or the following day, a sensor including a communication system for transmitting signal for sensing an amount of the setting retarder in a setting retarder tank after finishing a work and a signal for sensing an amount and a concentration of the sludge water in a sludge tank to a control center is provided, and a trouble due to an introduction of the excess retarder is avoided.