Abstract: A concrete mixer is disclosed having a mixing drum and a drag body is mounted in the drum which has a drag surface positioned to at least partially come into contact with concrete in the drum during a measuring phase in the concrete mixing operation. A hydraulic driving circuit is provided to oscillate the drag body at least during the measuring phase. A pressure sensor is connected in the hydraulic driving circuit for measuring the actual pressure value in the hydraulic driving circuit which is indicative of the flow resistance on the drag surface during the measuring phase of the mixing operation.

Abstract: The invention relates to a concrete mixer truck having a rotatably driven mixer drum, particularly a drum provided with interior mixing elements, and a hydraulic system as a drive source for the mixing process.It is intended to enhance the effect of the mixing process by transmitting vibration energy to the mixture materials. To this effect, a vibration generator is included in the hydraulic system in such a manner that pressure pulses generated in the flow of the hydraulic fluid are superimposed on the mixing movement in the form of vibrations. This superposition effect may be achieved with respect to the rotation of the drum and/or with respect to the movements of a separate mixing tool.