by means of a hinge 9 which facilitates mounting of the drum in its operative position and which is locked upon completion of the assembly the inner wall of the drum is provided with helical blades 12 of relatively large pitch whereby concrete fed into the drum through the opening 2 is drawn toward the drum bottom 3 upon rotation of the drum in one direction and whereby the concrete is discharged through the opening 2 upon rotation of the drum in the other direction the blades 12 are laid out so as to be specifically adapted for conveying concrete for transmitting driving torque to the drum a ring gear 13 is secured thereto exteriorly of the drum bottom 3 the ring gear 13 meshes with a pinion 14 fig3 of a fluid motor indicated at 15 the fluid motor 15 is mounted on a rocker arm 16 which is pivoted at its inner end on the stub shaft 7 at its outer end the rocker arm 16 is stabilized relative to the frame 4 by means of a movable torque brace 17 the fluid motor 15 is driven via hydraulic conduit lines by a pump not shown which is mounted on the frame 4 and driven by the internal combustion engine of the vehicle as by a separate motor provided within.