A system features an acoustic sensor configured to mount on a wall of a mixing drum, sense an acoustic characteristic of a mixture of a slurry, including concrete, contained in a mixing drum when rotating, and provide acoustic sensor signaling containing information about the acoustic characteristic sensed; and a signal processor configured to receive the acoustic sensor signaling, and determine corresponding signaling containing information about a slump characteristic of the mixture of concrete contained in the mixing drum, based upon the signaling received.