Abstract: A method and apparatus for mixing concrete in a concrete delivery mixing truck is provided which can yield a mix with an approximate required slump. This is achieved by monitoring the torque loading on hydraulic drive which rotates a mixing barrel and noting an anticipated minimum torque loading which, in turn, approximates to a required slump value. Liquid component is added to a mix until this minimum torque loading is noted. A CPU (17) is used to process information derived from a hydraulic pressure sensor (15) connected in the hydraulic drive motor used to rotate the mixing barrel. A volume/mass input sensor (21) can be used for meaning the amount of particulate ingredients, and a water volume sensor (25) can be used to measure the volume of liquid component added to the mix. When a known maximum volume of liquid component is added a computer can operate to prevent further liquid being added, unless it is purposely overridden.