Abstract: A method of and device for improving the quality of fresh concrete and preventing adhesion and hardening of the mixed fresh concrete in a rotary mixer drum of a concrete mixer truck or a stationary mixer drum of a concrete mixer plant which involves delivering selectively and continuously either cold or warm air into the mixed fresh concrete in the rotary or stationary concrete mixer drum in order to delay the hardening time of the mixed fresh concrete, and to avoid adhesion and hardening of the mixed fresh concrete on a plurality of blades and an inner periphery of the mixer drum.