Apparatus and methods produce substantially continuous batches of high-strength concrete. Portland cement, flyash, sand, water, and concrete chemical additives are premixed in a multi-stage process, prior to final mixing with the coarse aggregates. In sequence, the complete mixing process includes: 1) a twin-shaft compulsory mixer to blend the materials, then disposing the mixture into; 2) a horizontal screw conveyor, continuously mixing as the mixture passes through the housing, thereby disposed simultaneously with the coarse aggregates into; and 3) the mixer concrete delivery truck, wherein the concrete is mixed further.