To produce high quality concrete masonry units, block producers generally define concrete mixes by a trial process that makes it difficult to test new types of aggregates, such as Recycled Concrete Aggregate (RCA), because it interferes with production efficiency. Furthermore, block producers normally produce block in runs of thousands of units at a time, which makes it difficult to make many trial mixes with different RCA replacement ratios. The use of RCA for the production of concrete masonry units is explored in a laboratory setting by simulating the industrial manufacturing process.