Advocates of mixtures containing well graded combined aggregates argue that such mixtures have optimized packing and minimal voids and therefore minimize the cementitious paste required for a given workability. Opponents of well graded combined aggregates argue that they don’t necessarily lead to optimized performance, but might actually cost more. In an effort to resolve the controversy, a study was conducted at the National Ready Mixed Concrete Association Research Laboratory to determine whether well graded combined aggregates improve aggregate packing density and concrete performance. A summary of the research report is provided in this article.