The purpose of the investigation was to either validate or disprove the assumption that a water-cement ratio (W/C) in excess of 0.8 by weight for interior concrete containing 4-1/2-in. maximum size aggregate can be used in mass concrete construction, and to compare the properties of concrete containing 4-1/2-in. maximum size aggregate with those of the concretes containing 3- and 6-in. maximum size aggregates. The investigation consisted of a laboratory test program in which a series of six lean mass concrete mixtures, both with and without pozzolan, containing 4-1/2-in. maximum size aggregate were proportioned with identical W/C's that had been selected from the work of a previous investigation. Specimens were cast and tests were made to evaluate the mixtures for workability, strength, permeability, and durability.