This specification covers mill-mixed gypsum concrete, consisting essentially of calcined gypsum and suitable aggregate, requiring the addition of water only at the job site. Gypsum concrete is intended for use in the construction of poured-in-place roof decks or slabs. Two classes, based on the compressive strength and density, are covered. Gypsum concrete shall consist of calcined gypsum to which are added aggregates, wood chips, or wood shavings in proportion to meet the applicable requirements of this specification. Test method in this specification shall be performed in order to determine the physical properties of the gypsum concrete. Setting time is determined by the Vicat method.