Q.: If I specify strength, air content, and slump when I order concrete, is the ready-mixed concrete supplier obligated in any way to tell me the mix proportions? I haven't been getting this information, and though I don't absolutely have to know what material and how much of each material is in the mix, I'd feel a lot better if I had the information.
A.: The information might not only make you feel better, but might eventually lead you toward participation in more careful selection of mixes. ASTM C 94, Section 5.3.1 provides that "when the purchaser requires the manufacturer to assume full responsibility for the selection of the proportions for the concrete mixture...the purchaser shall also specify" 28-day or other compressive strength. Section 5.3.2 says "At the request of the purchaser [italics ours] the manufacturer shall, prior to the actual delivery of the concrete, furnish a statement to the purchaser, giving the dry weights of cement and saturated surface-dry-weights of fine and coarse aggregate and quantities, and name of admixtures (if any) and of water per cubic yard or cubic meter of concrete that will be used in the manufacture of each class of concrete ordered by the purchaser. [The manufacturer] shall also furnish evidence satisfactory to the purchaser that the materials to be used and proportions selected will produce concrete of the quality specified." All you should have to do is ask.