Specifications include, but are not limited to: 5.7 Concrete Mixture: Supplier shall: a. Prepare design mixtures for each type and strength of concrete, proportioned on the basis of laboratory trail mixture, according to ACI 301: 1. The mix designs shall be submitted at least three weeks prior to placement. 2. Shall be prepared by an approved independent testing laboratory utilizing the ACI 211.1 Trail. 3. Batch method with at least three points batched and plotted on a curve showing water/cementratious versus compressive or flexural strength. 4. Trail batches and design shall have been performed within 12 months of submittal. 5. Changes to approved mix designs or materials are not allowed without written approval of the District Engineer. b. Cementitious Materials, use fly ash pozzolan, ground granulated blast-furnace slag, and silica fume as needed to reduce the total amount of Portland cement, which would otherwise be used, by not less than 40 percent. c. Proportion normal weight concrete mixture for foundations and miscellaneous concrete shall meet or exceed the following requirements: 1. Minimum Compressive Strength 4500 psi at 28 days. 2. Maximum Water-Cementitious Materials Ratio 0.45. 3. Slump Limit 3 inches for before adding high-range water-reducing admixture or plasticizing admixture, plus or minus 1 inch. 4. Air Content 6 percent, plus or minus 1.5 percent at point of delivery.
