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<br />002420 <br /> <br />Durango Pumoing Plant - Stage 1 <br /> <br />2.03 COMPOSITION (MIXES) <br /> <br />A. Composition <br /> <br />I. Provide concrete composed of cement, pozzolan, sand, coarse aggregate, water, <br />and admixtures as specified, all well mixed and brought to the proper consistency. <br /> <br />B. Nominal Maximum Size of Aggregate <br /> <br />I. Use coarse aggregate in concrete as large as practicable, consistent with required <br />strength, spacing of reinforcement and embedded items, and placement thickness. <br /> <br />a. Use 2-inch, nominal, maximum-size aggregate in mass structural concrete <br />placements. <br /> <br />b. Use I-inch, nominal, maximum-size aggregate in structural concrete <br />placements. <br /> <br />c. Use I-inch coarse aggregate if the Contracting Officer determines that <br />proper placement of concrete with 2-inch, nominal, maximum size <br />aggregate is impractical. <br /> <br />C. Mix Proportions <br /> <br />1. Concrete mixes will be determined by the Government. <br /> <br />2. The proportions of ingredients will be established in accordance with test <br />procedure 421 1 ofUSBR Concrete Manual. Pozzolan shall be 20 percent, by <br />weight, of cementitious materials for concrete, except for mass structural <br />concrete. <br /> <br />3. The pozzolan content for mass structural concrete shall be 30 percent, plus or <br />minus 10 percent. The Government will adjust the percent pozzolan based on the <br />results of compressive strength tests and temperature rise tests in order to <br />minimize thermal cracking. <br /> <br />4. The Government will test concrete for compliance with specifications and shall <br />design and adjust the concrete mix proportions. <br /> <br />5. The proportions will be adjusted by the Government during the progress of the <br />work whenever the need for adjustment is indicated by test results for aggregates <br />and concrete. <br /> <br />6. Adjust as directed to obtain concrete having suitable workability, impermeability, <br />density, strength, and durability without the use of excessive cement. <br /> <br />7. Concrete strength: <br /> <br />a. 90 percent of all test cylinders exceed the design strength. <br /> <br />b. Structural and mass structural concrete: 4,000 pounds per square inch at <br />28 days. <br /> <br />c. Lean concrete: 3,000 pounds per square inch at 28 days. <br /> <br />Cast-in-Place Concrete <br />03300.16 <br />