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Paris Santa Fe-Frisco Depot Rehabilitation O KEYSTONE ARCHITECTS July 10, 2001 C. Mixing: 1. Prior to the placing of any concrete at the project, the Contractor shall submit to the Engineer for approval design mix formulas for the proposed mix which shall clearly state the proportions by weight and volume of each ingredient along with materials test results and air, slump and strength test results. It shall be the responsibility of the Contractor to furnish the concrete strengths as called for below. 2. Concrete for this work shall be designed for a compressive strength at 28 days of 3000 psi unless noted otherwise on plans, shall have a water cement ratio of not more than seven gallons of water per sack of cement, shall have entrained air of 3% - 5%, and shall have a slump of not more than six inches, except as approved by the Engineer, who may vary the slump for a more workable mix. Water reducing admixtures may permit greater initial slumps upon specific approval by Engineer. 3. Mixing shall be done in mixers of appr..oved design, opera.ting at th.e,manufac .ma'erls recommended speed and capacity. M~xers shall be eqmpped w~m automauc ttrne locks and water proportioning devices. Mixing time shall be not less than 10 minutes for mixers less than 27 cu. ft. capacity. Transit mixers shall mix the batch at least l0 minutes after the addition of water. Mix shall be mixed for a longer period of time if the mix shows signs of segregation, non-uniform consistency or early excess surface moisture. 4. Batching shall be done by weight using approved scales and devices. All weighing and measurements shall be capable of producing aggregate quantifies accurate to within 2% and cement to within 0.5%. Generally follow the recommendations of ACI 211, latest version. D. Placing: 1. Formwork shall be completed; excess water shall be removed; reinforcement shall be secured in place; expansion joint material, anchors, and other embedded items shall be positioned; and the entire preparation shall be reviewed by the Architect and the Engineer before placing concrete. 2. Concrete shall be placed in its final position as soon as possible after mixing and must be placed within two hours after water has been added to the dry materials. It should be placed in one continuous operation from construction joim to consu'uction joint. Do not permit more than 45 minutes to elapse before continuing placement against any fresh concrete that is not a construction joint. 3. In general it should not be necessary to add water to a properly designed and hatched mix. When necessary, minor adjustments may be made at the job, but care must be taken to prevent overwening the mix. In no case will retempering of concrete be allowed. 4. In placing, concrete shall not be allowed to drop a distance of more than six feet through free space except as noted for bored foundation piers or filled pipe piles. Internal ~~l~ltlal~, but should not be overdone. Care should be taken to keep the vibrators off the reinforcing steel, and to avoid segregation of the mix ingredients. 6. Concrete shall be placed in layers along beams and shall be well worked and vibrated into all comers and around all reinforcing steel. Concrete for slabs shall be Section 03300 Page 5-6