DIVISION 1 - GENERAL REQUIREMENTS - IDEAS-EC

3.4 MIXINGA. When the concrete is mixed completely in a truck mixer, 70 to 100 revolutions at the mixing speedspecified by the manufacturer are required to produce uniformity of the concrete.3.5 PLACING OF CONCRETEA. Preparation Before Placing:1. Remove hardened concrete and foreign materials from inner surfaces of conveyingequipment.2. Check formwork for completion, check position and securement of reinforcement, jointmaterial, sleeves, anchors, and other embedded items, and obtain approval on entirepreparation.3. Remove ice and excess water and sprinkle semiporous subgrades sufficiently to eliminatesuction.4. Do not place concrete on frozen ground.5. Do not place concrete during rain, sleet, or snow unless protection is provided.B. Depositing:1. Place concrete in final position to avoid segregation due to rehandling or flowing.2. Direct concrete down the center of forms. Use drop chutes where necessary to prevent thestream of concrete from being separated by striking reinforcing or other embedded objects.3. Spread concrete in horizontal lifts between 6 inches and 20 inches high. Lifts shall be of aheight to minimize surface defects and eliminate rock pockets.4. Deposit concrete continuously and rapidly enough so that the layer supporting the one beingplaced is still plastic. If continuous placement is impossible, locate construction joints whereshown or as approved. Do not deposit concrete that has partially hardened or becomecontaminated by foreign material.5. Remove temporary form spreaders when concrete reaches them.C. Compacting:1. Use high frequency vibrators in the placement of concrete forms. When concrete is beingplaced on hardened concrete or in bottom of forms, exercise care to ensure completeconsolidation. After the initial lift, vibrator shall penetrate through and into top of previouslift of concrete.2. Internal vibrators shall have a minimum frequency of 8,000 rpm. Overvibrating and use ofvibrators to transport concrete within forms shall not be allowed. Insert and withdrawvibrators at many points, from 18 to 30 inches apart, for 5 to 15-second duration. Keep aspare vibrator on the project site during all concrete placing operations.3. Once concreting is started, it shall be carried on as a continuous operation until the placing ofthe panel or section is completed, preventing fresh concrete from being deposited onconcrete which has hardened sufficiently to cause formation of seams and planes ofweakness within the section.4. Remove splashes or accumulations of hardened or partially hardened concrete or mortar onforms or reinforcement above general level of the concrete already in place before the workproceeds.5. Maintain reinforcement in proper position during concrete placement operations.3.6 FORM REMOVALA. Carefully remove forms to ensure the safety of the structure and avoid damage to concrete.03300 - 1004/07 CAST-IN-PLACE CONCRETE