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PGSF WMVD Storm and Combined Sewer - Construction Package 2 Cast-in-Place Concrete <br />Project No. 180162 03 30 00 - 14 <br /> <br />c. Before starting each pumping operation, prime the pump and line with a cement <br />slurry to lubricate the system. Waste cement slurry outside the forms. Equip hose <br />tip with a safety chain for recovery in case of hose blowout during pumping. Hose <br />or accessories shall not remain in the freshly placed concrete. <br />d. Use tremie placing techniques and equipment for pump placed concrete. Pump <br />discharge system shall remain full of concrete from pump to discharge point at <br />all times. Concrete pumping shall not occur until Owner’s Representative has <br />verified equipment including the tremie plug. Should the discharge line become <br />open, with zones empty of concrete, cease pumping and re-primed with tremie <br />plug installed before continuing. <br />3. Placing Concrete In Hot Weather: <br />a. In temperatures above 80 degrees F, place concrete in accordance with <br />ACI 305.1. <br />4. Placing Concrete In Cold Weather: <br />a. In temperatures below 40 degrees F, place concrete in accordance with <br />ACI 306.1. <br />5. Tremie Concrete: <br />a. To place concrete under water, use tremie placing techniques with equipment <br />and procedures for pump placed concrete as stated above. <br />1) Tremie/Seal Slab: <br />a) Place concrete in the slab by tremie tube (minimum 10 inch heavy gauge <br />steel pipes) pumping to avoid separation and segregation of the concrete <br />mix components. Separate the first concrete placed from the fluid in the <br />excavation using a plug in the tube, or other approved device. <br />b) Continuously place concrete until the tremie tube or pumping pipe is <br />removed from concrete at completion of the placement. If the area to be <br />placed exceeds 15 feet in any dimension, provide multiple, pre-positioned <br />tubes spaced at no more than 15 feet apart. Pump from one tube to the <br />next until the subsequent tube is sufficiently embedded into the fresh <br />concrete. Continue the placement by pumping into the next tube, and so <br />on until the entire slab is placed. <br />2) Maintain a minimum 12 inches of tremie pipe embedment in the concrete <br />during concrete placement. If at any time during the pour, the tremie pipe <br />orifice is removed from the concrete and concrete is discharged above the <br />rising concrete level, the placement will be considered to be defective and <br />corrective measures taken at Contractor’s expense. <br />3) If the tremie slab thickness exceeds 36 inches, it will be considered mass <br />concrete where precautions shall be taken to minimize thermal cracking. <br />Tremie slab concrete mix shall be pre-cooled such that the temperature of <br />the concrete delivered to the site does not exceed 70 degrees F. Methods of <br />pre-cooling the concrete mix include cooled batch water, shaded aggregates <br />and cement, and coarse aggregate stockpiles sprayed with water for an <br />evaporative cooling effect.