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3.05 MIXING CONCRETE: <br />A. The mixer and mixing time shall be in accordance with ACI 304. Hot weather <br />concreting shall comply with ACI 305, and cold weather concreting with ACI <br />306. <br />B. No additional water shall be added to batched concrete without the permission of <br />the Engineer. Such water shall be incorporated by additional mixing equal to at <br />least half of the total mixing required for the batch. Any addition of water above <br />that permitted by the limitation on specified water -cement ratio, shall be <br />accompanied by a quantity of cement sufficient to maintain the proper water - <br />cement ratio. <br />C. Concrete shall be mixed only in such quantities as are required for immediate use. <br />The maximum allowable time between charging of the material in the mixing <br />drum and final placing for mean ambient temperatures below 90°F shall be ninety <br />(90) minutes or 300 drum revolutions, whichever comes first. Concrete to be <br />delivered when the mean ambient temperature exceeds 90°F shall be mixed and <br />delivered in accordance with the requirements of ACI 305 "Guide to Hot -Weather <br />Concreting". Concrete not placed within these time limits, or if an initial set has <br />developed, shall not be used. Tempering concrete by adding water or by other <br />means will not be permitted. <br />3.06 PLACING CONCRETE: <br />A. Concrete shall not be placed prior to a recorded pre -placement inspection and <br />authorization to proceed by the Owner's Representative. <br />B. The slump may be increased up to 6 inches if concrete pumping is to be used. <br />The proposed mix design for pumped concrete shall be approved in advance by <br />the Engineer. <br />C. Conveying and placing of concrete shall be in accordance with ACI 304. <br />D. Each day's pour shall be properly scheduled to assure that concrete surfaces can <br />be finished correctly and the use of cold joints can be minimized. <br />E. All concrete shall be mechanically vibrated, except for slabs on grade that are six <br />inches or less in thickness. <br />F. Concrete shall be placed in layers not over 24 inches deep. Each layer shall be <br />consolidated by mechanical internal -vibrating equipment supplemented by hand <br />spading, rodding, and tamping to work concrete into all angles and narrow places. <br />Duration of vibration shall be limited to the time necessary to produce satisfactory <br />consolidation without causing objectionable segregation. Vibrators shall be <br />applied vertically and at uniformly spaced points not farther apart than the visible <br />