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002426 Durango Pumoing Plant - Stage 1 15. Aggregate will be rejected if it contains frozen particles. I B. Mixing 1. Thoroughly mix the concrete ingredients in mixers designed to ensure uniform distribution of all the component materials throughout the concrete at the end of the mixing period. 2. Mix batch size at least 10 percent of, but not in excess of, the rated mixing capacity of the mixer. 3. Admit water prior to and during charging of the central mixer with all other concrete ingredients. 4. If a central mixer is used, mix each batch for not less than 90 seconds after all materials are in the mixer. Increase the mixing time if concrete does not meet the uniformity requirements of ASTM C 94, annex AI. 5. Excessive overmixing which requires additions of water to maintain the required concrete consistency will not be permitted. 6. Continue initial mixing for truck mixers for not less than 70 revolutions nor more than 100 revolutions of the drum after all the ingredients, except approximately 5 percent of the water which may be withheld for tempering, are in the drum. 7. Provide a mixing speed of not less than 12 revolutions per minute nor more than 22 revolutions per minute. 8. Do not add additional water exceeding the design water content after the initial introduction of water to the concrete. 9. If the batched water content is less than the design water content, additional tempering water may be added to the concrete on arrival to the placement when the concrete slump is less than specified; however do not exceed the design water content and specified slump. After this tempering, do not add additional water to the concrete. 10. Continue mixing after adding tempering water, at the specified mixing speed for a minimum of 30 revolutions. After a prolonged period of agitation, 10 to 15 revolutions of the drum at mixing speed will be required just prior to discharging. Complete discharge of the concrete before the drum has revolved a total of300 revolutions. 11. Provide a batch ticket with each batch of concrete when delivered at the jobsite from commercial ready-mix plants, in accordance with ASTM C 94. C. Temperature I. Place concrete at a concrete temperature between 50 and 85 degrees F, except for mass structural concrete and place mass structural concrete at temperatures between 50 and 70 degrees F. 2. Determine the concrete temperature by placing a thermometer in the concrete immediately after sampling at the placement site. Cast-in-Place Concrete 03300 - 22