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3. The mixing operation shall begin within thirty (30) minutes after the cement has been <br />intermingled with the aggregates. <br />4. Truck -mixed concrete requires 70 to 100 revolutions at the mixing speed designated <br />by the manufacturer to produce uniform concrete. <br />5. If additional time elapses between initial mixing and discharge, the mixer is to be <br />operated at mixing speed for approximately 30 revolutions to enhance uniformity <br />prior to discharge. <br />6. The concrete shall be delivered to the site of the work and discharge shall be <br />completed within ninety (90) minutes or before the drum has been revolved 300 <br />revolutions, whichever comes first, after the introduction of the mixing water to the <br />cement and aggregates, or the introduction of the cement to the aggregates, when the <br />air temperature is 90° F or less. <br />7. When the air temperature exceeds 90° F, concrete shall be placed within a time <br />depending on air temperature and humidity as set forth by the guidelines of ACI 305 <br />— Hot Weather Concreting to prevent the temperature of the concrete from reaching <br />80° F. <br />8. On very hot days, the time for placement may be reduced to 30 minutes. The <br />Contractor shall schedule concrete pours for evening hours when hot days are <br />anticipated. <br />9. Truck mixers shall be revolving drum type and shall be equipped with a mixing water <br />tank. Only the prescribed amount of mixing water shall be placed in the tank for any <br />one batch, unless the tank is equipped with a device by which the amount of water <br />added to each batch can be readily verified. <br />10. No water from the truck mixer water system or elsewhere shall be added after the <br />initial introduction of mixing water for the batch, except when on arrival at the job <br />site the slump of the concrete is less than that specified. The drum shall be turned an <br />additional 30 revolutions, or more if necessary, at mixing speed. Water will not be <br />added to the batch at any later time. <br />1.5 JOB CONDITIONS <br />A. Environmental Requirements. <br />1. Do not place concrete during rain, sleet, or snow unless adequate protection is <br />provided and Engineer's approval is obtained. <br />2. Do not allow rain water to increase mixing water or damage surface finish. <br />Cast -In -Place Concrete February 2017 03300-5 <br />