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B. Water shall be measured by volume or by weight. The water - measuring <br />device shall be capable of control to 1/2% accuracy. All measuring <br />devices shall be subject to approval. Admixtures shall be dispensed <br />either manually with use of calibrated containers or measuring tanks, or <br />by means of an approved automatic dispenser designed by the <br />manufacturer of the specified admixture. <br />3.02 MIXING <br />A. Concrete shall be ready -mixed or transit - mixed, as produced by <br />equipment acceptable to the Engineer. No hand - mixing will be permitted. <br />Adding water in controlled amounts during the mixing cycle shall be done <br />only with the express approval of, and under the direction of, the <br />Engineer. <br />B. Ready -mix or transit -mixed concrete shall be transported to the site in <br />watertight agitator or mixer trucks loaded not in excess of rated capacities <br />for the respective conditions as stated on the name plate. Discharge at <br />the site shall be within 1 -1/2 hours and within one hour when ambient <br />temperature is above 85 degree F after cement was first introduced into <br />the mix. Central mixed concrete shall be plant -mixed a minimum of 1 -1/2 <br />minutes per batch and then shall be truck -mixed or agitated a minimum of <br />8 minutes. Agitation shall begin immediately after the pre -mixed concrete <br />is placed in the truck and shall continue without interruption until <br />discharge. Transit -mixed concrete shall be mixed at mixing speed for at <br />least 10 minutes immediately after charging the truck, followed by <br />agitation without interruption until discharged. <br />C. All central plant and rolling stock equipment and methods shall conform to <br />the latest Truck Mixer and Agitator Standards of the Truck Mixer <br />Manufacturers' Bureau of the National Ready -Mixed Concrete <br />Association, as well as ACI Standard 304 and ASTM Specification C94. <br />D. The retempering of concrete or mortar which has partially hardened, that <br />is, mixing with or without additional cement, aggregate, or water, will not <br />be permitted. <br />E. Attention is called to the importance of dispatching trucks from the <br />batching plant so that they shall arrive at the site of the work just before <br />the concrete is required, thus avoiding excessive mixing of concrete while <br />waiting or delays in placing successive layers of concrete in the forms. <br />December 2006 03300 -8 06 -5723 <br />