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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 <br />permitted. Adding water in controlled amounts during the mixing <br />cycle shall be done only with the express approval of, and under the <br />direction of, the Engineer. <br />1 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 <br />capacities for the respective conditions as stated on the name plate. <br />Discharge at the site shall be within 1-1/2 hours and within one hour <br />when ambient temperature is above 85 degree F after cement was <br />first introduced into the mix. Central mixed concrete shall be <br />plant -mixed a minimum of 1-1/2 minutes per batch and then shall be <br />truck -mixed or agitated a minimum of 8 minutes. Agitation shall begin <br />immediately after the pre -mixed concrete is placed in the truck and <br />shall continue without interruption until discharge. Transit -mixed <br />concrete shall be mixed at mixing speed for at least 10 minutes <br />1 immediately after charging the truck, followed by agitation without <br />interruption until discharged. <br />1 C. All central plant and rolling stock equipment and methods shall <br />conform to the latest Truck Mixer and Agitator Standards of the Truck <br />Mixer Manufacturers' Bureau of the National Ready -Mixed Concrete <br />F� <br />Association, as well as ACI Standard 304 and ASTM Specification <br />C94. <br />D. The retempering of concrete or mortar which has partially hardened, <br />that is, mixing with or without additional cement, aggregate, or water, <br />will not 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 <br />before the concrete is required, thus avoiding excessive mixing of <br />concrete while waiting or delays in placing successive layers of <br />concrete in the forms. <br />3.03 FIELD TESTS <br />1 07/03 <br />A. Sets of four field control cylinder specimens will be taken at random <br />by the Engineer during the progress of the work, in conformity with <br />ASTM Designation C31; the total number of specimens taken on the <br />project may average one set per 150 cu yds, and in general not less <br />than one set of specimens will be taken on any one day when <br />concrete is being placed. When average ultimate 28 -day strength of <br />control cylinders in any set falls below the required ultimate strength <br />03300 -8 03- 3148.A <br />