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2.06 MIXING <br /> Concrete may be mixed at the site of the work,in a central-mix plant,or in truck mixers. Mixing time shall <br /> be measured from the time water is added to the mix,or cement contacts the aggregate. All concrete shall <br /> be homogeneous and thoroughly mixed,and there shall be no lumps or evidence of undispersed cement. <br /> Mixers and agitators which have an accumulation of hard concrete or mortar shall not be used. Ready- <br /> mixed concrete shall be mixed and delivered in accordance with ASTM C94. <br /> A. General <br /> The temperature of mixed concrete,immediately before placing shall not be less than 50'F nor <br /> more than 90'F. Aggregates and water shall be heated or cooled as necessary to produce concrete <br /> within these temperature limits. Neither aggregate nor mixing water shall be heated to exceed <br /> 1500 F. <br /> When mixed at the site of the work or in a central-mixing plant,the mixing time shall not be less <br /> than 50 seconds nor more than 90 minutes. <br /> The time elapsing from the time water is added to the mix(or the cement comes in contact with <br /> aggregate)until the concrete is deposited in place at the site of the work shall not exceed 45 <br /> minutes when the concrete is hauled in non-agitating trucks,nor more than 90 minutes when <br /> hauled in truck mixers or truck agitators. If hydration inhibitors are used,this time may be <br /> extended. Contractor shall submit all admixtures as part of mix design. <br /> The batch shall be so charged into the drum that a portion of the mixing water shall enter in <br /> advance of the cement and aggregates. The flow of water shall be uniform and all water shall be <br /> in the drum by the end of the first 1/4 of the specified mixing time. <br /> Cement shall be charged into the mixer by means that will not result in loss of cement due to the <br /> effect of wind,or in accumulation of cement on surfaced of hoppers or in other conditions which <br /> reduce or vary the required quantity of cement in the concrete mixture. <br /> 2.07 TRANSPORTING MIXED CONCRETE-MIXED CONCRETE OR TRUCK MIXERS <br /> Truck agitators shall be loaded not to exceed the manufacturer's guaranteed capacity. They shall maintain <br /> the mixed concrete in a thoroughly mixed and uniform mass during hauling. <br /> No additional mixing water shall be incorporated into the concrete during hauling or after arrival at the <br /> delivery point,unless requested by Contractor and approved by the Engineer. If additional water is to be <br /> incorporated into the concrete,the drum shall be revolved not less than 30 revolutions at mixing speed after <br /> the water is added and before discharge is commenced. <br /> The Contractor shall furnish a water measuring device in good working condition,mounted on each transit <br /> mix truck,for measuring the water added to the mix on the site by the Engineer. <br /> Each load of ready mixed concrete delivered at the job site shall be accompanied by the ticket showing <br /> volume of concrete,the weight of cement in pounds,the total weight of all ingredients in pounds,and <br /> amount of additional water that can be added on-site. The ticket shall also show the time of day at which <br /> the materials were batched and the reading of the revolution counter at the time the truck mixer is charged. <br /> 2.08 COMPRESSIVE STRENGTH <br /> A. Structural Concrete <br /> Structural concrete compressive strength requirements consist of a minimum strength which must <br /> be obtained before various loads or stresses are applied to the concrete and,for concrete <br /> 9/17 Section 03310-Page 3 of 8 <br />