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6.3.3 If requested, the Contractor shall provide a Concrete Truck Mixer <br />Certification. This certification shall show the various pick-up and <br />throw-over configurations and wear marks so that the wear on the <br />blades can be checked. Blades shall be replaced when any part or <br />section is worn one inch I1 ") or more below the original height of <br />the manufacturer's design. A copy of the manufacturer's design, <br />showing the dimensions and arrangement of blades, shall be <br />available to the Engineer at all times. <br />6.4 MIXING AND DELIVERY <br />Concrete shall be mixed and delivered alongside the forms with one of the <br />following combinations of operations: <br />6.4.1 CENTRAL MIXED <br />The materials completely mixed in a stationary mixer and trans- <br />ported to the delivery point in a truck agitator, a truck mixer <br />operating as a truck agitator, or an approved non-agitating truck. <br />6.4.2 SHRINK MIXED <br />The materials partially mixed or blended in a stationary mixer and <br />the mixing completed in a truck mixer enroute to or at the job. <br />6.4.3 TRANSIT MIXED <br />The materials completely mixed in a truck mixer. <br />6.5 TRUCK MIXING <br />Concrete mixed entirely in a truck mixer equipped with a mechanical <br />counter shall be partially mixed at the plant or in transit for not less than <br />20 revolutions of the drum at mixing speed. The revolutions of the drum <br />at charging speed shall not be counted as mixing revolutions. The <br />concrete shall be mixed between fifty and one hundred (50 & 100) <br />revolutions of the mixer drum at mixing speed at the delivery site before <br />discharge of the concrete. <br />6.6 LOAD CONTROL <br />The Engineer will take slump tests made from samples taken at approxi- <br />mately the one-quarter (1/4) and three-quarter (3/4) points of the load. <br />When the above pairs of slumps differ by more than two inches 12") the <br />truck or agitator will not be re-used until the condition causing this non- <br />uniformity has been corrected. <br />6.7 RETEMPERING <br />Water shall not be added to mixed batches of concrete to increase the <br />slump without specific written authorization of the Engineer. When <br />batches delivered to the job show an unduly low slump las might occur <br />during hot weatherl, the Engineer, at his sole discretion may grant <br />permission for the Contractor to use retarders. <br />SPEC B -CONCRETE <br />PAGE 10 <br />