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5.3 CHANGES IN PROPORTIONING <br />5.3.1 CHANGES BY ENGINEER <br />Should it be impossible to obtain concrete of the required strength <br />and workability; changes in proportions, materials, or both may be <br />made by the Engineer. <br />5.3.2 CHANGES BY CONTRACTOR <br />Changes by the Contractor, during the progress of work, may be <br />made in proportions or materials originally approved. Evidence, <br />satisfactory to the Engineer, shall be submitted showing that new <br />materials or conditions proposed shall produce concrete meeting <br />the specific requirements. <br />5,3.3 STATEMENT OF PROPOSED PROPORTIONING <br />A statement of the proposed concrete proportioning shall be <br />submitted for approval by the Engineer prior to the placing of any <br />concrete. <br />6 MIXING AND TRANSPORTATION OF CONCRETE <br />Concrete shall be mixed and transported in approved equipment in a manner that <br />will deliver uniform and homogeneous concrete to the forms as recommended in <br />ACI 301. <br />6.1 READY-MIXED CONCRETE <br />Job-mixed concrete shall be mixed and transported in accordance with <br />ASTM C 94. <br />6.2 HAND-MIXED CONCRETE <br />Hand mixing shall be permitted only for grouting mortar and neat cement <br />grout. <br />6.3 MIXING EQUIPMENT <br />6.3.1 Mixers may be stationary mixers or truck mixers. Agitators may be <br />truck mixers or truck agitators. Truck mixers shall be equipped <br />with approved revolution counters and water meters. Stationary <br />mixers shall be equipped with an acceptable timing device that will <br />not permit the batch to be discharged until the specified mixing <br />time has elapsed. <br />6.3.2 Each unit shall have attached thereto, in a prominent place, a metal <br />plate or plates on which are plainly marked the various uses for <br />which the equipment is designed. Information shall include the <br />volumetric capacity of mixed concrete the drum or container can <br />hold and the speed of rotation of the mixing drum, blades, or <br />paddles. <br />SPEC B • CONCRETE <br />PAGE 9 <br />