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maximum permissible mass variation above,except that no scale shall be required having a capacity of less than 500 kg,with <br /> 0.5-kg graduations. <br /> 90-5.03 PROPORTIONING <br /> • Proportioning shall consist of dividing the aggregates into the specified sizes, each stored in a separate bin, and <br /> combining them with cementitious material and water as provided in these specifications. Aggregates shall be proportioned <br /> by mass. <br /> • At the time of batching,aggregates shall have been dried or drained sufficiently to result in a stable moisture content <br /> such that no visible separation of water from aggregate will take place during transportation from the proportioning plant to <br /> the point of mixing. In no event shall the free moisture content of the fine aggregate at the time of batching exceed 8 percent <br /> of its saturated,surface-dry mass. <br /> • Should separate supplies of aggregate material of the same size group,but of different moisture content or specific <br /> gravity or surface characteristics affecting workability, be available at the proportioning plant, withdrawals shall be made <br /> from one supply exclusively and the materials therein completely exhausted before starting upon another. <br /> • Bulk Type IP(MS)cement shall be weighed in an individual hopper and shall be kept separate from the aggregates <br /> until the ingredients are released for discharge into the mixer. <br /> • Bulk cement and supplementary cementitious material may be weighed in separate, individual weigh hoppers or <br /> may be weighed in the same weigh hopper and shall be kept separate from the aggregates until the ingredients are released <br /> for discharge into the mixer. If the cement and supplementary cementitious material are weighed cumulatively,the cement <br /> shall be weighed first. <br /> • If cement and supplementary cementitious material are weighed in separate weigh hoppers,the weigh systems for <br /> the proportioning of the aggregate,the cement,and the supplementary cementitious material shall be individual and distinct <br /> from all other weigh systems. Each weigh system shall be equipped with a hopper, a lever system, and an indicator to <br /> constitute an individual and independent material weighing device. The cement and the supplementary cementitious material <br /> shall be discharged into the mixer simultaneously with the aggregate. <br /> • The scales and weigh hoppers for bulk weighing cement, supplementary cementitious material, or cement plus <br /> supplementary cementitious material shall be separate and distinct from the aggregate weighing equipment. <br /> • For batches of one cubic meter or more,the batching equipment shall conform to one of the following combinations: <br /> A. Separate boxes and separate scale and indicator for weighing each size of aggregate. <br /> B. Single box and scale indicator for all aggregates. <br /> C. Single box or separate boxes and automatic weighing mechanism for all aggregates. <br /> • In order to check the accuracy of batch masses, the gross mass and tare mass of batch trucks, truck mixers, truck <br /> agitators, and non-agitating hauling equipment shall be determined when ordered by the Engineer. The equipment shall be <br /> weighed on scales designated by the Engineer. <br /> 90-5.03A PROPORTIONING FOR PAVEMENT <br /> • Aggregates and bulk supplementary cementitious material for use in pavement shall be proportioned by mass by <br /> means of automatic proportioning devices of approved type conforming to these specifications. <br /> • The Contractor shall install and maintain in operating condition an electronically actuated moisture meter that will <br /> indicate,on a readily visible scale,changes in the moisture content of the fine aggregate as it is batched within a sensitivity of <br /> 0.5 percent by mass of the fine aggregate. <br /> • The batching of cement, supplementary cementitious material,or cement plus supplementary cementitious material <br /> and aggregate shall be interlocked so that a new batch cannot be started until all weigh hoppers are empty,the proportioning <br /> devices are within zero tolerance, and the discharge gates are closed. The interlock shall permit no part of the batch to be <br /> discharged until all aggregate hoppers and the cement and supplementary cementitious material hoppers or the cement plus <br /> supplementary cementitious material hopper are charged with masses that are within the tolerances specified in <br /> Section 90-5.02,"Proportioning Devices." <br /> • If interlocks are required for cement and supplementary cementitious material charging mechanisms and cement and <br /> supplementary cementitious material are weighed cumulatively, their charging mechanisms shall be interlocked to prevent <br /> the introduction of mineral admixture until the mass of cement in the cement weigh hopper is within the tolerances specified <br /> in Section 90-5.02,"Proportioning Devices." <br /> • If concrete is completely mixed in stationary paving mixers, the supplementary cementitious materials shall be <br /> weighed in a separate weigh hopper and the supplementary cementitious material and cement shall be introduced <br /> simultaneously into the mixer proportionately with the aggregate. If the Contractor provides certification that the stationary <br /> mixer is capable of mixing the cement, supplementary cementitious material, aggregates, and water uniformly before <br /> Contract No. 10-OM7104 <br /> 80 <br />