shall be provided that will be capable of measuring and batching the
mixing water within the specified tolerances for each batch. The
mechanism for delivering water to the mixers shall be free from leakage
when the valves are closed. The filling and discharge valves for the
water batcher shall be so interlocked that the discharge valve cannot
be opened before the filling valve is fully closed. When a water meter
is used, a suitable strainer shall be provided ahead of the metering
device.
c. Admixture Dispensers - A separate batcher or dispenser shall be
provided for each admixture. Each plant shall be equipped with the
necessary calibration devices that will permit convenient checking of
the accuracy of the dispensed volume of the particular admixture. The
batching or dispensing devices shall be capable of repetitively
controlling the batching of the admixtures to the accuracy specified.
Piping for liquid admixtures shall be free from leaks and properly
valved to prevent backflow or siphoning. The dispensing system shall
include a device or devices that shall detect and indicate the presence
or absence of the admixture or provide a convenient means of visually
observing the admixture in the process of being batched or discharged.
Each system shall be capable of ready adjustment to permit varying the
quantity of admixture to be batched. Each dispenser shall be
interlocked with the batching and discharge operations so that each
admixture is added separately to the batch in solution in a separate
portion of the mixing water in a manner to ensure uniform distribution
of the admixtures throughout the batch during the required mixing
period. Storage and handling of admixtures shall be in accordance with
the manufacturer's recommendations.
d. Moisture Control - The plant shall be capable of ready adjustment
to compensate for the varying moisture content of the aggregates and to
change the masses of the materials being batched. A moisture meter
complying with the provisions of COE CRD-C 143shall be provided for
measurement of moisture in the fine aggregate. The sensing element
shall be arranged so that the measurement is made near the batcher
charging gate of the sand bin or in the sand batcher.
e. Scales - Adequate facilities shall be provided for the accurate
measurement and control of each of the materials entering each batch of
concrete. The weighing equipment and controls shall conform to the
applicable requirements of NIST HB 44, except that the accuracy shall
be within 0.2 percent of the scale capacity. The Contractor shall
provide standard test weights and any other auxiliary equipment
required for checking the operating performance of each scale or other
measuring device. Tests shall be made at the frequency required in
paragraph TESTS AND INSPECTIONS and in the presence of a Government
inspector. Each weighing unit shall include a visible indicator that
shall indicate the scale load at all stages of the weighing operation
and shall show the scale in balance at zero load. The weighing
equipment shall be arranged so that the concrete plant operator can
conveniently observe the indicators.
f. Operation and Accuracy - [The weighing operation of each material
shall start automatically when actuated by a single starter switch and
shall end automatically when the designated amount of each material has
been reached. These requirements can be met by providing an automatic
batching system as defined in the NRMCA CPMB 100.] [The weighing
operation of each material shall begin automatically when actuated by
one or more starter switches and shall end when the designated amount
SECTION 03701
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