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 or in fine aggregate 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 manufacturers 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 weights 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 fine aggregate bin or in the fine aggregate
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
quality assurance representative. 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 NRMCA CPMB 100.] [The weighing operation
of each material shall start automatically when actuated by one or more
starter switches and shall end when the designated amount of each
material has been reached. These requirements can be met by providing
a semiautomatic or automatic batching system as defined by NRMCA CPMB
100.] There shall be equipment to permit the selection of [_____]
preset mixes each by the movement of not more than two switches or
other control devices. Cumulative weighing will not be permitted. The
weigh batchers shall be so constructed and arranged that the sequence
and timing of batcher discharge gates can be controlled to produce a
ribboning and mixing of the aggregates, water, admixtures, and
cementitious materials as the materials pass through the charging
hopper into the mixer. The plant shall include provisions to
facilitate the inspection of all operations at all times. Delivery of
materials from the batching equipment shall be within the following
limits of accuracy:
MATERIAL
PERCENT
Cementitious materials ..................... .. 1
SECTION 03700
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