indicated material is within the applicable tolerance.] The batching
system shall be equipped with an accurate recorder or recorders that meet
the requirements of NRMCA CPMB 100. Separate bins or compartments shall be
provided for each size group of aggregate and cement, pozzolan, and GGBFS.
Aggregates shall be weighed either in separate weigh batchers with
individual scales or cumulatively in one weigh batcher on one scale.
Aggregate shall not be weighed in the same batcher with cement, pozzolan,
or GGBFS. If both cement and pozzolan or GGBFS are used, they may be
batched cumulatively provided that the portland cement is batched first.
If measured by mass, the mass of the water shall not be batched
cumulatively with another ingredient. Water batcher filling and
discharging valves shall be so interlocked that the discharge valve cannot
be opened before the filling valve is fully closed. An accurate mechanical
device for measuring and dispensing each admixture shall be provided. Each
dispenser shall be interlocked with the batching and discharging operation
of the water so that each admixture is separately batched and discharged
automatically in a manner to obtain uniform distribution throughout the
batch in the specified mixing period. Admixtures shall not be combined
prior to introduction in water. The plant shall be arranged so as to
facilitate the inspection of all operations at all times. Suitable
facilities shall be provided for obtaining representative samples of
aggregates from each bin or compartment. All filling ports for
cementitious materials bins or silos shall be clearly marked with a
permanent sign stating the contents.
3.1.2.2
Scales
The equipment for batching by mass shall conform to the applicable
requirements of NIST HB 44, except that the accuracy shall be plus or minus
0.2 percent of scale capacity. The Contractor shall provide standard
reference masses and any other auxiliary equipment required for checking
the operating performance of each scale or other measuring devices. The
tests shall be made at the frequency required in paragraph TESTS AND
INSPECTIONS and in the presence of a Government inspector.
3.1.2.3
Batching Tolerances
Tolerances on determination of mass:
PERCENT OF REQUIRED
MATERIAL
MASS
Cementitious materials
-0 to +2
Aggregate
2
Water
1
Chemical admixture
-0 to +6
For volumetric batching equipment, the following tolerances shall apply to
the required volume of material being batched:
Water:
Plus or minus 1 percent.
Chemical admixtures:
Zero to plus 6 percent.
3.1.2.4
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. [An electric moisture meter complying with the
SECTION 03373
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