of each material has been reached. These requirements can be met by
providing a semiautomatic or automatic batching system as defined by
the NRMCA CPMB 100.] There shall be equipment to permit the selection
of [_____] preset mixtures each by the movement of not more than two
switches or other control devices. 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:
PERCENT OF
MATERIAL
REQUIRED MASS
Cementitious materials .............................. 0 to
+2
Water ....................................................
1
Aggregate smaller than
37.5 mm (1-1/2 in.) size ...............................
2
Aggregate larger than
37.5 mm (1-1/2 in.) size ...............................
3
Chemical admixtures ................................. 0 to
+6
Note: When water or chemical admixtures are measured by volume, they shall
meet the same tolerance percent as stated in the chart.
g.
Interlocks - Batchers and mixers shall be interlocked so that:
(1) The charging device of each batcher cannot be actuated until
all scales have returned to zero balance within plus or minus 0.2
percent of the scale capacity and each volumetric device has reset
to start or has signaled empty.
(2) The charging device of each batcher cannot be actuated if the
discharge device is open.
(3) The discharge device of each batcher cannot be actuated if
the charging device is open.
(4) The discharge device of each batcher cannot be actuated until
the indicated material is within the allowable tolerances.
(5) Admixtures are batched automatically and separately with the
water.
(6) The mixers cannot be discharged until the required mixing
time has elapsed.
h. Recorder - An accurate recorder or recorders shall be provided and
shall conform to the following detailed requirements:
(1) The recorder shall produce a graphical or digital record on a
single visible chart or tape of the weight or volume of each
material in the batchers at the conclusion of the batching cycle.
The record shall be produced prior to delivery of the materials to
the mixer. After the batchers have been discharged, the recorder
shall show the return to empty condition.
SECTION 03701
Page 33
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