devices. The tests shall be made at the specified frequency in the
presence of a Government inspector. The weighing equipment shall be
arranged so that the plant operator can conveniently observe all dials or
indicators.
3.2.5
Batching Tolerances
(A)
Tolerances with Weighing Equipment
PERCENT OF REQUIRED
MATERIAL
WEIGHT
Cementitious materials
0 to
plus 2
Aggregate
plus
or minus 2
Water
plus
or minus 1
Chemical admixture
0 to
plus 6
(B)
Tolerances with Volumetric Equipment
For volumetric batching equipment used for water and admixtures, the
following tolerances shall apply to the required volume of material being
batched:
PERCENT OF REQUIRED
MATERIAL
MATERIAL
Water:
plus or minus 1 percent
Chemical admixtures:
0 to plus 6 percent
3.2.6
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.
3.2.7
Concrete Mixers
**************************************************************************
NOTE: Retain bracketed phrase unless it is desired
to prohibit truck mixers, in which case delete.
**************************************************************************
Mixers shall be stationary mixers [or truck mixers]. Mixers shall be
capable of combining the materials into a uniform mixture and of
discharging this mixture without segregation. The mixers shall not be
charged in excess of the capacity recommended by the manufacturer. The
mixers shall be operated at the drum or mixing blade speed designated by
the manufacturer. The mixers shall be maintained in satisfactory operating
condition, and the mixer drums shall be kept free of hardened concrete.
Should any mixer at any time produce unsatisfactory results, its use shall
be promptly discontinued until it is repaired.
3.2.8
Stationary Mixers
Concrete plant mixers shall be drum-type mixers of tilting, nontilting,
horizontal-shaft, or vertical-shaft type, or shall be pug mill type and
shall be provided with an acceptable device to lock the discharge mechanism
until the required mixing time has elapsed. The mixing time and uniformity
SECTION 03300A
Page 37
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