PERCENT OF REQUIRED
MATERIAL
MASS
Aggregate
plus or minus 2
Water
plus or minus 1
Chemical admixture
0 to plus 6
b. Volumetric Tolerances - 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
provisions of COE CRD-C 143 shall be provided for measuring 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.]
3.1.3
Concrete Mixers
The concrete 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.
3.1.3.1
Stationary Mixers
Concrete plant mixers shall be tilting, nontilting, horizontal-shaft,
vertical-shaft, or pugmill 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 shall conform to all the requirements in
ASTM C 94/C 94M applicable to central-mixed concrete.
3.1.3.2
Truck Mixers
Truck mixers, the mixing of concrete therein, and concrete uniformity shall
conform to the requirements of ASTM C 94/C 94M. A truck mixer may be used
either for complete mixing (transit-mixed) or to finish the partial mixing
done in a stationary mixer (shrink-mixed). Each truck shall be equipped
with two counters from which it will be possible to determine the number of
revolutions at mixing speed and the number of revolutions at agitating
speed.
3.1.4
Conveying Equipment
The conveying equipment shall conform to the following requirements.
3.1.4.1
Buckets
The interior hopper slope shall be not less than 58 degrees from the
SECTION 03301A
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