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, and concrete uniformity shall conform
to the requirements of ASTM C 94/C 94M. A truck mixer may be used for
complete mixing or to finish the partial mixing begun in a stationary
mixer. 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
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NOTE: Experience has shown that to reduce problems
associated with placement rates, the minimum
conveying capacity should be 75 cubic meters per
hour (100 cubic yards per hour).
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The conveying equipment shall have a capacity of at least [_____] cubic
meters yards per hour. Concrete shall be conveyed from mixer to trench as
rapidly as practicable and within the time interval specified in the
section titled PLACING by methods that will prevent segregation or loss of
ingredients. Any concrete transferred from one conveying device to another
shall be passed through a hopper that is conical in shape and shall not be
dropped vertically more than 1.5 m 5 feet, except where suitable equipment
is provided to prevent segregation and where specifically authorized.
3.1.4.1
Buckets
The interior hopper slope shall be not less than 58 degrees from the
horizontal; the minimum dimension of the clear gate opening shall be at
least five times the nominal maximum-size aggregate; and the area of the
gate opening shall not less than 0.2 square meters 2 square feet. The
maximum dimension of the gate opening shall not be greater than twice the
minimum dimension. The bucket gates shall be essentially grout tight when
closed and may be manually, pneumatically, or hydraulically operated except
SECTION 03373
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