as per the manufacturer's specifications. Devices and tools shall be
maintained at the plant location to check the feeder's calibration at the
Contracting Officer's request. A technician shall be provided that is
skilled in calibration of the feed devices and the maintenance and repair of
the plant control system. The technician shall be available within 30
minutes notice during all scheduled plant operations. The technician could
be one or more of the Contractor's personnel.
b. Cement, Pozzolan, and Aggregate Feed - Cement, pozzolan, and
aggregate shall be uniformly, continuously, and simultaneously fed (at
the proper ratios and quantity for the mixture required) into the mixer
by belt, auger, vane feeder, or other acceptable method. The feed bins
or silos for each ingredient shall be kept sufficiently full and shall
be of sufficient size to ensure a uniform flow at a constant rate for a
specific mixture. The feed bins shall have a low-level indicator that
both warns the operator and can shut the plant down if insufficient
material is available for a uniform and continuous flow.
c. Water and Admixture Dispensers - The liquid-dispensing devices
shall be capable of metering and dispensing within the specified
requirements. The liquid valves shall be free from leakage in the
closed position. The dispensers shall have attachments and/or be
installed in such a manner that will permit convenient checking of
their accuracy. Plumbing shall be leak-free and properly valved to
prevent backflow and siphoning. The dispenser shall be interlocked
with the electronic plant control and shall warn the operator and shut
down the plant if insufficient liquid is available. Separate nozzles
for each liquid shall be properly located at the mixer to assure
uniform distribution of each liquid to the materials entering the mixer.
d. Continuous Mixer(s) - The continuous mixer(s) shall have proper
introduction of ingredients as specified by the manufacturer and shall
not be charged in excess of the manufacturer's recommended capacity.
Mixer(s) shall be capable of combining the materials into a uniform
homogeneous mixture and of discharging this mixture without
segregation. The mixer(s) shall operate at the blade speed designated
by the manufacturer and shall be capable of changing retention time of
the ingredients in the mixer. This should be accomplished by manually
resetting the mixer(s) blade angles. Mixing time (ingredient retention
time in the mixer) shall be predicated upon the uniformity,
homogeneity, and consistency of the resultant mixture. Samples for
uniformity testing shall be taken at 2-minute intervals and tested as
per COE CRD-C 55 and paragraph REQUIREMENT. The mixer(s) shall be
maintained in satisfactory operating condition and mixer blades shall
be kept free of hardened concrete. Should mixer(s) at any time produce
unsatisfactory results, its use shall be promptly discontinued until it
is repaired. Suitable facilities shall be provided for obtaining
representative samples of concrete for testing. All necessary
platforms, shelters, tools, labor, and equipment shall be provided for
obtaining samples.
e. Segregation - A means shall be used to reduce and minimize
segregation and waste which would otherwise result from the continuous
stream of concrete being fed into the batch haul devices (concrete
buckets, dump trucks, etc.). The equipment shall retain the concrete
between tracks or other means of transport to prevent the need for
stopping the mixer. These devices could include, but not be limited
to, small-volume conveyor discharge hopper with a large gate that is
automatically opened on a timed interval, thereby dumping a series of
SECTION 03701
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