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 be 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
that buckets larger than 1.5 cubic meters 2 cubic yards shall not be
manually operated. The design of the bucket shall provide means for
positive regulation of the amount and rate of deposit of concrete in each
dumping position.
3.1.4.2
Transfer Hoppers
Concrete may be charged into nonagitating hoppers for transfer to other
conveying devices. Transfer hoppers shall be capable of receiving concrete
directly from delivery vehicles and have conical-shaped discharge features.
The transfer hopper shall be equipped with a hydraulically operated gate
and with a means of external vibration to effect complete discharge.
Concrete shall not be held in nonagitating transfer hoppers more than 30
minutes.
3.1.4.3
Trucks
Truck mixers operating at agitating speed or truck agitators used for
transporting plant-mixed concrete shall conform to the requirements of ASTM
C 94/C 94M. Nonagitating equipment may be used for transporting
plant-mixed concrete over a smooth road when the hauling time is less than
15 minutes. Bodies of nonagitating equipment shall be smooth, watertight,
metal containers specifically designed to transport concrete, shaped with
rounded corners to minimize segregation, and equipped with gates that will
permit positive control of the discharge of the concrete.
3.1.4.4
Chutes
When concrete can be placed directly from a truck mixer, agitator, or
nonagitating equipment, the chutes attached to this equipment by the
manufacturer may be used. A discharge deflector shall be used when
required by the Contracting Officer. Separate chutes and other similar
equipment will not be permitted for conveying concrete.
3.1.4.5
Belt Conveyors
Belt conveyors shall be designed and operated to assure a uniform flow of
concrete from mixer to final place of deposit without segregation of
ingredients or loss of mortar and shall be provided with positive means for
preventing segregation of the concrete at the transfer points and the point
of placing. Belt conveyors shall be constructed such that the idler
spacing shall not exceed 900 mm 36 inches. The belt speed shall be a
minimum of 90 m 300 feet per minute and a maximum of 230 m 750 feet per
minute. If concrete is to be placed through installed horizontal or
sloping reinforcing bars, the conveyor shall discharge concrete into a pipe
or elephant trunk that is long enough to extend through the reinforcing
bars.
3.1.4.6
Concrete Pumps
Concrete may be conveyed by positive displacement pump when approved. The
pumping equipment shall be piston or squeeze pressure. The pipeline shall
be rigid steel pipe or heavy-duty flexible hose. The inside diameter of
SECTION 03301A
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