the desired purpose. Sieves shall meet the applicable requirements of ASTM
E 11, except for the frame size requirements. The equipment shall be
arranged so that all controls will be enclosed and operable from a single
position commanding a view of the screen device and the scale or scales.
Communication shall be provided from the batch plant operation to this
control area. The Contractor shall be responsible for charging of the
assembly as directed, disposal of waste material, and proper service and
maintenance of the assembly. Each sieve shall be provided with individual
controls for frequency and angle. The contractor shall run correlation
tests with equipment as used for ASTM C 136 before concrete placement
begins and at least every 60 days while concrete is being placed. The
correlation test will determine the optimum angle, volume of feed, and the
frequency for each sieve.]
3.1.5
Transporting Equipment
Transporting equipment shall be designed, operated, and maintained so that
it does not cause or permit segregation or loss of material. The concrete
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.
3.1.5.1
Buckets
Bottom-dump buckets shall conform to the following requirements: the
interior hopper slope shall be not less than 70 degrees from the
horizontal; the minimum dimension of the clear gate opening shall be at
least five times the nominal maximum size of the aggregate, and the area of
the gate opening shall not be less than 0.2 square meters 2 square feet;
the bucket gates shall be grout-tight when closed, shall be of the double
clamshell type, and shall be manually, pneumatically, or hydraulically
operated; and the gate-opening mechanism shall be designed to close the
gates automatically when the control is released or when the air or
hydraulic line is broken. If gate actuation is dependent on integral air
or hydraulic reservoirs, the capacity of the reservoirs shall be sufficient
to open and close the gates three times without recharging the reservoir.
3.1.5.2
Trucks
Truck mixers or agitators used for transporting central-mixed concrete
shall conform to the applicable requirements of ASTM C 94/C 94M. Truck
mixers shall not be used to transport concrete with larger than 37.5 mm
1-1/2 inch nominal maximum-size aggregate or 50 mm 2 inch or lower slump.
Nonagitating trucks may be used for transporting central-mixed concrete
over a smooth road when the hauling time is less than 15 minutes and the
slump is less than 75 mm 3 inches. Bodies of nonagitating trucks 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.
3.1.5.3
Chutes
When concrete can be placed directly from a truck mixer, agitator, or
nonagitating truck, the chutes supplied by the truck manufacturer as
standard equipment may be used. A discharge deflector shall be used when
required by the Contracting Officer. Separate chutes and other similar
equipment shall not be permitted for conveying concrete except when
specifically approved and in no case shall slump be increased to
SECTION 03700
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