OO-C-2868
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not less than 20 yd (15.3 m ). The compartment tops shall be of sufficient
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size to facilitate loading by a standard commercial 2-1/2 yd (2 m ) front end
loader. The interior of the compartments shall be free from obstructions, and
the sides shall be sloped from top to bottom, or the lower portion of the sides
shall be sloped, to insure free flow of the material and prevent bridging. The
sand compartment shall be furnished with a moisture sensing device located so as
to be visible to the plant operator at the controls. The moisture sensing device
shall be the direct reading, pen or dial type calibrated to show the percentage
of free moisture by weight. A separate conversion chart, table, or dial scale
shall be furnished to facilitate converting the amount of free moisture in
volume per 100 pounds (lb) or 45 kilograms (kg) of sand. A means shall be
provided to weigh the aggregate and shall have a capacity of not less than
20,000 lb (9070 kg) and shall be calibrated in increments of 20 lb (9 kg) or
less with a weighing tolerance within 2 percent for each aggregate material
being weighed.
3.7.2 Cement bin. The cement bin or silo, shall have a capacity of not
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less than 740 cubic feet (21 m ) of cement and shall include a pressure relief
valve and filter vent. The cement bin shall be provided with self-loading
means, mechanical, or pneumatic. A low pressure/high volume air injection shall
be provided to insure free flow of the dry cement from the bin. The cement
hatcher, equipped with filter vent system, shall be provided with a hopper sized
to hold a full batch of cement for the mixer. A dust collector system shall
also be provided. A means shall be provided to weigh the cement having a
capacity of not less than 3,600 lb (1632 kg) and shall be calibrated in
increments of not more than 3 lb (1.36 kg). The cement bin shall be provided
with a content indicator of the high-low type, located so as to be visible to
the plant operator at the controls.
3.7.2.1 Cement bin loading system. When specified (see 6.2), the unit
shall be provided with a cement bin loading system which shall enable the
operator to load the cement bin while standing on the ground. The loading
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system shall incorporate a hopper of not less than 6 cubic foot (.17 m )
capacity, with debagger and utilizing the manufacturer's design.
3.7.3 Batch conveyor or delivery conveyor(s). Material transfer shall be
accomplished either by a motor driven batch conveyor of the inclined trough or
channeled belt type at least 24 inches (610 mm) wide (with 3-piece trough type
idlers or rollers), with a foldable, remountable, retractable discharge head, or
by motor driven conveyor(s) for each material being delivered to the hatcher.
The batch conveyor shall be covered to guard the materials against inclement
weather. All troughing idler bearings shall be either of the antifriction or
bronze bearing type with dustproof seals. Idlers shall be designed to insure
true running and self-centering of the conveyor belt with the width and running
speed of the conveyor belt, so as to assure efficient movement of material,
without spillage and pileup at receiving points, when the plant is operating at
full capacity. An accessible adjustment for maintaining proper belt tension
shall be provided, as well as a cleaning device capable of removing foreign
material adhering to the pulley side of the belt. The height of the conveyor(s)
discharge head(s) shall be compatible with the charging height of the mixer. A
water feeding system with automatic metering controls shall be installed on the
conveyor(s), discharge head(s), or on a location directly over the mixer
receiving opening for adding the required amount of water to obtain the desired
concrete mixtures.
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