safety cages and access platforms must be additionally provided. Provide
ladder with stainless steel fall prevention device on inside of silo from
manhole in top of silo to bottom of silo. [Provide silo roof enclosure and
unloader room enclosure each with single one by 2 meter 3 by 7 foot access
door, [_____] by [_____] meter foot double door, two windows, ventilator,
[heater], insulated metal panel siding to match boiler plant walls and
electrical lighting and convenience receptacles. Unloader room enclosure
shall have reinforced concrete floor.]
2.12.17.1
Construction
Construct silo of steel with refractory lining or of concrete staves with
steel hoops and concrete roof. Roof accessories shall include manhole,
relief valve and vent filter. Bottom of silo shall be [conical, sloped a
minimum of 45 degrees.] [flat with a steel plate feeding hopper in bottom
of silo to funnel ash into inlet of rotary vane feeder.] Provide hopper
with expansion joints and sufficient poke holes with cover or cap.
2.12.17.2
Concrete Stave Silo
Construct concrete stave silo of either lightweight solid or hollow precast
concrete staves with post-tensioned steel reinforcing hoops around the
exterior. Mechanically measure and mix materials in concrete staves.
Vibrate and shape the staves under pressure and steam or air cure.
a.
Wall Coating: Coat interior surface with a three-step process of
a brush coat, scratch coat, and finish trowel coat of a mixture of
fine sand and portland cement in accordance with the silo
manufacturer's recommendations. Apply each coat successively to
produce a smooth interior surface. Work mixture into the formed
horizontal and vertical grooves to permanently interlock the
concrete staves. Brush coat the exterior surface with a double
application of waterproof mixture. Mixture shall include a
chemical agent for waterproofing and portland cement, sand, and
water. Work coating into joints and over the steel reinforcing
hoops to form a weatherproof protective coating.
b.
Steel Reinforcing Hoops: Galvanized steel rods not less than 14 mm
9/16 inch in diameter with not less than 16 mm 5/8 inch rolled
threads. Join hoop ends together with nuts and heavy malleable
galvanized iron lugs or heavy duty galvanized steel lugs to a
close tolerance for a tight fit. Electrogalvanize rods, nuts, and
lugs to ensure adequate protection against corrosion.
Rods shall
be high quality, metallurgically sound steel with tensile strength
not less than 448 MPa 65,000 psi, yield point not less than 276 MPa
40,000 psi, and a minimum elongation of 14 percent in 229 mm 9
inches. Reinforcing shall be sufficient to resist the maximum
lateral pressure and loads imposed by the ash pressure within the
silo. Structurally connect hoop rods that pass through silo
outlets on inspection frames together.
c.
Hollow Concrete Stave Silos: Construct silo of precast concrete
staves with lateral air spaces. Cast staves from a well
proportioned mix of portland cement and an expanded clay light
weight aggregate. Minimum compressive strength of the concrete at
28 days shall be 34.50 MPa 5,000 psi. Hollow staves shall be 92
mm thick by 250 mm wide by 762 mm long 3 5/8 inches thick by 10
inches wide by 30 inches long with five lateral air cores per
stave, except that shorter starter staves may be provided to
SECTION 15502N
Page 139
Previous Page
