2.11.16.1
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 the ash into the inlet of the rotary vane feeder]. Provide
hopper with expansion joints and sufficient poke holes with cover or cap.
2.11.16.2
Concrete Stave Silo
Construct 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 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 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 pounds per square inch, yield point
not less than 276 MPa 40,000 pounds per square inch, and a minimum
elongation of 14 percent in 229 mm 9 inches. Reinforcing shall be
sufficient to resist maximum lateral pressure and loads imposed by
ash pressure within the silo. Structurally connect together hoop
rods that pass through silo outlets on inspection frames.
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 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 used to permit
horizontal joints to be staggered.
d.
Solid Concrete Stave Silos: Construct silo of solid lightweight
precast concrete staves. Solid staves shall be not less than 92
mm thick and 250 mm wide by 762 mm long 3 5/8 inches thick and 10
inches wide by 30 inches long, except starter staves may be
shorter. Solid staves shall be constructed from a well
proportioned mix of portland cement, washed sand and gravel which
is free from injurious organic impurities and contains less than 5
SECTION 15501N
Page 104
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