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6-24-97
FLY ASH
STABILIZATION OF SOILS
207-R-336
DESCRIPTION:
This work shall consist of stabilizing the subgrade soils by
mixing fly ash in conjunction with lime or cement with the soils.
This may be used to stabilize the natural ground under
embankments and to the subgrade under pavements.
MATERIAL: The
materials shall be in accordance with the following:
Fly ash
............................901.02.
Hydrated lime ......................913.04.
Portland cement ...................901.
Water ..............................913.01
Asphalt material for curing seal shall be AE-150 Type I in
accordance with 404.
Reactive Soils are those soils which, when mixed with at least 9%
fly ash, compacted in accordance with AASHTO T 99 Method C, and
cured for 48 hours at 49E C (120E F), shall show a strength gain
of at least 345 KPa greater than that obtained for similarly
prepared untreated control specimens.
EQUIPMENT: The
machinery, tools and equipment necessary for proper execution of
the work shall be available on the project site and approved by
the Engineer prior to the commencing of construction operations.
STORAGE AND HANDLING:
- Fly Ash shall be stored in weather
protected conditions with adequate protection from ground
dampness. The storage facility shall be approved by the
Engineer prior to commencement of any fly ash work.
- Each shipment shall be accompanied
by a bill of lading and by a certificate of compliance
stating conformance to the applicable specification
requirements.
- The Contractor's safety measures
shall be in accordance with applicable OSHA requirements.
MIXTURE COMPOSITION:
- Sample: The
contractor shall provide 140 kg (310 lb), minimum,
samples of the soil to be modified and 25 kg (55 lb),
minimum, samples of the fly ash to be used at
least 45 days prior to the use of the fly ash.
- Mix Design: Fly ash shall be proportioned
within, but not limited to, an approximate range of 9% to
15% of soil as determined by the oven - dry test basis.
The required proportion of fly ash will be established by
the Engineer prior to construction using samples of soil
and fly ash and the Department's laboratory design
procedure for soil stabilization. The Engineer reserves
the right to make such adjustments of fly ash
proportioning as are considered necessary during the
progress of the work.
If a lime, cement, and fly ash combination is used, the
proper combination of lime and cement to fly ash ratio
will be determined in the laboratory. An approximate
range of ratios of lime and cement to fly ash will be 1:9
to 1:1 and 1:3 to 1:4 respectively.
The source or type of fly ash shall not be changed during
the progress of the work without written permission of
the Engineer. The Engineer may, however, based on
laboratory test results, direct that different types of
fly ash be used on different portions of the project. The
different types shall not be mixed in the same project
portion.
CONSTRUCTION REQUIREMENTS:
- Temperature and Weather Limitations: Fly
ash modification shall only be performed with a minimum
soil temperature, measured 100 mm (4 in.) below the
surface, of 7E C (45E F), and with the air temperature
rising. Fly ash shall not be mixed with frozen soils or
with soil containing frost.
- Preparation of Existing Soils: All
deleterious material, such as stumps, roots, turf, etc.
and aggregate larger than 75 mm (3 in.) shall be removed.
Any soft organic soils shall be removed as directed by
the Engineer.
- Scarification and Pulverizing: The soil
surface shall be scarified to the required depth with a
machine of such design that a visible indication is given
at all times the cutting is to the required depth.
Moisture shall be added if necessary.
- Fly Ash Application: The Department
reserves the right to increase or decrease the quantity
of the fly ash used, based on test results, as directed
by the Engineer.
The fly ash application shall include a curing period of
seven days if the specified gradation is achieved. Curing
periods may be extended at the discretion of the Engineer
if the gradation is not being achieved.
Fly ash shall be spread only on that area where the
initial mixing operation can be completed during the same
working day.
Any fly ash that has been exposed to the open air for a
period of 6 hours or more before mixing will not be
accepted unless approved by the Engineer.
Heavy traffic or equipment shall not be permitted on the
spread fly ash except for that required for spreading,
watering, or mixing.
Spreading Fly Ash: Fly ash shall be uniformly spread
at the specified quantities. Fly ash shall not be applied
when wind conditions are such that blowing fly ash
becomes objectionable to adjacent property owners or
creates a hazard to traffic on adjacent highways.
When fly ash is used in conjunction with lime or cement,
the lime, cement, and fly ash shall be spread separately.
They may, however, if directed by the Engineer, be
pre-blended and stored dry. Pre-blended mixes shall be
placed dry unless directed otherwise by the Engineer. If
both lime and cement and fly ash are used and spread
separately, conditioned fly ash, at water contents
between 15% and 25%, and dry lime shall be used.
Fly ash which has been damaged by rain prior to or during
the mixing operations, which has been damaged while
spreading, or which has been displaced by the
Contractor's equipment or other traffic, shall be
replaced.
- Moisture Control: At the completion of the
mixing operation, the moisture content of the mixture
shall be within 3 percentage points below to optimum
moisture content.
- Test Section: The first section of each
mixing operation, shall be a test section to demonstrate
the acceptability of the Contractor's equipment and
methods, and to provide a check of the resulting finish
grade elevation and the compacted thickness of the
stabilized layer. Changes in equipment shall be made as
needed based on the results of the test section. If
changes in methods or requirements are made, additional
test sections shall be constructed as required by the
Engineer. Additional test sections shall be constructed
if
recommended in the Geotechnical Report. The length of the
section shall be as long as necessary to use one truck of
fly ash. Test sections may be waived by the Engineer.
- Mixing: After the fly ash has been spread,
it shall be mixed with the pulverized soil. Fly ash shall
not be mixed below the specified depth. Mixing shall be
accomplished with mixing devices approved by the Engineer
and shall be continued until the resulting mixture is
homogeneous and uniform in appearance. Water shall be
added to the mixture so the moisture content is no less
than optimum for fly ash-soil mixture, but no more than
optimum plus 3%. The friable mixture of soil and fly ash
shall be free from clods and lumps exceeding 25 mm (1
in.) in size. After initial mixing, the fly ash treated
layer shall be shaped to the approximate section and
lightly compacted, prior to curing, to minimize the
evaporation loss and to prevent excessive wetting from
rain. The surface shall be crowned to provide proper
drainage.
Prior to compaction, the fly ash stabilized soil mixture
shall be pulverized such that 100% of the mixture passes
a 25 mm (1 in.) sieve and 60% passes a 4.75 mm (No. 4)
sieve, excluding the non-slaking fraction.
- Compaction: Compaction of the mixture shall
begin immediately after the mixing process is complete.
The mixture shall be compacted to at least 100% of the
maximum dry density of the fly ash stabilized mixture
within the special subgrade treatment zone and to at
least 95% of the maximum dry density of the fly ash
stabilized mixture below the special subgrade treatment
zone. The maximum dry densities will be determined in
accordance with AASHTO T 99 or one point proctors in
accordance with AASHTO T 272. The density of the soil-fly
ash mixture will be determined by the Engineer near the
end of the finishing operations. Any portion of the
soil-fly ash mixture having density less than specified
shall be corrected or removed and replaced. The in-place
dry density shall be determined by the Engineer in
accordance with AASHTO T 191 or T 239.
The average compacted thickness of modified soils
constructed shall be within 10% of the specified
thickness, except that the thickness at any one place may
be within 15% of that specified.
The Department reserves the right to determine the actual
thickness of the completed and cured layer by coring or
by other means. The Engineer will perform at least one
test every 280 m2 (335 syd) for each compacted
layer to ensure that the fly ash is spread at the
specified rate. All deficient areas shall be corrected.
During the compaction phase, the shape of the course
shall be maintained by blading and the surface shall be
sloped to the required lines, grades and cross-sections.
Compaction shall be continued until the minimum specified
density is obtained.
Compaction of some stabilized soils may result in the
formation of horizontal shear planes, resulting in a
thin, platey structure in the upper part of the compacted
layer. These compaction planes shall be removed by light
scarification with a spike-toothed harrow, weeder, or
nail drag, and the loosened material then moistened and
recompacted with a pneumatic-tired roller.
- Curing and Protection: After the mixture
has been finished as specified, it shall be protected
against drying for 14 calendar days. The surface shall be
maintained in a moist condition by sprinkling for the
above mentioned period or until a curing seal coat is
placed. Equipment used to apply the curing seal and
curing water shall be of a size and weight such that the
surface is not damaged.
Heavy traffic or equipment other than curing equipment
shall not be allowed on the finished surface until
completion of curing, unless permitted by the Engineer. A
satisfactory curing day shall be any day when the
temperature of the completed subgrade does not fall below
7E C (49E F) and the air temperature rises. All damage to
the curing seal prior to completion of curing, shall be
immediately resealed.
The curing seal shall consist of the asphalt material
specified and shall be uniformly applied at the rate of 1
kg/m2 (2 lb/syd) with approved distributing
equipment. The actual rate and application temperature of
asphalt material will be determined by the Engineer.
If the asphalt material is tacky, a sand blotter material
shall be applied at a rate by approximately 3 kg/m2
(5 lb/syd) when directed by the Engineer.
Other acceptable curing material or methods may be used
upon written permission of the Engineer.
The stabilized surface shall be protected against
freezing for seven calendar days after placement.
The stabilized subgrade shall be completely covered with
the specified pavement courses before work is suspended
for the winter months. When the stabilized subgrade is
not completely covered by the specified pavement courses,
the Contractor shall be responsible for all work
necessary to protect and maintain the uncompleted work
during the winter months. The Contractor shall perform
any work necessary to repair or restore the uncompleted
work before the beginning of spring paving operations.
- Maintenance: The Contractor shall maintain the
entire fly ash stabilized soil mixture in a manner
satisfactory to the Engineer. Maintenance shall include
immediate repairs of any defective or damaged portions of
the stabilized subgrade.
METHOD OF MEASUREMENT: Stabilized soils will
be measured in square meters (square yards) of the thickness
specified. The width for measurement shall be as shown on the
plans. Asphalt material used as a curing seal will be measured in
megagrams (tons). Water will not be measured for payment. Fly
ash, lime, and cement will be measured megagrams (tons). The fly
ash, lime, and cement, may be weighed in trucks or freight cars.
If the fly ash, lime, or cement is shipped in trucks, it may be
weighed at the place of loading, at the place of unloading, or at
such other place as the Engineer may designate. The Engineer may
accept original signed bills in lieu of weighing.
Extra earth
excavation or embankment due to the Contractor's method of
construction requiring more than one lift to construct the fly
ash stabilized soil layer as shown on the plans will not be
measured.
Contract
Quantities: When the project is constructed essentially
to the lines, grades or dimensions shown on the plans and the
Contractor and Engineer have previously agreed in writing that
the plan quantities are accurate, no further measurement shall be
required. If errors are discovered after work has been started
corrective measurements shall be made.
When the plans have
been altered or when disagreement exists between the Contractor
and the Engineer as to the accuracy of the plan quantities before
any work is started which would affect the measurement, either
party shall have the right to request in writing, and thereby
cause the quantities involved to be measured.
BASIS OF PAYMENT: Fly ash stabilized
soil will be paid for at the contract unit price per square meter
(square yard) at the thickness specified, complete in place. Fly
ash, lime, cement, and asphalt curing seal will be paid for at
the contract unit price per megagram (ton).
Payment will be
made under:
Pay Item
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Metric Pay Unit
Symbol
(English Pay Unit Symbol)
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Asphalt Curing Seal
|
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......................Mg (TON)
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Cement
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......................Mg (TON)
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Fly Ash
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......................Mg (TON)
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Fly Ash Stabilized Soil
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.......................m2 (SYD)
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Lime
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......................Mg (TON)
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The costs of
replacing fly ash damaged by rain prior to or during the mixing
operations; the replacement of fly ash damaged by the
Contractor's operations; the water necessary for moisture control
or for the stabilization process; correction of deficient areas;
repair of damage to the curing seal; furnishing and spreading the
sand blotter; the extra materials, methods, and construction
techniques required to protect, maintain, or repair portions of
the uncompleted work left during the winter months; and all extra
earth excavation or embankment due to more than one lift being
required to construct the fly ash stabilized soil layer will be
included in the costs of the pay items.
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