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6-24-97
LIME-KILN DUST MODIFICATION
207-R-333
DESCRIPTION: This work shall consist of the upgrading
of fine grained soils by uniformly mixing lime-kiln dust with the
soils to aid compaction by drying out wet areas, and to provide a
working platform for subsequent construction.
MATERIALS: Materials shall be in accordance with
the following:
Hydrated lime.......................913.04.
Water ................................913.01.
Lime-kiln dust
shall be in accordance with the following requirements:
- Total calcium and magnesium non-volatile oxides shall
consist of a minimum of 60% lime-kiln dust.
- Available calcium hydroxide in accordance with ASTM C
25 and total magnesium oxide content calculated to be
equivalent calcium hydroxide shall consist of 30% of
lime-kiln dust.
- Sieve Analysis: Gradation shall be as follows:
Sieve
|
% Passing
|
4.75 mm (No. 4) |
95-100 |
600 mm (No. 3) |
90-95 |
150 mm (No. 100) |
70-80 |
STORAGE AND HANDLING:
Lime-kiln
dust shall be stored in accordance with the manufacturer's
recommendations so its chemical composition shall not be
affected.
MIXTURE COMPOSITION:
- Samples: The Contractor shall provide 50 kg (110
lb), minimum, samples of the soil to be modified, and 5
kg (11 lb), minimum, samples of the lime-kiln dust to be
used at least 20 days prior to use of the lime.
- Mix Designs: Lime shall be proportioned as
required by oven-dry test results of the mixture of
lime-kiln dust and soil. The required proportion of
lime-kiln dust will be established by the Engineer prior
to construction, using samples of soil and lime-kiln dust
modified soil. The Engineer will reserve the right to
make such adjustments of lime-kiln dust proportioning as
are necessary during the progress of the work within the
range specified.
The source or type of lime-kiln dust shall not be changed
during the progress of the work without permission of the
Engineer. However, the Engineer may choose, based on
laboratory test results, to use different types of
lime-kiln dust on different portions of the project
limits. The different types of lime-kiln dust shall not
be mixed in the same project portion.
CONSTRUCTION REQUIREMENTS:
- Temperature and Weather Limitations: Lime-kiln
dust modification shall only be performed with a minimum
soil temperature of 7E C (45E F), measured 100 mm (4 in.)
below the surface, and with the air temperature rising.
Lime-kiln dust shall not be mixed with frozen soils or
with soil containing frost.
- Preparation of Subgrade: All deleterious material,
including stumps, roots, turf, and aggregates larger than
75 mm (3 in.) shall be removed. All soft organic soils
shall be removed as directed by the Engineer.
- Spreading of Lime: The subgrade shall be scarified
or disked to the specified depth with a machine of such
design that a visible indication is given at all times
that the cutting is to the specified depth prior to
distribution of the lime-kiln dust. The lime kiln dust
shall then be distributed uniformly over the surface by
means of a cyclone, screw-type, or pressure manifold type
distributor. The Engineer may reject procedures which do
not provide an uniform distribution of lime-kiln dust.
Lime-kiln dust shall not be applied when wind conditions
are such that blowing lime-kiln dust becomes
objectionable to adjacent property owners or creates a
hazard to traffic on adjacent highways.
The spreading of lime-kiln dust shall be limited to that
amount which can be incorporated into the soil within the
same work day. If weather causes cessation of work, or
exposure of the lime-kiln dust to washing or blowing, the
Engineer may require additional lime-kiln dust to be
spread.
- Mixing: The lime-kiln dust, soil, and water when
necessary, shall be thoroughly mixed by rotary speed
mixers or a disc harrow. The mixing shall continue until
it has been determined by the Engineer that a homogeneous
layer of the required thickness has been obtained, and
such that 100% of the material, exclusive of rock
particles, shall pass a 25 mm (1 in.) sieve and at least
60% shall pass a 4.75 mm (No. 4) sieve. The loose
thickness of a single lime-kiln dust modified layer shall
not exceed 200 mm (8 in.) if a disc harrow is used and
360 mm (14 in.) if a rotary speed mixer is used.
- Compaction: Compaction of the mixture shall begin
immediately after mixing. If compaction is to be delayed,
the surface of the lime-kiln dust modified soils shall be
crown-graded and sealed immediately after mixing.
Compaction shall be continued until the lime-kiln dust
modified layer has a density of not less than 100% of the
maximum dry density within the special subgrade treatment
zone or 95% of the maximum dry density below the special
subgrade treatment zone. Maximum dry densities will be
determined in accordance with AASHTO T 99 or one point
proctors in accordance with AASHTO T 272.
If required density can not be achieved in the field, a
one point proctor shall be performed to verify the target
density. The standard dry density of the lime-kiln dust
treated soil shall be obtained by one point proctor in
accordance with AASHTO T 272. The field in-place dry
density shall be obtained by the Engineer in accordance
with AASHTO T 191 or T 239.
Aeration by means of further mixing, or the addition of
water and further mixing, may be required to achieve the
required compaction.
- Finishing: When compaction of the lime-kiln dust
modified soil is determined to be nearing completion, the
surface shall be shaped to the required lines, grades,
and cross section. Compaction shall then be continued
until the specified compaction is obtained.
The average compacted thickness of the modified subgrade
constructed shall be within 10% of the specified
thickness. However, the thickness at one given 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 means of
coring, use of a phenolphthalein solution, or by other
means. The Engineer will perform at least one test every
280 m2 (335 syds.) for each compacted lift to
ensure that the lime is spread at the specified rate. All
deficient areas shall be acceptably corrected.
METHOD OF MEASUREMENT
The modified
subgrade will be measured by the square meter (square yard) of
the thickness specified. The width for measurement will be as
shown on the plans. Water will not be measured.
Lime kiln-dust will
be measured by the megagram (ton). It may be weighed in either
trucks or freight cars. If it is shipped in trucks, it may be
weighed at the place of loading, at the place of unloading, or
where otherwise directed by the Engineer. The Engineer may accept
original signed bills in lieu of weighing.
Contract
Quantities: If the work is constructed to the lines, grades,
or dimensions shown on the plans, and the Contractor and the
Engineer have previously agreed in writing that the plan
quantities are accurate, further measurement will not be required
except when errors are discovered after work has been started.
Corrective measurements will then be made.
Should the method
of construction require extra earth excavation or embankment due
to the need for more than one lift to construct the lime-kiln
dust modified soil layer as shown on the plans, such extra earth
excavation and embankment will not be measured.
BASIS OF PAYMENT: The accepted quantities of modified
subgrade of the thickness specified will be paid for at the
contract unit price per square meter (square yard). Lime
kiln-dust will be paid for at the contract unit price per
megagram (ton).
Payment shall be made under:
Pay Item
|
|
Metric Pay Unit
Symbol
(English Pay Unit Symbol)
|
Modified Subgrade,_______mm
thickness
|
|
......................m2 |
Modified Subgrade, _______in
thickness
|
|
......................SYS |
Lime-Kiln Dust
|
|
......................Mg (TON) |
The costs of
removal of deleterious materials, scarification of the subgrade,
spreading of lime, mixing of the lime and soil, sealing of the
surface of the lime-kiln dust modified soils, compaction of the
resultant mixture, shaping the subgrade, work required due to
adjustments of lime-kiln dust proportioning made by the Engineer,
additional lime-kiln dust required due to weather conditions,
correction of lime-kiln dust deficient areas, water required for
the modification process, required extra earth excavation and
embankment due to method of construction, and cost of modified
subgrade trimming as required shall be included in the costs of
the pay items.
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