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6-24-97
CEMENT STABILIZATION OF SOILS
207-R-337
DESCRIPTION: This work shall consist of
stabilizing the soils by uniformly mixing portland 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:
Portland cement, type II.......... 901.01(b)
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
thoroughly with at least 4 percent potland cement, 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
(50 psi) 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:
- Portland cement 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 cement 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 standards.
MIXTURE COMPOSITION:
- Sample: The contractor shall provide 135 kg
(300 lb), minimum, samples of the soil to be modified,
and 20 kg (45 lb), minimum, samples of the cement be used
at least 45 days prior to the use of the cement.
- Mix Design: Cement shall be applied at an
approximate rate of 3% to 10% of the dry soil weight as
determined by oven-dry test. The required proportion of
cement shall be established by the Engineer prior to
construction, using samples of soil and cement, and the
Department's laboratory design procedure for soil
stabilization. The Engineer reserves the right to make
such adjustments of cement proportioning as are
considered necessary during the progress of the work.
The source or type of cement shall not be changed during
the progress of the work without written permission of
the Engineer. The Engineer may, based on laboratory test
results, direct the use of different types of cement on
different portions of the project. The different types
shall not be mixed in the same project portion.
CONSTRUCTION REQUIREMENTS:
- Temperature and Weather Limitations: Cement
modification shall only be performed with a minimum soil
temperature measured 100 mm (4 in.) below the surface of
7E C (49E F), and with the air temperature rising. Cement
shall not be mixed with frozen soils or with soil
containing frost.
- Preparation of Existing Roadway: All
deleterious material, such as stumps, roots, turf, etc.
and aggregate larger than 75 mm (3 in.) shall be removed.
All soft organic soils shall be removed as directed by
the Engineer.
- Scarification and Pulverizing: The existing
soils shall be scarified to the required depth with a
machine of such design that a visible indication is given
at all time that the cutting is to the required depth.
Moisture shall be added if necessary.
- Cement Application: The specified
quantities of cememt shall be uniformly spread. If bagged
cement is used, the cement piles shall be leveled by hand
raking or with a drag before mixing commences. Graders
shall not be used for this purpose. The Engineer may
suspend the spreading operation under windy conditions.
The Department reserves the right to increase or decrease
the quantity of the cement used based on test results, as
directed by the Engineer.
The cement 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 specified gradation is not achieved.
All cement that has been exposed to the open air for a
period of six hours or more before mixing will not be
accepted unless approved by the Engineer.
Cement which has been damaged by hydration due to rain
prior to or during the mixing operations, which has been
damaged while spreading contrary to the above mentioned
requirements, or which has been displaced by the
Contractor's equipment or other traffic, shall be
replaced.
Cement shall be spread only on that area where the
initial mixing operation can be completed during the same
working day.
Heavy traffic or equipment shall not be permitted on the
spread cement other than that required for spreading,
watering, or mixing.
- Moisture Control: At the completion of the
mixing operation, the moisture content of the mixture
shall be between 3 percentage points below to optimum
moisture content for sandy soils and between -2 to +1
percentage points of the optimum moisture content for
silty and clayey soils.
- 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, 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 directed by the Engineer. Additional
test sections shall be constructed if recommended in the
Geotechnical Report. Test sections may be waived by the
Engineer. The length of the section shall be as long as
necessary to use one truck of cement.
- Dry Mixing: Dry mixing of soil and cement
is required when mixing equipment other than a traveling
mixing plant is used. After the cement is spread, it
shall be mixed with the pulverized soil. 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. Cement shall not
be mixed below the specified depth.
When any part of the operations from the start of soil
and cement mixing through final compaction are
interrupted for any reason for more than 30 minutes, the
entire thickness of the subgrade shall be thoroughly
loosened, reprocessed, and shall be completed within the
specified time limits for these operations. When the
uncompacted soil-cement mixture is wetted by rain so that
the average moisture content exceeds the specified limits
at the time of final compaction, the portion being
processed shall be reconstructed.
- Moist Mixing:
- With Equipment Other Than a Traveling Mixing
Plant. Water shall be immediately applied and
incorporated into the dry mixed soil-cement mixture
in quantities which will produce the required
moisture content for the soil-cement mixture.
Water supply and pressure distributing equipment
shall be provided which will ensure the application
of all water required on the section being processed
within 3 hours. Each application or increment of
water shall be at least partially incorporated into
the mixture, if necessary, to avoid excessive
concentration of water on and near the surface.
After the last increment of water has been added,
mixing shall be continued until a uniform mixture of
soil, cement, and water is obtained. The uniformity
of the mixture shall be controlled by the
cement-water application rate per square meter
(square yard) for the specified depth. Satisfactory
moisture distribution along the edges of the section
and for the full depth of the treatment shall be
obtained.
When water application and moist mixing is completed,
the moisture content, on the basis of dry weight, in
the portion of the mixture passing a 25 mm (1 in.)
sieve and 60% passing a 4.75 mm (No. 4) sieve,
exclusive of gravel or stone retained on these
sieves, shall be as specified under section e.
- With a Traveling Mixing Plant. After the
cement is spread, it shall be mixed with soil and
water with a traveling mixing plant. Mixing shall be
at such rate that, or shall be repeated until, a
uniform mixture of soil, cement and water is
obtained. A satisfactory mixture along the edges of
the section and for the full depth of treatment shall
be achieved. At the completion of the mixing
operation, the moisture content and gradation of the
mixture shall be as specified. Mixing shall not be
done below the specified depth.
Prior to compaction, the cement stabilized soil
mixture shall be pulverized so 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.
Prior to the beginning of the compaction, the mixture
shall be in a loose condition for its full depth and
width. The mixture shall then be compacted, using tamping
rollers in conjunction with other compaction equipment
for the entire width, to at least 100% of the maximum dry
density of the cement stabilized mixture in accordance
with AASHTO T 99 or one point proctor in accordance with
AASHTO T 272 within the special subgrade treatment zone
and to a least 95% of the maximum dry density of the
cement stabilized mixture in accordance with AASHTO T 99
or one point proctor in accordance with AASHTO T 272
below the special subgrade treatment zone. The density of
the soil-cement mixture will be determined by the
Engineer near the end of the finishing operations. Any
portion of the soil-cement mixture having density less
than specified shall be corrected or removed and
replaced. The in-place dry density will be determined by
the Engineer in accordance with AASHTO T 191 or T 239.
The average compacted thickness of the modified soil
shall be within 10% of the specified thickness, except
that the thickness at 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
other means. The Engineer will perform at least one test
every 280 m2 (335 sys) for each compacted lift
to ensure that the cement is spread at the specified
rate. All deficient areas shall be corrected.
Throughout this operation, 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.
- Curing and Protection: After the treated
area 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 seal
coat is placed, whichever occurs first. Equipment used to
apply the curing seal and curing water shall be of a size
and weight such that the treated area is not damaged.
Heavy traffic or equipment other than curing equipment
shall not be allowed on the finished area 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). All damage occuring 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
approximately 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 treated area 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 work necessary to
protect and maintain the uncompleted work during the
winter months. The Contractor shall perform all work
necessary to repair or restore the uncompleted work
before the beginning of spring paving operations.
- Maintenance: The Contractor shall maintain the
entire cement 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: Cement stabilized soils will be
measured in square meters (square yards) of the thickness
specified. The width for measurement will be as shown on the
plans. Water will not be measured. Cement and the asphalt used as
a curing seal will be measured in megagrams (tons).
The cement
may be weighed in trucks or freight cars. If the 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.
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 will be
made. If errors are discovered after work has been started,
corrective measurements will 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, either party shall, before any work is started which
would affect the measurement, have the right to request in
writing and thereby cause the quantities involved to be measured.
BASIS OF PAYMENT: Cement stabilized soils
will be paid for at the contract unit price per square meter
(square yard) at the thickness specified, complete in place.
Cement and the asphalt curing seal will be paid for at the
contract unit price per megagram (ton).
Payment will 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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Cement Stabilized
Soils
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......................m2 (SYS)
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The costs of
replacing cement damaged by hydration due to rain prior to or
during the mixing operations; the replacement of cement damaged
by the Contractor's operations; the loosening and reprocessing of
the soil and cement mixture when operations are interrupted for
more than 30 minutes; the reprocessing caused by the average
moisture content exceeding the specified limits at final
compaction; 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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