ITEM 206 CHEMICALLY STABILIZED SUBGRADE
206.01
Description
206.02
Materials
206.03
Submittals
206.04 Test
Rolling
206.05
Construction
206.06 Mixture
Design for Chemically Stabilized Soils
206.07 Method
of Measurement
206.08 Basis of
Payment
206.01 Description. This work consists of
constructing a chemically stabilized subgrade by mixing cement, lime, or lime
kiln dust into the subgrade soil using the method for the specified chemical.
The Contract Documents include an estimated quantity for the specified
chemical.
206.02 Materials. Furnish materials conforming to:
Portland
cement....................................................... 701.04
Lime (quick
lime)................................................. 712.04.B
Lime kiln
dust...................................................... 712.04.C
Furnish
water conforming to 499.02.
For
the curing coat, furnish rapid setting emulsified asphalt conforming to 702.04 or the curing materials specified in 451.02.
206.03 Submittals. Submit, for the Engineer’s
acceptance, a report that lists the type of equipment to be used, speed of the
intended equipment usage, rate of application of the chemical, and calculations
that demonstrate how the required percentage of chemical will be applied.
Submit the report to the Engineer for acceptance at least 2 workdays before the
stabilization work begins.
If
the pay item for Mixture Design for Chemically Stabilized Soils is included in
the Contract Documents, prepare and submit reports according to Supplement
1120.
206.04 Test Rolling. When specified, test roll prior to chemical stabilization with a proof
roller conforming to 204.06.
206.05
Construction. Perform chemical stabilization work when the
air temperature is 40 °F (5 °C) or above and when the soil is not frozen.
Do not perform this work during wet or unsuitable weather.
A. Spreading. Shape the subgrade to the approximate profile
grade prior to spreading the chemical so as to permit the construction of a
uniformly compacted course of chemically treated soil to the thickness shown on
the plans. The addition of the chemical will raise the subgrade profile
approximately 1 inch (25 mm). Remove this excess material during the fine
grading.
If the pay item for
Mixture Design for Chemically Stabilized Soils is not included in the Contract
Documents, use the following spreading percentage rate for the specified
chemical. The percentage is based on a dry density for soil of 110 pounds per
cubic foot (1760 kg/m3):
Chemical |
Spreading Rate |
Cement |
6 % |
Lime |
5 % |
Lime Kiln Dust |
7 % |
Spread the chemical
uniformly on the subgrade using a mechanical spreader at the approved rate and
at a constant slow rate of speed.
Use a distribution
bar with a maximum height of 3 feet (1 meter) above the subgrade. Use a
canvas shroud that surrounds the distribution bar and extends to the subgrade.
Minimize dusting when
spreading the chemical. Control dust according to 107.19. Do not spread the chemical
when wind conditions create blowing dust that exceeds the limits in 107.19.
Do not spread the
chemical on standing water.
B. Mixing. Immediately after spreading the chemical, mix
the soil and chemical as follows.
1.
Cement or Lime Kiln Dust. Mix
the chemical and soil using a power driven transverse type mixer equipped with
a computer controlled volumetric water readout. Continue mixing until the
cement or lime kiln dust is thoroughly incorporated into the soil and is a uniform
color.
Do not water during
the initial mixing.
Perform the initial
mixing so that 60 percent of the soil mixture passes the No. 4 sieve (4.75 mm)
and 100 percent passes the 1 inch sieve (25mm), exclusive of aggregate larger
than the No. 4 sieve (4.75 mm) size.
After the initial
mixing, remix the soil and introduce water through the mixer to bring the mixed
material to at least optimum moisture. Uniformly distribute the water in
sufficient quantity to hydrate the cement or lime kiln dust.
If the chemical and
soil can be mixed to the required gradation and the water can be added to bring
the soil mixture to the required moisture content in one mixing, then only one
mixing of the soil, water and chemical is required.
Restrict the addition
of water when the moisture content of the soil exceeds 3 percent above optimum
moisture. Add water to the mixed soil within 2 hours after the initial
mixing.
Once the water is
added to the mixture, complete the mixing, compacting, and shaping within 2
hours from start to finish.
2.
Lime. Mix the lime and soil
using a power driven transverse type mixer equipped with a computer controlled
volumetric water readout. If necessary, add water to bring the mixed material
to at least 3 percent above optimum moisture content. Continue mixing
until the lime is thoroughly incorporated into the soil, all soil clods are
reduced to a maximum size of 2 inches (50 mm), and the mixture is a uniform
color.
After the initial
mixing, lightly compact the material to seal it against rain or excessive
drying by using a steel wheel or pneumatic tire roller.
Allow the lime and
soil mixture to cure (mellow) for a period of not less than 24 hours and not
more than 7 days. If more than 7 days elapse between initial mixing and
final mixing, add an additional 0.5 percent of lime during the final
mixing. Furnish the additional lime at no cost to the Department unless
the delay beyond the 7-day limit is caused by conditions beyond the Contractor’s
control.
Perform the final
mixing until the soil mixture is completely pulverized with all clods reduced
to a maximum size of 1 inch (25 mm) and at least 60 percent of the clods
passing the No. 4 (4.75 mm) sieve, exclusive of aggregate larger than the No. 4
sieve (4.75 mm). Continue mixing until the lime is uniformly distributed
throughout the pulverized soil.
During final mixing,
return the mixture to the moisture contents stated above, then shape and
compact the mixture.
3.
Mixture Depth Check. Check the
uniformity of the mix by digging trenches or a series of holes at regular
intervals for the full depth of treatment and inspecting the color and depth of
the exposed material. Use diluted hydrochloric acid or phenolphthalein to
indicate the presence of calcium and ensure that the chemical is mixed to the
desired depth.
C. Compacting. Start compaction no more than 30 minutes after
the final mixing.
Compact all
chemically stabilized subgrade to the requirements in 204.03,
except use 98 percent of the maximum dry density for acceptance.
Determine the maximum dry density for acceptance by using the Ohio Typical
Moisture Density Curves, the moisture density curves from the Contractor’s
mixture design submittal, or the maximum dry density obtained by test section
method.
Use a vibratory
footed roller weighing at least 10 tons (9 metric tons).
Use the moisture
controls according to 203.07.A, except ensure
that the moisture content at time of compaction is at or above optimum.
Perform the final
rolling using a smooth drum roller. Do not use vibration during the final
rolling.
The Contractor may
either shape and fine grade the chemically stabilized subgrade before the
curing period, or shape the subgrade before the curing period and fine grade
after the curing period. If fine grading before the curing period, fine grade
the same day as mixing, compacting, and shaping. If fine grading after the
curing period, shape the subgrade approximately 1 inch (25 mm) above the
profile grade and typical sections. In either case, fine grade the subgrade to
the profile grade and typical sections within the tolerances in 203.08.
D. Curing. Immediately after the compaction and shaping of
the chemically stabilized subgrade, cover the surface with curing coat for
curing the chemically stabilized subgrade. Use a rate of 1 gallon per 30
square feet (1.36 liters per square meter) for emulsions or a rate of 1 gallon
per 150 square feet (0.27 liters per square meter) when the curing
materials in 451.02 are used.
Apply the curing coat
before the surface dries. If the curing coat is delayed or the surface
starts to dry out, indicated by turning white, apply water for temporary curing
until the curing coat can be applied. Do not apply the curing coat unless
the curing coat can set up before it rains. When the application of
curing coat must be delayed, keep the chemically stabilized subgrade wet by
using water until the curing coat can be applied.
Cure the chemically
stabilized subgrade for at least five days before the placement of the
overlying course.
E. Proof Rolling. After the curing period, proof
roll the chemically stabilized subgrade according to Item 204.
F. Protection. Drain and maintain the work according to 203.04.A.
Do not operate any
equipment on the chemically stabilized subgrade during the curing period.
Do not allow the
chemically stabilized subgrade to freeze during the cure period.
Cover the completed
chemically stabilized subgrade with the aggregate base within 60 calendar days.
206.06 Mixture Design for Chemically Stabilized Soils. When
included in the plans, perform a mixture design for chemically stabilized soils
according to Supplement
1120.
206.07 Method of Measurement. The Department
will measure chemically stabilized subgrade by the number of square yards
(square meters) computed from the profile grade and typical sections accepted
in place.
The
Department will measure cement, lime, and lime kiln dust by the number of tons (metric
tons) incorporated in the complete and accepted work.
The
Department will measure Test Rolling according to 204.08
as specified for Proof Rolling.
The
Department will measure Curing Coat by the number of square yards (square
meters) computed from the profile grade and typical sections accepted in place.
206.08 Basis of Payment. The
Department will pay lump sum for all work, labor, and equipment described in 206.06. The Department will pay two-thirds of
the lump sum amount bid when the soil sampling and testing is complete and the
report is accepted by the Department. The Department will pay one-third
of the lump sum amount bid when the chemically stabilized subgrade is completed
and accepted by the Department, and the field verification test results are all
submitted.
The
Department will pay for accepted quantities at the contract prices as follows:
Item
Unit
Description
206
Square
Yard
Cement Stabilized Subgrade,
(Square
Meter)
__inches deep
206
Square
Yard
Lime Stabilized Subgrade,
(Square
Meter)
__ inches deep
206
Square
Yard
Lime Kiln Dust Stabilized
(Square
Meter)
Subgrade, __ inches deep
206
Ton (Metric
Ton) Cement
206
Ton (Metric Ton)
Lime
206
Ton (Metric
Ton) Lime
Kiln Dust
206
Square Yard
Curing Coat
(Square Meter)
206
Hour
Test Rolling
206
Lump
Sum
Mixture Design for Chemically
Stabilized Soils