### **ITEM P-157 CEMENT KILN DUST (CKD) TREATED SUBGRADE**

DESCRIPTION

**157-1.1** This item shall consist of constructing one or more courses
of a mixture of soil, cement kiln dust, and water in accordance with
this specification, and in conformity with the lines, grades, thickness,
and typical cross sections shown on the plans.

MATERIALS

**157-2.1 CEMENT KILN DUST**. Cement kiln dust shall contain a minimum
of 40% CaO and be capable of providing the soil modification specified
for this project. Cement Kiln Dust from the
(\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_) Cement Plant(s) is(are) a
pre-approved source for cement kiln dust for this project. All other
sources shall be identified and approved in advance of stabilization
operations in order that laboratory tests can be completed prior to
commencing work.

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> **NOTE TO ENGINEER: Enter the known acceptable sources of cement kiln
> dust. If no sources have been pre-identified, delete the 2nd
> sentence.**

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Cement kiln dust shall be stored and handled in closed waterproof
containers until immediately before distribution. Temporary storage
(less than 12 hours) of cement kiln dust in open pits may be allowed
provided that wetting of the cement kiln dust by rain or subgrade
moisture is not allowed. Cement kiln dust exposed to moisture prior to
mixing with soils shall be discarded.

**157-2.3 WATER.** Water used for mixing or curing shall be reasonably
clean and free of oil, salt, acid, alkali, sugar, vegetable, or other
substances injurious to the finished product. Water shall be tested in
accordance with and shall meet the suggested requirements of AASHTO T
26. Water known to be of potable quality may be used without testing.

**157-2.4 SOIL.** The soil for this work shall consist of on site
materials or selected materials from other sources and shall be uniform
in quality and gradation, and shall be approved by the Engineer. The
soil shall be free of roots, sod, weeds, and stones larger than 2 1/2
inches and have a sulfate content of less than 1.0%.

COMPOSITION

**157-3.1 CEMENT KILN DUST**. Samples for evaluation of cement kiln dust
effectiveness shall be taken from each layer of CKD treated subgrade
after it has been properly mixed and moisture conditioned. Cement kiln
dust shall be added until a Plasticity Index of less than (\_\_\_\_) is
reached. When the cement kiln dust treated material is used as a base
material, it shall be added until minimum CBR of (\_\_\_\_) and/or a
7-day accelerated (100°F) compressive strength (Section 8.5 of ASTM
C-593) of (\_\_\_\_\_\_) psi is achieved. Payment will be based on the
amount of cement kiln dust required to obtain the minimum soil
properties specified.

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> **NOTE TO ENGINEER: Enter the desired properties for the treated
> material.**

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**157-3.2 TOLERANCES.** At final compaction, the CKD and water content
for each course of subgrade treatment shall conform to the following
tolerances:

> [Material/Properties Target Tolerance Specifications]{.underline}
>
> Cement Kiln Dust (\_\_\_\_)% 0 to +2% % Total Dry Materials
>
> Moisture Content Optimum 0% to 6% ASTM D-1557
>
> Plastic Index \< (\_\_\_\_) None ASTM D-4318

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> **NOTE TO ENGINEER: Enter the appropriate values as identified in
> paragraph 3.1**

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WEATHER LIMITATIONS

**157-4.1 WEATHER LIMITATION.** The cement kiln dust-treated subgrade
shall not be mixed while the atmospheric temperature is below 40 F or
when conditions indicate that temperatures may fall below 40 F within 24
hours, or when soil or subgrade is frozen.

EQUIPMENT

**157-5.1 EQUIPMENT**. The equipment required shall include all
equipment necessary to complete this item such as: grading and
scarifying equipment, a spreader for the cement kiln dust, mixing or
pulverizing equipment, sheepsfoot and pneumatic or vibrating rollers,
sprinkling equipment, and trucks.

CONSTRUCTION METHODS

**157-6.1 GENERAL.** It is the primary requirement of this specification
to secure a completed subgrade containing a uniform cement kiln
dust/soil mixture, free from loose or segregated areas, of uniform
density and moisture content, well mixed for its full depth, and with a
smooth surface suitable for placing subsequent courses. It shall be the
responsibility of the Contractor to regulate the sequence of his/her
work, to use the proper amount of cement kiln dust, maintain the work,
and rework the courses as necessary to meet the above requirements.

Prior to beginning any cement kiln dust treatment the subgrade shall be
constructed and brought to grade as specified in Item P 152
\`\`Excavation and Embankment\'\' and shall be shaped to conform to the
typical sections, lines, and grades as shown on the plans. Any wet or
unstable areas shall be corrected, as directed by the Engineer, by
over-excavating, scarifying, adding cement kiln dust, and/or compacting
until it is of uniform stability. The Contractor shall be required to
roll the subgrade, as directed by the Engineer, and correct any soft
areas that this rolling may reveal.

**157-6.2 APPLICATION.** Cement kiln dust shall be spread only on that
area where the first mixing operations can be completed during the same
working day. The application and mixing of cement kiln dust with the
soil shall be accomplished by the methods hereinafter described as \"Dry
Placing\".

**a. Dry Placing.** The cement kiln dust shall be spread uniformly over
the top of the subgrade by an approved screw type spreader box or other
approved spreading equipment. The amount of cement kiln dust spread
shall be the amount required for mixing to the specified depth which
will result in the percentage determined in the job mix formula.

The cement kiln dust shall be distributed in such a manner that
scattering by wind will be minimal. Cement kiln dust shall not be
applied when wind conditions, in the opinion of the Engineer, are
detrimental to a proper application. The CKD/soil mixture shall be
moisture conditioned, as directed by the Engineer, until the proper
moisture content has been reached.

**157-6.3 MIXING.** The mixing procedure shall be the same for \"Dry
Placing\" as hereinafter described:

The full depth of the treated subgrade shall be mixed with a rotary
pulvamixer, disc and field cultivator or, other suitable methods as
approved by the Engineer. Cement kiln dust shall not be left exposed for
more than 1 hour after distribution.

Required moisture contents shall be established by the Engineer based on
laboratory tests with the site soils at the specified cement kiln dust
percent to be used for soil modification. Final moisture content of the
mix, immediately prior to compaction shall be determined in accordance
with ASTM C-593 (Modified Proctor) and shall not be less than the
optimum moisture content or more than 6 percent over optimum.

If the soil cement kiln dust mixture contains clods greater than 1-1/2
inch in size, they shall be reduced in size by additional pulverization.

As a minimum, one soil sample will be obtained and tested for each 25
tons of CKD incorporated. Testing shall include Plastic Index
Determination (ASTM D-4318) and 7-day accelerated compressive strengths
(Section 8 ASTM C-593).

Areas that fall below specified values will need to be reworked, as
directed by the Engineer.

**157-6.4 COMPACTION.** Compaction of the soil/cement kiln dust mixture
shall be delayed for a minimum of 24 hours after mixing the cement kiln
dust into the subgrade. The field density of the compacted mixture shall
be at least 90 percent of the maximum density as determined by ASTM
D-1557. The in-place field density shall be determined in accordance
with ASTM D-1556 or ASTM D 2167. Testing frequency shall be a minimum of
1 compaction test per 5000 square feet of stabilized base or as directed
by the Engineer.

All irregularities, depressions, or weak spots that develop shall be
corrected immediately by scarifying the areas affected, adding or
removing material as required, and reshaping and recompacting. The
surface of the course shall be maintained in a smooth condition, free
from undulations and ruts, until other work is placed thereon or the
work is accepted.

In addition to the requirements specified for density, the full depth of
the material shown on the plans shall be compacted to the extent
necessary to remain firm and stable under construction equipment. After
each section is completed, tests will be made by the Engineer. If the
material fails to meet the density requirements, it shall be reworked to
meet these requirements. Throughout this entire operation, the shape of
the course shall be maintained by blading, and the surface upon
completion shall be smooth and shall conform with the typical section
shown on the plans to the established lines and grades specified. Should
the material, due to any reason or cause, lose the required stability,
density, and finish before the next course is placed or the work is
accepted, it shall be recompacted and refinished at the sole expense of
the Contractor.

**157-6.5 FINISHING AND CURING.** After the final layer or course of
cement kiln dust treated subgrade has been compacted, it shall be
brought to the required lines and grades in accordance with the typical
sections. The finished surface shall not vary more than 3/8 inch when
tested with a 16-foot straightedge applied parallel with and at right
angles to the pavement centerline. Any variations in excess of this
tolerance shall be corrected by the Contractor, at his/her own expense,
in a manner satisfactory to the Engineer.

After the cement kiln dust treated course has been finished as specified
herein, the surface shall be protected against rapid drying by either of
the following methods for a period of not less than three days or until
the pavement section is placed.

**a.** Maintain in a thorough and continuously moist condition by
sprinkling.

**b.** Apply a 2-inch layer of earth on the compacted course and
maintain in a moist condition.

**157-6.6 THICKNESS.** The thickness of the cement kiln dust treated
subgrade shall be determined by depth tests or cores taken at intervals
so that each test shall represent no more than 300 square yards. When
the base deficiency is more than 1/2 inch, the Contractor shall correct
such areas in a manner satisfactory to the Engineer. The Contractor
shall replace, at his/her expense, the base material where borings are
taken for test purposes.

**157-6.7 MAINTENANCE.** The Contractor shall maintain, at his/her own
expense, the entire cement kiln dust treated subgrade in good condition
from the start of work until all the work has been completed, cured, and
accepted by the Engineer.

**157-6.8 HANDLING AND SAFETY.** The Contractor shall obtain from the
Supplier of the cement kiln dust the instructions for, proper safety and
handling of the cement kiln dust.

METHOD OF MEASUREMENT

**157-7.1** The amount of cement kiln dust treated subgrade to be paid
for shall be based on the number of square yards completed and accepted.

The amount of cement kiln dust utilized is based upon an application
rate of (\_\_\_) percent (by dry weight of soil).

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> **NOTE TO ENGINEER: Enter the estimated percentage of kiln dust for
> the project.**

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BASIS OF PAYMENT

**157-8.1** Payment shall be made at the contract unit price per square
yard for the cement kiln dust treated subgrade for the thickness
specified. The price shall be full compensation for furnishing all
material, and for all preparation, delivering, placing and mixing these
materials, and all labor, equipment, tools and incidentals necessary to
complete this item.

Payment will be made under:

Item P 157 8.1 Cement kiln dust treated subgrade per square yard

TESTING REQUIREMENTS

> ASTM D-1557 Moisture-Density Relations of Soils and Soil-Aggregate
> Mixtures Using 10 lb (7.1 kg) Rammer and 18-in. Drop

ASTM D-1556 Density of Soil in Place by the Sand-Cone Method

ASTM D-2167 Density and Unit Weight of Soil in Place by the
Rubber-Balloon Method

ASTM D-2922 Density of soil in place by the Nuclear Density Method.

AASHTO T 26 Quality of Water to be Used in Concrete

ASTM C-593 Fly Ash and other Pozzolans for use with Lime

> ASTM D-4318 Liquid Limit, Plastic Limit and Plastic Index of Soils

**END OF ITEM P-157**