### **ITEM P-155 LIME-TREATED SUBGRADE**

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> **The soluble sulfate contents of the soils should be checked during
> design to determine if stabilization with lime, cement, and/or fly ash
> can react and induce heave. Contents as low as 0.5% soluble sulfates
> have resulted in the formation of ettringnite and thaumasite, which
> expands when available water is present.**

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DESCRIPTION

**155-1.1**  This item shall consist of constructing one or more courses
of a mixture of soil, lime, and water in accordance with this
specification, and in conformity with the lines, grades, thicknesses,
and typical cross sections shown on the plans.

MATERIALS

**155-2.1 HYDRATED LIME.**  All lime shall be manufactured high-calcium
quicklime, low-calcium quicklime, or hydrated lime, as defined by ASTM C
51, and conform to the requirements of ASTM C 977. By product lime or
any form of calcium oxide (CaO), calcium hydroxide (Ca(OH)2), magnesium
oxide (MgO) or magnesium hydroxide (Mg(OH)2), alone or in combination,
that are not directly produced from quicklime produced from calcining
limestone, shall not be permitted.

**155-2.2 COMMERCIAL LIME SLURRY.**  Commercial lime slurry shall be a
pumpable suspension of solids in water.  The water or liquid portion of
the slurry shall not contain dissolved material in sufficient quantity
naturally injurious or objectionable for the purpose intended.  The
solids portion of the mixture, when considered on the basis of
\`\`solids content,\'\' shall consist principally of hydrated lime of a
quality and fineness sufficient to meet the following requirements as to
chemical composition and residue.

**a. Chemical Composition.**  The \`\`solids content\'\' of the lime
slurry shall consist of a minimum of 70%, by weight, of calcium and
magnesium oxides.

**b. Residue.**  The percent by weight of residue retained in the
\`\`solids content\'\' of lime slurry shall conform to the following
requirements:

Residue retained on a No. 6 (3360 micron) sieve ‑‑‑‑‑‑ Max. 0.0%

Residue retained on a No. 10 (2000 micron) sieve ‑‑‑‑‑ Max. 1.0%

Residue retained on a No. 30 (590 micron) sieve ‑‑‑‑‑‑ Max. 2.5%

**c. Grade.**  Commercial lime slurry shall conform to one of the
following two grades:

Grade 1.  The \`\`dry solids content\'\' shall be at least 31%

by weight, of the slurry.

Grade 2.  The \`\`dry solids content\'\' shall be at least 35%,

by weight, of the slurry.

**155-2.3 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 test.

**155-2.4 SOIL.**  The soil for this work shall consist of materials on
the site 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 (60 mm).

COMPOSITION

**155-3.1 LIME.**  Lime shall be applied at the rate specified on the
plans for the depth of subgrade treatment shown.

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> **This paragraph should specify the amount of lime to be incorporated
> either by percent of dry weight or by the desired performance
> criteria. Samples for determination of lime content should be from
> material, which will represent the final placement of material to be
> treated. The Lime content should be sufficient to lower the Liquid
> Limit to less than 30 and the Plasticity Index to less than 10.**
>
> **The project specifications should address the percent of lime to be
> used in the project. If the exact percent is not specified, the
> contractor should be provided with some means to estimate (for bidding
> purposes) the quantity of lime to be used in the project.**

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**155-3.2 TOLERANCES.**  At final compaction, the lime and water content
for each course of subgrade treatment shall conform to the following
tolerances:

  ------------------------------------ ----------------------------------
  **Material**                         **Tolerance**

                                       

  Lime                                 \+ 0.5%

  Water                                \+ 2%, ‑0%
  ------------------------------------ ----------------------------------

WEATHER LIMITATIONS

**155-4.1 WEATHER LIMITATION.**  The lime‑treated subgrade shall not be
mixed while the atmospheric temperature is below 40 F (4 C) or when
conditions indicate that temperatures may fall below 40 F (4 C) within
24 hours, when it is foggy or rainy, or when soil or subgrade is frozen.

EQUIPMENT

**155-5.1 EQUIPMENT.**  The equipment required shall include all
equipment necessary to complete this item such as: grading and
scarifying equipment, a spreader for the lime or lime slurry, mixing or
pulverizing equipment, sheepsfoot and pneumatic or vibrating rollers,
sprinkling equipment, and trucks.

CONSTRUCTION METHODS

**155-6.1 GENERAL.**  It is the primary requirement of this
specification to secure a completed subgrade containing a uniform lime
mixture, free from loose or segregated areas, of uniform density and
moisture content, well bound 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 lime, maintain the work, and rework
the courses as necessary to meet the above requirements.

Prior to beginning any lime 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.  The material to be treated
shall then be excavated to the secondary grade (proposed bottom of lime
treatment) and removed or windrowed to expose the secondary grade.  Any
wet or unstable materials below the secondary grade shall be corrected,
as directed by the Engineer, by scarifying, adding lime, and compacting
until it is of uniform stability.  The excavated material shall then be
spread to the desired cross section.

If the Contractor elects to use a cutting and pulverizing machine that
will remove the subgrade material accurately to the secondary grade and
pulverize the material at the same time, he will not be required to
expose the secondary grade nor windrow the material.  However, the
Contractor shall be required to roll the subgrade, as directed by the
Engineer, and correct any soft areas that this rolling may reveal before
using the pulverizing machine.  This method will be permitted only where
a machine is provided which will ensure that the material is cut
uniformly to the proper depth and which has cutters that will plane the
secondary grade to a smooth surface over the  entire width of the cut. 
The machine must give visible indication at all times that it is cutting
to the proper depth.

**155-6.2 APPLICATION.**  Lime 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 lime with the soil shall be
accomplished by the methods hereinafter described as \`\`Dry Placing\'\'
or \`\`Slurry Placing.\'\'  When hydrated lime is specified, the
Contractor may use either method.

**a. Dry Placing.**  The lime 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 lime spread shall be the amount
required for mixing to the specified depth that will result in the
percentage determined in the job mix formula.

The lime shall be distributed in such manner that scattering by wind
will be minimal.  Lime shall not be applied when wind conditions, in the
opinion of the Engineer, are detrimental to a proper application.  A
motor grader shall not be used to spread the lime.  The material shall
be sprinkled, as directed by the Engineer, until the proper moisture
content has been reached.

**b. Slurry Placing.**  The lime shall be mixed with water in trucks
with approved distributors and applied as a thin water suspension or
slurry.  Commercial lime slurry shall be applied with a lime percentage
not less than that applicable for the grade used.  The distribution of
lime shall be attained by successive passes over a measured section of
subgrade until the proper amount of lime has been spread.  The amount of
lime spread shall be the amount required for mixing to the specified
depth that will result in the percentage determined in the job mix
formula.  The distributor truck shall continually agitate the slurry to
keep the mixture uniform.

**155-6.3 MIXING.**  The mixing procedure shall be the same for \`\`Dry
Placing\'\' or \`\`Slurry Placing\'\' as hereinafter described:

**a. First Mixing.**  The full depth of the treated subgrade shall be
mixed with an approved mixing machine.  Lime shall not be left exposed
for more than 6 hours.  The mixing machine shall make two coverages. 
Water shall be added to the subgrade during mixing to provide a moisture
content above the optimum moisture of the material and to ensure
chemical action of the lime and subgrade.  After mixing, the subgrade
shall be lightly rolled to seal the surface and help prevent evaporation
of moisture.  The water content of the subgrade mixture shall be
maintained at a moisture content above the optimum moisture content for
a minimum of 48 hours or until the material becomes friable.  During the
curing period, the material shall be sprinkled as directed.  During the
interval of time between application and mixing, lime that has been
exposed to the open air for 6 hours or more, or to excessive loss due to
washing or blowing will not be accepted for payment.

**b. Final Mixing.**  After the required curing time, the material shall
be uniformly mixed by approved methods.  If the mixture contains clods,
they shall be reduced in size by blading, discing, harrowing,
scarifying, or the use of other approved pulverization methods so that
the remainder of the clods shall meet the following requirements when
tested dry by laboratory sieves:

  ---------------------------------------------------- ------------------
                                                       **Percent**

  Minimum of clods passing 1-1/2\\ inch sieve          100

  Minimum of clods passing No. 4 sieve                 60
  ---------------------------------------------------- ------------------

**155-6.4 COMPACTION.**  Compaction of the mixture shall begin
immediately after final mixing.  The material shall be aerated or
sprinkled as necessary to provide optimum moisture.  The field density
of the compacted mixture shall be at least 93 percent of the maximum
density of laboratory specimens prepared from samples taken from the
material in place.  The specimens shall be compacted and tested in
accordance with ASTM D 698.  The in‑place field density shall be
determined in accordance with ASTM D 1556 or ASTM D 2922.  Any mixture
that has not been compacted shall not be left undisturbed for more than
30 minutes.  The moisture content of the mixture at the start of
compaction shall not be below nor more than 2 percentage points above
the optimum moisture content.  The optimum moisture content shall be
determined in accordance with ASTM D 698 and shall be less than that
amount which will cause the mixture to become unstable during compaction
and finishing.

The material shall be sprinkled and rolled 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 by
sprinkling and rolling.  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 and to the established lines and grades.  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.

When nuclear gages are to be used for density determination, testing
shall be done in accordance with Section 120.

**155-6.5 FINISHING AND CURING.**  After the final layer or course of
lime‑treated subgrade has been compacted, it shall be brought to the
required lines and grades in accordance with the typical sections.  The
completed section shall then be finished by rolling, as directed, with a
pneumatic or other suitable roller sufficiently light to prevent hair
cracking.  The finished surface shall not vary more than 3/8 inch (9 mm)
when tested with a 16‑foot (4.8 meter) 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.

The completed section shall be moist‑cured for a minimum of 7 days
before further courses are added or any traffic is permitted, unless
otherwise directed by the Engineer.  Subsequent courses shall be applied
within 14 days after the lime‑treated subgrade is cured.

**155-6.6 THICKNESS.**  The thickness of the lime‑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 (250 square meters). 
When the base deficiency is more than 1/2 inch (12 mm), 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.

**155-6.7 MAINTENANCE.**  The Contractor shall maintain, at his/her own
expense, the entire lime‑treated subgrade in good condition from the
start of work until all the work has been completed, cured, and accepted
by the Engineer.

METHOD OF MEASUREMENT

**155-7.1** The yardage of lime-treated subgrade to be paid for shall be
the number of square yards (square meters) completed and accepted.

**155-7.2** The amount of lime to be paid for shall be the number of
tons (kg) of Hydrated Lime, or the calculated equivalent thereof, used
as authorized. \"Calculated Equivalent\" will be determined by the
Engineer as follows:

**a.** Hydrated lime delivered to the project in dry form will be
measured according to the actual tonnage either spread on the subgrade
or batched on site into a slurry, whichever is applicable.

**b.** Lime delivered to the project in slurry form will be paid for on
the basis of certified chemical composition tickets and batch weight
tickets. The owner shall reserve the right to have the dry lime content
verified by an independent testing laboratory. If the chemical
composition is reported on the basis of Pebble Quicklime, the equivalent
hydrated lime will be determined in accordance with paragraph c. below.

**c.** If Pebble Quicklime is delivered to the project in dry form it
will be measured for payment on the basis of the following formula:

Total Quicklime (CaO)(Tons) x %Purity x 1.32 Factor + Total Quicklime
(CaO)(Tons) x % Impurities x 1.00 Factor = Equivalent Hydrated Lime
Ca(OH)~2~(Tons).

The foregoing will apply whether the quicklime is spread dry (if
allowed) or batched into a slurry.

BASIS OF PAYMENT

**155-8.1**  Payment shall be made at the contract unit price per square
yard (square meter) for the lime‑treated subgrade of the thickness
specified.  The price shall be full compensation for furnishing all
material, except the lime, and for all preparation, delivering, placing
and mixing these materials, and all labor, equipment, tools and
incidentals necessary to complete this item.

**155-8.2**  Payment shall be made at the contract unit price per pound
(kg) of lime.  This price shall be full compensation for furnishing this
material; for all delivery, placing and incorporation of this material;
and for all labor, equipment, tools, and incidentals necessary to
complete this item.

Payment will be made under:

Item P‑155‑8.1 Lime‑treated subgrade---per square yard (square meter)

Item P‑155‑8.2 Lime---per pound (kg)

TESTING REQUIREMENTS

ASTM D 698 Moisture‑Density Relations of Soils and Soil‑Aggregate
Mixtures Using 5.5 lb (2.49 kg) Rammer and 12‑in. (305 mm) Drop

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

MATERIAL REQUIREMENTS

ASTM C 977 Quicklime and Hydrated Lime for Soil Stabilization

**END OF ITEM P-155**

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