### **ITEM P-158 FLY ASH 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.**
>
> **Soils should be tested by the Engineer prior to preparing the
> specification in order to assure that the fly ash can perform with the
> soils used in the project.**
>
> **At target design, the fly ash content should be such that the Liquid
> limit of the soils is reduced, the PH is increased, and an increase in
> bearing capacity is achieved.**

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DESCRIPTION

**158-1.1**  This item shall consist of constructing one or more courses
of a mixture of soil, fly ash, and water in accordance with this
specification, and in conformity with the lines, grades, thicknesses,
and typical cross sections shown on the plans.

MATERIALS

**158-2.1 FLY ASH.** Fly ash shall meet ASTM Specifications C-618,
Section 3.3 when sampled and tested in accordance with Sections 5,6, and
8, unless otherwise shown on the plans. Fly ash shall be of the Class
\"C\" designation containing a minimum of 25% CaO. The source of the ash
shall be identified and approved in advance of stabilization operations
in order that laboratory tests can be completed prior to commencing
work.

Fly Ash shall be stored and handled in closed weatherproof containers
until immediately before distribution. Temporary storage (less than 12
hours) of fly ash in open pits may be allowed provided that wetting of
the fly ash by rain or ground water is not allowed. Fly ash exposed to
moisture prior to mixing with soils shall be discarded.

**158-2.2 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.

**158-2.3 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

**158-3.1 FLY ASH.**  Fly ash 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 fly ash to be
> incorporated either by percent of dry weight or by the desired
> performance criteria. Samples for determination of fly ash content
> should be from material, which will represent the final placement of
> material to be treated. The fly ash content should be sufficient at
> target design, such that the liquid limit of the soils is reduced, the
> PH is increased, and an increase in bearing capacity is achieved.**
>
> **The project specifications should address the percent of fly ash 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 fly ash to be used in the project.
> Experience has shown that 15% of dry weight has been sufficient.**

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**158-3.2 TOLERANCES.**  At final compaction, the fly ash and water
content for each course of subgrade treatment shall conform to the
following tolerances:

**Material Tolerance**

Fly Ash + 0.5%

Water + 2%, ‑0%

WEATHER LIMITATIONS

**158-4.1 WEATHER LIMITATION.** The fly ash 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

**158-5.1 EQUIPMENT.**  The equipment required shall include all
equipment necessary to complete this item such as: grading and
scarifying equipment, a spreader for the fly ash, mixing or pulverizing
equipment, sheepsfoot and pneumatic or vibrating rollers, sprinkling
equipment, and trucks.

CONSTRUCTION METHODS

**158-6.1 GENERAL.**  It is the primary requirement of this
specification to secure a completed subgrade containing a uniform fly
ash 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 fly ash, maintain the work, and rework
the courses as necessary to meet the above requirements.

Prior to beginning any fly ash 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 fly ash 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 fly ash, 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.

**158-6.2 APPLICATION.**  Fly ash shall be spread only on that area
where the first mixing operations can be completed within 2 hours.  The
application and mixing of fly ash with the soil shall be accomplished by
the methods hereinafter described as \`\`Dry Placing.\'\' 

**a. Dry Placing.**  The fly ash 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 fly ash 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 fly ash shall be distributed in such manner that scattering by wind
will be minimal.  Fly ash 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 fly ash. 

**158-6.3 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 that utilizes a direct hydraulic
drive. Fly ash shall not be left exposed for more than 30 minutes after
distribution. The mixing machine shall make two coverages. Water shall
be added through use of a pulvamixer equipped with a spray bar in the
mixing drum capable of applying sufficient quantities of water to
achieve the required moisture content of the soil-fly ash mixture. The
system shall be capable of being regulated to the degree as to maintain
moisture contents within the recommended range.

Required moisture contents shall be established by the Engineer based on
laboratory tests with the site soils and specific fly ash to be used for
the treatment. Final moisture content of the mix, immediately prior to
compaction shall be determined in accordance with ASTM D 698 and shall
not be below nor more than 2 percent above the optimum moisture content
for maximum density of the mix. If moisture contents exceed the
specified limits, additional fly ash may be added to lower the moisture
content to the required limits. Lowering moisture contents by aeration
following addition of the fly ash will not be permitted.

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

**158-6.4 COMPACTION.**  Compaction of the soil-fly ash mixture shall
begin immediately after mixing of the fly ash and be completed within
two hours following incorporation of the fly ash. The field density of
the compacted mixture shall be at least 95 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 density shall be determined in
accordance with ASTM D 1556, ASTM D 2167 or ASTM D 2922.

All irregularities, depressions, or weak spots, which develop, shall be
corrected immediately by scarifying the areas affected, adding or
removing material as required, and reshaping and re-compacting. 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.

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> **If nuclear density machines are to be used for density
> determination, the machines shall be calibrated in accordance with
> ASTM D 2922. The nuclear equipment shall be calibrated using blocks of
> materials with densities that extend through a range representative of
> the density of the proposed fly ash treated subgrade material. (See
> appendix 1 for additional guidance).**

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**158-6.5 FINISHING AND CURING.**  After the final layer or course of
the fly ash 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 (9mm) 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 fly ash 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.

Maintain in a thorough and continuously moist condition by sprinkling.

Apply a 2-inch layer of earth of the completed course and maintain in a
moist condition.

**158-6.6 THICKNESS.**  The thickness of the fly ash 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.

**158-6.7 MAINTENANCE.**  The Contractor shall maintain, at his/her own
expense, the entire fly ash 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

**158-7.1**  The yardage of fly ash treated subgrade to be paid for
shall be the number of square yards (square meters) completed and
accepted.

**158-7.2**  The amount of fly ash to be paid for shall be the number of
pounds (kg) of fly ash used as authorized.

BASIS OF PAYMENT

**158-8.1**  Payment shall be made at the contract unit price per square
yard (square meter) for the fly ash treated subgrade of the thickness
specified.  The price shall be full compensation for furnishing all
material, except the fly ash, and for all preparation, delivering,
placing and mixing these materials, and all labor, equipment, tools and
incidentals necessary to complete this item.

**158-8.2**  Payment shall be made at the contract unit price per pound
(kg) of fly ash.  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‑158‑8.1 Fly ash treated subgrade---per square yard (square meter)

Item P‑158‑8.2 Fly ash---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 2167 Density and Unit Weight of Soil in Place by the
Rubber‑Ballon Method

AASHTO T 26 Quality of Water to be Used in Concrete

MATERIAL REQUIREMENTS

ASTM C 618 Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as
a Mineral Admixture in Concrete

**END OF ITEM P-158**

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