### **ITEM P-212 SHELL BASE COURSE**

DESCRIPTION

**212-1.1** This item shall consist of a base course composed of shell
and binder constructed on a prepared underlying course in accordance
with these specifications and shall conform to the dimensions and
typical cross section shown on the plans.

MATERIALS

**212-2.1 MATERIALS**.  The shell shall consist of durable particles of
\`\`dead\'\' oyster or clam shell.  The base material shall consist of
oyster shell, together with an approved binding or filler material,
blended or processed to produce a uniform mixture complying with the
specifications for gradation, soil constants, and compaction
capability.  Clam shell may be used only in combination with oyster
shell in the proportion up to and including 50%.

The shell shall be reasonably clean and free from excess amounts of clay
or organic matter such as leaves, grass, roots, and other objectionable
and foreign material.

The gradation of the blended or processed material shall meet the
requirements of the gradation given in the following table, when tested
in accordance with ASTM C 136.

Sieve Designation Percentage by Weight

(square openings) Passing Sieves

3 inch (75.0 mm) 100

3/4 inch (19.0 mm) 60-90

No. 4 (4.75 mm) 15-55

No. 200 (0.075 mm) 0-15

That portion of the material, including the blended filler, passing a
No. 40 (0.42 mm) mesh sieve shall be known as soil binder and shall have
a liquid limit of not more than 25 and a plasticity index of not more
than 8 as determined by ASTM D 4318.

If necessary, the Contractor shall blend or combine materials so that
the final processed material meets all the specifications.  The
Contractor shall make such modifications in materials and methods as are
necessary to secure a material that is capable of being compacted into a
dense and well-bonded base without an excess of soil binder.

**212-2.2 FILLER FOR BLENDING**.  If filler, in addition to that
naturally present in the base course material, is necessary for
satisfactory bonding of the material, or for changing the soil constants
of the material passing the No. 40 (0.42 mm) mesh sieve, or for
correcting the gradation to the limitations of the specified gradation,
it shall be uniformly blended with the base course material on the
pavement or at the plant.  The material for such purpose shall be
obtained from sources approved by the Engineer and shall be of a
gradation necessary to accomplish the specified gradation in the final
processed material.

CONSTRUCTION METHODS

**212-3.1 SOURCES OF SUPPLY**.  The Contractor shall notify the
Engineer, sufficiently in advance, of the intended source of supply of
shell.  the shell shall be obtained from approved sources.  The material
in the stockpile shall be handled in a manner that will secure a uniform
and satisfactory product.

**212-3.2 EQUIPMENT**.  All equipment necessary for the proper
construction of this work shall be on the project, in first-class
working condition, and approved by the Engineer before construction is
permitted to start.

The processing plant shall be designed, constructed, operated, and
capable of thoroughly mixing the shell, binder, and water in the
directed proportions to produce base material of the gradation and
consistency required.

**212-3.3 PREPARING UNDERLYING COURSE**.  The underlying course shall be
checked and accepted by the Engineer before placing and spreading
operations are started.  Any ruts or soft yielding places caused by
improper drainage conditions, hauling, or any other cause shall be
corrected at the Contractor\'s expense before the base course is placed
thereon.  Material shall not be placed on frozen subgrade or subbase.

**212-3.4 PLANT MIXING**.  The base material shall be uniformly blended
and mixed in an approved central or travel mixing plant.  The shell,
together with any blended material, shall be thoroughly mixed with the
required amount of water.  After the mixing is complete, the material
shall be transported to, or spread on, the underlying course without
undue loss of the moisture content.

**212-3.5 PLACING AND SPREADING**.  The base course material that is
correctly proportioned or that has been processed in a central plant
shall be placed on the prepared underlying course and compacted in the
thickness shown on the plans.  The depositing and spreading of the
material shall commence where designated and shall progress without
breaks.  The materials shall be deposited and spread in lanes in a
uniform layer and without segregation of size to such loose depth that,
when compacted, the layer shall have the required thickness.  The
material shall be spread by spreader boxes or other approved devices
that shall distribute the material in a uniform layer.  Dumping from
vehicles in piles requiring rehandling will not be permitted.  hauling
over the uncompacted base course shall not be permitted.

**212-3.6 TRAVEL PLANT MIX**.  When the use of a travel plant is
approved, sufficient quantities and proportions of all material
necessary shall be used to provide a base mixture that conforms to the
specified gradation, quality, and thickness.  If a windrow travel plant
is employed for mixing, the aggregate shall be placed in windrows
parallel to the pavement centerline. If a traveling plant is used which
mixes previously spread aggregates in-place, the material shall be
spread to a thickness that may be readily handled by the machine and
that will develop the proper thickness for each layer.  The base
material shall be of satisfactory moisture content to obtain maximum
density.

After the mixing has been completed, the base material shall be spread
to the required depth and width by a self-powered blade grader,
mechanical spreader, or other approved method.  In spreading, care shall
be taken to prevent cutting into the underlying layer.  The material
shall be bladed, disced, and dragged if necessary until a smooth,
uniform surface is obtained true to line, grade, and cross section and
in condition for compacting.

**212-3.7 MIXED IN-PLACE**.  When specified or permitted, the base
materials may be proportioned and mixed or blended in-place on the
underlying course.  the different layers shall be spread and placed in
the following manner with the relative proportions of the components of
the mixture designated by the Engineer.

The base aggregate shall be deposited and spread evenly on the subgrade
to a uniform thickness and width.  Then the binder or filler shall be
deposited and spread evenly over the first layer.  There shall be as
many layers of materials added as the Engineer may direct to obtain the
required base mixture.

After the required materials have been placed, they shall be thoroughly
mixed and blended using approved graders, discs, harrows, or
rotary-tillers, supplemented by other suitable equipment if necessary. 
The mixing shall continue until the mixture is uniform throughout. 
Areas of segregated material shall be corrected by the addition of
binder or filler material and then thoroughly remixed.  If necessary,
water in the required amount shall be uniformly applied as directed by
the Engineer prior to and during the mixing operations to maintain the
material at the proper moisture content.  When the mixing and blending
has been completed, the material shall be spread in a uniform layer
which, when compacted, will meet the requirements for thickness and
typical cross section.

**212-3.8 GENERAL METHODS FOR PLACING**.  The base course shall be
constructed in layers not less than 4 inches (100 mm) nor more than 6
inches (150 mm) of compacted thickness.  The aggregate, as spread, shall
be of uniform gradation with no pockets of fine or coarse materials. 
Unless otherwise permitted by the Engineer, the aggregate shall not be
spread more than 2,000 square yards (186 square meters) in advance of
the rolling.  Any necessary sprinkling shall be kept within this limit. 
No material shall be placed in snow or on a soft, muddy, or frozen
course.

When more than one layer is required, the construction procedure
described herein shall apply similarly to each layer.

The Engineer shall conduct tests to determine the maximum density and
the proper moisture content of the base material, and this information
will be available to the Contractor.  The base material shall be brought
to a satisfactory moisture content when rolling is started and any minor
variations prior to or during rolling shall be corrected by sprinkling
or aeration.

During placing and spreading operations, sufficient caution shall be
exercised to prevent the incorporation of subgrade, subbase, or shoulder
material into the base course mixture.

**212-3.9 COMPACTION**.  Immediately after completion of the spreading
operations, the base course shall be thoroughly compacted.  The number,
type, and weight of rollers shall be sufficient to compact the mixture
to the required density.

The field density of the compacted material shall be at least 100
percent of the maximum density of laboratory specimens prepared from
samples of the base material delivered to the jobsite.  The laboratory
specimens shall be compacted and tested in accordance with **\[ \]**. 
The in-place field density shall be determined in accordance with ASTM D
1556.  The moisture content of the material at the start of compaction
shall not be below nor more than 1-1/2 percentage points above the
optimum moisture content.

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> **The Engineer shall specify ASTM D 698 for areas designated for
> aircraft with gross weights of 60,000 pounds (27 200 kg) or less and
> ASTM D 1557 for areas designated for aircraft with gross weights
> greater than 60,000 pounds (27 200 kg).**

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**212-3.10 SURFACE TOLERANCE**.  After the course has been completely
compacted, the surface shall be tested for smoothness and accuracy of
grade and crown.  Any portion lacking the required smoothness of failing
in accuracy of grade or crown shall be scarified, reshaped, recompacted,
and otherwise manipulated as the Engineer may direct until the required
smoothness and accuracy are obtained.  The finished surface shall not
vary more than 3/8 inch (9 mm) from a 16-foot (4.8 m) straightedge when
applied to the surface parallel with, and at right angles to, the
centerline.

**212-3.11 THICKNESS**.  The thickness of the base course shall be
determined by depth tests or cores taken at intervals in such manner
that each test shall represent no more than 300 square yards (28 square
meters).  When the base deficiency is more than 1/2 inch (12 mm), the
Contractor shall correct such areas by scarifying, and replacing with
satisfactory materials, and then rolling, bonding, and refinishing in
accordance with these specifications.  The Contractor shall replace, at
his/her expense, the base material where borings have been taken for
test purposes.

**212-3.12 PROTECTION**.  Work on the base course shall not be
accomplished during freezing temperatures nor when the subgrade is wet. 
When the aggregates contain frozen materials or when the underlying
course is frozen, the construction shall be stopped.

Hauling equipment may be routed over completed portions of the base
course, provided no damage results and provided that such equipment is
routed over the full width of the base course, to avoid rutting or
uneven compaction.  However, the Engineer in charge shall have full and
specific authority to stop all hauling over completed or partially
completed base course when, in his/her opinion, such hauling is causing
damage.  Any damage resulting to the base course from routing equipment
over the base course shall be repaired by the Contractor at his/her own
expense.

**212-3.13 MAINTENANCE**.  Following the completion of the base course,
the Contractor shall perform all maintenance work necessary to keep the
base course in a condition satisfactory for priming.  After priming, the
surface shall be kept clean and free from foreign material.  The base
course shall be properly drained at all times.  If cleaning is necessary
or if the prime coat becomes disturbed, any work or restitution
necessary shall be performed at the expense of the Contractor.

METHOD OF MEASUREMENT

**212-4.1**  The quantity of shell base course to be paid for shall be
the number of cubic yards (cubic meters) of base course material placed,
bonded, and accepted in the completed base course.  The quantity of base
course material shall be measured in final position based upon depth
tests or cores taken as directed by the Engineer, at the rate of 1 depth
test for each 300 square yards (28 square meters) of base course, or by
means of average end areas on the complete work computed from elevations
to the nearest 0.01 foot (3 mm).  On individual depth measurements,
thicknesses more than 1/2 inch (12 mm) in excess of that shown on the
plans shall be considered as specified thickness, plus 1/2 inch (12 mm)
in computing the yardage for payment.  Base materials shall not be
included in any other excavation quantities.

BASIS OF PAYMENT

**212-5.1**  Payment shall be made at the contract unit price per cubic
yard (cubic meter) for shell base course.  This price shall be full
compensation for furnishing all materials and for all preparation,
hauling, and placing of these materials, and for all labor, equipment,
tools, and incidentals necessary to complete the item.

Payment will be made under:

Item P-212-5.1 Shell Base Course---per cubic yard (cubic meter)

TESTING REQUIREMENTS

ASTM C 136 Sieve Analysis of Fine and Coarse Aggregates

ASTM D 698 Moisture-Content 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 1557 Test for Laboratory Compaction Characteristics of Soil Using
Modified Effort

ASTM D 4318 Liquid Limit, Plastic Limit, and Plasticity Index of Soils

END OF ITEM P-212