# PART IV -- RIGID BASE COURSES

### **ITEM P-301 SOIL-CEMENT BASE COURSE**

DESCRIPTION

**301-1.1** This item shall consist of constructing a base course by
uniformly mixing together soil, portland cement, and water.  The mixed
material shall be spread, shaped, and compacted in accordance with these
specifications and in conformity to the dimensions and typical cross
section shown on the plans. Tests shall be required for each approved
soil that will be included in the treated layer.

Runway, taxiway, or apron pavements shall be built in a series of
parallel lanes using a plan of processing that reduces longitudinal and
transverse joints to a minimum.

MATERIALS

**301-2.1 PORTLAND CEMENT.**  Portland cement shall conform to the
requirements of ASTM **\[ \]**.

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> **The Engineer shall specify ASTM C 150, Type I, II, III, IV, or IV.**

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**301‑2.2  WATER.**  Water shall be clean and free from sewage, oil,
acid, strong alkalies, or vegetable matter.  Water of questionable
quality shall be tested in accordance with the requirements of AASHTO T
26. 

**301-2.3 SOIL.**  The soil shall consist of an approved select soil. 
The soil shall be free of roots, sod, weeds, and shall not contain
gravel or stone retained on a 1‑inch (25 mm) sieve or more than 45%
retained on a No. 4 sieve, as determined by ASTM C 136.

**301-2.4 BITUMINOUS MATERIAL.**  The types, grades, controlling
specifications, and application temperatures for the bituminous
materials used for curing the soil‑cement are listed in Table 1.  The
Engineer shall designate the specific material used.

**TABLE 1. BITUMINOUS MATERIALS**

  ---------------------- -------------------- --------------- -------------
  **Type and Grade**     **Specification**    **Application   
                                              Temperature**   

                                              **Deg. F**      **Deg. C**

  Cutback Asphalt                                             

  RC‑70                  ASTM D 2028          120‑160         50‑70

  RC‑250                 ASTM D 2028          160‑200         70‑95

  Emulsified Asphalt                                          

  RS‑1, SS‑1             ASTM D 977           75‑130          25‑55

  CRS‑1                  ASTM D 2397          75‑130          25‑55
  ---------------------- -------------------- --------------- -------------

CEMENT QUANTITY

**301-3.1 LABORATORY SOIL TESTS.**  Prior to base course construction,
laboratory tests of soils shall be made to determine the quantity of
cement required in the mix.

Test specimens containing various amounts of cement are to be compacted
in accordance with ASTM D 558, and the optimum moisture for each amount
of cement is to be determined.  Samples at the optimum moisture shall be
subjected to the wet‑dry and the freeze‑thaw test in accordance with
ASTM D 559 and D 560, respectively.

The specified cement content for construction shall be that at which the
weight loss of the specimens subjected to 12 cycles of either the
wet‑dry or the freeze‑thaw is not more than 14% for granular soils, 10%
for the more plastic granular and silty soils, and 7% for clay soils.

The compressive strength of soaked specimens should increase both with
age and with increase in cement content.

CONSTRUCTION METHODS

**301-4.1 WEATHER LIMITATIONS.**  The soil‑cement base shall not be
mixed or placed while the atmospheric temperature is below 35° F (2° C)
or when conditions indicate that the temperature may fall below 35° F
(2° C) within 24 hours, or when the weather is foggy or rainy, or when
the soil or subgrade is frozen.

**301-4.2 EQUIPMENT.**  The soil‑cement may be constructed with any
equipment that will meet the requirements for soil pulverization, cement
application, mixing, water application, incorporation of materials,
compaction, finishing, and curing specified herein.

**301-4.3 PREPARATION.**  The area to be paved shall be graded and
shaped to conform to the grades and typical cross section shown on the
plans.  Any soft or yielding areas in the subgrade shall be removed and
replaced with acceptable soil and compacted as specified.

**301-4.4 PULVERIZATION.**  The soil for the base course shall be so
pulverized that at the completion of moist‑mixing, 100% by dry weight
passes a 1‑inch (25 mm) sieve and a minimum of 80% passes a No. 4 sieve,
exclusive of gravel or stone retained on the No. 4 sieve.

**301-4.5 CEMENT APPLICATION, MIXING, AND SPREADING.**  Mixing of the
soil, cement, and water shall be accomplished either by the
mixed‑in‑place or the central‑plant‑mixed method.

The percentage of moisture in the soil, at the time of cement
application, shall not exceed the quantity that will permit a uniform
and intimate mixture of soil and cement during mixing operations, and it
shall not exceed the specified optimum moisture content for the
soil‑cement mixture.

**Method A -- Mixed-in-place.**  The specified quantity of cement shall
be spread uniformly on the soil.

Cement that has been displaced shall be replaced before mixing is
started.  After the cement has been applied, it shall be mixed with the
soil.  Mixing shall continue until the cement has been sufficiently
blended with the soil to prevent the formation of cement balls when
water is applied.

Immediately after the soil and cement have been mixed, water shall be
incorporated into the mixture.  Excessive concentrations of water on or
near the surface shall be avoided.  A water supply and pressure
distributing equipment shall be provided that will assure the
application within 3 hours of all mixing water on the section being
processed.  After all mixing water has been applied, mixing shall
continue until a uniform and intimate mixture of soil, cement, and water
has been obtained.

**Method B -- Central plant mixed.**  The soil, cement, and water shall
be mixed in a pugmill, either of the batch or continuous‑flow type.  The
plant shall be equipped with feeding and metering devices that will add
the soil, cement, and water into the mixer in the specified quantities. 
Soil and cement shall be mixed sufficiently to prevent cement balls from
forming when water is added.  Mixing shall continue until a uniform and
intimate mixture of soil, cement, and water is obtained.

The mixture shall be hauled to the project in trucks equipped with
protective covers.  The mixture shall be placed on the moistened
subgrade in a uniform layer by an approved spreader(s).  Not more than
30 minutes shall elapse between the placement of soil‑cement in adjacent
lanes.

The layer of soil‑cement shall be uniform in thickness and surface
contour and of such quantity that the completed base will conform to the
required grade and cross section.  Dumping of the mixture in piles or
windrows upon the subgrade will not be permitted.

Not more than 60 minutes shall elapse between the start of moist mixing
and the start of compaction of soil‑cement.

**301-4.6 COMPACTION.**  Immediately upon completion of the spreading
operations, the mixture 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 mixture shall be at least 98 percent
of the maximum density of laboratory specimens prepared from samples of
the cement‑treated base material taken from the material in place.  The
specimens shall be compacted and tested in accordance with ASTM D 558. 
The in‑place field density shall be determined in accordance with ASTM D
1556.  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 558 and
shall be less than that amount which will cause the mixture to become
unstable during compaction and finishing.

**301-4.7 FINISHING.**  Finishing operations shall be completed during
daylight hours, and the completed base course shall conform to the
required lines, grades, and cross section.  If necessary, the surface
shall be lightly scarified to eliminate any imprints made by the
compacting or shaping equipment.  The surface shall then be recompacted
to the required density.

**301-4.8 CONSTRUCTION JOINTS.**  At the end of each day\'s run, a
transverse construction joint shall be formed by a header or by cutting
back into the compacted material to form a true vertical face free of
loose material.

The protection provided for construction joints shall permit the
placing, spreading, and compacting of base material without injury to
the work previously laid.  Where it is necessary to operate or turn any
equipment on the completed base course, sufficient protection and cover
shall be provided to prevent damage to the finished surface.  A supply
of mats or wooden planks shall be maintained and used as approved and
directed by the Engineer.

Care shall be exercised to ensure thorough compaction of the base
material immediately adjacent to all construction joints.  When
spreading or compacting base material adjacent to a previously
constructed lane, care shall be taken to prevent injury to the work
already constructed.

**301-4.10 PROTECTION AND CURING.**  After the base course has been
finished to grade and compacted as specified herein, it shall be
protected against drying for a period of 7 days by the application of
bituminous material or other acceptable methods.  The curing method
shall begin as soon as possible, but no later than 24 hours after the
completion of finishing operations.  The finished base course shall be
kept moist continuously until the curing material is placed.

The bituminous material specified shall be uniformly applied to the
surface of the completed base course at the rate of approximately 0.2
gallon  per square yard (0.92 liter/square meter) with approved heating
and distributing equipment.  The exact rate and temperature of
application to give complete coverage without excessive runoff shall be
as specified.

At the time the bituminous material is applied, the surface shall be
dense, free of all loose and extraneous material, and shall contain
sufficient moisture to prevent penetration of the bituminous material. 
Water shall be applied in sufficient quantity to fill the surface voids
immediately before the bituminous curing material is applied.

The curing material shall be maintained and applied as needed by the
Contractor during the 7‑day protection period so that all of the
soil‑cement will be covered effectively during this period.

Finished portions of soil‑cement that are used by equipment in
constructing an adjoining section shall be protected to prevent
equipment from marring or damaging the completed work.

When the air temperature may be expected to reach the freezing point,
sufficient protection from freezing shall be given the soil‑cement for 7
days after its construction and until it has hardened.

Other curing materials such as moist straw or hay may be used if
approved.

**301-4.11 CONSTRUCTION LIMITATIONS.**  When any of the operations after
the application of cement are interrupted for more than 30 minutes or
when the uncompacted soil‑cement mixture is wetted by rain so that the
moisture content is exceeded by a small amount, the decision to
reconstruct the portion affected shall rest with the Engineer.  In the
event the uncompacted, rain‑wetted mixture exceeds the specified
moisture content tolerance, the Contractor shall reconstruct at his/her
expense the portion affected.  All material along the longitudinal or
transverse construction joints not properly compacted shall be removed
and replaced, at the Contractor\'s expense, with properly moistened and
mixed soil‑cement compacted to specified density.

**301-4.12 SURFACE TESTS.**  The finished surface shall not vary more
than 3/8 inch (9 mm) when tested with a 16‑foot (4.8 m) straightedge
applied parallel with, or at right angles to, the longitudinal axis of
the pavement.  Any variations in excess of this tolerance shall be
corrected by the Contractor, at his/her own expense, and in a manner
satisfactory to the Engineer.

**301-4.13 THICKNESS.**  The thickness of the soil‑cement base course
shall be determined from measurements of cores drilled from the finished
base or from thickness measurements at holes drilled in the base at
intervals so that each test shall represent no more than 300 square
yards (250 square meters).  The average thickness of the base
constructed during one day shall be within 1/2 inch (12 mm) of the
thickness shown on the plans, except that the thickness of any one point
may be within 3/4 inch (13 mm) of that shown on the plans.  Where the
average thickness shown by the measurements made in one day\'s
construction is not within the tolerance given, the Engineer shall
evaluate the area and determine if, in his/her opinion, it shall be
reconstructed at the Contractor\'s expense or the deficiency deducted
from the total material in place.

**301-4.14 MAINTENANCE.**  The Contractor shall be required to maintain,
at his/her own expense, the entire base course within the limits of
his/her contract in a condition satisfactory to the Engineer from the
time he starts work until all the work has been completed.  Maintenance
shall include immediate repairs of any defects that may occur either
before or after the cement is applied.  The work shall be done by the
Contractor at his/her own expense and repeated as often as necessary to
keep the area intact at all times.  Repairs shall be made in a manner
that will insure restoration of a uniform surface and the durability of
the part repaired.  Faulty work must be replaced for the full depth of
treatment.  Any low areas shall be remedied by replacing the material
for the full depth of treatment rather than by adding a thin layer of
soil‑cement to the completed work.

METHOD OF MEASUREMENT

**301-5.1**  The quantity of soil‑cement base course to be paid for
shall be the number of square yards (square meters) of completed and
accepted base course.

**301-5.2**  Portland cement shall be measured by the hundredweight.

BASIS OF PAYMENT

**301-6.1**  Payment shall be made at the contract unit price per square
yard (square meter) for soil‑cement base course.  This price shall be
full compensation for furnishing all materials, except portland cement,
and for all preparation, delivering, placing, and mixing of these
materials; and for all labor, equipment, tools and incidentals necessary
to complete the item.

**301-6.2**  Payment shall be made at the contract unit price per
hundredweight for cement. This price shall be full compensation for
furnishing this material and for all delivery, placing, and
incorporation of this material, and for all labor, equipment, tools, and
incidentals necessary to complete the item.

Payment will be made under:

Item P‑301‑6.1 Soil‑Cement Base Course---per square yard (square meter)

Item P‑301‑6.2 Portland Cement---per hundredweight

TEST REQUIREMENTS

ASTM C 136 Sieve Analysis of Fine and Coarse Aggregates

ASTM D 558 Moisture‑Density Relations of Soil‑Cement Mixtures

ASTM D 559 Wetting‑and‑Drying Tests of Compacted Soil‑Cement Mixtures

ASTM D 560 Freezing‑and‑Thawing Tests of Compacted Soil‑Cement Mixtures

ASTM D 1556 Test for Density of Soil In‑Place by the Sand Cone Method

AASHTO T 26 Quality of Water to be Used in Concrete

MATERIAL REQUIREMENTS

ASTM C 150 Portland Cement

ASTM D 977 Emulsified Asphalt

ASTM D 202 Cutback Asphalt

ASTM D 239 Cationic Emulsified Asphalt

**END OF ITEM P-301**

**Intentionally Left Blank**