ITEM 307 – BITUMINOUS PLANT-MIX SURFACE COURSE – GENERAL
307.1
Description
This
item includes general requirements that are applicable to all types of
bituminous plant mix surface courses irrespective of gradation of aggregate or
kind and amount of bituminous material. Derivations from these general
requirements will be indicated in the specific requirements for each type.
This
work shall consist of constructing one or more bituminous bound layers on a
prepared foundation in accordance with the Specifications and the specific
requirements of the type under contract, and in reasonably close conformity
with the lines, grades, thickness, and typical cross-sections shown on the
Plans within the tolerances specified or established by the Engineer.
307.2
Material Requirements
307.2.1
Composition and Quality of Bituminous Mixture
(Job-Mix
Formula). The bituminous mixture shall be composed of aggregate, mineral
filler, hydrated lime, and bituminous material.
At least three weeks prior to production, the
Contractor shall submit in writing a job-mix formula for each mixture supported
by laboratory test data along with samples and sources of the components and
viscosity-temperature relationships information to the Engineer for testing and
approval.
Each
job-mix formula submitted shall propose definite single values for:
1.
The percentage of aggregate passing each specified sieve size.
2.
The percentage of bituminous material to be added.
3.
The temperature of the mixture delivered on the road.
4.
The kind and percentage of additive to be used.
5.
The kind and percentage of mineral filler to be used.
After
the job-mix is established, all mixture furnished for the project shall conform
thereto within the following ranges of tolerances:
Passing
No. 4 and larger sieves
± 7 percent
Passing
No. 8 to No. 100 sieves (inclusive) ±
4 percent
Passing
No. 200 sieve ±
2 percent
Bituminous
Material ±
0.4 percent
Temperature
of Mixture ±
100C
Should
a change in source of material be proposed or should a job-mix formula prove
unsatisfactory, a new job-mix formula shall be submitted by the Contractor in
writing and be approved by the Engineer prior to production.
Approval
of a new job mix formula may require laboratory testing and verification.
The
mixture shall have a minimum compressive strength of 1.4 MPa.
The
mixture shall have a mass percent air voids with the range of 3 to 5.
The
mixture shall also have an index of retained strength of not less than70 when
tested by AASHTO T 165. For aggregates having maximum sizes over 25 mm, AASHTO
T 165 will be modified to use 150 mm x 150 mm cylindrical specimens. The 150 mm
(cylinders will be compacted by the procedures outlined in AASHTO T 167
modified to employ 10 repetitions of a molding load of 9.6 MPa, with no
appreciable holding time after each application of the full load.
307.2.2
Bituminous Material
The
kind of bituminous material to be used will be as called for in the Bill of
Quantities, while the type and grade will be specified in the Special
Provisions. The grade may be changed one step by the Engineer at no change in
unit price. It shall conform to the applicable requirements of Item 702,
Bituminous Materials.
307.2.3
Aggregates
Aggregates
shall conform to the applicable requirements of Item 703, Aggregates.
307.2.4
Mineral Filler
It
shall conform to the requirements of Item 703 A, Mineral Filler.
307.2.5
Hydrated Lime
It
shall conform to the requirements of Item 701, Construction Lime.
307.2.6
Proportioning of Mixture
The
proportion of bituminous material, on the basis of total dry aggregate, shall
be from 5.0 to 8.0 mass percent. The exact percentage to be used shall be fixed
by the Engineer in accordance with job-mix formula and other quality control
requirements.
Hydrated
lime shall be added to the mixture during the mixing operation in the amount of
one-half to one (0.5 to 1.0) mass percent, dry aggregate basis. The lower
percentage limit is applicable to aggregates which are predominantly
calcareous.
307.3
Construction Requirements
307.3.1
Weather Limitations
Bituminous
Plant mix shall not be placed on any wet surface, or when weather conditions
would prevent the proper handling or finishing of the bituminous mixtures.
307.3.2
Construction Equipment
1. Bituminous Mixing Plant
Sufficient
storage space shall be provided for each size of aggregate. The different
aggregate sizes shall be kept separated until they have been delivered to the
cold elevator feeding the drier. The storage yard shall be maintained neat and
orderly and the separate stockpiles shall be readily accessible for sampling.
Plants
used for the preparation of bituminous mixtures shall conform to the
requirements for all plants under (a) below except that scale requirements
shall apply only where weight proportioning is used. In addition, batch mixing
plants and continuous mixing plants shall conform to the respective
requirements which follow this Subsection.
a.
Requirements for all Plants.
Mixing
plants shall be of sufficient capacity and coordinated to adequately handle the
proposed bituminous construction.
1.
Plant Scales. Scales shall be accurate to 0.5 percent of the maximum load that
may be required. Poises shall be designed to be locked in any position to
prevent unauthorized change of position. In lieu of plant and truck scales, the
Contractor may provide an approved automatic printer system which will print the
weights of the material delivered, provided the system is used in conjunction
with an approved automatic batching and mixing control system. Such weights
shall be evidenced by a weight ticket for each load.
Scales
shall be inspected and sealed as often as the Engineer may deem necessary to
assure their continued accuracy. The Contractor shall have on hand not less
than ten 20-kg weights for testing the scales.
2.
Equipment for Preparation of Bituminous Material. Tanks for the storage of
bituminous material shall be equipped with the proper devices to heat and hold
the material at the required temperatures. The heating shall be accomplished by
steam coils, electricity, or other approved means so that no flame shall be in
contact with the tank. The circulating system for the bituminous material shall
be designed to assure proper and continuous circulation during the operating
period. Provision shall be made for measuring and sampling storage tanks.
3.
Feeder for Drier. The plant shall be provided with accurate mechanical means
for uniformly feeding the aggregate into the drier so that uniform production
and temperature will be obtained.
4.
Drier. The plant shall include a drier or driers which continuously agitate
during the heating and drying process. For cold-type bituminous mix, equipment
for mechanical cooling of the dried aggregate to the temperature prescribed for
cold mixtures shall be provided and shall be capable of supplying prepared
material for the mixer to operate at full capacity.
5.
Screens. Plant screens, capable of screening all aggregate to the specified
sizes and proportions and having normal capacities in excess of the full
capacity of the mixer, shall be provided.
6.
Bins. The plant shall include storage bins of sufficient capacity to supply the
mixer when it is operating at full capacity. Bins shall be arranged to assure
separate and adequate storage of appropriate fractions of the mineral
aggregates. Separate dry storage shall be provided for filler or hydrated lime
when used and the plant shall be equipped to feed such material into the mixer.
Each bin shall be provided with overflow pipes, of such size and at such
locations as to prevent backing up of material into other compartments or bins.
Each compartment shall be provided with individual outlet gate, constructed so
that when closed, there shall be no leakage. The gates shall cutoff quickly and
completely. Bins shall be so constructed that samples can be readily obtained.
Bins shall be equipped with adequate tell-tale devices to indicate the position
of the aggregates in the bins at the lower quarter points.
7.
Bituminous Control Gate. Satisfactory means, either by weighing or metering,
shall be provided to obtain the proper amount of bituminous material in the mix
within the tolerance specified. Means shall be provided for checking the
quantity or rate of flow of bituminous material into the mixer.
8.
Thermometric Equipment. An armored thermometric of adequate range in
temperature reading shall be fixed in the bituminous feed line at a suitable
location near the charging valve at the mixer unit. The plant shall also be
equipped with either an approved dial-scale, mercury-actuated thermometer, an
electric pyrometer, or other approved thermometric instrument so placed at the
discharge chute of the drier as to register automatically or indicate the
temperature of the heated aggregates. The Engineer may require replacement of
any thermometer by an approved temperature-recording apparatus for better
regulation of the temperature of aggregates.
9.
Dust Collector. The plant shall be equipped with a dust collector constructed
to waste or return uniformly all or any part of the material to the hot
elevator collected as directed.
10.
Truck Scales. The bituminous mixture shall be weighed on approved scales
furnished by the Contractor or on public scales at the Contractor’s expense.
Such scales shall be inspected and sealed as often as the Engineer deems
necessary to assure their accuracy. (See paragraph I).
11.
Safety Requirements. Adequate and safe stairways to the mixer platform and
sampling points shall be provided, and guarded ladders to other plant units
shall be placed at all points where accessibility to plant operations is
required. Accessibility to the top of truck bodies shall be provided by a
platform or other suitable device to enable the Engineer to obtain sampling and
mixture temperature data. A hoist or pulley system shall be provided to raise
scale calibration equipment, sampling equipment and other similar equipment
from ground to the mixer platform and return. All gears, pulleys, chains,
sprockets, and other dangerous moving parts shall be thoroughly guarded and
protected. Ample and unobstructed space shall be provided on the mixing platform.
A clear and unobstructed passage shall be maintained at all times in and around
the truck loading area. This area shall be kept free from drippings from the
mixing platforms.
b.
Requirements for Batching Plants
1.
Weigh box or hopper. The equipment shall include a means for accurately
weighing each size of aggregate in a weight box or hopper suspended on scales
and of ample size to hold a full batch without hand raking or running over. The
gate shall close tightly so that no material is allowed to leak into the mixer
while a batch is being weighed.
2.
Bituminous Control. The equipment used to measure the bituminous material shall
be accurate to plus or minus 0.5 percent. The bituminous material bucket shall
be a non-tilting type with a loose sheet metal cover. The length of the
discharge opening or spray bar shall be less than ¾ the length of the mixer and
it shall discharge directly into the mixer. The bituminous material bucket, its
discharge valve or valves and spray bar shall be adequately heated. Steam jackets,
if used, shall be efficiently drained and all connections shall be so
constructed that they will not interfere with the efficient operation of the
bituminous scales. The capacity of the bituminous material bucket shall be at
least 15 percent in excess of the weight of bituminous material required in any
batch. The plant shall have an adequately heated quick-acting, non-drip,
charging valve located directly over the bituminous material bucket.
The
indicator dial shall have a capacity of at least 15 percent in excess of the
quantity of bituminous material used in a batch. The controls shall be
constructed so that they may be locked at any dial setting and will
automatically reset to that reading after the addition of bituminous material
to each batch. The dial shall be in full view of the mixer operator. The flow
of bituminous material shall be automatically controlled so that it will begin
when the dry mixing period is over. All of the bituminous material required for
one batch shall be discharged in not more than 15 seconds after the flow has
started. The size and spacing of the spray bar openings shall provide a uniform
application of bituminous material the full length of the mixer. The section of
the bituminous line between the charging valve and the spray bar shall be
provided with a valve and outlet for checking the meter when a metering device
is substituted for a bituminous material bucket.
3.
Mixer. The batch mixer shall be an approved type capable of producing a uniform
mixture with the job-mix tolerances. If not enclosed, the mixer box shall be
equipped with a dust hood to prevent loss of dust.
The
clearance of blades from all fixed and moving parts shall not exceed 25 mm
unless the maximum diameter of the aggregate in the mix exceed 30 mm, in which
case the clearance shall not exceed 40 mm.
4.
Control of Mixing Time. The mixer shall be equipped with an accurate time lock
to control the operation of a complete mixing cycle. It shall lock the weigh
box gate after the charging of the mixer until the closing of the mixer gate at
the completion of the cycle. It shall lock the bituminous material bucket
throughout the dry and wet mixing periods. The dry mixing period is defined as
the interval of time between the opening of the weigh box gate and the start of
introduction of bituminous material. The wet mixing period is the interval of
time between the start of introduction of bituminous material and the opening
of the mixer gate.
The
control of the timing shall be flexible and capable of being set at intervals
of 5 seconds or less throughout a total cycle of up to 3 minutes. A mechanical
batch counter shall be installed as a part of the timing device and shall be so
designed as to register only completely mixed batches.
The
setting of time interval shall be performed in the presence and at the direction
of the Engineer who shall then lock the case covering the timing device until
such time as a change is to be made in the timing periods.
c.
Requirement for Continuous Mixing Plants
1.
Aggregate Proportioning. The plant shall include means for accurately
proportioning each size of aggregate.
The
plant shall have a feeder mounted under each compartment bin. Each compartment
bin shall have an accurately controlled individual gate to form an orifice for
volumetrically measuring the material drawn from each compartment. The feeding
orifice shall be rectangular with one dimension adjustable by positive
mechanical means provided with a lock.
Indicators
shall be provided for each gate to show the respective gate opening in
millimeter.
2.
Weight Calibration of Aggregate Feed. The plant shall include a means for
calibration of gate openings by weighing test samples. Provision shall be made
so that materials fed out of individual orifice may be by passed to individual
test boxes. The plant shall be equipped to conveniently handle individual test
samples weighing not less than 50 kilograms. Accurate scales shall be provided
by the Contractor to weigh such test samples.
3.
Synchronization of Aggregate Feed and Bituminous Material Feed. Satisfactory
means shall be provided to afford positive interlocking control between the
flow of aggregate from the bins and the flow of bituminous material from the
meter or other proportioning device. This control shall be accomplished by
interlocking mechanical means or by any other positive method satisfactory to
the Engineer.
4.
Mixer. The plants shall include a continuous mixer of an approved type,
adequately heated and capable of producing a uniform mixture within the job-mix
tolerances. It shall be equipped with a discharge hopper with dump gates which
will permit rapid and complete discharge of the mixture. The paddles shall be
adjustable for angular position on the shafts and reversible to retard the flow
of the mix. The mixer shall have a manufacturer’s plate giving the net volumetric
contents of the mixer of the several heights inscribed on a permanent gauge.
Charts shall be provided showing the rate of feed or aggregate per minute for
the aggregate being used.
2. Hauling Equipment
Trucks
used for hauling bituminous mixtures shall have tight, clean, smooth metal beds
which have been thinly coated with approved material to prevent the mixture
from adhering to the beds. Each truck shall have a cover of canvass or other
suitable material of such size as to protect the mixture from the weather. When
necessary, such that the mixture will be delivered on the road at the specified
temperature, truck beds shall be insulated and covers shall be securely fastened.
Truck
beds shall be drained prior to loading.
3. Bituminous Pavers
The
equipment shall be self-contained, power-propelled units, provided with an
adjustable activated screed or strike-off assembly, heated if necessary, and
capable of spreading and finishing courses of bituminous plant mix material in lane
widths applicable to the specified typical section and thickness shown on the Plans.
Pavers
shall be equipped with a control system capable of automatically maintaining
the screen elevation as specified herein. The control system shall be automatically
actuated from either a reference line or surface through a system of mechanical
sensors or sensor directed mechanisms or devices which will maintain the paver
screed at a predetermined transverse slope and at the proper elevation to
obtain the required surface. When directed, the transverse slope control system
shall be made inoperative and the screed shall be controlled by sensor directed
automatic mechanisms which will independently control the elevation of each end
of the screed from reference lines or surface.
The
controls shall be capable of working in connection with any of the following
attachments.
a.
Ski-type device of not less than 9 m in length or as directed by the Engineer.
b.
Taut stringline (wire) set to grade.
c.
Short ski or shoe
The
Contractor shall furnish the long ski, the short ski or shoe and furnish and
install all required stakes and wire for a taut stringline.
Should
the automatic control systems become inoperative during the day’s work, the
Contractor will be permitted to finish the day’s work using manual controls,
however, work shall not be resumed thereafter until the automatic control
system has been made operative.
The
Contractor shall provide and have ready for use at all times enough covers, as
may be necessary, for use in any emergency such as rain, chilling wind, on
unavoidable delay, for the purpose of covering or protecting any material that
may have been dumped and not spread.
4. Rollers
The
equipment shall be of the steel and/or pneumatic tire type and shall be in good
condition, capable of reversing without backlash, and shall be operated at
speeds slow enough to avoid displacement of the bituminous mixture. The number
and weight of rollers shall be sufficient to compact the mixture to the
required density while it is still in a workable condition. The use of
equipment which results in excessive crushing of the aggregate will not be
permitted.
307.3.3
Conditioning of Existing Surface
Immediately
before placing the bituminous mixture, the existing surface shall be cleaned of
loose or deleterious material by brooming or other approved means.
Contract
surface or curb, gutters, manholes and other structures shall be painted with a
thin, uniform coating of bituminous material prior to the bituminous mixture
being placed against them.
307.3.4
Preparation of Bituminous Material
The
bituminous material shall be heated so as to avoid local overheating and
provide a continuous supply of the bituminous material to the mixer at a
uniform temperature. The temperature of asphalt cement delivered to the mixer
shall be as required to achieve a kinematic viscosity in the range of 150-300mm2 /s,
as determined by AASHTO T 201. Asphalt cement shall not be used while it is
foaming nor shall be heated above 1590C at any time after delivery
in the project.
307.3.5
Preparation of Aggregate
Aggregates
for pug mill mixing shall be heated, dried and delivered to the mixing unit at
a temperature within the range ±170C of the bitumen. Moisture
content of the aggregate shall not exceed one mass percent at the time it is
introduced into the mixing unit. Flames used for drying and heating shall be properly
adjusted to avoid damage to the aggregate and to avoid soot on the aggregate.
Moisture content of the mixture from drum dryer plants shall not exceed three
(3) percent of the output, as determined by AASHTO T 110.
307.3.6
Mixing
The
dried aggregates and the bituminous material shall be measured or gauged and
introduced into the mixer in the amount specified by the job mix formula.
After
the required amounts of aggregate and bituminous material have been introduced
into the mixer, the material shall be mixed until a complete and uniform
coating of the particles and a thorough distribution of the bituminous material
throughout the aggregate is secured.
307.3.7
Spreading and Finishing
The
mixture shall be spread and struck off to the grade and elevation established.
Bituminous pavers shall be used to distribute the mixture either over the
entire width or over such partial width as may be practicable.
The
longitudinal joint in one layer shall offset that in the layer immediately
below approximately 15 cm; however, the joint in the top layer shall beat the
center line of the pavement if the roadway comprises two (2) lanes, or at lane
lines if the roadway is more than two (2) lanes, unless otherwise directed.
On
areas where irregularities or unavoidable obstacle makes the use of mechanical
spreading and finishing equipment impracticable, the mixture may be placed and
finished by hand tools.
The
mixture shall be placed at a temperature not less than 1070C as
measured in the truck just prior to dumping into the spreader.
When
tar is used, the mixture shall be placed at between 660C and 1070C.
When
production of the mixture can be maintained and when practical, pavers shall be
used in echelon to place the wearing course in adjacent lanes.
307.3.8
Compaction
Immediately
after the mixture has been spread, struck off and surface irregularities
adjusted, it shall be thoroughly and uniformly compacted by rollers as
specified under paragraph No. 4 of Subsection 307.3.2.
The
surface shall be rolled when the mixture is in proper condition and when the
rolling does not cause under displacement, cracking and shoving. Rolling shall
begin at the sides and proceeds longitudinally parallel toward the road
centerline, each trip overlapping ½ the roller width, gradually progressing to
the crown of the road. When paving in echelon or abutting a previously placed lane,
the longitudinal joint should be rolled first followed by the regular rolling
procedure. On superelevated curves, the rolling shall begin at the low side and
progress to the high side overlapping of longitudinal trips parallel to the
centerline.
Rollers
shall move at a slow but uniform speed with the drive roll or wheels nearest
the paver.. Rolling shall be continued until roller marks are eliminated and a
minimum of 97 mass percent of the density of the laboratory compacted specimens
prepared in accordance with AASHTO T 166 has been obtained.
Any
displacement occurring as a result of the reversing of the direction of a
roller, or from other causes, shall be corrected at once by the use of rakes
and addition of fresh mixture when required. Care shall be exercised in rolling
not to displace the line and grade of the edges of the bituminous mixture.
To
prevent adhesion of the mixture to the rollers, the wheels shall be kept
properly moistened with water or water mixed with very small quantities of
detergent or other approved material. Excess liquid will not be permitted.
Along
forms, curbs, headers, walls and other places not accessible to the rollers,
the mixture shall be thoroughly compacted with hot hand tampers, smoothing
irons or with mechanical tampers.
307.3.9
Joints
Placing
of the bituminous paving shall be continuous as possible. Rollers shall not
pass over the unprotected end of a freshly laid mixture unless authorized by
the Engineer. Transverse joints shall be formed by cutting back on the previous
run to expose the full depth of the course. When directed by the Engineer, a
brush coat of bituminous material shall be used on contact surfaces of
transverse joints before additional mixture is placed against the previously
rolled material.
307.3.10
Acceptance, Sampling and Testing
The
contractor shall cut full depth samples as directed, from the finished
pavement, for testing. Samples shall be neatly cut by saw or core drill. Each
sample shall be at least 150 mm x 150 mm or 100 mm diameter full depth. At
least one, but not more than three samples shall be taken for each full day’s
operation. If no core samples were taken during the day’s operation, core
samples shall be taken from the completed pavement for every 100 L. M. per
lane. The contractor shall supply and furnish new material to backfill boreholes
left by the samples taken.
No
acceptance and final payment shall be made on completed asphalt pavement unless
core test for thickness determination is conducted, except for Barangay Roads
where the implementing office is allowed to waive such test.
The
samples obtained will be used to measure the thickness of the pavement. The
same samples will be used to test the density of the compacted pavement by
AASHTO T 166.
The
compacted pavement shall have a density equal to, or greater than 97mass
percent of the density of a laboratory specimen. The asphalt pavement
represented by the cores shall not be accepted if the deficiency in density is
more than 2%.
The
compacted pavement shall have a thickness tolerances of -5 mm. Thickness in
excess of the specified thickness shall not be considered in the payment of
asphalt pavement. The asphalt pavement represented by the core shall not be
accepted if the deficiency in the core thickness is more than 5 mm. Averaging
of the density and thickness of asphalt cores is not permitted.
If
the deficiency in the core thickness is more than 5 mm, additional layer may be
permitted in order to meet the designed thickness, however, the minimum
additional asphalt overlay thickness should be dependent on the minimum
thickness capacity of asphalt paver but it should not be less than 50 mm and
that proper construction procedures are followed.
307.3.11
Surface Tolerances
The
surface will be checked by the use of a 3-m straight-edge at sites selected by
the Engineer. The straight-edge will be applied at right angles, as well as,
parallel to the centerline of the roadbed.
The
variation of the surface from the testing edge of the straight-edge between any
two contacts with the surface shall not exceed 6 mm.
Tests
will be made immediately after initial compaction and any variations detected
shall be corrected by removing or adding materials, as may be necessary.
Rolling shall then be continued as specified. After final rolling, the
smoothness of the course shall be checked again and any area defective in
texture or composition shall be corrected, including removal and replacement of
unsatisfactory material at the Contractor’s expense as directed by the
Engineer.
307.4
Method of Measurement
The
area to be paid for under this item shall be the number of square meters (m2)
of asphalt pavement placed, compacted and accepted based on the thickness and
densities of the cores taken in accordance with subsection 307.3.10 (Acceptance,
Sampling and Testing).
307.5
Basis of Payment
The
accepted quantity, measured as prescribed in Section 307.4 will be paid for as
provided in the respective items for the specified type of bituminous plant
mix.
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