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Suggested Polymer Modified Asphalt Specifications

XXX.010 General
XXX.020 Materials and Manufacture
XXX.030 Performance
XXX.040 Storage
XXX.050 Requirements for PGM Binder
XXX.051 Sampling of PGM Binder
XXX.052 Mix Design for PGM Binder
XXX.053 Quality Control for PGM Binder

XXX.010 General. The requirements of AASHTO MP1-98 shall apply, deviations from these are as follows.

PG Binders with the suffix “M” (e.g., PG 70-22M, PG 76-22M) shall meet the requirements for a PGM Binder.

For this specification, the Owner's Department of Engineering shall be the known as the Department . The Department's Laboratory shall be known as the Laboratory and the Monitoring Team shall consist of appointed representatives of the Department.

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XXX.020 Materials and Manufacture. The requirements of the AASHTO MP1-98 “Materials and Manufacture” Section shall be completely replaced with the following:

5.1 The PG Binder shall be an asphalt cement from the refining of crude petroleum, or combination of asphalt cements from the refining of crude petroleum, or asphalt cements and suitable liquid from the refining of crude petroleum, and possible organic modifiers for performance enhancement. Material from the crude refining stream will be considered neat. Liquid from crude refining may be used for adjustments, but shall not be used for the purpose of substitution of crude refined asphalt cement in a PG Binder. In the event of a failure investigation where binders exhibit unusual properties a supplier may be requested by the Laboratory to supply information about the makeup of a PG Binder. Failure to cooperate will mean removal from the certification list.

5.2 A modifier may be any organic material of suitable manufacture that is proven compatible with asphalt cement (does not separate appreciably in routine storage), and that is dissolved, dispersed or reacted in asphalt cement to improve its performance. Performance enhancement is defined as a decrease in the temperature susceptibility of the asphalt cement while maintaining or improving desirable properties in a neat asphalt cement such as coatability, adhesiveness and cohesiveness. The use of modifiers shall be limited to 6.0 percent by PG Binder weight.

5.3 The use of previously used materials must be approved by the Department. Since no standard test procedures exist for reprocessed materials (and original tests were not developed with the use of such materials in mind), appropriate test methods may be chosen by the Department for review. Department approval does not relieve the binder supplier from full responsibility for content and use of any previously used material nor guarantee suitable performance enhancement as defined above. The detected presence in a PG Binder sample of any unapproved previously used material will mean immediate removal from the certification list. Approved reprocessed materials will be limited to 6.0 percent by PG Binder weight.

5.4 The PG Binder shall be homogeneous, free from water and deleterious materials, and shall not foam when heated to 350F (175C). The asphalt binder (before modification or after modification if liquid modifier used) shall be proven fully compatible with a negative result by means of the Spot Test per AASHTO T 102 using standard naphtha solvent. If standard naphtha shows a positive result, a retest using 35 percent Xylene/ 65 percent Heptane (volume) may be used.

5.5 The PG Binder shall be at least 99.0 percent soluble as determined by ASTM D 5546 or D 2042. Any insoluble component shall be substantially free of fibers and have discrete particles less than 75µm.

5.6 Flash point shall be 500F (260C) min. Mass loss on RTFO of final PG grade binder shall be 0.5 percent max.

5.7 PG 58-28 shall have a minimum Viscosity (ASTM D2171 @ 60C) of 800 poise and PG 64-22 shall have a Penetration ( ASTM D5) between 55 and 75.

5.8 Direct Tension testing is not required, unless otherwise required in this specification.

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XXX.030 Performance. Should excess fat spots, regular random areas of flushing, or excess drainage occur on a project and not be attributable to over rolling, plant operation, or mix quality compared to the JMF, the PG Binder will be rejected. This rejection includes any PGM Binders with an incompatible polymer or that have been improperly handled. The Contractor will not be allowed to use any of the rejected PG Binder. Correction of problem areas will be at the Department's discretion depending on the problem severity, but if an unsafe condition exists, the area in question will be removed and replaced. Before work is resumed, the Contractor or PG Binder supplier shall show to the Laboratory the material properties and compatibility of another PG Binder, by reporting actual test data, and that proper binder production equipment is in use.

The Contractor has a responsibility to ensure traffic is not released early on the mat, unless overridden by the Department. This Contractor responsibility includes allowing sufficient cooling time when night paving before morning rush hour release of traffic. Should traffic be on the mat in a manner leading to flushing or excess surface/tire adhesion and tracking of binder, the mat area in question shall be evaluated for removal and replacement or repair. Any removal and replacement or repair shall be at the Contractor's expense, unless the responsibility was overridden by the Department.

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XXX.040 Storage. PG Binder storage shall be in accordance with Contractor's Plant Operation Quality Control Plan, with the following additions:

A separate storage tank shall be used whenever a Contractor is providing a binder other than a PG Binder to customers other than the Department (excepting winter carryover work) or switching between different PG Binders because of alternating mix types.

When the Contractor switches between two different binder grades and is going to use the same storage tank, the storage tank shall be at least 90 percent empty by tank height. When the Contractor is switching to a PGM Binder or a PG Binder used to make a PGM Binder, the storage tank shall be at least 95 percent empty by tank height.

PGM Binder shall not be stored at the asphalt concrete mixing plant over the winter. No PG Binder to be used in producing a PGM Binder at the asphalt concrete mixing plant will be stored at the facility over the winter. SBR polymer shall be stored in a heated area over winter, but shall not exceed supplier requirements.

The Monitoring Team representing the Department shall be notified before the delivery of the first load of each type of PG Binder with sufficient lead time to allow for verification of the storage tank condition and if the storage tank meets handling requirements of the binder supplier. The Monitoring Team may sample the first storage tank load or give the Contractor permission to proceed with no tank verification.

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XXX.050 Requirements for PGM Binder. A PGM Binder shall meet the requirements of Table A and shall be obtained through modification of a non-oxidized, neat asphalt binder by using a styrene butadiene latex rubber compound (SBR polymer) or a styrene butadiene styrene polymer block copolymer (SBS polymer). The polymer supplier shall certify to the refiner and Contractor that the polymer used meets a minimum 68 percent by weight butadiene content. SBS polymer modification shall be performed prior to shipment to the asphalt concrete mixing plant (preblend). SBR polymer modification shall be performed at the asphalt concrete mixing plant. Asphalt plants utilizing SBR modification shall be equipped with a SBR polymer flow meter and monitoring system. The system shall be approved by the Department prior to use. It shall consist of a magnetic flow meter capable of measuring the SBR polymer within 2.0% and a totalizer interfaced with a data logging computer. The computer shall produce printouts of the logged data every 5 minutes for drum plants or for every batch when a batch plant is utilized. The logged data shall include time, date, flow rate and flow total. For drum plant production, the SBR polymer shall be introduced directly into the asphalt cement line through means of an in-line motionless blender capable of providing a homogenous blend for sampling. A sampling valve shall be located between the in-line blender and the drum. For batch plant production the SBR polymer shall be added into the pug mill after the aggregate has been completely coated with bitumen. Mixing shall be continued for a minimum of 20 seconds after the SBR polymer is added and as long as required to provide a uniform mixture.

For each project, the PGM Binder supplier shall give the Contractor a handling guide specifying temperature, circulation, shelf life, and other requirements for assuring the PGM Binder will perform as desired. This handling guide will be given to the Monitoring Team and be available in the plant control room and plant laboratory. If PGM Binder is retained at the asphalt concrete mixing plant for more than two weeks before use or beyond the supplier recommended shelf life, whichever is less, a top and bottom sample test (material property difference between samples taken from the top and bottom of the storage tank) shall be performed by the Laboratory on samples retrieved by the Contractor at the Department's direction and material on hand shall not be used until approved.

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XXX.051 Sampling of PGM Binder. The Contractor shall take two 1-quart (1 liter) binder samples from the first transport truck load, before incorporation into the storage tank. The Contractor will label the samples with binder type, supplier, project number and date and retain them in the plant laboratory for future reference by the Department.

In addition to the above sampling requirements, twice during each project (once if project has less than 3000 tons (3000 metric tons) of mix), the Monitoring Team will direct the Contractor to take two 1 quart (1 liter) samples of a PGM Binder, except when SBR polymer is incorporated into batch plants. In this case the base binder and SBR polymer shall be sampled and stored independently. Samples shall be taken from the binder line between the last piping ‘tee’ and inlet into the plant. They shall be labeled and handled as above. All samples shall be held after project completion until the Department's Engineer of Tests collects or releases them.

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XXX.052 Mix Design for PGM Binder. The PGM Binder supplier, as well as the polymer type, shall be identified on the Job Mix Formula (JMF) submittal. A change in binder or polymer source will require a redesign. The PGM Binder shall be graded, except for Direct Tension, and provide the actual pass temperatures confirming the grade requirement. All dated data shall be reported with the JMF submittal. In addition to the PG Binder grading, the dated test results for the requirements of Table A shall be reported. All data shall be neatly summarized on one page. No data shall be more than three months old. If SBR polymer is added at the asphalt concrete mixing plant, the JMF shall contain data from the SBR polymer supplier for total solids (percent) and ash (percent). As well, the submittal shall contain the target amount of SBR polymer greater than or equal to 3.0 for 70-22M or 4.0 percent for 76-22M to achieve the properties specified. A letter of certification from the polymer supplier verifying percent butadiene in the SBS or SBR polymer shall be included in the JMF submittal.

Each JMF submittal shall report supplier recommended temperatures for mixing and compaction. A maximum of 10 percent reclaimed asphalt concrete pavement or reclaimed bituminous aggregate base may be used. If used it shall be included in the JMF. At no time shall the amount of reclaimed asphalt concrete pavement or reclaimed bituminous aggregate base in production exceed 10 percent of the mix by dry weight.

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XXX.053 Quality Control for PGM Binder. The Contractor's Plant Operation Quality Control Plan shall include plans for meeting this specification and any handling requirements of the PGM Binder supplier. If the Contractor does additional testing or plant modifications, this shall be explained in the plan.

A pre-approved asphalt ignition oven is required to obtain an aggregate sample from an asphalt concrete sample. The asphalt ignition oven may be used in place of hot bin or belt samples.

Some solvent testing may be performed early in a project as information in helping to verify plant operation and determining an Asphalt Content Nuclear Gauge (AC Gauge) or asphalt ignition oven calibration. However, any solvent testing shall be accompanied by an asphalt ignition oven test.

For SBR polymers added at the asphalt concrete mixing plant, the flow meter printouts shall be totaled for each day's production. The percent of polymer versus neat binder in the mix shall be calculated each day and recorded. Calculation worksheets and printouts shall be available in the plant laboratory for review by the Monitoring Team. A +/- 0.2 percent tolerance from the target amount of SBR polymer shall be used as a guide for an acceptable amount of SBR polymer use, but shall not be consistently low. To clarify, if the target amount of SBR polymer is 3.5% of the asphalt content, then the latex shall be added as 3.3% to 3.7% of the asphalt content. Disposition of all data records shall be at the direction of the Department's Engineer of Test.

Table A Material Requirements for PGM Binder

Test/Requirement
Final PG Binder Grade
Actual Pass Temperature
RTFO Mass Loss, percent
Phase Angle, max
Elastic Recovery, min
Toughness, in lb
Tenacity, in lb
Ductility, in, min
Separation, F max
Homogeneity
SBR Polymer
70-22M (a)
Report
<0.5
80

100
60
28
 
 

SBR Polymer
76-22M (b)
Report
<0.5
76

125
72
28
 
 

SBS Polymer
70-22M (c)
Report
<0.5
80
65
 
 

10
None Visible

SBS Polymer
76-22M (c)
Report
<0.5
76
75
 
 

10
None Visible

Notes
d
j
e
e
f
g,e
g,e
k,e
h
i,e

a. Post blended PGM Binder made from neat certified or pre-approved standard PG Binder grade and rubber solids amount equal to or above 3.0 percent by weight of total binder to achieve the PG Binder grade.
b. Post blended PGM Binder made from neat certified or pre-approved standard PG Binder grade and rubber solids amount equal to or above 4.0 percent by weight of total binder to achieve the PG Binder grade.
c. Preblended PGM Binder with a base binder of at least -22 grade or stiffer. 
d. As required by Section XXX.052.
e. PGM Binder
f. ASTM D 6084, 10cm @ 25C, hold 5 min. before cutting, on RTFO material
g. ASTM D 5801, 50cm/min @ 25C
h. Softening point difference of top and bottom of frozen sealed aluminum tube conditioned at 340F for 48 hours. Compatibility of polymer and neat binder is sole responsibility of supplier. PGM Binder shall be formulated to retain dispersion for 3 days minimum. Failure in the field to retain dispersion for this time will mean automatic removal from certification list.
i. Heat a minimum 400 gram sample at 177C for 2.5-3 hours. Pour entire sample over a hot No 50 (300 µm) sieve at 340F. Look for retained polymer lumps.
j. Actual high and low temperature achieved by PGM Binder beyond required grade, but shall not grade out to the next standard PG Binder grade for low temperature.
k. ASTM D 113, @ 4C, 1 cm/min

IMPORTANT NOTICE TO THE ENGINEER. The foregoing is for engineers only for the purpose of assisting them in preparing job specifications. Suggested specifications are for use under what may be termed “average conditions”. No single standard specifications, however, will cover satisfactorily all variations in local conditions relevant to individual jobs. Before adopting suggested specifications, the owner's engineer should give particular consideration to any special problems and make such changes as are necessary. Nothing contained herein shall be construed as recommendations or inducements to practice any invention covered by patent without permission of the patent owner.


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