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8/3/2019 Recpe for Hima Revp
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Walter J Tappeiner, Pavement Consultant, E-Mail: [email protected]
High-Modulus Asphalt Mix -
A Case for Using Recycled LDPE
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High-Modulus Asphalt Mix – A Case for Using Recycled LDPE 2011
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Principle of Long-Life Asphalt Pavements
1. Long-Life Asphalt Pavements
In the quest for designing and constructing durable asphalt pavements for heavy highway and
airport traffic, engineers look for good quality aggregates and special bituminous binders, and for
advanced methods of asphalt mix design and performance based evaluation. Many of thetraditionally used asphalt binder and mixture specifications, and related test methods, have been
developed during the first half of the 20th Century. Bitumen grades and asphalt mix properties
characterized using simple empirical tests are not adequate for design and construction of heavy-
duty long-life pavements. To be able to tailor more efficiently asphalt mix properties to structural
and functional performance requirements of individual pavement layers, special bituminous binders
and mixtures are needed. Engineers who face this challenge look increasingly at polymer modified
asphalt as a potential solution.
Design and construction of long life asphalt pavements requires usually the following:
•A strong and uniform foundation.
•Design of high quality asphalt mixtures the performance of which is tailored to structural
and functional requirements of individual pavement layers (layer function concept); high
modulus rut resistant asphalt mix is a good choice for upper (binder) and lower base
course.
•Specify appropriate construction tolerances and ensure effective quality control during
asphalt mix production and pavement construction. Pavement courses must be uniform in
composition and density.
• Specify and verify adequate bonding between and good joint construction within pavement
courses.
• Select pavement structures based on catalogues developed using mechanistic pavementdesign, or design individual pavement structures using mechanistic design parameters
appropriate for long pavement life.
Figure 1: Principle of Long-Life Asphalt Pavement
Wearing Course: functional and structural Properties;
renew as required (for example, every 10 to 15 years)
Upper (or binder) and lower base course; pr imary
structural pavement courses; design and construct to
meet long-lif e requirements (40 to 50 years)
Strong and uniform foundation (sub-grade)
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High-Modulus Asphalt Mix – A Case for Using Recycled LDPE 2011
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This paper reviews and summarizes materials and performance requirements of high modulus
asphalt mixtures. In France high modulus asphalt (Enrobé à Module Élevé , or EME ) has been
used for more than 20 years as a solution to reducing rutting and increasing the stiffness of
pavement structural courses for better load distribution. These types of mixtures are recommended
for design and construction of long-life pavements.
In France and in other countries hard paving grade bitumen (EN 13924: PEN 10/20 and 15/25) is
widely used to achieve the properties specified for ELE mixtures. Specially formulated polymer
modified bitumen (PMB) are used effectively as alternative when hard paving grade bitumen is not
available. Hard PMB grades that are suitable for EME mixtures can be formulated and produced
wherever PEN 50-70 or similar standard bitumen and additives that increase initial asphalt binder
and mixture stiffness are available.
2. Bituminous Binders for High-Modulus Asphalt Mix
a. Shear Strength and Deformation Resistance of Asphalt Mixtures
Huschek, S. reviews in his paper “The Deformation Behavior of Asphalt Concrete under Tri-Axial Compression” (AAPT, 1985) deformation and shear resistance of asphalt mixtures. Referring to the
dissertation by Nijboer, L.W . (Plasticity as a Factor in the Design of Dense Bituminous Carpets,1948) he postulates that total deformation resistance is made up of the following three
components:
• Initial resistance
• Internal friction
• Viscous resistance
Real and apparent cohesion and aggregate particle interlock are key contributors to initial
resistance to deformation and to asphalt mix elastic modulus. Asphalt binders that exhibit high
cohesive strength at low strains confine the aggregate structure of asphalt mix. By increasing
confinement of the aggregate structure, friction between aggregate particles is increased. The
combination of high cohesive strength at low strains and of increased internal friction enhances
shear strength and modulus value of asphalt mixtures.
Little, D.N. provides in his paper “Analysis of the Influence of Low Density Polyethylene Modification of Asphalt Concrete on Mixture Shear Strength and Deformation Resistance” (ASTM STP 1108, 1992 ) an example of the contribution that polymers and PMB can make to increase
shear strength and modulus of asphalt mix (see Table 3 of Little’s paper, reproduced as Figure 2below). The effect of PMB formulated to obtain high initial cohesive strength and shear resistance
of asphalt mix is further demonstrated in Figure 3, which shows unpublished test results obtained
at the Texas Transportation Institute (1988).
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High-Modulus Asphalt Mix – A Case for Using Recycled LDPE 2011
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Figure 2: Excerpt from Paper by Little, D. N ( ), 1992
Figure 3: Stress-Strain Response of Different Asphalt Mixtures (unpublished, based on Research
conducted by Little, D. L. (1988)
Stress-Strain Response of Asphalt Mixtures
PE SBS Control
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High-Modulus Asphalt Mix – A Case for Using Recycled LDPE 2011
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Christensen, D.W . and Bonaquist R. (Rut Resistance and Volumetric Composition of Asphalt Concrete Mixtures, AAPT, 2005) use the term asphalt mix resistivity to describe the effect of
aggregate structure and binder viscosity on shear strength and rut resistance of asphalt mix. Table
17 of their paper shows that binder grade is the most significant contributor to rut resistance of
asphalt mix. Binder grade (in this case expressed as PG-grade) is related to binder stiffness. To
achieve asphalt mix properties typically specified for high-modulus asphalt mixtures, hard
unmodified bitumen or special PMB is required. Polymer type, properties and dosage are all very
important for such special applications.
The importance of polymer type is also reflected in AUSTROADS Technical Report AP-T41/06: “Specification Framework for Polymer Modified Binders and Multigrade Bitumen” . For high
modulus and highly shear resistant asphalt mixtures, use of PMB formulated with appropriate
plastomeric polymers is recommended. This recommendation is based on extensive laboratory
and accelerated field tests (ALF).
In the European framework of PMB specifications cohesive strength (or deformation energy) basedon force-ductility or direct tensile strength testing is an important specification parameter. The
deformation energy parameter is calculated as the work expended to stretch a PMB sample from
200 to 400 mm (Figure 4 below). While this parameter provides useful information about cohesive
strength of a binder under these specific test conditions (applicable to elastomer modified PMB), it
is not useful to assess a binder’s contribution to initial strength and stiffness. For this purpose, the
area under the primary peak of the force-elongation curve should be taken into consideration,
which is closely linked to initial resistance and modulus.
Figure 4: Force Ductility and Deformation Energy
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Hard paving-grade bitumen shows excellent initial resistance to deformation, but does not exhibit
high deformation energy between 200 and 400 mm extension. The same applies to asphalt
modified with polyethylene and/or natural rock asphalt (asphaltite), both of which are used in
France for EME 2 mix. Elastomeric polymers can also be used, but require high dosages of high-
molecular weight polymer, which tends to yield PMB that is difficult to work with. Addition of special
viscosity-reducing polymers such as SASOBIT would be an option, but this increases further costs
of modification. Plastomers, such as LDPE, impart on asphalt mixtures high initial stiffness without
affecting workability of asphalt mix.
b. Hard Paving Grade Bitumen
Hard paving grade bitumen is now standardized in Europe under EN 13924 (-1) and is widely used
for EME 1 and EME 2 asphalt mixtures. The UK Specifications for Road Works (Series 900: Road Pavements – Bituminous Bound Materials, 2010 ) specify in Section 930 use of PEN 10/20 or PEN
15/25 for EME 2 asphalt mixtures. Other grades of bitumen or special grades of PMB may be used
subject to approval by relevant authorities.
c. Polymer Modified Bitumen for EME Mix
In France PE is frequently mentioned as additive for EME type mixtures. A selection of relevant
literature references is provided below:
• TRB Circular 503: Perpetual Bituminous Pavements (2001): includes a contribution by Jean- Francois Corte, LCPC (Development and Use of Hard-Grade Asphalt and of High-Modulus Asphalt Mixes in France ). In this article polyethylene and asphaltite are mentioned as suitable
additives to achieve the special properties of EME. Figure 5 below (reproduced from Corte’s
paper) shows the effectiveness of recycled PE for achieving rut resistant (and high modulus)asphalt mixtures.
Figure 5: Effect of Bituminous Binder on Rut Resistance of Asphalt Mix
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High-Modulus Asphalt Mix – A Case for Using Recycled LDPE 2011
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• In the paper “Special Bitumen” by Jean-Noël Onfield use of polyethylene and other
plastomers for high-modulus asphalt mixtures is mentioned several times.
• Contractors and material suppliers in France have developed proprietary asphalt mixtures
that meet specifications for high modulus asphalt. For several of these special asphalt
mixtures polyethylene is used as additive.
• In Spain CICLOPLAST (a non-profit society, which is committed to promoting recycling and
use of recycled plstic0 and DITECPESA (a company specialized in development and use of
asphalt products) have entered into an agreement to evaluate and promote use of recycled
plastic in asphalt pavements. Under this agreement more than 2000 tons of plastic
(recycled film used as greenhouse cover) was used in 2010 in a highway project in Almeria.
• Comprehensive research carried out about ten years earlier in several European countries
(sponsored in part by the European Community) on use of recycled plastic evaluated a
large number of PMB formulations using virgin and recycled polyethylene. The four-year
research program concluded that select recycled plastic, especially recycled film used in
horticultural and agricultural applications0 is suitable as asphalt additive. More informationabout recycled PE characterization and selection criteria for use as asphalt additive is
provided in Section 4 below.
3. Use of Recycled LDPE as Asphalt Modifier
Over the last thirty years several hundred papers and reports were published around the world on
use of polyethylene and other plastics as asphalt modifier. Until the late 1990s selection criteria
were usually limited to a few basic plastic properties, such as density and melt flow rate;
applications at project level were often based on trial and error. Because of this largely empirical
approach some of the projects did not perform as expected.
Comprehensive research carried out since the late 1990s on use of virgin and recycled
polyethylene as asphalt additive focused on developing performance based application criteria (for
example, “Performance Characteristics of PMB – The Contribution of Recycled Polyethylene” by
Legnani, G. and Tappeiner, W.J. in Rassegna del Bitume, 2003 ; in Italian language; “Study of Recycled Polyethylene Materials as Asphalt Modifiers ” by Ho, S. and others, 2006; NRC, Canada; Behavior of Reclaimed Polyethylene Modified Asphalt Cement for Paving Purposes, by V.S. Punith et.al., Journal of Materials in Civil Engineering, ASCE, 2011). These studies show that when
properly selected and used as asphalt modifier, recycled PE offers attractive performance and cost
advantages.
Use of recycled PE in high modulus asphalt mixtures offers the following advantages:• Recycling and re-use of plastic offers environmental benefits; recycled PE is readily available
at reasonable costs.
• Asphalt mix produced with recycled PE (typically less than one percent by mass of mix) can be
safely recycled.
• Good performance when used within the framework of the layer function concept; high-
modulus asphalt mix plays a key role in this concept.
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• High-modulus asphalt mixtures allow reducing layer thickness by 15 to 30 % when compared
to traditional base and binder courses. This offers important savings on raw materials such as
aggregates and bitumen. Thickness reduction in conjunction with high-modulus asphalt mix is
now widely accepted by road authorities, and is incorporated in pavement design in France
(SETRA/LCPC ) and in the UK (DMRB HD 26/06: Pavement Design ).
4. Recycled LDPE Selection Criteria and Quality Control
Recycled plastic, including film from agricultural and horticultural applications, is readily available in
many countries. Hurley, S. presents in “Agricultural Plastic Film Use and Recycling in California” (2008 ) results of a study carried out on use and recycling of agricultural plastic film. Costs of
recycling and lack of recycling facilities were listed as impediments to broader acceptance of
recycling by film users. These perceived problems can be overcome if PMB production or
construction companies that are interested in this special application organize collection, transport
and sorting/cleaning of such film. Using recycled material from selected sources and industrial
applications allows more effective utilization of such material than would, for example, be possiblewhen household waste is recycled.
During the first two decades of using PE and other plastic as asphalt modifier, simple polymer
properties were employed as basis for selection. Properties such as density and Melt Flow Index
(MFI) are useful but do often not provide sufficient Information about performance potential of
recycled plastic as asphalt additive. One of the reasons for this limitation is that density and MFI
are often masked by the presence of processing agents, color pigments, and other additives used
at the time of manufacturing plastic goods.
Based on research carried out from the lte 1990s onwards one or more of the following tests is
recommended for assessing the suitability of REC PE as asphalt modifier:
o Molecular Weight and Molecular Weight Distribution
Weight-Average Molecular Weight Mw
Number-Average Molecular Weight Mn
Polydispersity Index Mw /Mn
o Fourier Transform Infra Red (FTIR) Spectroscopy for Identification of Impurities (polymersother than PE)
o Differential Scanning Calorimetry (DSC)/Differential Thermal Analysis for identification of
different types of PE (LDPE; LLDPE; MDPE/HDPE)
o Shear-Rate dependent Melt Viscosity (at 190°C) for evaluating interaction (and miscibility)of REC-PE with bitumen. Critical values were identified below which good quality PMBcan be formulated with PE.
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5. Summary
Traffic volumes and traffic loads are increasing faster in many developing countries than in
industrialized countries. In most developing countries, hard paving grade bitumen (EN 13924),
which is used in Europe for high modulus, highly rut resistant asphalt mixtures, is not available at a
competitive price. Use of special grades of PMB, which can be formulated and produced using
locally available raw materials, offers a sound and overall cost-effective alternative.
Use of special asphalt mixtures within a sound layer function concept improves performance,
longevity and cost effectiveness of asphalt pavements. The technology required to design and
produce high modulus asphalt mixtures is readily available. Use of selected recycled LDPE in
accordance with current know-how and practices offers performance, cost and environmental
benefits.
In IM-40 “Perpetual Asphalt Pavements – A Synthesis” published by the Asphalt Pavement
Alliance key recommendations for further investigations include development of high-modulus
asphalt pavements and of mix designs for high-modulus asphalt mixes. The EME technology is
already well developed in Europe. Adaptation of this proven technology to climate and traffic
conditions of other regions should be feasible; because of performance, cost and environmental
benefits consideration should be given to using recycled plastic to achieve the high modulus values
and superior rut resistance required for these mixtures.
PEN 10-20 or Special PMB for EME 2
Limted Supply of PEN 10-20/15-25As Alternative use special PMB, such as
PMB formulted with recycled PE
Europen Layer Function Concept
EME 2 for Binder/Base Course Functional/Structural Wearing Course
Long Life (Perpetual) Pavement
Good Foundation (Sub-Grade) Superior Paving Materials