Sousa, Vorobiev, Rowe and Ishai...Sousa, Vorobiev, Rowe and Ishai 2 mining. The activation, made by nano-monomolecular particle coating, was aimed at obtaining thixotropic and shear-thinning

Sousa, Vorobiev, Rowe and Ishai

REACTED AND ACTIVATED RUBBER – AN ELASTOMERIC ASPHALT EXTENDER

Dr. Jorge B. Sousa

CONSULPAV – Consultores e Projectistas de Pavimentos, Lda.

Rua da Zona Industrial, nº6 A

Casais da Serra

2665-305 Milharado

Mafra, Portugal

+351 917 549971

[email protected]

Engr. Andrey Vorobiev

Alltech Investments Ltd.

11 Minskaya Street

Moscow 121108, Russia

+7 495 786 67 50

[email protected]

Dr. Geoffrey M. Rowe*

Abatech Inc.

PO Box 356

Blooming Glen, PA 18911

+1 (267) 261-8481

[email protected]

and

Prof. Ilan Ishai

Department of Civil & Environmental Engineering

Technion – Israel Institute of Technology

Haifa, Israel

+972 52 2539668

[email protected]

*Corresponding Author

August 1st, 2012 (Rev. 11/15/12)

Word count: 6,8889 (4,889 + 2,000, 1 table and 7 figures)


ABSTRACT

Asphalt rubber mixtures have traditionally been difficult to produce requiring specialized plant

and equipment resulting in higher costs of manufacture. This in part is due to the need to

produce asphalt rubber binder by blending at high temperatures for a significant time period

(around 190oC for typically 45 minutes to 1 hour). The complexities in the process have resulted

in asphalt rubber mixes being significantly more expensive to produce than conventional paving

mixtures. A new technology which produces a “Reacted and Activated Rubber” (RAR), which

is an elastomeric asphalt extender, has been developed by hot blending and activation of a rubber

granulate with a selected asphalt binder and activated mineral binder stabilizer (AMBS). RAR

achieves similar results comparable to other types of polymer modified binders (PMB).

However, a principle advantage with RAR is that it can be easily added to any HMA

manufacturing facility using systems designed to feed particulate material into a batch plant

(pug-mill) or drum mix plant. This paper describes how RAR is produced from raw constituent

materials. Various tests on binder contrast the performance to typical paving grades and PMBs

that are used in the USA. The implementation of RAR in various types of asphalt mixtures will

be discussed and demonstrative examples of test results are provided. Tests on mixtures in

wheel tracking and fatigue demonstrate how the binder performance tests translate into mixture

performance. In all cases evaluated, the RAR mixtures out-perform non-modified and even

conventional rubber modified equivalent materials.


1

INTRODUCTION

The need for improved material performance has spurred the adoption of modified asphalt

systems. Rubber has been used as a modifier in the USA on road projects since the late 1940’s

(1). A few years after the first roads were repaved the process of adding crumb rubber from

waste tires was developed in Phoenix, Arizona in 1965. This process is a well-developed system

of asphalt modification with nearly 50-years of development. However, today asphalt rubber

mixtures are still difficult to produce requiring specialized plant and equipment resulting in

higher costs of manufacture. This is due in part to the need to produce asphalt rubber binder by

blending at high temperatures for a significant time period (around 190oC for typically 45

minutes to 1 hour). The complexities in the process have resulted in asphalt rubber mixes being

significantly more expensive to produce than conventional paving mixtures.

Since 2009 significant understanding of improved materials performance has been

obtained with a unique mineral mined and activated to produce an activated mineral binder

stabilizer (AMBS). AMBS has been shown to improve the rheology and crack resistance of

dense and stone matrix asphalt (SMA) mixtures (2). Subsequently, it was decided to conduct

trials of AMBS with various formulations of asphalt and crumb rubber. This development work

has resulted in a new technology which produces a “Reacted and Activated Rubber” (RAR),

which is an elastomeric asphalt extender. This development is achieved by a hot blending and

activation of crumb rubber with a selected asphalt binder and AMBS.

RAR achieves similar results comparable and better than other types of polymer modified

binders (PMB) and conventional asphalt rubber (AR). However, a principle advantage with

RAR is that it can be easily added to any HMA manufacturing facility using systems designed to

feed particulate material into a batch plant (pug-mill) or drum mix plant. This paper describes

how RAR is produced from raw constituent materials. Various tests on binder contrast the

performance to typical paving grades and PMBs that are used in the USA. The implementation

of RAR in various types of asphalt mixtures will be discussed and demonstrative examples of

test results are provided. Tests on mixtures in wheel tracking and fatigue demonstrate how the

binder performance tests translate into mixture performance. In all cases evaluated, the RAR

mixtures out-perform non-modified equivalent materials.

BACKGROUND

The components of RAR are asphalt, crumb rubber and an activated mineral binder stabilizer.

The asphalt cements or (bitumen as referred to in Europe and elsewhere) conceptually can be any

straight run plain soft bitumen. The use of the softer asphalt grades enables production of HMA

at conventional mixing and laying temperatures without losing the proper workability, despite

the addition of the crumb rubber.

The Crumb Rubber is usually consisting of scrap tires that are processed and finely

ground by any proven industrial method. The scrap tires consist of combination of automobile

tires and truck tires, and should be free of steel, fabric or fibers before grinding. For the

production of RAR, the crumb rubber particles should be finer than 1.0 mm. A 30-40 mesh

maximum particle size is preferred.

The Activated Mineral Binder Stabilizer (AMBS) is a new binder stabilizer that was

developed to prevent excessive drainage of the bitumen in SMA mixes during mix haulage,

storage and lay down. This stabilizer (industrially known as “iBind”) is an activated micro-

ground raw silica mineral (40μm and finer), which is a waste by-product of Phosphate Industries


2

mining. The activation, made by nano-monomolecular particle coating, was aimed at obtaining

thixotropic and shear-thinning properties for the asphalt, since the binder film/mastic in the mix

should possess high viscosity at rest (haulage, storage and after laying) - for reducing drain-

down, and low viscosity in motion (mixing and laying) - for maintaining the proper workability

(2).

During the research and development work, RAR was produced and tested at different

formulations, dictated by the type and relative proportions of its three components. As an

average, a typical RAR blend contains about 62% Crumb Rubber, 22% soft bitumen, and 16%

AMBS. After the material has reacted in the blending equipment another 10% AMBS is added

in a coating mixer unit to prevent re-coagulation of the product. RAR has been found to enhance

the properties of the plain bitumen to higher levels than polymer modified asphalt, and even

higher than conventional asphalt rubber blends. A hypothesized basic model for the mechanism

of RAR as a bitumen enhancer is illustrated in FIGURE 1.

The crumb rubber particles contain a large amount of inorganic materials that are electro-

statically surface charged (fillers, vulcanization materials, and various additives). The activator

of the silica mineral particles of the AMBS is composed of organic molecules that are partly

electro-statically surface charged (ammonium head) and contains organic hydrophobic chains.

When the activator particles are present in a liquid medium, such as asphalt binder, they can be

attracted and connected to other particles with opposite charge. Charged organic chains of the

activator in the AMBS are able to create a connected network of particles. When the fine RAR

particles (elastomeric material) are blended in the liquid medium with the activated silica

particles, the charged molecules of the AMBS particles are connected to the rubber particles at

charged sites on the inorganic materials. In this way, when all the above materials are blended

together with the hot liquid bitumen, an inner network of the elastomeric material and the AMBS

particles is formed in the bitumen. This network, together with the unique elastic and networking

capabilities of the elastomeric material derived from the reaction and activation of rubber at high

temperatures structurally enhances the bitumen resulting in improved mechanical properties.

These are evident in the elastic behavior and better performance in tests such as the bending

beam fatigue test. RAR is also coated with a special formulation of AMBS that once dispersed

into the bitumen also attaches itself to the aggregate. This connection improves binder aggregate

interactions improving moisture sensitivity responses. As such the new networks bound

aggregate, bitumen, elastomeric material and AMBS particles. Such a network cannot be formed

when just rubber and bitumen are blended together (without AMBS), as in any conventional

asphalt rubber technology.

As different from the common asphalt rubber binder, the industrially prepared RAR

(which comes in dry granulated form), can be fed directly to the pugmill or the dryer drum of

any asphalt mixing plant. The common auxiliary feeders used in any asphalt plant are adequate.

RAR should be added to the asphalt mix, in laboratory or mixing plant, after the bitumen is

applied to the mixer - first mix aggregate and filler, then add the asphalt, and after the asphalt has

well coated the aggregate, add the RAR. Then complete the mixing cycle in about 30 seconds,

until the RAR has evenly distributed and been absorbed by the asphalt.

Mixing temperature of RAR asphalt mixes is identical to that of the mixes it replaces

(usually about 170 C to 180 C). However if high RAR contents are used (such as, for example

3.5% in gap grade asphalt rubber mixes) then the aggregates may require a slightly higher

temperature so that the mix reaches the mixing temperature faster. In laboratory, before

compaction, the mix of RAR, bitumen and aggregate must age in the oven for 1 hour at 170o C.


3

This simulates the time it usually takes between mixing in the plant and compaction in the field.

During this time RAR coatings are activating the bitumen and aggregate surfaces.

RAR improves binder qualities and from this perspective, the higher percentage of RAR

that can be used is preferable. This is supported by some of the discussion in the sections of this

paper. Significant improvements in binder properties can be seen when the RAR percentage in

the combined binder is above 15%. However, there is a point after which there is not enough

plain bitumen to coat the aggregates or the viscosity becomes too high. That will cause the

increase of mix air voids and VMA after compaction, beyond acceptable ranges. This also may

create partially coated aggregates.

Experience has shown that there should always be at least about 4% of plain bitumen (by

weight of the total mix) in all mixes, to allow complete aggregate coating and sufficient

workability. As such, the difference to regular binder contents can be replaced by RAR. As an

example, if in an SMA the mix design requires 6% bitumen content, then in a RAR mix design

we would expect 4% of regular binder and 2% of RAR (that is 33% of the combined binder). In a

dense graded mix, with regular binder content of about 5%, then a minimum of 4% of

conventional asphalt should be used with about 1% RAR. The quantity of base binder also

depends on the mix gradation and the fine/coarse split of the gradation envelop. In all cases, the

optimum combined binder content (asphalt + RAR) should be determined according to a

standard mix design procedure. As a general guidance, the following are the RAR content in the

combined binder and the total mix, for the different types of HMA mixes:

• In Dense Graded mixes – 20% of the combined binder or 1% of the total mix.

• In SMA mixes – 30% of the combined binder or 2% of the mix.

• In GAP Graded mixes – 40% of the combined binder or 3-4% of the mix.

• In OPEN Graded Friction courses – 50% of the combined binder or 4 to 5% of the

mix.

When using RAR asphalt mixes, no other additives are generally required since RAR is

formulated to improve adhesion, fatigue and rutting resistance when compared to an identical

mix without RAR.

In the R&D stages of the Reacted and Activated Rubber, extensive testing effort was

dedicated to characterize the properties and behavior of the new rubber binder. Since RAR is

intended to replace part of the non-modified bitumen in a HMA mix, the physical and

rheological properties of the combined binder (RAR + asphalt) was studied at variable

proportions of RAR in the original bitumen (3).

EXPERIMENTAL

Binder testing

Traditional binder has been conducted to define properties such as penetration, Brookfield

viscosity, softening point and resilience (ASTM D5329) on RAR modified binder. In this

example a RAR material was produced using a 35/50 Pen which also graded as a PG70-22. The

results from this evaluation are presented in FIGURE 2 which shows data from two trial

production runs (Trial 1 and 2). The changes in these properties are very significant particularly

as the RAR content increases above 15% of the binder.

This RAR was then combined with a typical PG64-22 used in the USA obtained from

Ergon. This testing was conducted by Dongre Testing Laboratories and evaluated how the RAR


4

affects the PG grade using laboratory blended samples of the resulting binder and the methods

contained within AASHTO M320. The results from the DSR and BBR testing are summarized

in FIGURE 3. The high temperature performance was controlled marginally by the data after the

RFTOT aging procedure.

In addition, testing has also been performed in the newer Multiple Stress Creep and

Recovery (MSCR) test, as specified in ASTM D7405 or AASHTO TP70, which has more

recently been introduced to better define the binder performance in relationship to permanent

deformation with the evaluation of the Jnr parameter (4). The concept of this parameter is very

important for ensuring that the material adopted tends to maintain good behavior characteristics

as the magnitude of stress increases.

The normal specification criterion for a conventional binder is the material shall have a

value of Jnr 4 (1/kPa) with this value reducing to 2, 1 and 0.5 for heavy duty, very heavy and

extreme grades respectively. The data obtained for the RAR modified PG64-22 binder are

presented in

FIGURE 4 which shows how the data varies as a function of addition level. The addition

levels of RAR correspond to 7, 14, 21, 28, 35 and 42 % for each of the trials conducted. These

numbers have been indicated for most of the lower addition levels but a few have been omitted

for the high addition levels for the sake of clarity. As the addition level increases the Jnr reduces

and the percent recovery increases which is to be expected.

Also shown on this graph is a line that has been suggested as representing the difference

between modifiers that have elastomeric performance versus those that can be considered non-

elastic. While the position of this line may be considered somewhat arbitrary it is interesting to

note as the modification level increases then the RAR modified material changes from a material

that would be classified as a non-elastic material to a material that would be classified as elastic.

This data would suggest that an addition level of around 25 to 30% would ensure sufficient

elastic recover to be classified as an elastomeric modifier whereas to have a product that would

be suitable for very heavy traffic that approximately 25% addition would be required. It should

be noted that the adoption of a very heavy grade would be considered equivalent to 2-grade

bumps using the system as specified in AASHTO M320. It is interesting to note the percent

recoveries obtained from the two tests (ASTM D7405 and ASTM D5329) are in very good

agreement (see FIGURE 5) considering these are conducted at very different test temperatures,

rates of loading and test conditions.

Mixture testing

To investigate the effect of the binder properties on mixture performance the RAR was added to

several different types of mixtures including SMA and those used in normal asphalt rubber gap

graded mixes (AR-GAP). Mixes were chosen so that good contrast in performance could be

obtained. For example in the study conducted for permanent deformation some good performing

materials were selected as controls and the performance of the RAR modified materials were

compared to these. One of the major issues when comparing results from different modifiers is

how that modifier affects items such as the aggregate structure (for example VMA and air voids)

and the effect that these parameters might have on the property being evaluated. In order to

reflect this concern we have often compared against several mixture types with very different


5

structures. While these comparisons are not perfect we consider this a valid approach as this

alternate RAR modification developed.

Fatigue

Extensive flexural fatigue tests, using the four point bending beam test device (ASSHTO T321),

were performed on variety HMA mixes. The conditions selected for the tests were to load at a

frequency of 10 Hz at a temperature of 20oC and a constant displacement to obtain a level of

between a nominal 250 and 700x10-6

strain. Generally 4 data points (2 at a high strain level and

2 at a low strain level) were evaluated to obtain a log-log fatigue relationship. From this

expression the mean life at a strain of 500x10-6

was estimated and the associated standard error.

Tests were made on polymer modified SMA mixes, AR-GAP conventional mixes and

dense graded mixes. These are compared to RAR gap graded mixes which were formulated

having the same binder content and add mix content as the reference AR-GAP “A” mix. The

reference AR GAP “A” Graded mix had 8.23% AR (Asphalt Rubber) Binder and 1% Portland

cement or hydrated lime, giving a total additive content of 9.23%. It should be noted that some

differences exist in the void levels of these mixes. The SMA and AR GAP mixes had void

contents in the range 6 to 7% whereas the RAR and Dense mixes were compacted to void

content levels of about 4%.

The RAR-GAP (RAR gap-graded) mixes were formulated so that the sum of

conventional binder plus the RAR would equal same amount, i.e. 9.23%. These are referenced

by a code that first represents the binder content followed by the RAR percentage. For example

“B6.19RAR3.04” indicates 6.19% asphalt binder and 3.04% RAR in the blend used. The ratios

used for all the blends are 6.19%/3.04%, 5.45%/3.78% and 4.71%/4.52%. With this RAR

containing 62% crumb rubber it can be easily computed that the mixes had about 19%, 23% and

28% of crumb rubber in the binder. The results from this testing are presented in FIGURE 6,

from which it can be observed that the RAR-GAP mixes outperform all other mixes tested.

Moreover the mix with 49% RAR in the combined binder (i.e. B4.71RAR4.52), has a fatigue life

that is about 7 times longer than the conventional Asphalt Rubber gap graded mixes.

One of the issues observed on close inspection of the fatigue beams and data was that in

all cases the specimen had not cracked at the end of the test. In the alternate ASTM D7640

procedure the specimen is tested to a point when crack initiation has occurred (5). If this was

applied to these results it is anticipated that the more highly modified RAR materials would have

a still longer life. This aspect will be investigated in the next phase of testing.

Permanent deformation

Permanent deformation of asphalt mixtures can be accessed via a range of different laboratory

techniques. However, often materials engineers make use of simple wheel tracking tests that

have the ability to mimic the traffic loading. In the USA the two most common methods used

are the Hamburg and the Asphalt Pavement Analyzer (APA) devices. Both of these are covered

by ASHTO specifications. In Europe, wheel tracking tests are specified in EN12697-22. This

standard allows wheel tracking in small scale devices that are commonly run throughout Europe.

The device used is similar to the Hamburg device with the exception that a rubber wheel is used

in place of the steel wheel adopted in the USA and is essentially the same as that used during the

validation work conducted during the SHRP (6). A test temperature of 60oC was used in this

work as it is much more simulative of hotter climates where deformation problems occur.


6

The concept used in this tested was to compare the RAR modified materials to some

well-known good performing products. A polymer modified SMA material with fiber addition

(referenced as Fiber/PMB) is considered the initial control. The same mix type but with a blend

of polymer and AMBS (referenced as AMBS/PMB) provides a second control of a good

performing product with respect to permanent deformation. These mixtures have good

performance history when used in a previous road project (2). The RAR mixtures have all been

used with a gradation typical of AR-GAP mixtures since this allows more space within the

aggregate structure to accommodate binder as used for the fatigue testing. Without modification

these mixtures would be expected to have more deformation than SMA mixes. The same blend

percentages were used for this testing as described earlier for the fatigue testing – that is a total

asphalt plus RAR content of 9.23% in the materials. All the data obtained were averaged from

two replicates with the exception of the B6.19RAR3.04 material which had a total of 4

replicates. The detailed data obtained from this testing are presented TABLE 1 and summarized

in FIGURE 7 which shows that the high binder content materials with the RAR additive have

lower deformation than the well performing SMA mixtures.

DISCUSSION

The concept of pre-reaction and pre-coating a rubber particle with asphalt binder is

attractive since the rubber components that are available to swell and interact with the binder

structure prior to importation into a hot mix. Further, the use of an activated mineral binder

stabilizer appears to result in an improved structure significantly increasing the fatigue and

cracking properties of the material. The use of fillers in composite materials has been studied for

many years and many mechanisms have been proposed, for example crack pinning (7), which

results in enhanced behavior. Since this material is a new innovation the true understanding of

the complex interactions is currently not fully understood. However, the performance testing

carried out on both binder and mixture specimens enables a reasonable translation of

specimen/laboratory performance to expected field performance. It is interesting to note that the

mixtures with the low deformation can also have very high fatigue performance as evidenced by

the fatigue test data presented earlier.

The initial focus of development work with AMBS (2) and subsequently RAR was to

develop materials to prevent drain-down in SMA and porous asphalt mixtures without the need

for fibers. RAR has been evaluated with SMA and other open graded mixtures (8) and has been

found to be a very effective modifier to prevent drain-down. This was an expected result since

the primary components have been designed to accomplish this.

With an engineering focus on “green” environmentally friendly materials it is of interest

to note that two of the principle components of RAR are from waste product streams. AMBS,

the main mineral component, is a waste material from the phosphate industry whereas scrap tires

are a major waste stream worldwide. RAR can easily be considered as a green environmentally

friendly material which will help find reuse for materials that would otherwise be confined to

landfills.

When asphalt modification is developed, one of the key objectives is to consider how the

material can be added to a hot-mix plant. In the case of this material several paths for addition

exist. With drum mix plants a particulate feed system would deliver the material to a point in the

drum where efficient incorporation can take place (8). We intend to investigate the use of

specialty feed systems in existence on plants, such as RAS feed systems to assess the mixing and

incorporation efficiency. With batch plants the addition is somewhat easier since the material


7

can be added directly to the pug-mill at a pre-defined point in the mixing cycles. It should be

noted that the cost of plant modifications for handling a material such as this is minimal and

many plants in the USA already have existing systems that can be sued or adapted.

Other work that has been conducted with this additive shows that the material has an

ability to significantly recover deformation after loading has been removed. The effect has been

described in detail elsewhere (8) and has been observed for the wheel tracking data and also for

Marshall test specimens. Delayed elastic recovery is consistent with the testing reported in this

paper such as the percent recovery in the MSCR test. It should be noted that in the MSCR the

full recovery is not obtained for strongly networked materials after the end of the rest period but

rather extends for some time thereafter.

The plots of Jnr versus elastic recovery clearly show that as the percentage of RAR is

increased above 25% a strong elastic recovery is anticipated. While test is empirical in that the

stress and strain states are poorly defined since the specimen is clearly being tested in a non-

linear region, it does provide a useful indication that the RAR is behaving in an effective manner.

One of the major concerns that some highway authorities have is the need to increase the binder

content of a mixture to achieve enhanced durability. One of the benefits of a designed additive

such as RAR is that the effective binder content can be significantly increased. However, care

must be taken in the mix design phase to ensure that the resulting material can be compacted in a

reasonable manner. If too much RAR is used then there can be a tendency for the void content to

increase since the mixture becomes more difficult to compact as the RAR content increase. This

can be observed to some extent by inspection of the void contents in TABLE 1, with the higher

void contents being associated with the mixes with the largest amount of rubber.

The performance achieved in the different test devices suggest that this material can

behave like a high-value polymer modified binder. End performance testing of mixes can easily

be specified to ensure that quality materials are being consistently produced, as with any other

system of modification. One principle advantage of this modification system is the flexibility

that it gives to a contractor. The addition of RAR is controlled on as needed basis without the

need for hot liquid storage tanks. Unused RAR can be stored for until needed at ambient

temperature conditions.

SUMMARY

This development combines an existing technology of rubber in asphalt mixes but produces a

product that has been reacted with an activated mineral binder stabilizer in a unique manner.

The product has been subjected to extensive laboratory investigation and tests performed during

the R&D stage, has shown that HMA, produced with RAR, outperforms conventional HMA and

even modified and conventional asphalt rubber mixes. In general, RAR is an elastomeric asphalt

extender that modifies asphalt, increasing its PG grading, resilience, and recovery properties.

Different types of HMA produced with RAR showed much better stability, rutting and fatigue

resistance under attractive cost/benefit conditions. The main advantages of RAR as an asphalt

modifier in hot asphalt mixes are as follows:

Easy and fast production. No need for AR or modifier blenders.

No need for re-heat cycles associated with conventional AR in the asphalt mixing plant or

job site.

Since the RAR product is a dry granulated material it is easy to handle, store and

transport.


8

RAR can be fed to any asphalt mixing plant directly to the pugmill or the dryer drum.

When blended with the asphalt binder in the mixing plant, a unique asphalt rubber binder

is formed to provide better resilience and recovery and higher viscosity and softening

point.

With increasing RAR content in the combined binder (RAR plus asphalt) any PG Grade

binder can be formed (both positive and negative temperature gains to the PG grade).

With the correct RAR content, any type of hot AR mix can be produced (Dense Graded,

SMA, Open Graded, Gap Graded, etc.).

Can make new improved hot AR mixes (with even more crumb rubber) that are stronger

more resilient, and exhibit better recovery, rutting and fatigue resistance.

RAR eliminates the need for cellulose fibers in SMA/porous mixes.

Further experimental work is being conducted to further develop the ideas presented in this paper

and these will include field implementations of the technology and evaluation of pavement

performance.

ACKNOWLEDGEMENTS

The author would like to thank the technician's team of CONSULPAV for their devoted

laboratory work and data analysis during the R&D stages. Dr. Raj Dongre laboratory and team

is acknowledged for the production of various data referenced. Appreciation is expressed to Mr.

George Way and Mr. Jerry Thayer for their detailed review of the paper and various suggestions.

Special thanks are rendered to the indispensable Mr. Ronen Peled and his team for RAR

production and quality control.

REFERENCES

1. Lewis, R.H. and J.Y. Welborn. The Effect of Various Rubbers on the Properties of Petroleum

Asphalts. Public Roads, Vol. 28, No. 4, October, 1954, p. 64.

2. Ishai, I., J.B. Sousa and G. Svechinsky, Activated Minerals as Binder Stabilizers in SMA

Paving Mixtures, CD ROM Compendium, 90th Annual Meeting of the Transportation

Research Board – TRB, Washington DC, January 2011

3. Sousa, J.B. and F. Silva, Development Studies Study of RuBind Stage 5 – PG Grade

Evaluation TA and TA2 RuBind Formulations, Realized for RuBindTM

, CONSULPAV –

Consultores e Projectistas de Pavimentos, Lda, Casais da Serra, Portugal, June 2012

4. D’Angelo, J., R.Q. Kluttz, R. Dongre and K. Stephens, Revision of the Superpave High

Temperature Binder Specification: The Multiple Stress Creep Recovery Test, Journal of The

Association of Asphalt Paving Technologists, Vol. 76, pp. 123, 2007.’

5. Rowe, G.M., P. Blankenship and T. Bennert, Fatigue assessment of conventional and highly

modified asphalt materials with ASTM and AASHTO standard specifications, Paper

submitted for publication, 4PB conference, UC Davis, September 2012.

6. Sousa, J.B. R.B. Leahy, J. Harvey and C.L. Monismith., Permanent Deformation Response

of Asphalt Aggregate Mixes, Part 1 – Test Method Selection, Strategic Highway Research

Program, National Research Council, Report SHRP-A-415, 1994.

7. Smith, B.J. and S.A.M. Hesp, Crack Pinning in Asphalt Mastic and Concrete: Effect of Rest

Periods and Polymer Modifiers on the Fatigue Life, 2nd

Eurasphalt & Eurobitume Congress,

Barcelona, 2000.


9

8. Sousa, J.B., A. Vorobiew, I. Ishai and G. Svechinsky, Elastomeric Asphalt Extender – A New

Frontier on Asphalt Rubber Mixes, Paper submitted to be presented at the Fifth International

Asphalt Rubber Conference, October 2012.


1

FIGURE 1 Suggested model for the mechanism of RAR as an asphalt extender

FIGURE 2 Traditional binder properties, a) Viscosity, b) Ring and Ball Softening Point, c)

Penetration and d) Resilience

FIGURE 3 PG Passing temperatures for high and low condition for trial 1 and 2 data sets

FIGURE 4 Non-recoverable creep compliance (Jnr) versus % recovery

FIGURE 5 % Recovery (ASTM D7405) vs. Recovery %/Resilience (ASTM D5329)

FIGURE 6 Flexural Fatigue results on different HMA mixes comparing to RAR ones, tested

in accordance with AASHTO M321 at 10Hz, 20oC and 500x10-6 strain

FIGURE 7 Wheel tracking data on GAP graded mixtures with RAR and PMB/SMA mixes

TABLE 1 Wheel tracking data on mixtures modified with RAR and two SMA controls


1

FIGURE 1 Suggested model for the mechanism of RAR as an asphalt extender


2

FIGURE 2 Traditional binder properties, a) Viscosity, b) Ring and Ball Softening Point, c)

Penetration and d) Resilience


3

FIGURE 3 PG Passing temperatures for high and low condition for trial 1 and 2 data sets


4

FIGURE 4 Non-recoverable creep compliance (Jnr) versus % recovery


5

FIGURE 5 % Recovery (ASTM D7405) vs. Recovery %/Resilience (ASTM D5329)


6

FIGURE 6 Flexural Fatigue results on different HMA mixes comparing to RAR ones,

tested in accordance with AASHTO M321 at 10Hz, 20oC and 500x10

-6 strain


7

FIGURE 7 Wheel tracking data on GAP graded mixtures with RAR and PMB/SMA mixes


8

TABLE 1 Wheel tracking data on mixtures modified with RAR and two SMA controls

Mixture Ref./Type B6.19RAR3.04

RAR-GAP

B5.45RAR3.7

RAR-GAP

B4.71RAR4.52

RAR-GAP

AMBS/PMB

SMA

Fibers/PMB

SMA

Replicate 1 2 3 4 1 2 1 2 1 2 1 2

Air Voids, % 4.3 3.9 4.7 5.6 5.3 5.4 6 6.7 3.9 4.9 4.1 4.8

Deformation at

120min., mm 1.17 1.30 2.58 1.77 1.47 1.64 1.23 1.45 2.36 2.24 2.71 3.03

Average

deformation, mm 1.71 1.56 1.34 2.30 2.87

Sousa, Vorobiev, Rowe and Ishai...Sousa, Vorobiev, Rowe and Ishai 2 mining. The activation, made by nano-monomolecular particle coating, was aimed at obtaining thixotropic and shear-thinning

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