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Aging Characteristics of AR Binders
Comparison of Laboratory and Field AgingProperties of Asphalt-Rubber and OtherBinders in Arizona
Krishna Prapoorna Biligiri* – George B. Way**
* Arizona State University, Tempe, Arizona, United States of America** Consulpav International, Inc. United States of America
[email protected]; [email protected];
ABSTRACT. Over the last 40 years, Arizona has successfully used asphalt-rubber (AR)binders as defined by the American Society for Testing and Materials International to reducecracking in pavements and associated maintenance costs. Typically, AR binders consist of18-22% ground tire rubber from scrap tires by weight of the asphalt binder. Since the 1970s,researchers and engineers in Arizona have investigated the aging properties of AR and otherasphalt binders using conventional tests such as penetration, softening point, and viscosity.In addition to the routine binder tests, the American Association of State Highway andTransportation Officials developed the Performance Grade (PG) asphalt binder gradingsystem in the 1990s. PG binder grading system is composed of measuring the fundamentalasphalt binder properties such as Shear Modulus and phase angle. Shear modulus is relatedto the elastic property and phase angle determines the viscous-like component of the asphaltbinder. One of the findings of this paper was to establish a relationship between the routinetests of long-term (~20 years) asphalt field-aged binders and the PG system. In addition,conventional binder tests were used to predict the viscosity-temperature relationships (i.e.temperature susceptibility). Furthermore, the temperature susceptibility of the asphaltbinders was related to the PG of the binders. Another of the findings of the study was that theAR binder over time had less cracking and less aging compared to the other asphalt binders.This study is envisioned to provide further understanding of the degree of field agingproperties to pavement performance over time. At the same time, this work will assist inbridging the gap between the traditional routine tests such as penetration and viscosity andfundamental binder parameters such as shear modulus and phase angle in addition to thePG-system. Consequentially, this paper will be helpful in examining binder aging andpavement performance data so that they may be used in various parts of the world that as ofyet have not adopted the PG-system. Also, the outcomes will be valuable to be able to use theolder routine binder tests to estimate the PG-equivalent grade, and draw conclusions aboutthe aging characteristics of these binders.
KEYWORDS: Asphalt Rubber Binder, Aging, Penetration test, Viscosity, Shear Modulus, PhaseAngle, Original, RTFO, PAV
2 Biligiri and Way
1. Introduction
The Arizona Department of Transportation (ADOT) conducted numerousresearch and special studies of asphalt-rubber (AR) and neat asphalt (bitumen) overa 30 year period (Way, 1972-1999; Forstie, 1977; Stroud, 1991; Bouldin, 1994;ADOT 1988; Lytton, 1993; Reese, 1998; Sousa, 1995). Although these variousstudies were directed at a myriad of topics, many of them contained original ARand neat binders’ properties. During the later years, aged properties weredetermined for binders extracted from cores. This resulted in the creation of adatabase that contained properties of AR and neat asphalt both at original and fieldaged conditions. Along with this information, traffic, climatic data and pavementperformance measurements of cracking and rutting were also added to the database.The database contained different binder grading selection methods, includingpenetration, aged residue, viscosity, and the Performance Grading (PG) methodsince 1997. As these different binder grading selection specifications changed, theassociated binder tests also changed, and older tests were set aside for newer tests.Presently in the United States, the PG system is used for grading and specificationof almost all binders. However, this is not the case worldwide where manycountries use the penetration and/or viscosity grading system for specification.Given the nature and substance of the ADOT binder database, it appeared that thedatabase could be useful in addressing several purposes.
2. Objectives and Scope of the Work
The purpose of this study was to add to the literature of knowledge on the agingcharacteristics of asphalt-rubber (AR) and neat asphalt binders using more than 25years of test data from field studies. The scope of the work included:
Assemble unaged and aged AR and neat asphalt binder test data thatconstitutes a wide range of penetration, viscosity, and Performance grades(PG), original, Rolling Thin Film Oven (RTFO), and Pressure AgingVessel (PAV) aging conditions; over 157 test sections and 318 variety ofbinders; with more than 957 test data points.
Develop reasonable relations that describe the rate of binder aging for neatand AR binders.
Provide relationships for older routine binder grading tests such aspenetration and viscosity to newer PG binder grading tests such as G*Shear Modulus and phase angle, with respect to binder aging.
Evaluate the relationship between the PG PAV G* and to binder agingand cracking.
Evaluate the long term (over 10 years) aging of neat asphalt and ARbinder cracking.
Biligiri and Way 3
Such relationships are deemed to be helpful in examining binder aging andpavement performance data so that they may be used in various parts of the world,that as of yet, have not adopted the PG binder system.
3. History and Description of Asphalt Binders
The various research projects that comprised the source of data for this studyconsisted mostly of unmodified neat asphalt used in dense graded hot mixes. Thedense graded mixes were constructed from 1956 to 1995. The earliest mixesconstructed from 1956 until 1965 were designed on a project engineer judgmentalbasis. The gradation of the mix typically followed 1966 specifications when ADOTadopted the Hveem design method. The 1956 to 1965 mixes contained binders of200/300, 120/150 or 85/100 penetration specified and tested in accordance with theAmerican Association of State Highway and Transportation Officials (AASHTO,2005). For the most part, the binders were specified and tested in a mannersubstantially in accordance with the American Society for Testing and MaterialsInternational (ASTM, 2009). In 1966, ADOT adopted the Hveem method of design(Morris 1967, 1970; Way, ASTM, 1997). In the early 1980s, ADOT adopted theMarshall mix designed method (Way, ASTM, 1997). Table 1 shows the typicalaverage Hveem and Marshall Design values of dense graded asphalt mixtures from1966 to the 1990s. Over this long period of time, the binder grades that were usedor tried included 200/300, 120/150 or 85/100, 60/70 and 40/50 penetration(AASHTO, 2005); AR2000 and AR4000; AC 30 and AC 40 (AASHTO, 2005);PBA 3, PBA 4, PBA 6, PBA 7 (PCCAS, 1991; Caltrans, 2006); and since 1997,Performance Grades such as PG 70-10.
AR in Arizona is a mixture of 80% hot paving grade asphalt (bitumen) with 20percent ground tire rubber produced from waste tires. Over the decades, AR hasbeen used as a stress absorbing membrane interlayer (SAMI) (Way, 1976), gap oropen graded mix (Sousa, 2006). The SAMI consists of placing an AR seal coatapplied at a rate of 2.0-3.0 L/m2. On top of the AR seal coat aggregate, chips areapplied at a rate of 10.5-16 kg/m2. The SAMI is then overlaid with dense gradedasphalt (neat asphalt binder) or AR gap graded or AR open graded mix (AR binder).Properties of the AR gap and open graded mixes are shown in Tables 2 and 3,respectively. Historically, it has been shown that less cracking occurs over timewith AR binders than neat asphalt binders as shown in Figure 1 (Sousa, 2006).
4. Description of AASHTO, ASTM and PG Binder Tests
The binder tests in the database include the penetration at 4 and 25 oC,microviscosity at 25 oC, absolute viscosity at 60 oC, kinematic viscosity at 135 oCand softening point. The penetration, absolute viscosity and kinematic viscositytests were specified and tested in accordance with AASHTO requirements whichare similar to the ASTM testing requirements. Table 4 shows the associatedAASHTO and ASTM specifications and tests.
4 Biligiri and Way
Table 1. Average Hveem and Marshall Dense Graded Asphalt Mixture Properties
Aggregate Properties AverageMetric US Customary Sand Equivalent 6525 mm 1 inch 100 Water Absorption 1.10%19 mm 3/4 inch 97 Asphalt Absorption 0.45%
12.5 mm 1/2 inch 85 Oven Dry Spec. Grav. 26289.5 mm 3/8 inch 736.4 mm 1/4 inch 62 Strength Properties Average
4.75 mm #4 54 Hveem Stability 422.36 mm #8 43 Hveem Cohesion 127
2 mm #10 401.18 mm #16 32 Marshall Stability 14.75 kN; 3277 psi0.6 mm #30 22 Marshall Flow 2.8 mm; 11; .01 in.0.4 mm #40 17 Immersion Compression Average0.3 mm #50 13 Dry Strength 2.9 MPa; 413 psi
0.15 mm #100 7 Wet Strength 1.6 MPa; 225 psi75 µm #200 4.5 Wet Str. w/ Cement 2.2 MPa; 329 psi
Average Miscellaneous Average5.40% Film Thickness 11 microns2.286 Hveem CKE 5.22.423
Average17%
5.60%10.90%83.50%
VolumetricsVMA
Air VoidsVolume of Asphalt
Volume of Aggregate
Sieve Size Average %Passing
HMA PropertiesAsphalt Cont. by Wt. of Mix
Bulk Specific GravityTh. Max. Spec. Gravity
Biligiri and Way 5
Table 2. Average Hveem and Marshall Asphalt Gap Graded Mixture Properties
Aggregate Properties AverageMetric US Customary Sand Equivalent 8525 mm 1 inch 100 Water Absorption 1.60%19 mm 3/4 inch 100 Asphalt Absorption 0.50%
12.5 mm 1/2 inch 88 Oven Dry Spec. Gravity 2.6429.5 mm 3/8 inch 736.4 mm 1/4 inch 53 Strength Properties Average
4.75 mm #4 35 Marshall Stability 9.9 kN; 2195 lb2.36 mm #8 20 Marshall Flow 3.25 mm; 13
2 mm #10 191.18 mm #16 15 Immersion Compression Average0.6 mm #30 10 Dry Strength No Test0.4 mm #40 7 Wet Strength No Test0.3 mm #50 6 Wet Strength w/ Cement No Test
0.15 mm #100 475 µm #200 2.5
Miscellaneous Average7.30% Film Thickness 27 microns2.2712.396
20%5.20%
14.80%80.00%
VolumetricsVMA
Air VoidsVolume of Asphalt
Volume of Aggregate
Sieve Size Average %Passing
HMA PropertiesAsphalt Cont. by Wt. of Mix
Bulk Specific GravityTh. Max. Spec. Gravity
6 Biligiri and Way
Table 3. Average Hveem and Marshall Asphalt Open Graded Mixture Properties
Aggregate Properties AverageMetric US Customary Sand Equivalent 8525 mm 1 inch 100 Water Absorption 1.50%19 mm 3/4 inch 100 Asphalt Absorption 0.60%
12.5 mm 1/2 inch 99 Oven Dry Spec. Gravity 2.6429.5 mm 3/8 inch 996.4 mm 1/4 inch 68 Strength Properties Average
4.75 mm #4 37 Marshall Stability No Test2.36 mm #8 10 Marshall Flow No Test
2 mm #10 191.18 mm #16 6 Immersion Compression Average0.6 mm #30 4 Dry Strength No Test0.4 mm #40 4 Wet Strength No Test0.3 mm #50 3 Wet Strength w/ Cement No Test
0.15 mm #100 275 µm #200 1.6
Miscellaneous Average9.20% Film Thickness 65 microns1.9812.456
33%20.20%23.80%56.00%
VolumetricsVMA
Air VoidsVolume of Asphalt
Volume of Aggregate
Sieve Size Average %Passing
HMA PropertiesAsphalt Cont. by Wt. of Mix
Bulk Specific GravityTh. Max. Specific Gravity
Biligiri and Way 7
Figure 1. Cracking of Asphalt Dense Graded and Asphalt-Rubber Pavements
Table 4. AASHTO and ASTM Grade Specifications and Test Methods
Asphalt Grade AASHTO Specification ASTM Specification
Penetration M-20 D-946
Viscosity-AC and AR M-226 D-3381
PBA Caltrans Caltrans
PG M-320 D-6373
Asphalt Test AASHTO Test Method ASTM Test Method
Penetration T-49 D 5
Absolute Viscosity T-202 D 2171
Kinematic Viscosity T-201 D 2170
Softening Point T-53 N/A
PG Tests G* and T-315 D 7175
8 Biligiri and Way
The microviscometer tests were conducted in a manner consistent withpublished research literature and equipment manufacturer suggested test procedures(ASTM, 1961; Fink, 1961). Microviscosities of unaged and aged binder weremeasured on a Hallikainen sliding plate microviscometer at a constant temperatureof 25 oC. Glass plates were used with unaged binder except for those viscositiesabove 5 MPa∙s (50 Megapoise). For unaged binders with viscosities above 5 MPa∙sand all core-aged binders, steel plates were used. For all binder samples that weretested successively with lighter weights, smaller shear rates were imposed. Usuallyfour shear rates were imposed on a sample. Based on the shear rates and stresses,the microviscosity was determined for a shear rate of 0.05 /sec (Peters, 1975).
4.1 Summary of Database Binder Tests
Binder tests were conducted on the samples from the tank at the time ofconstruction, referred to as the original unaged binder. None of the binders in thedatabase was specified to be modified and virtually all were unmodified, neatasphalts, albeit some modification may have been done but not reported. Later asrequired by the various research studies, cores from the pavement sections weretaken and the binders were extracted by means of an ADOT extraction test (Soxhlet,1996). In all, 157 different test sites were cored and binders were recovered fromthose cores. The tested binders varied in age from construction, and were in therange of 1 month to 264 months.
In addition to the binder database of penetration and viscosity, ADOT beganroutinely testing binder by the PG method in 1996 and adopted the PG method forspecifying binder in 1997 (AASHTO, 2005). From 1996 to 1999, a database of theG* Shear Modulus and phase angle was assembled. This database contains thebinders at original unaged, Rolling Thin Film Oven (RTFO) and Pressure AgingVessel (PAV) conditions with G* and for 318 binders for a total of 957 G* and pairs. Given the amount of binder test data in the database, it is not possible toreprint all the data in this paper. Therefore, the range of the test data results wassummarized in a tabular form as shown in Table 5.
5. Discussion of Cracking and Rutting Measurements, and Traffic in Arizona
In addition to the binder tests, cracking and rut depth were measured as part ofpavement condition survey at the time of coring the sections. Cracking (%) is arepresentation of the area of the high traffic lane that is cracked (Way, 1979).Standard photos of the level of cracking were used to visually estimate thepercentage of cracking as shown in Figure 2. Cracking is estimated as a percentageof area equal to 81 m2 which represents an area of 27 m of length off of the 3 mtravel lane. This is the same concept as illustrated in the AASHO Road Test(AASHO, 1962). As part of an ADOT research study, it was found that the area canbe converted to linear meters of cracking by the following formula (Way, 1979):
Linear Meters of Cracking = 4.2 * Cracking in percent
Biligiri and Way 9
Table 5. ADOT Performance Graded Binders Summary, Core-Age Samples
The range of cracking was from 0 to 80%. Also, rut depth is representative ofthe maximum rut measured by a 1.2 m straight edge placed across the wheel pathsin the high traffic lane. The rut depths ranged from 0 to 17.8 mm. The amount oftraffic loading in 80 kN (18 kip) equivalent single axle loads (ESALs) wasestimated from the amount of vehicular traffic and classification. The cumulativetraffic loading from time of construction ranged from 4000 to 59 million ESALs.
Asphalt Tests - Unaged Range, SI Units Range, US UnitsAge in Months Original 0 Months Original 0 Months
Penetration 4oC 10 – 124 decimeter 10 – 124 decimeter
Penetration 25oC 20 – 254 decimeter 20 – 254 decimeter
Microviscosity 25oC 7000 – 1280000 70000 – 12800000 Poise
Absolute Viscosity 60oC 25.0 – 1572 Pa∙s 250 – 15720 Poise
Kinematic Viscosity 135oC 147 – 1214 mm2
/s 147 – 1214 cStSoftening Point 35 – 62.2 o
C 95 – 144 oF
Asphalt Tests – Core Aged Range, SI Units Range, US UnitsAge in Months 1 – 264 1 – 264
Penetration 4oC (200 g, 60s) 0 – 40 decimeter 0 – 40 decimeter
Penetration 25oC (100 g, 5s) 1 – 115 decimeter 1 – 115 decimeter
Microviscosity 25oC 30000 – 54000000 Pa∙s 300000 – 54000000 Poise
Absolute Viscosity 60oC 82.2 – 35000 Pa∙s 822 – 350000 Poise
Kinematic Viscosity 135oC 218 – 1732 mm2
/s 218 – 1732 cStSoftening Point 45 – 88 o
C 113 – 190 oF
Performance Grading G* Shear Modulus δ Phase AngleOriginal Unaged 0.24 – 5.0 kPa 46.2 – 89.6
Rolling Thin Film Oven (RTFO) 0.46 – 4.5 kPa 49.5 – 88.9Pressure Aging Vessel (PAV) 525 – 12573 kPa 31.0 – 68.2
10 Biligiri and Way
Figure 2. ADOT Standard Cracking Photos, % by Area of High Traffic LaneCracked (Way, 1979)
5.1 Cracking Data Analyses
Figure 3 extends the relationship of cracking versus age from 192 to 264months previously shown in Figure 1. The relationship continues to show that thedegree of cracking for AR binder is much less than the neat asphalt binder. Theslow rate of aging of AR corresponds to the observed reduction in cracking overtime. It is hypothesized that AR binders typically have greater film thickness thatalso contribute to the slower rate of aging compared to neat asphalt binders.
6. Binder Data Analysis
6.1 Penetration
The relationship between core-aged penetration test data and time in months forneat asphalt and AR binders is shown in Figure 4. The objective was to observe thetrend and then determine the degrees of correlation in order to describe the rate ofbinder aging. As seen, the AR binders age much slower than the neat asphaltbinders.
Biligiri and Way 11
Neat AsphaltCracking = 0.0001Age2 + 0.0662Age
R² = 0.4210n = 157
Asphalt RubberCracking = 0.0002Age2 - 0.0120Age
R² = 0.8184n =13
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300
Cra
ckin
g (%
)
Age (months)
Neat AsphaltCore-Age Penetration = -10.6ln(Age) + 62.42
R² = 0.403n = 157
Asphalt RubberCore-Age Penetration = -16.3ln(Age) + 133.3
R² = 0.356n = 13
0
30
60
90
120
150
0 50 100 150 200 250 300
Cor
e A
ge P
enet
rati
on @
25
o C (
0.1
mm
)
Age (months)
Figure 3. Time versus Cracking for Pavements with Neat Asphalt and Asphalt-Rubber Binders, Arizona Study
Figure 4. Time versus Core-Age Penetration at 25 oC for Pavements with Neat
Asphalt and Asphalt-Rubber Binders, Arizona Study
12 Biligiri and Way
Neat AsphaltCore-Age Microviscosity @ 25 oC = 5.004e0.019Age
R² = 0.555n = 157
0
50
100
150
200
250
300
350
400
450
500
550
0 50 100 150 200 250 300
Cor
e A
ge M
icro
visc
osit
y @
25
o C (
106
cP)
Age (months)
Neat Asphalt
Asphalt Rubber
6.2 Viscosities at Different Temperatures
The relationships between the different core-age viscosities such asmicroviscosity at 25 oC, absolute viscosity at 60 oC, and kinematic viscosity at 135oC with respect to time for neat asphalt and AR binders are shown in Figures 5, 6,and 7, respectively. The observed trends are similar for the three temperatures inthat the rates of aging for the AR binders are slower than the neat asphalt binders.
7. G* Shear Modulus – Phase Angle Relationships for Binders
The original unaged, RTFO and PAV binder test data was utilized to establishrelationship between G* and for the 318 PG binders that represents a total of 957pairs (Section 4). Figure 8 presents the G* – relationship for the data, which isoften referred to as a Black-Space diagram. The trend is consistent and rational(highly correlated form of cause and effect relationship) with the process of binderaging in that the binder gets stiffened i.e. less viscous with a higher G* and lower .This is analogous to the observed field-aging characteristics that are also supportedby the penetration and viscosity test results as described previously.
Figure 5. Time versus Core-Age Microviscosity at 25 oC for Pavements with Neat
Asphalt and Asphalt-Rubber Binders
Biligiri and Way 13
Neat AsphaltCore-Age Kinematic Viscosity @ 135 oC = 453.9e0.004Age
R² = 0.410n = 157
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300
Cor
e-A
ged
Kin
emat
ic v
isco
sity
@ 1
35o C
(cS
t)
Age (months)
Neat Asphalt
Asphalt Rubber
Neat AsphaltCore-Age Absolute Viscosity @ 60 oC = 6175.e0.014Age
R² = 0.441n = 157
0
100000
200000
300000
400000
0 50 100 150 200 250 300
Cor
e A
ge A
bsol
ute
visc
osit
y @
60
o C (
cP)
Age (months)
Neat Asphalt
Asphalt Rubber
Figure 6. Time versus Core-Age Absolute Viscosity at 60 oC for Pavements with
Neat Asphalt and Asphalt-Rubber Binders
Figure 7. Time versus Core-Age Kinematic Viscosity at 135 oC for Pavements with
Neat Asphalt and Asphalt-Rubber Binders
14 Biligiri and Way
d= -5.5703 Ln(G*) + 89.198R2 = 0.961
n = 957
0
20
40
60
80
100
120
0 2000 4000 6000 8000 10000
d(D
egre
es)
G* (kPa) Original RTFO PAV
Figure 8. Relationship between - Phase Angle and G* - Shear Modulus for
Arizona Neat Asphalt Binders at Original, Rolling Thin Film Oven (RTFO),
Pressure Aging Vessel (PAV) Conditions
Following the development of Figure 8, it was recognized that there were 157aged penetration and aged microviscosity values, with 957 G* and pairs. Sincethere is no direct way to relate microviscosity, and and/or G*, it was decided thatanalysis be done using an empirical approach. In this method, the paired and G*values were listed in the order of decreasing (89.6 to 31.0o) and an increasingmicroviscosity (30000 – 54000000 Pa∙s). Relationships between age andmicroviscosity as well as were established as shown in Figure 9. As observed,with advancement in age, the binder microviscosity increased and decreased.
Figure 10 presents the hypothetical (but mathematical) relationship of withrespect to age. Cores were extracted from both neat asphalt and AR test sectionsthat were not part of the previous datasets to test the underlying hypothesisdemonstrated in Figure 9. As seen, the core-aged neat asphalt binder points arewithin the PAV zone. The relationships validate the previously shown penetrationand viscosity data, which infer that the PAV method of aging ostensibly used forneat asphalt binders is rational and represents approximately 15 years of agingperiod and 15% cracking. But, for the AR binder, the points are above thehypothetical trend line indicative of the fact that the viscous component () changesat a slower rate for AR binder when compared to the neat asphalt (bitumen).
Biligiri and Way 15
Microviscosity @ 25 oC = 3.9214e0.0221Age
R2 = 0.6048n = 957
d@ 25 oC = 86.365e-0.0042Age
R2 = 0.8605n = 957
0
10
20
30
40
50
60
70
80
900
200
400
600
800
1000
1200
1400
1600
1800
0 50 100 150 200 250 300
d, P
hase
Ang
le (D
egre
es)
Mic
rovi
scos
ity
@25
o C (
106
P)
Age (months)
Laboratory Correlationd= 86.365e-0.0042Age
R2 = 0.8605n = 957
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300
d, P
hase
Ang
le (D
egre
es)
Age (months)
PAV Zone
Core-Age Asphalt Rubber Binder
Core-Age Neat Asphalt Binder
Figure 9. Relationship between Age and (a) Microviscosity at 25 oC (b) - Phase
Angle at 25 oC, Arizona Neat Asphalt Binders
Figure 10. Correlation of Age versus Laboratory and Field Core-Age - Phase
Angle at 25 oC, Arizona Neat and Asphalt-Rubber Binders
16 Biligiri and Way
Neat AsphaltG* = 33486 Age - 351822
R2 = 0.9469n = 957
0.0E+00
5.0E+06
1.0E+07
1.5E+07
2.0E+07
0 50 100 150 200 250 300
G*
(Pa)
Age (months)
Core Age Neat Core Age AR
Similar to the previously developed relationships of versus age, a hypotheticalcorrelation of binder G* with respect to age was also established as shown inFigure 11. More than the majority of the data points of core-age neat asphaltbinders are above the hypothetical trend line, and more than the majority of the datapoints of core-age AR binders are below the trend line. These findings are beinginvestigated further by the authors.
Figure 11. Correlation of Age versus Laboratory and Field Core-Age G* - Shear
Modulus at 25 oC, Arizona Neat and Asphalt-Rubber Binders
8. Discussion
The purpose of this study was to add to the literature of knowledge on the agingcharacteristics of asphalt-rubber (AR) and neat asphalt binders using more than 25years of data from field studies. A large amount of unaged and aged neat asphaltdata and a smaller amount of AR data were assembled and reviewed to observe theamount of binder aging that takes place in the field. This database is of benefit toshow the manner and degree to which binder aging and the correspondingpenetration and viscosity of the neat asphalt changed over time, and the increase inthe degree of cracking.
Biligiri and Way 17
Reasonable relationships (correlations) were found to describe the rate of agingfor neat asphalt binders and to a limited degree practical to the AR binders.Undoubtedly, other factors contribute to the cracking of pavements including thepavement structure; pavement and base thickness and soil support (strength). Thisis probably one of the reasons that the coefficients of determination (R2) relatingpenetration and viscosity, and indirectly to cracking over time were fair to good.
The G* (Shear Modulus) – (Phase Angle) relationship was consistent andrational (highly correlated form of cause and effect) with respect to aging in that thebinder stiffened i.e. was less viscous with a higher G* and lower . This wasindicative of the observed field-aging characteristics also supported by thepenetration and viscosity test results.
The hypothetical relationship of with respect to age using field cores of bothneat asphalt and AR test sections (that were not part of the previous datasets) werefound to be within the PAV zone. The relationships validated the penetration andviscosity trends, which implied that the PAV aging method ostensibly used for neatasphalt binders was rational and represented approximately 15 years of agingperiod and 15% cracking. However, for the AR binder, the data points did notmatch the hypothetical trend line indicating that the viscous component () forthese binders changed at a slower rate than the neat asphalt binder.
A hypothetical correlation of binder G* witsh respect to age was alsoestablished. Further investigation is being carried out by the authors in this aspect.
Note that the penetration-viscosity and G – relationships developed in thisstudy were primarily based on the neat asphalt binders. There is a limited amountof literature on the aging characteristics of AR binder, and almost no information isavailable on AR aging in terms of PAV G* and relationships. Therefore, this studypresents a fair understanding of the AR aging characteristics. Nonetheless, suchrelationships are deemed to be helpful in examining aging of the binder andpavement performance data so that they may be used in various parts of the worldthat have not yet adopted the PG grading system.
Furthermore, this study would be valuable in understanding field aging of neatasphalt and AR for other comparative binder aging research studies. For instance,this could include examining the field aging test results within the predictive binderaging procedure available in the Mechanistic Empirical Pavement Design Guide ofthe United States (MEPDG, 2004). Additionally, it can aid in developing laboratoryaging methods of the AR mixtures.
18 Biligiri and Way
9. Bibliography
AASHO (1961) “The AASHO Road Test, Report 5, Pavement Research,” Publication No.954, National Academy of Sciences, National Research Council, Washington, D.C., 1961.
AASHTO (2005) “American Association of State Highway and Transportation Officials”,Standard Specifications, 25th Edition, 2005.
ADOT (1998) Arizona DOT, Recycle Extraction and Test Results from Routine LaboratoryTests circa 1988-1998.
ASTM (1961) “Papers on Road and Paving Materials and Symposium on Microviscometry”American Society for Testing and Materials, Special Technical Publication No. 309,Atlantic City, New Jersey, June 25-30, 1961.
ASTM (2009) “Section Four, Construction, Volume 04.03, Road and Paving Materials;Vehicle-Pavement Systems,” American Society for Testing and Materials, 2009.
Bouldin, M., Way, G. B., and Rowe, G. M., (1994) “Designing Asphalt Pavements forExtreme Climates”, Transportation Research Record 1436, Washington, D. C., 1994.
Caltrans (2006), “State of California, Department of Transportation, Standard Specifications,”May 2006.
Fink, D. F. and R. L. Griffin, “Determination of Viscosity of Bituminous Materials SlidingPlate Microviscometer Method,” American Society for Testing and Materials, SpecialTechnical Publication No. 309, Atlantic City, New Jersey, June 25-30, 1961, Appendix,Page 89-93.
Forstie, D., and Way, G. B. (1977) “Stripping on the Snowbowl to Kendrick Park Project(S210-504)”, Arizona Special Study, July, 1977.
Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures(2004), Final Report, National Research Council, Washington, D. C., March 2004.
Lytton, R (1993) “Development and Validation of Performance Prediction Models andSpecifications for Asphalt Binders and Paving Mixes,” SHRP-A-357, National ResearchCouncil, Washington D. C., 1993.
Morris, G. R. (1967) “Arizona Highway Department, Proceedings of Asphaltic ConcreteSeminar, District 1”, Phoenix, Arizona, United States, August 1967.
Morris, G. R. (1970) “Need for Proper Design of Asphaltic Concrete Pavement”, 19th AnnualRoads and Streets Conference, University of Arizona, Tucson, Arizona, United States,April 16-17, 1970.
PCCAS (1991) “Twenty-Third Pacific Coast Conference on Asphalt Specifications,” BechtelCenter of the University of California, United States, May 28-29, 1991.
Peters, R. J. (1975) “Compositional Considerations of Asphalt for Durability Improvement,”Transportation Research Record of the National Academies, No. 544, 1975.
Reese, R. (1998) “CalTrans, Asphalt recoveries and DSR tests of Arizona test sites forfatigue study”, January-April, 1998.
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Soxhlet (1996) “Extraction of Asphalt From Bituminous Mixtures by Soxhlet Extraction,”Arizona DOT Materials Testing Manual, 1996.
Stroud, J. (1991) “AC End Product Study”, Arizona DOT, April, 1991.
Sousa, J. B., Way, G. B., Harvey, J. T., and Hines, M. (1995) “Comparison of Mix DesignConcepts”, Transportation Research Record No. 1492, 1995.
Sousa, J. B., Way, G. B., Zareh, A. (2006), “Asphalt-Rubber Gap Graded Mix DesignConcepts”, Asphalt Rubber 2006, Palm Springs, California, 2006.
Way, G. B. (1972) “Brenda Stripping Test”, Arizona Department of Transportation, ReportTD100:A2720301, March 1972.
Way, G. B. (1975) “Blending Study”, Arizona Department of Transportation, Special Study,February 1975.
Way, G. B. (1976) “Prevention of Reflective Cracking Minnetonka-East (1976): A CaseStudy”, Report No. HPR-1-13(224), Arizona Department of Transportation, May 1976.
Way, G. B. (1978) “Asphalt Properties and their relationship to Pavement Performance inArizona”, Association of Asphalt Paving Technologists, Volume 47, February 1978.
Way, G. B. (1979) “Prevention of Reflective Cracking Minnetonka-East (1979) AddendumReport”, Report No. 1979-GW1, Arizona Department of Transportation, August 1979.
Way, G. B. (1980) “Environmental Factor Determination from In-Place Temperature andMoisture Measurements under Arizona Pavements”, Report #FHWA/AZ-80/157,Arizona Department of Transportation, September 1980.
Way, G. B. (1997) “Arizona's SHRP Experience, Progress of Superpave Evaluation andImplementation”, American Society for Testing and Materials, STP 1322, 1997.
Way, G. B.., Bernabe, G., and Khanal, P. (1999) “Asphalt PG Grading Study”, ArizonaDepartment of Transportation, Pacific Coast Conference on Paving Asphalt, SanFrancisco, California, United States, December 1999.
