Comparison of Laboratory and Field Aging Properties of Asphalt-Rubber and Other Binders in Arizona

Transcription

1 Comparison of Laboratory and Field Aging Properties of Asphalt-Rubber and Other Binders in Arizona Krishna Prapoorna Biligiri* George B. Way** * Arizona State University, Tempe, Arizona, United States of America ** Consulpav International, Inc. United States of America krishna.biligiri@asu.edu; wayouta@cox.net; 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 reduce cracking in pavements and associated maintenance costs. Typically, AR binders consist of 18-22% 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 other asphalt binders using conventional tests such as penetration, softening point, and viscosity. In addition to the routine binder tests, the American Association of State Highway and Transportation Officials developed the Performance Grade (PG) asphalt binder grading system in the 1990s. PG binder grading system is composed of measuring the fundamental asphalt binder properties such as Shear Modulus and phase angle. Shear modulus is related to the elastic property and phase angle determines the viscous-like component of the asphalt binder. One of the findings of this paper was to establish a relationship between the routine tests 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 asphalt binders was related to the PG of the binders. Another of the findings of the study was that the AR 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 aging properties to pavement performance over time. At the same time, this work will assist in bridging the gap between the traditional routine tests such as penetration and viscosity and fundamental binder parameters such as shear modulus and phase angle in addition to the PG-system. Consequentially, this paper will be helpful in examining binder aging and pavement performance data so that they may be used in various parts of the world that as of yet have not adopted the PG-system. Also, the outcomes will be valuable to be able to use the older routine binder tests to estimate the PG-equivalent grade, and draw conclusions about the aging characteristics of these binders. KEYWORDS: Asphalt Rubber Binder, Aging, Penetration test, Viscosity, Shear Modulus, Phase Angle, Original, RTFO, PAV Aging Characteristics of AR Binders

2 2 Biligiri and Way 1. Introduction The Arizona Department of Transportation (ADOT) conducted numerous research and special studies of asphalt-rubber (AR) and neat asphalt (bitumen) over a 30 year period (Way, ; Forstie, 1977; Stroud, 1991; Bouldin, 1994; ADOT 1988; Lytton, 1993; Reese, 1998; Sousa, 1995). Although these various studies were directed at a myriad of topics, many of them contained original AR and neat binders properties. During the later years, aged properties were determined for binders extracted from cores. This resulted in the creation of a database that contained properties of AR and neat asphalt both at original and field aged conditions. Along with this information, traffic, climatic data and pavement performance measurements of cracking and rutting were also added to the database. The database contained different binder grading selection methods, including penetration, aged residue, viscosity, and the Performance Grading (PG) method since As these different binder grading selection specifications changed, the associated 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 specification of almost all binders. However, this is not the case worldwide where many countries use the penetration and/or viscosity grading system for specification. Given the nature and substance of the ADOT binder database, it appeared that the database 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 aging characteristics of asphalt-rubber (AR) and neat asphalt binders using more than 25 years of test data from field studies. The scope of the work included: Assemble unaged and aged AR and neat asphalt binder test data that constitutes a wide range of penetration, viscosity, and Performance grades (PG), original, Rolling Thin Film Oven ( RTFO), and Pressure Aging Vessel ( PAV) aging conditions; over 157 test sections and 318 variety of binders; with more than 957 test data points. Develop reasonable relations that describe the rate of binder aging for neat and AR binders. Provide relationships for older routine binder grading tests such as penetration 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 aging and cracking. Evaluate the long term (over 10 years) aging of neat asphalt and AR binder cracking.

3 Biligiri and Way 3 Such relationships are deemed to be helpful in examining binder aging and pavement 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 study consisted mostly of unmodified neat asphalt used in dense graded hot mixes. The dense graded mixes were constructed from 1956 to The earliest mixes constructed from 1956 until 1965 were designed on a project engineer judgmental basis. The gradation of the mix typically followed 1966 specifications when ADOT adopted the Hveem design method. The 1956 to 1965 mixes contained binders of 200/300, 120/150 or 85/100 penetration specified and tested in accordance with the American Association of State Highway and Transportation Officials (AASHTO, 2005). For the most part, the binders were specified and tested in a manner substantially in accordance with the American Society for Testing and Materials International (ASTM, 2009). In 1966, ADOT adopted the Hveem method of design (Morris 1967, 1970; Way, ASTM, 1997). In the early 1980s, ADOT adopted the Marshall mix designed method (Way, ASTM, 1997). Table 1 shows the typical average Hveem and Marshall Design values of dense graded asphalt mixtures from 1966 to the 1990s. Over this long period of time, the binder grades that were used or 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 AR in Arizona is a mixture of 80% hot paving grade asphalt (bitumen) with 20 percent ground tire rubber produced from waste tires. Over the decades, AR has been used as a stress absorbing membrane interlayer (SAMI) (Way, 1976), gap or open graded mix (Sousa, 2006). The SAMI consists of placing an AR seal coat applied at a rate of L/m 2. On top of the AR seal coat aggregate, chips are applied at a rate of kg/m 2. The SAMI is then overlaid with dense graded asphalt (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 time with 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 o C, microviscosity at 25 o C, absolute viscosity at 60 o C, kinematic viscosity at 135 o C and softening point. The penetration, absolute viscosity and kinematic viscosity tests were specified and tested in accordance with AASHTO requirements which are similar to the ASTM testing requirements. Table 4 shows the associated AASHTO and ASTM specifications and tests.

4 4 Biligiri and Way Table 1. Average Hveem and Marshall Dense Graded Asphalt Mixture Properties Sieve Size Average % Aggregate Properties Average Metric US Customary Passing Sand Equivalent 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 mm 3/8 inch mm 1/4 inch 62 Strength Properties Average 4.75 mm #4 54 Hveem Stability mm #8 43 Hveem Cohesion mm # mm #16 32 Marshall Stability kn; 3277 psi 0.6 mm #30 22 Marshall Flow 2.8 mm; 11;.01 in. 0.4 mm #40 17 Immersion Compression Average 0.3 mm #50 13 Dry Strength 2.9 MPa; 413 psi 0.15 mm #100 7 Wet Strength 1.6 MPa; 225 psi 75 µm # Wet Str. w/ Cement 2.2 MPa; 329 psi HMA Properties Asphalt Cont. by Wt. of Mix Bulk Specific Gravity Th. Max. Spec. Gravity Volumetrics VMA Air Voids Volume of Asphalt Volume of Aggregate Average Miscellaneous Average 5.40% Film Thickness 11 microns Hveem CKE Average 17% 5.60% 10.90% 83.50%

5 Biligiri and Way 5 Table 2. Average Hveem and Marshall Asphalt Gap Graded Mixture Properties Sieve Size Average % Aggregate Properties Average Metric US Customary Passing Sand Equivalent 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 mm 3/8 inch mm 1/4 inch 53 Strength Properties Average 4.75 mm #4 35 Marshall Stability 9.9 kn; 2195 lb 2.36 mm #8 20 Marshall Flow 3.25 mm; 13 2 mm # mm #16 15 Immersion Compression Average 0.6 mm #30 10 Dry Strength No Test 0.4 mm #40 7 Wet Strength No Test 0.3 mm #50 6 Wet Strength w/ Cement No Test 0.15 mm # µm # HMA Properties Asphalt Cont. by Wt. of Mix Bulk Specific Gravity Th. Max. Spec. Gravity Volumetrics VMA Air Voids Volume of Asphalt Volume of Aggregate Miscellaneous Average 7.30% Film Thickness 27 microns % 5.20% 14.80% 80.00%

6 6 Biligiri and Way Table 3. Average Hveem and Marshall Asphalt Open Graded Mixture Properties Sieve Size Average % Aggregate Properties Average Metric US Customary Passing Sand Equivalent 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 mm 3/8 inch mm 1/4 inch 68 Strength Properties Average 4.75 mm #4 37 Marshall Stability No Test 2.36 mm #8 10 Marshall Flow No Test 2 mm # mm #16 6 Immersion Compression Average 0.6 mm #30 4 Dry Strength No Test 0.4 mm #40 4 Wet Strength No Test 0.3 mm #50 3 Wet Strength w/ Cement No Test 0.15 mm # µm # HMA Properties Asphalt Cont. by Wt. of Mix Bulk Specific Gravity Th. Max. Specific Gravity Volumetrics VMA Air Voids Volume of Asphalt Volume of Aggregate Miscellaneous Average 9.20% Film Thickness 65 microns % 20.20% 23.80% 56.00%

7 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 8 Biligiri and Way The microviscometer tests were conducted in a manner consistent with published research literature and equipment manufacturer suggested test procedures (ASTM, 1961; Fink, 1961). Microviscosities of unaged and aged binder were measured on a Hallikainen sliding plate microviscometer at a constant temperature of 25 o C. Glass plates were used with unaged binder except for those viscosities above 5 MPa s (50 Megapoise). For unaged binders with viscosities above 5 MPa s and all core-aged binders, steel plates were used. For all binder samples that were tested successively with lighter weights, smaller shear rates were imposed. Usually four 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 of construction, referred to as the original unaged binder. None of the binders in the database was specified to be modified and virtually all were unmodified, neat asphalts, albeit some modification may have been done but not reported. Later as required by the various research studies, cores from the pavement sections were taken 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 from those cores. The tested binders varied in age from construction, and were in the range of 1 month to 264 months. In addition to the binder database of penetration and viscosity, ADOT began routinely testing binder by the PG method in 1996 and adopted the PG method for specifying binder in 1997 (AASHTO, 2005). From 1996 to 1999, a database of the G* Shear Modulus and phase angle was assembled. This database contains the binders at original unaged, Rolling Thin Film Oven (RTFO) and Pressu re Aging Vessel (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 to reprint all the data in this paper. Therefore, the range of the test data results was summarized in a tabular form as shown in Table Discussion of Cracking and Rutting Measurements, and Traffic in Arizona In addition to the binder tests, cracking and rut depth were measured as part of pavement condition survey at the time of coring the sections. Cracking (%) is a representation 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 the percentage of cracking as shown in Figure 2. Cracking is estimated as a percentage of area equal to 81 m2 which represents an area of 27 m of length off of the 3 m travel 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 can be converted to linear meters of cracking by the following formula (Way, 1979): Linear Meters of Cracking = 4.2 * Cracking in percent

9 Biligiri and Way 9 Table 5. ADOT Performance Graded Binders Summary, Core-Age Samples Asphalt Tests - Unaged Range, SI Units Range, US Units Age in Months Original 0 Months Original 0 Months Penetration 4 o C decimeter decimeter Penetration 25 o C decimeter decimeter Microviscosity 25 o C Poise Absolute Viscosity 60 o C Pa s Poise Kinematic Viscosity 135 o C mm 2 /s cst Softening Point o C o F Asphalt Tests Core Aged Range, SI Units Range, US Units Age in Months Penetration 4 o C (200 g, 60s) 0 40 decimeter 0 40 decimeter Penetration 25 o C (100 g, 5s) decimeter decimeter Microviscosity 25 o C Pa s Poise Absolute Viscosity 60 o C Pa s Poise Kinematic Viscosity 135 o C mm 2 /s cst Softening Point o C o F Performance Grading G* Shear Modulus δ Phase Angle Original Unaged kpa Rolling Thin Film Oven (RTFO) kpa Pressure Aging Vessel (PAV) kpa The range of cracking was from 0 to 80%. Also, rut depth is representative of the maximum rut measured by a 1.2 m straight edge placed across the wheel paths in the high traffic lane. The rut depths ranged from 0 to 17.8 mm. The amount of traffic loading in 80 kn ( 18 kip) equivalent single axle loads (ESALs) was estimated from the amount of vehicular traffic and classification. The cumulative traffic loading from time of construction ranged from 4000 to 59 million ESALs.

10 10 Biligiri and Way Figure 2. ADOT Standard Cracking Photos, % by Area of High Traffic Lane Cracked (Way, 1979) 5.1 Cracking Data Analyses Figure 3 extends the relationship of cracking versus age from 192 to 264 months previously shown in Figure 1. The relationship continues to show that the degree of cracking for AR binder is much less than the neat asphalt binder. The slow rate of aging of AR corresponds to the observed reduction in cracking over time. It is hypothesized that AR binders typically have greater film thickness that also 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 for neat asphalt and AR binders is shown in Figure 4. The objective was to observe the trend and then determine the degrees of correlation in order to describe the rate of binder aging. As seen, the AR binders age much slower than the neat asphalt binders.

11 Biligiri and Way 11 Cracking (%) Neat Asphalt Cracking = Age Age R² = n = 157 Asphalt Rubber Cracking = Age Age R² = n = Age (months) Figure 3. Time versus Cracking for Pavements with Neat Asphalt and Asphalt- Rubber Binders, Arizona Study Core Age 25 o C (0.1 mm) Neat Asphalt Core-Age Penetration = -10.6ln(Age) R² = n = 157 Asphalt Rubber Core-Age Penetration = -16.3ln(Age) R² = n = Age (months) Figure 4. Time versus Core-Age Penetration at 25 o C for Pavements with Neat Asphalt and Asphalt-Rubber Binders, Arizona Study

12 12 Biligiri and Way 6.2 Viscosities at Different Temperatures The relationships between the different core-age viscosities such as microviscosity at 25 o C, absolute viscosity at 60 o C, and kinematic viscosity at 135 o C 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 in that 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 establish relationship between G* and for the 318 PG binders that represents a total of 957 pairs (Section 4). Figure 8 presents the G* relationship for the data, which is often 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 binder aging 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 supported by the penetration and viscosity test results as described previously. 550 Core Age 25 o C (10 6 cp) Neat Asphalt Core-Age 25 o C = 5.004e 0.019Age R² = n = 157 Neat Asphalt Asphalt Rubber Age (months) Figure 5. Time versus Core-Age Microviscosity at 25 o C for Pavements with Neat Asphalt and Asphalt-Rubber Binders

13 Biligiri and Way 13 Core Age Absolute 60 o C (cp) Neat Asphalt Asphalt Rubber Neat Asphalt Core-Age Absolute 60 o C = 6175.e 0.014Age R² = n = Age (months) Figure 6. Time versus Core-Age Absolute Viscosity at 60 o C for Pavements with Neat Asphalt and Asphalt-Rubber Binders Core-Aged Kinematic 135 o C (cst) Neat Asphalt Asphalt Rubber Neat Asphalt Core-Age Kinematic 135 o C = 453.9e 0.004Age R² = n = Age (months) Figure 7. Time versus Core-Age Kinematic Viscosity at 135 o C for Pavements with Neat Asphalt and Asphalt-Rubber Binders

14 14 Biligiri and Way d= Ln(G*) R 2 = n = 957 d(degrees) 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 157 aged penetration and aged microviscosity values, with 957 G* and pairs. Since there is no direct way to relate microviscosity, and and/or G*, it was decided that analysis be done using an empirical approach. In this method, the paired and G* values were listed in the order of decreasing (89.6 to 31.0 o ) and an increasing microviscosity ( Pa s). Relationships between age and microviscosity 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 with respect to age. Cores were extracted from both neat asphalt and AR test sections that were not part of the previous datasets to test the underlying hypothesis demonstrated in Figure 9. As seen, the core-aged neat asphalt binder points are within the PAV zone. The relationships validate the previously shown penetration and viscosity data, which infer that the PAV method of aging ostensibly used for neat asphalt binders is rational and represents approximately 15 years of aging period and 15% cracking. But, for the AR binder, the points are above the hypothetical trend line indicative of the fact that the viscous component ( ) changes at a slower rate for AR binder when compared to the neat asphalt (bitumen).

15 Biligiri and Way o C (10 6 P) o C = e Age R 2 = n = 957 d@ 25 o C = e Age R 2 = n = d, Phase Angle (Degrees) Age (months) Figure 9. Relationship between Age and (a) Microviscosity at 25 o C (b) - Phase Angle at 25 o C, Arizona Neat Asphalt Binders d, Phase Angle (Degrees) Laboratory Correlation d= e Age R 2 = n = 957 PAV Zone Core-Age Asphalt Rubber Binder Core-Age Neat Asphalt Binder Age (months) Figure 10. Correlation of Age versus Laboratory and Field Core-Age - Phase Angle at 25 o C, Arizona Neat and Asphalt-Rubber Binders

16 16 Biligiri and Way Similar to the previously developed relationships of versus age, a hypothetical correlation of binder G* with respect to age was also established as shown in Figure 11. More than the majority of the data points of core-age neat asphalt binders are above the hypothetical trend line, and more than the majority of the data points of core-age AR binders are below the trend line. These findings are being investigated further by the authors. 2.0E E+07 Neat Asphalt G* = Age R 2 = n = 957 Core Age Neat Core Age AR G* (Pa) 1.0E E E Age (months) Figure 11. Correlation of Age versus Laboratory and Field Core-Age G* - Shear Modulus at 25 o C, Arizona Neat and Asphalt-Rubber Binders 8. Discussion The purpose of this study was to add to the literature of knowledge on the aging characteristics of asphalt-rubber (AR) and neat asphalt binders using more than 25 years of data from field studies. A large amount of unaged and aged neat asphalt data and a smaller amount of AR data were assembled and reviewed to observe the amount of binder aging that takes place in the field. This database is of benefit to show the manner and degree to which binder aging and the corresponding penetration and viscosity of the neat asphalt changed over time, and the increase in the degree of cracking.

17 Biligiri and Way 17 Reasonable relationships (correlations) were found to describe the rate of aging for neat asphalt binders and to a limited degree practical to the AR binders. Undoubtedly, other factors contribute to the cracking of pavements including the pavement structure; pavement and base thickness and soil support (strength). This is probably one of the reasons that the coefficients of determination (R 2 ) relating penetration and viscosity, and indirectly to cracking over time were fair to good. The G* (Shear Modulus) (Phase Angle) relationship was consistent and rational (highly correlated form of cause and effect) with respect to aging in that the binder stiffened i.e. was less viscous with a higher G* and lower. This was indicative of the observed field-aging characteristics also supported by the penetration and viscosity test results. The hypothetical relationship of with respect to age using field cores of both neat asphalt and AR test sections (that were not part of the previous datasets) were found to be within the PAV zone. The relationships validated the penetration and viscosity trends, which implied that the PAV aging method ostensibly used for neat asphalt binders was rational and represented approximately 15 years of aging period and 15% cracking. However, for the AR binder, the data points did not match the hypothetical trend line indicating that the viscous component ( ) for these binders changed at a slower rate than the neat asphalt binder. A hypothetical correlation of binder G* witsh respect to age was also established. Further investigation is being carried out by the authors in this aspect. Note that the penetration-viscosity and G relationships developed in this study were primarily based on the neat asphalt binders. There is a limited amount of literature on the aging characteristics of AR binder, and almost no information is available on AR aging in terms of PAV G* and relationships. Therefore, this study presents a fair understanding of the AR aging characteristics. Nonetheless, such relationships are deemed to be helpful in examining aging of the binder and pavement performance data so that they may be used in various parts of the world that have not yet adopted the PG grading system. Furthermore, this study would be valuable in understanding field aging of neat asphalt and AR for other comparative binder aging research studies. For instance, this could include examining the field aging test results within the predictive binder aging procedure available in the Mechanistic Empirical Pavement Design Guide of the United States (MEPDG, 2004). Additionally, it can aid in developing laboratory aging methods of the AR mixtures.

18 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., AASHTO (2005) American Association of State Highway and Transportation Officials, Standard Specifications, 25th Edition, ADOT (1998) Arizona DOT, Recycle Extraction and Test Results from Routine Laboratory Tests circa 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, ASTM (2009) Section Four, Construction, Volume 04.03, Road and Paving Materials; Vehicle-Pavement Systems, American Society for Testing and Materials, Bouldin, M., Way, G. B., and Rowe, G. M., (1994) Designing Asphalt Pavements for Extreme Climates, Transportation Research Record 1436, Washington, D. C., Caltrans (2006), State of California, Department of Transportation, Standard Specifications, May Fink, D. F. and R. L. Griffin, Determination of Viscosity of Bituminous Materials Sliding Plate Microviscometer Method, American Society for Testing and Materials, Special Technical Publication No. 309, Atlantic City, New Jersey, June 25-30, 1961, Appendix, Page Forstie, D., and Way, G. B. (1977) Stripping on the Snowbowl to Kendrick Park Project (S ), Arizona Special Study, July, Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (2004), Final Report, National Research Council, Washington, D. C., March Lytton, R (1993) Development and Validation of Performance Prediction Models and Specifications for Asphalt Binders and Paving Mixes, SHRP-A-357, National Research Council, Washington D. C., Morris, G. R. (1967) Arizona Highway Department, Proceedings of Asphaltic Concrete Seminar, District 1, Phoenix, Arizona, United States, August Morris, G. R. (1970) Need for Proper Design of Asphaltic Concrete Pavement, 19 th Annual Roads and Streets Conference, University of Arizona, Tucson, Arizona, United States, April 16-17, PCCAS (1991) Twenty-Third Pacific Coast Conference on Asphalt Specifications, Bechtel Center of the University of California, United States, May 28-29, Peters, R. J. (1975) Compositional Considerations of Asphalt for Durability Improvement, Transportation Research Record of the National Academies, No. 544, Reese, R. (1998) CalTrans, Asphalt recoveries and DSR tests of Arizona test sites for fatigue study, January-April, 1998.

19 Biligiri and Way 19 Soxhlet (1996) Extraction of Asphalt From Bituminous Mixtures by Soxhlet Extraction, Arizona DOT Materials Testing Manual, Stroud, J. (1991) AC End Product Study, Arizona DOT, April, Sousa, J. B., Way, G. B., Harvey, J. T., and Hines, M. (1995) Comparison of Mix Design Concepts, Transportation Research Record No. 1492, Sousa, J. B., Way, G. B., Zareh, A. (2006), Asphalt -Rubber Gap Graded Mix Design Concepts, Asphalt Rubber 2006, Palm Springs, California, Way, G. B. (1972) Brenda Stripping Test, Arizona D epartment of Transportation, Report TD100:A , March Way, G. B. (1975) Blending Study, Arizona Department of Transportation, Special Study, February Way, G. B. (1976) Prevention of Reflective Cracking Minnetonka -East (1976) : A Case Study, Report No. HPR-1-13(224), Arizona Department of Transportation, May Way, G. B. (1978) Asphalt Properties and their relationship to Pavement Performance in Arizona, Association of Asphalt Paving Technologists, Volume 47, February Way, G. B. (1979) Prevention of Reflective Cracking Minnetonka-East (1979) Addendum Report, Report No GW1, Arizona Department of Transportation, August Way, G. B. (1980) Environmental Factor Determination from In -Place Temperature and Moisture Measurements under Arizona Pavements, Report #FHWA/AZ-80/157, Arizona Department of Transportation, September Way, G. B. (1997) Arizona's SHRP Experience, Progress of Superpave Evaluation and Implementation, American Society for Testing and Materials, STP 1322, Way, G. B.., Bernabe, G., and Khanal, P. (1999) Asphalt PG Grading Study, Arizona Department of Transportation, Pacific Coast Conference on Paving Asphalt, San Francisco, California, United States, December 1999.