Performance Characteristics of Arizona Asphalt-Rubber and

Performance Characteristics of ArizonaAsphalt-Rubber and Conventional Mixesusing Beam Fatigue and Simple ShearTests

George B. Way, P.E., Chief Engineer, Consulpav International,

[email protected]

Kamil Kaloush, Ph.D., P.E., Professor, Arizona State University,

[email protected]

Jorge Sousa, Ph.D., Director, Consulpav International,

[email protected] Prapoorna Biligiri, Ph.D., Research Scientist, Arizona State

[email protected]

ABSTRACT. The Arizona Department of Transportation (ADOT) supported research toperform the Four Point Bending Beam and Simple Shear tests to evaluate the fatiguecracking, shear and rutting characteristics of asphalt-rubber (AR) mixes and many othervariants of hot mix asphalt. It is noteworthy that the two test techniques and principles weredeveloped as part of the United States nationally funded Strategic Highway ResearchProgram (SHRP). The numerous mixes included asphalt-rubber gap graded (ARAC),asphalt-rubber open graded (ARFC), conventional dense graded, Stone Matrix Asphalt(SMA), and conventional open graded. The mixes were evaluated at various air void levelsand temperatures so the assessment was undertaken in conjunction with the various highwaypaving projects constructed in a wide range of climatic zones. In addition, evaluation of ARbinders as well as other conventional and modified performance graded binders wasperformed to complement mixture properties. The main purpose of this paper is to addressthe subtleties (strengths and weaknesses) of the laboratory testing methodologies to assessthe pavement performance. The scope of work includes documentation of the test results ofthe bending beam and shear-test procedures. Furthermore, recommendations of thesuitability of the test methods are provided based on the laboratory testing and observationof the field performance of about 20 years. It is envisaged that the findings from the studywill help provide guidance related to any potential improvements to enhance the testingcapability to assess pavement performance.

KEYWORDS: asphalt rubber, 4PB,PG, MEPDG, Shear test, cracking, rutting

2 Asphalt Rubber 2012

1. Purpose of Paper

The purpose of this paper is to further review the history of the experimentaluse of the four point bending beam (4PB) test in the design of several pavingprojects constructed in Arizona from 1993 to the present. Also, to report on theresults of the 4PB testing associated with these projects designed and constructedfrom 1993 to the present. From this historical body of information and data, discussthe positive qualities and areas of concern of the 4PB testing method as well assuggestions for possible improvements. Results of the testing may also be used toestimate cracking performance and to improve the predictive qualities of theanalysis of test results. Considerable background information related to this studycan be found in the first paper presented at the Four Point Bending proceedingssecond workshop [1].

2. Background of Use by ADOT of Four Point Bending Beam Test

As noted in the previous paper the Arizona Department of Transportation(ADOT) has long been interested in improving the design, construction andperformance of its pavements. ADOT has used several different volumetric asphalthot mix design methods including the Hveem, Marshall and Superpave method.

In 1993 the Strategic Highway Research Program (SHRP) recommended thefour point bending beam (4PB) test to estimate the fatigue cracking [2]. The ADOTbecame very interested in implementing the 4PB test just as it supported theimplementation of the asphalt binder PG grading system, aggregate consensusproperties and the gyratory compactor [3], [4]. However, both the shear test and4PB tests required very specialized and expensive equipment. Nevertheless, ADOTcontracted with a private consulting testing service to conduct shear test and 4PBtesting on several experimental projects designed and built during 1993 to 1995.Later in about 1999 Arizona State University (ASU) acquired the 4PB equipmentand another set of ADOT projects were designated for 4PB tests in order to furtheradvance the future implementation of the Mechanistic-Empirical Pavement DesignGuide (MEPDG),[5].

3. 4PB Testing in the 1990’s

In the 1990's the 4PB test equipment at the University of California at Berkeley(UCB) was used for 4PB tests requested by the ADOT in a manner as described aspart of the SHRP Research Project A-003A [6], [7]. In the early 1990’s 4PB testwas conducted at UCB with a very unique and expensive electro-mechanical-hydraulic loading device within an environment chamber. The device was designedand built by Cox in cooperation with input from UCB, Figure 1.

Performance Characteristics of Arizona AR Mixes, 4PB and Shear 3

Figure 1. Original Cox SHRP 4PB and RSST-CH, shear testing equipment atUniversity of California at Berkeley

4. ADOT Support of 4PB Testing 1993-1995

The ADOT contracted with a consulting company to design and test HMAmixes in Arizona using the new 4PB test equipment. The consulting companyrecognized the cumbersomeness and cost of the UCB testing equipment wouldmake the use of this equipment impossible to be used in a field constructionsituation. Therefore the consulting company invented a means of placing the 4PBequipment, along with temperature control chamber, in a trailer to be used at aconstruction field site. The ADOT contracted with the firm to do such testing onthree major overlay projects from 1993 to 1995. One of the authors of this paper Dr.Sousa co-developed the equipment in the trailer with assistance from the Coxequipment company and was involved in the design and testing with this equipmentin Arizona, Figure 2. Several project reports that summarized all of the design andfield 4PB testing were developed and submitted to the ADOT [3], [8], [9], [10].


Figure 2. Trailer with Cox equipment to test RSST-CH, shear test and 4PBspecimens in the field [11]

5. ADOT Support of Arizona State University 4PB Testing 1999 to the Present

Following the earlier 1993-1995 4PB efforts and subsequent national researchthe ADOT contracted with ASU to sample various project HMA mixes and conducttesting consistent with the new Mechanistic Empirical Pavement Design Guide(MEPDG) pavement design procedure. This testing included 4PB testing. Theselected projects included SHRP gyratory mixes as well as Marshall design asphaltrubber gap graded (ARAC) and specially designed asphalt rubber open graded(ARFC) mixes. The mixes were sampled as loose hot mix on the project and thenbrought back to the ASU laboratory for testing. Since the earlier testing conductedfrom 1993-1995 there had been much improvement in the testing protocol anddocumentation. The 4PB testing conducted by ASU is essentially in compliancewith the AASHTO protocols, [2]. Additional details about the ASU testingprocedure and 4PB fatigue calculations see the previous 4PB report [1].

6. Summary Background of the Flexural Beam Fatigue Test

Load associated fatigue cracking is one of the major distress types occurring inflexible pavement systems. The action of repeated loading caused by trafficinduced tensile and shear stresses in the bound layers, which will eventually lead toa loss in the structural integrity of a stabilized layer material. Fatigue initiated


cracks at points where critical tensile strains and stresses occur. Additionally, thecritical strain is also a function of the stiffness of the mix. Since the stiffness of anasphalt mix in a pavement layered system varies with depth; these changes willeventually effect the location of the critical strain that varies with depth; thesechanges will eventually effect the location of the critical strain that causes fatiguedamage. Once the damage initiates at the critical location, the action of trafficeventually causes these cracks to propagate through the entire bound layer.

Over the last three to four decades of pavement technology, it has been commonto assume that fatigue cracking normally initiates at the bottom of the asphalt layerand propagates to the surface (bottom-up cracking).

During the 1990's testing the 4PB fatigue model shown in equation 1 was usedto estimate the loading repetitions to failure as a function of the strain applied to thebeam.

Nf = k1 * (εt) ^ k2 (1)

εt = tensile strain at the critical location. Strain is in actual test units, example0.000100 mm/mm (inch/inch).

Nf is the number of load cycles which represent a surrogate for 18 kipEquivalent Single Axle Loads which ultimately lead to fatigue cracking in thepavement.

Later and currently the most common model form used to predict the numberof load repetitions to fatigue cracking is a function of the tensile strain and mixstiffness (modulus), equation 2.

32

111

kk

tf E

KN

32 kkt1 )E()(K

(2)

where:

Nf = number of repetitions to fatigue cracking

Ɛt = tensile strain at the critical location

E = stiffness of the material, MPa (ksi)

K1, K2, K3 = laboratory calibration parameters


In the laboratory, two types of controlled loading are generally applied forfatigue characterization: constant stress and constant strain. All of the 4PB testingconducted and reported in this study is a constant strain controlled loading.

7. Testing Equipment

Flexural fatigue tests were performed according to the AASHTO T321-03 [12],and SHRP M-009 [13]. The flexural fatigue test has been used by variousresearchers to evaluate the fatigue performance of pavements [6], [14]. Figure 3shows the flexural fatigue apparatus. The device is typically placed inside anenvironmental chamber to control the temperature during the test.

The cradle mechanism allows for free translation and rotation of the clamps andprovides loading at the two center points as shown in Figure 3. Pneumatic actuatorsat the ends of the beam center it laterally and clamp it. Servomotor driven clampssecure the beam at four points with a pre-determined clamping force. Haversine orsinusoidal loading is applied to the beam via the built-in digital servo-controlledpneumatic actuator. The innovative “floating” on-specimen transducer measuresand controls the true beam deflection irrespective of loading frame compliance. Thetest is run under either a controlled strain or a controlled stress loading. Note theAASHTO T321-03 states the following in relation to the application of the testingdevice loading and resultant deflection: “…The loading device shall be capable ofproviding repeated sinusoidal loading at a frequency of 5 to 10 Hz, subjectingspecimen to 4-point bending with free rotation and horizontal translation at all loadand reaction points; and forcing the specimen back to its original position (i.e. zerodeflection) at the end of each load pulse.”


Figure 3. ASU 4PB Testing Apparatus & Loading Characteristics [15]

8. Projects and Materials

Since 1993 several projects have been sampled and tested. Figure 4 shows theirapproximate location. The projects along with their traffic loading in 80 kN (18 kip)single axle loads per year are shown in Table 1. The projects are mostly overlayprojects of varying thickness from 50mm to 100 mm in thickness. All the projectshave a nominal 19 mm thick ARFC surfacing except for the Perryville project(project number 2) which did not have an ARFC surface. The projects representvarious asphalt mixes including dense graded HMA, ARAC and ARFC. An averagegradation of each type of mix is shown in Table 2, along with their respectivetypical average binder content, air voids and voids in the mineral aggregate (VMA).


Figure 4. Project locations

Table 1. Project location and traffic loading

Project

ID

Name Route

#

Milepost Year

Built

ESAL’s/yr(000’s)

1 Deer Valley I-17 224.5 NB 1993 1000

2 Perryville I-10 112.3 WB 1995 3000

3 Sedona I-17 299.0 NB 1995 600

A Antelope Wash US 93 95.1 2006 200

B Burro Creek US 93 138.0 2006 200

C Buffalo Range I-40 224.7 2001 2200

D Salt River Int. Various 2001

E Silver Springs I-40 79.5 2006 1500

FBadger

Springs

I-17 256.0 2005 600

G Kohl’s Ranch SR 260 266.0 2007 100

H Two Guns I-40 230.0 2003 1500

I Jackrabbit I-40 268.0 2003 2000


Table 2. Average percent passing and various mix propertiesSieve

mm

Dense

HMA

ARAC ARFC

25.40 100 100 100

19.00 98 100 100

12.70 81 82 100

9.50 69 73 100

6.40 57 49 68

4.75 50 37 36

2.36 36 20 7

2.00 32 18 6

1.18 25 12 4

0.60 17 8 3

0.42 14 6 2

0.30 11 5 2

0.15 6 3 2

0.075 4 1.7 1.2

% Binder 4.9 7.0 9.2

% Air Voids 6.6 8.6 18

% VMA 16.0 20.0 32.0

9. 4PB Test Results in Terms of Equation 1

For each project a full report was prepared with considerable detailedinformation [3], [8], [9], [16], [17], [18], [19], [20]. In the first 4PB paper [1] the4PB test results in the 1990's and 2000's were shown in extensive tables in terms ofequation 1. This was done so that the early 4PB test results in the 1990's could becompared to the ASU test results in the 2000's. The 4PB tests were conducted at theappropriate estimated fatigue temperature or range of temperatures. During designor using construction field samples to prepare the 4PB test at least six testspecimens were prepared and a straight line fitted to the test results as shown inFigure 5. The correlation R2 values were typically greater than 0.90. Table 3 showsa summary of the average 1990's test results for the three projects. Table 4 showsthe ASU 4PB test results.

The Table 3 results are for typical dense grade mixes of various asphalt bindercontent, construction air voids. From the derived k1 and k2 coefficients it waspossible to calculate the number of load repetitions to failure (Nf) at a constant


strain. For this paper a 100 micro-strain (.000100) level was selected for thecalculation of the load repetitions to failure. As can be seen for the 1990's data theoverall average Nf value for the dense mixes was calculated to be 1.26E+08 at anaverage temperature of 18.8°C.

Table 4 shows the test results for the mixes tested by ASU in the 2000's (note airvoids measured using the Corelok device [21]. Reviewing the ASU test resultsconducted on the dense graded mixes at an average temperature of 21.1°C gave anaverage Nf value of 1.29E+08 which indicates that both sets of tests arecomparable in estimating the Nf which is a good measure of the usefulness andaccuracy of the 4PB test. It should be noted that it is probably not appropriate toaverage the k1 and k2 coefficients albeit the end result Nf values can be averaged.

Figure 5. Example number of load cycles versus strain at 50 percent of initialstiffness. Each data point is a separately compacted beam


Table 3. 4PB equation 1 dense graded avg test results for 1993-1995 projects

Mix PG/AC % % Test Calc. Nf at

Type Binder Bind Air Temp k1 k2 є = 0.0001

Site Grade Voids °C

1 SHRP H 70-10 4.2 7.2 20 2.37E-10 -5.36 2.44E+08

2 SHRP 76-10 4.4 6.3 30 4.31E-04 -3.23 7.30E+07

3 SHRP 70-22 4.8 5.8 15 1.60E-08 -4.19 1.24E+08

All Average All 4.6 6.0 18.8 9.39E-05 -4.10 1.26E+08

Table 4. 4PB equation 1 ASU average test results for 2002-2008 projects

Mix PG/AC % % Air Test Calc. Nf at

Type Binder Bind Voids Temp k1 k2 є = 0.0001

Site Grade °C

All AC 70-10 4.8 7.1 21.1 8.79E-12 -5.07 1.29E+08

All ARAC 58-22 7.2 10.0 21.1 7.50E-09 -5.53 7.75E+09

All ARFC 58-22 9.2 18.4 21.1 3.14E-07 -6.09 3.84E+13

10. 4PB Test Results in Terms of Equation 2

It is recognized that currently 4PB test results are expressed in a fatigueequation as shown in equation 2 and expressed in Figure 6 with further testing atstandard temperatures of 4.4, 21.1 and 37.8 ºC. with selected project results shownin Table5 (note this is not all of the test results).


Figure 6. Example number of load cycles versus strain at various temperatures

Table 5. 4PB equation 2 ASU generalized fatigue equations

ProjectMix Type

50% of Initial Stiffness, So @ N=50 Cycles

Material Type K1 K2 K3 R2

G Kohls Ranch PG 64-22 Conventional HMA 1.61E-04 4.48 1.06 0.92

C Buffalo Ranch PG 64-22 Conventional HMA 1.32E-03 4.95 1.53 0.97

E Silver Springs PG 70-22 Conventional HMA 3.28E-03 4.20 1.28 0.74

H Two Guns PG 64-22 Conventional HMA 1.94E-04 5.14 1.55 0.72

I Jack Rabbit PG 64-22 Conventional HMA 6.26E-04 3.53 0.62 0.97

C Buffalo Ranch PG 70-40 ARAC 2.50E-02 4.32 1.27 0.75

F Badger Springs PG 70-28 ARAC 2.97E-05 6.68 2.12 0.66

H Two Guns PG 76-34 ARAC 1.18E-08 8.18 2.60 0.79

C Buffalo Ranch PG 70-40 ARFC 7.81E+03 3.00 1.53 0.99

B Burro Creek PG 70-22 ARFC 1.10E-04 4.86 3.07 0.71

A Antelope Wash PG 70-22 ARFC 9.00E-09 5.30 1.87 0.96


E Silver Springs PG 70-28 ARFC 1.045 2.36 0.45 0.33

F Badger Springs PG 70-28 ARFC 0.749 4.18 1.46 0.95

H Two Guns PG 76-34 ARFC 4.58E+03 3.70 2.01 0.65

I Jack Rabbit PG 76-40 ARFC 5.99E+02 5.12 2.74 0.65

Table 5 test results were further reviewed with regard to the calculation, whichare shown in Table 6. The Nf values were derived by averaging all of thegeneralized equations at a constant strain and representative stiffness. Therepresentative stiffness values are an average from the 4PB testing. As can be seenthe mixes with asphalt rubber (AR) and a higher binder content have the higherlevel of load repetitions to failure.

Table 6. 4PB equation 2 ASU calculated Nf Load Repetitions

Strain Material

Type

E Stiffness

MPa (ksi)

Nf Load

Repetitions

.000100 AC 2760 (400) 9.15E+07

.000100 ARAC 1110 (160) 8.48E+10

.000100 ARFC 345 (50) 3.81E+11

.000500 AC 2760 (400) 5.42E+04

.000500 ARAC 1110 (160) 1.17E+06

.000500 ARFC 345 (50) 2.16E+07

.001000 AC 2760 (400) 2.75E+03

.001000 ARAC 1110 (160) 2.20E+04

.001000 ARFC 345 (50) 2.32E+05

11. Cracking Performance 1990’s to the Present

Table 7 is a summary of the ADOT percent cracking for each of the projectsunder review from their time of construction to 2011. The percent cracking shownin Table 7 is representative of the degree of cracking shown in Figure 7, [22]. Ascan be seen in Table 5 the Perryville project, number 2, pavements with low bindercontent and no ARFC surface have the greatest degree of surface cracking. All ofthe other projects have an ARFC surfacing and their percent cracking is 4 percent


or lower. Rut depth and skid resistance are also satisfactory for all of the reportedprojects.

Figure 7. Percent cracking levels

Table 7. Cracking performance of experimental projectsYear

Built YR YR YR YR YR YR YR YR YR YR YR YR YR YR

3 4 5 6 7 8 9 10 11 12 13 14 15 16

1-Deer Valley 1993 0 0 0 0 0 0 0 0 0 3 3 3 RP

2-4.3% 1995 0 0 0 0 0 0 1 4 7 8 RP

2-4.3% 1995 0 0 0 0 0 1 2 7 8 8 RP

2-3.8% 1995 0 0 1 15 15 15 20 25 30 30 RP

2-4.0% 1995 0 0 0 0 0 2 4 6 10 10 RP

2-ARAC 6.3% 1995 0 0 0 0 0 0 0 0 0 0 0 0 0 0

3-SHRP 1995 0 0 0 1 1 1 3 3 3 3 3 4 4 4

3-SHRP 1995 0 0 0 0 0 0 0 0 0 1 1 1 2 2

3-SHRP 1995 0 0 0 0 0 0 0 0 4 4 4 4 4 4

3-ARAC 1995 0 0 0 0 0 0 0 0 0 0 0 1 1 1

3-ARAC 1995 0 0 0 0 0 0 0 0 0 0 0 0 1 1


Year

Built YR YR YR YR YR YR YR YR YR YR

1 2 3 4 5 6 7 8 9 10

C-Buffalo Range 2001 0 0 1 1 2 2 3 3 3 3

E-Silver Springs 2006 0 0 0 0 0 0

F-Badger Springs 2005 0 0 0 0 0 0 0

G-Kohl's Ranch 2007 0 0 0 0 0 0

H-Two Guns 2003 0 0 0 0 0 0 0 0

I-Jackrabbit 2003 0 0 0 0 0 0 0

RP is section re-paved

12. Asphalt Binder A and VTS Properties

The neat unmodified binders used in this study were characterized by using thePG grading system. However, the AR binders at present cannot be characterizedwith the PG grading system mainly because the AR binders contain rubber particlesthat are about 1 mm in size. The PG grading system uses a dynamic shearrheometer (DSR) that uses parallel plates to test the asphalt binder and the platesare separated by a 1 mm gap. Thus the AR particles are too large to test in the DSRrheometer. ASU devised a method of estimating the PG grade by plotting routinebinder tests on a log log plot and determining A-VTS parameters, Figure 8. In theMEPDG manual there is a table where the A-VTS values can be associated with aparticular PG grade. For example Table 8 is derived from a paper presented inSouth Africa [23]. As the paper showed how the A-VTS values for unmodifiedasphalt PG grades PG 58-22 and PG 64-16 changed after blending with scrap tirerubber to make AR. The A-VTS values become equivalent to PG 70-40 and PG76-34 as indicated in the MEPDG manual PG, A-VTS crossover table. This methodallows a means to use AR binder in the MEPDG until such time as a test isdeveloped to determine the DSR PG grade according to SHRP.


Figure 8. MEPDG Binder A -VTS Properties for Asphalt and Asphalt-Rubber

Table 8. Equivalent AR PG grades by using the A-VTS values

Binder Type Orig. Original RTFO RTFO

A VTS A VTS

PG 58-22 base

asphalt

11.164 -3.764 11.076 -3.722

PG 58-22 after

rubber added (AR)

8.3595 -2.726 8.0475 -2.598

AR binder

equivalent A-VTS

like a PG 70-40

8.129 -2.648 8.129 -2.648

PG 64-16 base

asphalt

11.163 -3.755 11.116 -3.728

PG 64-16 after

rubber added (AR)

8.39 -2.738 8.543 -2.781

AR binder

equivalent A-VTS

like a PG 76-34

8.532 -2.785 8.532 -2.785


13. Discussion of four point bending beam test results

The use of the 4PB test as a pavement analysis tool and/or design tool has beenunder research investigation since at least the late 1980’s. Over the years themanner in which this tool is used to estimate or predict fatigue cracking should beused has evolved.

Three asphalt mix and binder types were evaluated including the typical densegrade mix, AR gap and open graded mixes. The 4PB test discriminated between thethree mixes indicating that the AR mixes would have longer fatigue lives which areconsistent with field observations over a 6 to 16 year period.

Various neat unmodified asphalt binder types were evaluated including PG 70-10, PG 76-10, PG 70-22, PG 64-22 as well AR which is a highly modified asphalt.The PG graded asphalt binders used in the dense grade mix indicated similarpredicted fatigue lives which are probably due to the asphalt binder contents beingof a similar amount of 4.6 to 4.8 percent by weight of the mix. The 4PB test resultsfor the AR gap graded mixes and open grade mixes had higher amounts of bindercontent of 7.2 and 9.2 respectively, also by weight of the mix. This higher amountof binder along with the gap graded and open graded gradations provided for agreater film thickness which along with the binder content contributes to the higherfatigue life.

Surprisingly even though the AR mixes have higher binder content they havehigher air voids as well. Dense graded mixes average about 6.0 to 7.1 percent airvoids whereas the AR gap and open graded mixes average 10.0 and 18.4respectively. Normally such high air voids would be suspected to lower fatiguelives. However, even with high air voids the mixes gave very much higher fatiguelives. This is probably due to the nature of the AR elastic properties whichcontribute to higher binder amount, higher film thickness as well polymer likeelastic recovery properties.

AR presently cannot be PG graded with the DSR due to the rubber particle size;however ASU used the A and VTS properties of the AR binder to estimate the PGgrades which varied from PG 70-22 to PG 76-40. Such PG grades coupled with thehigher binder content and elastic properties of the AR all contributed to the longerfatigue life.

As this paper and the previous paper has shown even with changes in the 4PBfatigue equations comparable values of predicted fatigue failure can be obtained. Inaddition the 4PB appears to predict the relative order of field cracking performanceas shown in Figure 9 even though there is beam variability. In addition unusual mixtypes like the gap graded and open graded AR mixes can be successfully tested.

Although this is only a small example of what the 4PB test can predict, it is astart and will greatly help to reinforce confidence in using this test method in the


future. Much work still remains in how to interpret and integrate the 4PB test into apractical pavement design and mix control procedure.

Figure 9. General cracking trend of ADOT dense graded with no asphalt rubber

and asphalt rubber mixes

13. Simple Shear Tests and Rutting

The repetitive simple shear at constant height tests (RSST-CH) were conductedin conjunction with the ADOT 4PB testing 1993-1995. The tests were done in thetrailer on both compacted and core hot mix samples in accordance with the SHRPtesting procedure developed at the University of California at Berkeley [24], [25],[26], [27], [28]. Figure 10 shows graphically the manner in which the sample wastested. The RSST-CH tests were conducted at the same high temperature as the PGgraded asphalt environmental temperature, which typically was at 70ºC (158ºF).The AR mixes and other hot mixes were designed to have less than 10 mm (0.40inches) of rutting after 10 years of traffic. Results of the design tests indicated thatthe mixes would have very good rut resistance which for AR was verified on the I-10 Perryville demonstrates in Table 9.


Figure 10. Constant height repetitive simple shear test apparatus

Table 8. AR Gap Graded Mix Rut Depths

Year

afterConstruction

RutDepth

mm

RutDepth

inches

Comment

1 4.8 0.19 1.2 m (4 ft) straight edge,maximum single value










10 No measure

11 No measure

12 3.6 0.14 Laser measure, average over 457m (1500 ft)




14. Conclusions

The 4PB test was conducted by a consultant and ASU on HMA mixes obtainedfrom various test projects constructed in Arizona by the Arizona Department ofTransportation (ADOT). The HMA mixes included typical dense graded, gapgraded with asphalt rubber binder and open graded asphalt rubber. The 4PB test foreach type of mix estimated the number of repetitions to a loss of 50% of the initialstiffness. The 50% loss of initial stiffness is surrogate indicator of the number ofload repetitions to 10 % cracking in the field. Annual field cracking surveys by theADOT were reported on and they appear to comport with the ranking of 4PBfatigue cracking. Furthermore the 4PB test results and the field performance of theAR mixes demonstrate that AR gap graded and open graded mixes have superiorfatigue cracking properties.

The repetitive simple shear at constant height tests (RSST-CH) wereconducted in conjunction with the ADOT 4PB testing 1993-1995. The tests weredone in the trailer on both compacted and core hot mix samples in accordance withthe SHRP testing procedure developed at the University of California at Berkeley.Results of those tests on a particular test project indicated good rut resistance forthe AR gap graded mix which favorably corresponds to 15 years of in service rutmeasurements.

4PB and the repetitive simple shear at constant height test results have shownthat they can be used to derive the superior cracking resistance and rut resistance of


AR mixes and that such cracking and rutting resistance has been verified on testprojects constructed from 1993 to 2007.

15. Acknowledgements

The authors thank Mark Bouldin for all his expert contribution to the testingand reporting on the 1993-1995 projects. Thanks, also to several ASU students fortheir contribution to sampling, testing and conducting numerous 4PB researchstudies and preparing reports. In particular we thank Aleksander Zborowski,Mohammad Abojaradah, Andres Sotil, Krishna Biligiri, Maria Rodezno, WalledZeiada, Luiz de Mello and Luiz Guilherme and of course Kenny Witczak forkeeping track of all the field sampling and laboratory testing.

16. Disclaimer

The contents of this report reflect only the views of the authors. The authors donot endorse specific standards, proprietary products or manufacturers. Associations’,trade or manufacturers’ names appear herein solely because they are consideredessential to the object of this report.

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[17]Kaloush, ASU, 2008. PERFORMANCE EVALUATION OF ASPHALTRUBBER MIXTURES IN ARIZONA – BURRO CREEK AND ANTELOPEWASH PROJECTS. Final Report. Arizona State University. Report prepared forthe Arizona DOT. July, 2008.

[18]Kaloush, ASU, 2006. PERFORMANCE EVALUATION OF ASPHALTRUBBER MIXTURES IN ARIZONA – TWO GUNS AND JACKRABBITPROJECTS. Final Report. Arizona State University. Report prepared for theArizona DOT. July, 2006.

[19]Kaloush, ASU, 2002. PERFORMANCE EVALUATION OF ARIZONAASPHALT RUBBER MIXTURES USING ADVANCED DYNAMICMATERIAL CHARACTERIZATION TESTS– BUFFALO RANGE PROJECT.Final Report. Arizona State University. Report prepared for the Arizona DOT.July, 2002

[20]Kaloush, ASU, 2008. PERFORMANCE EVALUATION OF ASPHALTCONCRETE MIXTURES IN ARIZONA – KOHL’S RANCH PROJECT. FinalReport. Arizona State University. Report prepared for the Arizona DOT. July,2008.

[21]Corelok, 2009. www.instrotek.com/corelok.htm


[22]Way, G. B., 1979, “Prevention of Reflective Cracking Minnetonka-East”,Report Number 1979GWI, Arizona Department of Transportation, August 1979.

[23]Kaloush, 2011, Kaloush, Kamil, Maria Carolina Rodenzo, Krishna P. Biligiri,George B. Way, Mark Belshe, “Mechanistic-Empirical Pavement Design GuideImplementation and Pavement Preservation Strategies with Asphalt Rubber",The 30th Annual Southern Africa Transport Conference, CSIR InternationalConvention Center, Pretoria, South Africa, July 11-14, 2011.

[24]Sousa, J. B. et al., "Permanent Deformation Response of Asphalt-AggregateMixes - Parts I, II and III," Report Prepared for SHRP A-003A, University ofCalifornia at Berkeley, May, 1993 A.

[25]Sousa, J. B., Weissman, S. L. , Sackman L. J. and Monismith, C. L. "Anonlinear elastic viscous with damage model to predict permanent deformationof asphalt concrete mixes," Transportation Research Record no.1384, pp 80-93,1993 A.

[26]Sousa, J., J. Craus and C.L. Monismith, "Summary Report on PermanentDeformation in Asphalt Concrete," Strategic Highway Research Program,Report No. SHRP-A/IR-91-104, Washington, D.C. 1991 A.

[27]Sousa, J.B., A. Tayebali, J. Harvey, P. ttendricks and C. Monismith, "Sensitivityof Strategic Highway Research Program A-003A Testing Equipment to MixDesign Parameters for Permanent Deformation and Fatigue", TransportationResearch Record no.1384, pp 69-79, 1993 A.

[28]Monismith, C. L, 1994. Permanent Deformation Response of Asphalt-Aggregate Mixes. Strategic Highway Research Program. National ResearchCouncil, SHRP-A-415, 1994.

Documents

Performance Characteristics of Arizona Asphalt-Rubber and