Development of mix design procedures for gap-graded asphalt-rubber asphalt concrete

              DEVELOPMENT OF MIX

DESIGN PROCEDURES FOR

GAP- GRADED ASPHALT-RUBBER

ASPHALT

CONCRETE

Final Report 524

Prepared by:

Anne Stonex

James M. Carusone

MACTEC Engineering and Consulting

3630 E. Wier Ave.

Phoenix, AZ 85040

November 2007

Prepared for:

Arizona Department of Transportation

206 South 17th Avenue

Phoenix, Arizona 85007

in cooperation with

U. S. Department of Transportation

Federal Highway Administration

The contents of the report reflect the views of the authors who are responsible for the facts and the

accuracy of the data presented herein. The contents do not necessarily reflect the official views or

policies of the Arizona Department of Transportation or the Federal Highway Administration. This

report does not constitute a standard, specification, or regulation. Trade or manufacturers’ names that

may appear herein are cited only because they are considered essential to the objectives of the report.

The U. S. Government and the State of Arizona do not endorse products or manufacturers.

Technical Report Documentation Page

1. Report No.

FHWA- AZ- 06- 524

2. Government Accession No.

3. Recipient's Catalog No.

5. Report Date

November 2007

4. Title and Subtitle

DEVELOPMENT OF MIX DESIGN PROCEDURES FOR GAP-GRADED

ASPHALT- RUBBER ASPHALT CONCRETE

6. Performing Organization Code

7. Author

Anne Stonex and James M. Carusone

8. Performing Organization Report No.

4975- 03- 3008 Final Report

10. Work Unit No.

9. Performing Organization Name and Address

MACTEC Engineering and Consulting, Inc.

3630 East Wier Avenue

Phoenix, Arizona 85040

11. Contract or Grant No.

SPR- PL- 1( 03) 524

13. Type of Report & Period Covered

FINAL REPORT

November 30, 2007

12. Sponsoring Agency Name and Address

Arizona Department of Transportation

206 S. 17th Avenue

Phoenix, Arizona 85007

Project Manger: Christ Dimitroplos

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared in cooperation with the U. S. Department of Transportation, Federal Highway Administration

16. Abstract

A research project was conducted to identify and document current modifications to ARIZONA 815c ( 75- blow

Marshall method) used to develop gap- graded asphalt rubber asphalt concrete ( GG AR AC) mix designs, and to

develop and test improvements to provide a standard mix design method for use by contractors and consultants.

Based on field performance data provided by the Arizona Department of Transportation ( ADOT), the existing mix

design method was successful and should serve as the standard for comparison of proposed improvements.

Best practices were synthesized to develop proposed improvements. Three aggregate sources and two asphalt-rubber

( AR) binders were used for initial testing of the existing ( control) mix design method and of the proposed

changes. Rebound of compacted AR AC specimens was evaluated, as were Rice test results at 6% and 7% AR

binder by weight of mix. The composition of the AR binders ( rubber gradation and content) had more effect on

the results than which mix design method was used. Additional replicate testing was performed by MACTEC and

ADOT to confirm these findings. Changes to the AR AC mix design method consist primarily of making and

curing Rice specimens in the same manner as Marshall specimens, tighter temperature ranges for mixing and

compaction, incorporating Asphalt Institute calculations in a “ User’s Guide”, and improving presentation. An

ADOT construction project was used as an “ acid test” to pilot the proposed mix design method and provide

materials for a four- laboratory round robin to evaluate the precision of testing AR AC materials. The precision of

round robin testing appears very similar to that of conventional asphalt concrete mixtures based on data from

Proficiency Sample Programs of the AASHTO Materials Reference Laboratory and ADOT. The results indicate

that the mix design method developed can be used by qualified laboratories to provide suitable AR AC mix

designs.

17. Key Words

Asphalt- rubber, asphalt- rubber asphalt concrete,

AR AC, Gap- graded asphalt concrete mixtures,

Marshall mixture design, rubber- modified asphalt

concrete

18. Distribution Statement

Document is available to the U. S.

Public through the National

Technical Information Service,

Springfield, Virginia, 22161

19. Security Classification

Unclassified

20. Security Classification

Unclassified

21. No. of Pages

264

22. Price

23. Registrant's Seal

SI* ( MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol

LENGTH LENGTH

in inches 25.4 millimeters mm mm millimeters 0.039 inches in

ft feet 0.305 meters m m meters 3.28 feet ft

yd yards 0.914 meters m m meters 1.09 yards yd

mi miles 1.61 kilometers km km kilometers 0.621 miles mi

AREA AREA

in2 square inches 645.2 square millimeters mm2 mm2 Square millimeters 0.0016 square inches in2

ft2 square feet 0.093 square meters m2 m2 Square meters 10.764 square feet ft2

yd2 square yards 0.836 square meters m2 m2 Square meters 1.195 square yards yd2

ac acres 0.405 hectares ha ha hectares 2.47 acres ac

mi2 square miles 2.59 square kilometers km2 km2 Square kilometers 0.386 square miles mi2

VOLUME VOLUME

fl oz fluid ounces 29.57 milliliters mL mL milliliters 0.034 fluid ounces fl oz

gal gallons 3.785 liters L L liters 0.264 gallons gal

ft3 cubic feet 0.028 cubic meters m3 m3 Cubic meters 35.315 cubic feet ft3

yd3 cubic yards 0.765 cubic meters m3 m3 Cubic meters 1.308 cubic yards yd3

NOTE: Volumes greater than 1000L shall be shown in m3.

MASS MASS

oz ounces 28.35 grams g g grams 0.035 ounces oz

lb pounds 0.454 kilograms kg kg kilograms 2.205 pounds lb

T short tons ( 2000lb) 0.907 megagrams

( or “ metric ton”)

mg

( or “ t”)

mg megagrams

( or “ metric ton”)

1.102 short tons ( 2000lb) T

TEMPERATURE ( exact) TEMPERATURE ( exact)

º F Fahrenheit

temperature

5( F- 32)/ 9

or ( F- 32)/ 1.8

Celsius temperature º C º C Celsius temperature 1.8C + 32 Fahrenheit

temperature

º F

ILLUMINATION ILLUMINATION

fc foot candles 10.76 lux lx lx lux 0.0929 foot- candles fc

fl foot- Lamberts 3.426 candela/ m2 cd/ m2 cd/ m2 candela/ m2 0.2919 foot- Lamberts fl

FORCE AND PRESSURE OR STRESS FORCE AND PRESSURE OR STRESS

lbf poundforce 4.45 newtons N N newtons 0.225 poundforce lbf

lbf/ in2 poundforce per

square inch

6.89 kilopascals kPa kPa kilopascals 0.145 poundforce per

square inch

lbf/ in2

SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380

TABLE OF CONTENTS

Executive Summary ....................................................................................................... 1

1. Introduction................................................................................................................ 5

1.1. Organization of the Report .................................................................................. 7

2. Development of a Mix Design Procedure.................................................................. 9

2.1. Document Existing Modifications to Arizona 817 c ........................................... 9

2.2. Material Selection................................................................................................ 9

2.2.1. Aggregates ..................................................................................................... 9

2.2.2. Rubber............................................................................................................ 9

2.2.3. Asphalt Cement............................................................................................ l0

2.2.4. Asphalt Rubber Binders............................................................................... l0

2.3. Pilot AR- AC Mix Design- Control Mixes.......................................................... 12

2.3.1. Issues With CKC and Grey Mountain AR AC Control Mixes.................... 13

2.3.2. Salt River Control Mixes ............................................................................. 13

2.4. Version 1 to Existing ADOT AR- AC Mix Design Procedure........................... 16

2.4.1. List of Proposed Procedural Changes to AR AC Mix Design Method ....... 16

2.4.2. Mix Designs - Version 1 Mixes ................................................................... 17

2.4.3. Analysis of Rice Results at 6.0% and 7.0% AR Binder Content................. 19

2.4.4. AR- AC Rebound of Compacted Specimens................................................ 20

2.4.5. Round 2 Replicate Testing ADOT Central Lab and MACTEC. ................. 22

3. Round Robin Testing for Verification of Proposed AR- AC Mix Design Method.. 27

3.1. Project and Materials Selection ......................................................................... 27

3.2. Materials Designs .............................................................................................. 28

3.2.1. Asphalt- Rubber Binder Design.................................................................... 28

3.2.2. AR- AC Mix Design ..................................................................................... 28

3.3. Preparation of AR Binder Samples for Round Robin Testing........................... 29

3.4. Instructions and Distribution of Samples for Round Robin Testing ................. 30

3.5. Basics of Estimating Variability of Test Methods and

Acceptable Ranges of Test Results ................................................................... 30

3.5.1. Considerations Regarding Volumetric Calculations and Analysis.............. 32

3.6. Round Robin Test Results ................................................................................. 33

3.7. Additional Considerations ................................................................................. 38

3.7.1. Laboratory Technicians and Equipment ...................................................... 38

3.7.2. Field Performance........................................................................................ 39

3.7.3. Resistance to Moisture Damage................................................................... 40

3.7.4. Marshall Method for AR- AC....................................................................... 40

4. Conclusions.............................................................................................................. 41

Appendix A: Existing Modifications to ARIZ 815c Used for AR- AC Mix Designs until

2006 ( Version 5- 28- 03)............................................................................... 43

Appendix B: Initial Control Mix Design Data................................................................... 57

Appendix C: Initial Version 1 Mix Design Data Round 1............................................... 129

Appendix D: Rebound and Rice Data.............................................................................. 133

Appendix E: Round 2 Mix Design Data.......................................................................... 145

Appendix F: Big Bug Round Robin Preliminary Data and Analyses.............................. 171

Appendix G: Big Bug Round Robin Normalized Data and Analyses ............................. 211

Appendix H: ARIZ 832 Draft September 6, 2007 Marshall Mix Design Method for

AR- AC........................................................................................................ 237

References..................................................................................................................... .. 256

List of Tables

Table 1 Binder 1 Design Profile ................................................................................... 11

Table 2 Binder 1 Rubber Gradation, Percent Passing ( ARIZ 714)............................... 11

Table 3 Binder 2 Design Profile ................................................................................... 11

Table 4 Binder 2 Rubber Gradation, Percent Passing ( ARIZ 714)............................... 12

Table 5 Design Binder and Air Voids Contents, Salt River Control Mixes ................. 15

Table 6 Design Binder and Air Voids Contents, Salt River Version 1 Mixes.............. 17

Table 7 Original Big Bug AR Binder Design Profile ................................................... 28

Table 8 Big Bug Binder Rubber Gradation, Percent Passing ( ARIZ 714) ................... 28

Table 9 Big Bug AR Binder Design Profile – Updated for Round Robin Testing........ 29

Table 10 Compiled Round Robin Results for Aggregate Specific Gravity.................... 34

Table 11 Compiled Round Robin Results for Rice at 6.0% AR Binder Content ........... 35

Table 12 Multilaboratory Proficiency Sample Program Ranges for Gmm Results........ 35

Table 13 Within Laboratory Standard Deviation ( 1s) Ranges of Gsb Results ............... 36

Table 14 Preliminary AR Binder Content Selection....................................................... 37

Table 15 Normalized AR Binder Content Selection....................................................... 38

Table 16 Compiled CKC AR- AC Control Mix Design Data ......................................... 69

Table 17 Compiled Grey Mountain AR- AC Control Mix Design Data......................... 70

Table 18 Compiled Round 1 Salt River AR- AC Control Mix Design Data .................. 71

Table 19 Compiled CKC AR- AC Version 1 Mix Design Data.................................... 130

Table 20 Compiled Grey Mountain AR- AC Version 1 Mix Design Data.................... 131

Table 21 Compiled Round 1 Salt River AR- AC Version 1 Mix Design Data ............. 132

Table 22 Rebound Experiment Using 2000 g Weight First Round of Control

and Version 1 Designs ................................................................................ 134

Table 23 Rebound Experiment Using 2000 g Weight Repeats 1 and 2 of Control

and Version 1 Designs ................................................................................ 135

Table 24 Rebound Experiment Using 2000 g Weight Soufflé Mix.............................. 136

Table 25 Statistical Analysis of MACTEC’s Measured Rice Values ( Gmm)

for Salt River Aggregate at 6.0% and 7.0% AR Binder Contents .............. 137

Table 26 Single Factor ANOVA for Rice Data ........................................................... 138

Table 27 Rice Data Two- Way ANOVA for Relative Effects of Binder

and Design Method..................................................................................... 142

Table 28 Combined ADOT MACTEC Control Mix Data Rounds 1 and 2 Salt River

Aggregate with Binders 1 and 2, Source Data for Plots ............................. 146

Table 29 Combined ADOT MACTEC Version 1 Mix Data Rounds 1 and 2

Salt River Aggregate with Binders 1 and 2, Source Data for Plots ............ 147

Table 30 Legend Key for Plots ..................................................................................... 148

Table 31 One- Way Analysis of Variance Results Matrix............................................. 167

Table 32 Two- Way Analysis of Variance Results Matrix ADOT and MACTEC

( Rounds 1 and 2) B1 vs. B2, Control vs. Version 1 Mixes......................... 169

Table 33 Big Bug Round Robin Compiled Preliminary Round Robin Source Data

for Plots....................................................................................................... 177

Table 34 Duncan’s Multiple Range Test ...................................................................... 185

Table 35 Preliminary Statistical Analysis of Big Bug Round Robin Data

at 6.5% AR Binder Content ........................................................................ 186

Table 36 Preliminary Statistical Analysis of Big Bug Round Robin Data

at 7.5% AR Binder Content ........................................................................ 192

Table 37 Preliminary Statistical Analysis of Big Bug Round Robin Data

at 8.5% AR Binder Content ........................................................................ 198

Table 38 Summary of Duncan’s Multiple Comparisons of Mean Results

( Preliminary Data) ...................................................................................... 204

Table 39 Statistical Analysis of Bulk Specific Gravity of Marshall Specimens .......... 205

Table 40 Big Bug Round Robin Normalized Compiled Round Robin Source Data

for Plots....................................................................................................... 212

Table 41 Statistical Analysis of Normalized Big Bug Round Robin Data

at 6.5% AR Binder Content ........................................................................ 218

Table 42 Statistical Analysis of Normalized Big Bug Round Robin Data

at7.5% AR Binder Content ......................................................................... 224

Table 43 Statistical Analysis of Normalized Big Bug Round Robin Data

at 8.5% AR Binder Content ........................................................................ 228

Table 44 Summary of Duncan’s Multiple Comparisons

of Mean Normalized Results ...................................................................... 232

Table 45 Precision Calculations for Results of Big Bug Round Robin ........................ 233

Table 46 Comparison of Multilaboratory Precision of Test Results ........................... 236

List of Figures

Figure 1 2,000 gram Rebound “ Puck” and Dial Indicator ............................................. 21

Figure 2 Instructions for Big Bug Round Robin ............................................................ 31

Figure 3 CKC B1 Control Trial A Mix Design.............................................................. 58

Figure 4 CKC B2 Trial A Mod Mix Design .................................................................. 64

Figure 5 GM B1 Control Trial A Mix Design................................................................ 72

Figure 6 GM Trial B Crusher Fines Paramount Mix Design......................................... 78

Figure 7 GM B2 Control A Mix Design ........................................................................ 83

Figure 8 GM B2 Control Trial B Crusher Fines Mix Design ........................................ 88

Figure 9 Salt River B1C1 Mix Design ........................................................................... 93

Figure 10 Salt River B1C2 Mix Design ........................................................................... 99

Figure 11 Salt River B1C3 Mix Design ......................................................................... 105

Figure 12 Salt River B2C1 Mix Design ........................................................................ 111

Figure 13 Salt River B2C2 Mix Design ........................................................................ 117

Figure 14 Salt River B2C3 Mix Design ......................................................................... 123

Figure 15 MACTEC Rounds 1 & 2 and ADOT Round 2 Effective Binder Volume

Salt River B1 Control and Version 1 .......................................................... 149

Figure 16 MACTEC Rounds 1 & 2 and ADOT Round 2 Effective Binder Volume

Salt River Controls B1 & B2 ...................................................................... 150

Figure 17 MACTEC Rounds 1 & 2 and ADOT Round 2 VMA

Salt River Controls B1& B2 ....................................................................... 151

Figure 18 MACTEC Rounds 1 & 2 and ADOT Round 2 VMA

Salt River Version 1 B1 & B2 .................................................................... 152

Figure 19 MACTEC Rounds 1 & 2 and ADOT Round 2 VMA

Salt River B1 Control & Version 1............................................................. 153

Figure 20 MACTEC Rounds 1 & 2 and ADOT Round 2 VMA

Salt River B2 Control & Version 1............................................................. 154

Figure 21 MACTEC Rounds 1 & 2 and ADOT Round 2 VFA

Salt River B2 Control & Version 1............................................................. 155

Figure 22 MACTEC Rounds 1 & 2 and ADOT Round 2 VFA

Salt River Version 1 B1 & B2 .................................................................... 156

Figure 23 MACTEC Rounds 1 & 2 and ADOT Round 2

VFA Salt River Controls B1 & B2 ............................................................. 157

Figure 24 MACTEC Rounds 1 & 2 and ADOT Round 2

VFA Salt River B1 Control & Version 1.................................................... 158

Figure 25 MACTEC Rounds 1 & 2 and ADOT Round 2 Air Voids

Salt River B1 Control & Version 1............................................................. 159

Figure 26 MACTEC Rounds 1 & 2 and ADOT Round 2 Air Voids

Salt River B2 Control & Version 1............................................................. 160

Figure 27 MACTEC Rounds 1 & 2 and ADOT Round 2 Air Voids

Salt River Controls B1 & B2 ...................................................................... 161

Figure 28 MACTEC Rounds 1 & 2 and ADOT Round 2 Air Voids

Salt River Version 1 B1 & B2 .................................................................... 162

Figure 29 MACTEC Rounds 1 & 2 and ADOT Round 2 Stability

Salt River Version 1 B1 & B2 .................................................................... 163

Figure 30 MACTEC Rounds 1 & 2 and ADOT Round 2 Stability

Salt River Controls B1 & B2 ...................................................................... 164

Figure 31 MACTEC Rounds 1 & 2 and ADOT Round 2 Stability

Salt River B2 Control & Version 1............................................................. 165

Figure 32 MACTEC Rounds 1 & 2 and ADOT Round 2 Stability

Salt River B1 Control & Version 1............................................................. 166

Figure 33 Big Bug Version 2 Mix Design ..................................................................... 176

Figure 34 Preliminary Big Bug Effective Binder Volume............................................. 179

Figure 35 Preliminary Big Bug VMA............................................................................ 180

Figure 36 Preliminary Big Bug VFA ............................................................................. 181

Figure 37 Preliminary Big Bug Air Voids ..................................................................... 182

Figure 38 Preliminary Big Bug Stability........................................................................ 183

Figure 39 Preliminary Big Bug Flow ............................................................................. 184

Figure 40 Normalized Big Bug Effective Binder Volume............................................. 214

Figure 41 Normalized Big Bug VMA............................................................................ 215

Figure 42 Normalized Big Bug VFA ............................................................................. 216

Figure 43 Normalized Big Bug Air Voids ..................................................................... 217

1

EXECUTIVE SUMMARY

The purpose of this study was to develop a standard mix design method for the Arizona

Department of Transportation ( ADOT) gap- graded asphalt- rubber asphaltic concrete

( AR- AC) mixtures that can be used by contractors and consultants. The Department is

seeking to transfer AR- AC mix design responsibilities to industry, similar to the current

practice for standard Marshall and Superpave asphaltic concrete mixtures.

The first task was to review and document ADOT’s existing Marshall- based mix design

procedure for AR- AC, based on interviews with ADOT personnel, and a review of

ADOT’s AR- AC performance data. Field performance data provided by ADOT indicated

that more than 96% of AR- AC pavements provided generally good performance.

Therefore, the ADOT mix design method was considered a successful standard for

comparison of proposed improvements.

Methods and practices for AR- AC mix design used by industry and other agencies were

reviewed and synthesized to develop proposed improvements to the existing ADOT

procedure. Rice testing according to ARIZ 8061 was evaluated at two asphalt- rubber

( AR) binder contents, 6% and 7% by total weight of AR- AC mixture, to determine

whether the binder content should be increased to 7% for testing. Findings indicated that

results for samples at both binder contents fall within the precision of the test procedure;

either may be used, as the level of precision is equivalent.

Rebound of mix specimens after compaction was also measured and evaluated, with and

without constraining weights. Rebound has been a concern for AR- AC mix designers,

but no documentation of actual measurements of this anecdotal phenomenon could be

found. This may be the only study to address specimen rebound. Findings indicated that

most mixes exhibit some slight shrinkage as they cool which appears to be normal

volume change. Few mixes rebound. A failed mix design trial for another project

provided a mix which did visibly rebound, but the measurements were small. It was

decided that mixes that rebound should be discarded and redesigned.

As directed by the Technical Advisory Committee ( TAC), MACTEC developed new mix

designs for initial testing, using three different sources of aggregate and two different AR

binders. The same source of rubber was used in both AR binders. Gradation was varied

so that one binder used a rubber gradation on the coarse side, and the other used a

gradation on the fine side of the allowable rubber gradation limits. Rubber content was

varied to meet the required AR properties. The quantity of rubber required is a function

of the rubber gradation and the source and grade of the base asphalt cement.

ADOT’s original mix design procedure ( newly documented) was used to develop

“ control” AR- AC mix designs, which established aggregate gradation targets. The

Version 1 modified mix design procedure was then applied to the established aggregate

gradations for the respective sources. These initial designs performed for Task 1 are

referred to as “ Round 1” in this report.

1 Arizona Department of Transportation. ( ADOT) Materials Testing Manual. 1985. Section 806.

2

The Version 1 designs seemed to highlight differences in the effects of the two AR

binders on resulting volumetric properties. It appeared that the different binders had more

effect on the results than the choice of mix design procedure. However, two of the

aggregate sources had relatively high water absorption and yielded more variable test

results than the third. The question arose as to whether the Version 1 method better

distinguished AR- related differences in volumetric results or was the cause of these

differences. Therefore to better distinguish the effects of binder and mix design method,

additional testing was focused on mixes using less absorptive and less variable Salt River

aggregates.

As work with the Version 1 Marshall mix design method proceeded and the need for

additional replicate testing was identified, the project TAC decided to waive

the planned gyratory portion of the study to allow full evaluation of the Marshall

approach. It appeared that appropriate modifications to the Marshall method could be

established to provide a readily useable standard mix design procedure. It also appeared

that more resources would be required to thoroughly research the application of gyratory

compaction to AR- AC materials, while it was not clear if it would be possible to develop

a gyratory mix design method.

The next step was to further explore the relative effects of binder versus mix design

method using the relatively consistent Salt River aggregate source, and whether these

effects could be reproduced by other laboratories. MACTEC batched aggregate and

provided prepared binder to ADOT for “ shadow” or replicate testing of control and

Version 1 mixes, which is referred to as “ Round 2” in this report. Extensive analysis of

the results of Round 2 testing supported the initial findings that the AR binders had more

effect on volumetric results than the differences between the control and Version 1 mix

design procedures. ADOT’s results generally fell within the range of MACTEC’s results

for Rounds 1 and 2. The relatively close conformance of the results indicated that both

methods ( control and Version 1) could be reproduced by another laboratory.

Presentations of preliminary results were delivered at meetings of the Pacific Coast

Conference on Asphalt Specifications and at the Arizona State University Paving and

Materials Conference, rather than in workshop format. Comments were solicited. In

addition, the test results and the proposed Version 1 mix design procedure were

distributed for review and comment among the project team ( which also included Speedie

& Associates ( Speedie) and Rinker Materials Corporation Arizona ( Rinker) and two

others experienced with these materials including Western Technologies Inc. ( WTI)).

Results indicated that any of the modifications could be adopted but some were not

needed; Version 2 incorporated selected changes to clarify and streamline lab procedures.

ADOT offered an opportunity to use a 2004 AR- AC construction project to pilot the

proposed Version 2 AR- AC Marshall mix design method and provide materials for round

robin testing by the project team. The project selected provided an “ acid test” as the

subject “ Big Bug” aggregate materials have high water absorption and corresponding

increased testing variability. MACTEC performed the original mix design, and

developed an alternate AR binder for subsequent round robin testing. ADOT personnel

3

sampled the aggregate stockpiles and delivered these materials to MACTEC for

distribution among the participating laboratories.

Round robin testing was performed by four laboratories: ADOT, Speedie, Rinker and

MACTEC. These labs batched the aggregates and used prepared AR binder as would

normally be done for a new mix design or a verification of an existing design.

MACTEC compiled and analyzed the test results, which consist of a limited number of

physical tests ( which are also possible sources of variability) and calculated the

volumetric properties of interest. One of the participating laboratories experienced some

equipment problems that affected its results. To remove inaccuracies contributed by

variability of other tests, results were normalized by using overall averages of aggregate

specific gravity and Rice results to recalculate volumetric properties for each laboratory.

MACTEC performed statistical analyses to determine whether the mean results of the

respective laboratories for the properties of interest were statistically similar, and to

group and rank statistically different means. Precision of the proposed Version 2 mix

design procedure was evaluated with respect to results of Marshall asphaltic concrete

proficiency sample programs of the AASHTO Materials Reference Laboratory ( AMRL)

and ADOT, and ASTM precision statements for bulk and maximum theoretical specific

gravities. Although the normalized round robin results for some of the volumetric

properties did show significant differences among the respective laboratories, the

precision of the round robin testing performed by the individual laboratories is generally

within the ranges established for conventional asphaltic concrete materials.

The results of this study indicate that the proposed Version 2 AR- AC mix design

procedure is generally as repeatable and reproducible as a 75- blow Marshall mix design

for conventional asphalt concrete. Version 2 is presented in Appendix H as ARIZ 8322,

Marshall Mix Design for Asphaltic Concrete ( Asphalt- Rubber) [ AR- AC]. It has been

used for ADOT AR- AC projects in 2006. Some refinements may be made with

continuing use, but major procedural changes are not expected.

2 ADOT Materials Testing Manual. 1985. Section 832.

4

5

1. INTRODUCTION

The purpose of this study was to develop standard mix design methods for gap- graded

asphalt- rubber asphaltic concrete ( AR- AC) mixtures that can be used by contractors and

consultants. The AR- AC aggregate gradation is gapped on the coarse side of the

maximum density line to provide sufficient void space to accommodate the rubber

particles in the asphalt- rubber ( AR) and high AR binder contents. To date, ADOT’s

Central Laboratory has been responsible for performing the mix designs for these

materials which has at times been a strain on ADOT’s limited resources. The Department

is seeking to transfer AR- AC mix design responsibilities to industry, similar to the

current practice for standard Marshall and Superpave asphaltic concrete mixtures.

The scope of the study was originally divided into three tasks as follows:

• Task One: Review and Documentation of Current Methods

o Review Marshall mix design criteria

o Interview ADOT personnel

o Review industry standards and practices

o Compare various methods and procedures

o Synthesize best practices

o Look for correlations with field performance

o Develop and test proposed mix design improvements

􀂃 Select three AR- AC mixes

􀂃 Apply recommended improvements to the same materials

􀂃 Check for rebound

􀂃 Evaluate the effects of recommended changes to the mix design procedure

• Task Two: Development of Superpave Gyratory Methods

o Development of mix design procedures using the Standard Highway Research

Program ( SHRP) gyratory compactor

• Task Three: Testing Round Robins, Validation, and Presentation of Work

o Compare results of minimum of 3 mixes ( Round 1)

o Analyze results and conduct workshop

o Prepare formatted Arizona Test Method

o Preparation of Final Report, Technical and Project Presentations

The Technical Advisory Committee ( TAC) redirected some efforts as deemed

appropriate based on ADOT’s needs and on the results of each phase of testing. The

original work plan was to focus on the mixture properties of the material, and not on the

properties of the asphalt- rubber binder. However at ADOT’s request, the effects of rubber

gradation and rubber content of the AR binder on AR- AC mixture volumetrics were

incorporated. The impacts on mixture volumetrics were found to be significant.

6

The Executive Summary summarizes the work performed. ADOT provided AR- AC

performance data, the original formatted mix design method ARIZ 815c3, and ADOT’s

Proficiency Sample Program data for 75- blow Marshall testing performed over the last

ten years. The performance data showed the original ADOT mix design method was a

successful standard for comparison of proposed improvements.

Task One also included a review of various industry methods and practices for AR- AC

mix design, synthesis of best practices to develop proposed improvements, and laboratory

evaluation of the proposed improvements. As one of the proposed improvements, Rice

testing ARIZ 8064 was evaluated at two AR contents, 6% and 7% by total weight of AR-AC

mixture, to determine whether the AR content should be increased to 7% for Rice

testing. Rebound of mix specimens after compaction was also measured and evaluated,

with and without constraining weights.

For Task One, instead of using three existing AR- AC mix designs as planned, the TAC

tasked MACTEC to develop new mix designs using three different sources of aggregate

and two different AR binders. This created some overlap between Tasks One and Three.

The second planned task was to develop AR- AC mix design procedures using the SHRP

( Superpave) Gyratory Compactor. As work with the Marshall- based method proceeded

and the need for additional replicate testing was identified, the project TAC decided to

waive the gyratory work to allow full evaluation of the Marshall approach. It appeared

that appropriate modifications to the Marshall- based method could be established to

provide a readily useable standard mix design procedure. It also appeared that more

resources would be required to thoroughly research application of gyratory compaction to

AR- AC materials, while it was not clear if the desired result could be achieved.

Task Three was redirected by the TAC to further explore the relative effects of AR binder

versus mix design method using the relatively consistent Salt River aggregate source, and

whether these effects could be reproduced by other laboratories.

Workshop presentations were deferred and will likely be used to present the results of

this study along with the proposed AR- AC mix design method and new end result

specifications being implemented for AR- AC in accordance with ADOT 4155.

For Task Three, ADOT offered an opportunity to use a 2004 ADOT AR- AC construction

project to pilot the proposed standard ADOT mix design method and to provide materials

for round robin testing by the project team. The parties involved believed this would be a

superior way to conclude this study. The project selected provided an “ acid test” as the

subject aggregate materials have high water absorption and corresponding increased

testing variability.

3 Ibid. Section 815c.

4 Ibid. Section 806.

5 Arizona Department of Transportation ( ADOT). Standard Specifications for Road and Bridge

Construction. 2000. Section 415.

7

Round robin testing was performed by four laboratories: ADOT, Speedie, Rinker, and

MACTEC. MACTEC compiled and analyzed the results. The precision of the round

robin testing performed by the individual laboratories is generally within the ranges

established for conventional asphaltic concrete materials.

The results of this study indicate that the proposed AR- AC mix design procedure is

generally as repeatable and reproducible as a 75- blow Marshall mix design for

conventional asphaltic concrete.

1.1 ORGANIZATION OF THE REPORT

Chapter 1 is this Introduction.

Chapter 2 presents the development of the AR- AC mix design procedure from

documentation of the existing ADOT Marshall- based AR- AC method to development

and testing of the proposed Version 1modifications. It includes discussions of the

respective specifications and materials, findings of the analyses of Rounds 1 and 2 test

data, and the list of changes included in Versions 1 and 2 of the proposed AR- AC mix

design procedure. Test results and corresponding compilations, plots, and statistical

analyses are presented in Appendices A through E.

Chapter 3 covers the round robin testing of the Version 2 mix design method and

analyses in detail, including materials selection, AR binder preparation, instructions for

handling and testing, data reported, considerations regarding volumetric calculations, and

findings of the analyses. Test results and corresponding compilations, plots, and

statistical analyses are presented in Appendices F and G.

Chapter 4 presents the conclusions of this study.

The current version of the mix design procedure is in Appendix H.

8

9

2. DEVELOPMENT OF A MIX DESIGN PROCEDURE

2.1 DOCUMENT EXISTING MODIFICATIONS TO ARIZONA 815c

The first task of this study was to determine and document any modifications to the ARIZ

815c6 Marshall Mix Design Method that ADOT has been using to design mixes to meet

the requirements of Section 4137 Asphaltic Concrete ( Asphalt- Rubber). A meeting was

held with ADOT materials managers and laboratory personnel to go through the ARIZ

815c procedure line by line to identify and describe in detail the modifications used for

designing gap- graded AR- AC mixes. ADOT provided an electronic copy of ARIZ 815c

for a technical review of drafts. ARIZ 815c Modified for Asphaltic Concrete ( Asphalt-

Rubber) Version 5- 28- 03 was submitted as the first scheduled deliverable for this project,

and is presented in Appendix A.

2.2 MATERIALS SELECTION

Materials selection was a critical part of the experimental plan. The mix design method

to be developed must be applicable to the full range of aggregate, asphalt, and asphalt-rubber

materials available throughout Arizona that are suitable for use in AR- AC mix-tures.

The project TAC took an active role in determining what materials should be

included in the study.

2.2.1 Aggregates

The TAC identified three sources of aggregate for the bulk of the mix design testing that

represented a wide range of physical properties such as specific gravity and water

absorption. The aggregate sources designated were:

• Salt River ( Rinker 19th Avenue plant, Phoenix metropolitan area)

• Grey Mountain ( US 189 Milepost 454, northern Arizona)

• CKC Construction ( 1234 E. Airport Rd. Safford, Arizona)

Details of properties of aggregates from these respective sources are included in the

corresponding mix design summaries presented in Appendix B.

2.2.2 Rubber

The project proposal excluded evaluation of the effects of rubber gradation and content

on the resulting AR binders due to funding constraints. However, ADOT expressed great

interest in the effects of these factors on mixture volumetrics. It was thus decided to

deviate from the project proposal and develop and use AR binders that incorporated,

respectively, relatively coarse or fine rubber gradations within the relatively broad

gradation limits for Type B rubber in ADOT Section 10098, Asphalt- Rubber Material.

Type B rubber is used in AR binders for gap- and open- graded asphaltic concrete mixes,

and the specified gradation limits are shown in Table 2.

6 ADOT. Materials Testing Manual. 1985. Section 815c.

7 ADOT Standard Specifications for Road and Bridge Construction 2000 Section 413

8 Ibid. Section 1009

10

ADOT’s and MACTEC’s experience with AR materials indicated that rubber gradation

would affect the rubber content of the binder and volumetric properties of AR- AC,

particularly the arrangement of the mixture voids. For example, coarsening the rubber

gradation would typically increase the amount of rubber required to achieve the specified

AR binder properties, and would tend to increase Voids in the Mineral Aggregate ( VMA)

of AR- AC mixes.

2.2.3 Asphalt Cement

Most of the AR binders used by ADOT are classified as Type 2, which requires a

Performance Grade ( PG) binder 58- 22 ( ideal for climates with temperatures ranging from

58° Celsius down to - 22° Celsius) for the base asphalt cement. 9 Type 1 AR binders

require a stiffer grade of base asphalt cement, PG 64- 16, for areas with higher pavement

operating temperatures and heavy traffic. Type 3 AR binders require a softer PG 58- 28

and are used where enhanced resistance to low temperature cracking is needed.

2.2.4 Asphalt- Rubber Binders

MACTEC compiled a number of existing AR binder design profiles for consideration by

the TAC, and TAC members also suggested specific AR binders for use in this study.

Two Type 2 AR formulations were selected and designated Binder 1 and Binder 2. The

selected binders were produced and tested by MACTEC using the designated component

sources and grades. However, due to variations in the physical properties of the asphalt

and rubber materials since design, some of the selected formulations required adjustments

in rubber content, or a different source or grade of asphalt to meet specifications. Binder

1 used Para- mount PG 58- 22. The source of the base asphalt cement for Binder 1 was

changed from Chevron to Paramount. Binder 2 used Ergon Snowflake PG 58- 22. The

Ergon Snowflake asphalt cement available at that time for use in Binder 2 actually graded

as a PG 58- 28 rather than PG 58- 22, but since the resulting AR binder properties met

requirements for and conformed to the original Type 2 design, it was used as a Type 2.

The design profiles, components, and rubber gradations for Binder 1 and Binder 2 are

presented in Tables 1 through 4. Crumb Rubber Manufacturers ( CRM) was the source of

rubber for both AR binders.

9 Ibid

11

Table 1 Binder 1 Design Profile

Minutes of Reaction Specified

Test Performed 60 90 240 360 1440 Limits

Viscosity, Haake at 177° C, cP 2000 2300 2800 2900 2700 1500- 4000

Resilience at 25° C, % Rebound

( ASTM D5329) 37 37 37 20 Minimum

Ring & Ball Softening Point, ° F

( ASTM D36) 135.5 137 140 140 138 130 Minimum

Needle Penetration at 4° C, 200g, 60

sec., 1/ 10mm ( ASTM D5) 32 30 31 15 Minimum

Rubber source and type: CRM Type B ( coarse gradation)

Rubber content: 24.2% by weight of asphalt cement, 19.5 % by weight of total binder

Asphalt cement source and grade: Paramount PG 58- 22

Table 2 Binder 1 Rubber Gradation, Percent Passing ( ARIZ 71410)

Sieve Size Result (%) Specified Limits (%)

No. 8 100

No. 10 100 100

No. 16 69.5 65 – 100

No. 30 30.4 20 – 100

No. 50 10.7 0 – 45

No. 200 0.4 0 – 5

Table 3 Binder 2 Design Profile

Minutes of Reaction Specified

Test Performed 60 90 240 360 1440 Limits

Viscosity, Haake at 177° C, cP 2000 2100 2600 2400 2300 1500- 4000

Resilience at 25° C, % Rebound

( ASTM D5329) 39 42 42 20 Minimum

Ring & Ball Softening Point, ° F

( ASTM D36) 143 140 145 144.5 139.5 130

Minimum

Needle Penetration at 4° C, 200g,

60 sec., 1/ 10mm ( ASTM D5) 29 30 34 15 Minimum

Rubber source and type: CRM Type B ( fine gradation)

Rubber content: 22.7 % by weight of asphalt cement, 18.5 % by weight of total binder

Asphalt cement source and grade: Ergon Snowflake PG 58- 28

10 ADOT. Materials Testing Manual. 1985. Section 714

12

Table 4 Binder 2 Rubber Gradation, Percent Passing ( ARIZ 71411)

Sieve Size Result Specified Limits

No. 8 100

No. 10 100 100

No. 16 93.7 65 – 100

No. 30 40.6 20 – 100

No. 50 9.6 0 – 45

No. 200 0.7 0 – 5

Binder 1 did require a somewhat higher content of the coarser- graded rubber ( 24.2% vs.

22.7%) to provide properties similar to Binder 2 made with the finer- graded rubber.

2.3 PILOT AR- AC MIX DESIGNS – CONTROL MIXES

Field performance data provided by ADOT indicated that approximately 104 AR- AC

mixes were designed and placed from August 1989 through March 2001. Of these AR-AC

mixes, bleeding was reported for three that were used as urban arterial pavements in

the Phoenix metropolitan area, and rutting ( believed to be due to structural issues)

occurred in one mix placed on I- 8 near Yuma. Based on this information, as of April

2001, less than four percent of ADOT’s AR- AC pavements had exhibited severe distress

during a time period of over eleven years. Based on the historically good performance of

AR- AC mixes placed throughout Arizona, the existing mix design method was

considered to be successful. Therefore it was designated as the control method for this

study, the standard to which the results of the proposed improvements would be

compared. The method to be developed needs to provide at least the same quality AR-AC

material as the existing method, including adequate AR binder content to promote

long term durability and compliance with specifications.

ADOT AR- AC specifications at the time of this research were limited to requirements for

physical properties of aggregate ( gradation, sand equivalent, fractured faces and

abrasion); effective voids content ( 5.5 ± 1.0%); minimum VMA ( 19.0%); maximum

binder absorption ( 1.0%); and use of 1.0% portland cement or hydrated lime by aggregate

weight as a mineral admixture.

The testing plan allowed for a total of six mix designs to be performed according to the

newly documented existing ADOT AR- AC mix design method to serve as the controls

for this part of the study. AR Binder 1 was used to establish AR- AC control mix designs

with aggregates from each of the three designated sources. In some cases, appropriate

mix designs that met volumetric requirements could not be developed using Binder 1; the

related data for these are identified as “ Trial Summaries.” Design binder contents were

then determined for Binder 2 using similar gradations. The control AR- AC mix design

summaries and trial summaries are presented in Appendix B, along with compilations of

the properties of interest ( effective binder volume, VMA, voids filled with asphalt

( VFA), effective air voids, Marshall stability and flow) for each.

11 Ibid

13

2.3.1 Issues with CKC and Grey Mountain AR- AC Control Mixes

The TAC members selected the CKC and Grey Mountain aggregates to represent types of

aggregate materials present in the respective southern and northern parts of Arizona that

may present challenges to mix designers.

2.3.1.1 CKC Aggregates

The CKC source was selected specifically because ADOT’s Central Lab had experienced

problems in developing acceptable volumetric AR- AC mix designs when combining

these aggregate materials with an AR binder made with relatively coarse- graded rubber,

like Binder 1. It was necessary for ADOT to request an alternate AR binder made with a

finer gradation of rubber to obtain an appropriate mix design. The CKC aggregate

exhibited high water absorption which historically increases variability in laboratory mix

testing.

As shown on the CKC AR- AC design and trial summaries, MACTEC experienced the

same problems as ADOT when mixing the CKC aggregate with Binder 1. Increasing the

content of Binder 1 increased the mix VMA, and the mixture voids remained excessive

( 7.9%) even with 8.5% binder by total mix weight. It seemed as if the coarser rubber

particles in the binder were not allowing the aggregate matrix to consolidate and

interlock.

The aggregate blend was modified to provide a slightly denser matrix, but the gradations

of the available stockpiled materials did not allow a significant change in the composite

gradation. None of the stockpiles provided sufficient fines to close up the mix voids

while remaining within ADOT 41312 aggregate gradation limits. Therefore a suitable

mix design could not be developed for the combination of Binder 1 and the available

CKC aggregate materials.

However, when Binder 2 was substituted for Binder 1 the mixture voids dropped into an

acceptable range of 6.1% at 7.5% AR binder content, and 5.4% at 8.5% AR binder. This

also mirrored ADOT’s experience.

2.3.1.2 Grey Mountain Aggregates

The combination of Grey Mountain aggregates and Binder 1 exhibited a trend of

increased VMA with increased AR binder content similar to that of the CKC materials,

but less pronounced. It was possible to develop an AR- AC mix design with Gradation

Trial A and Binder 1. However the resulting combination of high VMA and high binder

content caused decreased Marshall stability and increased Marshall flow, which indicated

that properties were somewhat marginal. Such a design would not be recommended.

A wider range of stockpile gradations was available from the Grey Mountain source

which made it possible to evaluate the effects on the voids structure of either substituting

12 ADOT. Standard Specifications for Road and Bridge Construction. 2000. Section 413

14

or blending in a “ dirtier,” i. e., finer, crusher fines material with the clean crusher fines.

The change in gradation due to blending these two fine aggregate materials was small

enough to fall within production tolerances from Gradation A mix design targets ( see

Appendix B). Limited trials indicated that this small change in gradation resulted in a

drop from 7.5% to 6.9% effective air voids at 7.5% Binder 1 content by mix weight.

Substituting the finer crusher fines to further densify the gradation ( Gradation B with

crusher fines) had a profound effect on the voids content, dropping it down to 4.0% at

7.5% Binder 1 by mix weight.

No difficulties were encountered with developing suitable AR- AC mix designs using

Binder 2 with trial aggregate Gradation A. The finer rubber gradation produced an

acceptable mix design.

2.3.1.3 Discussion

The voids structure of asphaltic concrete and AR- AC mixtures depends on a number of

factors including, but not limited to:

• Aggregate particle size – gradation.

• Aggregate particle shape – examples include cubical, flat, angular.

• Aggregate surface texture – fine or coarse grains, glassy or rough, size and

number of surface voids, etc.

These factors affect how aggregates pack together when compacted. The Uncompacted

Void Content ( ARIZ 24713) used for Superpave mixes may be considered as an index of

such factors.

In AR- AC mixes, the discrete swollen rubber particles that remain in the AR binder after

interaction with the asphalt cement may also affect how aggregates pack together. The

rubber particles must also be accommodated within the aggregate matrix and may fill

some voids. However if the voids are too small to accommodate them, the rubber

particles may interfere with stone- to- stone contact and force the aggregate particles apart,

which increases VMA and mixture voids. In such cases, increasing the AR binder

content increases the number of interfering rubber particles and consequently increases

VMA and mixture voids. Finer rubber particles do not take up as much space as coarser

rubber and are more likely to fit within the aggregate matrix.

ADOT AR- AC mixes are limited to very low fines content in order to promote stone- on-stone

contact in the aggregate matrix and to provide sufficient void space to

accommodate a relatively high content of AR binder that includes discrete rubber

particles. ADOT specifications limit the amount of minus No. 200 material in any of the

component stockpiles to a maximum of 6.0%. Although design AR binder contents are

high compared to conventional mixes, AR- AC mixes do not require high contents of fine

aggregate particles in the mix to avoid drain down or minimize potential for bleeding.

13 ADOT. Materials Testing Manual. 1985. Section 247

15

The lack of allowable fines leaves the mix designer with few options for closing up high

voids AR- AC mixes. If changing the aggregate stockpile or bin blend proportions and

AR binder content cannot reduce the voids enough, then it may not be possible to develop

a suitable mix design with a specific AR binder that fully complies with binder

specification requirements and includes relatively coarse- graded rubber. This situation is

both illustrated in Appendix B in MACTEC’s control mix design trials with CKC

aggregate and Binder 1, and supported by ADOT’s experience with this source.

The control mix design trials performed with the Grey Mountain aggregate ( also

presented in Appendix B) indicate that adding a relatively small proportion of fines can

have major impacts on reducing effective voids contents of gap- graded mixes. However

the crusher fines material used to adjust the Grey Mountain mixes with Binder 1 does not

meet ADOT limits for maximum 6% minus No. 200 material and could not be used

without waiving these requirements.

Although the relative impact of adding fines would be material- specific, mix designers

must have some means to adjust mixture voids. The first option would be to seek a finer

crumb rubber material to use in the AR binder. In cases where finer rubber is not

available and an acceptable AR- AC mix design cannot be developed otherwise,

consideration should be given to allowing use of aggregate stockpiles that include more

than 6.0% passing the No. 200 sieve, raising the upper gradation limit for the composite

aggregate blend including admixture to three or four percent passing the No. 200, or both.

2.3.2 Salt River Control Mixes

No problems were encountered in developing control mixes for the Salt River aggregates.

The mix design data for the control mixes with Binder 1 and Binder 2 are included in

Appendix B. As requested by the project TAC, MACTEC performed two additional

replicate designs for the Salt River control mixes with each binder using the established

target gradation. Results were relatively consistent and are summarized in Table 5. The

limited replicate data show design contents of Binder 2 ( finer rubber) are slightly lower

than those for Binder 1 ( coarser gradation) at corresponding air voids contents.

Table 5 Design Binder and Air Voids Contents, Salt River Aggregate Control

Mixes

Mix ID* Binder 1

% by mix weight Air Voids, % Binder 2

% by mix weight Air Voids, %

B1C1 7.5 5.6 --

B1C2 7.3 5.5 --

B1C3 7.3 5.4 --

B2C1 7.1 5.6

B2C2 7.1 5.5

B2C3 6.8 5.4

Average 7.37% 5.5% 7.0% 5.5%

* Mix ID Example: B1 C1 = Binder 1 Control Mix Trial 1

16

2.4 MODIFICATIONS TO EXISTING ADOT AR- AC MIX DESIGN

PROCEDURE

Development of the Version 1 modifications to the mix design procedure began during

initial documentation of the existing AR- AC mix design method. MACTEC solicited

input from the ADOT Materials staff, the project team and TAC, and other local

consultants who design AR- AC mixes for counties and municipalities.

The primary procedural changes considered included making and treating the Rice

specimens in the same manner as the loose Marshall specimens, and adding weights to

the surface of compacted Marshall specimens to prevent rebound while cooling prior to

extrusion from the molds. Rice tests of AR- AC mixes have customarily been performed

at 6.0% AR binder content, although AR binder content is rarely less than 7.0% by

weight of mix. Thus, a comparison of results of Rice testing at 6.0% and at 7.0% AR

binder was deemed necessary. A complete list of the modifications proposed is presented

in Section 2.4.1.

ARIZ 815c14 includes considerable explanation and exposition of calculations which

makes its presentation lengthy and cumbersome. ADOT Materials staff requested

changes in the presentation format to clarify the method and make it easier to use, and

modification of the volumetric calculations to conform to those used by the Asphalt

Institute for design of Marshall and Superpave mixes. 15,16

2.4.1 List of Considered Procedural Changes to AR- AC Mix Design Method

1. Include mineral admixture in the mix as part of the aggregate.

2. Use “ Wet Prep” method of admixture addition – mix dry admixture

thoroughly with dry aggregate to distribute uniformly throughout, then blend,

then add 3% water by aggregate weight and mix thoroughly to wet.

3. Batch aggregates in oven dry condition.

4. Fabricate Rice specimens at 7.0 % AR binder by total mix weight instead of

6.0 %, and include the required 1% admixture by dry aggregate weight ( added

and wet prepped as in step 2 above) but omit liquid anti- strip.

5. Cure Rice specimens at the same temperature ( 325 º F ± 10 º F) and for the same

amount of time ( 2 hours) as for the loose mixture for Marshall specimens.

6. Mixing temperature: AR binder at 350 º F, aggregate at 325 º F

7. Compaction temperature: 325 º F to 335 º F

8. Cool the compacted AR- AC specimens vertically in the molds ( with base

plate underneath and 2000grams ± 10 gram steel disc on top of specimen) to

less than or equal to 90 º F before extruding them.

14 Ibid, Section 815c

15 The Asphalt Institute. “ Mix Design Methods for Asphalt Concrete and Other Hot- Mix Types”, Chapter 4

16 The Asphalt Institute. “ Superpave Mix Design”, Chapter 4

17

The changes listed were incorporated to develop “ Version 1” mix designs for each

aggregate source, using the composite aggregate gradations developed for the

respective control mix designs with Binder 1 and Binder 2.

2.4.2 Mix Designs – Version 1 Mixes

2.4.2.1 Salt River Aggregate Version 1 Mixes

No problems were encountered in developing Version 1 mix designs for the Salt River

aggregates. As requested by the project TAC, MACTEC performed two additional

replicate designs for the Salt River aggregate Version 1 mixes with each binder using the

established control gradation. The Version 1 mix designs with AR Binders 1 and 2 are

included in Appendix C. Results were relatively consistent and are summarized in Table 6.

Table 6 Design Binder and Air Voids Contents for Salt River Aggregate

Version 1 Mixes

Mix ID* Binder 1

% by mix weight Air Voids, % Binder 2

% by mix weight Air Voids, %

B1PC1 8.0 5.6

B1PC2 8.1 5.6

B1PC3 8.2 5.6

B2PC1 6.9 5.4

B2PC2 6.7 5.5

B2PC3 6.7 5.4

Average 8.10 5.60 6.77 5.43

* Mix ID Example: B1PC1 = Binder 1, Version 1 Mix Design Trial 1

The limited data show Version 1 mix design contents of Binder 2 ( finer rubber) are 1.1%

to 1.5% lower than those for Binder 1 ( coarser gradation) at similar air voids contents.

Compared to the results listed in Table 5, design contents for Binder 1 Version 1 mix

designs increased by 0.5% to 0.9% ( average content 8.1%) over the range of Binder 1

contents determined for the control mix designs ( range 7.3%- 7.5%, average 7.37%).

However the Version 1 design contents of Binder 2 showed very little difference from the

control mix design value range of 6.8%- 7.1% with average of 7.0%. The effects of the

difference in AR binder composition, rubber gradation, and content, appeared to be

accentuated by the Version 1 method.

2.4.2.2 CKC Aggregate Version 1Mix Designs

Work on Version 1 designs was limited to a trial using 7.5% and 8.5% Binder 2 by

weight of the modified composite aggregate gradation used in the control mix. The data

are summarized in Appendix C. Effective air voids of the Version 1 mix were higher

than the control, but no conclusions can be drawn from the limited data.

18

2.4.2.3 Grey Mountain Aggregate Version 1 Mix Designs

Work on Version 1 designs was limited to a trial using 7.5% and 8.5% Binder 2 by

weight of the original aggregate gradation ( A) used in the control mix design. The data

are summarized in Appendix C. Effective air voids of the Version 1 mix were lower than

the control design with Binder 2, but no conclusions can be drawn from the limited data.

2.4.2.4 Discussion of Results

The purpose of the additional mix testing with the Salt River aggregates was to permit

evaluation of the variability of both the control and Version 1 design methods and of the

materials being used. The Salt River aggregate has proved to be a good, sound, durable

material for use in asphaltic concrete, with low water absorption and relatively consistent

physical properties. It has historically proven to be less variable than the CKC or Grey

Mountain aggregates and thus was the best choice for replicate testing to evaluate the

effects of binder and mix design method on the results. Volumetric properties evaluated

included effective binder volume, VMA, VFA, and effective air voids content.

Some volumetric differences due to binder composition were expected and occurred. In

plots of the control mix data, the data tend to group by binder but there is some overlap.

However the plots of the Version 1 mixes show very distinct differences between

volumetric properties of mixes made with Binder 1 and those made with Binder 2 at

corresponding binder contents. 17 The magnitudes of these differences are greater than

would be expected for the relatively minor changes to the mix design procedure and

represent significant practical differences in the results as follows:

• Air Voids – more than 2% difference between Binder 1 and Binder 2 mixes

• VMA – up to 2% difference

• Voids Filled – up to 10% difference

These large differences do follow expected trends for the rubber gradations and relative

contents, but raised the following questions:

1. Did the changes to the mix design method cause these differences in

volumetric results, or simply better distinguish binder related differences in

mixture properties that had been occurring but had not been recognized?

2. Are the differences repeatable and reproducible?

a. With these same materials?

b. With other materials?

17 Referenced plots are included in compiled data plotted for MACTEC- ADOT Rounds 1 and 2 that is

presented in Appendix E, but are presented with other results and not alone due to the large number of plots

included with this report.

19

A program of replicate testing by ADOT and MACTEC was implemented as Round 2 of

this study to answer these questions. Repeatability typically refers to the precision of

testing expected, i. e., the acceptable range of results, for a single test operator or

laboratory. Reproducibility typically refers to the precision of testing expected for two or

more different laboratories. Round 2 activities and findings are discussed in Section 2.5

of this report.

2.4.3 Analysis of Rice Results at 6.0% and 7.0% AR Binder Content

While performing the control and Version 1 mix designs with aggregate materials from

the respective sources, MACTEC prepared and tested corresponding sets of Rice

specimens at AR binder contents of 6.0% and 7.0% by total mix weight. Additional

replicate Rice testing of control and Version 1 mixes was also performed during Round 2.

The dry back procedure was used because it is the referee method, although it

incorporates more possible sources of variation. The increased variability is reflected in

the precision and bias statements for the corresponding ASTM D 2041, Standard Test

Method for Theoretical Maximum Specific Gravity and Density of Bituminous Paving

Mixtures, developed from AMRL Proficiency Sample Program data with and without dry

back. 18 Results and statistical analyses of Rice testing are presented in Appendix D.

To validate the data, the measured Rice value at one binder content was used to calculate

the effective specific gravity of the aggregate, Gse, using Equation 1. The calculated Gse

value was used in Equation 2 to calculate the Rice value at the other binder content.

b

b

mm

mm

mm b

se

G

P

G

P

P P

G

−

−

= Equation 1

b

b

se

s

mm

mm

G

P

G

P

P

G

+

= Equation 2

Where

Gse = Effective specific gravity of the aggregate- admixture blend

Gmm = Maximum theoretical specific gravity of the AR- AC at AR binder content Pb

Pb = AR binder content at which the Rice test was performed

Gb = Specific gravity of the AR binder

Ps = Aggregate content, percent by total weight of mix ( 100- Pb)

Pmm = Percent by weight of total loose mixture = 100%

Results of the measured and calculated Rice values were then compared. The differences

between measured and calculated Rice values at 6.0% and 7.0% AR binder contents are

no greater than 0.012, which is at the limit of the acceptable range of two results obtained

18ASTM. “ ASTM D 2041- 03a, Standard Test Method for Theoretical Maximum Specific Gravity and

Density of Bituminous Paving Mixtures.” ASTM Book of Standards 2005, Volume 4.03, pp. 177- 180.

20

on the same material by a single operator according to ARIZ 417b. 19 The maximum

difference was obtained for a control mix made with the Grey Mountain aggregate. Only

one of the mixes made with the Salt River aggregate yielded a difference of greater than

0.004 between measured and calculated Rice values at 6% and 7% AR binder contents.

Thus the variability of the results for both the control and Version 1 mixes appears to fall

within the acceptable range for this test.

Analysis of variance ( ANOVA) was also used to evaluate the relative effects on Rice

results of AR binder ( Binder 1 or Binder 2) and design method ( control or Version 1).

The results of the analysis indicate negligible effects of these factors on the Rice results.

The effects of interaction of binder and method were stronger than either factor alone but

were still negligible. The analysis indicates that including mineral admixture does not

measurably increase variability of Rice test results and is feasible. Including the

admixture in the Rice specimens also simplifies calculations.

2.4.3.1 Summary

Rice testing for AR- AC mix design may be performed at either 6.0% or 7.0% AR binder

content on mix specimens that include lime as a mineral admixture. Although no testing

was done with cement as a mineral admixture, it is expected that these results would

apply to cement. Although samples fabricated with 7.0% AR binder were reportedly

more difficult to work with, the quality of the results of this study did not appear to be

affected. Asphalt- rubber is very sticky, so increasing the binder content can make it more

difficult to break up any clumps of fine aggregate particles as required by the test

procedure.

The TAC decided to continue using the lower 6.0% AR binder content for AR- AC mix

design to facilitate handling and breakup of the Rice specimens, as the analysis of results

indicated no need to change. The same type and proportion of mineral admixture

included in the Marshall specimens should be included in the Rice specimens.

2.4.4 AR- AC Rebound of Compacted Specimens

For purposes of this study, rebound is defined as a measurable increase in the height of a

compacted AR- AC specimen after completion of compaction and prior to extrusion. This

phenomenon has been observed occasionally and reported anecdotally during the last 20

years or so, but MACTEC was not able to find any indication that rebound of AR- AC

mixes has ever been formally documented. 20

In the early 1990s, AR- AC mixes were developed for demonstration projects throughout

the U. S. in response to the legislative mandate of the 1991 Intermodal Surface Trans-portation

Efficiency Act ( ISTEA) to include scrap tire rubber in asphalt pavements.

Rebound was occasionally reported during attempts at mix design verification by

19 ARIZ 417b Maximum Theoretical Specific Gravity of Field Produced Bituminous Mixtures ( Rice Test),

December 1987.

20 “ Use of Scrap Tire Rubber – State of the Technology and Best Practices.” Caltrans, 2005

21

laboratories that had little if any experience in working with asphalt- rubber materials.

The Principal Investigator has personal knowledge of four such cases, of which all but

one seemed to be generally resolved by substituting hand Marshall compaction ( the

referee method) for mechanical compaction and improving temperature control during

mixing and compaction. In those three cases, it was found that the mechanical Marshall

hammers had not been calibrated to the referee hand method; some states did not require

it. The exception was a dense- graded mix which exhibited some volumetric issues and

likely did not have enough void space to accommodate the rubber particles in the binder.

Although AR- AC specimen rebound is not often observed, most of the local consultants

informally surveyed by MACTEC indicate that they routinely take some action to prevent

specimen rebound during AR- AC mix design. Several of the laboratories keep base

plates on top of the specimen in the Marshall mold during cooling, and others place

weights of up to 5,000 grams directly on the top surface of the compacted Marshall

specimen. Base plates do not assure uniform contact with the specimen and thus were

not considered appropriate for this study.

MACTEC had steel weights with handles (“ pucks”) fabricated to fit on top of 4- inch

diameter AR- AC Marshall specimens inside the compaction mold. Puck weight was

2,000 ± 10 grams. Figure 1 shows a picture of the puck and of the dial indicator that was

used to measure vertical displacement of the puck over time.

Figure 1: 2,000 gram Rebound “ Puck” and Dial Indicator

Results of rebound testing are presented in Appendix D. The results for the Round 1 and

Round 2 control and Version 1 mixes show that height change was negligible for most of

the specimens tested with or without the 2,000 gram weight. The data indicate that most

of the specimens experienced some minor shrinkage upon cooling. The 2,000 gram

weight did not appear to make a practical difference in height of compacted specimens of

mixes that did not swell.

22

By chance, a mix design trial for a different project yielded specimens that were observed

to puff up like a soufflé in the Marshall molds after compaction. This mixture was

duplicated and tested for rebound with and without the 2,000 gram puck. Results for the

“ soufflé mix” are also included in Appendix D. Although un- weighted specimens did

exhibit rebound, increases in height measured no more than 0.014 inch. The pucks did

succeed in preventing rebound of the soufflé mix.

2.4.4.1 Summary of Rebound Evaluation

This rebound evaluation may be the first to be documented. Results indicated that

changes in AR- AC specimen height after compaction are generally negligible, and that

most specimens exhibit minor shrinkage while cooling in the molds. Although weights

may be used to prevent rebound, there is no compelling reason to require their use.

It was the consensus of the project team and TAC that AR- AC specimens that exhibit

noticeable rebound after compaction should be considered as indicators of mixture

volumetric issues. Such specimens should be discarded and the composite aggregate

gradation should be adjusted to better accommodate the AR binder.

2.4.5 Round 2 Replicate Testing – ADOT’s Central Lab and MACTEC

Review with the TAC of MACTEC’s results of replicate tests of control and Version 1

mixes made with Binder 1 and Binder 2, respectively, indicated that more testing was

needed to evaluate the effects of the Version 1 modifications, as well as their

repeatability.

A focused test plan and handling instructions were developed for both ADOT and

MACTEC to evaluate MACTEC’s Round 1 results, and Round 2 of testing was initiated.

MACTEC presented the instructions for making specimens of Version 1 mixes in the

format of the proposed revised mix design procedure as Version 9- 26- 03, updated 10- 29-

03. This was an intermediate draft to be applied only to this replicate testing phase of this

study and was not intended to be the final version. The control mix replicates were to be

made according to the existing ADOT mix design method.

MACTEC batched the Salt River aggregate materials for ADOT to use for “ Round 2” rep-licate

testing for control and Version 1 AR- AC mixes. The aggregate samples were de-livered

to ADOT’s Central Laboratory along with lime admixture, batch sheets, six gallons

each of Binder 1 and Binder 2, and a 2000- gram rebound “ puck” as a template for ADOT to

duplicate. MACTEC also prepared and tested three more replicates each of the Salt River

control and Version 1 mixtures with Binders 1 and 2, respectively, for Round 2.

When ADOT personnel began to fabricate specimens for the Version 1 mixes, it became

apparent that there had been a misunderstanding as to how MACTEC had incorporated

the lime admixture in these mixes during the Round 1 testing. MACTEC had reported

that the lime was substituted for 1% of the crusher fines in the composite blend, and

viewed this simply as a modification of the existing laboratory procedure. However

23

ADOT was concerned that this approach could be construed as a policy change regarding

admixture addition, which was not intended. ADOT therefore instructed MACTEC to

incorporate lime in the Version 1 mixes the same as for the control mixes, by determining

the composite aggregate blend and then adding 1% lime by total dry weight of aggregate.

MACTEC batched new specimens for the Version 1 mixes for Round 2 testing.

MACTEC compiled and plotted test results of Rounds 1 and 2. Microsoft Excel was used

to calculate means, standard deviations, and outlier limits ( according to the ADOT

method for dispute resolution) for the respective data sets. The one- way analysis of

variance ( ANOVA) feature of the Excel Data Analysis package was used to evaluate the

statistical validity of combining MACTEC’s data from Rounds 1 and 2, for respective

binders and content levels. MACTEC considered this particularly important due to the

difference in batching aggregates and admixture for the Version 1 method between

rounds. Results of these analyses indicate that MACTEC’s data from Rounds 1 and 2

may be combined at levels of confidence ranging from 95% to 99%. Printouts of the

ANOVA analysis are included in Appendix E. The results are summarized in the One-way

ANOVA Results Matrix also in Appendix E.

Two- way ANOVA was used to evaluate the relative effects of both Binders 1 and 2 as

well as the mix design method ( existing ADOT versus Version 1) on the results. The

results are also presented in Appendix E. These ANOVAs indicate that although there

are some effects of mix design method, binder is clearly the primary source of differences

among the control and Version 1 mixtures tested by MACTEC.

The ADOT results were provided in two compilations, with voids analyses performed

based on Rice values at 6.0% and 7.0% AR binder content, respectively. MACTEC had

based voids analyses for the control mixes on Rice at 6.0%, and used Rice at 7.0% for

volumetric calculations for the Version 1 mixes. The corresponding ADOT data

compilations were used for comparison in the various plots and analyses of variance

which are presented in Appendix E.

A full set of 24 plots of MACTEC’s and ADOT’s combined Rounds 1 and 2 test results

for control and Version 1 mixes made with Salt River aggregates and Binder 1 and

Binder 2 were generated and are presented in Appendix E of this report. A detailed

legend is provided to facilitate review of the plots. Differences between Rounds 1 and 2

in batching and gradation of the Version 1 mixes appear to be reflected in the plots of

MACTEC’s results, which typically bracket the ADOT Round 2 results.

The plots of VMA, VFA, and effective air voids results versus AR binder content for the

replicates from both Rounds 1 and 2 illustrate that the distinctions between binders

highlighted in the Round 1 Version 1 mix results still exist. However the differences are

smaller. Since one of the Version 1 modifications ( approach to adding lime) was elimi-nated

along with the related minor difference in composite gradation, this shift toward the

control mix results makes sense. The remaining differences seem most likely to be bin-der

related. The plots also illustrate the two- way ANOVA results. For each binder,

24

results of control and Version 1 mixes tend to overlap. However the volumetric results of

Binder 1 mixes generally differ from those of Binder 2 mixes.

After visual examination of the plots with ADOT Round 2 data added indicated similar

results, MACTEC performed numerous ANOVAs to evaluate and compare results with

respect to design method, binder, and laboratory. It was necessary to tabulate the

ANOVA results to look for patterns and correlations.

Two- way ANOVA of the ADOT results were performed to evaluate the relative effects

of binder and mix design method. The individual ANOVAs are presented in Appendix E.

To facilitate review, these ANOVA results are summarized in the Two- Way ANOVA

Results Matrix included in Appendix E along with the results of the corresponding

analysis of MACTEC data. The statistical analysis indicates that binder had a very strong

effect on test results from both laboratories, and that the design method used ( control

versus Version 1) had relatively little impact. This finding validates the mix design

procedure that ADOT has been using and indicates that only the most useful and practical

of Version 1 mix design modifications should be adopted. It also validates a considerable

body of experience and anecdotal data that has long indicated that the AR binder is a key

factor in AR- AC mixture volumetrics.

The findings of the analyses of Round 1 and 2 results are summarized as follows:

• Review of plots of VMA, VFA, and effective air voids results indicate that

both the control ( existing ADOT) and Version 1 mix design methods

generally distinguish between Binder 1 and Binder 2 for these properties.

• The respective averages of MACTEC and ADOT Round 2 test results are in

substantial agreement for both binders and design methods, except for

Marshall stability.

• ADOT’s stability results were systematically higher than MACTEC’s.

• Results of Marshall stability and flow tests do not reliably distinguish among

binders.

• Effective binder volume appears relatively insensitive to binder type or design

method used in this study.

• Analysis of variance indicates that the mixes made with Binder 1 ( Paramount

PG 58- 22 with 24.4% coarse CRM rubber by weight of AC) exhibited greater

variability than mixes made with Binder 2 ( Ergon PG 58- 28 with 22.7% fine

CRM rubber by weight of AC). This is best illustrated by comparison and

ANOVA of MACTEC’s Round 1 and Round 2 test results for control mixes

made with the respective binders.

25

• In spite of the variations in individual mix property values, the agreement

between averages of ADOT and MACTEC Round 2 test results remains very

good for the binders and procedures used. This indicates that the overall AR-AC

mix design results can be reproduced by other laboratories.

• The ANOVA results matrix shows relatively good agreement between

MACTEC Round 1 and ADOT Round 2 results, in spite of differences in

binder storage time and Version 1 aggregate gradation. This further supports

MACTEC’s conclusion that the AR- AC design results are reproducible.

• ANOVA of the ADOT and MACTEC data indicates that the effects of the

binder are consistently very strong, while mix design method within this study

has relatively little if any effect.

• Based on the findings to date, it is not necessary to adopt each of the changes

to the existing ADOT mix design method for AR- AC that MACTEC

originally proposed. Recommended changes are limited to the following:

o Use oven- dry batching only when aggregates can not be air- dried to a

moisture content of less than 3%.

o Use “ Wet Prep” method of admixture addition – add 1% admixture by

aggregate weight and mix thoroughly to distribute, and then thoroughly

mix in 3% water by aggregate weight.

o Fabricate Rice specimens with 1% admixture by weight of aggregate

( added by wet prep) and 6% AR binder by total mix weight.

o Cure Rice specimens at the same temperature ( 330 º F ± 5 º F) for the same

amount of time ( 2 hours) as the loose AR- AC mixture used to make

Marshall specimens.

o Set mixing temperature: AR binder at 350 º F, aggregate at 325 º F.

o Set compaction temperature: 330 º F ± 5 º F.

o Cool the compacted specimens upright in the molds to less than or equal

to 90 º F before extruding them. Specimens should not be extruded until

just prior to testing.

o Do not place weights on top of compacted AR- AC specimens while

cooling in the mold. Mixes that exhibit rebound in the mold should be

discarded and redesigned.

26

The TAC concurred with the findings of the analyses and the recommended changes to

the mix design method, which are relatively minor. These changes were incorporated as

Version 2 of the AR- AC mix design procedure.

The results of the Round 2 replicate testing indicated that the control and Version 1

methods were relatively repeatable within a single laboratory and that the resulting mix

designs could be substantially reproduced by another laboratory. However the replicate

testing was performed on mixes made with a single source of relatively consistent high

quality aggregate materials, batched by a single laboratory under tightly controlled

conditions, so more evaluation would be useful.

The next task was to use round robin testing to evaluate whether the proposed Version 2

mix design method was robust enough to be used by other qualified laboratories to design

AR- AC mixes, using aggregate materials of varying quality that are more challenging to

work with than the Salt River materials.

27

3. ROUND ROBIN TESTING FOR VERIFICATION OF

PROPOSED AR- AC MIX DESIGN METHOD

The purpose of the round robin testing was to provide an “ acid test” for the proposed mix

design procedure. The round robin was intended to simulate real world mix design

and/ or verification operations. Participants would start with bulk samples of respective

aggregate stockpile materials, mineral admixture and prepared AR binder. Each

participating laboratory would measure aggregate specific gravity and absorption

properties; batch aggregates to meet composite gradation targets and mix with the

prepared AR binder; compact, condition, and test mixture specimens fabricated with a

range of AR binder contents; and calculate volumetric properties. The results would be

used to select a design AR binder content for each of three sets of replicate results.

3.1 PROJECT AND MATERIALS SELECTION

ADOT provided the opportunity to use a 2004 ADOT AR- AC construction project to

pilot the proposed standard ADOT AR- AC mix design method and provide materials for

round robin testing by the project team ( Speedie and Associates, Rinker, ADOT’s Central

Lab, and MACTEC). In addition, ADOT planned to obtain samples for acceptance

testing during construction to characterize the mix as produced and placed ( including

compaction results) so that the performance of the resulting pavement can be monitored

over time by periodic surveys. The parties involved believed this would be the best way

to conclude this study.

ADOT selected the following ARAC construction project to pilot the proposed mix

design method.

Project Name: Badger Springs – Big Bug

Project No.: IM- 017- B( 005) A

TRACS No.: 017 YV 256 H611501C

Project Location: I- 17 NB and SB MP 263- 255

The project was called “ Big Bug” and the source of the aggregate was the Dugas Pit.

ADOT personnel obtained bulk samples of the designated project aggregate materials

from the Dugas Pit, including clean crusher fines, 3/ 8” and 3/ 4” stockpile materials, for

use in the mix design and round robin testing. ADOT delivered the aggregate samples to

MACTEC in late June, 2004.

The Dugas aggregate has relatively high water absorption: more than 1.5% for the coarse

fraction, and more than 2% for the fine fraction.

28

3.2 MATERIALS DESIGNS

3.2.1 Asphalt- Rubber Binder Design

A Type 2 AR binder was designed and produced by Speedie and Associates ( Speedie) in

June 2004 for use in the AR- AC mix design. The AR binder design profile is presented

in Table 7. The rubber, CRM, which came from the same source, was included with

Binders 1 and 2 for Rounds 1 and 2 of this study. The PG 58- 22 asphalt was from

Chevron ( a different source than used in Rounds 1 and 2). Sieve analysis results in Table

8 show that the rubber gradation was coarse and very similar to that used in Binder 1.

ADOT provided samples of this AR binder to MACTEC for use in the mix design.

Table 7 Original Big Bug AR Binder Design Profile

Test Performed Minutes of Reaction

60 120 240 1440

Specified

Limits

Viscosity, Haake at 177° C, cP 2100 1900 2300 2700 1500- 4000

Resilience at 25° C, % Rebound

( ASTM D3407) 31 33 35 34 20 Minimum

Ring & Ball Softening Point, ° F

( ASTM D36) 139 138 140 143 130 Minimum

Needle Penetration at 4° C, 200g,

60 sec., 1/ 10mm ( ASTM D5) 23 22 30 25 15 Minimum

Rubber source and type: CRM Type B ( coarse gradation)

Rubber content: 25.8% by weight of asphalt cement, 20.5 % by weight of total binder

Asphalt cement source and grade: Chevron PG 58- 22

Table 8 Big Bug AR Binder Rubber Gradation, Percent Passing ( ARIZ 71421)

Sieve Size Results

( percent passing

Specified Limits

( percent passing)

No. 8 100

No. 10 100 100

No. 16 78 65 - 100

No. 30 28 20 - 100

No. 50 4 0 - 45

No. 200 0 0 - 5

3.2.2 AR- AC Mix Design

MACTEC performed the AR- AC mix design according to the procedure described. The

mix design summary and detailed test results are presented in Appendix F. The design

AR binder content of 7.8% yielded a target air voids content of 5.7%.

21 ADOT. Materials Testing Manual. 1985. Section 714

29

3.3 PREPARATION OF ASPHALT- RUBBER BINDER SAMPLES FOR

ROUND ROBIN TESTING

It was discovered that the amount of AR binder originally prepared and submitted for use

in the mix design was not sufficient to complete the planned round robin testing.

Therefore MACTEC prepared and tested AR specimens using the source and grade of

respective asphalt cement and rubber materials used in the original binder design

developed by Speedie and Associates. However, differences in the properties of

PG 58- 22 asphalt cement samples received by MACTEC’s laboratory three months after

completion of the original AR binder design required some adjustments to the AR blend.

It was necessary to increase the rubber content from 25.8% to 26.6% by weight of asphalt

cement to provide an AR binder that fully complied with specifications throughout the

24- hour laboratory interaction period. The updated binder design data is presented in

Table 9. MACTEC does not know if any similar adjustments to rubber content were

required during field blending of the AR binder for AR- AC construction on the Big Bug

project in September 2004.

Table 9 AR Binder Design Profile for Round Robin Testing Version 2 Mix Design

Minutes of Reaction Specified

Test Performed 60 90 240 360 1440 Limits

Viscosity, Haake at 177° C, cP 1600 2100 2000 1900 1500- 4000

Resilience at 25° C, % Rebound

( ASTM D5329) 35 37 35 20 Minimum

Ring & Ball Softening Point, ° F

( ASTM D36) 152 152 153 147 130

Minimum

Needle Penetration at 4° C, 200g,

60 sec., 1/ 10mm ( ASTM D5) 20 22 23 15 Minimum

Rubber source and type: CRM Type B ( coarse gradation)

Rubber content: 26.6 % by weight of asphalt cement, 21.0 % by weight of total AR

binder

Asphalt cement source and grade: Chevron PG 58- 22

Since the AR binder is a major factor in mix volumetrics, it was important to assure that

there was a sufficient amount of the updated binder for the participating laboratories to

complete their testing. MACTEC was tasked to prepare 20 gallons of the AR binder

represented by Table 9 in order to provide sufficient material. The change in the binder

was expected to cause some changes in volumetric properties compared to the original

mix design, but comparisons to the original design were not necessary. Since each of the

round robin participants was using the new AR binder material, the conduct and analysis

of the round robin testing would not be affected, although the individual test results were

expected to differ from the original design parameters.

30

3.4 INSTRUCTIONS AND DISTRIBUTION OF SAMPLES FOR ROUND

ROBIN TESTING

MACTEC prepared instructions for conduct of the round robin testing for the Version 2

mix design method to promote procedural uniformity among the participants, to highlight

differences between the revised ADOT AR- AC mix design procedure and current

practice, and to list the data items required to complete the round robin. A copy of the

sheet of instructions is presented in Figure 2. MACTEC also provided an electronic

spreadsheet file for data entry and corresponding hard copy, which clearly showed what

test results and data items were required for MACTEC’s analysis of the results.

MACTEC delivered copies of these documents, individual and target composite aggre-gate

gradation data, and the revised ADOT AR- AC mix design procedure along with bulk

samples of the individual aggregate and admixture materials and five one- gallon cans of

asphalt- rubber binder to the participating laboratories during the last week of October and

first week of November 2004. Each lab was instructed to determine aggregate specific

gravities ( bulk oven dry, saturated surface dry ( SSD), and apparent) and absorption of the

composited coarse and fine fractions, to fabricate and test three replicates of the mix

design using the updated AR binder, including one set of Rice tests per replicate, and to

report their test results to MACTEC. Each replicate included three AR binder contents.

To provide a better simulation of the entire mix design process, the aggregates for the

round robin were not pre- batched as they were in Rounds 1 and 2. Two of the partici-pating

laboratories reported some minor departures in their aggregate blends from the

target composite gradation due to variations from the overall average gradation within the

stockpile samples. They were not instructed to do any artificial blending. The largest

difference from the target gradation was a 2% increase on the percentage passing the No.

8 sieve ( 23% vs. 21%); a few screens showed a plus or minus 1% difference, but percent-age

passing No. 200 was within 0.4% or less from the target. Such minor departures

remain well within production tolerances and make this simulation more realistic,

particularly for mix design verification.

3.5 BASICS OF ESTIMATING VARIABILITY OF TEST METHODS AND

ACCEPTABLE RANGES OF TEST RESULTS

To facilitate review of the round robin results and analyses presented herein, this section

includes a brief summary of how testing variability is estimated, and how acceptable

ranges for various numbers of individual test results are established.

The basic statistic for evaluating precision of tests of construction materials is the stan-dard

deviation of the population of measurements ( test results), which is typically ex-pressed

in terms of the one- sigma limit ( 1s). 22 The one- sigma limit may be established

for single- operator precision or multilaboratory precision. Limits for multilaboratory

precision are larger due to different test operators, equipment, and laboratory

environments that provide more sources of variability or error.

22 ASTM. “ ASTM C 670- 03, Standard Practice for Preparing Precision and Bias Statements for Test

Methods for Construction Materials” ASTM Book of Standards 2006

31

Round Robin testing is required to verify the proposed Marshall mix design procedure for ADOT 413

Asphalt Rubber Asphaltic Concrete ( ARAC). To assure that sufficient AR binder is available to complete

the testing, MACTEC has prepared 5 one- gallon cans of AR binder for each participating laboratory. These

will be distributed with along bulk samples of the respective component aggregate materials and hydrated

lime mineral admixture, and copies of these instructions, the mix design procedure, pertinent information

from MACTEC’s original mix design, and blank Mix Design Data Report Form.

PLEASE READ THESE INSTRUCTIONS BEFORE PROCEEDING

1. Read the entire mix design procedure first and follow it exactly – there are some important differences

from the previous procedure for Rice specimens, and temperature control. If you have any questions,

contact Anne Stonex immediately at 602- 437- 0250 ( MACTEC), or Scott Thompson if Anne is not

available.

2. Each lab shall complete three replicates of the mix design, with one set of Rices per replicate. Please

present the results for each replicate ( 3 plugs each at 3 AR binder contents and 1 set of Rices)

separately for inclusion in the statistical analysis. A blank Mix Design Data Report Form is attached

and an electronic copy will be provided.

3. Check aggregate gradations with washed sieve analysis. Batch aggregates in oven dry condition to

meet mix design gradation targets for the respective sieve sizes.

4. Determine specific gravities ( bulk oven dry, SSD, and apparent) and absorption of the composited

coarse and fine aggregate fractions.

5. Use “ Wet Prep” method of admixture addition – mix the designated proportion of lime with the dry

aggregate, then add 3% water by aggregate weight and mix thoroughly

6. Include admixture ( added by wet prep) in the Rice specimens, and 6% AR binder by total mix weight.

7. Cure Rice specimens at the same temperature ( 330 ± 5 º F) for the same amount of time ( 2 hours) as the

loose GG AR AC mixture.

8. Batch Marshall specimens at 6.5%, 7.5%, and 8.5% AR binder content by total mix weight.

9. Mixing temperature for Marshall and Rice specimens is: AR binder @ 350 º F, aggregate @ 325 º F

10. Compaction temperature for Marshall specimens is 330 ± 5 º F

11. DO NOT place any weights on the compacted Marshall specimens.

12. Cool the compacted specimens in the molds to ≤ 90 º F before extruding them. Specimens shall be

cooled, extruded, and bulk specific gravity determined within 8 hours from the time of compaction.

13. Measure and report Marshall stability and flow.

14. For each replicate of the mix design, and for each binder content, use Asphalt Institute formulas in the

User’s Guide to calculate mixture volumetrics including: effective binder volume, VMA, VFA,

effective air voids, effective specific gravity of aggregate– admixture blend, binder absorption and

effective binder content.

15. Report results to MACTEC by no later than Monday, November 15, 2004 on the provided Mix Design

Data Report Form ( e- mail transmittal to astonex@ mactec. com is preferred).

Figure 2 Instructions For Round Robin Mix Design Testing

32

The commonly used term coefficient of variation ( COV) refers to the one- sigma limit in

percent ( 1s%) and is sometimes used as the basis of precision statements for physical

tests. The COV is calculated by dividing the standard deviation ( 1s) by the average of

the test results and multiplying by 100%.

The acceptable difference between two test results for construction materials has been

standardized as the difference two sigma limit ( d2s), which is calculated by multiplying

1s by 2√ 2 rounded to 2.83. The acceptable difference expressed in percent ( d2s%) is

simply 1s% multiplied by 2.83. The level of confidence for d2s is 95%, which means

that this difference would be exceeded on average no more than once in 20 correctly

performed tests.

ASTM C 67023 includes a table of multiplier factors to use for numbers of test results

ranging from 2 through 10; the multiplier increases as the number of test results increase.

Therefore, this ASTM procedure cautions that an index of precision ( d2s) based on the

difference of two results should not be applied to cases where more than two results are

compared. However if differences among more than two results fall within the narrower

acceptable range for two results, the resulting testing precision is well within the

acceptable range.

ADOT supplied multilaboratory statistics ( 1s, d2s, 1s%, d2s%) from the last 10 years of

their asphaltic concrete proficiency sample program for information. MACTEC also

reviewed multilaboratory and single operator Marshall Proficiency Sample Program

( PSP) statistics presented on the AASHTO Materials Reference Laboratory ( AMRL)

website and in the study “ Effects of Test Variability on Mixture Volumetrics and Mix

Design Verification” by Hand and Epps24 to evaluate the quality of the testing performed.

Analyses of precision of test results obtained for this study are primarily concerned with

acceptable differences between two or more laboratories, rather than for a single operator.

However to evaluate possible problems with test performance, replicate results from the

respective participating laboratories for bulk and maximum theoretical specific gravities

were reviewed with respect to single operator precision information. The ranges of

results were within acceptable limits compared to precision statements and ranges of

available Marshall proficiency sample program results, and no problems were identified.

3.5.1 Considerations Regarding Volumetric Calculations and Analysis

The ultimate products of the mix design procedure are loose mix specimens for Rice

determination and a series of compacted Marshall specimens at designated binder

contents, for which bulk density, stability and flow are measured. Each activity involved

in making and testing these mix specimens is a possible source of variation or error

which may be reflected in the final test results. These activities include materials

sampling, sieve analysis and batching, mixing aggregates with admixture and AR binder,

23 Ibid

24 Hand, Adam J. and Amy Epps. “ Effects of Test Variability on Mixture Volumetrics and Mix Design

Verification.” Journal of the Association of Asphalt Paving Technologists, Vol. 69, pages 635- 674, 2000.

33

and conditioning, compacting, and testing the resulting mix specimens. The AR binder

may introduce additional variability.

Volumetric properties including effective binder volume, air voids content, VMA, and VFA,

are calculated rather than measured. Marshall stability and flow are not volumetric

properties and are of limited interest for AR- AC materials. AR binder content is

controlled in the laboratory along with aggregate gradation. As pointed out by Hand and

Epps, 25 direct property measurements are limited to the following tests, of which each has

its own range of variability:

• Asphalt cement specific gravity ( Gb).

• Combined aggregate specific gravity ( Gsb).

• Bulk specific gravity of compacted Marshall specimens ( Gmb).

• Maximum theoretical specific gravity of the mix ( Gmm).

Because of these considerations, two approaches were used to evaluate the round robin

data. For preliminary evaluation, AR- AC mixture volumetric properties were calculated

for each laboratory’s replicates based on the corresponding aggregate specific gravities

and absorption, and respective Rice and Gmb results supplied. The compiled results are

listed and plotted in Appendix F, which also includes the statistical analysis using

ANOVA, and groups and ranks mean results for the volumetric properties, Marshall

stability and flow.

The second approach was to normalize the data for analysis by using single values for

Gsb, absorption, and Gmm for volumetric calculations for each laboratory’s data. It was

decided that the most representative values would be the overall averages of the values

for Gsb, absorption, and Gmm measured by the laboratories.

3.6 ROUND ROBIN TEST RESULTS

The results of round robin testing and analyses are presented in Appendices F

( preliminary) and G ( normalized). As customary for round robin exercises, the names of

the laboratories have been coded as A, B, C, and D. Each laboratory determined specific

gravities ( bulk oven dry, SSD, and apparent) and absorption of the composited coarse and

fine aggregate fractions. These results are compiled and presented in Table 10. Labs A

and C submitted the aggregate and Rice results, along with Marshall specimen results for

bulk specific gravity, stability and flow, but did not perform the requested volumetric

calculations.

The non- normalized volumetric results for each laboratory were calculated based on the

individual laboratory’s aggregate results, Rice results, and the calculations in the User’s

Guide. These are compiled and plotted in Appendix F. The overall values in the

25 Ibid

34

rightmost column of Table 10 were used to normalize the aggregate results, except that

the numerical overall average for water absorption ( 2.08%) was slightly lower than, and

thus replaced with, the corresponding calculated value of 2.14%.

Table 10 Compiled Round Robin Results for Aggregate Specific Gravity

Laboratory MACTEC D B A C

Source of Data

Original

Mix

Design

Round

Robin

Round

Robin

Round

Robin

Round

Robin

Overall

Round

Robin

" Average"

Coarse Aggregate

Bulk OD Specific

Gravity 2.744 2.731 2.750 2.765 2.743 2.747

SSD Sp. Gravity 2.786 2.783 2.798 2.811 2.794 2.797

Apparent Specific

Gravity 2.886 2.879 2.888 2.897 2.89 2.889

Water Absorption 1.55% 1.88% 1.74% 1.66% 1.85% 1.78%

Fine Aggregate

Bulk OD Specific

Gravity 2.719 2.682 2.722 2.695 2.708 2.702

SSD Specific

Gravity 2.778 2.761 2.782 2.765 2.79 2.775

Apparent Specific

Gravity 2.889 2.912 2.896 2.900 2.951 2.915

Water Absorption 2.17% 2.94% 2.21% 2.63% 3.05% 2.71%

Combined Coarse & Fine without Mineral Admixture

Bulk OD Specific

Gravity 2.735 2.713 2.739 2.740 2.731 2.731

SSD Specific

Gravity 2.783 2.775 2.792 2.794 2.793 2.789

Apparent Specific

Gravity 2.874 2.891 2.891 2.898 2.911 2.898

Water Absorption 1.77% 2.29% 1.89% 2.00% 2.14% 2.08%

Compiled Rice results are presented in Table 11, along with related precision calculations

for the round robin testing. The precision statement for ASTM D 2041 for single

operator, dry back procedure cites a “ 1s” value of 0.0064 for the bowl method. Although

the ADOT method uses flasks, this is the only available comparison for a single operator.

Based on this value, the allowable difference among three results would be 3.3( 0.0064) =

0.0211, and the allowable difference among six results ( Lab A) would be 4.0( 0.0064) =

0.0256. The results in Table 11 are within these ranges. The overall average Rice value

of 2.512 was used to normalize volumetric calculations.

35

Table 11 Compiled Round Robin Results for Rice at 6.0% AR Binder Content

Laboratory MACTEC D B A C

Rice Results

Original

Mix

Design*

Round

Robin

Round

Robin

Round

Robin

Round

Robin

Rice 1 2.516 2.507 2.505 2.522 2.533

Rice 2 2.519 2.499 2.509 2.517 2.520

Rice 3 2.523 2.497 2.499 2.497 2.525

Rice 4 2.515

Rice 5 2.507

Rice 6 2.509

Rice Precision Calculations Overall

Average 2.519 2.501 2.504 2.511 2.526 2.512

Standard Deviation

( 1s) 0.0035 0.0053 0.0050 0.0088 0.0066 0.0106

d2s 0.0099 0.0150 0.0142 0.0250 0.0186 0.0299

COV ( 1s%) 0.139 0.212 0.201 0.351 0.260 0.421

d2s% 0.394 0.599 0.569 0.994 0.735 1.190

* Original mix design used different AR binder than Round Robin

Table 12 presents additional comparisons for Rice testing, including ranges of average

Rice results gleaned from AMRL and ADOT Proficiency Sample Program ( PSP)

multilaboratory statistics, along with the corresponding precision statistics from

ASTM D 2041- 03a, with and without dry back. The multilaboratory ASTM statistics

may include results from bowls and flasks, which may account for some of the

differences from ADOT PSP data.

Table 12 Multilaboratory Proficiency Sample Program Ranges for Rice Results

Range of Results

AMRL

Gmm

Results

ADOT

Gmm Results

ADOT

MAX

Density

ASTM D 2041- 03a

Precision for

2 results

Average 2.417- 2.591 2.420- 2.460

Dryback

( Bowl

only)

No

Dryback

1 Standard

Deviation 0.011- 0.020 0.012- 0.0243 0.0193 0.016

2 Standard

Deviations 0.031- 0.057 0.033- 0.069 0.055 0.044

Coefficient Of

Variation ( 1s%) 0.43- 0.84 0.477- 0.988 0.38- 0.99

Coefficient Of

Variation ( 2s%) 1.27- 2.37 1.349- 2.795 1.08- 2.80

36

Laboratory A experienced problems with their Marshall hammer during round robin

testing. It is not clear if these problems were resolved before round robin testing was

completed, but their Marshall compaction equipment was subsequently replaced. Lab A

asked for additional samples of materials to make and test additional replicates, and

submitted data for eight sets of replicates. These results were checked for outliers

according to ADOT methods. No outliers were identified, although one data point was

right at the upper outlier limit. Thus results for each of the 8 replicates were included in

the statistical analysis. This unbalanced the experimental design, but it does not appear to

have interfered with the One- Way ANOVA analysis.

For each laboratory, results of aggregate bulk specific gravity ( Gsb) testing were also

reviewed. Standard deviations were calculated for combined sets of replicate plugs at

each of the three AR binder contents, and are shown on the compiled data sheets in

Appendix F for each participating laboratory. Gsb is directly measured, so these values

were not affected by normalizing the data for volumetric calculations. Because these

specimens were to be tested for stability and flow, no paraffin or parafilm could be used.

This factor would be expected to increase variability of Gsb measurement, particularly

for specimens with relatively high air voids contents. The ranges of standard deviations

within each laboratory are compiled in Table 13. The within laboratory results are

considered equivalent to single operator precision for this comparison, although in some

cases more than one person performed the testing. Comparisons of within laboratory

standard deviations with AASHTO Materials Reference Library ( AMRL) statistics for

ASTM D 2726- 00 do not indicate any serious or systematic problems with the precision

of the round robin Gsb testing.

Table 13 Within Laboratory Standard Deviation ( 1s) Ranges of Gsb Results

Lab ID Number of

Replicates

Round Robin

Range of 1s values

ASTM

D 2726- 00

A 9

6

0.007- 0.015

0.025

B 9 0.007- 0.011

C 9 0.006- 0.008

D 9 0.009- 0.020

Single Operator

1s limit= 0.0124

2 sample

d2s limit = 0.035

ASTM D 2726- 04 provides precision data only for mixes made with aggregates with

water absorption less than 1.5%, which does not apply to the highly absorptive Dugas

aggregate used in the round robin. Although the single operator precision limits for

nominal ¾ - inch mixes are very similar to those listed in Table 13, the multilaboratory

limits are much tighter for low absorption aggregates. A multilaboratory comparison of

precision of test results is included in Appendix F which supports that Gsb testing among

the respective laboratories was generally performed within acceptable limits.

Preliminary analysis of this round robin experiment indicated that at least two of the

means differed for each property of interest at each AR binder content, except for

Marshall stability at 6.5 and 7.5% AR content. When at least two means were found to

differ, Duncan’s Multiple Range Test was used to compare and rank the respective

37

means, to identify which means were statistically similar and which differed. The

Duncan test can be applied to unequal sample sizes. 26 The Summary of Duncan’s

Multiple Range Comparisons is presented graphically in Appendix F. Lines are used to

group like means and distinguish among groups. Results for Labs A and C were often

similar to each other, while Labs B and D often grouped with each other.

To evaluate the practical differences among the results, design AR contents were

determined for the respective AR- AC mix design replicates and are presented in Table

14. Labs C and D would have selected AR contents of 8.5% to meet mix design air voids

criteria of 5.5% ± 1%, while Lab B’s data would allow slightly lower AR contents of

8.0% to 8.3%. Lab A did not achieve the design air voids requirements within the given

range of AR contents, which may be related to the previously noted equipment problems.

Table 14 Preliminary AR Content Selection

Lab Set B C D A

No. % AR,

% Air voids

% AR,

% Air voids

% AR,

% Air voids

% AR,

% Air voids

1 8.2% AR,

5.5% AV

8.5% AR,

6.5% AV

8.5% AR,

5.6% AV

8.5% AR,

7.1% AV

2 8.3% AR,

5.6% AV

8.5% AR,

6.2% AV

8.5% AR,

5.6% AV

At 7.5 and 8.5% AR,

6.8% AV

3 8.0% AR,

5.4% AV

8.5% AR,

6.2% AV

8.5% AR,

5.7% AV

8.5% AR,

6.8% AV

1R 8.5% AR,

9.1% AV

2R 8.5% AR,

8.6% AV

3R 8.5% AR,

9.0% AV

4 At 7.5 and 8.5% AR,

8.6% AV

5 8.5% AR,

9.0% AV

Normalizing the results removed some of the noise from the data, and results converged

so that statistical differences were eliminated from VMA at 6.5 and 7.5% AR content,

from VFA at 6.5% AR, and effective air voids at 6.5% AR. The normalized results are

compiled and plotted in Appendix G, along with ANOVA and the Summary of Duncan’s

Multiple Range Comparison tests. When there was a difference in means, results from

Labs A and C still tended to group together and results from Labs D and B generally

continued to form a second group. However normalizing had no effect on the measured

values for Marshall Gsb, stability, or flow.

26 Montgomery, Douglas C. Design and Analysis of Experiments Second Edition. John Wiley & Sons,

1984. pp 66- 68

38

To evaluate the practical effects of normalizing the data, AR contents were selected based

on the normalized results and determinations are presented in Table 15.

Table 15 Normalized AR Content Selection

Lab Set B C D A

No. % AR,

% Air voids

% AR,

% Air voids

% AR,

% Air voids

% AR,

% Air voids

1 8.4% AR,

5.4% AV

8.5% AR,

5.8 % AV

8.5% AR,

5.8 % AV

8.5% AR,

6.8% AV

2 8.5% AR,

5.4% AV

8.5% AR,

5.9 % AV

8.5% AR,

6.1 % AV

At 7.5 and 8.5% AR,

6.6% AV

3 8.3% AR,

5.5% AV

8.5% AR,

6.0 % AV

8.5% AR,

6.2 % AV

8.5% AR,

7.4 % AV

1R 8.5% AR,

9.1% AV

2R 8.5% AR,

8.7 % AV

3R 8.5% AR,

9.3 % AV

4 At 7.5 and 8.5% AR,

8.6% AV

5 8.5% AR,

9.1% AV

For Labs C and D, the range of voids at 8.5% AR converged; the voids for Lab C drop-ped

and those for Lab D increased. For Lab B, the selected AR content shifted from 8.0-

8.3% to 8.3- 8.5% to correspond more closely with results from Labs C and D. Lab A

results were based on values that were close to the overall averages selected for normal-izing

the data so little change was achieved. Lab A results did not meet the ADOT

design criterion for effective air voids, which may be related to the compactor problems

encountered. However results of the other 3 participating labs are in close agreement.

3.7 ADDITIONAL CONSIDERATIONS

3.7.1 Laboratory Technicians and Equipment

Although the round robin results reported herein have been coded as customary to protect

the participants, there is some additional information that should not be omitted from the

analysis. Technician experience with the highly modified AR- AC materials appears to be

a factor in repeatability ( within lab) and reproducibility ( between laboratories) in the

design procedure.

During the round robin phase of this study, Lab A not only had major problems with

Marshall hammer calibration, but also lost the technicians who had the most experience

with working with AR- AC mixtures. Lab C, whose results often grouped closely with

those of Lab A, routinely performed conventional mix design testing but had relatively

39

limited experience in designing AR- AC mixes. Labs B and D, whose results also tended

to group closely together and often differed from the other two labs, had fairly extensive

experience in designing AR binders and AR- AC mixes.

3.7.2 Field Performance

Although ADOT AR- AC mixes have historically performed well, sections of the subject

AR- AC mixture and several others constructed in 2004 experienced significant failures.

AMEC Earth & Environmental, Inc. evaluated three of these AR- AC projects including

Big Bug for ADOT and determined that the primary cause was moisture susceptibility

due to high in- place air voids. 27

The subject AR- AC mixture for the Big Bug project was placed on the north and south

bound lanes of I- 17 between mileposts 263 and 256 at night from September 1 to October

4, 2004. The AR- AC was placed at a nominal compacted thickness of two inches on a

new replacement layer in accordance with ADOT 417. Results of acceptance tests

indicated that AR binder content and aggregate gradation were generally within limits. 28

In- place compaction was not an acceptance requirement for AR- AC mixes at that time.

The AR- AC was surfaced with a nominal 2/ 3- inch thick layer in accordance with ADOT

414 Asphaltic Concrete Friction Course ( Asphalt- Rubber), which failed rapidly by

raveling during the winter and was replaced in spring 2005. Additional distress, including

rutting and potholes, developed during summer 2005 that was related to the AR- AC

rather than the friction course. Areas of the AR- AC mix stripped severely, particularly in

the southbound lanes. Although it is clear that water entered the AR- AC layer, questions

remain as to why the water did not drain out.

Forensic data from the failure investigation by AMEC included air voids contents of 31

cores obtained from this project that ranged from 4.9 to 10.8%, with an average of 8.1%.

Four cores had 6.0% air voids or less; three had 10.0% air voids or more.

At this time, ADOT agrees with AMEC that the observed moisture damage in the

projects reviewed is most likely due to inadequate compaction. Marginally low ambient

temperatures during and immediately after construction are considered to be a primary

reason that compaction was not achieved. Night paving at higher elevations conflicts with

the need for relatively high placement and compaction temperatures.

In an effort to avoid such failures in the future, ADOT has implemented a new

specification for AR- AC: in ADOT 41529 Asphaltic Concrete ( Asphalt- Rubber)- End

Product. ADOT 415 adds compaction requirements, including a target of 7.0% in- place

air voids, with Upper Limit of 9.0% and Lower Limit of 4.0% in- place air voids. AMEC

applied these requirements in its forensic analysis and found that the failing materials

were not in compliance, which supports the value of the density requirements.

27 Hanson, Douglas I. and Joseph Phillips. “ Forensic Analysis Asphalt Rubber Asphalt Concrete ( ARAC)”

Report No. 1, AMEC Earth & Environmental, Inc., Phoenix, AZ, May 18, 2006.

28 Ibid

29 ADOT. Standard Specifications for Road and Bridge Construction 2000. Section 415

40

3.7.3 Resistance to Moisture Damage

Neither the ADOT 415 AR- AC End Product specification nor the proposed laboratory

mix design procedure addresses testing to evaluate resistance to moisture damage. There

are some issues to be addressed in determining what method and limits to use for such

testing. The standard immersion- compression test is not appropriate for AR- AC

materials, as the unconfined AR- AC specimens slump and deform during conditioning.

AMEC and others have suggested consideration of tensile strength ratio as a criterion for

evaluating resistance to moisture damage. However, further research is needed to assess

whether this approach will do a better job of predicting AR- AC resistance to moisture

damage than it did when ADOT evaluated use of such tests for predicting susceptibility

of conventional asphaltic concrete mixes to moisture damage.

3.7.4 Draft ARIZ 832 ( October 17, 2006) Marshall Method for AR- AC

The proposed mix design method is currently designated as Draft ARIZ 832 ( October 17,

2006) Marshall Mix Design Method for Asphaltic Concrete ( Asphalt- Rubber) [ AR- AC].

It is presented in Appendix H. Technical changes from Version 2 used in the round robin

primarily consist of reducing temperatures for mixing ( aggregate at 325 ± 3° F instead of

330 ± 5° F), and for curing and compaction ( 300 ± 5° F instead of 330 ± 5° F). Other

changes were made to improve clarity and presentation of the text and calculations. The

October 17 draft is currently under review by ADOT and industry and may be revised

during the approval process. Further refinements may be suggested as the AR- AC mix

design procedure is implemented and used, and may include addition of some method of

evaluating resistance to moisture damage.

Decreasing the mixing and compaction temperatures from that used in the Big Bug round

robin may have some related effects on mixture volumetrics. The increased AR binder

stiffness at lower temperatures is likely to increase the air voids contents measured in the

mix design, which would increase design AR binder content. High AR binder contents

are intrinsic to the performance properties of the desired product, as long as they are not

excessively high.

What is most important is that future AR- AC mixes designed according to this procedure

are able to provide the same enhanced performance properties that ADOT has grown to

expect from the pre- 2004 mixes.

41

4. CONCLUSIONS

Based on the results of testing performed in Rounds 1 and 2, and results of the Round

Robin, Draft ARIZ 832 ( October 17, 2006) appears to be an acceptable and appropriate

procedure for the intended purpose. Although mix design results are somewhat variable,

evaluation of the statistics for the same tests applied to conventional asphaltic concrete

materials indicates the measured variability is very similar.

It does not appear that using asphalt- rubber binder makes the testing of the AR- AC

mixtures significantly more variable than the testing of conventional or polymer modified

asphaltic concrete materials. This was a major concern during this study. No extra

laboratory equipment will be required to perform ARIZ 832. However, as for any

bituminous material, experience, properly operating equipment, and good practices are

required to achieve representative results. Additional training may be appropriate for

technicians who are not experienced in working with AR- AC materials.

The most substantial changes from the previous modified ADOT 815c30 AR- AC mix

design procedure are in the preparation and treatment of the Rice specimens. AR- AC

Rice specimens will include mineral admixture and no liquid antistrip will be added. Rice

specimens will be prepared at 6.0% AR binder content and cured at the same time and

temperature as the loose Marshall specimens. Temperatures for mixing, and for curing

and compacting AR- AC specimens have been modified and the allowable ranges are now

tighter to reduce variability. Volumetric calculations are performed according to national

standards. Rebound is now addressed: no confining weights will be used to prevent

specimen rebound, and if rebound is observed after compaction, the specimens will be

discarded and the target aggregate gradation will be adjusted to better accommodate the

AR binder.

Implementation of ARIZ 832 and ADOT 415 began on a limited basis during the 2006

construction season. It appears that there is a “ learning curve” involved in meeting AR-AC

compaction requirements. A combination of favorable ambient temperatures, proper

equipment, and good practices for materials handling and equipment operation are

needed to meet the requirements.

This study has documented that the asphalt- rubber binder is a major factor in AR- AC

volumetrics. This supports experience and practical observations by ADOT personnel

and others who have been involved in AR- AC mix design. Finer rubber gradations in the

AR binder are likely to facilitate AR- AC mix design. Coarse rubber gradations in the AR

binder may interfere with establishing an appropriate aggregate matrix ( target gradation)

and may not permit development of a suitable AR- AC mix design. If this occurs, the first

alternate should be to try using a binder made with a finer rubber gradation. However in

cases where suitably fine crumb rubber is not available, adjustment of the aggregate

gradation may be necessary.

30 Ibid. Section 815c

42

43

APPENDIX A

EXISTING MODIFICATIONS TO ARIZ 815C31

USED FOR AR- AC MIX DESIGNS UNTIL 2006

( VERSION 5- 28- 03)

31 Ibid

Existing Modifications to ARIZ 815c Currently Used for Asphalt- Rubber Mix Designs Version 5- 28- 03

44

Note: This document describes the existing modifications to the ARIZ 815 mix design

procedure that ADOT currently uses in design of Section 413 Asphaltic Concrete

( Asphalt- Rubber) mixes. No changes were made to Figures 1 through 11 that remain in

current use but are not attached to this version for ease of transmittal. MACTEC’s

recommended revisions to ARIZ 815c for use in the proposed mix design procedure

being developed for GAP- Graded Asphalt Rubber Concrete will be presented in a

separate document.

ARIZ 815c

Modified for Asphaltic Concrete ( Asphalt- Rubber)

May 2003

( 23 Pages including Figures 1 through 11)

MARSHALL MIX DESIGN METHOD

FOR ASPHALTIC CONCRETE ( ASPHALT- RUBBER)

( A Modification of AASHTO T 245)

Scope

1. This method is used to design Section 413 Asphaltic Concrete ( Asphalt- Rubber)

mixes using four- inch Marshall apparatus.

Apparatus

2. The apparatus necessary includes all items required to perform the individual test

methods referred to in this procedure as follows:

ARIZ 201c Sieving of Coarse and Fine Graded Soils and Aggregates

ARIZ 210b Specific Gravity and Absorption of Coarse Aggregate

ARIZ 211c Specific Gravity and Absorption of Fine Aggregate

ARIZ 410c Compaction and Testing of Bituminous Mixtures Utilizing Four- Inch

Marshall Apparatus ( see AASHTO T 245 for required equipment)

ARIZ 415b Bulk Specific Gravity of Compacted Bituminous Mixes

ARIZ 806e Maximum Theoretical Specific Gravity of Laboratory Prepared

Bituminous Mixtures ( Rice Test).

Materials

3. ( a) Mineral Aggregate - The mineral aggregate for the asphaltic concrete

shall be produced material from the source( s) for the project. Use of natural sand is not

permitted in asphalt- rubber mixtures.

1) Mineral aggregate from each source shall be tested for compliance to the

project requirements for Abrasion ( AASHTO T 96).

Existing Modifications to ARIZ 815c Currently Used for Asphalt- Rubber Mix Designs Version 5- 28- 03

45

2) The mineral aggregate shall be combined using the desired percentages of

the different produced materials.

3) The composite blend of mineral aggregate shall be tested for compliance to

the grading limits in Table 413- 2 of the specifications according to ( ARIZ

201) Gradation, modified so that the No. 8 sieve is the smallest coarse

sieve.

4) The composite blend of mineral aggregate shall conform to the requirements

of Table 413- 3 of the specifications for Sand Equivalent ( AASHTO T 176)

and for Crushed Faces ( ARIZ 212)

( b) Bituminous Material - The bituminous material used in the design shall be the

asphalt- rubber conforming to the requirements of Section 1009 of the specifications,

which is to be used in the production of the asphaltic concrete. No dilution with extender

oil, kerosene, or other solvents is allowed. The specific gravity of the bituminous

material sha