April 2008
Research Report: UCPRC- RR- 2008- 07
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Authors:
D. Jones, P. Fu, J. Harvey, and F. Halles
Partnered Pavement Research Program ( PPRC) Contract Strategic Plan Element 4: 12:
Full- Depth Reclamation with Foamed Asphalt
PREPARED FOR:
California Department of Transportation
Division of Research and Innovation
Office of Roadway Research
PREPARED BY:
University of California
Pavement Research Center
UC Davis, UC Berkeley
DOCUMENT RETRIEVAL PAGE Research Report: UCPRC- RR- 2008- 07
Title: Full- Depth Pavement Reclamation with Foamed Asphalt: Final Report
Authors: D. Jones, P. Fu, J. Harvey, and F. Halles
Prepared for:
Caltrans
FHWA No.:
CA101069C
Work Submitted Date:
October 30, 2008
Date:
April 2008
Strategic Plan Element No:
4.12
Status:
Final
Version No:
03/ 31/ 10
Abstract:
A comprehensive study on full- depth reclamation ( FDR) of pavements with foamed asphalt has been completed for the
California Department of Transportation by the University of California Pavement Research Center. A literature review
revealed that very little research had been carried out on the reclamation of thick asphalt pavements ( multiple overlays
over a relatively weak base or subgrade). A mechanistic sensitivity analysis was carried out to identify key variables in
the design of recycled pavements consisting primarily of recycled asphalt pavement. The findings of this analysis and
the literature review were used to formulate a work plan for laboratory and field studies to address issues specific to
recycling these thick asphalt pavements.
A number of FDR projects were observed during the course of the study. Material was collected for a comprehensive
laboratory investigation, which identified a number of key issues pertaining to mix design, including appropriate test
methods for California, preparation of specimens ( mixing moisture content and aggregate temperature), asphalt binder
selection, target asphalt and active filler contents, aggregate gradations ( fines content), specimen curing, and the
interpretation of results. Visual assessments and Falling Weight Deflectometer testing were also carried out on selected
projects at regular intervals. The study concluded that FDR with foamed asphalt combined with a cementitious filler is
an appropriate pavement rehabilitation option for California. Projects should be carefully selected with special care
given to roadside drainage. Appropriate mix and structural design procedures should be followed, and construction
should be strictly controlled to ensure that optimal performance and life are obtained from the pavement. The following
recommendations are made:
 FDR with foamed asphalt combined with a cementitious filler should be considered as a rehabilitation option on
thick, cracked asphalt pavements on highways with an annual average daily traffic volume not exceeding 20,000
vehicles. The technology is particularly suited to pavements where multiple overlays have been placed over relatively
weak supporting layers, and where cracks reflect through the overlay in a relatively short time. Higher traffic
volumes can be considered provided that adequate strength and durability can be achieved with the in- place
materials. Alternatively, the recycled layer can be used as a subbase under a new base layer.
 Project selection, mix design, and construction should be strictly controlled to ensure that optimal performance is
obtained from the rehabilitated roadway.
 Full- depth reclamation with asphalt emulsions and partial- depth reclamation with asphalt emulsions and foamed
asphalt should also be evaluated, and guidelines prepared for choosing the most appropriate technology for a given
set of circumstances.
Keywords:
Full- depth recycling, Full- depth reclamation, Deep in situ recycling, Foamed asphalt, Foamed bitumen
Proposals for implementation:
Related documents:
Signatures:
D. Jones
1st Author
J. Harvey
Technical Review
D. Spinner
Editor
J. Harvey
Principal Investigator
T. J. Holland
Caltrans Contract
Manager
ii UCPRC- RR- 2008- 07
DISCLAIMER
The contents of this report reflect the views of the authors who are responsible for the facts and accuracy
of the data presented herein. The contents do not necessarily reflect the official views or policies of the
State of California or the Federal Highway Administration. This report does not constitute a standard,
specification, or regulation.
PROJECT OBJECTIVES
The objective of this project was to develop guidelines for improved mix and structural design and
construction for full- depth reclamation ( FDR) of cracked asphalt concrete with foamed asphalt.
This objective will be met after completion of the following six tasks:
1. Perform literature survey, and technology and research scan.
2. Perform mechanistic sensitivity analysis.
3. Undertake assessment of Caltrans projects built to date based on available data.
4. Measure properties on Caltrans Full- Depth Pavement Reclamation with foamed asphalt projects to
be built in the future.
5. Carry out laboratory testing to identify specimen preparation and test methods, and develop
information for mix design, structural design, and construction guidelines.
6. Prepare interim guidelines for project selection, mix design, structural design, and construction.
This document covers Tasks 1 through 5.
UCPRC- RR- 2008- 07 iii
ACKNOWLEDGMENTS
The University of California Pavement Research Center acknowledges the following individuals and
organizations who shared experiences and/ or provided assistance, information, documentation, or
materials:
 The staff of the UCPRC laboratory who assisted with the preparation and testing of materials during
the laboratory study
 Mr. Joseph Peterson and Ms. Julia Rockenstein, Caltrans
 Ms. Dawn Becky, Caltrans
 Staff from the Caltrans Colusa, Sierraville, and New Cuyama Maintenance Stations
 Prof. Kim Jenkins, University of Stellenbosch, South Africa
 Mr. Dave Collings, A. A. Loudon Consulting Engineers, South Africa
 Prof. Mofreh Saleh, University of Canterbury, New Zealand
 Mr. Hechter Theyse, Council for Scientific and Industrial Research, South Africa
 Mr. Panos Kokkas, Ms. Oleysa Tribukait and Ms. Darlene Comingor, County of Yolo, Department
of Planning and Public Works
 Mr. John Rainey, Rainey Geotechnical
 The staff of Western Stabilization
 The staff of Durham Construction
 Shell, Paramount, and Valero refineries
 Graniterock Company and Granite Construction
iv UCPRC- RR- 2008- 07
UCPRC- RR- 2008- 07 v
EXECUTIVE SUMMARY
A comprehensive study on full- depth reclamation with foamed asphalt has been completed for the
California Department of Transportation ( Caltrans) by the University of California Pavement Research
Center. The study, based on a series of work plans approved by Caltrans, included a literature review, a
mechanistic sensitivity analysis of theoretical California pavement designs that incorporate foamed
asphalt, bi- annual assessments of four full- depth reclamation with foamed asphalt projects, and a
comprehensive, four- phase laboratory study. The project culminated in the preparation of interim
guidelines for project selection, mix design, structural design, and construction ( Full- Depth Pavement
Reclamation with Foamed Asphalt: Guidelines for Project Selection, Design and Construction), which
can be used in conjunction with the South African Guidelines for the Design and Use of Foamed Bitumen
Treated Materials and the Wirtgen Cold Recycling Manual. The California guideline provides specific
information for recycling thick asphalt pavements, and is based on the extensive laboratory testing
program and the assessment of reclamation projects in the state.
A literature review of current practice revealed that, although considerable research has been carried out
on the use of full- depth reclamation with foamed asphalt on pavements consisting of relatively thick
granular layers and thin surface treatments, very little research had been carried out on full- depth
reclamation of thick asphalt pavements with foamed asphalt ( multiple overlays over a relatively weak base
or subgrade). A mechanistic sensitivity analysis was therefore carried out to identify key variables in the
design of recycled pavements consisting primarily of recycled thick asphalt pavement. The findings of the
literature review and the sensitivity analysis were used to formulate a work plan for laboratory and field
studies that would address the issues specific to recycling these thick asphalt pavements. A comprehensive
write- up of the literature was not included in this report as similar reviews have been documented by other
researchers.
A number of recently completed construction projects ( 03- COL- 20, 05- SB, SLO- 33, 07- Ven- 33, 03- SIE-
89) were visited, and construction on projects on state and county routes was observed. Large quantities of
material for laboratory testing were collected from these projects. Visual assessments and Falling Weight
Deflectometer ( FWD) testing were carried out in the spring and fall each year during the course of the
study. Key observations include:
 Some fatigue cracking was evident on sections of the 03- COL- 20 ( PM10.2/ 28.2, EA03- 339004)
project towards the end of the study, some eight years after construction. The project was
considered a success by Caltrans, given that a design life equivalent to about five years of traffic
was expected.
vi UCPRC- RR- 2008- 07
 On the 03- SIE- 89 ( PM20.0/ 29.6, EA03- 0A7004) project, random areas of cracking ( thermal and
fatigue) were observed along the length of the road after about four years of trafficking. The cracks
were sealed the following year. A microsurfacing was applied over the entire section as a pavement
preservation intervention in 2008 ( seven- years after construction).
 On the first Route- 33 project constructed ( 05- SB, SLO- 33- PM0.0/ 12.6, EA05- OA4004), severe
distress in the form of alligator cracking and deformation was observed within 12 months after
construction ( 2005) on a number of sections of the road. A forensic investigation attributed this
distress to a combination of poor drainage ( blocked culverts and filled- in side drains) and the
incomplete drying of the recycled layer ( studies have shown that foamed asphalt- treated layers only
gain strength when the compaction moisture has dried back sufficiently). No active filler was used
in this project, which may have also contributed to the poor initial strength. Areas of deformation
continued to appear throughout the period of evaluation. FWD measurements indicated that these
problems were all associated with weak subgrades and low base stiffness, and not with the
surfacing.
 On the second Route 33 project ( 07- VEN- 33- PM48.5/ 57.5, EA07- 249304), constructed 12 months
later in 2006, no distress was observed apart from some isolated cracking associated with slope
instability. Construction was monitored and a number of concerns were noted with respect to the
addition of water, quality control behind the recyclers, and the lack of attention given to drainage.
 FWD measurements on all of the sections indicated that the asphalt concrete layer stiffness was
only influenced by temperature, with the values comparable between the different test subsections.
Asphalt concrete stiffnesses on distressed and intact subsections on the same project were not
significantly different. The moisture content in the pavement structure had a significant influence on
the foamed asphalt layer stiffness, with differences as high as 40 percent between wet and dry
seasons, which was of a higher relative magnitude than the seasonal variation of subgrade stiffness.
 The effects of temperature on foamed asphalt mix stiffness were quantified by field measurements.
The average temperature sensitivity coefficient for the four sections on 03- COL- 20 and 07- VEN- 33
in Ventura County was 1.3 psi/° F ( 0.016 MPa/° C).
Heavy Vehicle Simulator ( HVS) testing was carried out on one of the projects ( Route 89); however, the
test site was not representative of the mainline ( or typical foamed asphalt pavements) and little useful
information was gained. The HVS study is documented in a separate report.
A comprehensive laboratory investigation was carried out in four phases in conjunction with the field
assessments. Although a comprehensive factorial design was prepared at the beginning of the study, it was
clear that the number of tests required to complete the full factorial was impractical in terms of material
UCPRC- RR- 2008- 07 vii
requirements and laboratory resources. A phased approach was therefore adopted, which entailed a series
of small experiments based on a series of partial factorial experimental designs. By following this
approach, researchers were able to gain an understanding of key issues influencing the performance of
foamed asphalt mixes, and use the findings to adjust the testing program and relevant factorial elements to
make the best use of resources. The testing was carried out on material sourced from two projects. This
material consisted of predominantly recycled asphalt pavement ( RAP) (± 90 percent) together with a small
percentage (± 10 percent) of the natural aggregate from the underlying layer. The aggregates ( RAP plus
underlying layer) were of granitic origin and quartzitic origin for the two projects respectively, and
although representative of a relatively large proportion of California, the results, specifically those
pertaining to active and semi- active fillers, are not necessarily applicable for all materials found in the
state. No recycling projects were undertaken on other representative aggregate types ( e. g., basalt) during
the UCPRC study and therefore tests with these materials could not be undertaken. The phases included:
 Phase 1 included specimen preparation procedures, test methods, and the development and
assessment of analysis techniques. These formed the basis for testing in the later phases of the
study. Foamability characteristics of a selection of California asphalts, and the temperature
sensitivity of mixes were also assessed in this phase. A method to visually evaluate the fracture
faces of tested specimens in a consistent way was developed in addition to these assessments.
 Phase 2 covered investigations into the effects of asphalt binder properties, recycled asphalt
pavement ( RAP) sources, RAP gradations, mixing moisture content, and mixing temperature on
foamed asphalt mix properties. It also investigated different laboratory test methods for assessing
the strength and stiffness characteristics of foamed asphalt mixes, and the development of an
anisotropic model relating laboratory stiffness tests to field stress states. This work was performed
on specimens without active or semi- active fillers so that the effects of the asphalt alone could be
evaluated.
 Phase 3 extended the objectives of Phase 2 with more detailed investigations on variables related to
RAP sources and asphalt binder characteristics.
 Phase 4 focused on the role and effects of active, semi- active, and inert fillers on foamed asphalt
mix performance, as well as issues pertaining to curing.
The findings of the laboratory study identified a number of key issues that have been incorporated into the
mix design guideline. These include appropriate test methods for California, preparation of specimens
( mixing moisture content and aggregate temperature), asphalt binder selection, target asphalt and active
filler contents, aggregate gradations ( fines content), specimen curing, and the interpretation of results.
viii UCPRC- RR- 2008- 07
Based on field and laboratory results, a small analysis was carried out to determine appropriate gravel
factors for foamed asphalt- treated materials. Assuming a mix design of 3.0 percent foamed asphalt and
between 1.0 and 2.0 percent portland cement for the foamed asphalt base, as well as a period of curing, a
Gravel Factor of 1.4 is recommended as an interim for designing foamed asphalt- treated pavements in
California, until additional information from long- term field studies is obtained. This is based on a range
of between 1.32 and 1.47 for wet and dry seasons, respectively.
The study concluded that full- depth reclamation with foamed asphalt combined with a cementitious filler
is an appropriate pavement rehabilitation option for California. Projects should be carefully selected with
special care being given to roadside drainage. Appropriate mix and structural design procedures should be
followed, and construction should be strictly controlled to ensure that optimal performance and life is
obtained from the pavement. Premature failures will in most instances be attributed to poor project
selection ( e. g., weak subgrades and/ or poor drainage), or poor construction ( e. g., poor asphalt dispersion,
incorrect mixing moisture content, poor compaction, and poor surface finish).
The following recommendations are made:
 Full- depth reclamation with foamed asphalt combined with a cementitious filler should be
considered as a rehabilitation option on thick, cracked asphalt pavements on highways with an
annual average daily traffic volume not exceeding 20,000 vehicles per day, provided that an
appropriate pavement design can be achieved. The technology is particularly suited to pavements
where multiple overlays have been placed over a relatively weak base course layer, and where
cracks reflect through the overlay in a relatively short time. Higher traffic volumes can be
considered provided that adequate strength and durability can be achieved with the in- place
materials. Alternatively, the recycled layer can be used as a subbase underneath a new base layer.
 Project selection, mix design, and construction should be strictly controlled to ensure that optimal
performance is obtained from the rehabilitated roadway.
 Full- depth reclamation with asphalt emulsions and partial- depth reclamation with asphalt emulsions
and foamed asphalt should also be evaluated, and guidelines prepared for choosing the most
appropriate technology for a given set of circumstances.
UCPRC- RR- 2008- 07 ix
TABLE OF CONTENTS
EXECUTIVE SUMMARY........................................................................................................................ v
LIST OF TABLES ............................................................................................................................... ... xiii
LIST OF FIGURES ............................................................................................................................... .. xv
1. INTRODUCTION................................................................................................................... ...... 1
1.1 Background..................................................................................................................... .... 1
1.2 Project Objectives................................................................................................................ 1
1.3 Overall Project Organization ............................................................................................... 2
1.4 Structure and Content of this Report ................................................................................... 3
1.5 Terminology ........................................................................................................................ 3
1.6 Measurement Units.............................................................................................................. 4
2. LITERATURE SURVEY.............................................................................................................. 5
2.1 Introduction ......................................................................................................................... 5
2.2 Background..................................................................................................................... .... 6
2.2.1 Unbound Granular Materials................................................................................... 7
2.2.2 Cemented Materials................................................................................................. 7
2.2.3 Asphaltic Materials ................................................................................................. 8
2.3 Foamed Asphalt Properties of Interest ................................................................................ 8
2.4 Structural Design ................................................................................................................. 8
2.4.1 South African Guidelines ........................................................................................ 9
2.4.2 Wirtgen Manual..................................................................................................... 11
2.5 Life- Cycle Costs ................................................................................................................ 11
3. MECHANISTIC SENSITIVITY ANALYSIS........................................................................... 13
3.1 Introduction ....................................................................................................................... 13
3.2 Objectives .......................................................................................................................... 13
3.3 Background..................................................................................................................... .. 14
3.3.1 Roles of Foamed Asphalt and Active Fillers in Mix Properties............................ 14
3.3.2 Transfer Functions................................................................................................. 15
3.4 Sensitivity Analysis ........................................................................................................... 16
3.4.1 Input Variables ...................................................................................................... 16
3.4.2 Responses Under Loading..................................................................................... 17
3.4.3 Structural Response versus Layer Thickness and Stiffness................................... 18
3.4.4 Proposed Regression Model.................................................................................. 18
3.4.5 Example................................................................................................................. 20
3.5 Summary of Observations ................................................................................................. 21
4. ASSESSMENT OF PROJECTS BUILT TO DATE................................................................. 23
4.1 Introduction ....................................................................................................................... 23
4.1.1 Test Sections ......................................................................................................... 24
4.2 Heavy Vehicle Simulator ( HVS) Study on Route 89 ........................................................ 26
4.3 Bi- Annual Monitoring Study............................................................................................. 28
4.4 Visual Assessments ........................................................................................................... 29
4.4.1 Route 20 ( 03- COL- 20) .......................................................................................... 29
4.4.2 Route 89 ( 03- SIE- 89) ............................................................................................ 30
4.4.3 Route 33 ( 05- SB, SLO- 33)..................................................................................... 32
4.4.4 Route 33 ( 07- VEN- 33).......................................................................................... 37
4.5 Other Projects .................................................................................................................... 47
4.6 Falling Weight Deflectometer Assessments ...................................................................... 47
4.6.1 Test Strategy.......................................................................................................... 47
4.6.2 Test Subsections.................................................................................................... 48
4.6.3 Backcalculation Methods ...................................................................................... 50
4.6.4 Subsurface Temperature Calculations................................................................... 50
x UCPRC- RR- 2008- 07
4.6.5 Local Precipitation in 2006 and 2007.................................................................... 51
4.6.6 Resilient Modulus Characterization of Route 20 and Route 33 ( Ventura)............ 51
4.6.7 Resilient Modulus Characterization of Route 33 ( 05- SB, SLO- 33)....................... 58
4.6.8 Summary ............................................................................................................... 62
4.7 Preconstruction Assessment with Falling Weight Deflectometer ..................................... 63
4.7.1 Introduction ........................................................................................................... 63
4.7.2 Using Deflection Modulus to Approximate Subgrade Modulus........................... 63
4.7.3 Comparison of Pre- and Post- Construction FWD Measurements......................... 64
4.7.4 Interim Guidelines for Preconstruction FWD Testing .......................................... 64
4.8 Assessment of Planned Projects ........................................................................................ 65
4.9 Summary of Recommendations......................................................................................... 65
5. LABORATORY STUDY: OVERVIEW .................................................................................. 67
5.1 Introduction ....................................................................................................................... 67
5.2 Laboratory Study Phases ................................................................................................... 67
5.3 Materials ............................................................................................................................ 68
5.3.1 Aggregates............................................................................................................. 68
5.3.2 Asphalt Binders ..................................................................................................... 69
5.4 Test Methods ..................................................................................................................... 69
6. LABORATORY STUDY: PHASE 1......................................................................................... 71
6.1 Introduction ....................................................................................................................... 71
6.2 Experiment Design ............................................................................................................ 71
6.2.1 Materials................................................................................................................ 71
6.3 Assessment of Specimen Preparation Procedures and Test Methods................................ 72
6.3.1 Comparison of Test Methods ................................................................................ 73
6.3.2 Revised Triaxial and Flexural Beam Test Procedures .......................................... 73
6.3.3 Testing under Unsoaked and Soaked Conditions.................................................. 74
6.3.4 Curing.................................................................................................................... 75
6.3.5 Differentiating the Effects of Foamed Asphalt and Active Filler ......................... 75
6.3.6 Mixing Temperature.............................................................................................. 76
6.3.7 Specimen Compaction Methods............................................................................ 76
6.3.8 Summary of Recommendations from Preliminary Testing................................... 77
6.4 Assessment of Foamability Characteristics ....................................................................... 77
6.4.1 Quantifying Foam Characteristics......................................................................... 77
6.4.2 Experiment Factorial ............................................................................................. 79
6.4.3 Test Procedure: General ....................................................................................... 80
6.4.4 Test Procedure: Foaming Temperature Considerations ....................................... 80
6.4.5 Test Procedure: Definition of the Half- Life ......................................................... 81
6.4.6 Test Results ........................................................................................................... 82
6.4.7 Summary of Recommendations for Foamability Characteristics.......................... 85
6.5 Assessment of Temperature Sensitivity of Foamed Asphalt Mix Stiffness ...................... 86
6.5.1 Introduction ........................................................................................................... 86
6.5.2 Background ........................................................................................................... 86
6.5.3 Materials and Test Methods .................................................................................. 87
6.5.4 Effects of Confining Stress, Deviator Stress, and Temperature ............................ 88
6.5.5 Model Development .............................................................................................. 91
6.5.6 Summary ............................................................................................................... 94
6.6 Fracture Face Image Analysis ........................................................................................... 95
6.6.1 Fundamentals of Fracture Face Image Analysis ................................................... 95
6.6.2 Analysis of Foamed Asphalt Mixes ...................................................................... 97
6.6.3 Preferred Test Conditions for FFAC ................................................................... 101
6.6.4 Image Processing Procedure ............................................................................... 101
6.6.5 Laboratory Applications of Fracture Face Image Analysis................................. 103
6.6.6 Summary of Recommendations for Fracture Face Analysis............................... 105
UCPRC- RR- 2008- 07 xi
7. LABORATORY STUDY: PHASE 2....................................................................................... 107
7.1 Introduction ..................................................................................................................... 107
7.2 Experiment Design .......................................................................................................... 107
7.2.1 Test Matrix .......................................................................................................... 107
7.2.2 Materials.............................................................................................................. 107
7.2.3 Specimen Fabrication and Test Procedures......................................................... 111
7.3 Assessment of Strength ................................................................................................... 115
7.3.1 Effects of Unsoaked versus Soaked Testing ....................................................... 115
7.3.2 Effects of Compaction Effort and Density .......................................................... 119
7.3.3 Effects of Binder Grade....................................................................................... 121
7.3.4 Comparison of Different Test Methods............................................................... 123
7.3.5 Summary of Recommendations for Strength Testing ......................................... 124
7.4 Assessment of Stiffness ................................................................................................... 125
7.4.1 Introduction ......................................................................................................... 125
7.4.2 Background ......................................................................................................... 125
7.4.3 Revised Experiment Factorial for Stiffness Assessment..................................... 128
7.4.4 Free- Free Resonant Column Test ( FFRC) .......................................................... 128
7.4.5 Triaxial Resilient Modulus Test .......................................................................... 132
7.4.6 Flexural Beam Test ............................................................................................. 135
7.4.7 Summary ............................................................................................................. 136
7.5 Assessment of Mixing Moisture Content ........................................................................ 137
7.5.1 Introduction ......................................................................................................... 137
7.5.2 Revised Experiment Factorial ............................................................................. 138
7.5.3 Visual Analysis of Loose Mix............................................................................. 139
7.5.4 Fracture Face Observations ................................................................................. 143
7.5.5 Strength and Stiffness Test Results ..................................................................... 144
7.5.6 Discussion ........................................................................................................... 147
7.5.7 Summary of Recommendations for Mixing Moisture Content ........................... 148
7.6 Assessment of Mixing Temperature................................................................................ 148
7.6.1 Introduction ......................................................................................................... 148
7.6.2 Revised Experiment Factorial ............................................................................. 151
7.6.3 Test Results and Discussion ................................................................................ 152
7.6.4 Summary of Recommendations for Aggregate Mixing Temperatures ............... 152
7.7 Relating Laboratory Resilient Modulus Tests to Field Stress States............................... 153
7.7.1 Introduction ......................................................................................................... 153
7.7.2 Constitutive Model.............................................................................................. 153
7.7.3 Finite Element Model.......................................................................................... 155
7.7.4 Virtual FWD Backcalculation ............................................................................. 155
7.7.5 Compaction- Induced Residual Stress and Normalization ................................... 156
7.7.6 General Structural Response Due to Anisotropy................................................. 156
7.7.7 Effects of Other Structural Parameters................................................................ 159
7.7.8 Summary ............................................................................................................. 162
8. LABORATORY STUDY: PHASE 3....................................................................................... 163
8.1 Introduction ..................................................................................................................... 163
8.2 Experiment Design .......................................................................................................... 163
8.2.1 Testing Matrix ..................................................................................................... 163
8.2.2 Materials.............................................................................................................. 163
8.2.3 Testing Parameters .............................................................................................. 165
8.3 Assessment of Loading Rate ........................................................................................... 167
8.4 Assessment of Fines Content........................................................................................... 170
8.4.1 Summary of Recommendations for Fines Content in Mix Designs.................... 172
8.5 Assessment of Asphalt Source......................................................................................... 173
8.5.1 Summary of Recommendations for Asphalt Binder Selection............................ 174
xii UCPRC- RR- 2008- 07
9. LABORATORY STUDY: PHASE 4....................................................................................... 177
9.1 Introduction ..................................................................................................................... 177
9.2 Background..................................................................................................................... 177
9.3 Experiment Design .......................................................................................................... 178
9.3.1 Testing Matrix ..................................................................................................... 178
9.3.2 Materials.............................................................................................................. 178
9.3.3 Testing Parameters .............................................................................................. 180
9.4 Assessment of Cement Content and Fines Content ......................................................... 181
9.4.1 Introduction and Revised Experimental Design.................................................. 181
9.4.2 Results ................................................................................................................. 182
9.4.3 Summary of Recommendations for Cement and Fines Contents........................ 185
9.5 Assessment of Asphalt Content and Fines Content ......................................................... 185
9.5.1 Introduction and Revised Experimental Design.................................................. 185
9.5.2 Results ................................................................................................................. 186
9.5.3 Summary of Recommendations for Asphalt Binder and Fines Contents............ 188
9.6 Assessment of Filler Type and Content........................................................................... 188
9.6.1 Introduction and Revised Experimental Design.................................................. 188
9.6.2 Results ................................................................................................................. 189
9.6.3 Interaction Between Active Fillers and Foamed Asphalt.................................... 192
9.6.4 Summary of Recommendations for Filler Type and Content.............................. 194
9.7 Assessment of Resilient Modulus with Portland Cement................................................ 194
9.7.1 Introduction and Revised Experimental Design.................................................. 194
9.7.2 Test Methods ....................................................................................................... 195
9.7.3 Results ................................................................................................................. 195
9.7.4 Summary of Recommendations for Resilient Modulus Testing ......................... 198
9.8 Assessment of Long- Term Strength Development.......................................................... 198
9.8.1 Introduction and Revised Experimental Design.................................................. 198
9.8.2 Results ................................................................................................................. 198
9.8.3 Summary of Recommendations for Strength Development................................ 200
9.9 Assessment of Potential Shrinkage During Curing ......................................................... 200
9.9.1 Summary of Recommendations for Shrinkage.................................................... 201
9.10 Assessment of Permanent Deformation Resistance......................................................... 201
9.10.1 Summary of Recommendations for Deformation Resistance ........................... 203
9.11 Assessment of Curing Mechanisms................................................................................. 203
9.11.1 Summary of Recommendations for Curing....................................................... 207
10. DERIVED GRAVEL FACTORS FOR FOAMED ASPHALT............................................. 209
10.1 Introduction ..................................................................................................................... 209
10.2 Experimental Design ....................................................................................................... 209
10.3 Derivation of Gravel Factors ........................................................................................... 211
10.4 Recommended Gravel Factors......................................................................................... 213
11. RECOMMENDATIONS FOR GUIDELINES ....................................................................... 215
11.1 Introduction ..................................................................................................................... 215
11.2 Project Selection .............................................................................................................. 215
11.3 Mix Design ...................................................................................................................... 216
11.4 Structural Design ............................................................................................................. 218
11.5 Construction................................................................................................................... . 218
12. CONCLUSIONS AND RECOMMENDATIONS................................................................... 221
12.1 Conclusions ..................................................................................................................... 221
12.2 Recommendations ........................................................................................................... 222
13. REFERENCES..................................................................................................................... ..... 223
APPENDIX A: BACKCALCULATED FWD RESULTS .................................................................. 233
APPENDIX B: PERFORMANCE GRADE CERTIFICATION TESTS ......................................... 251
APPENDIX C: CALCULATION OF THE ANISOTROPY PARAMETER................................... 268
UCPRC- RR- 2008- 07 xiii
LIST OF TABLES
Table 3.1: Mechanistic Analysis Parameters for Each Pavement Structure............................................... 17
Table 3.2: Sensitivity Analysis Regression Results ................................................................................... 19
Table 4.1: UCPRC FWD Sensor Locations ............................................................................................... 29
Table 4.2: Preconstruction FWD Test Sections on Route 33 ( 07- VEN- 33) .............................................. 40
Table 4.3: FWD Test Sections on Route 20 ............................................................................................... 48
Table 4.4: FWD Test Sections on Route 33 ( 05- SB, SLO- 33) ................................................................... 49
Table 4.5: Test Sections on Route 33 ( 07- VEN- 33) .................................................................................. 50
Table 4.6: Summary of Rainfall near Test Sections................................................................................... 51
Table 4.7: Test Results for Route 20 and Route 33 ( Ventura) ................................................................... 56
Table 4.8: Summary of Normalized Foamed Asphalt Layer Resilient Modulus ....................................... 57
Table 4.9: Test Results for Route 33 in Santa Barbara and San Luis Obispo Counties1............................ 59
Table 6.1: Experimental Design for Foamability Characteristics .............................................................. 79
Table 6.2: Foam Characteristics of Different Asphalt Binders .................................................................. 83
Table 6.3: Temperature Sensitivity Test Specimen Detail ......................................................................... 87
Table 6.4: Model Fitting Results for Specimens A- 15, B- 30, and C- 45 .................................................... 92
Table 6.5: Interim Diagnosis Chart for Foamed Asphalt Mix Characteristics ......................................... 104
Table 7.1: Factorial Design for Phase 2 Laboratory Study ...................................................................... 108
Table 7.2: Basic Properties of the RAP Materials Used in Phase 2 ......................................................... 109
Table 7.3: Average Foam Characteristics for Phase 2 Testing................................................................. 111
Table 7.4: Specimen Preparation for Each Batch of Mix......................................................................... 111
Table 7.5: Summary of Flexural and Tensile Strength Test Results ........................................................ 118
Table 7.6: Effects of Compaction Effort on Density and Strength .......................................................... 120
Table 7.7: Effects of Asphalt Grade on Flexural or Tensile Strength ...................................................... 122
Table 7.8: Revised Factorial Design for Stiffness Assessment ................................................................ 129
Table 7.9: Free- Free Resonant Column Unsoaked Stiffness Test Results ............................................... 129
Table 7.10: Triaxial Resilient Modulus Test Results ............................................................................... 132
Table 7.11: Monotonic Flexural Beam Test Results ................................................................................ 136
Table 7.12: Revised Factorial Design for Mixing Moisture Content Study............................................. 138
Table 7.13: Mixing and Compaction Moisture Contents ......................................................................... 139
Table 7.14: Strength Test and FFAC Results for Different Mixing Moisture Contents .......................... 145
Table 7.15: Effect of Aggregate Temperature on Expected Foamed Asphalt Dispersion ( 6).................. 149
Table 7.16: Revised Factorial Design for Mixing Temperature Study .................................................... 151
Table 7.17: Temperature Sensitivity Test Results.................................................................................... 152
Table 7.18: Factorial for General Structural Response Analysis ............................................................. 157
Table 7.19: Factorial for Investigating the Effects of Layer Stiffness ..................................................... 160
Table 7.20: Log- Linear Regression Model Fitting Results ...................................................................... 161
Table 8.1: Factorial Design for Phase 3 Laboratory Study ...................................................................... 164
Table 8.2: Asphalt Binder Description for Phase 3 Testing ..................................................................... 164
Table 8.3: Measured Mixing Moisture Content and Its Variation ........................................................... 165
Table 8.4: Unsoaked ITS Test and Fracture Energy Results for Phase 3 Testing.................................... 168
Table 8.5: Soaked ITS Test and Fracture Energy Results for Phase 3 Testing ........................................ 169
Table 9.1: Factorial Design for Phase 4 Laboratory Study ...................................................................... 179
Table 9.2: Revised Factorial Design for Cement and Fines Content Assessment.................................... 181
Table 9.3: Mixing Moisture Content Measurements for Phase 4, Task 1 ................................................ 182
Table 9.4: Results Summary for Assessment of Cement and Fines Contents.......................................... 183
Table 9.5: Revised Factorial Design for Asphalt and Fines Content Assessment.................................... 186
Table 9.6: Mixing Moisture Content Measurements for Phase 4, Task 2 ................................................ 186
Table 9.7: Results Summary for Assessment of Asphalt and Fines Contents.......................................... 187
Table 9.8: Revised Factorial Design for Filler Type Assessment ............................................................ 189
xiv UCPRC- RR- 2008- 07
Table 9.9: Mixing Moisture Content Measurements for Phase 4, Task 3 ................................................ 189
Table 9.10: Results Summary for Assessment of Filler Type and Content ............................................. 190
Table 9.11: Revised Factorial Design for Resilient Modulus Testing ..................................................... 194
Table 9.12: Phase 4 Triaxial Specimen Mix Design and Test Condition................................................. 195
Table 9.13: ITS Test Results for Preliminary Curing Experiment ........................................................... 195
Table 9.14: Model Fitting Results for Triaxial Resilient Modulus Testing ............................................. 197
Table 9.15: Revised Factorial Design for Strength Development Testing............................................... 198
Table 9.16: Mixing Moisture Content Measurements for Phase 4, Task 5 .............................................. 198
Table 9.17: ITS Results for Strength Development Testing .................................................................... 199
Table 9.18: Shrinkage Measurements for Selected Triaxial Specimens .................................................. 201
Table 9.19: Permanent Deformation Resistance Test Details .................................................................. 202
Table 10.1: Parameters for the Gravel Factor Design Exercise ............................................................... 209
Table 10.2: Empirical Design Results of Pulverized Asphalt Concrete Bases ........................................ 210
Table 10.3: Structure Design Exercise Results ........................................................................................ 211
Table 10.4: Comparison of Design Structures ......................................................................................... 213
UCPRC- RR- 2008- 07 xv
LIST OF FIGURES
Figure 3.1: Assumed load and pavement structure. ................................................................................... 16
Figure 3.2: Contours of the first principal strain for a typical structure in Structure E.............................. 17
Figure 3.3: Strain responses and subgrade rutting life of structures in Structure A................................... 18
Figure 3.4: Typical relationship between strain- at- break and flexural stiffness. ....................................... 21
Figure 4.1: Timeline of construction and assessments. .............................................................................. 28
Figure 4.2: Centerline crack on 03- COL- 20 ( 2006– 2008)......................................................................... 30
Figure 4.3: Fatigue Cracking in inner wheelpath on 03- COL- 20 ( 2007)................................................... 30
Figure 4.4: Fatigue cracking in outer wheelpath on 03- COL- 20 ( 2008).................................................... 30
Figure 4.5: Spalled cracks through open- graded friction course on 03- COL- 20 ( 2008)............................ 30
Figure 4.6: Longitudinal cracks in hill section on 03- COL- 20 ( 2007– 2008)............................................. 30
Figure 4.7: Outer wheelpath cracking on 03- SIE- 89.................................................................................. 31
Figure 4.8: Sealed outer wheelpath cracks on 03- SIE- 89. ......................................................................... 31
Figure 4.9: Thermal cracking on 03- SIE- 89............................................................................................... 31
Figure 4.10: Sealed transverse cracks on 03- SIE- 89.................................................................................. 31
Figure 4.11: Pavement preservation treatment on 03- SIE- 89. ................................................................... 32
Figure 4.12: Early cracking with pumping on 05- SB, SLO- 33 ( April 2006).............................................. 32
Figure 4.13: Severe distress ( 1) on 05- SB, SLO- 33 ( April 2006)............................................................... 32
Figure 4.14: Severe distress ( 2) on 05- SB, SLO- 33 ( April 2006)............................................................... 33
Figure 4.15: Severe distress ( 3) on 05- SB, SLO- 33 ( July 2006)................................................................. 33
Figure 4.16: Digouts on 05- SB, SLO- 33 ( July 2006). ................................................................................ 33
Figure 4.17: New distress next to digout on 05- SB, SLO- 33 ( July 2006). ................................................. 33
Figure 4.18: Filled in side drains on 05- SB, SLO- 33.................................................................................. 34
Figure 4.19: Blocked culvert on 05- SB, SLO- 33........................................................................................ 34
Figure 4.20: Proximity of irrigated fields to damaged road on 05- SB, SLO- 33. ........................................ 34
Figure 4.21: Plough furrows perpendicular to road on 05- SB, SLO- 33...................................................... 34
Figure 4.22: Poor construction joint on 05- SB, SLO- 33............................................................................. 35
Figure 4.23: Construction defect on 05- SB, SLO- 33. ................................................................................. 35
Figure 4.24: Area of thin asphalt concrete on 05- SB, SLO- 33. .................................................................. 35
Figure 4.25: Trash compacted into asphalt concrete on 05- SB, SLO- 33. ................................................... 35
Figure 4.26: New areas of distress on 05- SB, SLO- 33 ( May 2008). .......................................................... 35
Figure 4.27: New distress on previous digout on 05- SB, SLO- 33 ( May 2008). ......................................... 36
Figure 4.28: Distress associated with access road drainage on 05- SB, SLO- 33 ( May 2008). .................... 36
Figure 4.29: Test pit # 1 on 05- SB, SLO- 33. ............................................................................................... 37
Figure 4.30: Test pit # 2 on 05- SB, SLO- 33. ............................................................................................... 37
Figure 4.31: Core showing fines contamination. ( 1).................................................................................. 37
Figure 4.32: Core showing fines contamination. ( 2).................................................................................. 37
Figure 4.33: Fines pumped through base and asphalt concrete.................................................................. 37
Figure 4.34: Preconstruction fatigue ( alligator) cracking on 07- VEN- 33.................................................. 38
Figure 4.35: Preconstruction transverse cracking on 07- VEN- 33.............................................................. 38
Figure 4.36: Preconstruction longitudinal cracking on 07- VEN- 33........................................................... 39
Figure 4.37: Preconstruction cracking associated with slope instability on 07- VEN- 33. .......................... 39
Figure 4.38: Preconstruction patching on 07- VEN- 33............................................................................... 39
Figure 4.39: Preconstruction maintenance overlay on 07- VEN- 33. .......................................................... 39
Figure 4.40: Pre- construction landslide repair on 07- VEN- 33................................................................... 39
Figure 4.41: Drainage structure on 07- VEN- 33......................................................................................... 39
Figure 4.42: Deflection modulus calculated from FWD testing on 07- VEN- 33........................................ 41
Figure 4.43: Prepulverization on on 07- VEN- 33. ...................................................................................... 42
Figure 4.44: Cement kiln dust application on 07- VEN- 33......................................................................... 42
Figure 4.45: Foamed asphalt injection ( Train 1) on 07- VEN- 33. .............................................................. 42
xvi UCPRC- RR- 2008- 07
Figure 4.46: Foamed asphalt injection ( Train 2) on 07- VEN- 33. .............................................................. 42
Figure 4.47: Initial compaction with padfoot roller on 07- VEN- 33........................................................... 43
Figure 4.48: Water application behind recycling train on 07- VEN- 33. ..................................................... 43
Figure 4.49: Shaping and compaction with steel wheel roller on 07- VEN- 33........................................... 43
Figure 4.50: Final compaction with rubber- tired roller on 07- VEN- 33. .................................................... 43
Figure 4.51: Brooming on 07- VEN- 33. ..................................................................................................... 43
Figure 4.52: Temporary striping application on 07- VEN- 33..................................................................... 43
Figure 4.53: Surface ready for traffic on 07- VEN- 33. ............................................................................... 44
Figure 4.54: Area of segregated aggregate on 07- VEN- 33. ....................................................................... 44
Figure 4.55: Area demarcated for rework on 07- VEN- 33.......................................................................... 44
Figure 4.56: Longitudinal crack on 07- VEN- 33. ....................................................................................... 45
Figure 4.57: Longitudinal crack and loss of oversize stone on 07- VEN- 33. ............................................. 45
Figure 4.58: Transverse cracking on 07- VEN- 33. ..................................................................................... 45
Figure 4.59: Shearing in the asphalt concrete on 07- VEN- 33.................................................................... 45
Figure 4.60: Roughness in asphalt concrete on 07- VEN- 33. ..................................................................... 45
Figure 4.61: Cracking around centerline striping on 07- VEN- 33.............................................................. 46
Figure 4.62: Cracking around edge striping on 07- VEN- 33. ..................................................................... 46
Figure 4.63: Debris from slope instability on 07- VEN- 33......................................................................... 46
Figure 4.64: Blocked drain. ( 1) on 07- VEN- 33. ........................................................................................ 46
Figure 4.65: Blocked drain, including excess asphalt concrete from paving on 07- VEN- 33. ( 2).............. 46
Figure 4.66: Longitudinal cracking on 07- VEN- 33 ( April 2007). ............................................................. 47
Figure 4.67: Longitudinal cracking on 07- VEN- 33 ( May 2008). .............................................................. 47
Figure 4.68: Damage associated with landslide ( July 2006)...................................................................... 47
Figure 4.69: Backcalculated Resilient Modulus for Section SR20- A. ....................................................... 52
Figure 4.70: Temperature dependency of backcalculated AC modulus on Route 20. ............................... 53
Figure 4.71: Mean FA Resilient Modulus values after temperature normalization. .................................. 55
Figure 4.72: Conceptual illustration of moisture sensitivity of foamed asphalt modulus. ......................... 57
Figure 4.73: Temperature dependency of backcalculated AC modulus on SR33- SB/ SLO. ...................... 58
Figure 4.74: Subgrade modulus for all sections on Route 33 ( SB, SLO) ( 11/ 2007)................................... 60
Figure 4.75: Foamed asphalt layer modulus for all sections on SR33- SB/ SLO ( 11/ 2007)........................ 61
Figure 4.76: Subgrade modulus for all sections on SR33- SB/ SLO. .......................................................... 62
Figure 4.77: Foamed asphalt layer modulus for all sections on SR33- SB/ SLO. ....................................... 62
Figure 4.78: Comparison between pre- and postconstruction modulus determinations............................. 64
Figure 6.1: RAP gradation for Phase 1 laboratory study............................................................................ 72
Figure 6.2: Correlation between WLB10 thermometers. ........................................................................... 81
Figure 6.3: Two definitions of half- life of asphalt foam. ........................................................................... 82
Figure 6.4: Theoretical and observed foam decay curve............................................................................ 84
Figure 6.5: Load sequence of triaxial resilient modulus test...................................................................... 88
Figure 6.6: Dependency of resilient modulus on bulk stress...................................................................... 89
Figure 6.7: Effect of specimen temperature on resilient modulus.............................................................. 90
Figure 6.8: Interaction of deviator stress and temperature. ........................................................................ 90
Figure 6.9: Relation between resilient modulus and temperature. ............................................................. 93
Figure 6.10: Comparison of measured and predicted resilient modulus. ................................................... 94
Figure 6.11: Microstructure of foamed asphalt mixes................................................................................ 96
Figure 6.12: Tested ITS specimen and resulting fracture faces. ................................................................ 98
Figure 6.13: Effect of asphalt droplet size distribution on FFAC values. ................................................ 100
Figure 6.14: Glare elimination on fracture face images. .......................................................................... 103
Figure 6.15: Typical fracture faces showing different symptoms. ........................................................... 104
Figure 7.1: Phase 2 RAP gradation. ......................................................................................................... 109
Figure 7.2: Visual properties of aggregates from Route 33 and Route 88. .............................................. 110
Figure 7.3: Surface texture of typical RAP particles................................................................................ 110
Figure 7.4: Flexural beam test preparation and configuration.................................................................. 114
Figure 7.5: Effect of side drain water on foam asphalt base stiffness. ..................................................... 116
UCPRC- RR- 2008- 07 xvii
Figure 7.6: Comparison of unsoaked and soaked strength test results..................................................... 119
Figure 7.7: Effect of compaction effort on unsoaked density. ................................................................. 120
Figure 7.8: Effect of compaction effort on soaked ITS strength. ............................................................. 121
Figure 7.9: Effect of binder grade and compaction effort on soaked ITS strength. ................................. 121
Figure 7.10: Effect of binder grade on strength. ...................................................................................... 123
Figure 7.11: Comparison of ITS- 152 mm and UCS test results............................................................... 124
Figure 7.12: Repeatability of FFRC tests. ................................................................................................ 129
Figure 7.13: Correlation of beam and triaxial specimen FFRC resilient modulus values........................ 130
Figure 7.14: Correlation between FFRC resilient modulus and modulus of rupture. .............................. 130
Figure 7.15: Correlation between FFAC and material constants for soaked resilient modulus ............... 134
Figure 7.16: Microscope images of various mixing moisture contents.................................................... 139
Figure 7.17: Soil particles connected by a water bridge........................................................................... 141
Figure 7.18: Fine particle spatial structure at low mixing moisture content ( State- C)............................. 141
Figure 7.19: Particle agglomeration when mixing moisture content is high ( State- D). ........................... 142
Figure 7.20: Fracture faces of specimens with different mixing moisture contents................................. 143
Figure 7.21: Effects of mixing moisture content on FFAC values........................................................... 146
Figure 7.22: Effects of asphalt dispersion on soaked ITS test results. ..................................................... 146
Figure 7.23: Effects of asphalt dispersion on unsoaked ITS test results. ................................................. 146
Figure 7.24: Effects of asphalt dispersion on soaked UCS test results. ................................................... 146
Figure 7.25: Correlations between resilient modulus parameters and FFAC values. .............................. 147
Figure 7.26: Cement temperature (° C) prior to recycling ( cold).............................................................. 149
Figure 7.27: Recycled material ( cold). ..................................................................................................... 149
Figure 7.28: Cement temperature prior to recycling ( warm).................................................................... 150
Figure 7.29: Recycled material ( warm).................................................................................................... 150
Figure 7.30: Poor asphalt dispersion on cold aggregate........................................................................... 150
Figure 7.31: Asphalt strings in recycled material..................................................................................... 150
Figure 7.32: Asphalt globules on recycler tires........................................................................................ 150
Figure 7.33: Expected recycler tire appearance. ...................................................................................... 150
Figure 7.34: Poor surface compaction in areas of recycling in cold temperatures................................... 151
Figure 7.35: Good surface compaction in areas of recycling in normal temperatures. ............................ 151
Figure 7.36: Notation of stresses in a cylindrical coordinate system. ...................................................... 154
Figure 7.37: A typical FEM mesh ( partial) and tensile zones. ................................................................. 157
Figure 7.38: Increase in angular tensile zone ( rtensile_  ) with increasing applied loads ( p). ...................... 158
Figure 7.39: Deflection basins for various loads and α2 values................................................................ 158
Figure 7.40: Backcalculation results for structural response assessment................................................. 159
Figure 7.41: Backcalculation results for all scenarios.............................................................................. 161
Figure 8.1: Phase 3 RAP gradations ( Route 33 material)......................................................................... 165
Figure 8.2: Definition of the fracture energy index.................................................................................. 166
Figure 8.3: Correlation of ITS values at different loading rates............................................................... 167
Figure 8.4: Unsoaked ITS values as a function of fines and asphalt content. .......................................... 170
Figure 8.5: Soaked ITS values as a function of fines and asphalt content. .............................................. 170
Figure 8.6: Soaked ITS fracture energy as a function of fines and asphalt content. ................................ 172
Figure 8.7: Effects of asphalt content on ITS values for different asphalt sources. ................................. 173
Figure 8.8: Effects of asphalt content on ITS fracture energy for different asphalts. .............................. 173
Figure 9.1: Saturation pH levels for various active fillers........................................................................ 180
Figure 9.2: Effect of cement and fines contents on ITS values................................................................ 183
Figure 9.3: Effect of cement and fines contents on fracture energy index............................................... 183
Figure 9.4: Effect of cement and fines contents on ductility index.......................................................... 184
Figure 9.5: Fracture faces of soaked ITS specimens at various cement contents..................................... 184
Figure 9.6: Effect of asphalt and fines contents on ITS values. ............................................................... 187
Figure 9.7: Effect of asphalt and fines contents on fracture energy index. .............................................. 187
Figure 9.8: Effect of asphalt and fines contents on ductility index. ......................................................... 188
Figure 9.9: Effect of filler type and content on soaked ITS results.......................................................... 191
xviii UCPRC- RR- 2008- 07
Figure 9.10: Effect of filler type and content on fracture energy index. .................................................. 191
Figure 9.11: Effect of filler type and content on ductility index. ............................................................. 191
Figure 9.12: Effect of filler type and content on soaked ITS results........................................................ 191
Figure 9.13: Comparison of predicted and measured ITS results. ........................................................... 193
Figure 9.14: Comparison of predicted and measured fracture energy index results. ............................... 193
Figure 9.15: Triaxial Resilient Modulus test results under various conditions. ....................................... 196
Figure 9.16: ITS results for strength development testing in 40° C forced draft oven. ............................ 199
Figure 9.17: Apparatus for measuring shrinkage of cured specimens. .................................................... 201
Figure 9.18: Triaxial permanent deformation test results......................................................................... 203
Figure 9.19: Curing process for foamed asphalt. ..................................................................................... 204
Figure 9.20: Theoretical fracture paths for uncured and cured specimens............................................... 205
Figure 9.21: Fracture face and magnified images of uncured and cured specimens................................ 206
Figure A. 1: Backcalculated Resilient Modulus for Section SR20- A. ...................................................... 234
Figure A. 2: Backcalculated Resilient Modulus for Section SR20- B. ..................................................... 235
Figure A. 3: Backcalculated Resilient Modulus for Section SR33- Ven- A. .............................................. 236
Figure A. 4: Backcalculated Resilient Modulus for Section SR33- Ven- B. .............................................. 237
Figure A. 5: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- A. ....................................... 238
Figure A. 6: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- B......................................... 239
Figure A. 7: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- C......................................... 240
Figure A. 8: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- D. ....................................... 241
Figure A. 9: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- E......................................... 242
Figure A. 10: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- F. ...................................... 243
Figure A. 11: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- G. ..................................... 244
Figure A. 12: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- H. ..................................... 245
Figure A. 13: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- I........................................ 246
Figure A. 14: Backcalculated Resilient Modulus for Section SR33- SB/ SLO- J........................................ 247
Figure C. 1: Cross section of a beam and the strain and stress distributions............................................. 268
Figure C. 2: Equivalent homogeneous beam and stress and strain distributions....................................... 269
UCPRC- RR- 2008- 07 xix
ABBREVIATIONS USED IN THE TEXT
CAL/ APT Caltrans Accelerated Pavement Testing
Caltrans California Department of Transportation
CSB Cemented subbase
CT Computed Tomography ( X- ray)
CTB Cement- treated base
DISR Deep in- situ recycling
DGAC Dense- graded asphalt concrete
DSLR Digital single- lens reflex camera
DCP Dynamic Cone Penetrometer
ESAL Equivalent Standard Axle Load
EKF Extended Kalman Filter method
FWD Falling Weight Deflectometer
FOBack Finite element Open source Backcalculation
FFAC Fracture Face Asphalt Coverage
FFIA Fracture Face Image Analysis
FFRC Free- Free Resonant Column ( resilient modulus or test)
FDR Full- depth recycling/ pavement reclamation
GE Gravel Equivalent
HVS Heavy Vehicle Simulator
HMA Hot- mix asphalt
ITS Indirect Tensile Strength
LEAP2 Layered Elastic Analysis Program
LVDT Linear Variable Displacement Transducer
MMC Mixing moisture content
MDD Multi- depth Deflectometer
OGAC Open- graded asphalt concrete
OMC Optimum moisture content
PPRC SPE 4.12 Partnered Pavement Research Center Strategic Plan Element 4.12
PM Post mile
PMS Pavement Management System
PG Performance Grade binder
RAC- G Rubberized asphalt concrete, gap- graded
RAC O Rubberized asphalt concrete, open- graded
RAP Reclaimed asphalt pavement
RMS Root Mean Square
TSR Tensile Strength Retained
UCS Unconfined or Uniaxial Compressive Strength test
UCPRC University of California Pavement Research Center
xx UCPRC- RR- 2008- 07
CONVERSION FACTORS
SI* ( MODERN METRIC) CONVERSION FACTORS
Symbol Convert From Convert To Symbol Conversion
LENGTH
mm millimeters inches in mm x 0.039
m meters feet ft m x 3.28
km kilometers mile mile km x 1.609
AREA
mm2 square millimeters square inches in2 mm2 x 0.0016
m2 square meters square feet ft2 m2 x 10.764
VOLUME
m3 cubic meters cubic feet ft3 m3 x 35.314
MASS
kg kilograms pounds lb kg x 2.202
TEMPERATURE ( exact degrees)
C Celsius Fahrenheit F ° C x 1.8 + 32
FORCE and PRESSURE or STRESS
N newtons poundforce lbf N x 0.225
kPa kilopascals poundforce/ square inch lbf/ in2 kPa x 0.145
* SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380.
( Revised March 2003)
UCPRC- RR- 2008- 07 1
1. INTRODUCTION
1.1 Background
Full- depth reclamation/ recycling ( FDR), or deep in- situ recycling ( DISR), of damaged asphalt concrete
pavement with foamed asphalt to provide a stabilized base for a new asphalt concrete wearing course is a
pavement rehabilitation strategy of increasing interest worldwide. It offers a rapid rehabilitation process,
with minimal disruption to traffic. Most importantly, it reuses aggregates in the pavement, thereby
minimizing the environmental impacts associated with extraction and transport of new aggregates.
In March 2000 the technology was presented to California Department of Transportation ( Caltrans)
pavement engineers at the South African Pavement Technology Workshop, which was held at the
University of California Pavement Research Center ( UCPRC) facilities in Richmond ( UC Berkeley), as
part of the Caltrans Accelerated Pavement Testing ( CAL/ APT) contract. Caltrans built its first project with
this technology soon after ( a 10 mile [ 16 km] pilot study on Route 20 in Colusa County). Caltrans also
approved a UCPRC study to investigate the use of the technology under California material, traffic, and
environmental conditions.
Most Caltrans FDR projects are performed on pavements with thick, cracked asphalt concrete layers,
which distinguishes California practice from that of other states and countries investigating and using this
technology. Pavement technology in South Africa and Australia typically relies on good quality granular
material or cement- treated base and subbase layers for the primary load- carrying capacity of the
pavement, with the thin asphalt concrete (< 2.0 in. [ 50 mm]) or aggregate surface treatment layers ( chip
seals) providing little or no structural integrity. Consequently, in those countries the recycled material
consists mostly of recycled natural aggregate and cracked cement- stabilized layers, which is accordingly
reflected in their research and experience. Practice in Europe has been intermediate between that of
California and South Africa, with the recycled material generally consisting of a mix of asphalt bound and
natural aggregate materials.
1.2 Project Objectives
The research presented in this report is part of Partnered Pavement Research Center Strategic Plan
Element 4.12 ( PPRC SPE 4.12), titled “ Development of Mix and Structural Design and Construction
Guidelines for Full- Depth Reclamation ( FDR) of Cracked Asphalt Concrete as Stabilized or Unstabilized
Bases” being undertaken for Caltrans by the UCPRC. The objective of the study is to adapt, modify, and
2 UCPRC- RR- 2008- 07
improve existing mix design, structural design, and construction guidelines for full- depth reclamation
( FDR) of cracked asphalt concrete with foamed asphalt to suit California conditions.
1.3 Overall Project Organization
This UCPRC project is a comprehensive study, carried out in a series of phases, involving the following
primary elements ( 1):
 Phase 1
- Literature review, and technology and research scan.
- Mechanistic sensitivity analysis.
 Phase 2
- Assessment of Caltrans projects built to date based on field monitoring and previously collected
data.
- Accelerated Pavement Testing ( Heavy Vehicle Simulator [ HVS]) experiment.
- Assessment of planned Caltrans projects prior to construction.
 Phase 3
- Laboratory testing to identify specimen preparation and test methods, and develop information
for mix design, structural design, and construction guidelines.
 Phase 4
- Project selection, mix design, structural design, and construction guidelines.
Deliverables
The reports prepared during this study document background studies, data from construction, HVS tests,
laboratory tests, subsequent analyses, and recommendations. On completion of the study this suite of
documents will include:
 One first- level report covering the HVS study on Route 89;
 One detailed research report ( this document) detailing the various tasks completed in the study;
 One guideline documenting project selection, mix design, structural design, and construction
procedures; and
 One four- page summary report and one longer, more detailed summary report capturing the entire
study’s conclusions.
A series of conference and journal papers documenting various components of the study have also been
prepared.
UCPRC- RR- 2008- 07 3
1.4 Structure and Content of this Report
This report presents an overview of the work carried out to meet the objectives of the study, and is
organized as follows:
 Chapter 2 provides a summary of the literature.
 Chapter 3 presents findings of the mechanistic sensitivity analysis, which provided direction for
subsequent laboratory testing and structural design considerations.
 Chapter 4 summarizes the bi- annual visual and Falling Weight Deflectometer assessments on four
FDR projects in California.
 Chapter 5 introduces the laboratory study.
 Chapter 6 covers the first phase of laboratory testing, which familiarized the research team with the
equipment, procedures, and test methods, and provided a basic understanding of the attributes of
typical California foamed asphalt mixes.
 Chapter 7 summarizes the second phase of laboratory testing, which included investigations into:
- The effects of asphalt binder properties, recycled asphalt pavement ( RAP) sources, RAP
gradations, and mixing moisture content on foamed asphalt mix properties;
- Assessment of different laboratory test methods for measuring the strength and stiffness
characteristics of foamed asphalt mixes; and
- Development of an anisotropic model relating laboratory stiffness tests to field stress states.
 Chapter 8 provides an overview of Phase 3 of the laboratory study, which extended the objectives
of Phase 2 with more detailed investigations on variables related to RAP sources and asphalt binder
characteristics.
 Chapter 9 details the final phase of laboratory testing, which focused on the role and effects of
active fillers and curing procedures.
 Chapter 10 summarizes the derivation of a recommended Gravel Factor for foamed asphalt- treated
layers.
 Chapter 11 summarizes key issues for consideration in the guideline documentation.
 Chapter 12 provides conclusions and recommendations.
1.5 Terminology
A variety of terms are used for describing the recycling of pavements, including but not limited to full-depth
recycling or reclamation, partial- depth recycling or reclamation, deep in- situ recycling, cold in- place
recycling ( cold foam recycling/ reclamation), and hot in- place recycling. In this document, the terms " full-depth
reclamation," abbreviated as FDR, and " full- depth reclamation with foamed asphalt," abbreviated as
FDR- foamed asphalt or FDR- FA are used throughout.
4 UCPRC- RR- 2008- 07
1.6 Measurement Units
Use of metric units was Caltrans practice when this project was begun, and during much of its execution.
Metric units have always been used by the UCPRC in the design and layout of HVS test tracks, and for
laboratory and field measurements and data storage. Caltrans has recently returned to the use of U. S.
standard units. In this report, English metric and units ( provided in parentheses after the English units) are
provided in general discussion. In keeping with convention, only metric units are used in laboratory and
field data analyses. A conversion table is provided on Page iv at the beginning of this report.
UCPRC- RR- 2008- 07 5
2. LITERATURE SURVEY
2.1 Introduction
Comprehensive literature surveys on full- depth pavement reclamation with foamed asphalt ( FDR- foamed
asphalt) have been undertaken by a number of practitioners ( 2- 5). Another similar general review was
considered unnecessary. Instead, a review of new literature on key issues pertaining to the University of
California Pavement Research Center ( UCPRC) work plan was carried out, summarizing the basic
conclusions of previous research and the conditions under which those conclusions were drawn. Gaps
between current understanding and actual performance observation were identified, together with research
needs for application of the technology under California conditions. Although foamed asphalt stabilization
can be used in both in- place full- depth reclamation ( FDR) and in plant mixes, only the former is
considered in this study.
Soil stabilization with foamed asphalt ( or bitumen as it is referred to in the literature elsewhere) is a
relatively old technology, but has had limited application until recently due to patent restrictions and a
lack of suitable application equipment. Recently, developments in full- depth reclamation equipment, more
stringent environmental and traffic delay concerns, and expiration of the patent has led to increasing
interest in the technology. Recent research and implementation was mostly undertaken in South Africa
and Australia, but a number of states in the U. S. and some European and Asian counties are now also
implementing the technology and reporting on research. The technology was presented to Caltrans
pavement engineers by the UCPRC at a South African Pavement Technology Workshop in 2000. Since
then, the technology has been investigated as a means to recycle cracked asphalt pavement into a
stabilized base, thereby eliminating reflective cracking associated with overlay rehabilitation technologies,
and reducing the quantities of aggregate and the length of construction periods associated with
conventional reconstruction procedures. FDR- foamed asphalt generally also permits placement of the
asphalt overlay after recycling faster than do current FDR technologies using cement and standard asphalt
emulsions. Although extensive state- of- the- practice reviews have been carried out ( 4,5) and relatively
comprehensive guidelines ( 3,6) are available, these are mostly applicable to reclamation of relatively thin
asphalt surfacings over thicker granular or lightly cemented bases. Only limited published research is
available on the use of the technology in recycling thick, cracked asphalt pavements.
6 UCPRC- RR- 2008- 07
2.2 Background
Asphalt or bitumen foaming is a process in which a small quantity of water is injected into hot asphalt,
temporarily transforming it to foam. The viscosity of the asphalt is greatly reduced, facilitating easy
mixing with aggregates or recycled asphalt pavement ( RAP) at ambient temperature. The foaming process
is accomplished in a specially designed expansion chamber after which it is injected from nozzles onto the
loose aggregate. The bubbles break down after a period lasting between a few seconds up to 60 seconds
( depending on the properties of the asphalt, and ambient and aggregate temperatures) after which the
binder returns to its original state.
The technology was first developed at Iowa State University in 1956 by Professor Ladis Csanyi while
researching the viscosity of asphalt binders and the effects of steam injection on this property. Mobil Oil
Australia acquired the patent rights in 1968, and improved the process by using water at ambient
temperature rather than steam, thus making this process more practical for field application.
Foamed asphalt stabilization differs from asphalt emulsion stabilization in a number of ways. Particle
coating differs in that foamed asphalt tends to coat the smaller aggregate particles and fines ( smaller than
0.08 in. [ 2.0 mm]) forming a mastic that adheres to larger particles, whereas asphalt emulsion tends to coat
the larger particles, to which the uncoated fine particles adhere. The strength, stiffness, and water
susceptibility of these two mixes are reportedly similar if the parent aggregates, asphalt content, and active
filler content are all the same ( 7). However, foamed asphalt has been favored in the past due to shorter
curing times and resultant earlier opening to traffic linked to the lower water contents in foamed asphalt
stabilization compared to those in emulsion treatments. Ramanujam and Jones ( 8) reported that foamed
asphalt- treated sections performed better than emulsion- treated sections, which became slick and showed
signs of permanent deformation after rain during construction and prior to sealing. Recent developments
in emulsion technology have apparently addressed some of the past limitations, although limited published
information is available.
Active ( portland cement, lime) and/ or inert ( fly ash, mineral fines) fillers are usually added to foamed
asphalt mixes to improve certain properties, including workability, stiffness, and strength, or to reduce
moisture sensitivity. The behavior of the mix will depend on the application rate of the filler and the
asphalt binder content ( Figure 2.1), and appropriate choices need to be made depending on the desired
result. In California, FDR will primarily be used to rehabilitate cracked pavements and to counter the
effects of reflective cracking from lower layers ( original asphalt concrete wearing course and overlays
and/ or cement treated bases). Different combinations of asphalt binder and filler will result in a base with
properties similar to unbound granular materials ( very low binder and filler contents), cemented materials
UCPRC- RR- 2008- 07 7
( low binder and high active filler content), or asphaltic materials ( high binder and low active filler
content).
2.2.1 Unbound Granular Materials
If the pavement is recycled and compacted without the addition of foamed asphalt or active filler, the new
base will behave in a similar manner to one constructed with conventional granular materials. Although
the binder in the original asphalt concrete may provide some cementation, the stabilizing effect will be
limited because of extensive aging and inconsistent distribution through the new layer. A base constructed
with this material is unlikely to crack, but thicker hot- mix asphalt ( HMA) surfacings may be necessary to
prevent permanent deformation and/ or fatigue associated with lower strength and stiffness of the unbound
materials. The savings on asphalt binder and cement costs are generally insignificant compared to the high
cost of thicker HMA surfacings.
Figure 2.1: Matrix of the basic characteristics of road- building materials. ( 9)
2.2.2 Cemented Materials
When higher percentages of cement ( more than 2.0 percent) and moderate amounts of foamed asphalt
( less than 2.0 percent) are mixed with the RAP, the properties of the treated material will be similar to
8 UCPRC- RR- 2008- 07
those of conventional cement- treated materials. Increasing cement contents correspond to decreasing
stress dependency and moisture susceptibility. However, higher cement contents result in materials that
typically have high stiffness ( resilient modulus) and tensile strength, but are prone to shrinkage, which
may induce cracking. Lower flexibility can also lead to early fatigue cracking. Although, these shrinkage
and fatigue cracks are often discrete, with the cemented material between cracks retaining considerable
stiffness and strength, they tend to eventually reflect through the HMA surfacing, which will require some
form of overlay at a relatively early stage. Elimination of reflection cracking is one of the goals of FDR.
2.2.3 Asphaltic Materials
Higher asphalt contents ( higher than 4.0 percent) with lower cement contents ( less than 2.0 percent) result
in materials with lower stress dependency, little or no shrinkage, and improved fatigue life. However,
these materials are subject to permanent deformation and more rapid fatigue damage of the HMA
surfacing resulting from the relatively high tensile strains associated with the low stiffness of the recycled
base. They are also more sensitive to temperature change.
2.3 Foamed Asphalt Properties of Interest
The performance of a foamed asphalt base is dependent on a number of properties. These need to be
understood in order to ensure that mix- designs are optimal and that construction procedures are adjusted
appropriately. Issues and properties of interest in the UCPRC study include:
 Preparation of representative laboratory specimens ( Sections 6.3, 8.3, and 9.11)
 Moisture sensitivity and testing under unsoaked and soaked conditions ( Section 6.3)
 Foaming properties of the asphalt binder ( Sections 6.4)
 Temperature sensitivity of foam asphalt- treated materials ( Section 6.5)
 Influence of mixing moisture content on foam asphalt distribution ( Section 7.5)
 Strength of foamed asphalt mixes ( Section 7.3 and Chapters 8 and 9)
 Stiffness and fatigue properties of foamed asphalt mixes ( Sections 7.4 and 9.7)
 Influence of fines content on mix performance ( Sections 8.4 and 9.4)
 Influence of asphalt source on mix performance ( Section 8.5)
 Influence of different active fillers on mix performance ( Section 9.6)
 Cracking properties ( Section 9.9)
2.4 Structural Design
The most complete structural design guides for pavement structures with foamed asphalt are published in
the South African Interim Technical Guideline: The Design and Use of Foamed Bitumen Treated
UCPRC- RR- 2008- 07 9
Materials ( 3) and the Wirtgen Cold Recycling Manual ( 6). Empirical design charts and mechanistic-empirical
design guides and equations are provided in those documents. The design equations and charts
in the South Africa guideline were developed based on mechanistic- empirical principles and calibrated
with results from one South African HVS test ( 10) and later updated with results from a second HVS test
on a different recycled roadway ( 11). The design guides in the Wirtgen manual are based on a
combination of South African HVS testing and laboratory and field performance, as well as international
laboratory and field studies.
Limited unpublished research on determining Gravel Equivalent values for foamed asphalt- treated
materials has been carried out by Caltrans.
2.4.1 South African Guidelines
The South African guideline offers two approaches to the structural design of pavements with foamed
asphalt, namely a catalog ( lower volume roads and lower reliability) and a mechanistic- empirical
approach ( higher volume roads and higher reliability).
In the mechanistic- empirical approach, the service life of the foamed asphalt- treated base is divided into
two phases. In the first phase, termed the “ effective fatigue phase,” the stiffness of the treated base
decreases under repetitive loading from a high initial value until a stiffness value similar to the parent
aggregate is reached. The number of load repetitions required to reach this state is termed the “ effective
fatigue life.” The stiffness reduction is attributed to the breaking down of the cohesive bonds. Thereafter,
the stiffness remains relatively constant in a phase termed “ equivalent granular state.” In later research,
these three terms were renamed to “ constant stiffness state,” “ stiffness reduction phase,” and “ Phase- 1
life” ( 11) in order to equate performance of foamed asphalt bases with that of cement- treated bases in line
with terminology used in the South African mechanistic pavement design analysis method ( 12). The
Phase- 1 life is believed to be related to the ratio of maximum principal strain to the strain- at- break of the
treated material in a flexural beam strength test and can be expressed as follows ( Equation 2.1):
  b
Neff a SR   ( 2.1)
where: Neff = phase 1 fatigue life;
SR = strain ratio, where SRε = ε/ εb;
ε = the maximum tensile strain at the bottom of the layer;
εb = the strain- at- break from laboratory flexural beam tests;
a, b = regression constants.
In the following “ constant stiffness phase,” the development of fatigue cracking in the HMA surfacing
will be accelerated due to the reduced base stiffness. Confinement of the underlying layers will also be
10 UCPRC- RR- 2008- 07
reduced. The critical failure mode in this phase is permanent deformation ( rutting), believed to be related
to load repetition, relative density, stress ratio, and the ratio of cement and asphalt contents. Permanent
deformation equations from the South African guidelines and later updates are shown in Equations 2.2 and
2.3:
 C C RD C PS C SR C  cem bit  
PD FB N /
,
10 1 2 3 4 5
30
 1     ( 2.2)
where: NPD, FB = structural capacity ( load repetitions);
RD = relative density;
PS = plastic strain (%);
SR = stress ratio;
cem/ bit = ratio of cement and asphalt contents (%);
C1- C5 = regression constants.
N c SR c c CEM c BIN c RD c SAT c PS c CEM 5 6 7 8
2
2 3 4
3
1 log   (   )     ( 2.3)
where: N = load repetitions;
CEM = cement content (%);
BIN = asphalt binder content (%);
SAT = saturation level (%);
C1- C8 = regression constants.
A major shortcoming of the South African guideline equations is the limited calibration with field
performance ( 10,13). The structures on which the models were calibrated represent only two structure
types. In both calibration projects, recycled materials were aggregate and cement- treated aggregate
respectively, with very little RAP from the thin surface treatments. After recycling, the roads were again
surfaced with chip seals that did not contribute to the structural integrity of the roads. In California, the
pavement structures typically selected for recycling with foamed asphalt will have multiple layers of
asphalt materials ( up to 8.0 in. [ 200 mm] and thicker) and will be surfaced after recycling with at least
2.0 in. ( 50 mm) of HMA. Therefore, in typical South African projects, shear failure at the top of the
treated base will be a more critical failure mode than fatigue ( tension) at the bottom of the layer, and
hence the failure mechanisms assumed in the South African guidelines and the transfer functions based on
them are probably not appropriate for California applications.
The mix designs of the treated materials in the two projects were also similar, with the first having
1.8 percent residual binder and 2.0 percent cement, and the second 2.3 percent residual binder and
1.0 percent cement. These materials would be classified as FB2 ( UCS of 1,400 to 2,000 kPa and ITS of
100 to 300 kPa [ UCS of 200 to 290 psi and ITS of 15 to 45 psi]) or FB3 ( UCS of 700 to 1,400 kPa and
ITS of 300 to 500 kPa [ UCS of 100 to 200 psi and ITS of 44 to 73 psi]) in the South African guideline.
The models were not calibrated against projects with stronger FB1 ( UCS of 1,400 to 2,000 kPa and ITS of
300 to 500 kPa) materials.
UCPRC- RR- 2008- 07 11
An extensive study by Collings, et al. ( 14) on a nine- year- old road recycled with foamed asphalt indicated
considerable inconsistency between actual performance and that predicted by the method in the guideline.
No significant resilient modulus reduction was observed, and after nine years there was no substantial
difference in the stiffness of two identical structures that had significantly different traffic and loading
histories.
The South African structural design method for foamed asphalt- treated layers is currently being rewritten
based on additional research carried out since the original guideline was prepared.
2.4.2 Wirtgen Manual
The Wirtgen manual provides three approaches for structural design, namely structural numbers,
mechanistic- empirical, and stress ratio limits. Choice of method is linked to traffic and required reliability.
The structural number approach is based on the AASHTO Guide for the Design of Pavement Structures
( 15), while the mechanistic empirical approach is based on the South African guideline.
The stress ratio limit approach was developed by Jenkins ( 4) and is based on research performed at the
Delft University of Technology. This research showed that when a granular material in a pavement
structure is subjected to loading, the ratio of the maximum deviator stresses induced in the granular layer
relative to the strength of that material ( i. e., the stress ratio) will determine the rate of permanent
deformation or rutting. Similar findings have been found in a number of other research projects around the
world. Jenkins found that this deviator stress ratio should be limited to between 0.40 and 0.45 for foamed
asphalt materials in order to ensure satisfactory material performance. The method is described in the
Wirtgen manual ( 6).
2.5 Life- Cycle Costs
The determination of accurate life- cycle costs and cost- benefits of recycling pavements with foamed
asphalt as an alternative to more conventional techniques ( overlay or reconstruction) is difficult given that
there is very little documented long- term performance data for foamed asphalt treated roads available.
Therefore, only scenarios based on estimated lives and failure modes can be used to obtain an indication
of the potential benefits.
12 UCPRC- RR- 2008- 07
UCPRC- RR- 2008- 07 13
3. MECHANISTIC SENSITIVITY ANALYSIS
3.1 Introduction
The designs of full- depth foamed asphalt recycled pavements in California to date have been largely
empirical and based on a visual survey of the road, coring, test pits, and laboratory testing focused on
Indirect Tensile Strength ( ITS) and R- value tests. The results have been used to determine the depth of
recycling and to prepare a mix design. Mix designs have typically required between 2.0 percent and
3.0 percent foamed asphalt and between 1.0 percent and 1.5 percent portland cement or other active filler.
Design lives have typically been calculated for five years due to a lack of reliable performance prediction
models and limited practical experience. The first Caltrans full- depth reclamation with foamed asphalt
( FDR- foamed asphalt) section on State Highway 20 in Colusa County built in 2000 exceeded this design
life without the development of any significant distress, indicating that current performance expectations
may be somewhat conservative. However, other projects with design lives of ten years in California and in
other states have shown significant early distresses, indicating knowledge gaps in the key issues
influencing performance. A mechanistic sensitivity analysis was therefore included in the work plan for
the University of California Pavement Research Center ( UCPRC) study ( 1) to identify key properties
affecting the expected performance of materials recycled with foamed asphalt, the expected distress
mechanisms ( failure modes), as well as the likely reasons for the variability of observed performance over
time.
3.2 Objectives
The objectives of this part of the UCPRC study included:
 Identification of the key properties affecting expected performance of materials recycled with
foamed asphalt,
 Identification of the expected distress mechanisms of materials recycled with foamed asphalt, and
 Preliminary estimation of the acceptable ranges of the properties of FDR- foamed asphalt materials
for a range of typical Caltrans rehabilitation pavement structures.
These objectives were met by undertaking a mechanistic sensitivity analysis on a factorial of typical
Caltrans pavement structures. The analysis included materials in the three overlapping classes of FDR-foamed
asphalt materials, namely granular, cemented, and asphaltic materials, and was expected to
identify gaps in the existing knowledge with regard to properties and existing performance models. A
range of properties for each type of material were considered in the analysis, simulating the effects of
14 UCPRC- RR- 2008- 07
different mix designs, and using properties and performance models for existing similar materials. The
following variables were included in the factorial in addition to the FDR- foamed asphalt mix variables:
 Stiffness of underlying layers,
 Thickness of the FDR- foamed asphalt layer, and
 Thickness and stiffness of the asphalt concrete surface layers.
This sensitivity analysis was carried out prior to the laboratory and field tests discussed in the following
chapters, during which the key material properties identified were measured. The models used in this
analysis were proposed by various researchers in the literature, but only very limited validation studies
had been reported. The limitations of this preliminary sensitivity analysis should therefore be considered
when interpreting its results.
3.3 Background
3.3.1 Roles of Foamed Asphalt and Active Fillers in Mix Properties
The asphalt binder and active filler ( e. g., cement) contents are the two main variables in a foamed asphalt
mix design. Depending on the quantities added, mixes from the same parent material may behave as a
granular material ( low asphalt and cement contents), a cemented material ( higher cement content), or an
asphalt- bound material ( higher foamed asphalt content). Mixes in each category have different properties,
are suited to different existing pavement conditions, and will have different inputs in the structural design
( see Section 2.2).
Test results from comprehensive laboratory studies in South Africa ( 16,17) clearly demonstrated the roles
of foamed asphalt and cement in the mix properties. In flexural beam tests, both the stiffness and flexural
strength ( stress- at- break) increased significantly with increasing cement content, but the flexibility ( strain-at-
break) was reduced. Conversely, flexibility was significantly improved by increasing the asphalt
content, but stiffness was reduced. Based on these findings, fatigue of the foamed asphalt layer was
incorporated as the primary distress mechanism in the South African design method ( 3). The transfer
function in the design model uses tensile strain at the bottom of the FDR- foamed asphalt layer as the
critical response, which implies a “ fatigue type” distress, with fatigue life a function of the material
properties ( fatigue resistance or flexibility) and the structural response under traffic load. Increasing the
cement content reduces the tensile strain in the foamed asphalt layer by increasing stiffness at the expense
of flexibility, while an increase in the asphalt content improves flexibility but may also increase strain by
reducing stiffness. A trade- off between asphalt and cement content is therefore required to optimize the
design, which will depend on the project parameters ( e. g., recycling depth, percentages asphalt concrete
and granular base recycled, quality of the subgrade, and local environmental characteristics), and the
project constraints ( e. g., budget and pavement profile requirement).
UCPRC- RR- 2008- 07 15
3.3.2 Transfer Functions
Balancing the stiffness and flexibility of the foamed asphalt layer to achieve maximum service life within
certain constraints was the main focus of this sensitivity analysis. Fatigue of the foamed asphalt layer was
the critical distress mode considered because the tensile strains in the asphalt concrete overlay are
typically relatively small before the foamed asphalt layer has lost most of its stiffness under traffic
loading. Additionally, the rutting of the subgrade was also considered since another important role of the
foamed asphalt layer is to provide protection to the underlying layers. Transfer functions for fatigue in the
foamed asphalt layer and rutting in the subgrade were selected as described below.
Foamed Asphalt Fatigue
The transfer function to calculate the “ effective fatigue life” or “ Phase- 1 life” ( 11) suggested in the South
African guideline is:
    a b t b
f N  10   /  ( 3.1)
where: Nf = effective fatigue life of foamed asphalt layer
εt = the maximum tensile strain at the bottom of the layer
εb = the strain- at- break from laboratory flexural beam test
a, b = regression coefficients related to a reliability requirement ( e. g., for a South African
Category B road where 90% reliability is required, a = 6.499 and b = 0.708).
This transfer function was developed in South Africa based on limited laboratory and HVS testing.
Another more widely- used transfer function for fatigue life of conventional hot- mix asphalt ( HMA) is
shown in Equation 3.2 ( 18).
18.4    4.325 10 3   3.291 * 0.854  N  C    E  f t  ( 3.2)
where: C = a function of air voids and asphalt volume in HMA
| E* | = asphalt mixture stiffness modulus, in psi or kPa/ 6.894
These two transfer functions use the same response variable ( maximum tensile strain εt) but different
material property variables ( εb or | E* |). However, if it is considered that increasing the stiffness | E* | by
adjusting the cement or asphalt contents usually decreases the flexibility ( strain- at- break εb), then the basic
idea is similar. Equation 3.2 was therefore modified for use in the sensitivity analysis as follows
( Equation 3.3):
  1 2
0
    f t FA N  E ( 3.3)
where: EFA = the stiffness or Young’s modulus of the foamed asphalt mix
α0, α1, α2 = regression coefficients as functions of material properties α0> 0, α1, α2< 0
Equation 3.3 was considered more appropriate for use in the sensitivity analysis because EFA is also an
input parameter in a mechanistic analysis, while strain- at- break ( εb) is not.
16 UCPRC- RR- 2008- 07
Subgrade Rutting
Equation 3.4 ( 18) was adopted for subgrade rutting in the sensitivity analysis.
1/ 0.223 0.0105
  

  


v
r N

( 3.4)
where: Nr = rutting life ( in terms of load repetition) of the pavement structure assuming minimal
rutting of the asphalt concrete layer
εv = maximum vertical strain at the top of the layer ( compressive is positive).
3.4 Sensitivity Analysis
3.4.1 Input Variables
Five structure scenarios that could potentially be used in California were analyzed with the foamed asphalt
layer stiffness and thickness as the sensitivity analysis input variables ( Figure 3.1 and Table 3.1). The
values for the existing underlying layers ( subgrade) and the new asphalt concrete wearing course overlay
were fixed for this analysis. Structures A through D were combinations of stiff or soft subgrade, with or
without aggregate subbase. Structure E had a cement- treated subbase layer under the existing asphalt
concrete layer ( this is an unlikely pavement structure in California, but was included for comparison
purposes). The load was a single wheel with 40 kN ( 9,000 lb) vertical load and 700 kPa ( 100 psi) tire
contact pressure. For structure type E, the cement- treated base ( CTB) layer in the original pavement
became the cemented subbase ( CSB) layer after recycling.
The sensitivity coefficients of the tensile strain in the foamed asphalt layer and subgrade rutting life to the
two variables in the structural design ( stiffness and thickness of the foamed asphalt layer) were obtained
by mechanistic analysis and regression.
Single 40 kN wheel with
circular contact area and
700 kPa contact pressure
Stiffness Thickness
Asphalt concrete EAC HAC
Foamed asphalt base EFA HFA
Aggregate subbase or
cement- treated subbase ESB or ECSB HSB or HCSB
Subgrade ESG Infinite
Figure 3.1: Assumed load and pavement structure.
y
x
z
UCPRC- RR- 2008- 07 17
Table 3.1: Mechanistic Analysis Parameters for Each Pavement Structure
Parameter A B StruCct ure D E
EAC ( MPa)
HAC ( mm)
2,000
50
2,000
50
2,000
50
2,000
50
2,000
50
EFA ( MPa)
HFA ( mm)
Variable: 400 ~ 2,000
Variable: 150 ~ 300
ESB ( MPa)
HSB ( mm)
ECSB ( MPa)
HCSB ( mm)
ESG ( MPa)
-
-
-
-
100
250 MPa
250 mm
-
-
100
-
-
-
-
60
250 MPa
250 mm
-
-
60
-
-
3,500 MPa
270 mm
100
Note: The Poisson’s ratios for all the materials are assumed to be 0.35.
3.4.2 Responses Under Loading
The strain responses under the assumed load were calculated using LEAP2 ( Layered Elastic Analysis
Program [ 19]). Full bonding was assumed between all layers.
For Structures A through D, the horizontal strain at the bottom of the foamed asphalt layer immediately
under the center of the load was the maximum first principal strain in this layer, which is consistent with
the assumptions of Equation 3.2. Consequently this strain was used as εt in Equation 3.3.
For Structure E, the analysis was more complicated due to the presence of the stiffer cement- treated
subbase layer under the foamed asphalt layer. Along the symmetry axis where x = 0 and y = 0, there is a
local maximum value of the first principal strain at mid- depth of the foamed asphalt layer. The tensile
strain at the bottom of the layer is relatively small since it is constrained by the cemented layer. The
contours of the first principal strain within the asphalt concrete and foamed asphalt layers for a typical
structure ( with EFA = 800 MPa ( 116 ksi) and HFA = 200 mm [ 8 in.]) are shown in Figure 3.2, where this
local maximum first principal strain is marked as εp, axis. This local maximum value was used as the critical
tensile strain εt in Equation 3.3 for this scenario.
Figure 3.2: Contours of the first principal strain for a typical structure in Structure E.
18 UCPRC- RR- 2008- 07
3.4.3 Structural Response versus Layer Thickness and Stiffness
The effects of EFA and HFA on the output variables, tensile strain of the foamed asphalt layer, and the
rutting life ( calculated in equivalent standard axle loads [ ESALs]) of the subgrade for Structure A are
shown in Figure 3.3, which indicates that as stiffness and thickness of the foamed asphalt layer increase,
the tensile strain in the foamed asphalt layer decreases and rutting life increases. The behavior of
Structures A through D is similar in terms of the effects of EFA and HFA on the output variables.
3.4.4 Proposed Regression Model
Based on the above observations, the relation between the strain responses ( or the life) and the foamed
asphalt layer stiffness and thickness can be expressed by the following regression equation ( Equation 3.5).
The effects of EFA and HFA are different for Structure E, but the equation is still applicable.
0
100
200
300
400
500
600
700
0 500 1000 1500 2000 2500
E_ FA ( MPa)
( microstrain)
H_ FA= 15 cm
H_ FA= 20 cm
H_ FA= 25 cm
H_ FA= 30 cm
t, FA ε
107
106
105
104
103
102
0 500 1000 1500 2000 2500
E_ FA ( MPa)
SG Rutting Life ( repetitions)
H_ FA= 15 cm
H_ FA= 20 cm
H_ FA= 25 cm
H_ FA= 30 cm
( a) Strain responses ( b) Subgrade rutting life
Figure 3.3: Strain responses and subgrade rutting life of structures in Structure A.
   


 


  


 


 
,0
2
,0
0 1 ln , ln ln ln
FA
FA
FA
FA
FA FA E
E
H
A E H A  H  ( 3.5)
where: A( EFA, HFA) = the response ( the tensile strain at the bottom of the foamed asphalt or the
rutting life of the structure)
EFA, 0, HFA, 0 = the stiffness and the thickness of the foamed asphalt layer for a “ standard”
case ( 800 MPa and 20 mm in this study)
A0 = the tensile strain at the bottom of the foamed asphalt or rutting life for the
“ standard” case ( i. e., A0 = A( EFA, 0, HFA, 0)
β1 β2 = regression constants. These two constants can be regarded as “ sensitivity
coefficients.” Each characterizes the sensitivity of the response to a variable.
If HFA is increased by 10%, the tensile strain will increase by 10β1%.
The sensitivity coefficients ( β1, β2) of the tensile strain in the foamed asphalt layer and subgrade rutting life
to the two structural design variables ( stiffness and thickness of the foamed asphalt layer) were derived by
mechanistic analysis and regression. The advantages of increasing the stiffness or flexibility for a given
condition were determined by comparing the sensitivity coefficients and the constant in Equation 3.5.
UCPRC- RR- 2008- 07 19
The regression results for Equation 3.5 are shown in Table 3.2. The R2 values for most cases are larger
than 0.995 which indicates that Equation 3.5 is reasonable.
Table 3.2: Sensitivity Analysis Regression Results
εp. axis or εt. FA
( microstrain)
εv, SG
( microstrain)
Rutting Life
Structure ( Repetitions)
A0 β1 β2 A0 β1 β2 A0 β1 β2
A
B
C
D
E
322
199
380
210
142
- 1.22
- 1.12
- 1.26
- 1.10
0.14
- 0.53
- 0.35
- 0.60
- 0.34
- 1.11
875
363
1,075
446
141
- 1.29
- 0.94
- 1.33
- 0.96
- 0.62
- 0.47
- 0.27
- 0.51
- 0.27
- 0.20
77,401
4,088,002
29,614
1,365,229
253,235,912
5.77
4.21
5.96
4.31
2.80
2.12
1.20
2.31
1.22
0.91
The following observations were made from the regression results.
 For all cases, β1 and β2 for subgrade rutting life were always positive. Increasing the foamed asphalt
stiffness or thickness always increased the rutting life due to the better protection provided to the
subgrade. For the two scenarios without a subbase layer ( Structures A and C), the rutting life for the
standard case was relatively short. Doubling the foamed asphalt stiffness did not improve rutting
life to an acceptable value and these results therefore indicate that the presence of a relatively stiff
subbase is needed to protect the subgrade.
 The presence of a subbase layer under the foamed asphalt layer reduced the tensile strain in this
layer by up to 40 percent for the standard cases ( from 322 μstrain to 190 μstrain or from 380 μstrain
to 210 μstrain). Conversely, the change of subgrade stiffness from 60 MPa to 100 MPa ( 8.7 to
14.5 ksi) with no subbase only reduced the tensile strain by 10 to 15 percent. This confirms the
previous conclusion that a granular subbase layer under the foamed asphalt recycled layer is
beneficial.
 For most scenarios β1 was approximately three times larger than β2. As an example, increasing the
foamed asphalt thickness by 33 percent ( from 6.0 in. to 8.0 in. [ 150 mm to 200 mm]) or doubling
the foamed asphalt stiffness resulted in the same reduction of tensile strain in the foamed asphalt
layer and increase in rutting life. An increase in the thickness of the foamed asphalt layer by 2.0 in.
( 50 mm) might be more appropriate in many instances, since increasing the stiffness would
normally require an increase in the cement content. This decision would, however, depend on
factors such as the comparative costs of increasing the recycled depth versus adding more cement,
the consistency of recycling depth, and the potential for reduced fatigue resistance if the thicker
foamed asphalt layer cannot be adequately compacted.
 For Structures A through D, the presence of an aggregate subbase reduced both β1 and β2, with
much greater impact to β2 compared to β1. With a subbase present, increasing the foamed asphalt
layer stiffness is much less effective than increasing the layer thickness.
20 UCPRC- RR- 2008- 07
 For Structure E, β1 for εt. FA was positive. This implies that increasing the thickness of the foamed
asphalt layer will increase the tensile strain in this layer, which will decrease its fatigue life. The
responses for the standard case and the two sensitivity coefficients are all much smaller than for the
other four structures. The foamed asphalt layer in this structure prevents the propagation of
reflection cracking from the cracked cement- treated subbase, and provides a uniform support to the
asphalt concrete layer. Most of the structural capacity in the pavement is provided by the cemented
subbase. Foamed asphalt bases with granular material properties ( as opposed to asphaltic or
cemented) would be sufficient for this structure.
 For Structure E, the calculated rutting life using Equation 3.4 was significantly higher than
50 million repetitions, which was beyond the range for which this equation was calibrated ( 18).
This implies that rutting in unbound layers is unlikely to occur in a structure with a thick cement-treated
subbase ( note that this structure was included for control purposes and is not typical in
California).
Equation 3.3 can be rewritten to semiquantitatively consider the tradeoff between stiffness and flexibility
on fatigue life of the foamed asphalt layer, as follows ( Equation 3.6):
f t FA lnN ln ln lnE 0 2       ( 3.6)
If A = εt and A0 = εt, 0, then substituting Equation 3.5 into Equation 3.6, results in ( Equation 3.7):
  FA FA
FA
FA
f t E E
H
lnN ln H ln ,0 1 2 2
,0
0 ,0
1 2
1 1
  1     
 
    


 


  

  

  ( 3.7)
where: α1, α2, β2< 0
The benefit in terms of increased fatigue life of the foamed asphalt layer by increasing its stiffness by
adding more cement depends on the value of ( α1β2 + α2). If the value is greater than zero, the treatment
will be beneficial. It should be noted that the values of α1 and α2 may differ for different parent materials,
different compaction levels, and even different cement contents.
3.4.5 Example
The following example uses test results from studies in South Africa ( 16). These results are shown in
Figure 3.4 which shows strain- at- break versus stiffness in flexural beam tests for the same parent material
( ferricrete) with different cement and asphalt contents. Combining these data with Equation 3.3, which
was developed in the same study, a new fatigue transfer function ( Equation 3.8) can be derived in the
same format as Equation 3.3.
UCPRC- RR- 2008- 07 21
1.077 1010    1.23  0.988   f t FA N  E ( 3.8)
where: εt = is the tensile strain in the foamed asphalt layer
EFA = the stiffness of the foamed asphalt layer in MPa
0
500
1000
1500
2000
2500
0 100 200 300 400 500 600 700
Strain- at- Break ( Microstrain)
Stiffness- at- Break ( MPa)
1.8% Asphalt, 2.0% Cement
3.0% Asphalt, 2.0% Cement
3.0% Asphalt, 1.0% Cement
Figure 3.4: Typical relationship between strain- at- break and flexural stiffness.
When comparing Equation 3.8 with Equation 3.3, it can be seen that α1 = - 1.23 and α2 = - 0.988. For
Structures A through D, ( α1β2 + α2) was within the range of - 0.57 to - 0.25. Therefore flexibility of the
foamed asphalt mix was more desirable than stiffness. Doubling the stiffness reduced the fatigue life by
between 25 and 57 percent.
3.5 Summary of Observations
The findings indicated by the results of the sensitivity analysis can be summarized as follows:
 The presence of an aggregate or cement- treated subbase will have a significantly beneficial
influence on the performance of an FDR- foamed asphalt- treated layer and asphalt concrete
surfacing. Reduced life can be expected if the milling depth breaks through the existing aggregate
or cement- treated base into the subgrade. Retaining a portion of the existing base layer should be
considered when identifying candidate projects and preparing structural designs incorporating a
foamed asphalt layer. On roads with thin existing aggregate base layers, consideration can be given
to importing a layer of aggregate base material, spreading it on the surface to the desired thickness,
and then incorporating it into the recycled layer in order to retain the existing base as a subbase in
the new structure.
 Increasing the thickness of the recycled layer ( i. e., increasing the recycling depth) will be beneficial,
provided that adequate compaction can be achieved at the bottom of the layer.
22 UCPRC- RR- 2008- 07
 Foamed asphalt layer designs with lower binder and cement contents ( i. e., similar behavior to
granular materials) should only be considered for pavements with an underlying cement- treated
subbase.
 Depending on certain structural and material characteristics, increasing foamed asphalt stiffness by
adding cement can either