report tm02/01 - validation and revision of …...report no. abtr/rd/tm-02/01 subject area...

Report No. ABTR/RD/TM-02/01

Subject Area Bituminous Material and Mixes

Project No. 8454-000001

Report Date August 2002

Title Validation and Revision of Asphalt Concrete Mix Type Selection and Characteristics Study

Type of Report Final

Author(s) Alberta Transportation, Technical Standards Branch and EBA Engineering Consultants Ltd.

No. of Pages 71 Appendix A – 17 Appendix B – 5

Performing Organization Name and Address EBA Engineering Ltd. 14535 – 118 Avenue Edmonton, AB T5L 2M7

Sponsoring Agency Name and Address Alberta Transportation Technical Standards Branch 2nd Floor, 4999 – 98 Avenue Edmonton, AB T6B 2X3

Supplementary Notes Abstract Current asphalt concrete pavement mix type selection protocols, developed by Alberta Transportation in the late 1980s, replaced an informal system of selecting aggregate properties, asphalt cement grades, and Marshall mix design requirements. Subsequent to their initial development and implementation, several significant developments in pavements engineering (e.g. the Strategic Highway Research Program, updating of Equivalent Single Axle Load (ESAL) factors, and the implementation of segregation specifications) have occurred. This report presents the results of a research study carried out to validate the current mix type selection criteria. A network analysis of the rutting performance of over 6,600 km of primary highways representing 365 paving projects between 5 and 15 years in age formed the basis for the analysis. New protocols and criteria for the selection of mix types, based on design traffic and climate zone for typical highway loadings and conditions, are presented. Mix types are defined by aggregate and mix design criteria to primarily address high temperature rutting performance and durability. A separate protocol was developed for selecting both conventional and Performance Graded (PG) asphalt binders to address low temperature cracking performance and high temperature rutting performance. The results of this study was used by Alberta Transportation to produce a Design Bulletin in July 2003 titled “Revisions to Pavement Design Manual for the Selection of ACP Mix Types and Asphalt Binders”.

Distribution Unlimited

Key Words PG Asphalt Binder Asphalt Mix Types Project Co-ordinator

Peter Ing

ALBERTA TRANSPORTATION DD IISSCCLLAAIIMMEERR The opinions, findings and conclusions expressed in this report are those of the author. The contents do not necessarily reflect the official view or policies of the Government of Alberta. This report does not constitute a standard, specification or regulation. The Government of Alberta does not endorse products or manufacturers. Trade or manufacturer’s names appear herein only because they are considered essential to the object of this document.

VALIDATION AND REVISION OF ASPHALT CONCRETE MIX TYPE SELECTION AND

CHARACTERISTICS STUDY

Prepared by:

ALBERTA TRANSPORTATION TECHNICAL STANDARDS

and

EBA ENGINEERING CONSULTANTS LTD.

AUGUST 2002

- i -

TABLE OF CONTENTS Page EXECUTIVE SUMMARY...........................................................................................................vi 1. INTRODUCTION............................................................................................................. 1

1.1 Background................................................................................................................ 1 1.2 Objectives .................................................................................................................. 2

2. DEVELOPMENT OF PRESENT MIX TYPE SELECTION CRITERIA AND CHARACTERISTICS ....................................................................................................... 3

3. VALIDATION OF PRESENT MIX TYPE SELECTION CRITERIA............................ 4

3.1 Research Methodology.............................................................................................. 4 3.2 Development of Project Database............................................................................. 5

3.2.1 Projects............................................................................................................. 5 3.2.2 Traffic/ESALs .................................................................................................. 5

3.2.3 Actual and Design Mix Types ......................................................................... 6 3.2.4 Climate, Pavement Temperatures .................................................................... 7 3.2.5 Asphalt Binder Stiffness .................................................................................. 7 3.2.6 Rut Data ........................................................................................................... 8 3.2.7 Analysis Sections ............................................................................................. 9

3.3 Analysis .................................................................................................................. 10 3.3.1 Theoretical Rutting Models ........................................................................... 10

3.3.2 Factors Affecting Rutting and Variability of Rutting ....................................11 3.3.3 Definition of a Maximum Rut Index .............................................................13 3.3.4 Asphalt Binder Stiffness ................................................................................ 15 3.3.5 Pavement Structure Type............................................................................... 16

3.3.6 Overlays or New Construction....................................................................... 16 3.3.7 Seal Coat or No Seal Coat.............................................................................. 16 3.3.8 Actual Mix Type ............................................................................................17

3.3.8.1 Actual Mix Type and Rate of ESAL Application Effects ....................... 17

3.3.8.2 Actual Mix Type and Climate Zone Effects ............................................22 3.3.8.3 Mix Types Containing RAP .....................................................................27

3.4 Summary and Conclusions ...................................................................................... 31

- ii -

TABLE OF CONTENTS (cont.,)

. DEVELOPMENT OF NEW MIX TYPE SELECTION CRITERIA.............................. 35

4.1 Marshall Mix Design and Conventional and PG Binders ....................................... 36

4.1.1 New ESAL Groupings ................................................................................... 36 4.1.2 Proposed New Mix Types.............................................................................. 37 4.1.3 Proposed Aggregate and Mix Design Criteria ............................................... 41 4.1.4 New High Temperature Zones....................................................................... 46

4.1.5 Mix Type Selection........................................................................................ 48 4.1.6 Asphalt Binder Selection ............................................................................... 48

4.1.6.1 Rehabilitation of Transverse Cracked Pavements ................................... 51

4.1.6.2 New Construction, Final Stage Paving and Rehabilitation of Non-Transverse Cracked Pavements ............................................................... 51

4.1.7 Design Examples............................................................................................54 4.1.8 Impact Assessment ......................................................................................... 58

4.1.8.1 Mix Types ................................................................................................ 58 4.1.8.2 Asphalt Binder ......................................................................................... 59

4.2 Superpave Mix Design and Conventional and PG Binders.....................................60 4.2.1 Background ....................................................................................................60

4.2.2 Binder Selection.............................................................................................61 4.2.3 Proposed ESAL Groupings ............................................................................61 4.2.4 Mix Type Selection and Design Criteria ....................................................... 61

5. RECOMMENDATIONS FOR FURTHER STUDY....................................................... 68 6. REFERENCES ................................................................................................................ 70

- iii -

Appendix A - Summary of the Development of AT's Present Mix Type Selection Criteria Appendix B - Factors Affecting Rutting Variability Case Studies

- As-Built Binder Properties - Seal Coats - Underlying Pavement Properties

Volume 2 Appendices Volume 2 is a series of Appendices prepared to provide documentation of data used in this research and has not been published. Volume 2 contains the following Appendices: Appendix C - Database Fields Appendix D - 2000 Rut Profiles Appendix E - Populated Database Tables Table 3.1 - Summary of Rut Statistics After 5 to 15 Years Performance for all Analysis

Sections Table 3.2 - Present ESAL Ranges Compared to Allowable ESAL Ranges Based on

Specific Rutting Criteria Table 4.1 - Proposed New Mix Types and Characteristics Table 4.2 - Comparison of Present and Proposed New Mix Types Table 4.3a - Summary of Mix Designs Not Complying with Proposed Criteria Table 4.3b - Summary of Mix Designs Not Complying with Suggested Criteria Table 4.4 - ESAL Criteria for Selection of Mix Types Table 4.5 - Selection of Conventional Asphalt Grades for Rehabilitation of Transverse

Cracked Pavements Table 4.6 - Selection of High Temperature PG Grade for Rehabilitation of Non-

Transverse Cracked Pavements, First Stage and Final Stage Pavement Table 4.7 - Summary of Mix Type Quantities Based on Existing

and New Selection Criteria Based on 2002 Draft Program Table 4.8 - Proposed Superpave Aggregate Criteria Table 4.9 - Proposed Superpave Mixture Criteria Table 4.10 - Recommended Nominal Maximum Size Aggregate for Superpave Mixtures

- iv -

Figures Figure 3.1 - Theoretical Rutting Models Figure 3.2 - Hwy 16:24 EBL near km 6.2 Figure 3.3 - Hwy 16:24 EBL near km 6.2 - close-up of outer wheelpath Figure 3.4 - Hwy 16:24 EBL Rut Profile Figure 3.5 - Cumulative ESALs vs. Rut Index by Rate of ESAL Application

and Climate Zone - Actual Mix Type 1 Figure 3.6 - Cumulative ESALs vs. Rut Index by Rate of ESAL Application






and Climate Zone - Actual Mix Type 7 Figure 3.12 - Cumulative ESALs vs. Rut Index by Design Mix Type








and Climate Zone for Mixes Containing RAP - Actual Mix Type 2 Figure 3.20 - Cumulative ESALs vs. Rut Index by Design Mix Type



and Climate Zone for Mixes Containing RAP - Actual Mix Type 5

- v -

Figure 3.23 - Cumulative ESALs vs. Rut Index by Design Mix Type and Climate Zone for Mixes Containing RAP - Actual Mix Type 6

Figure 3.24 - Determination of ESAL Ranges Corresponding to a Rut Index of 15 mm for Actual Mix Type 2

Figure 3.25 - Determination of ESAL Ranges Corresponding to a Rut Index of 15 mm for Actual Mix Type 4

Figure 4.1 - High Temperature Zones for Mix Type Selection Figure 4.2 - Low Temperature PG Grade for Alberta Weather Station Locations Figure 4.3 - Asphalt Binder Selection Flow Chart

- vi -

EXECUTIVE SUMMARY

Current asphalt concrete Mix Type selection protocols, mix type characteristics and properties were developed by Alberta Transportation in the late 1980s. These replaced an informal system of selecting aggregate properties, asphalt cement grades and Marshall mix design requirements. Subsequent to their initial development and implementation, several significant developments in pavements engineering (e.g. the Strategic Highway Research Program and Superpave PG Binder Specifications and Mix Design), updating of ESAL factors and the implementation of segregation specifications, have occurred. These developments, combined with 10 years of field performance, have led to this study to review and update Mix Type selection protocols. The study was comprised of three phases: 1. Document the background to AT's existing mix type selection criteria. 2. Validate the present mix type selection criteria. 3. Revise or develop new mix type selection protocols including criteria for the selection of

Performance Graded (PG) Binders and Superpave Mixtures based on Alberta experience and conditions.

A network analysis of the rutting performance of over 6600 km of Primary Highways representing 365 paving projects between 5 and 15 years in age formed the basis for the analysis. The results of Phase 2 of the study indicated that the present Equivalent Single Axle Load (ESAL) criteria ranges used as the basis for the selection of Mix Types appear to be generally conservative in terms of providing acceptable high temperature performance. The present ESAL ranges could be increased for all Mix Types without compromising rutting performance. Phase 3 resulted in the development of new protocols and criteria for the selection of Mix Types. Mix Types are defined by aggregate and mix design criteria to primarily address high temperature rutting performance and durability. A separate protocol was developed for selecting asphalt grades to primarily address low temperature cracking performance. These protocols would apply to typical highway loadings and conditions; additional guidelines may need to be developed for urban applications. The implementation of the new protocols will result in the increased usage of 12.5 mm topsize mixes and overall should result in more efficient utilization of aggregate resources and reduced aggregate processing costs. The new protocols will introduce the use of several PG asphalt binders, re-introduce the use of 120-150A and increase the use of 300-400A. Overall, these new

- vii -

protocols should have significant impacts on new pavement construction quality, future maintenance and seal coat needs, and improved pavement service life. The development of these new Mix Type Selection protocols and criteria was based on the performance of projects which have experienced ESAL applications of less than 6 x 106 in the vast majority of cases. However, there are a significant number of projects being designed and constructed today with Design ESALs of 10 x 106 to 20 x 106 or more. These ESAL ranges significantly exceed present performance experience and will require pavement performance monitoring and evaluation in order to provide ongoing validation, verification and necessary modification of the new Mix Type criteria established in this research.

- 1 -

1. INTRODUCTION

1.1 Background Current asphalt concrete Mix Type selection protocols, mix type characteristics and properties were developed by Alberta Transportation (AT) in the late 1980s. These replaced an informal system of selecting aggregate top size, asphalt cement grade, and Marshall mix design requirements. These selection protocols and standards were developed to allow mix types to be selected, based on Design ESALs and climate region, in order to optimize high temperature rutting performance and low temperature cracking performance of asphalt pavements constructed on the primary and secondary highway networks. Subsequent to their initial development and implementation, several significant changes and initiatives have occurred that may affect their appropriateness and technical validity: 1. Changes to TAC Vehicle Weights and Dimension Regulations in 1989 2. The Strategic Highway Research Program (SHRP) and Superpave PG Binder

Specifications and Mix Design 3. The development and implementation of a Segregation Specification in 1993 by AT 4. Updating of ESAL factors (KPMG, 1995). 5. Improved quality of construction through the implementation of EPS (End Product

Specifications). More recently, concerns have been raised by AT and the contracting and consulting engineering sectors regarding the increased use of specific mixes (Mix Types 1 and 2) and the effects of aggregate top size and mix type on segregation potential during paving construction. In view of the previously noted developments combined with over 10 years of field performance since the original design protocols and standards were implemented, the review and updating of mix type selection protocols was considered both important and timely.

- 2 -

1.2 Objectives The objectives of this research study were: Phase 1. Document the background, technical inputs and assumptions related to the

development of present mix type selection criteria, design maps and mix type characteristics.

Phase 2. Validate present mix type selection criteria, including the updating of rutting models, based on analysis of available rutting performance data, and design, as-built, climatic and traffic related properties of projects constructed both prior to and after implementation of present mix type selection criteria.

Phase 3. Revise or develop new mix type selection protocols resulting from the analysis of rutting performance and the results of research on low temperature cracking, and develop and incorporate criteria for selection of SHRP PG Binder and Superpave Mix Design and aggregate properties based on Alberta experience and conditions.

It should be noted that this research study focussed on rural highway loadings and conditions and that additional guidelines may need to be developed for urban applications.

- 3 -

2. DEVELOPMENT OF PRESENT MIX TYPE SELECTION CRITERIA AND CHARACTERISTICS The objectives of this phase of the project was to provide the background, technical inputs and assumptions related to the development of the present mix type selection criteria. Two major investigations (Palsat, 1986) (McMillan, 1989) were carried out by Alberta Transportation in the mid-eighties as part of a co-operative research program with the University of Alberta. These studies focused primarily on evaluating the influences of asphalt cement characteristics on both the low and high temperature performance of a wide variety of pavements constructed across Alberta. The present mix type selection criteria was based on the findings of this research. These design criteria provided AT pavement designers with a more rational approach for selecting asphalt cement grades and aggregate and other mix design parameters based upon anticipated traffic loadings and climatic conditions across Alberta. The present methodology for selecting mix types can be summarized as follows: • The 20 year Design ESALs for the project are calculated. • The project climate zone is selected from the four current climatic zones (A to D) on the

design map developed for this purpose. • The project Asphalt Mix Type is selected on the basis of both Design ESALs and

climatic zone. • Each current Mix Type has specified aggregate and mix characteristics and an

associated asphalt cement grade. A detailed summary of the development of the present mix type selection criteria is presented in Appendix A.

- 4 -

3. VALIDATION OF PRESENT MIX TYPE SELECTION CRITERIA

3.1 Research Methodology The present mix type selection criteria were developed with the objective of specifying asphalt mix, aggregate and asphalt binder properties that would result in rural highway pavements that would provide acceptable rutting performance. It was recognized that improvements in rutting resistance could result in more low temperature cracking, especially on more heavily trafficked highways, due to the limited number of asphalt cement grades available in the mid-eighties. The objectives of this phase of the project therefore were to assess the validity of the present criteria in terms of rutting performance. A network level approach was taken due to the availability of extensive construction inventory and mix design data. Also, continuous rut profile data for both the Secondary and Primary Highway network were available. This comprehensive data provided for an unparalleled research opportunity that only a few years ago would not have been possible. The research methodology adopted was: 1. All Primary Highway paving projects constructed from 1985 through 1995 were

identified. 2. The impacts of changes to ESAL factors on historic traffic data prior to and following

implementation were reviewed. 3. For each identified paving project, the following information was assembled into a

database: • Pavement structure and construction history. • Cumulative ESALs from the time of paving construction to 2000. • 20 year Design ESALs at the time of project construction. • The Actual Mix Type of the asphalt concrete mix used during paving construction

using present mix type selection criteria. • The Design Mix Type of the asphalt concrete mix that would have been selected

using present mix type selection criteria. • Climate Zone. • All year 2000 rut data (100 m reporting interval for both wheelpaths of the tested

lane). • High and low air and pavement temperature data. • Calculated Binder Stiffness based on the original asphalt cement grade.

- 5 -

4. Trend and statistical analyses were carried out in an attempt to correlate variables with rut performance and to develop rut performance models.

5. New ESAL ranges were established for the present four climate zones and Mix Types based on rutting performance.

3.2 Development of Project Database

3.2.1 Projects All paving projects constructed from 1985 to 1995 were identified based on a review of the Pavement Management System (PMS) database. This resulted in the selection of overlay, final paving and new construction pavements constructed prior to and after implementation of the present mix type selection criteria and with 5 years to 15 years of rutting performance, and reflected a broad range in traffic loadings and climate regions. Only Primary Highway projects were selected because the range in ESALs would be greater than for Secondary Highway projects. 3.2.2 Traffic/ESALs AT's Primary 1998 History.xls data file of ESAL statistics was used to obtain ESAL data for the following years: • 1985 • 1987 • 1989 • 1991 • 1993 • 1995 • 1996 • 1997

The ESAL values for the 1998 year within the 1998 data file were not used due to known concerns with inconsistencies with these data. AT's 1999 ESAL statistics were not used for the same reason. ESAL values for the years for which data were not available (i.e. 1986, 1988, 1990, 1992 and 1994) were simply interpolated linearly between the two existing data sets to provide an estimate of ESALs for that year. For the years 1998 through 2000, the 1997 ESAL values were extrapolated using a growth rate of 3%.

- 6 -

3.2.3 Actual and Design Mix Types The following aggregate, asphalt binder and asphalt mix properties were all considered to have an influence to some degree on high temperature rutting performance: • Asphalt Binder properties, e.g. penetration and viscosity, both as supplied and in-situ. • Aggregate properties, e.g. topsize, (% MF,−− 5000), percent fractures of the plus 5000 µm

material, fine aggregate angularity, gradation. • Asphalt Mix Properties, e.g. Marshall Stability and Flow, design air voids, VMA and

voids filled with asphalt, Retained Stability. • As-Built Asphalt Pavement Properties, e.g. asphalt content, % compaction, in-situ air

voids, gradation. It was felt that modeling rutting performance against individual aggregate, asphalt binder and asphalt mix properties would not be practical due to the interactive effects and relationships of the many possible variables. A more practical approach was taken which was to characterize the asphalt concrete mix used on each project in accordance with the present mix type criteria. This would allow the performance of asphalt mixes used prior to the use of the present criteria to be evaluated and compared to asphalt mixes used after the present criteria were implemented. AT Construction Quality Assurance Summary Reports for 1985 through 1995 and the Marshall Stability Test System Index Report were used to assemble the following data for each paving project: • Marshall Mix Design Number • Number of Blows • Aggregate Designation and Class and % passing the 12.5 mm sieve of the reported

design gradation. This information was used to determine the Actual Aggregate Class. For asphalt mixes that used a Des 1 Class 16 aggregate, if the % passing the 12.5 mm sieve was ≥95%, the aggregate was classed as 12.5 mm; if <95%, it was classed as 16 mm.

• % Manufactured fines added (if available); this was used to estimate the % MF,-5000. • % Reclaimed Asphalt Pavement (RAP); asphalt mixtures containing RAP were

analyzed separately. • Asphalt Cement Grade

- 7 -

This information was used to determine the "Actual Mix Type" used on the project based upon the present criteria. For each project, the 20 year Design ESALs were used to determine the "Design Mix Type" using the present Design Map for selecting the climate zone. This would correspond to the mix type that would have been selected using the present criteria. It should be noted that the "Actual Mix Type" and "Design Mix Type" may not be the same on every project. 3.2.4 Climate, Pavement Temperatures Temperature data from the weather stations available within the LTPPBind computer program (FHWA, 1999) were used for determining high air temperatures for each project. T20mm pavement temperatures were selected as the appropriate temperature value to use for subsequent analysis. T20mm temperatures were calculated on the basis of the original SHRP equation:

78.17)9545.0)(2.422289.000618.0( 220 −++−= LatLatTT airmm

Where:

T20mm = high pavement design temperature at a depth of 20 mm Tair = seven-day average high temperature, °C Lat = the geographical latitude of the project in degrees

The T20mm temperature was determined at a reliability of both 50% and 98%. 3.2.5 Asphalt Binder Stiffness Historical AT asphalt test results were examined to provide an overview of the asphalt rheology that might be expected for the various asphalt grades for the years relative to the projects selected. Following this review, average values were selected for penetration @ 25°C, absolute viscosity @ 60°C and kinematic viscosity @ 135°C for each asphalt grade (i.e.: 150-200A, 200-300A, 300-400A). This rheology data was plotted on a Bituminous Test Data Chart and used to extrapolate a low temperature penetration value for each grade. The conventional penetration value (@ 25°C) and the extrapolated value for

- 8 -

0°C were used as input to the Shell Bands program (Shell, 1990) to calculate the high temperature binder stiffness. The binder stiffness was calculated for a loading time of 0.2 seconds over a range of temperatures. As the intent was to have a relative stiffness measure for each project, the slow loading time used was considered acceptable. (It can be noted that the original work (as reported in the Appendix) was based on a loading rate of 0.5 seconds). This stiffness versus temperature data were then used to develop an equation for stiffness as a function of temperature which allowed specific stiffness values of the original asphalt cement grade reported in the project mix design to be calculated for each analysis section in the database as a function of the T20mm temperature. 3.2.6 Rut Data The rut depth information collected by Alberta Transportation on the Primary Highway network in 2000 used a vehicle-based inertial profiling system with a 5-point laser rut bar. The following data were available for the entire network: • average outer wheelpath rut depth for each 100 m reporting interval • average inner wheelpath rut depth for each 100 m reporting interval. For each analysis section, the average value of both the outer wheelpath rut and inner wheelpath rut (based on each 100 m reporting interval) were input into the database. In addition, the maximum rut depth for each 100 m interval was determined by selecting the greater of the inner and outer wheelpath value and recording the higher value as the maximum rut. The average and standard deviation of the maximum rut values were determined for each analysis section. (An analysis of the data indicated that the average value of the standard deviation of 100 m average rut depths was about 1.7 mm.) The average maximum rut value plus one standard deviation was used as the rut index for all subsequent analysis. In excess of 75,000 individual rut measurements were included in the overall database. This represented over 7,500 km of Primary Highways. Selected summary statistics grouped by the total numbers of ESALs applied from the time of most recent paving to year 2000 are presented in Table 3.1. Note that this includes all paving projects included in this research which varied in age from 5 to 15 years.

- 9 -

Table 3.1 Summary of Rut Statistics After

5 to 15 Years Performance for all Analysis Sections ESAL Group Average of 100 m Maximum

Rut Value 1 (mm)

Average of 100 m Average Rut Value 2

(mm) ≤500,000 2.8 1.8

>500,000 to ≤1,000,000 3.2 2.3 >1,000,000 to ≤3,000,000 3.7 2.8

>3,000,000 to ≤6,000,000 5.8 4.2 >6,000,000 5.8 4.4

All Groups Combined 3.5 2.5

1 the Maximum Rut Value is the greater of the inner and outer wheelpath rut 2 the Average Rut Value is the average of the inner and outer wheelpath rut

Previous research carried out in the mid-eighties (McMillan, 1989) indicated that rutting was not a significant pavement distress except on relatively high traffic primary highways. The data presented in Table 3.1 would also indicate that the past rutting performance was not a significant system wide pavement distress. 3.2.7 Analysis Sections The database included records for each inventory section as defined in the PMS database. This resulted in multiple records for the same project typically dictated by pavement width changes, and different rut index values for each inventory section even if other project-related attributes were constant. Rather than use the inventory sections, individual analysis sections were identified for multiple contiguous inventory sections where the following attributes or values were the same: • control section number • direction or lane code • year of paving • Marshall Stability Test (MST) number • cumulative ESALs Any project where the MST design reported that Reclaimed Asphalt Pavement (RAP) was used was excluded from the initial analysis. All analysis sections less than 250 m in length were also excluded.

- 10 -

The analysis incorporated a total of 773 analysis sections representing over 6600 km of Primary Highways consisting of: • 34 sections (293 km) were identified as being constructed with a Type 1 mix. • 117 sections (1061 km) were identified as being constructed with a Type 2 mix. • 149 sections (1331 km) were identified as being constructed with a Type 3 mix. • 220 sections (1580 km) were identified as being constructed with a Type 4 mix. • 194 sections (1705 km) were identified as being constructed with a Type 5 mix. • 57 sections (666 km) were identified as being constructed with a Type 6 mix. • 2 sections (18 km) were identified as being constructed with a Type 7 mix.

3.3 Analysis The objectives of the analysis activities were to identify any trends of Actual Mix Types, cumulative ESALs, climate zone and other factors with rutting performance, and, if possible, develop rutting performance models that could be used to revise or develop new Mix Type Selection Criteria. 3.3.1 Theoretical Rutting Models The present mix type selection criteria was developed on the basis that each Mix Type would provide a similar level of rutting performance for the Design ESALs and climate conditions it was selected under. This concept is presented in Figure 3.1.

- 11 -

Figure 3.1 Theoretical Rutting Models

These theoretical rutting models demonstrate the following: • within a given Mix Type, the cumulative ESALs required to achieve a critical rutting

index increases as the climate zone changes from Zone A to Zone D, i.e. as the summer temperatures decrease.

• as aggregate and asphalt mix properties are enhanced, i.e. moving from Mix Type 6 to Mix Type 2, the cumulative ESALs required to achieve a critical rutting index increases.

3.3.2 Factors Affecting Rutting and Variability of Rutting The following factors and their assumed influence on high temperature rutting performance were identified in a qualitative fashion (all other factors being equal) as: • Traffic - as ESALs increase, rutting increases • Asphalt Binder Stiffness - as Stiffness increases, rutting decreases • Pavement Temperature - as temperature increases, rutting increases • Aggregate Top Size - as topsize increases, rutting decreases • Manufactured Fines - as the percent of manufactured fines increases, rutting decreases • % Fractures - as the % Fractures increases, rutting decreases

- 12 -

• No. of Blows used in the Mix Design - as the number of blows increases, the design asphalt content decreases and rutting decreases.

• Traffic Speed – as speeds reduce, rutting increases. For all individual analysis sections identified, a preliminary trend analysis was carried out to assess project rut index statistics based on cumulative ESALs for different Mix Types and climatic zones. This analysis indicated a very high variability in rutting performance for each Mix Type with no apparent trends evident. Variation in the following factors could affect rutting variability within a project with uniform traffic, a uniform most recent rehabilitation strategy and a single mix design: • underlying pavement structure • actual overlay thickness • % compaction • asphalt content • longitudinal profile, e.g. grades • seal coat • rut shape • traffic wander • wander of data collection vehicle. Variation in the following factors could affect rutting variability between projects with similar traffic and the same reported mix types: • ESAL factors • climate • as-built binder properties • seal coat • rut shape. The potential influence of as-built binder properties, seal coats and underlying pavement properties on rutting performance are demonstrated in three case studies included in Appendix B. Therefore, it should be recognized that there may be many factors other than cumulative ESALs and mix type characteristics that can influence rutting performance that cannot be accounted for directly in the analysis.

- 13 -

3.3.3 Definition of a Maximum Rut Index It was recognized that it would not be possible to design an asphalt concrete mixture that would provide infinite resistance to traffic loadings. Accordingly, it was considered necessary to identify a "design" rut value. This value could be considered the maximum value that when exceeded might trigger a preservation or rehabilitation treatment. Rut values below this value would be considered "tolerable". However, it is recognized that it should be an objective to be able to design an asphalt mixture, within economical and practical limits, to provide minimal rutting over the pavement's service life. A maximum tolerable rut index value of 15 mm (the rut index was calculated by first selecting the maximum of the inner or outer wheelpath rut depth and averaging these values throughout the section, and adding one standard deviation to this average value) was selected based on engineering judgement and not safety considerations. It can be noted that the original research and mix type selection, as documented in Appendix A, considered limiting rutting values of 5 and 10 mm in the development of the selection criteria. As these values were based on rutting models, they represent predicted average values. The analysis using the maximum rut index (discussed later in this Section), considered the upper range of the calculated values, rather than a statistical model; therefore, the index as developed for this study is considered to represent similar rutting levels as the original work. Figures 3.2 and 3.3 present photographs of the eastbound driving lane of Hwy 16:24 near km 6.2. The variation in average rut depth based on a 100 m reporting intervals is presented in Figure 3.4. The ruts in the vicinity of km 6.2 would roughly correspond to the selected maximum rut index value of 15 mm.

- 14 -

Figure 3.2 Hwy 16:24 EBL near km 6.2

Figure 3.3 Hwy 16:24 EBL near km 6.2 - close-up of outer wheelpath

- 15 -

Figure 3.4 Hwy 16:24 EBL Rut Profile

It has been reported by others (Willis, 2000) that tire hydroplaning potential exists with a water depth of about 6 mm or greater. In consideration of a 2% pavement cross-slope, this 6 mm water depth could be achieved with a 15 mm rut depth. This value compares with the maximum tolerable rut index value of 15 mm selected based on the average plus one standard deviation. 3.3.4 Asphalt Binder Stiffness The model form identified in the original research, discussed in Section A.4 in Appendix A, was used to evaluate the relationship between rut performance, cumulative ESALs and original asphalt binder stiffness for all analysis sections. Unlike the original research, the correlation obtained was very poor indicating that the variation in the rutting data was such that a statistical meaningful model to describe measured ruts may not be possible. Potential reasons for these variations were discussed previously. Notwithstanding, the analysis sections were grouped in ranges of binder stiffness for the purpose of visually assessing any trends in the rutting statistics. The use of binder stiffness in the analysis allows the interactive effects of binder rheological properties and high

- 16 -

temperature climatic effects to be evaluated together. It was observed that higher stiffness values for the binder could be observed to generally correspond to lower rut values. This relationship is not unexpected as stiffer asphalt binders (e.g. 150-200A) are used in warmer climate regions and for higher Design ESALs. However the overlap of the data distributions did not allow this observation to be considered as meaningful within the context of developing a predictive model. 3.3.5 Pavement Structure Type The analysis sections were grouped according to the underlying pavement structure type, e.g. Full Depth pavement, granular base or soil cement base, to ascertain whether any better trends would result than had been observed for the larger data set. This evaluation of the data showed similar levels of scatter for all base types and it was concluded that the pavement structure type did not have a significant influence on rut performance. This observation is consistent with the underlying premise adopted for this work that the measured rutting was primarily a function of the mix and aggregate characteristics of the most recently placed asphalt concrete layer. 3.3.6 Overlays or New Construction The analysis sections were grouped based on whether the most recently placed asphalt concrete layer was an overlay or new construction. Evaluation of the data showed similar scatter for both applications and it was concluded that the difference of overlay versus new construction did not have a significant influence on rut performance. 3.3.7 Seal Coat or No Seal Coat The analysis sections were grouped based on whether or not the most recently placed asphalt concrete layer had been seal coated. It was hypothesized that a recent seal coat application could provide a temporary rut repair and that older seal coats could exacerbate the measured rutting due to chip embedment in wheelpath locations. The evaluation of the data showed similar scatter for all seal coat scenarios and it was concluded that on a network level, that the existence of a seal coat did not have a significant influence on rut performance. However, as discussed in Appendix B, there is a potential for the performance of a seal coat to affect rutting performance within a project.

- 17 -

3.3.8 Actual Mix Type The discussions presented in the previous section concluded that asphalt binder stiffness, pavement structure type, application as an overlay or new construction, and seal coat effects did not appear to have an observable influence on measured rutting performance. Subsequent analysis focused on evaluating the effects of Actual Mix Type, Climate Zone and cumulative ESALs on the measured rutting performance of all analysis sections. Projects where Reclaimed Asphalt Pavement (RAP) was used, were analyzed separately. 3.3.8.1 Actual Mix Type and Rate of ESAL Application Effects The interpretation of the analysis results was complicated by the fact that cumulative ESALs from the year of most recent paving to the year 2000 for each project was a function of both the historical daily ESALs as well as the age of the project. For example, the following two actual projects have about the same cumulative ESALs from the year of most recent paving to the year 2000:

Project Year of Paving 20 Year Design ESALs

Total Cumulative ESALs to 2000 from

Year of Paving

Average ESALs per year

Hwy 1:20 1985 4.8 x 106 3.1 x 106 0.21 x 106 Hwy 2:30 1995 16.9 x 106 3.3 x 106 0.66 x 106

In this example, although both projects have carried the same number of ESALs, the rate of ESAL applications on Hwy 2:30 is about three times greater than on Hwy 1:20. Further, even though the total ESALs applied on both projects is the same, it could be expected that higher ruts would develop on Hwy 2:30 assuming all other factors being equal because the pavement is younger and not as stiff due to lesser environmental-related aging. The effects of rate of ESAL applications are presented in Figures 3.5 through 3.11 for each Actual Mix Type. Note that only mix types where the Actual Mix Type is equal to or lower than the Design Mix Type have been included. For example, if the Actual Mix Type was 4, only cases where the corresponding Design Mix Type was 4, 3, 2, and 1 are plotted. This therefore excludes analysis sections where a Mix Type 4 was used but a Mix Type 5, 6, 7 or 8 would have been selected based on the existing selection criteria. This was to exclude the performance of "over-designed" sections from the analysis.

- 18 -

Each point on Figures 3.5 through 3.11 represents the 2000 rut index (maximum average plus one standard deviation) and corresponding cumulative ESALs from the year of most recent paving to the year 2000 for each analysis section. Also, for each analysis section point, the rate of ESAL applications (based on four ranges of <50,000 ESALs/year, 50,000 to 100,000 ESALs/year, 100,000 to 500,000 ESALs/year and >500,000 ESALs/year) and the climate zone (based on existing criteria) are identified by different symbols. An overall review of all data in Figures 3.5 through 3.11 indicates: • Higher rates of ESAL applications are associated with higher cumulative ESAL values. • There are no trends that suggest that higher rates of ESAL application are associated

with higher rut index values.

- 19 -

Figure 3.5 Cumulative ESALs vs. Rut Index by Rate of

ESAL Application and Climate Zone - Actual Mix Type 1

Figure 3.6 Cumulative ESALs vs. Rut Index by Rate of

ESAL Application and Climate Zone - Actual Mix Type 2

- 20 -

Figure 3.7 Cumulative ESALs vs. Rut Index by Rate of ESAL Application

and Climate Zone - Actual Mix Type 3



- 21 -





- 22 -



3.3.8.2 Actual Mix Type and Climate Zone Effects The effects of climate zone are presented in Figures 3.12 through 3.18 for each Actual Mix Type. Each point on Figures 3.12 through 3.18 represents the 2000 rut index (maximum average plus one standard deviation) and corresponding cumulative ESALs from the year of most recent paving to 2000 for each analysis section. Within each Figure, the Design Mix Type and the climate zone (based on existing criteria) are identified by different symbols. A large scatter of points is noted with no apparent trend that would suggest that the rutting performance could be statistically modelled. Figures 3.12 through 3.18 were reviewed and based on a visual interpretation, a line was established that defined an upper range of rut index vs. cumulative ESALs for each climate zone. This upper envelope was extrapolated beyond the existing data points based on engineering judgement. Virtually all data points for a given climate zone fall below this line. Therefore, for a given mix type, it can be reasonably concluded that a maximum rut index value of 15 mm over the range of cumulative ESALs represented for the analysis sections analyzed, would not be exceeded.

- 23 -

An overall review of all the data indicates: • There is a high variability in rutting performance within a given Actual Mix Type. • The distribution of rut index values for Actual Mix Types 1 and 2 are very similar. For

Actual Mix Types 1, the maximum rut index values are about 10 mm to 12 mm; however, maximum cumulative ESALs are about 5 x 106. Similarly for Mix Types 2, maximum values are about 10 mm to 12 mm with no rut performance data above about 6 x 106 cumulative ESALs. For Mix Types 2, analysis sections with the highest rut index values, i.e. >7 mm, would have been designed as Mix Types 1 using the present criteria.

• For Actual Mix Types 3, there is a wide distribution of rut index values with maximum rut index values in the 12 mm to 15 mm range and maximum cumulative ESALs up to about 8 x 106. This higher cumulative ESAL range reflects the greater use of this mix type in the mid- to late-eighties and virtually no use after the present criteria were introduced. Analysis sections with the highest rut index values, i.e. >8 mm, would have been designed as Mix Types 1 using the present criteria.

• For Actual Mix Types 4, maximum rut index values are in the 12 mm to 15 mm range and maximum cumulative ESALs are up to about 5 x 106. Analysis sections with the highest rut index values, i.e. >8 mm, would have been designed as Mix Types 1 or 2 using the present criteria.

• For Actual Mix Types 5, the vast majority of rut index values are below about 8 mm. Most of the analysis sections with rut index values greater than 8 mm would have been designed as Mix Types 1, 2 or 4 using the present criteria.

• For Actual Mix Types 6, maximum rut index values are in the 10 mm to 12 mm range. Analysis sections with rut index values greater than 8 mm would have been designed as Mix Types 2, 4 or 5 using the present criteria. There are a few analysis sections with rut index values in the 2 mm to 5 mm range for cumulative ESALs in the 1x106 range.

• There are very limited rut performance data available for Mix Types 7. • Overall there is a very similar range in rut index values for all Actual Mix Types. These

rut index values are being achieved at lower cumulative ESALs for higher Actual Mix Types. For example, for Mix Types 6, rut index values of 8 mm to 12 mm are being achieved at cumulative ESALs less than 0.5 x 106; for Mix Types 2, these rut index values are being achieved at about 2 x 106 cumulative ESALs.

• There is very little rutting performance data available for Mix Types 1, 2 and 4 for cumulative ESALs above about 5 x 106.

- 24 -

Figure 3.12 Cumulative ESALs vs. Rut Index by Design Mix Type




- 25 -





- 26 -





- 27 -



3.3.8.3 Mix Types Containing RAP Mix Types containing Reclaimed Asphalt Pavement (RAP) were analyzed separately. The Actual Mix Type was estimated based on the reported aggregate top size and aggregate components reported in the Marshall Stability Test System Index Report. In general, the equivalent virgin asphalt cement grade was assumed to be one grade harder than the asphalt cement grade used in the mix design, e.g. if 200-300A was used in the mix design, the equivalent virgin asphalt cement grade was assumed to be 150-200A. In the cases where 150-200A was used in the mix design, the equivalent virgin asphalt cement grade was assumed to be 150-200A. A total of 61 analysis sections representing 34 projects were included in the analysis. As described in Section 3.3.8.1, a separate figure has been prepared for each Actual Mix Type (Mix Types 1 and 7 were not represented). Figures 3.19 to 3.23 present the rut index vs. cumulative ESALs for all available Actual Mix Types containing RAP.

- 28 -

Figure 3.19 Cumulative ESALs vs. Rut Index by Design Mix Type and Climate Zone for Mixes Containing RAP - Actual Mix Type 2


- 29 -



- 30 -


A review of Figures 3.19 through 3.23 and a comparison to Figures 3.12 through 3.18 which represent Actual Mix Types without RAP indicates: • In general, the rutting performance of Actual Mix Types containing RAP would appear

to be consistent with Actual Mix Types not containing RAP. • One exception is Actual Mix Types 3 containing RAP. Analysis sections with

maximum rut index values greater than 8 mm tend to be associated with RAP contents between 25% and 45%. It is noted that these analysis sections would have been designed as Mix Types 1 or 2 using the present criteria. Further, it should be noted that Mix Types 3 were used primarily during the period preceding the introduction of the present criteria and have not been used since about 1991.

The present Specification 3.50 Asphalt Concrete Pavement - EPS allows the incorporation of RAP into all Asphalt Concrete Mix Types. All mixes containing RAP must meet the requirements of Table 3.50.3.2 Asphalt Concrete Mix Types and Characteristics.

- 31 -

The following documents outline the requirements for assessing the quality of an asphalt concrete pavement for recycling, mix design of asphalt mixtures containing RAP, calculating the % MF,-5000 in asphalt mixtures containing RAP and asphalt rheology design of asphalt mixtures containing RAP:

• TLT-301/00 Mix Design Method for Asphalt Concrete Pavement • TLT-RACP Recycling Asphalt Concrete Pavement (Pre-Engineering

Assessment) • TLT-314/00 Percent Manufactured Fines in Bituminous Mixtures

The rutting performance of asphalt Mix Types containing RAP can be expected to be similar to asphalt Mix Type mixtures without RAP. Present specifications and TLT procedures are considered sufficient to ensure that asphalt mixtures containing RAP meet specified Asphalt Concrete Mix Type requirements.

3.4 Summary and Conclusions Figures 3.12 through 3.18 were used to determine new ESAL ranges for the present four climatic zones and for Asphalt Mix Type 2, 4 and 6. This is illustrated in Figures 3.24 and 3.25 for Asphalt Mix Types 2 and 4. The upper ESAL limit for each of these three Mix Types was established for two rut criteria: • An average plus one standard deviation (0 + ó) = 15 mm • An average plus one standard deviation = 16.5 mm The latter criteria was selected to assess the sensitivity of the upper ESAL limit to a less conservative rut criteria. The new "allowable" ESAL ranges based on these two rut criteria, along with the present ESAL ranges are presented in Table 3.2. Ranges were not established for Asphalt Mix Types 3 as this mix type has not been used since the present selection criteria was introduced in the early nineties.

- 32 -

Figure 3.24 Determination of ESAL Ranges Corresponding

to a Rut Index of 15 mm for Actual Mix Type 2

Figure 3.25 Determination of ESAL Ranges Corresponding

to a Rut Index of 15 mm for Actual Mix Type 4

- 33 -

Table 3.2 Present ESAL Ranges Compared to Allowable ESAL Ranges Based on Specific Rutting Criteria

Present Asphalt Mix Type Present Climatic

Zone 1 2 4 5 6 7

A Present Criteria >2.01 1.0-2.0 0.5-1.0 0.3-0.5 <0.3 - 0 + ó = 15 mm >3.0 2.0-3.0 1.0-2.0 <.8 0 + ó = 16.5 mm >4.0 2.0-4.0 1.0-2.0 <1.0

B Present Criteria >3.0 1.5-3.0 0.7-1.5 0.4-0.7 <0.4 - 0 + ó = 15 mm >4.0 2.5-4.0 1.0-2.5 <1.3 0 + ó = 16.5 mm >5.0 3.0-5.0 1.5-3.0 <1.5

C Present Criteria >4.0 2.0-4.0 1.0-2.0 0.5-1.0 0.2-0.5 <0.2 0 + ó = 15 mm >6.0 3.5-6.0 2.0-3.5 <1.8 0 + ó = 16.5 mm >8.0 4.0-8.0 2.0-4.0 <2.0

D Present Criteria >5.0 2.5-5.0 1.5-2.5 0.8-1.5 0.3-0.8 <0.3 0 + ó = 15 mm >10.0 4.0-10.0 2.0-4.0 <2.3 0 + ó = 16.5 mm >11.0 5.0-11.0 3.0-5.0 <3.0

1 ESAL ranges x 106

Based upon a review of these data, the following observations and conclusions can be made: • For Mix Types 2 and 4, the new ESAL ranges based on the 15 mm rut criteria are about

50% to 100% higher than the present ranges. The ESAL ranges based on the 16.5 mm rut criteria are about 0% to 30% higher than the ranges based on the 15 mm rut criteria.

• For Mix Type 6, the new ESAL ranges based on the 15 mm rut criteria are about 300% higher than the present ranges. The ESAL ranges based on the 16.5 mm rut criteria are about 10% to 20% higher than the ranges based on the 15 mm rut criteria.

• The present ESAL ranges for all Mix Types appear to be generally conservative in terms of providing acceptable high temperature performance. Restated in a different way, the present ESAL values can be increased for all Mix Types without compromising high temperature performance.

- 34 -

Increasing the ESAL values for all Mix Types would provide some significant performance and economic benefits due to two main factors: • In general, the unit cost of Mix Types increases from Mix Type 6 to Mix Type 1

because aggregate processing costs increase as specification requirements become more stringent.

• In general, 12.5 mm topsize aggregate mixes (Mix Types 4, 5 and 6) provide a reduced potential for segregation during paving. This could result in direct and indirect cost savings due to lower bid prices, reduced maintenance costs and reduced/deferred seal coat costs.

- 35 -

4. DEVELOPMENT OF NEW MIX TYPE SELECTION CRITERIA Section 3 described the second phase of this project which was to validate present mix type selection criteria based on the analysis of the rutting performance of paving projects constructed between 1985 and 1995. The primary conclusion of that phase was that present ESAL values could be increased for all Mix Types without compromising high temperature performance. Although the option existed to simply update the present ESAL ranges and maintain the existing climate zones and mix types, an opportunity was provided to re-engineer the present Mix Type selection protocols for the following reasons: • Although considered "state-of-the-art" at the time, the present Mix Type selection

protocols were based on limited research and the technologies in pavements engineering available in the mid-1980's.

• The SHRP and C-SHRP research programs advanced technologies in the areas of asphalt binder characterization and mix design and provide more rationale, engineering-based protocols for selecting asphalt binders to address rutting performance at high temperatures, and transverse cracking performance at low temperatures.

• The C-SHRP Performance Correlation of Paving Grade Asphalts Research Project (C-SHRP, 1994) and specifically the construction of the Lamont Test Road (Gavin and Dunn, 1997), significantly advanced our knowledge of the effects of binder properties on low temperature cracking performance of pavements in cold climates.

• The objective of AT and the paving industry to construct segregation-free pavements and the recognition that 12.5 mm topsize mixes may provide a reduced potential for truck-to-truck segregation provided the opportunity to develop a new "heavy-duty" 12.5 mm top size Mix Type.

• The underlying technical basis for the present Mix Type Selection protocols was to select Mix Types, based on traffic and climate zone, to firstly provide rutting resistance and secondly to optimize low temperature cracking performance for the three asphalt cement grades available at that time - 150-200A, 200-300A and 300-400A. It was understood and accepted that some level of low temperature cracking would still occur on newly constructed pavement structures in many cases. With the development of PG binder specifications, the opportunity now exists to design and construct new pavement structures that have the potential to provide an acceptable level of rutting performance and also not crack at low temperatures.

- 36 -

Therefore, the third phase of this project was to develop new Mix Type Selection protocols and criteria with the following objectives: • For new construction pavements, and overlays on non-transverse cracked pavements1 -

"To provide constructable, durable, and economical transverse crack-free pavements with tolerable rutting after a 20 year service life".

• For overlays of transverse cracked pavements2 - "To provide constructable, durable and economical pavements with tolerable rutting after a 20 year service life".

The new protocols and criteria have been developed, to the extent possible, to minimize the number of changes and maintain simplicity and straight forwardness of use. Also, criteria have been developed for Mix Type selection protocols for the selection of SHRP PG Binder and Superpave Mix Design and aggregate properties.

4.1 Marshall Mix Design and Conventional and PG Binders 4.1.1 New ESAL Groupings New ESAL Groupings with consistent limits were developed to replace the present groups which have unique limits for each Mix Type and Climate Zone. The traffic levels used by SHRP Superpave (AASHTO, 2001) have been selected as the basis and have been modified for AT based on Alberta traffic conditions, engineering judgement and experience.

SHRP Traffic, million ESALs

AT Traffic, million ESALs

<0.3 <1.0 0.3 to < 3.0 1.0 to < 3.0 3.0 to < 10.0 3.0 to < 6.0 10.0 to < 30 6.0 to < 10.0

> 30 10.0 to <20.0 > 20.0

Although ESAL groupings of 10.0 to <20.0 million ESALs and >20 million ESALs have been selected, criteria have only been developed for a combined ESAL grouping of >10 million ESALs. This is due to the limited rutting performance data available for cumulative

1 A "non-transverse cracked pavement" can be defined as a pavement without transverse cracks, or with a very

low transverse crack frequency. 2 Transverse cracked pavements can include low temperature cracks and reflected shrinkage cracks from

underlying cement stabilized base course layers.

- 37 -

ESALs above about 5 million. As rut performance data is gathered for ESALs in the 10 to 15 million range, criteria for the 10.0 to 20.0 million ESALs, and >20.0 million ESALs should be developed. 4.1.2 Proposed New Mix Types A Mix Type is presently defined by three components: • aggregate criteria • mix design criteria • asphalt binder criteria Aggregate and mix design criteria generally dominate high temperature rutting performance and durability. Binder criteria generally dominate low temperature cracking performance. As such, the new Mix Types are defined by aggregate and mix design criteria to primarily address high temperature rutting performance and durability, and a separate protocol has been developed for selecting asphalt grades to primarily address low temperature cracking performance. The proposed new Mix Types are grouped and designated by their application:

Application New Mix Type Designations High Service H1, H2

Medium Service M1 Low Service L1 Specialty S1, S2, S3

This designation convention would allow for new mix types to be developed and designated without requiring renumbering of designations. The proposed new Mix Types and aggregate and Marshall Mix Design criteria are presented in Table 4.1. For comparison purposes, the new and present Mix Types are presented in Table 4.2. Mix Type H1 - This Mix Type is for very high service applications. It will replace Mix Types 1 and 2 which are considered to be very similar in properties and performance. Mix Type H2 - This is a new Mix Type for high service applications. It is essentially a Mix Type 2 with a 12.5 mm top size.

- 38 -

Mix Type M1 - This Mix Type is for medium service applications and replaces Mix Types 3, 4 and 5. Mix Type L1 - This Mix Type is for low service applications and replaces Mix Types 6 and 7. It would also be specified for community airports with air void requirements reduced to 3.0% to 3.5%. Mix Type S1 - This Mix Type is essentially the same as the present Mix Type 8 and is used as a first lift to mitigate roughness or problems associated with excessive crack filler where a two lift, 70 mm total thickness, overlay is designed. Mix Type S2 - This is a new Mix Type for thin overlays, i.e. 30 mm single lift applications. Mix Type S3 - This is a new large top size Mix Type for asphalt concrete base pavement applications. This Mix Type would be specified for base lifts of a minimum thickness of 80 mm and would be surfaced with a minimum of 60 mm ACP. The Mix Type for the surface layer would be selected based on project design ESALs and climate zone.

- 39 -

Table 4.1 Proposed New Mix Types and Characteristics

Aggregate Criteria Marshall Mix Design Criteria

Mix Type

Top Size ( m m )

% MF. −−5000 (min) Note 1)

% Fractures +5000

(2 face s ) * (min)

Marshall Stability N

(min) No. of Blows

Flow ( m m )

Air Voids (%)

VMA % (min) by % Air Voids

Voids Filled with Asphalt %

Retained Stability %

(min) 3.5 4.0

H1 16 75 98 (one face)90* 12000 75 2 to 3.5 Note 3 13.0 13.5 65-75 70

H2 12.5 70 80* 12000 75 2 to 3.5 Note 3 13.5 14.0 65-75 70

M1 12.5 50 60* 8000 75 2 to 3.5 Note 3 13.5 14.0 65-75 70 L1 12.5 50 60* 5300 50 2 to 4 Note 3,4 13.5 14.0 65-78 70

S1 10.0 60 70* 5300 Note 2 2 to 4 Note 3 14.5 15.0 65-78 70

S2 10.0 75 90* 10000 75 2 to 3.5 Note 3 14.5 15.0 65-75 70

S3 25 40 60* 8000 75 2 to 4 Note 3 11.5 12.0 65-78 70

Note 1 - The Percentage of Manufactured Fines in the -5000 Portion of the Combined Aggregate. Note 2 - Use the same number of blows as for the surface course. Note 3 - The Design Air Voids shall be chosen as the lowest value, within the range of 3.5 to 4.0% inclusive, such that all other mix design criteria are met. Note 4 - Air Void limits listed in Note 3 shall be reduced by 0.5% for community airports. VMA at 2 .5% Air Voids shall be a minimum of 12.5%.

Minimum Theoretical Fi lm Thickness Requirements (µm ) Design Air Voids Mix Types H1, H2, M1, S2 Mix Type L1 4.0 and 3.9 6.0 6.5 3.7 and 3.8 6.1 6.6 3.5 and 3.6 6.2 6.7 3.3 and 3.4 - 6.8 3.0, 3.1 and 3.2

Community Airports only; L1 - 6.9

- 40 -

Table 4.2 Comparison of Present and Proposed New Mix Types

Aggregate Criteria Marshall Mix Design Criteria

Equivalent Present Mix Type

New Mix

Type

Top Size

( m m )

% MF, −− 5000 (min) Note 1

% Fractures

+5000 (2 faces)*

(min)

Marshall Stability

N (min)

No. of Blows

Flow ( m m )

Air Voids (%)

VMA % (min) by % Air Voids

Voids Filled with Asphalt

%

Retained Stability % (min)

3.5 4.0 H1 16 75 98 (one

face)90* 12000 75 2 to 3.5 Note 5 13.0 13.5 65-75 70

1 16 75 98 (one face)90*

12000 75 2 to 3.5 Note 5 13.0 13.5 65-75 70

2 16 70 70* 12000 75 2 to 3.5 Note 5 13.0 13.5 65-75 70 H2 12.5 70 80* 12000 75 2 to 3.5 Note 5 13.5 14.0 65-75 70 M1 12.5 50 60* 8000 75 2 to 3.5 Note 5 13.5 14.0 65-75 70

3 16 40 60* 8000 75 2 to 3.5 Note 5 13.0 13.5 65-75 70 4 12.5 50 60* 8000 75 2 to 3.5 Note 5 13.5 14.0 65-75 70 5 12.5 Note 2 60* 8000 75 2 to 3.5 Note 5 13.5 14.0 65-75 70 L1 12.5 50 60* 5300 50 2 to 4 Note 5,6 13.5 14.0 65-78 70

6 12.5 Note 2 60* 5300 50 2 to 4 Note 5 13.5 14.0 65-78 70 7 12.5 Note 2 60* 5300 50 2 to 4 Note 5,6 13.5 14.0 65-78 70 S1 10.0 60 70* 5300 Note 4 2 to 4 Note 5 14.5 15.0 65-78 70

8 10.0 Note 2 60* 5300 Note 4 2 to 4 Note 5 14.5 15.0 65-78 70 S2 10.0 75 90* 10000 75 2 to 3.5 Note 5 14.5 15.0 65-75 70 S3 25 40 60* 8000 75 2 to 4 Note 5 11.5 12.0 65-78 70

Note 1 - The Percentage of Manufactured Fines in the -5000 Portion of the Combined Aggregate. Note 2 - All f ines manufactured by the process of crushing shall be incorporated into the mix for Asphalt Mix Types 5, 6, 7 and 8. Note 3 - Use the same asphalt grade as for the lift above. Note 4 - Use the same number of blows as for the surface course. Note 5 - The Design Air Voids shall be chosen as the lowest value, within the range of 3.5 to 4.0% inclusive, such that all other mix design

criteria are met. Note 6 - Air Void limits listed in Note 5 shall be reduced by 0.5% for community airports. VMA at 2.5% Air Voids shall be a minimum of 12.5%. Note 7 - Theoretical Film Thickness requirements shall be as follows depending upon the specified Mix Type and Design Air Voids. The

Theoretical Film Thickness value shall be established in accordance with TLT-311.

- 41 -

4.1.3 Proposed Aggregate and Mix Design Criteria The proposed Mix Types have resulted in minor modifications to existing criteria as well as new values which will require changes to aggregate and mix design specifications. In addition, the present specification requirements for the maximum percent passing the 80 µm sieve and retained stability were reviewed. An assessment of these changes was carried out to assess their reasonableness and impact on the contracting and aggregate processing industries. All mix design data in AT's database (which included AT Contract Number 5758/96 through 6364/01) were available for review. These data were used as a benchmark to identify what possible impacts may result. The available data for each Mix Type were screened to include only full mix designs reported. Designs where RAP was used were analyzed separately. Where multiple designs were reported for a project, only one design was selected as representative. % MF, −−5000 and % Fractures +5000 (2 faces) Table 4.3a provides a summary of this analysis. Mix Type H1 will replace Mix Types 1 and 2. These requirements are unchanged from the present criteria for Mix Type 1. Therefore the impacts should be negligible. Mix Type H2 is essentially equivalent to the present Mix Type 2 but with a 12.5 mm topsize. The requirements for % MF,-5000 remain unchanged. Slightly more processing to achieve the 80% minimum % Fractures +5000 (2 faces) requirement may be required. These mixes are for high service applications and should provide a reduced segregation potential. The overall impacts are considered small. Mix Type M1 replaces Mix Types 3, 4 and 5. The overall impacts are considered negligible. Mix Type L1 replaces Mix Types 6 and 7. The overall impacts are considered negligible. Mix Type S1 is essentially identical to the present Mix Type 8. Impacts are considered negligible.

- 42 -

Mix Type S2 is a new 10 mm topsize mix for thin overlay applications. Benchmarking the new requirements against the Mix Types 8 assessed indicates minor extra processing will be required in a small minority of cases to meet % MF,-5000 and % Fractures +5000 (2 faces) requirements. Mix Type S3 is a new large topsize mix. Impacts on the contracting and aggregate processing industries are considered negligible. Maximum Percent Passing the 80 µµm Sieve Size Table 4.3b provides a summary of this analysis. The present maximum specification limit for all Designation 1 aggregate in Table 3.2.3.1 of Specification 3.2 Aggregate Production and Stockpiling is 10%. Alberta Transportation is unique amongst major transportation agencies in Alberta in allowing up to 10% passing the 80 µm sieve size. City of Edmonton, Calgary and Lethbridge maximum specification limits are generally between 7% and 8% depending on mix type. The effects of mineral filler content on asphalt mix properties, compactability and performance have been previously reported by EBA (1988). This study recommended a maximum value of 8% be considered. A review of 132 mix designs indicated only one would not comply with a maximum specification limit of 8%. It is recommended that AT further investigate reducing the present maximum specification limit from 10% to 8%.

Retained Stability Table 4.3b provides a summary of this analysis. The present specification limit for Mix Types in Table 3.50.3.2 of Specification 3.50 Asphalt Concrete Pavement - EPS is 70%. This value has been unchanged, probably since its original inclusion in the specifications. Retained stability provides an indication of the susceptibility of moisture damage to the mix. Adhoc observations and experience suggest that asphalt stripping and surface ravelling tends to be associated with mixtures having retained stability values less than 80%. An increase in the minimum retained stability value of 80% should be considered. The data presented in Table 4.3b suggest that Mix Types 2 have the greatest degree of non-compliance with an 80% minimum limit for retained stability. This is somewhat disconcerting as these mixes are used in heavy traffic applications which would exacerbate

- 43 -

the potential damage and premature failure. It is interesting to note that the degree of non-compliance of Mix Types 1 is significantly less. It is anticipated that this change would have a minor impact on the contracting and aggregate processing industries. It may result in the use of anti-stripping agents on a small number of projects. It is recommended that AT further investigate increasing the minimum retained stability to 80%.

- 44 -

Table 4.3a Summary of Mix Designs Not Complying with Proposed Criteria Equivalent Mix Type No. of Mix Designs Not Complying to the Specified Criteria

Present Criteria Designs % MF, −− 5000 % Fractures +5000 (2 faces) Mix Type Compared To Evaluated Criteria Non −− Compliance Criteria Non −− Compliance

1 H1 36 75 0 (0%) 90 0 (0%) 2 H1 30 75 15 (50%) 90 15 (50%) H2 30 70 0 (0%) 80 4 (13%)

4 H2 23 70 11 (52%) 80 4 (17%) M1 23 50 0 (0%) 70 1 (4%)

5 M1 18 50 1 (5%) 60 0 (0%) 6 L1 8 50 0 (0%) 60 0 (0%) 7 L1 1 50 0 (0%) 60 0 (0%) 8 S1 16 60 0 (0%) 70 0 (0%) S3 16 75 2 (13%) 90 3 (19%)

- 45 -

Table 4.3b Summary of Mix Designs Not Complying with Suggested Criteria Equivalent Mix Type No. of Mix Designs Not Complying to the Specified Criteria

Present Criteria Designs Retained Stability % Maximum Percent Passing 80 Sieve Mix Type Compared To Evaluated Criteria Non −− Compliance Criteria Non −− Compliance

1 H1 36 80 2 (6%)1 ≤8.0 0 (0%)

2 H1 30 80 7 (23%)2 ≤8.0 0 (0%)

H2 30 80 7 (23%)² ≤8.0 0 (0%)

4 H2 23 80 2 (9%)3 ≤8.0 0 (0%) M1 23 80 2 (9%)3 ≤8.0 0 (0%)

5 M1 18 80 0 (0%) ≤8.0 0 (0%)

6 L1 8 80 2 (25%)4 ≤8.0 1 (13%) 7 L1 1 80 0 (0%) ≤8.0 0 (0%)

8 S1 16 80 1 (6%)5 ≤8.0 0 (0%)

S3 16 80 1 (6%)5 ≤8.0 0 (0%)

1 - 75%, 75% 2 - 73%, 74%, 74%, 75%, 76%, 76%, 78% 3 - 77%, 79% 4 - 75%, 78% 5 - 79%

- 46 -

4.1.4 New High Temperature Zones The weather station data from the LTPPbind software program were utilized to determine appropriate high temperature zones based on T20mm temperatures calculated using the LTPP high temperature model and the original SHRP high temperature model, both for a reliability of 98%. Figure 4.1 shows the high temperature zones developed for the province. It can be noted that this approach resulted in three zones compared to the four used previously. The calculated high pavement temperature grade requirements were plotted to allow the zones to be identified as shown in Figure 4.1. Although there were no clear lines, geographic features were selected that were considered reasonable to establish the temperature zones. This approach offers a desirable ease of use and consistency with the existing selection methodology and is not considered to involve significant performance risks. The high temperature zones in Figure 4.1 are based on the SHRP high temperature model and high temperature grades of 58, 52 and 46 for Zones 1, 2 and 3 respectively. The zones determined by this study have been labeled as 1, 2, and 3. Zone 1 is the area of the province south of the Red Deer River and east of Highway 36 and, south of Warner at the intersection of Highway 36 and Highway 4, east of Highway 4. Zone 2 is the area of the province south of the North Saskatchewan River, not including that area defined as Zone 1. Zone 3 is the area of the province north of the North Saskatchewan River. The high temperature zones are used in the selection of project Mix Types only. Selection of project asphalt binder grades is described in Section 4.1.6.

- 47 -

Figure 4.1 High Temperature Zones for Mix Type Selection

- 48 -

4.1.5 Mix Type Selection As previously discussed, aggregate and mix design criteria dominate high rutting temperature performance and pavement durability whereas asphalt binder criteria generally dominate low temperature cracking performance. Therefore the selection of a Mix Type is based on the 20 year Design ESALs and the high temperature zone the project is located in. The new selection criteria is presented in Table 4.4. The ESAL limits have been determined from an examination of Figures 3.12 through 3.18, Figure 3.24 and 3.25, Figure 4.1, the data presented in Table 3.2 and engineering judgement. The 20 year Design ESALs are determined based on AT ESAL History Reports. Traffic growth over the 20 year period is accounted for as outlined in the AT Pavement Design Manual. Regardless of the actual design life of the pavement, the designer should determine the expected ESALs for 20 years and select the Mix Type for that traffic. This concept has been verified based on rutting performance at WesTrack and has been clarified in the AASHTO Provisional Standard (1999).

Table 4.4 ESAL Cri teria for Selection of Mix Types ESALs (millions)1 High Temperature

Zone < 1.0 1.0 to < 3.0 3.0 to < 6.0 6.0 to <10.0 ≥≥ 10.0 1 L1 H2 H1 H1 H1 2 L1 M1 H2 H1 H1 3 L1 M1 M1 H2 H1

1 ESAL criteria at the total ESALs (in millions) in the design lane that will be applied to the pavement over a 20 year period.

The selection of Mix Types S1, S2 and S3 is based on specific pavement design requirements and is not contingent on Design ESALs or high temperature zone. 4.1.6 Asphalt Binder Selection The selection of the asphalt binder grade is based on the general philosophy originally developed for AT's mix type selection criteria. This approach is very similar to the Superpave PG Binder selection protocol except that the high temperature grade selection considers traffic loading in the initial steps for selecting asphalt binder characteristics.

- 49 -

A significant underlying philosophy in the asphalt binder selection process is the consideration as to when the use of modified asphalts is warranted. For AT, modified asphalts are used to provide improved low temperature characteristics and therefore are only warranted in situations where pre-existing low temperature transverse cracking does not exist. Further, higher costs associated with the use of modified asphalt has been determined by AT to be justified only for higher trafficked roadways. This philosophy is imbedded in the binder selection protocols presented in this report. It is noted that AT utilizes asphalt specifications based on penetration and viscosity tests for conventional asphalt cements and asphalt specifications based on the Superpave Performance Graded (PG) system for modified asphalt cements. Unlike conventional penetration/viscosity-based specifications, for the Superpave system the physical property requirements are constant among all performance grades. The distinction among the various binder grades is the specified minimum and maximum temperatures at which the requirements must be met. For example, a binder classified as a PG XX-YY means that the binder will meet the high temperature physical property requirements up to a temperature of XX°C and the low temperature physical property requirements down to YY°C. Attempts were made to develop a geographical zone based selection system for selecting the low temperature PG grade. Based on the TAC Low Temperature Model and 98% reliability, the low temperature PG grade was determined for each of the 173 Alberta weather stations in the LTPPBind database. This is presented in Figure 4.2. A review of the distribution did not identify geographical zones that could be used to select the low temperature grade.

- 50 -

Figure 4.2 Low Temperature PG Grade for Alberta Weather Station Locations

Red Deer

Lethbridge

Medicine Hat

Drumheller

Fort McMurray

Brooks

Edson

Hinton

Barrhead

Athabasca

Peace River

Grande Prairie

CamroseDrayton Valley

Banff

Jasper

Whitecourt

Wetaskiwin

Lloydminster

High Level

Grande Cache

Canmore

Bonnyville

Rocky Mountain House<= -40

Between -37 and -40

Between -34 and -37

> -34

Low Pavement Temperature - 98% Reliability

C. McMillan - June 5, 2002

- 51 -

4.1.6.1 Rehabilitation of Transverse Cracked Pavements Table 4.4, ESAL Criteria for Selection of Mix Types, is used to select the appropriate mix type for the project based on the design ESALs and high temperature zone. Figure 4.1 shows the High Temperature Zones for the Province. Rehabilitation of transverse cracked pavements shall use conventional asphalt grades. Transverse cracked pavements can include low temperature cracks and reflected shrinkage cracks from underlying cement stabilized base course layers. The conventional asphalt grades are selected using Table 4.5 based on 20 year design ESALs and High Temperature Zone.

Table 4.5 Selection of Conventional Asphalt Grades for Rehabilitation of Transverse Cracked Pavements

ESALs (millions)1 High Temperature

Zone < 1.0 1.0 to < 3.0 3.0 to < 6.0 6.0 to <10.0 ≥ 10.0

1 150-200A 150-200A 150-200A 120-150A 120-150A 2 200-300A 200-300A 150-200A 150-200A 120-150A 3 200-300A 200-300A 150-200A 150-200A 150-200A


4.1.6.2 New Construction, Final Stage Paving and Rehabilitation of Non-Transverse

Cracked Pavements For new construction and the rehabilitation or final paving of non-transverse cracked pavements, the use of modified asphalts may be justified in order to construct a pavement with a low risk of developing transverse cracking. A "non-transverse cracked pavement" can be defined as a pavement without transverse cracks, or with a very low transverse crack frequency. The methodology is presented in a flow chart format in Figure 4.3. The high temperature PG grades are selected using Table 4.6 based on 20 year design ESALs and High Temperature Zone. Due to the wide range in pavement temperatures that can occur in Alberta, there will be occasions where the desirable PG grade does not exist in Menu 1. The process described in Figure 4.3 allows for the selection of modified binders for very high traffic applications, i.e.

- 52 -

Design ESALs >6.0 x 106. However, the significantly higher costs of a modified binder are not deemed justified for low traffic applications. For Design ESALs less than 0.5 x 106 when the desirable PG grade is a modified asphalt binder, the binder selection process allows for the high temperature grade to be reduced by 6°C with a corresponding increase in Mix Type from L1 to M1. An M1 mix type has enhanced rutting resistance characteristics over an L1: 75 blows vs. 50 blows and a minimum Marshall Stability of 8000 N vs. 5300 N. The equivalent to an M1 mix type with 300-400A asphalt cement (equivalent to PG 46-37) was used in the Lamont Test Road. After 10 years performance and about 0.20 x 106 ESAL applications, no transverse cracks have appeared and ruts measured in 2001 are less than 4 mm.

- 53 -

- 54 -

Table 4.6 Selection of High Temperature PG Grade for Rehabilitation of Non-Transverse Cracked Pavements, First Stage and Final Stage Pavements

ESALs (millions)1 High

Temperature Zone

< 1.0 1.0 to < 3.0 3.0 to < 6.0 6.0 to <10.0 ≥ 10.0

1 58-YY 58-YY 58-YY 64-YY 64-YY 2 52-YY 52-YY 58-YY 58-YY 64-YY 3 52-YY 52-YY 58-YY 58-YY 58-YY


Life cycle cost analyses have been conducted considering potential service lives, potential maintenance cost savings and potential user cost savings to evaluate the economic viability of using modified asphalts on a project specific basis. The premium cost of modified asphalt will vary with time as competition develops in the market place. The design ESAL limits, which warrant the use of modified asphalt, have been selected based on these considerations and will need to be reviewed as costs become better defined. 4.1.7 Design Examples The following examples demonstrated the binder selection protocol. Example 1 Hwy 40:28 Design ESALs = 0.49 x 106 High Temperature Zone 3 (Figure 4.1) Closest Weather Stations – Jasper East Gate, Entrance, Coalspur. Only Jasper East Gate was selected for this example. Design 1.1 Overlay Over Transverse Cracked Pavement Step 1 • Determine Asphalt Mix Type (Table 4.4 ) = L1 Step 2 • Determine Conventional Asphalt Grade (Table 4.5) = 200-300A Therefore, Mix Type L1 with Conventional Asphalt Grade 200-300A would be selected for this project.

- 55 -

Design 1.2 Overlay or Final Stage Paving Over Non-transverse Cracked Pavement Step 1 • Determine Asphalt Mix Type (Table 4.4) = L1 Step 2 • Determine High Temperature PG Grade (Table 4.6) = 52-YY Step 3 • Determine Design Low Temperature, TDESIGN

• From the LTPPBind Weather Database for the Jasper East Gate weather station (and based on the TAC Low Temperature Model):

Reliability TAC Design Low Temp. (°C)

PG Low Temp. Grade

90.0% 93.5% 98.0% 99.0% 99.99%

-35.7 -37.0 -40.0 -41.6 -49.4

-37 -37 -40 -46 -46

• Therefore TDESIGN = −− 40.0°C @ 98% reliability Step 4 • Desirable PG Grade = 52-40 Step 5 • Desirable PG Grade = 52-40 does not exist in Menu 1 Step 6 • Based on data for the Jasper East Gate weather station, a PG Low

Temperature Grade of –37 would result in a Reliability of 93.5%. For this project, this is considered acceptable.

• New Desirable PG Grade = 52-37 Step 7 • New Desirable PG Grade 52-37 does not exist in Menu 1 Step 8 • For Design ESALs ≤ 0.5 x 106, increase the Mix Type from L1 to M1 and

reduce High Temperature PG Grade by 6°C • Therefore Modified Desirable PG Grade = 46-37 • This grade does exist in Menu 1.

Therefore, Mix Type M1 with Conventional Asphalt Grade 300-400A would be selected for this project.

Example 2 Hwy 35:06 Design ESALs = 4.0 x 106 High Temperature Zone 3 (Figure 4.1) Closest Weather Stations – Berwyn, Peace River A and Peace River Crossing. Only Berwyn was selected for this example.

- 56 -

Design 2.1 Overlay Over Transverse Cracked Pavement Step 1 • Determine Asphalt Mix Type (Table 4.4) = M1 Step 2 • Determine Conventional Asphalt Grade (Table 4.5) = 150-200A Therefore, Mix Type M1 with Conventional Asphalt Grade 150−−200A would be selected for this project. Design 2.2 New Construction First Stage Pavement For this example, the thickness of the final stage ACP is assumed to be 90 mm. Step 1 • Determine Asphalt Mix Type (Table 4.4) = M1 Step 2 • Determine High Temperature PG Grade (Table 4.6) = 58-YY Step 3 • Determine Low Temperature, TDESIGN

• From the LTPPBind Weather Database for the Berwyn weather station (and based on the TAC Low Temperature Model) and reducing TDESIGN by 3°C as the depth below the final surface is <100 mm:

Reliability Modified TAC Design Low Temperature for Depth Below the Final Surface <100 mm (°C)

PG Low Temperature Grade

75.0% 76.0% 98.0% 98.9% 99.9%

−− 33.9 −− 34.0 −− 36.1 −− 37.0 −− 42.3

−−34 −−34 −−37 −−37 −−40

• Therefore TDESIGN = −− 36.1°C @ 98% reliability. Step 4 • Desirable PG Grade = 58-37 Step 5 • Desirable PG Grade does not exist in Menu 1 Step 6 • Based on data for the Berwyn weather station:

PG Low Temperature Grade = −− 40 for >98.9% Reliability PG Low Temperature Grade = −− 37 for ≤98.9% and >76% Reliability PG Low Temperature Grade = −− 34 for ≤76% Reliability

• Based on engineering judgement, use original TDESIGN = -36.1°C • Desireable PG Grade remains as 58-37.

Step 7 • Desirable PG Grade 58-37 does not exist in Menu 1 Step 8 • For Design ESALs > 0.5 x 106 to ≤ 5.0 x 106, select the closest PG Grade to

meet low temperature requirements from Menu 1 which is PG58-34. Therefore, Mix Type M1 with PG58-34 would be selected for this project.

- 57 -

Example 3 Hwy 1:20 Design ESALs = 11.0 x 106 High Temperature Zone 1 (Figure 4.1) Closest Weather Stations – Medicine Hat A, Suffield A, Foremost. Only Medicine Hat A selected for this example.

Design 3.1 Overlay Over Transverse Crack Pavement Step 1 • Determine Asphalt Mix Type (Table 4.4) = H1 Step 2 • Determine Conventional Asphalt Grade (Table 4.5) = 120-150A Therefore, Mix Type H1 with Conventional Asphalt Grade 120−− 150A would be selected for this project. Design 3.2 Overlay or Final Stage Pavement Over Non-transverse Cracked Pavement Step 1 • Determine Asphalt Mix Type (Table 4.4) = H1 Step 2 • Determine High Temperature PG Grade (Table 4.6) = 64-YY Step 3 • Determine Design Low Temperature, TDESIGN

• From the LTPPBind Weather Database for the Medicine Hat A weather station (and based on TAC Low Temperature Model):

Reliability TAC Design Low Temperature (°C)

PG Low Temperature Grade

90.0% 93.0% 98.0% 99.0% 99.9%

-33.3 -34.0 -36.4 -37.5 -43.2

-34 -34 -37 -40 -46

• Therefore TDESIGN = −− 36.4°C @ 98% reliability Step 4 • Desirable PG Grade = 64-37 Step 5 • Desirable PG Grade does not exist in Menu 1 Step 6 • Based on data for the Medicine Hat A weather station: PG Low Temperature Grade = −− 40 for 99% Reliability

PG Low Temperature Grade = −− 37 for <99% and >93.0% Reliability PG Low Temperature Grade = −− 34 for ≤93.0% Reliability

• Based on engineering judgement, the original Desireable PG Grade remains as 64-37.

Step 7 • Desirable PG Grade 64-37 does not exist in Menu 1 Step 8 • For Design ESALs ≥ 5.0 x 106, select the closest PG grade to meet low

temperature requirements from Menu 2 which is PG64-37. Therefore, Mix Type H1 and Modified Asphalt Binder PG64-37 would be selected for this project.

- 58 -

4.1.8 Impact Assessment 4.1.8.1 Mix Types An assessment of the impact of the implementation of the new Mix Type selection criteria was carried out. A draft of the 2002 program was used as the basis of the assessment. All paving projects greater than 5 km in length were selected. For each of these projects, the following information and data were assembled: • The climatic zone using the present criteria • Year 2000 ESALs/day/direction • 20 Year Design ESALs based on 3% growth • The Mix Type based on existing criteria. • The climate zone using the new criteria. • The Mix Type based on the new criteria. • An estimate of asphalt mix quantity based on the following assumptions - 11.8 m

pavement width and an 80 mm asphalt concrete thickness. A summary of total asphalt mix quantities for each mix type based upon both the present and new selection criteria and mix types is presented in Table 4.7.

Table 4.7 Summary of Mix Type Quantities Based on Existing and New Selection Criteria Based on 2002 Draft Program

Existing Criteria New Criteria Mix Type No. of

Projects Quantity (t) Mix Type No. of

Projects Quantity (t)

1 24 1,302,000 H1 13 644,000 2 26 672,000 H2 14 567,000 4 15 403,000 M1 39 1,302,000 5 16 531,000 - 6 23 889,000 L1 40 1,375,000 7 2 64,000 -

Total 106 3,888,000 106 3,888,000

It should be noted when interpreting these data that the Mix Type based on the existing criteria identifies the asphalt cement grade. Under the new criteria, the selection of the asphalt cement grade is determined separately from the selection of the Mix Type.

- 59 -

A review of the data presented in Table 4.7 indicates the following impacts will result from the implementation of the new criteria: • Using the existing criteria, about 2,000,000 t of 16 mm topsize mixes (Mix Types 1

and 2) would be utilized. Based on the new criteria, the quantity of 16 mm topsize mix (Mix Type H1) would be reduced to about 600,000 t or by about 70%. The corresponding reduction of about 1,400,000 t of Mix Types 1 and 2 would be made up with H2 and M1 Mix Types. As it is generally accepted that 12.5 m topsize mixes have a reduced segregation potential as compared to 16 mm topsize mixes, the significant reduction in 16 mm topsize mixes could affect new pavement construction quality, and future maintenance and seal coat needs.

• Using the existing criteria, about 2,000,000 t of high stability mixes (Mix Types 1

and 2) would be utilized. Based on the new criteria, the quantity of high stability mixes (Mix Types H1 and H2) would be reduced to about 1,200,000 t or by about 40%. The corresponding reduction of about 800,000 t of Mix Types 1 and 2 would be made up of M1 Mix Type. This will reduce the amount of manufactured fines required which could reduce aggregate processing costs and reduce reject or waste of aggregate resources.

• Using the existing criteria, about 1,000,000 t of lower stability mixes (Mix Types 6 and

7) would be utilized. Based on the new criteria, the quantity of lower stability mixes (Mix Type L1) would increase to about 1,400,000 t or by about 40%. This would increase the quantity of high durability mixes on low traffic highways which would improve service life and reduce future maintenance needs.

4.1.8.2 Asphalt Binder It is anticipated that the new asphalt binder selection criteria will have the following impacts: • introduction of modified asphalts to the selection process, graded using the PG grading

system: PG58-34, PG58-37, PG64-34, PG64-37 • re-introduction in the use of 120-150A in Zone 1 and 2 • increase in the use of 300-400A • reduction in the use of 150-200A

- 60 -

The introduction of PG asphalt binders will increase the capital cost of construction with improved serviceability and reduced maintenance costs anticipated. The re-introduction of 120-150A should not have any significant impacts on the industry with improved rutting performance anticipated. The increase in the use of 300-400A may require some adjustments to compaction procedures with significantly improved low temperature cracking performance anticipated.

4.2 Superpave Mix Design and Conventional and PG Binders 4.2.1 Background Superpave (Superior Performing Asphalt Pavements) is a product of the Strategic Highway Research Program (SHRP) and is considered the most important new development in the field of asphalt technology in decades. The Superpave system comprises specifications, test methods and selection criteria for binders, aggregates and asphalt mixtures. Superpave designed mixtures have been used on selected Alberta primary highway projects since 1996. These projects have included new construction (both first and final stage paving), and overlay rehabilitation construction. The quantity of Superpave mixtures used to date in Alberta exceeds one million tonnes. Although Alberta's utilization of Superpave mixtures has generally exceeded that of other Canadian jurisdictions, there does not exist a sufficient database to relate mixture characteristics to performance (e.g. rutting). This is due to the limited service period of Alberta Superpave projects and the wide range of mixture variables, including design compactive effort, aggregate nominal maximum size and binder grade. Therefore, the proposed Superpave mix type selection protocols and specified design requirements provided herein, generally follow current AASHTO guidelines (i.e. AASHTO MP2-01 and PP28-01). Some revisions have been included which represent more stringent requirements than those provided in the AASHTO guidelines. In most cases these revisions have previously been adopted by AT, generally due to the limited performance information for Superpave mixtures. Where additional revisions are recommended, a rationale is provided for these changes. ESAL groupings have been selected to provide consistency with the proposed "conventional" mix type selection protocols. Superpave mixture design methodology is considered relevant to the full range of dense graded asphalt concrete applications. Therefore, it is not considered appropriate to attempt to identify specific applications for Superpave mixtures, versus Marshall designed mixtures.

- 61 -

The utilization of a Superpave mixture for a particular project will depend, in part, on AT and industry preference with respect to Superpave implementation, and should consider several factors including industry capability and early performance information as it becomes available. 4.2.2 Binder Selection As with conventional Marshall mixtures, the selection of an appropriate binder for Superpave mixtures should consider project specific traffic loading, climatic conditions and pavement application (e.g. new construction, overlay rehabilitation of cracked or non-cracked pavements). Therefore, generally the binder selection methodology described in Section 4.1.6 should be used for Superpave mixtures. The "bumping" to a higher traffic level mix type to compensate for a potential deficiency in binder high temperature performance is not recommended for Superpave mixtures. 4.2.3 Proposed ESAL Groupings The ESAL groupings proposed for conventional mix types, described in Section 4.1.1 are considered appropriate for Superpave mix type selection and mixture design criteria. As noted, these ESAL groupings have been altered somewhat from the current AASHTO groupings, to reflect Alberta traffic loading conditions, particularly in the intermediate to high traffic range (i.e. 3.0 to 10.0 million ESALs). 4.2.4 Mix Type Selection and Design Criteria The proposed methodology for mix type selection generally follows current AASHTO (and AT) protocols. Subsequent to the selection of an appropriate binder grade for a project, the Superpave "mix type" with the corresponding design criteria and aggregate requirements are selected based on the 20-year Design ESALs. Tables 4.8 and 4.9 present the proposed Superpave aggregate criteria (i.e. consensus properties) and mixture design criteria, respectively.

- 62 -

Table 4.8 Proposed Superpave Aggregate Criteria

Superpave Aggregate Consensus Property Requirements Design Traffic

ESAL (million)

Coarse Aggregate Angularity1

Fine Aggregate Angularity2

Sand Equivalent3

Flat and/or Elongated Particles4

< 1.0 - /60 40 40 1.0 to < 3.0 75/70 45 45 3.0 to < 6.0 85/80 45 45 6.0 to < 10.0 95/90 45 45

10.0 to < 20.0 95/90 45 50 > 20.0 95/90 45 50

10

1 Minimum percent fracture plus 5000 µm fraction (one face / two or more faces) 2 Minimum percent uncompacted void content, minus 2500 µm fraction 3 Minimum percent, minus 2500 µm fraction 4 Maximum percent, 5:1 maximum-to-minimum ratio, plus 2500 µm fraction Note:

For 20mm and 25mm NMS mixtures located 60mm or greater from the pavement surface, the aggregate requirements may be amended to those corresponding to design traffic <1.0 million ESALs.

With respect to aggregate criteria (Table 4.8), the aggregate requirements for ESAL category 6.0 to <10.0 million have been revised to the AASHTO requirements for 10 to <30 million. The fine aggregate angularity requirement for ESAL categories 1.0 to <3.0 million has been revised to the AASHTO requirement for 3 to <10 million ESALs. As well, the sand equivalent requirements for >10 million has been increased to 50 versus the current AASHTO requirement of 45. This "bumping" of the criteria for aggregate properties is considered prudent given the significant influence of aggregate characteristics in providing acceptable performance in terms of instability rutting. The impacts of these revisions are considered negligible given that they are generally consistent with the coarse aggregate angularity (i.e. fracture) and manufactured fine content requirements for conventional mix types. As noted in Table 4.8, the aggregate criteria for large nominal maximum size (NMS) base course mixtures has been relaxed in view of the location of these mixtures within the pavement structure and the potential economic benefit associated with their use. It is recommended that current AT aggregate "source" property requirements outlined in Specification 3.2 Aggregate Production and Stockpiling, including Los Angeles Abrasion, plasticity index and detrimental matter, be maintained for Superpave mixtures.

- 63 -

The proposed Superpave mixture criteria presented in Table 4.9 generally correspond to the AASHTO guidelines. As previously stated, where the revised AT ESALs groupings lie within a wider grouping within the AASHTO guidelines, the move stringent requirements have been proposed. The dust-to-binder ratio requirements differ from AASHTO, in part, due to the calculation method (i.e. AT uses the effective binder content by mass of aggregate; AASHTO is based on mass of mix) and are consistent with those currently specified by AT. The design ESAL category of <0.3 million has not been included in the proposed criteria. No experience exists with a design compaction effort of 50 gyrations, which in most cases would be a lower compaction effort than a 50 blow Marshall. Although this type of mixture may be appropriate for residential or local roadways, performance evaluation under typical low traffic highway loading conditions should be undertaken prior to including this ESAL category.

- 64 -

Table 4.9 Proposed Superpave Mixture Criteria

Superpav e Compaction

Parameters Superpave Mixture Design Requirements

Design Traffic ESAL

(million)

Number of Gyrations

Required Density (% of Theoretical Maximum Specific

Gravity)

Voids in Mineral Aggregate (minimum %)

Nominal Maximum Size (mm)


(%)

Dust- to- Binder Ratio

1 Ninitial Ndesign Nmaximum Nin i t ia l Ndesign Nmaximum 25 20 12.5 10

< 1.0 7 75 115 <90.5 65-78 0.6-1.2 for 1.0 to <3.0 7 75 115 Fine 3.0 to <6.0 8 100 160 Mixtures 6.0 to <10.0 8 100 160 96.0 <98.0 12.0 13.0 14.0 15.0 0.7-1.5 for 10.0 to <20.0 8 100 160 <89.0 65-75 Coarse

>20.0 9 125 205 Mixtures

1 The Dust -to-Binder Ratio is defined as the ratio of the percent of aggregate passing the 80 µm sieve size to the percent of effective binder content (by mass of dry aggregate).

Note: Design ESALs are the anticipated project traffic level expected on the design lane over a 20-year design period. Regardless of the actual design life of the roadway, determine the design ESAL for 20 years and choose the appropriate N des ign level.

The moisture susceptibility of Superpave mixtures will be evaluated for acceptance according to AASHTO T283, Resistance of Compacted Bituminous Mixture to Moisture Induced Damage. The minimum acceptance value shall be 80%, on specimens not subjected to the optional freeze cycle condit ioning.

- 65 -

The current design criteria for moisture susceptibility, minimum tensile strength ratio (TSR) of 80%, has been maintained. AT should consider an amendment to include the optional freeze cycle. This amendment is strictly in recognition of the fact that freeze/thaw cycles are consistent with Alberta climatic conditions. As AT has been requiring the submission of TSR results for conditioned specimens subjected to the freeze cycle in addition to those not, the potential impact of this revision (i.e. in terms of passing or failing the criteria) would best be ascertained from a review of this data. The second aspect with regards to the selection of a Superpave mix type relates to aggregate gradation characteristics. Within the Superpave system, gradation characteristics are typically specified in terms of: • aggregate nominal maximum size (NMS) with corresponding gradation limits • fine or coarse aggregate gradations (i.e. gradations plotting above or below the

restricted zone, respectively) Several aspects of the Superpave gradation terminology differ from conventional mixtures. As noted, within Superpave the "top size" of the aggregate gradation is identified using the term nominal maximum size (NMS). The NMS is defined as one size larger than the first standard sieve size to retain more than 10 percent. In some respects it is difficult to compare Superpave gradations to conventional mix gradations in Alberta (i.e. Designation 1, Class 12.5 mm and 16 mm). Firstly, a 16 mm sieve size is not used in Superpave. Secondly, the NMS of a Designation 1 Class 16mm gradation could be 12.5 mm or 20 mm depending on whether there is more or less than 10% passing the 12.5 mm sieve size. These distinct differences in gradation terminology make it difficult in some cases to compare the two different specifications. The restricted zone is an area on either side of the maximum density line (when plotted on a 0.45 power gradation chart) in the intermediate sand size range. During the initial period of Superpave implementation, designers were encouraged to avoid gradations which passed through the restricted zone, in part, to avoid a mixture with a "humped gradation" which may be prone to compaction problems and/or permanent deformation. Furthermore, coarse gradations (i.e. those plotting below the restricted zone) were favoured for higher traffic loading applications. More recently the restricted zone and coarse gradation superiority philosophies have been challenged. The consensus currently is that there is no discernable difference in permanent deformation or fatigue performance between gradations below, above, or through the restricted zone. As such, it is likely that the restricted zone guideline will be dropped from the Superpave system. This may (or may not) require that a new

- 66 -

method for describing gradation types is developed. One suggested approach is that if the gradation plot passes above the maximum density line at the 2.36 mm (or the metric 2.5 mm) sieve size, the gradation is termed fine, and if below it is termed coarse. To date on AT projects, the selection of a fine or coarse graded Superpave mixture gradation has been the Contractor's choice. This has resulted in the vast majority of Superpave mixtures utilized in Alberta being coarse graded. Based on adhoc observations with respect to the preliminary performance of these mixes in specific applications it is considered prudent, in some cases, to specify Superpave mixtures as coarse or fine graded. Specific applications for fine graded mixtures might include, for example, first stage paving and base course construction. Coarse graded mixtures may be preferred for applications where enhanced macro-texture and skid resistance are desired, or for improved rut resistance. In other cases, the choice of a fine or coarse graded mixture may not be critical and could be left to the contracting industry to provide the most economical product. Although some preliminary performance information (EBA, 2001) indicates that gradation characteristics are a significant influencing factor on mixture performance, further evaluation is required before specification revisions are considered. Therefore it is proposed that the current requirements for gradation limits and the restricted zone guideline be maintained. The selection of the aggregate NMS should consider the intended lift thickness requirements specific to the project. The optimum aggregate NMS should preferably provide a minimum "lift thickness/NMS" ratio of 4:1 for coarse graded surfacing mixtures and 3:1 for fine graded mixtures and coarse graded lower lift mixes. Table 4.10 provides the recommended aggregate NMS for coarse and fine graded mixtures as they correspond to the proposed conventional mix types and typical applications. Therefore, the intent is that a designer would select the appropriate NMS for a Superpave mixture based on the corresponding conventional Marshall mix which would be considered appropriate for a specific application.

- 67 -

Table 4.10 Recommended Nominal Maximum Size Aggregate for Superpave Mixtures

Conventional New Mix Type

Typical Design ESAL Range

(million)

Typical Lift Thickness

( m m )

Typical Application Recommended Aggregate Nominal Maximum Size for Superpave Mixtures

( m m ) Coarse Graded Mixtures Fine Graded Mixtures

H1 > 3.0 30 - 60 Surfacing (1 or 2 lifts) for very high service

20 12.5

H2 1.0 to < 10.0 30 - 60 Surfacing (1 or 2 l ifts) for high service

12.5 12.5

M1 1.0 to < 3.0 30 - 60 Surfacing (1 or 2 l i f ts) for medium service

12.5 12.5

L1 < 1.0 30 - 60 Surfacing (1 or 2 l ifts) for low serv ice

10 or 12.5 12.5

S1 - ± 20 Leveling lifts 10 10 S2 - ± 30 Thin single lift overlays 10 10 S3 - Note 1 Base lifts 20 or 25 20 or 25

Note 1: Lift thickness 60 mm or greater for 20 mm NMS, 80 mm or greater for 25 mm NMS

- 68 -

5. RECOMMENDATIONS FOR FURTHER STUDY This study encompassed analysis of the high temperature rutting performance of 773 individual analyses sections representing 365 projects with a total length of over 6600 kms. These projects, paved between 1985 and 1995, represented 5 to 15 years of performance and total ESAL applications between about 15,000 and 11 x 106. However, the vast majority of projects experienced ESAL applications less than about 6 x 106. Mix Type selection criteria have been established for very high traffic applications in excess of 20 x 106 based on extrapolations of the available data and engineering judgement. Further, the study focused on rural highway loadings and conditions and the findings may not apply to urban highway applications. The only network level study of low temperature transverse cracking was carried out in the early 1980's which was supplemented by the Lamont Test Road in the 1990's. Both the high temperature rutting and low temperature cracking performance of modified asphalt binders under Alberta conditions have not yet been validated. The following recommendations are provided: 1. Mix type selection criteria need to be developed for high traffic urban highways where

traffic loading conditions (e.g. traffic speeds and lane distributions) differ from rural highways.

2. Mix type selection criteria for ESAL ranges greater than 6x106 will require validation as the criteria developed in the study are based upon the extrapolation of rutting performance data beyond 10x106 ESALs.

3. It is recommended that a formal Alberta LTPP (Long-term Pavement Performance) program be established by AT in order to provide ongoing validation and verification and necessary modification of the new Mix Type criteria established in this research. This program should include continued monitoring of the rutting performance of projects included in this research as well as new projects constructed following the new Mix Type and binder selection criteria. With present concerns and uncertainty with cost premiums and performance risks associated with modified binders this program should be expanded to monitor the long-term low temperature cracking performance of both conventional and modified asphalt binders representing a broad range of climate zones and traffic loadings.

4. In consideration of the high cost of the asphalt binder in asphalt concrete pavements, the effects of plant mixing conditions on the rheology of asphalt binders and resulting effects on low temperature cracking performance requires further research.

- 70 -

REFERENCES

(AASHTO, 1999) AASHTO Provisional Standards, Interim Edition, American Association of State Highway and Transportation Officials, May 1999.

(AASHTO, 2001) AASHTO, "MP2-01 Standard Specification for Superpave Volumetric Mix Design", American Association of State Highway and Transportation Officials, 2001.

(AI, 1988) Asphalt Institute, "Mix Design Methods for Asphalt Concrete", Manual Series No. 2 (MS-2), 1988.

(C-SHRP, 1994) EBA Engineering Consultants Ltd., "Performance Correlation of Paving Grade Asphalts, Canadian Strategic Highway Research Program, November 1994.

(EBA, 1988) EBA Engineering Consultants Ltd., "Alberta Transportation and Utilities Task Force Report for Improved Quality of ACP Construction", Alberta Transportation and Utilities, 1988.

(EBA, 1994) EBA Engineering Consultants Ltd., "Study of Hardening of Recovered Asphalts on City Projects", March 1994.

(EBA, 2001) EBA Engineering Consultants Ltd., "Superpave Pavement Permeability Study", Alberta Transportation, April 2001.

(FHWA, 1999) FHWA, "LTPPBind - Version 2.1", July 1999

(Gavin, 1993) Gavin, J., "Review of 1993 Abson Test Results", Alberta Transportation & Utilities, October 1993.

(Gavin, 1995) Gavin, J., "Summary of 1994 Laboratory Testing of Recovered Asphalts", Alberta Transportation & Utilities, March 1995.

(Gavin and Dunn, 1997)

Gavin, J., and Dunn, L., "The C-SHRP Lamont Test Road – Five Years of Performance Monitoring", Eighth International Conference on Asphalt Pavements, Proc. 1997.

- 71 -

REFERENCES

(KPMG, 1995) KPMG Management Consulting, "Protection of Alberta's Roads - A Study of Commercial Vehicle Weight and Safety Compliance", Alberta Transportation and Utilities, 1995.

(McLeod, 1976) McLeod, N.W., "Asphalt Cements: Pen-Vis Number and Its Application to Moduli of Stiffness", Journal of Testing and Evaluation, ASTM, Vol. 4, 1976.

(McMillan and Anderson, 1988)

McMillan, C.T., Anderson, K.O. "An Evaluation of the Influence of the Binder on Permanent Deformation of Asphalt Concrete", CTAA, Proc. 1988.

(McMillan, 1989) McMillan, C.T. "A Study of Pavement Deformation Characteristics of Asphalt Concrete Pavements in Alberta", M.Sc. Dissertation, University of Alberta, 1989.

(NRC, 1975) National Research Council, Associate Committee on the National Building Code, "Climatic Information for Building Design in Canada - 1975 - Supplement to the National Building Code, "NRC No. 13986.

(NRC, 1985) National Research Council, Associate Committee on the National Building Code, "Supplement to the National Building Code of Canada - 1985", NRC No. 23178.

(Palsat, 1986) Palsat, D.P. "A Study of Low Temperature Transverse Cracking in Alberta", M.Sc. Dissertation, The University of Alberta, 1986.

(Palsat, 1988) Palsat, D.P. "Low Temperature Cracking in Alberta", CTAA, Proc. 1988.

(Shell, 1990) Shell, "Bitumen and Asphalt Nomographs", Version 1989, Release ME1.1, January 1990.

(Willis, 2000) Willis, Terry, Personal Communication, May 2000.

APPENDIX A

SUMMARY OF THE DEVELOPMENT OF

ALBERTA TRANSPORTATION'S PRESENT MIX TYPE SELECTION CRITERIA

A-1

SUMMARY OF THE DEVELOPMENT OF AT's PRESENT MIX TYPE SELECTION CRITERIA

A.1 Evolution of AT Asphalt Cement Specifications

Asphalt cement specifications used by Alberta Transportation have been developed during the sixties, seventies and early eighties in an attempt to optimize the low and high temperature performance of asphalt concrete pavements. Prior to 1967, asphalt cements were graded only by penetration at 25°C. Two grades were in use: 150-200 pen and 200-300 pen. A minimum quantity of SC-3000 was also used. Significant changes were made to asphalt cement specifications in 1967 to improve low temperature performance of asphalt concrete pavements. An asphalt cement grade referred to as AC 275 had a specified minimum viscosity at 60°C of 275 poise and a minimum penetration at 25°C of 250 dmm to control temperature susceptibility of the asphalt and was the primary grade used through to the mid-seventies. In 1978, two new grades, designated as AC 27.5 and AC 60 and which were essentially "high viscosity" 200-300 pen and 150-200 pen asphalt cements respectively were introduced. The addition of a 'harder' 150-200 pen asphalt cement provided a more viscous binder that could be used on higher trafficked roadways, especially in warmer climates, where the softer AC 275 was leading to rutting problems. In 1980, asphalt cement specifications were further revised to include a total of 5 grades - a high viscosity 150-200 pen (150-200A), a high and medium viscosity 200-300 pen (200-300A, 200-300B) and a high and medium viscosity 300-400 pen asphalt cement (300-400A, 300-400B). The minimum and maximum viscosity limits approximately paralleled PVN (Penetration-Viscosity Number) lines as defined by McLeod (1976). These specifications are still in use and are included in Specification 5.7 Supply of Asphalt.

A.2 Asphalt Mix Design The Marshall Method of Mix Design has historically been used by AT to design asphalt concrete mixtures. In the sixties and seventies, the objective of mix design was simply to identify, for the gradation of aggregate produced for the project, an optimum asphalt content that would

A-2

provide adequate stability and durability. During that period very little emphasis was placed on optimizing aggregate or mix characteristics and it was assumed that if Marshall design characteristics met or exceeded Asphalt Institute criteria, an acceptably performing asphalt pavement would result. In the late seventies and throughout the eighties, AT placed greater emphasis on the engineering of aggregate and asphalt mixes. The inadequacies of the Marshall method of mix design were better known, and in the absence of more performance based or rational design procedures, specifications for mix properties and aggregate gradation and other characteristics evolved based upon historical performance and engineering judgement.

A.3 Low Temperature Performance of ACP in Alberta A.3.1 Introduction An extensive, system wide investigation into the low temperature performance of asphalt concrete pavements constructed by AT was initiated in 1984. The objectives of this research were to identify the major factors that were influencing the occurrence and frequency of low temperature cracking performance of asphalt concrete pavements and to provide more definitive design guidelines to the highway engineer to minimize or negate low temperature transverse cracking. The results of this investigation are reported in more detail in (Palsat, 1986) and (Palsat, 1988). A.3.2 Summary of AT Investigation The approach of this investigation involved a large scale transverse cracking survey of about 1000 km of asphalt concrete pavement representing 77 paving projects constructed on the rural highway network in Alberta between 1970 and 1979. A map included in the National Building Code (NRC, 1975) showing iso-temperature

contours on a 2.8°C interval for January design temperatures was modified based on comparisons to local weather station data for selected locations across the province. This modified map was used to select low minimum winter temperatures for each project included in the analysis.

A-3

This investigation identified that the major factors influencing low temperature transverse cracking behaviour were pavement thickness, original asphalt stiffness and pavement age. This research also identified a critical asphalt stiffness of 2.9 x 106 determined using McLeod's method (McLeod, 1976) based upon original asphalt characteristics (penetration at 25°C, PVN calculated using viscosity at 60°C) and a loading time of 20,000 secs, and the pavement temperature at a pavement depth of 50 mm based on site specific low temperature conditions. This critical stiffness value separated the behaviour of pavements exhibiting "acceptable" (non- or very low) from "non-acceptable" (medium to high) transverse cracking frequencies. Knowing the typical characteristics of asphalt cements used by AT and using this critical asphalt stiffness value, critical pavement temperatures were back-calculated using van der Poel's stiffness nomograph as modified by McLeod. These calculations were extended to determine critical ambient air temperatures that corresponded to an asphalt critical stiffness at either a 50 mm or 100 mm pavement depth. For the typical asphalt grades used by AT at the time, these critical ambient air temperatures were determined to be:

Ambient Air Temperature in °° C Resulting in a Critical Asphalt Stiffness of 2.9 x 106 at a Pavement Depth of:

Asphalt Grade 50 mm 100 mm 150-200A -37°C -43°C 200-300B -38°C -44°C 200-300A -43°C -49°C 300-400A -45°C -51°C

These values indicate, for an expected low ambient temperature of -43°C, that 200-300A or 300-400A would have to be used for the surface pavement course if transverse cracking is to be avoided. This chart also shows that any of the grades could be used for the construction of lower lifts without the asphalt binder critical stiffness being exceeded. Based on this approach, a map was developed to assist in the selection of asphalt grade to optimize low temperature performance based upon climatic region. This map is presented in Figure 1.

A-4

Figure 1 Design Map for Selecting Asphalt Cement Grades for Surface Courses

A-5

A.3.3 Conclusions The results of this research provided more definitive guidelines regarding asphalt grade selection to optimize low temperature pavement performance. However the design map developed could not be used as the only criteria for asphalt grade selection. There was still a need to quantify, in a similar way, the influence of asphalt characteristics on high temperature pavement performance and to develop a design method for the selection of asphalt grades to address pavement performance at both in-service temperature extremes.

A.4 High Temperature Performance of ACP in Alberta A.4.1 Introduction An extensive, system wide investigation into the high temperature performance of asphalt concrete pavements constructed by AT was initiated in 1986 with the objectives to determine the influence of the binder characteristics and the effects of temperature, specifically with respect to binder stiffness, on the permanent deformation of asphalt concrete pavements (McMillan, 1989). The results of this work would provide more definitive input into the development of design guidelines for the selection of asphalt grades to optimize high temperature performance. This study was conducted in two phases. The first phase, which was a field and laboratory study, examined the performance of pavements throughout the Alberta highway network and was a major input into the development of the present mix type selection criteria. The second phase examined the behaviour of mixes in the laboratory under repeated load testing. The results of the laboratory phase are reported in (McMillan, 1989) and (McMillan and Anderson, 1988) and were not used directly in the development of the mix type selection criteria. A.4.2 Field Phase Project Selection and Testing The field portion of this research involved the inspection of forty highway sites within the Provincial highway network representing all geographical locations and pavement structure types.

A-6

The sites inspected covered a significant range of the various parameters with cumulative ESALs (Equivalent Single Axle Loads) ranging from about 10,000 to over 3.5 million, asphalt concrete thicknesses between 50 and 300 mm, and asphalt binder with original penetration at 25°C from 160 to 317 (0.1 mm units) although the majority of the projects were constructed with a binder equivalent to a 200-300 penetration grade asphalt cement. Historical construction and mix design data were reviewed to define the characteristics of the as-built pavement structures. The ESAL values used were determined by AT as reported in the Pavement Management System database. The method used classified trucks as either single unit or tractor trailer combinations and use factors of 0.56 and 1.37 respectively for determining ESALs. The temperature values assigned to each project were based on July design air temperatures as presented in the National Building Code (NRC, 1985). At each site, rut depths were measured using a 1.8 m straight edge. The measured rut depths ranged between 0 mm and 29 mm; however; the average value was 4.6 mm. Of the forty sites inspected, twenty-eight sites were cored to obtain information on the current in-place material characteristics and to confirm historical structural data. Analysis and Model Development The analysis of the data involved correlating the various pavement, materials, traffic and climatic characteristics with the measured pavement rutting. The observed rutting was considered as the dependent variable, with all other parameters considered as independent variables. The independent variables considered included original Marshall mix design data, field quality control data gathered at the time of the original construction, and materials data collected from the cores taken for this study. As well, measures of asphalt temperature susceptibility, stiffness, and changes in binder rheology over time were calculated and included in the analysis. Asphalt binder stiffness was determined using McLeod's method (McLeod, 1976). PVN was calculated using penetration at 25°C and absolute viscosity at 60°C. A loading time of 0.5 seconds was used to be consistent with the laboratory phase of this study. The temperature used was a summer design air temperature for the area in which the project was located.

A-7

Two models were developed from the field phase of this study. One model, based upon 40 sites, used the rheological characteristics of the original asphalt supplied. The second model was based on the rheological characteristics of the recovered in-place data from the 28 cored sites. The model developed for the original asphalt supplied data was:

Rut depth (mm) = 2.6186 + 0.0060*(Daily Cumulative ESALs) - 0.0023*(Daily Cumulative ESALs)*Log(Original Binder Stiffness (kPa))

The second model developed, utilizing the rheological characteristics of the records in-place asphalt from the 28 cored sites, was:

Rut depth (mm) = 2.9630 + 0.0076*(Daily Cumulative ESALs) - 0.0024*(Daily Cumulative ESALs)*Log(Abson Stiffness (kPa))

Both models were very similar and showed that asphalt stiffness in conjunction with traffic loadings were the most significant variables correlated with the measured pavement rutting. A.4.3 Conclusions The models developed for the field phase of this investigation showed that the permanent deformation of asphalt concrete was most significantly correlated to the number of load applications and to the binder stiffness. This correlation had also been determined in the laboratory testing program conducted for this study. Results of the field phase suggested that Alberta highways subjected to loadings of less than about 0.5 million ESALs could use a 200-300A asphalt without risking a significant degree of rutting. Neither the field or laboratory phases suggested a correlation of mix design characteristics with permanent deformation. This was most likely influenced by the limited range of parameters and the proximity of Marshall characteristics to the optimal design values. Based on these results it was apparent that asphalt stiffness and therefore asphalt grade had an effect on the level of rutting that can be expected in an asphalt concrete pavement. Additionally, because the asphalt stiffness is greatly influenced by temperature, consideration must be given to the climatic conditions the pavement will experience in-

A-8

service. The recognition of these interactions contributed to the development of specific design guidelines presented in the next section.

A.5 Development of Design Guidelines A.5.1 Introduction The results of the two major research programs carried out by AT clearly identified the effects of asphalt binder stiffness on both the high and low temperature performance of asphalt concrete pavements in Alberta. This research identified that the transverse cracking of asphalt concrete pavements across the province was largely due to the use of highly temperature susceptible asphalts in the past and more recently to the use of less temperature susceptible but "harder" asphalts, i.e. stiffer asphalts, in an attempt to minimize rutting potential. This research also identified that the most serious rutting of the network was confined to a few highly trafficked highways, e.g. Hwy 1, Calgary to Medicine Hat; Hwy 16, Edmonton vicinity; Hwy 2, south of Calgary to north of Edmonton. A significant portion of this rutting on the provincial road network had been influenced by the extensive use of AC 275 (high viscosity, 200-300 pen) prior to 1978 and the use of mixtures of inadequate rutting resistance for the traffic loadings and climatic conditions. Further, it was anticipated that future increased traffic loadings would significantly increase the extent and severity of rutting on the network in spite of the use of stiffer asphalt cements. In fact, based on current traffic data it was estimated that traffic loadings, in terms of cumulative ESALs, over the period from 1990 to 2010 would be more than double those of the previous period from 1970 to 1990. Until acceptable performance based mix design methods and criteria were developed, a need was identified to expand current guidelines and rules-of-thumb and to provide more definitive and rational design criteria to be used in the design of asphalt concrete mixes.

A-9

The design criteria and guidelines developed addressed: • selection of asphalt grade • selection of aggregate characteristics

• topsize • manufactured and natural fines (minus 5000 µm sizes) • % fractures

• Marshall mix design factors • number of blows • minimum Marshall Stability, Marshall flow • VMA and air voids

These criteria and guidelines were based upon traffic loadings and the maximum anticipated summer air temperatures the pavement would be subjected to. The minimum winter air temperatures the pavement would be exposed to, which would effect low temperature cracking, were also considered in the development of the guidelines. A.5.2 Asphalt Grade Selection The criteria developed for asphalt grade selection was based upon using the 'softest' grade of asphalt cement that would provide acceptable rutting resistance. It was recognized that this improvement in rutting resistance would result in increased low temperature cracking on more heavily trafficked highways. Experience had indicated that the use of 200-300A on heavily trafficked highways had contributed significantly in rutting. Therefore 150-200A had evolved in the eighties as the standard asphalt grade designed for heavily trafficked highways. A design map was developed to allow a designer to select an appropriate asphalt grade for the anticipated design ESALs which were defined as the projected cumulative ESALs over the design life of the pavement. The development of this map was based upon the rut prediction models described earlier which taken into account more directly the effects of asphalt stiffness, traffic loadings and summer operating temperatures. In order to separate the effects of temperature on binder stiffness, a number of climatic zones based upon maximum summer temperatures were identified for the Province. These zones are presented in Figure 2.

A-10

Figure 2 High Temperature Design Map for Selecting Climatic Zone

A-11

Using the ten year average summer maximum temperature for each zone, binder stiffnesses were calculated following McLeod's method and using typical rheological properties for 150-200A and 200-300A and a loading time of 0.5 s. Using the rut prediction models, curves for rutting levels of 5 and 10 mm were established over the range of binder stiffnesses calculated and ESALs anticipated. For each zone, the ESAL levels (using 0.56 and 1.37 factors for single unit and tractor trailer combinations respectively) required to reach 5 and 10 mm ruts for a binder stiffness equivalent to 150-200A were determined. These levels identified the range of ESALs where 150-200A would be used. Below this range, 200-300A would be specified. (This would ensure that low temperature performance would be optimized where lower traffic conditions exist.) ESALs above this 10 mm limit would identify a need for enhancements to the quality of the aggregates being used in order to provide improved rutting resistance. This need for aggregate enhancements is justified as the development of the rut models was based upon the typical aggregate and mix characteristics used in the past. This work led to the development of the "ESAL Criteria for Selection of Asphalt Mix Type" shown in Table 1. The design map, in conjunction with Table 1, demonstrates that a pavement constructed near Edmonton, in central Alberta, using 150-200A asphalt could accept about double the total ESALs over its design life as compared to a pavement constructed near Lethbridge, in southern Alberta, with the same asphalt grade and still provide similar rutting performance. A.5.3 Asphalt Concrete Mixes It was necessary to categorize and identify mix types to aid the designer in specifying an appropriate mix type for a specific project. Eight asphalt mix type designations were developed and defined. Seven of the mix types were currently being used within AT, although without any formal designation. Within each mix type, in addition to asphalt grade selection, criteria were developed for each parameter identified. This is presented in Table 2. The basis for the criteria developed follows.

A-12

Aggregate Characteristics Department aggregate specifications include requirements for gradation, % fractures, Los Angeles abrasion and plasticity. Historically, both 12.5 mm and 16 mm topsize aggregates had been used in Alberta. Selection in the past was generally governed by achievement of acceptable % fractures and more recently considered both the increased rutting resistance that may be afforded by using larger topsize aggregates as well as the increased segregation potential of larger topsize aggregates. An extensive analysis of past mix designs performed by AT was carried out and the design characteristics (e.g. Marshall stability, Marshall air voids and VMA, aggregate gradation, % of manufactured fines in the -5000 portion of the aggregate) for both 12.5 mm and 16 mm mixes were analyzed and compared. This analysis helped define limits for the percentage of manufactured fines in the minus 5000 µm portion of the combined aggregate, termed "% MF,-5000", for each mix type. It was determined that the "% MF,-5000" for typical 16 mm topsize aggregates ranged from about 30 to 50%. The range for 12.5 mm topsize aggregates was from about 45 to 65%. Type 1 mix, for which ESAL criteria had not been developed yet, would require 16 mm topsize aggregate, 100% MF,-5000 and 100% fractures. This mix would be used on very high trafficked highways. Type 2 mix would be used on high trafficked highways and would have a requirement for 16 mm topsize aggregate, a minimum of 70% MF,-5000 and a minimum of 70% fractures. Types 3 and 4 were considered equivalent and their selection would be based on past experience or project specific design or materials constraints. The % MF,-5000 criteria is based upon the designated aggregate topsize. These criteria of 40 and 50% were somewhat restrictive compared to what has been experienced in the past. It was estimated that about half of the aggregate deposits used in the past would not be able to meet this requirement without the addition of manufactured fines. Types 5, 6 and 7 mixes would be used on lower trafficked highways, secondary roads and community airports and did not have a separate requirement for manufactured fines. Conventionally crushed aggregates meeting the specified gradation band and % fractures requirements would be acceptable. The use of 12.5 mm mixes on lower trafficked roads where risk of pavement rutting is very low afforded reduced segregation potential of the asphalt mix during construction which can reduce maintenance costs over the life of the pavement.

A-13

Marshall Design Parameters Marshall design characteristics developed are presented in Table 3 and generally conformed to Asphalt Institute criteria (1988). The minimum Marshall stability was increased from AT criteria for Types 1 and 2 mixes. Although it was recognized that high Marshall stability doesn't guarantee high rutting resistance, low Marshall stabilities tended to be associated with aggregate characteristics that were not desirable in a highly rut resistant mix. The number of blows to be used in the mix design was also based upon summer operating temperatures and ESAL levels and recognized that the risk of rutting or bleeding of mixes designed with 50 blows increased with increased summer temperature. A.5.4 Summary The design map and ESAL criteria developed which consider traffic loadings and climatic variations across the province would allow a more rational approach for specifying asphalt grade, aggregate characteristics and Marshall mix design parameters. For very low volume airports, mixes designed with 50 blows, 300-400A asphalt cement and 12.5 mm topsize aggregate would provide acceptable performance. As ESAL levels increase, stiffer asphalts, larger topsize aggregates, increased proportions of manufactured fines and 75 blows could be specified based upon maximum summer temperatures to ensure acceptable high temperature pavement performance.

Table 1 ESAL Criteria for Selection of Asphalt Mix Type Asphalt Mix Type Zone

11 2 3 or 4 5 6 72

A - > 1.0 0.5-1.0 0.3-0.5 < 0.3 - B - > 1.5 0.7-1.5 0.4-0.7 < 0.4 - C - > 2.0 1.0-2.0 0.5-1.0 < 0.5 - D - > 2.5 1.5-2.5 0.8-1.5 < 0.8 -

1 Criteria to be Developed 2 Community Airports

ESAL criteria given in Table 1 are the total ESALs (x 106) per direction that will be applied to the asphalt pavement over its design life.

A-14

Table 2 Asphalt Concrete Mix Types and Characteristics Asphalt

Mix Type Aggregate

Topsize (mm)

% MF -50001, 2

Fractures +5000 (2 faces) (Min)

Asphalt Cement

Type and Grade2

Marshall Stability3

N (Min)

No. of Blows3

1 16 100 100 150-200A 120-150A

PMA

12000 75

2 16 70 70 150-200A 12000 75 3 16 40 60 150-200A 6700 75 4 12.5 50 60 150-200A 6700 75 5 12.5 - 60 200-300A 6700 75 6 12.5 - 60 200-300A 4500 50 74 12.5 - 60 300-400A 4500 50 85 10 - 60 Note 1 Note 2

1 % Manufactured Fines in the -5000 Portion of the Combined Aggregate 2 For Surface Courses and for Virgin Mixes Only 3 For Marshall Mix Design 4 Community Airports 5 Levelling course Note 1 - Use the same asphalt grade as for the surface course. Note 2 - Use the same number of blows as for the surface course.

Table 3 Marshall Characteristics for Asphalt Mixes Characteristics Class 10 Class 12.5 Class 16

Marshall Stability, N

Refer to "Asphalt Concrete Mix Types and Characteristics" Table for minimum requirements.

Air Voids % 3 to 5 3 to 5 3 to 5 V.M.A. % 15.5 to 17.0 15.0 to 16.5 14.5 to 16.0 Flow mm 2 to 5 2 to 5 2 to 5 Retained Stability %

70 70 70

(i) Retained stability after 24 hours soaking at 60°C to be run at the recommended design asphalt content.

(ii) The minimum V.M.A. criteria may be reduced by up to 1% if experience indicates that the mixture will perform satisfactorily and all other criteria are met.

(iii) All asphalt mixtures designed for airport paving will have an air void requirements of 2 to 4% regardless of aggregate class.

A-15

A.5.5 Subsequent Modifications Prior to the formal development and implementation of the present mix type selection criteria, it was recognized that aggregate physical properties included in general specifications at that time were inadequate to provide sufficient rut resistance under high traffic loadings. In about 1989, an Enhanced Stability (ES) Mix Designation was developed with the following requirements: General Specification

Requirements 'ES' Mix Requirements

% Fractures (2 faces) 60+ 80+ % MF,-5000 Not Specified 70%

These ES Mixes were specified in Special Provisions until about 1992 when the present Mix Types were included in the General Specifications. The "% MF,-5000" was defined as the percent of manufactured fines in the minus 5000 µm portion of the combined job mix formula aggregate. Aggregate specifications required the pit run aggregate to be split such that the coarse aggregate fraction, before crushing, was to contain no more than 5% passing the 5000 µm sieve. This requirement was also specified for the production of additional manufactured fines necessary to meet the % MF,-5000 specification. The % MF,-5000 was a calculated value and was based on the assumption that all -5000 µm material in both the crushed coarse aggregate and manufactured fines stockpiles was manufactured, i.e. crushed material. Subsequently in the early nineties, new ESAL criteria for Asphalt Mix Types 1 and 7 were developed. Also aggregate topsize, % MF,-5000 and Fractures requirements for Asphalt Mix Type 1 were modified for Mix Types 3 through 8. More recently, Marshall design air void and VMA requirements were modified and VMA requirements were modified and Voids Filled with Asphalt and Film Thickness requirements introduced. The present ESAL criteria for selecting asphalt concrete mix types is presented in Table 4. The present Asphalt Concrete Mix Types and Characteristics included in Specification 3.50 Asphalt Concrete Pavement - EPS (Standard Specifications for Highway Construction, Edition 9, 2001) are presented in Table 5.

A-16

Table 4 AT ESAL Criteria for Selection of Asphalt Concrete Mix Types

Asphalt Mix Type Zone 1 2 3 or 4 5 6 71

A > 2.0 1.0 - 2.0 0.5 - 1.0 0.3 - 0.5 < 0.3 - B > 3.0 1.5 - 3.0 0.7 - 1.5 0.4 - 0.7 < 0.4 - C > 4.0 2.0 - 4.0 1.0 - 2.0 0.5 - 1.0 0.2 - 0.5 < 0.2 D > 5.0 2.5 - 5.0 1.5 - 2.5 0.8 - 1.5 0.3 - 0.8 < 0.3

April/94

1 Also for Community Airports. ESAL criteria given are the total ESALs (x106) in the

design lane that will be applied to the asphalt pavement over its design life.

A

-17

Table 5 Present Asphalt Concrete Mix Types and Characteristics

VMA % (min.) by % Air Voids


%

Flow mm

Retained Stability %

(min)

Asphalt Concrete

M i x Type

Class for Des 1

Aggregate

% MF,-5000 (Min)

(Note 1)

% Fractures +5000

(2 faces)* (Min)

Asphalt Cement Grade

Marshall Stability

N (min)

No. of B lows

Air Voids (%)

3 .5 4 .0 1 1 6 7 5 98 (one

face) 90*

1 5 0-200A 1 2 0 0 0 7 5 Note 5 13.0 13.5 6 5 t o 7 5 2 to 3 .5 7 0

2 1 6 7 0 70* 1 5 0-200A 1 2 0 0 0 7 5 Note 5 13.0 13.5 6 5 t o 7 5 2 to 3 .5 7 0 3 1 6 4 0 60* 1 5 0-200A 8 000 7 5 Note 5 13.0 13.5 6 5 t o 7 5 2 to 3 .5 7 0 4 12.5 5 0 60* 1 5 0-200A 8 000 7 5 Note 5 13.5 1 4 6 5 t o 7 5 2 to 3 .5 7 0 5 12.5 Note 2 60* 2 0 0-300A 8 000 7 5 Note 5 13.5 1 4 6 5 t o 7 5 2 to 3 .5 7 0 6 12.5 Note 2 60* 2 0 0-300A 5 30 0 5 0 Note 5 13.5 1 4 6 5 t o 7 5 2 to 4 7 0 7 12.5 Note 2 60* 3 0 0-400A 5 300 5 0 Note 5 ,6 13.5 1 4 6 5 t o 7 8 2 to 4 7 0 8 1 0 Note 2 60* Note 3 5 300 Note 4 Note 5 14.5 1 5 6 5 t o 7 8 2 to 4 7 0

Note 1 - The Percentage of Manufactured Fines in the -5000 Portion of the Combined Aggregate. Note 2 - All fines manufactured by the process of crushing shall be incorporated into the mix for Asphalt Mix Types 5, 6, 7 and 8. Note 3 - Use the same asphalt grade as for the l i f t above. Note 4 - Use the same number of blows as for the surface course. Note 5 - The Design Air Voids shall be chosen as the lowest value, within the range of 3.5 to 4.0% inclusive, such that all other mix

design criteria are met. Note 6 - Air Void limits listed in Note 5 shall be reduced by 1% for community airports. VMA at 2.5% Air Voids shall be a minimum of

12.5%. Note 7 - Theoretical Film Thickness requirements shall be as follows depending upon the specified Mix Type and Design Air Voids.

The Theoretical Fi lm Thickness value shall be establi shed in accordance with TLT-311.

Minimum Theoretical Film Thickness Requirements ( µµ m)

Design Air Voids (%) Mix Types 1, 2, 3, 4 and 5 Mix Type 6 and 7 4.0 and 3.9 6.0 6.5 3.7 and 3.8 6.1 6.6 3.5 and 3.6 6.2 6.7

APPENDIX B

FACTORS AFFECTING RUTTING

VARIABILITY CASE STUDIES

• As-Built Binder Properties • Seal Coats • Underlying Pavement Properties

B-1

FACTORS AFFECTING RUTTING VARIABILITY CASE STUDIES

The following examples demonstrate specific factors that may affect rutting measurements or performance that are very difficult or impossible to account for in the analysis. However, these factors are real and would have real effects on rutting performance. As-Built Binder Properties Asphalt binder properties have a secondary influence on mixture stiffness and rutting resistance as compared to aggregate properties. This influence is accounted for in the present Mix Type selection protocols and results in the use of a stiffer asphalt cement grade, i.e. 150-200A in warmer climate zones and where Design ESALs are higher. Both the City of Edmonton (EBA, 1994) and Alberta Transportation (Gavin, 1993) (Gavin, 1995) carried out extensive studies in 1993 and 1994 to measure and evaluate the degree of hardening of asphalt binders that was attributable to plant mixing and laydown at elevated temperatures. A review of these studies indicated that the recovered penetrations and viscosities immediately after construction for 150-200A and 200-300A asphalts used in hot mix applications in Alberta would be expected to fall in the following ranges:

Asphalt Cement Grade

Absolute Viscosity @ 60°° C (Pa.s) Immediately After Construction

Penetration @ 25°°C (dmm) Immediately After

Construction 150-200A 150-300 70-110 200-300A 90-180 100-160

These data suggest for a 150-200A asphalt cement binder that, based on asphalt plant type, plant operating conditions, mix temperatures, haul distances, mix storage times, etc., the range in as-built binder properties could be equivalent to three asphalt grades. While this could have a measurable affect on high temperature performance, it would also have very significant effects on low temperature performance. Seal Coat The performance of a seal coat can, in itself, significantly affect the measured ruts on a roadway. This is demonstrated in the following example. Hwy 2:24 SBL km 27.16 to km 36.43 was most recently overlaid with 90 mm ACP in 1983 and seal coated in 1985. Continuous rut profile data of the outer lane was collected by AT in 2000 and is presented in Figure 1. The rut profile shows that outer wheelpath ruts range from about 3 mm to over 15 mm. Figure 2 is a photo at about km 29 with outer wheelpath

B-2

rut depths of about 7 mm; Figure 3 is a photo of about km 35 with outer wheelpath rut depths of about 12 mm. Visual observations indicated that the higher ruts in the vicinity of km 35 are due to chip embedment. This difference in performance could be due to variations in the properties of the 1983 overlay that allow the chips to move into the underlying pavement under traffic or an excess application of emulsion during seal coat construction. Although this section of Hwy 2:24 was not included in the analysis because it was last paved in 1983, it is apparent that if it was, the rutting attributed to the asphalt mix properties may have been overstated due to seal coat effects. Underlying Pavement Properties For the purpose of this study, it was assumed that essentially any measured rutting could be attributed to the properties of the asphalt mix used in the most recent overlay. The following example demonstrates a project where a previous rehabilitation treatment appears to have had a significant effect on present rutting performance. According to AT's PMS database, the section of Hwy 12:08 between km 11.76 to km 20.44 has the following pavement structures. km 11.76 to km 15.739 1990

1977 80 mm ACP 225 mm ACBP

km 15.739 to km 20.44 1990 1983 1977

80 mm ACP Cold mill 50 mm and inlay travel lanes only 225 mm ACBP

Continuous rut profile data of the eastbound lane was collected by AT in 2000 and is presented in Figure 4. It is understood that the mill and inlay in 1983 was required to repair severe rutting due to a quality deficiency in the 1977 ACP as well as truck haul patterns. Even though the thickness of the pavement structure is identical in both sections, the effect of the cold mill and inlay treatment in 1983 on the rutting measured in 2000 is very apparent and is likely not attributable to variations in the properties of the asphalt mix used in the 1990 overlay.

B-3

Figure 1 Hwy 2:24 SBL Rut and IRI Profile

B-4

Figure 2 Hwy 2:24 SBL near km 29

Figure 3 Hwy 2:24 SBL near km 35

B-5

Figure 4 Hwy 12:08 Rut and IRI Profile

report tm02/01 - validation and revision of …...report no. abtr/rd/tm-02/01 subject area...

Documents