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Publication Number: FHWA-RD-02-016
Date: June 1999

Methodology for Determining Compaction Temperatures for Modified Asphalt Binders

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by

Kevin D. Stuart
Asphalt Team, HRDI-11
Federal Highway Administration
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296

FOREWORD

This report documents a Federal Highway Administration research study that was performed to assist asphalt mixture technologists in choosing an appropriate laboratory compaction temperature for asphalt mixture design. This temperature is important because it can affect both the optimum asphalt binder content and the mechanical properties of an asphalt mixture.

Historically, standardized procedures for determining what compaction temperature should be used in the laboratory for mixture design have not provided valid temperatures for many asphalt mixtures containing polymer-modified asphalt binders. The use of an incorrect laboratory compaction temperature as a basis for adjusting the temperature of a hot-mix asphalt plant has caused significant problems in the field. Therefore, paving contractors generally use plant temperatures recommended by the suppliers of polymer-modified asphalt binders. Standardized procedures for determining the compaction temperature to be used in the laboratory are based on the equiviscous principle, which was developed 30 to 40 years ago for unmodified asphalt binders. This principle states that the allowable compaction temperature range is the range that provides an asphalt binder viscosity from 250 to 310 mm2/s. There are methods for determining appropriate laboratory compaction temperatures for mixtures containing polymer-modified asphalt binders, but they require additional mixture tests to be performed during mixture design. A methodology like the equiviscous principle greatly reduces the amount of mixture testing that needs to be performed.

The use of polymer-modified asphalt binders is increasing and should continue to increase as more highway agencies use Superpave procedures for choosing asphalt binders. Manufacturers of polymer-modified asphalt binders are also currently developing new formulations so that their binders can be used in more applications. The development of a procedure for determining a valid compaction temperature is needed.

T. Paul Teng, P.E.
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.

FHWA-RD-02-016

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

METHODOLOGY FOR DETERMINING COMPACTION TEMPERATURESFOR MODIFIED ASPHALT BINDERS

5. Report Date

 

6. Performing Organization Code
7. Author(s)

Kevin D. Stuart

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

In-House Report

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, Virginia 22101-2296

13. Type of Report and Period Covered

Final Report
June 1999 - June 2001

14. Sponsoring Agency Code

 

15. Supplementary Notes

FHWA Contact: Kevin D. Stuart, HRDI-11

16. Abstract

The equiviscous principle, which is based on the viscosities of an asphalt binder, determines the compaction temperature to be used during asphalt mixture design. When this principle is used, theoretically, all asphalt binders should provide the same optimum asphalt binder content at a 4-percent design air-void level when all other variables, such as compaction effort and aggregate gradation, are held constant. The compaction temperature determined by this principle is also used by asphalt paving contractors as an indicator of how workable a mixture should be during construction.

The equiviscous principle was developed using unmodified asphalt binders. For some polymer-modified asphalt binders, the equiviscous principle gives a compaction temperature that is significantly higher than what is needed. Excessively high temperatures may damage the asphalt binder, generate fumes, cause asphalt binder draindown, and may lead to a low asphalt binder content in some mixtures.

The objective of this study was to find an asphalt binder or mastic property that can provide appro-priate compaction temperatures for use during asphalt mixture design. The data collected in this study strongly suggest that there is not a single viscosity range that can be used for all asphalt binders. It is recommended that the current standardized asphalt binder viscosity range be used for unmodified asphalt binders. For polymer-modified asphalt binders, this study recommends a different viscosity range.

The allowable compaction temperature range was based on obtaining an air-void range of 3.5 to 4.5 percent after each mixture was compacted using the Superpave gyratory compactor. This tolerance provided a relatively wide allowable compaction temperature range. Mechanical properties were not measured. The allowable compaction temperature ranges for these mixtures could be narrower if they were to be based on obtaining the same mechanical properties. Mechanical properties could be more sensitive than density to differences in age-hardening that occur during short-term oven aging and compaction. Additional studies are needed to determine this.

17. Key Words

Superpave, compaction temperature, equiviscous principle, modified asphalt binders.

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161.

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

46

22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

 

TABLE OF CONTENTS
 
Section
A. Background
B. Objective
C. Scope
D. Experimental Design
1. Aggregates
2. Asphalt Binders
3. Number of Mixing and Compaction Temperatures
E. Equiviscous Temperatures
F. Asphalt Mixture Design
1. Selection of N-Design
2. Optimum Asphalt Binder Content
G. Analysis of the Data
H. Potential Limitations of This Study
I. Results for the Mixtures With Diabase Aggregate and No Hydrated Lime
1. PG 58-28 Unmodified Asphalt Binder
2. Novophalt (PG 76-22) Polymer-Modified Asphalt Binder
3. Styrelf (PG 82-22) Polymer-Modified Asphalt Binder
4. Effective Asphalt Binder Contents
5. Recompacted Specimens
J. Results for the Mixtures With Diabase Aggregate and 1.25-Percent Hydrated Lime
1. Effect of Gyratory Compactor
2. PG 58-28 Unmodified Asphalt Binder
3. Novophalt (PG 76-22) Polymer-Modified Asphalt Binder
4. Styrelf (PG 82-22) Polymer-Modified Asphalt Binder
K. Results for the Mixtures With Limestone Aggregate
1. PG 58-28 Unmodified Asphalt Binder
2. Novophalt (PG 76-22) Polymer-Modified Asphalt Binder
3. Styrelf (PG 82-22) Polymer-Modified Asphalt Binder
L. Discussion on Recommended Compaction Temperatures
M. NCHRP Project 09-10
N. Conclusions
O. Recommendations
P. Final Comment
Q. References

LIST OF TABLES

Table No.

1. Aggregate properties for mixtures containing diabase
2. Aggregate properties for mixtures containing limestone
3. Superpave asphalt binder properties
4. Other properties of the asphalt binders
5. Experimental design
6. Brookfield viscosity (mm2/s) vs. test temperature
7. Equiviscous mixing and compaction temperatures (°C)
8. Mixture properties at a 4.0-percent air-void level for the diabase aggregate
9. Mixture properties at a 4.0-percent air-void level for the limestone aggregate
10. Effect of compaction temperature on the mixture with PG 58-28, diabase aggregate, and no hydrated lime
11. Air voids for the mixtures with diabase aggregate and no hydrated lime
12. Effect of compaction temperature on the mixture with Novophalt (PG 76-22), diabase aggregate, and no hydrated lime
13. Effect of compaction temperature on the mixture with Styrelf (PG 82-22), diabase aggregate, and no hydrated lime
14. Aggregate gradations before compaction, after compaction, and after recompaction
15. Effect of using two different gyratory compactors on the mixture with PG 58-28, diabase aggregate, and 1.25-percent hydrated lime
16. Effect of compaction temperature on the mixture with PG 58-28, diabase aggregate, and 1.25-percent hydrated lime
17. Air voids for the mixtures with diabase aggregate and 1.25-percent hydrated lime
18. Effect of compaction temperature on the mixture with Novophalt (PG 76-22), diabase aggregate, and 1.25-percent hydrated lime
19. Effect of compaction temperature on the mixture with Styrelf (PG 82-22), diabase aggregate, and 1.25-percent hydrated lime
20. Effect of compaction temperature on the mixture with PG 58-28, limestone aggregate, and 1.25-percent hydrated lime

21. Air voids for the mixtures with limestone aggregate
22. Effect of compaction temperature on the mixture with Novophalt (PG 76-22), limestone aggregate, and 1.25-percent hydrated lime
23. Effect of compaction temperature on the mixture with Styrelf (PG 82-22), limestone aggregate, and 1.25-percent hydrated lime
24. Allowable compaction temperature range from the Superpave gyratory compactor
25. Average compaction temperature
26. Allowable compaction temperature range from the Superpave gyratory compactor and the asphalt binders at viscosities of 250 and 310 mm2/s (280 ±30 mm2/s)
27. Viscosity range corresponding to the compaction temperature range from the Superpave gyratory compactor
 

PROJECT PERSONNEL


Asphalt Mixture Portion of the Study

Mr. Kevin D. Stuart, FHWA, Turner-Fairbank Highway Research Center, McLean, VA.

Dr. Pedro Romero, Assistant Professor, Department of Civil and Environmental Engineering, The University of Utah, Salt Lake City, UT.

Mr. Scott Parobeck and Mr. Frank Davis, SaLUT, Turner-Fairbank Highway Research Center, McLean, VA.

Asphalt Binder and Mastic Portion of the Study

Ms. Susan Needham and Dr. Aroon Shenoy, SaLUT, Turner-Fairbank Highway Research Center, McLean, VA.


SI* (Modern Metric) Conversion Factors


Methodology for Determining Compaction Temperatures for Modified Asphalt Binders

A. Background

The equiviscous principle, which is based on the viscosities of an asphalt binder, determines the compaction temperature to be used during asphalt mixture design. The compaction temperature is the temperature where the kinematic viscosity of an asphalt binder is 280 ±30 mm2/s. When this principle is used, theoretically, all asphalt binders should provide the same optimum asphalt binder content at a 4-percent design air-void level when all other variables, such as compaction effort and aggregate gradation, are held constant. Unaged asphalt binders are used to determine the compaction temperature. Therefore, the methodology assumes that each asphalt binder will age harden approximately the same prior to compaction.

The equiviscous principle was developed using unmodified asphalt binders. For some polymer-modified asphalt binders, the equiviscous principle gives a compaction temperature that is significantly higher than what is needed. Excessively high temperatures may damage the asphalt binder, generate fumes, cause asphalt binder draindown, and may lead to a low asphalt binder content in some mixtures.

The compaction temperature determined by the equiviscous principle is also used by the paving contractor as an indicator of how workable a mixture should be during construction relative to the workability of other asphalt binders. As the compaction temperature increases, the mixture may be more difficult to compact unless the mixing and compaction temperatures used in the field are increased. The paving contractor may also need to adjust the rolling pattern. Currently, the temperatures determined by the equiviscous principle for some polymer-modified asphalt binders are excessively high and should not be used to select temperatures for field use.

The compaction temperatures for mixtures containing polymer-modified asphalt binders that do not obey the equiviscous principle are usually based on past experience. An alternative method is to use the asphalt binder content provided by an unmodified asphalt binder. However, this method does not give the measure of workability needed by the asphalt paving contractor, especially for asphalt binders that the contractor has not used to a significant degree. A mixture containing a polymer-modified asphalt binder can also be compacted at several temperatures to find the temperature that gives the same asphalt binder content as an unmodified asphalt binder. However, a methodology like the equiviscous principle eliminates the need for these trial tests.

The compaction temperature used in the laboratory is also important because when volumetric design procedures are developed, including the procedure used by Superpave, the methodology used to determine the compaction temperature becomes an integral part of the procedure. Volumetric design procedures are developed to provide an optimum asphalt binder content based on field performance. If it is assumed that a particular volumetric design procedure does provide the optimum asphalt binder content, then arbitrarily changing the compaction temperature may lead to an asphalt binder content that is not the optimum content.

B. Objective

The objective of this study was to find an asphalt binder or mastic property that can provide the compaction temperatures needed for asphalt mixture design.

C. Scope

The Superpave gyratory compactor was used to compact a mixture with an unmodified asphalt binder at various temperatures to obtain the range in temperature that did not affect the volumetric properties of the mixture at N-design. Polymer-modified asphalt binders were then substituted for the unmodified asphalt binder. The volume of binder was kept constant. The temperature range that gave the same volumetric properties as the unmodified asphalt binder was found for each modified binder. The rheological properties of the asphalt binders and mastics used in the mixtures were then measured to determine what property provides temperatures that meet the temperature ranges given by the compaction process. The methodology was then repeated using two other aggregates.

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