Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

PUBLICATION NO. FHWA-HRT-22-019 FEBRUARY 2023 

Long-Term Pavement Performance 

Warm-Mix Asphalt Study Final Report, 

Volume II: SPS-10 Experimental Matrix 

and Research Plan
FOREWORD

Warm-mix asphalt (WMA), an innovative material that is part of the Federal Highway 

Administration Every Day Counts program, has been implemented by State highway agencies 

throughout the United States. WMA covers a variety of categories, each designed to allow for 

the production and compaction of asphalt concrete at temperatures lower than conventional 

hot-mix asphalt (HMA).

Recognizing that a knowledge gap exists in the comparison of WMA and HMA over the 

performance life of each type of pavement, the Long-Term Pavement Performance (LTPP) 

program initiated this research to design a national experiment to study the performance of 

WMA relative to HMA. New test sections were recruited into the LTPP program under the 

designation of the Specific Pavement Study-10 (SPS-10) experiment called “Warm Mix Asphalt 

Overlay of Asphalt Pavement Study.” 

The purpose of this volume of the report series is to document the research plan and 

experimental design for the SPS-10 experiment for the LTPP program. This experiment is 

designed to capture information on the short- and long-term performance of WMA relative to 

HMA. This experiment has been structured to ensure consistency and compatibility with the 

existing LTPP program objectives and database while addressing information gaps regarding 

WMA performance. The intent of the SPS-10 experiment is to capture not only field 

performance, but also laboratory test data that will provide both user-agencies and researchers a 

better understanding of the potential benefits of WMA. Collectively, this information could be 

used for performance prediction. 

Mark Swanlund 

Acting Director, Office of Infrastructure 

Research and Development 

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

(USDOT) 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-HRT-22-019 

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Long-Term Pavement Performance Warm-Mix Asphalt 

Study Final Report, Volume II: SPS-10 Experimental Matrix 

and Research Plan

5. Report Date

February 2023

6. Performing Organization Code:

7. Author(s)

Jason Puccinelli, Peter Schmalzer, Kevin Senn (ORCID 

0000-0002-9645-5370), Linda McDonald

8. Performing Organization Report No.

N/A

9. Performing Organization Name and Address

NCE

1885 S Arlington Ave, Ste 111

Reno, Nevada 89509

10. Work Unit No.

11. Contract or Grant No.

DTFH61-12-C-00017

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development

Federal Highway Administration

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report, September 2012–December 2014

14. Sponsoring Agency Code

HRDI-30

15. Supplementary Notes

Jack Springer (HRDI-30) served as the Contracting Officer’s Representative.

16. Abstract

The purpose of this report is to document the research plan and experimental design for the Specific Pavement 

Studies-10 (SPS-10) experiment for the Long-Term Pavement Performance (LTPP) program. Projects nominated 

for the SPS-10 experiment would be constructed specifically to satisfy experiment design cells within the 

experimental matrix and would adhere to the guidelines set forth in this research plan. Because these projects 

would be nominated prior to construction, all material properties, sampling, and construction activities could be

documented to ensure a complete data set. This document defines the goals/objectives of the SPS-10 experiment, 

the independent variables to be studied, and the methods used to control other factors that affect pavement 

performance.

17. Key Words

Asphalt concrete, General Pavement Studies, 

LTPP, material properties, pavement, Specific 

Pavement Studies, subgrade, warm-mix asphalt, 

performance monitoring, construction, SPS-10, 

hot-mix asphalt, experiment design

18. Distribution Statement

No restrictions. This document is available to the public 

through the National Technical Information Service, 

Springfield, VA 22161.

https://www.ntis.gov

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

33

22. Price

N/A

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
ii

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
iii

LONG-TERM PAVEMENT PERFORMANCE WARM MIX ASPHALT STUDY 

PROJECT REPORT SERIES

This volume is the second of six volumes in this research report series. Volume I is the final 

report, and volume II through volume VI contain detailed information about the design and 

operations of the experiment. The following list contains all the volumes of this report series: 

Volume Title Report Number

I Long-Term Pavement Performance Warm-Mix Asphalt 

Study, Volume I: Final Report 

FHWA-HRT-22-018 

II Long-Term Pavement Performance Warm Mix-Asphalt 

Study Final Report, Volume II: SPS-10 Experimental 

Matrix and Research Plan 

FHWA-HRT-22-019 

III Long-Term Pavement Performance Warm-Mix Asphalt 

Study Final Report, Volume III: SPS-10 Nomination 

Guidelines 

FHWA-HRT-22-020 

IV Long-Term Pavement Performance Warm-Mix Asphalt 

Study Final Report, Volume IV: SPS-10 Materials 

Sampling and Testing Requirements 

FHWA-HRT-22-021 

V Long-Term Pavement Performance Warm-Mix Asphalt 

Study Final Report, Volume V: SPS-10 Performance 

Monitoring Guide 

FHWA-HRT-22-022 

VI Long-Term Pavement Performance Warm-Mix Asphalt 

Study Final Report, Volume VI: SPS-10 Construction 

Documentation Guide 

FHWA-HRT-22-023 
iv

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION ................................................................................................ 1

CHAPTER 2. BACKGROUND................................................................................................... 3

CHAPTER 3. KEY CONSIDERATIONS .................................................................................. 7

CHAPTER 4. SPS-10 EXPERIMENTAL DESIGN .................................................................. 9

Replication Considerations .................................................................................................. 10

SPS-10 WMA Definition....................................................................................................... 10

Climate ................................................................................................................................... 10

Traffic Levels ......................................................................................................................... 11

WMA Types ........................................................................................................................... 12

RAP ........................................................................................................................................ 14

Pavement Structure .............................................................................................................. 15

Mixture Design ...................................................................................................................... 15

CHAPTER 5. TEST SECTION CONFIGURATION AND CONSTRUCTION 

CONSIDERATIONS .................................................................................................................. 17

CHAPTER 6. BENEFITS TO PARTICIPATING HIGHWAY AGENCIES ...................... 19

CHAPTER 7. SUPPLEMENTAL SECTIONS ........................................................................ 21

Recommended Supplemental Sections ................................................................................ 21

CHAPTER 8. PARTICIPATING AGENCY RESPONSIBILITIES ..................................... 23

REFERENCES ............................................................................................................................ 25
v 

LIST OF FIGURES

Figure 1. Graph. Distribution of annual traffic loading at LTPP sites. ......................................... 12

Figure 2. Diagram. Typical SPS-10 site layout. ........................................................................... 18
vi 

LIST OF TABLES

Table 1. NCHRP projects including WMA (as of 2014). ............................................................... 4

Table 2. Final experimental matrix for SPS-10. ............................................................................. 9

Table 3. Summary statistics of annual traffic loading at LTPP sites. ........................................... 12
vii 

LIST OF ABBREVIATIONS

AC asphalt concrete

ESAL equivalent single axle load 

ETG expert task group

FHWA Federal Highway Administration

GPS General Pavement Studies

HMA hot-mix asphalt

LTPP Long-Term Pavement Performance

NCHRP National Cooperative Highway Research Program 

PPDB pavement performance database

RAP recycled asphalt pavement

RAS recycled asphalt shingle

SPS Specific Pavement Studies

WMA warm-mix asphalt 
1 

CHAPTER 1. INTRODUCTION

The purpose of this report is to document the research plan and experimental design for the 

Specific Pavement Studies-10 (SPS-10) experiment for the Long-Term Pavement Performance 

(LTPP) program. This experiment is designed to capture information on the short- and long-term 

performance of warm-mix asphalt (WMA) relative to hot-mix asphalt (HMA). This experiment 

has been structured to ensure consistency and compatibility with the existing LTPP objectives 

and database while addressing information gaps regarding WMA performance. The experiment

will capture field performance and laboratory test data that will allow both user-agencies and 

researchers a better understanding of the potential benefits of WMA. Collectively, this 

information could be used for performance prediction. 

For the purposes of this experiment, WMA is defined as asphalt mixtures produced at least 17 °C 

(30 °F) below normal HMA production temperatures, or asphalt produced at or below 135 °C 

(275 °F). 

The SPS-10 experiment described in this document is intended for test sections not previously in 

the LTPP database. Projects nominated for the SPS-10 experiment would be constructed 

specifically to satisfy cells within the experimental matrix and would adhere to the guidelines 

outlined in this research plan. Because these sections would be nominated prior to construction, 

all material properties, sampling, and construction activities could be documented to ensure a 

complete data set. SPS experiments in the LTPP program are focused on very specific topics 

with limited independent variables. This document defines the goals/objectives of the SPS-10, 

the independent variables to be studied, and the methods used to control other factors that affect 

pavement performance.

Existing LTPP test sections that are rehabilitated with WMA technology are included in the 

General Pavement Studies-6 (GPS-6) and GPS-7 experiments. Details regarding the expanded 

GPS-6 and GPS-7 experiments can be found in the LTPP maintenance and rehabilitation data 

collection guide, which has been revised and expanded to account for WMA overlays of existing 

LTPP test sections (Simpson et al. 2021). 

3 

CHAPTER 2. BACKGROUND

WMA pavements were first constructed in Europe in 1997. The European experience has been 

documented in Warm-Mix Asphalt: European Practice (D’Angelo et al. 2008). The results of the 

tour were promising, but several challenges using WMA still needed to be addressed, including 

long-term performance. As a compaction aid with a number of benefits (i.e., extending the 

paving season, increasing haul distance, and reducing fuel consumption and emissions), WMA 

has become increasingly popular in the United States. The first WMA field trials in the United 

States were constructed in North Carolina and Florida in 2004 (Prowell and Hurley 2008). By 

2008, 32 States had conducted WMA field trials. Interest in WMA has continued to gain 

momentum, and in 2011, 30 States had specifications for WMA construction (Prowell, Hurley, 

and Frank 2012). In addition, the amount of WMA increased by 175 percent from 2009 to 2010, 

accounting for 13 percent of total asphalt production in the United States (Prowell, Hurley, and 

Frank 2012). 

At the time of the writing of this report, currently over 35 WMA technologies are offered in the 

United States that alter the properties of the asphalt binder to improve aggregate coating and 

compactability at lower production and compaction temperatures than conventional HMA 

(Corrigan 2011). The 35 technologies available can be grouped into the following four categories 

(some technologies are a combination of these categories):

• Foaming additive. 

• Chemical additive. 

• Organic additive. 

• Foaming process. 

The LTPP SPS-10 experiment focuses on the chemical additive and foaming process categories.

Given the growth and popularity of WMA, a number of States have conducted studies on WMA. 

Additionally, at the time of this research, the National Cooperative Highway Research Program 

(NCHRP) had sponsored eight studies on WMA. The majority of studies have investigated 

mixture design practices, engineering properties, and constructability. While NCHRP 9-49A was 

structured to address the long-term performance of WMA, the project’s 5-yr duration can only 

capture a fraction of the pavement’s intended design life (Martin et al. 2014). As such, a research 

plan is needed that successfully captures long-term performance and behavior over the typical 

20-yr design life while also obtaining materials testing results, construction details, pavement 

structure information, traffic levels, and climate data. Additionally, the SPS-10 experiment 

considers the use of recycled asphalt pavement (RAP). Initial research on the use of RAP with 

WMA has demonstrated improved mixture properties in terms of the blending of old and virgin 

(new) binders; however, studies have not evaluated the long-term performance aspects of the use 

of RAP with WMA, such as the effect of different production temperatures and asphalt 

production plant type on the blending process and final mixture and the optimal binder 

replacement determination procedures. 

Table 1 below summarizes the NCHRP-funded WMA studies considered. 
4 

Table 1. NCHRP projects including WMA (as of 2014).

Project 

Number Project Name Start Date End Date

09-33 A Mix Design Manual for Hot-Mix Asphalt

(Advanced Asphalt Technologies, LLC 2011) 7/1/2005 6/30/2010 

09-47 

Engineering Properties, Emissions and Field 

Performance of Warm Mix Asphalt Technologies 

(Anderson et al. 2008) 

3/31/2008 1/8/2009 

09-47A Properties and Performance of Warm Mix 

Asphalt Technologies (West et al. 2014) 7/31/2009 1/12/2013 

09-49 Performance of WMA Technologies: Stage 1 

Moisture Susceptibility (Martin et al. 2014) 7/26/2010 9/30/2013 

09-49A 

Performance of WMA Technologies: Stage II 

Long-Term Field Performance (Washington State 

University, Pennsylvania State UniversityAltoona, and Louisiana Transportation Research 

Center 2017) 

4/29/2011 7/28/2016 

09-52 Short-Term Laboratory Conditioning of Asphalt 

Mixtures (Newcomb et al. 2015a) 6/1/2012 11/30/2014 

09-53 Properties of Foamed Asphalt for Warm Mix 

Asphalt Applications (Newcomb et al. 2015b) 6/1/2012 8/31/2014 

09-55 

Recycled Asphalt Shingles in Asphalt Mixtures 

with Warm Mix Asphalt Technologies (West et 

al. 2018) 

6/10/2013 9/10/2016 

The LTPP WMA research team carefully considered how these NCHRP projects may be brought 

into the LTPP program as test sections. Other sections, such as those constructed as part of 

ongoing work under the Asphalt Research Consortium, were also evaluated. This evaluation was 

part of the original scope of work and was also encouraged during the initial WMA expert task 

group (ETG) meeting.

Integrating existing WMA sections into the LTPP program would provide a jump start in

evaluating the long-term performance of in-service sections. The LTPP program has rigorous 

guidelines for data collection, review, and storage. These guidelines apply to the test section

construction, materials sampling and testing, and performance monitoring data.

While the NCHRP (and other) test sections often had onsite personnel during construction and 

occasionally utilized LTPP practices for elements of the data collection, overall, these sections 

were not compatible with the existing LTPP pavement performance database (PPDB). The 

following summarizes the reasons that prevented the inclusion of these test sections in the 

SPS-10 experiment: 

• Use of short test sections: Standard LTPP test sections are 152.4 m (500 ft) in length, but 

most of the NCHRP projects were significantly shorter. 
5 

• Use of improper sampling and testing: The LTPP program prohibits destructive sampling 

within the test section, but the NCHRP projects performed coring within the test sections.

Also, materials sampling and testing processes were not conducted utilizing LTPP 

protocols. 

• Use of nonaccredited raters: The LTPP program requires distress surveys to be performed 

by accredited raters using specific forms and definitions. Although these definitions were 

largely incorporated, the surveys were performed by nonaccredited raters.

• Collection of limited data: Deflection and roughness data were collected on very few of 

the existing WMA projects, and the equipment used to collect the limited data were not 

calibrated per LTPP specification.

• Nonuse of LTPP forms: None of the data sets utilized LTPP forms. As a result, even if 

the information could be found, substantial effort would be needed to get it documented 

and entered into the LTPP PPDB.

While the test sections themselves were not recommended for inclusion into the LTPP PPDB, 

the lessons learned in the conduct of the above projects contributed to optimizing decisions made 

in association with the LTPP WMA projects.

7 

CHAPTER 3. KEY CONSIDERATIONS

The SPS-10 experiment has been designed to address information gaps that currently exist with 

WMA pavements. This chapter describes some of the key considerations used to develop the 

SPS-10 experimental design. 

The data needs for WMA center on how binder and mixture properties affect performance 

relative to HMA. The first factor in the experimental design allows a direct comparison of WMA 

to HMA in a comprehensive range of in situ climatic conditions and traffic loading. In addition, 

questions exist about the use of WMA technology in RAP-included mixtures. As a result, RAP 

was included in the experimental matrix. While various categories of WMA technologies are 

currently in use, pavement performance data on the applicability of each category under different 

in situ conditions have not been collected. 

Because WMA is relatively new, long-term field performance data are not available. Concerns 

with moisture sensitivity due to lower production temperatures and the presence of aggregate 

moisture have been documented but have not yet been thoroughly evaluated on in-service 

pavements. The SPS-10 is designed to address this concern as well as the effect of WMA over 

time on low-temperature cracking, fatigue cracking, rutting, and stiffness. 

Many factors were considered in developing the preliminary experiment design. However, given 

practical constraints—financial resources and size of the experimental matrix required to 

adequately represent all factors—the resulting experiment design reflects the prioritization of 

factors within a statistically sound full factorial, as described in the following section. This 

experiment will only consider mixture produced and placed at warm-mix temperatures. Mixtures

produced at normal hot-mix temperatures but placed at warm-mix temperatures, where the 

warm-mix technology is only used as a compaction aid, will not be considered as part of the core 

experiment. But such mixtures could be implemented as supplemental sections. 

9 

CHAPTER 4. SPS-10 EXPERIMENTAL DESIGN

SPS experiments typically consist of projects located across North America. Each project is 

selected and constructed to populate a specific set of site conditions/experimental factors. These 

factors are combined to develop an experimental matrix, which provides an overview of the 

projects required to achieve a statistically sound and robust experiment. The representation of 

WMA technology in the primary-tier factorial of the SPS-10 experiment is shown in table 2, 

which identifies the primary experimental factors and their relationships. The site factors are 

identified across the top of the matrix in table 2, while pavement mixture factors are listed on the 

left side. The factors included within the experimental design were selected based on input from 

the ETG assembled specifically for this study. While many characteristics (or independent 

variables) were considered, only the major factors discussed below were selected with assistance 

from the ETG and approval from the Federal Highway Administration (FHWA). Attempting to 

account for all of the independent variables would not be practical, especially those that have 

shown little or poor correlation with overall performance. 

Table 2. Final experimental matrix for SPS-10. 

Moisture Temperature Traffic

Number of

Projects 

Wet Freeze High 2 

Wet Freeze Low 2 

Wet No freeze High 2 

Wet No freeze Low 2 

Dry Freeze High 2 

Dry Freeze Low 2 

Dry No freeze High 2 

Dry No freeze Low 2 

Note: Projects consist of HMA control section and two different WMA 

categories (foaming process and chemical). 

Each row in table 2 represents the recommended quantity of projects to be nominated and 

constructed for the SPS-10 experiment. Each project location contains a minimum of three test 

sections (each of them 152.4 m [500 ft ] in length) constructed contiguously along a section of 

highway. The SPS-10 experiment is designed such that all factors (i.e., traffic, climate, subgrade, 

existing pavement structure, and asphalt production plant) are constant across all test sections at 

one project location. The WMA technology used varies in the core test sections in order to

directly compare the specific WMA technology to HMA under the same in situ conditions, 

eliminating confounding effects typically introduced when comparing pavement features at 

different locations. 

The core experiment avoids constructing an SPS-10 experiment where both WMA test sections 

are using technology from the same category. If an agency wants to evaluate different WMA 

technologies within the same category, additional test sections may be built so that the project 

has more than three test sections. However, each project must consist of test sections 

representing at least one WMA test section using a chemical additive, one WMA test section 

using foaming process, and at least one HMA control section. The three sections defined here 
10 

will be considered the “core” experiment and will be used to populate the national experimental 

design. Any additional test sections constructed within the project will be considered 

supplemental sections. While data will be collected and stored in the LTPP database for these 

supplemental sections, they will not be used to populate the national experimental matrix. 

Supplemental sections are valuable components of the SPS-10 project as they allow U.S. State 

and Canadian Provincial highway agencies to study specific mixtures of local interest.

REPLICATION CONSIDERATIONS

The experimental matrix in table 2 includes replication of the primary-tier factorials. A minimum 

of two projects must be recruited for each combination of primary-tier factorials of climate and 

traffic. If more than two projects are nominated and constructed for some cells within the matrix, 

they will be included in the LTPP database. The intent of the matrix is to achieve a balanced 

experiment with all factors represented but does not prevent or limit additional replicates from 

being included in the program. 

Including an adequate number of replications helps to estimate unbiased estimation of 

experimental errors in designed experiments. Estimation of experimental error is very important 

in inferential statistics to compare both main and interaction effects and to estimate the standard 

errors and confidence intervals for treatment means. In addition, to have an adequate number of 

replications, true replications are required to estimate unbiased experimental error. True 

replication is only achieved when treatment combinations within a factorial design are randomly 

assigned to replicated experimental units. Failure to randomly assign treatments to replications 

results in pseudoreplication. Experimental error computation obtained from pseudoreplication is 

not an independent estimate and underestimates the true error increasing the probability of errors 

occurring and the chances of detecting false-positive treatment differences. 

Having repeat test sections at one SPS-10 (i.e., multiple test sections using the same WMA 

technology) is not true replication. In the case of the SPS-10, true replication only occurs when 

multiple projects are constructed for each primary-tier factorial. As such, the experimental design 

in table 2 provides for at least two independent projects to be constructed under the same primary 

factorials.

SPS-10 WMA DEFINITION

For purposes of this LTPP experiment, WMA is defined by the following criteria: 

• A mixture produced at or below 135 °C (275 °F). 

• A mixture produced at least 17 °C (30 °F) below the production temperature of the HMA 

control.

The ETG developed this definition of WMA with consideration given to accommodate the 

water-foaming technologies. 

CLIMATE

Four climatic zones have been previously defined by the LTPP program: wet-freeze, dry-freeze, 

wet-no freeze, and dry-no freeze. The criteria established to distinguish wet and dry climates is 
11 

based on annual precipitation. Climates with annual precipitation of fewer than 508 mm/yr (20 

inches/yr) are considered dry by LTPP definitions. Conversely, wet climates are those receiving 

more than 508 mm/yr (20 inches/yr) of precipitation. The LTTP program uses the freezing index 

to define the freeze and no-freeze climates. A site located where the annual freezing index is 

greater than 83 °C d (150 °F d) is, according to LTPP definitions, in the freeze climatic zone by 

LTPP definitions. 

Climate is a site condition that is addressed in the project location experimental matrix. The 

SPS-10 experiment requires equal representation in all four climatic zones.

The SPS-10 experiment does not require the installation of an automated weather station onsite; 

however, having a fully functional weather station (maintained and operated as part of the 

National Oceanic and Atmospheric Administration or National Weather Service) in the nearby 

vicinity is preferable. 

TRAFFIC LEVELS

Traffic loading has a direct and significant impact on the long-term performance of pavements.

Annual traffic loading typically grows with time, and the rate of growth is dependent on many 

factors. This phenomenon can result in significant differences in annual loading between the 

beginning and end of the pavement service life. To ensure that the WMA experiment captures a 

range of loading conditions, two categories were established by evaluating measured loading at 

the existing LTPP sites. The distribution of average annual equivalent single axle loads 

(ESAL)/yr is provided in figure 1, while summary statistics are provided in table 3. These data 

were assembled from all LTPP locations where monitored traffic data are available and represent 

the annual average of all years collected for each location. The ESAL values reported are for one 

lane in one direction of travel (i.e., design ESALs). As can be seen in table 3, the mean for the 

data set is 338,000 ESALs/yr; however, the distribution is skewed, with approximately 

60 percent of the sites receiving less than 250,000 ESALs/yr. In addition, traffic loads continue 

to grow, thereby increasing ESAL levels. Some of the data included in figure 1 were captured in 

the early to mid1990’s and have not been adjusted for growth. Based on this distribution and 

considering the difficulties in obtaining lane closure in high-traffic areas, the low-traffic category 

is defined as sites receiving less than 500,000 ESALs/yr. A site with traffic greater than or equal 

to 500,000 ESALs/yr will fall into the high traffic category for purposes of this experiment.

Traffic information will be quantified and stored as part of the monitoring data from each site.

While test sections with only traffic data from either portable or permanent equipment will be 

considered for inclusion in the experiment, sections with a continuously operating permanent 

device are preferred for classification and weight data. This level of data collection is preferred 

for two reasons: to provide the accurate traffic loading measurements required to develop 

mechanistic and mechanistic/empirical design models and to provide the base data necessary to 

understand the intricacies of the interactions among pavement, traffic load, and environment. 

During the nomination process, selected project locations should have a full-time, fully 

operational weigh in motion on the same route and within close proximity to the SPS-10 

experiment project that captures traffic patterns equivalent to those seen at the test section 

location. 
12 

While data collection is preferred on the site continuously for the year, the minimum 

recommended data collection effort for each site is 2 wk of continuous classification data, four 

times/yr (a total of 8 wk of classification data/yr). The U.S. State or Canadian Provincial 

highway agency is responsible for ensuring that data collected are representative of local 

conditions, accounting for seasonal variation, weekday/weekend differences, and inconsistent 

truck loading patterns throughout the year. 

Source: FHWA. 

Figure 1. Graph. Distribution of annual traffic loading at LTPP sites. 

Table 3. Summary statistics of annual traffic loading at LTPP sites. 

Statistic

Average Annual Traffic Loading (1,000 

ESALs/yr)

Mean 338 

Median 195 

Standard deviation 377 

Minimum 2 

Maximum 2,172 

WMA TYPES

While there are over 35 different WMA products available, the products can be grouped into four 

broad categories based on the mechanisms used to modify the binder properties during mixing 

and compaction. The SPS-10 experimental matrix will focus on the chemical additive and 

foaming process categories for core test sections. The lists provided under each category are not 

Traffic Loading (1000 ESALs/yr)
13 

intended to be a comprehensive set, and other products meeting the definitions described below 

can be used in the SPS-10 experiment. 

Chemical additives are defined as water-free (nonaqueous) chemistry packages that modify the 

binder properties to enhance coating, adhesion, and workability at reduced temperatures, 

including surfactants, fatty acid chemical additives, cationic surface-active agents, and rheology 

modifiers. Examples of products that fall into this category include the following: 

• CECABASE®. 

• Evotherm®. 

• HyperTherm/QualiThermTM. 

• RedisetTM. 

Organic additives are plant-based, wax-based, or sulfur-extended materials designed to provide 

viscosity reduction, aid in asphaltenes dispersion, and act as a lubricant at mixing temperatures 

below that of conventional HMA. Organic additives are not included in the core experiment but 

are strongly encouraged for use in supplemental sections. Examples of organic additives include 

the following:

• BituTech PERTM. 

• LEADCAPTM. 

• Sasobit®. 

• SonneWarmixTM. 

• Thiopave®. 

Foaming additives are defined as water-containing materials added to the mixture to foam the 

asphalt. The most common foaming additive is synthetic zeolite. Zeolite contains 20–30 percent

water that is released at temperatures above the boiling point of water. The water from the zeolite 

foams the asphalt binder. Examples of foaming additives include the following:

• Advera®. 

• Aspha-min®. 

The foaming process category includes all WMA types that utilize assemblies/modifications to 

the asphalt production plant to foam binder without additives (other than water), including

foaming nozzles, expansion chambers, vortex mixers, and shearing devices. While the other 

categories may be added to the mixture using some type of nozzle or other addition, the key 

distinction between the foaming process category and others is the absence of additives. WMA 

technologies that fall into the foaming process category only utilize water. Examples of this 

category include the following:
14 

• Accu-ShearTM. 

• AQUABlackTM. 

• AquaFoam®. 

• Astec Green SystemTM. 

• Eco-FoamTM. 

• Gencor ultrafoamTM®. 

• Low emission asphalt. 

RAP

Results from the NCHRP 9-43 project indicate that binder from aged RAP will blend with virgin 

binder at WMA temperatures if the production temperatures exceed the high-temperature PG 

grade of the RAP binder (Prowell, Hurley, and Frank 2012). Field trials have been constructed in 

the United States using WMA technologies in mixes with RAP contents ranging from 

20-50 percent (Bonaquist 2011). Segments of the pavement community are interested in

evaluating the long-term performance of RAP-included WMA.

The LTPP SPS-5 experiment required all recycled test sections to have a RAP content of 

30 percent. The project description for the report NCHRP 9-46: Improved Mix Design, 

Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed 

Asphalt Pavement Content defines high-RAP content mixtures as those containing more than 25

percent RAP (West, Willis, and Marasteanu 2013). The current practice of U.S. State and

Canadian Provincial highway agencies must also be considered. Establishing a threshold 

incompatible with State practices could result in difficulties nominating and populating the 

experimental design with test sections. 

A multiple-factorial approach for RAP was not utilized in the SPS-10 experiment design. 

However, a requirement for all of the core test sections to have RAP contents between 10 percent

and 25 percent based on binder replacement (expressed as the amount of binder contribution 

from RAP as a percentage of total binder in the mixture) has been included. The U.S. State or 

Canadian Provincial highway agency is expected to follow standard practice for the RAP binder 

replacement. The three core test sections on each project must have the same RAP percentages 

and should achieve the same binder replacement levels. If an agency wishes to vary the RAP 

binder replacement levels or include recycled asphalt shingles (RAS), supplemental sections can 

be included. However, varying binder replacement levels were not incorporated into the national 

experimental design of core test sections. 

Contractors typically introduce additives to RAS stockpiles to ensure workability. In some cases, 

WMA additives are used for this purpose. If a WMA technology is added to the RAS stockpile, 

the material can still be used on supplement sections of an SPS-10 project as long as the control 

section is constructed at HMA temperatures (without additional WMA technology used during 

the mixing process). The stockpile additive will be documented and recorded in the LTPP 

database.
15 

PAVEMENT STRUCTURE

The SPS-10 experiment will only include new asphalt concrete (AC) overlays over existing 

HMA pavements. New construction, complete reconstruction, overlays of existing portland 

cement concrete, or composite pavements will not be allowed in the SPS-10 experiment. 

The U.S. State or Canadian Provincial highway agency’s standard practice will determine the 

thickness of the overlay. A strong correlation between the overlay thickness and the annual 

traffic loading is expected. As such, the overlay thickness will be treated as a covariate in the 

study and will not be a multilevel category in the experimental design. The agency-determined

thickness will be documented along with the design process and all inputs used in determining 

the design. The minimum overlay thickness required for the SPS-10 experiment is 51 mm 

(2 inches). This minimum thickness was selected to alleviate complications that arise when 

performing materials testing, ride quality, and structural testing on thin layers. The maximum 

overlay thickness required for the SPS-10 experiment is 102 mm (4 inches). 

Pavement structural factors (subgrade, subbase, base, binder, and surface course thicknesses) are 

not controlled as multilevel design factors in the SPS-10 experiments. The subgrade may be 

either fine or coarse-grained material. The base may be either a granular or stabilized type.

The pavement thickness (and depth of milling, or other surface preparation, if applicable) should 

remain constant across all test sections at any project location to allow for direct comparison 

between WMA and HMA. Similarly, the existing pavement structure thicknesses, surface 

distress types and extents, and subgrade conditions should be consistent throughout the project. 

For the SPS-10 experiment, tack coats must be required prior to the placement of all WMA and 

HMA lifts.

MIXTURE DESIGN

The SPS-10 experiment focuses on dense-graded asphalt mixtures for the core test sections. The 

mixture design will be developed by the U.S. State or Canadian Provincial highway agency in 

accordance with their standard practice. The mixture design for the WMA test sections should be 

identical to the HMA control. Some agencies allow minor adjustments to the mixture design 

between the HMA and WMA, while others forbid it. The agency standard practice will be 

allowed for the SPS-10 experiment. In addition, antistrip agents may be required in the HMA 

mixture, while some of the WMA additives interact with antistrip agents in a way that makes the 

mixture more susceptible to moisture damage. In such a case, slight changes to the mixture 

design between HMA and WMA are warranted and are acceptable in the SPS-10 experiment. 

The complete mixture design and volumetric mixture properties of the HMA and WMA mixtures 

will be documented and stored in the LTPP PPDB. 

If the agency wishes to study other mixture types (i.e., stone-matrix asphalt or open-graded 

friction course), test sections may be included in the SPS-10 experiment as supplemental 

sections. 

The binder used in the mixture will be selected using the agency’s normal practice. Modified 

binders (both polymer and rubber) are allowed in the SPS-10 experiment. Information on the 
16 

binder modifier type and quantity will be documented and stored in the LTPP database. Binder 

type and modifier type are not included in the SPS-10 experimental matrix and will be a 

covariate of the project.

The binder source, binder grade, and binder modification must be consistent across the three core 

test sections of each project. Should the agency wish to vary binder properties, supplemental 

sections can be included and will be monitored as part of the LTPP program. Direct comparisons 

between different binder types or different sources of the same binder type are not a part of the 

national experimental design for the SPS-10. 

In addition, aggregate type, source, and gradation must be consistent across the three core test 

sections of each project. Variations in aggregate properties will be allowed in supplemental 

sections. 
17 

CHAPTER 5. TEST SECTION CONFIGURATION AND CONSTRUCTION 

CONSIDERATIONS

The SPS-10 test pavements will be built as part of an overlay of existing asphalt pavement. In all 

cases, the cross section must be uniform. Lane-widening projects are not suitable for this 

experiment because of the difficulty of discerning the relationship of distresses developed in the 

existing lanes and in the widened test section.

Figure 2 illustrates the conceptual test site layout for the SPS-10 experiment. The experimental 

design requires a minimum length of 243.8 m (800 ft), with a core monitoring section of 152.4 m 

(500 ft ) that will be used for future nondestructive performance monitoring. A 15.2-m (50-ft) 

buffer on each side of the monitoring area is included to separate the destructive sampling area 

from the monitoring area. The destructive sampling area consists of 30.5 m (100 ft) on each side 

built at the same time with the same specifications to allow material sampling without disturbing 

the 152.4-m (500-ft) monitored area, including the outside (i.e., truck) lane only. Sufficient

asphalt plant production should be provided to ensure acceptable uniformity and consistency in 

the AC mixture delivered and placed. Transition zones are required between test sections and 

must be a minimum length of 243.8 m (800 ft). The project requires at least three different 

mixtures (one HMA and two WMA) to be produced at the same asphalt production plant, and 

each mixture may only be placed on the test section after the plant has reached steady-state 

operation. The transitions will also be used to ensure the paving train has reached uniform 

operation and is achieving consistent densities prior to paving within the test section. This 

requirement for steady-state operation may require longer transitions between the sections or 

some other use/disposal of mixture produced before the asphalt production plant achieves steadystate operation. The length of these transitions depends on onsite conditions, production plant 

configurations, and construction practices that influence the amount of material required to reach 

steady-state operations. The minimum project length is 1,219 m (4,000 ft). But the project length 

may be longer if more than the minimum number of sections are built and/or if the transition 

zones are longer than the minimum length. 

Each SPS-10 project must have a minimum of three test sections. One test section must consist 

of HMA as a control. The other two test sections must be WMA (as defined above): one using 

the foaming process and the other using a WMA chemical additive. Additional test sections may 

be constructed above this minimum. The additional sections will be agency-constructed 

supplemental sections and will be monitored using LTPP data collection guidelines. 

The job-mix formula for the HMA control and WMA sections must be identical (except for the

warm-mix technology). Obtaining consistent densities (and air voids) across all test sections is 

important to the SPS-10 experimental objectives. Care should be taken to ensure that rolling 

procedures and patterns as well as required compactive effort are established for each mixture so 

that uniform densities are achieved both within each 243.8-m (800-ft) monitoring/sampling 

length and within the entire experiment to facilitate appropriate comparisons of performance. In 

addition, the same compaction equipment must be used on all three test sections.
18 

Source: FHWA. 

1 ft = 0.3048 m

Figure 2. Diagram. Typical SPS-10 site layout. 
19 

CHAPTER 6. BENEFITS TO PARTICIPATING HIGHWAY AGENCIES

Though coordinated through the FHWA LTPP Program, the SPS-10 experiment is conducted for 

and by U.S. State and Canadian Provincial highway agencies. Therefore, the details of the 

experiment aim to address the needs of the highway community. However, the experimental 

rigor necessary to achieve the desired results from this research requires that participating 

agencies agree to the same experimental factors and required test sections. The statistical aspects 

of this experiment make the full cooperation of participating highway agencies crucial to its 

success. While all highway agencies will benefit from the information, knowledge, and products 

that result from this research, participating agencies will accrue additional direct benefits. Since a 

portion of this research will be conducted in their jurisdiction on test sections exposed to local 

climate and traffic loadings and constructed using their materials, mixture designs, 

specifications, and techniques, participating agencies will be able to make direct use of the 

results. The study will also allow highway agencies the opportunity to quantify the performance 

differences between their standard HMA and WMA technologies employed in their jurisdiction. 

In addition to these direct benefits, participating agencies will also receive ancillary benefits 

from their involvement in the experimental process, including valuable insights from and 

intellectual exchanges with the FHWA research team as well as other highway agency personnel. 

21 

CHAPTER 7. SUPPLEMENTAL SECTIONS

Sponsoring highway agencies can expand the experiment to address some of their own interests 

and concerns as well as incorporate innovative technology through the construction of 

supplemental sections. Additional WMA technologies can be constructed above the required 

minimum, and their performance can be directly compared to that of the core experimental test 

sections. Supplemental sections provide participating agencies the opportunity to conduct 

relatively economical, intensive pavement field research by taking advantage of the LTPP

program-provided research infrastructure and monitoring. 

The construction of supplemental sections is strongly encouraged. FHWA is prepared to assist 

interested U.S. State or Canadian Provincial highway agencies in the experimental design, data 

collection, and performance monitoring of such supplemental experiments. Further, if a group of 

participating agencies want to collaborate in such activities (i.e., as a pooled-fund study), FHWA 

is also prepared to work with these agencies to coordinate a multiState/Provincial supplemental 

experiment. The following section provides a list of recommended supplemental sections for 

consideration. 

RECOMMENDED SUPPLEMENTAL SECTIONS

Potential supplemental sections are provided in the following list, along with additional 

recommendations based on discussion with the ETG: 

• Organic WMA additives. 

• Foaming additives. 

• RAP of varying levels or the inclusion of RAP percentages outside the acceptable range 

for core test sections. 

• RAS. 

• Overlay layer of varying levels of thickness. 

• Varied binder grade. 

• Varied production temperatures or constructing sections with WMA technology produced 

at temperatures above the acceptable range for core test sections. 

• Varied WMA technologies. 

• Stone-matrix asphalt, gap-graded, or open-graded mixtures. 

• Varied aggregate sources. 

• Varied density levels. 

23 

CHAPTER 8. PARTICIPATING AGENCY RESPONSIBILITIES

Participating highway agencies play a key role in the development, construction, and conduct of 

the SPS, including the following activities:

• Participating in experiment and implementation plans. 

• Nominating test sites.

• Validating in situ conditions at the site.

• Providing inventory data of existing pavements.

• Preparing plans and specifications.

• Selecting construction contractors.

• Developing mixture designs.

• Sampling materials.

• Constructing test sections.

• Controlling, inspecting, and managing construction. 

• Collecting and submitting traffic data.

• Providing traffic control for all test site data collection.

• Collecting and reporting as-built construction data. 

• Conducting and reporting maintenance and rehabilitation activities. 

The primary role of FHWA is to provide coordination and technical assistance to participating 

highway agencies to help ensure uniformity and consistency in construction and data collection 

to achieve the desired study results. Some of the activities the FHWA LTPP program team will 

be responsible for include: 

• Development of experimental design. 

• Coordination among participating agencies. 

• Acceptance of nominated test sites.

• Development of uniform data collection guidelines and forms. 

• Coordination of materials sampling and testing. 

• Observation of pavement performance.

• Development and operation of comprehensive database and data entry platform. 

• Control of data quality.

• Analysis and reporting of data. 

25 

REFERENCES

Advanced Asphalt Technologies, LLC. 2011. NCHRP Project 09-33: A Manual for Design of 

Hot-Mix Asphalt with Commentary. Washington, DC: Transportation Research Board. 

Anderson, R., G. Baumgardner, R. May, and G. Reinke. 2008. NCHRP 09-47: Engineering 

Properties, Emissions, and Field Performance of Warm Mix Asphalt Technologies. 

Washington, DC: Transportation Research Board. 

Bonaquist, R. 2011. NCHRP 09-43: Mix Design Practices for Warm Mix Asphalt. Washington, 

DC: Transportation Research Board. 

Corrigan, M. 2011. “Warm-Mix Asphalt: The Path Forward.” Presented at the 2nd International 

Conference on Warm-Mix Asphalt. St. Louis, MO: National Asphalt Pavement 

Association. 

D’Angelo, J., E. Harm, J. Bartoszek, G. Baumgardner, M. Corrigan, J. Cowsert, T. Harman, M. 

Jamshidi et al. 2008. Warm-Mix Asphalt: European Practice. Report No. FHWA-PL-08-

007. Washington, DC: Federal Highway Administration. 

Martin, A., E. Arambula, F. Yin, L. Cucalon, A. Chowdhury, R. Lytton, J. Epps, C. Estakhri, and 

E. Park. 2014. NCHRP 09-49: Evaluation of the Moisture Susceptibility of WMA 

Technologies. Washington, DC: Transportation Research Board. 

Newcomb, D., A. Martin, F. Yin, E. Arambula, E. Park, and A. Chowdhury. 2015a. NCHRP 

09-52: Short-Term Laboratory Conditioning of Asphalt Mixtures. Washington, DC: 

Transportation Research Board.

Newcomb, D., E. Arambula, F. Yin, J. Zhang, A. Bhasin, W. Li, and Z. Arega. 2015b. NCHRP 

09-53: Properties of Foamed Asphalt for Warm Mix Asphalt for Warm Mix Asphalt 

Applications. Washington, DC: Transportation Research Board. 

Prowell, B., G. Hurley, and B. Frank. 2012. Warm-Mix Asphalt: Best Practices. Lanham, MD:

National Asphalt Pavement Association. 

Simpson, A., T. Thompson, J. Puccinelli, L. McDonald. Forthcoming. Long-Term Pavement 

Performance Maintenance and Rehabilitation Data Collection Guide. Washington, DC: 

Federal Highway Administration.

Washington State University, Pennsylvania State University-Altoona, and Louisiana 

Transportation Research Center. 2017. NCHRP 09-49A: Long-Term Field Performance 

of Warm Mix Asphalt Technologies. Washington, DC: Transportation Research Board. 

West, R., J. Willis, and M. Marasteanu. 2013. NCHRP Project 09-46: Improved Mix Design, 

Evaluation, and Materials Management Practices for Hot Mix Asphalt with High 

Reclaimed Asphalt Pavement Content. Washington, DC: Transportation Research Board. 
26 

West, R., C. Rodezno, G. Julian, B. Prowell, B. Frank, L. Osborn, and T. Kriech. 2014. NCHRP 

09-47A: Field Performance of Warm Mix Asphalt Technologies. Washington, DC: 

Transportation Research Board. 

West, R., F. Leiva, G. Julian, A. Taylor, E. Brown, and J. Willis. 2018. NCHRP 09-55: Using 

Recycled Asphalt Shingles with Warm Mix Asphalt Technologies. Washington, DC: 

Transportation Research Board. 
HRDI-30/02-23(WEB)E Recycled

Recyclable

Recommended Citation: Federal Highway Administration, Long-Term Pavement 

Performance Warm-Mix Asphalt Study Final Report, Volume II: SPS-10 Experimental 

Matrix and Research Plan (Washington, DC: 2023) https://doi.org/10.21949/1521715