CANADIAN USAGE AND PRACTICES FOR EVALUATING WARM MIX ASPHALT 1

MOISTURE SUSCEPTIBILITY 2

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Sina Varamini, MASc., EIT (Corresponding Author) 6

PhD Candidate 7

Department of Civil and Environmental Engineering 8

University of Waterloo 9

200 University Avenue West, 10

Waterloo, ON, Canada, N2L 3G1 11

Tel: 519-888-4567 ext. 30187 Email: svaramini@uwaterloo.ca 12

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14

Susan L. Tighe, PhD., P.Eng. 15

Professor and Canada Research Chair 16

Norman W. McLeod Professor in Sustainable Pavement Engineering 17

Director, Centre for Pavement and Transportation Technology 18

Department of Civil and Environmental Engineering 19

University of Waterloo 20

200 University Avenue West, 21

Waterloo, ON, Canada, N2L 3G1 22

Tel: 519-888-4567 ext. 33152 Email: sltighe@uwaterloo.ca 23

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Word count: 3129 words text + 9 tables/figures x 250 words (each) = 5379 words 27

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Submission Date: July 31, 201534

Varamini, Tighe 2

ABSTRACT 1

Warm Mix Asphalt (WMA) technology is gaining more acceptance by transportation agencies in 2

Canada due to the pressures from environmental agencies and environmental acts to reduce Green 3

House Gas (GHG) emissions generated by production and placement of paving mixtures. 4

However, WMA technology has certain functional considerations, namely moisture susceptibility 5

that need to be addressed in order to ensure it meets performance requirements in addition to 6

providing environmental benefits. To identify possible gaps in the current understanding and 7

performance of WMA, a Canada-wide survey has been prepared at the Centre for Pavement and 8

Transportation Technology (CPATT) located at the University of Waterloo to document the 9

Canadian state-of-art related to WMA technologies. This paper presents the results of this survey 10

on the preferred practices conducted by various Canadian transportation agencies. Furthermore, 11

these results are compared with the most recent survey of the United States Departments of 12

Transportation (DOTs) and industry conducted as part of the National Cooperative Highway 13

Research Program (NCHRP) project 09-49. 14

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Keywords: Warm Mix Asphalt, Usage Survey in Canada, Warm Mix Additives, Moisture 19

Susceptibility 20

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Varamini, Tighe 3

INTRODUCTION 1

Warm Mix Asphalt (WMA) is becoming more frequently used by transportation agencies due to 2

the pressures from environmental agencies and environmental acts to reduce Green House Gas 3

(GHG) emissions generated by production and placement of paving mixtures. WMA is defined as 4

a group of technologies that allow for a reduction in the production and placement temperatures of 5

conventional Hot Mix Asphalt (HMA). WMA technologies were first employed in Europe on the 6

later 1990s, and later gained interest in North America since 2002 in response to environmental 7

pressures related to greenhouse gas emissions. Since then several number of WMA technologies 8

have been developed with proven main benefits, particularly in paving contracts in the Canadian 9

province of Ontario including (1): 10

Reduced GHG emissions at the asphalt production and during paving operations 11

Reduced fuel consumption at the asphalt plant 12

Improved worker safety due to reduced asphalt fumes at paving sites 13

Improved compaction, and joint quality 14

Reduced fuel consumption and vehicle emissions associated with user delay in 15

construction zones due to lower compaction temperatures, and less time required to 16

re-opening lanes to traffic 17

Less potential to cracking due to reduced asphalt binder aging 18

Potential to extend the paving season due to increased workability at lower compaction 19

temperatures 20

Facilitating longer haul distances from the production facility to the paving site 21

Potential for higher reclaimed asphalt pavement (RAP) content 22

Despite the aforementioned environmental, economical, and safety benefits of WMA, changes 23

in the production and placement process have raised concerns in regards to the long-term 24

performance of WMA, particularly moisture susceptibility. 25

LITERATURE REVIEW: A BRIEF ON MOISTURE DAMAGE 26

Moisture damage in asphalt mixtures occurs due to loss of adhesion (the bonds between asphalt 27

and aggregate) and/or cohesion (the bonds between asphalt binder molecules), which subsequently 28

results in progressive strength reduction and decrease in stiffness of the mixture. Several 29

mechanisms have been cited to be contributing factors to moisture damage including detachment, 30

displacement, spontaneous, emulsification, film rupture, pore pressure, and hydraulic scouring (2). 31

However, not all these mechanisms are well understood due to the complexity of describing the 32

level of impact of individual or combined mechanisms on the moisture susceptibility of a given 33

mixture, as stated by Solaimanian et al. (3). Furthermore, researchers (4) have found that moisture 34

damage can be accelerated by mixture design or production issues, including those given in Table 35

1. 36

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Varamini, Tighe 4

TABLE 1 Factors Contributing to Moisture-related Distress (4) 1 Mix Design Binder and aggregate chemistry

Binder content

Air voids

Additives

Production Percent aggregate coating and quality of

passing the NO. 200 sieve

Temperature at plant

Excess aggregate moisture content

Presence of clay

Construction Compaction – high in-place air voids

Permeability – high values

Mix segregation

Changes from mix design to field production

(field variability)

Climate High rainfall areas

Freeze-thaw cycles

Desert issues (steam stripping)

Other Factors Surface draining

Subsurface drainging

Reheb strategies – chip seals over marginal

HMA materials

High truck ADTs

2

From a review of the literature (5) (6) (7) (8) (9) (10), the key factors that might contribute to the 3

moisture susceptibility of WMA are the excessive aggregate moisture content due to the lowered 4

production and placement temperatures, and introduction of additional moisture during the 5

production process of specific WMA technologies (i.e. foaming processes). This could possibly 6

affect the reduction of binder absorption by the aggregate, as well as the binder-aggregate bond. 7

The American Association of State Highway and Transportation Officials (AASHTO) T 8

283 (also referred to as “modified Lottman test”) is one of the most common procedures used to 9

evaluate moisture susceptibility of compacted asphalt mixtures, particularly HMA. In this test, the 10

severity of moisture sensitivity of a mixture is quantified as the percentage of tensile strength 11

retained after conditioning which is referred to as the Tensile Strength Ratio (TSR). The tensile 12

strength is determined by using the Indirect Tensile Strength (IDT) apparatus accordance with the 13

American Society for Testing and Materials (ASTM) test method D6931, “Standard Test Method 14

for Indirect Tensile Strength of Bituminous Mixtures” (11). 15

For this test, a minimum of six specimens are compacted by use of Marshall hammer or 16

the Superpave Gyratory Compactor (SGC) to a target percentage of air voids (7 ± 0.5 percent). The 17

compacted specimens are then separated into two subsets: conditioned and unconditioned. 18

Conditioning of specimens includes vacuuming to saturation range of 70 to 80 percent, a freezing 19

cycle (15 hours at -18ºC (-0.4ºF)), and a thaw cycle in warm-water (24 hours at 60ºC (140ºF)). 20

The AASHTO T 283 test is a result of modifications to the original Lottman test in an 21

attempt to improve its reliability. The AASHTO T 283 was adopted as the requirement for the 22

Superpave HMA mixture design. Following this adoption, the AASHTO T 283 has become the 23

most widely used procedure to evaluate moisture susceptibility. Despite its wide acceptance within 24

the industry, several studies have reported shortcomings of the test method. One of the major 25

shortcomings is the lack of ability of the test in predicting moisture susceptibility with reasonable 26

confidence as TSR does not always correlate closely with the field performance (3). 27

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Varamini, Tighe 5

Another frequently made complaint with regard to the test is the disagreement of the test 1

results between specimens with 100 mm (4-inch) and 150 mm (6-inch) diameters. An extensive 2

laboratory research work performed by Epps et al. (12) investigated the matter. Effect of other 3

factors on the test results were investigated including, different compaction methods (Superpave 4

Gyratory Compactor, Marshall, Hveem), degree of saturation (50, 75, and 90 percent), and the 5

freeze-thaw cycle. In this study five different types of aggregates were used with resistance to 6

moisture damage ranging from low to excellent. Specific to each mixture, asphalt cements with 7

performance grades of PG 58-28, 64-22, 64-28, and 70-22 were used. Results of this study have 8

shown that 150 mm (6-inch) SGC specimens provided less variable results than 100 mm (4-inch) 9

Marshall specimens. However, a number of transportation agencies have reported 100 mm 10

specimens showing less variability than 150 mm (6-inch) SGC specimens. This was concluded as 11

part of a survey compiled by AASHTO Materials Reference Laboratory (AMRL) (13) from 89 12

agencies participating in the program. Moreover, Kandhal and Rickards (14) have raised that IDT 13

apparatus used for moisture damage evaluation might not accurately simulate the pumping action 14

of traffic load. Instead, they suggested use of apparatus that enables moisture evaluation under a 15

cyclic mode. 16

Lack of reliability and repeatability of AASHTO T 283 is also reported by Tabib et al. (1) 17

on plant-produced samples collected for a study on evaluation of WMA projects across the 18

province of Ontario in Canada. This study concluded that TSR results were significantly variable 19

with values from 44 to 100 percent. It is further suggested by the study that variability within TSR 20

results might be due to a combination of factors such as production temperature variations 21

(resulting in different levels of aging), and possible improper blending or WMA additives or 22

anti-stripping agents. 23

To evaluate the effect of WMA additives on the moisture susceptibility of 24

laboratory-prepared mixtures, the AASHTO T 283 testing protocol has been employed in several 25

studies. Results obtained from these studies raised concerns about WMA mixtures as many 26

mixtures failed the TSR requirements. However, such mixtures have not shown evidence of 27

moisture damage in the field. The cause of discrepancy between the laboratory and field is further 28

suggested to be due to how WMA mixtures are aged and conditioned prior to compaction, as stated 29

by Mogawer et al. (15). This possible cause of discrepancy is evaluated in several studies. These 30

studies concluded that an increase in laboratory conditioning temperature and/or time prior to 31

compaction may provide a better correlation between the laboratory and field results. 32

PURPOSE AND DESIGN OF THE CANADIAN SURVEY 33

The Ministry of Transportation of Ontario (MTO), and the Centre for Pavement and 34

Transportation Technology (CPATT) located at the University of Waterloo (UW) in Ontario are to 35

evaluate the moisture susceptibility of WMA. The main objective of this research project is to 36

evaluate the ability of AASHTO T 283 to detect moisture susceptibility of WMA. Other objectives 37

of this research includes (1) suggesting recommendations to improve laboratory conditioning 38

protocols, and (2) evaluate any potential difference in WMA moisture susceptibility measured on 39

laboratory and plant produced mixtures. Another objective of the survey was to identify possible 40

gaps in the WMA that needs to be closed with further research. Finally, the survey provided an 41

opportunity for respondents to share information regarding the construction, materials, and 42

performance of previously placed WMA pavements, as well as willingness to participate in the 43

project. 44

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Varamini, Tighe 6

To acquire insights in the most common type of technologies and evaluation procedures 1

Canadian agencies use for WMA for inclusion in the work plan, a survey was distributed in 2

January 2015 by CPATT. 3

The survey was conducted in a mail-back form with an e-mail invitation containing a 4

brief description of the objectives of the study and the purpose of the study. The invitation was 5

distributed to two technical Transportation Association of Canada (TAC) standing committees of 6

the Chief Engineer’s Council: (1) Pavements, and (2) Soils and Materials Standing Committees. 7

The distribution of the survey was completed after receiving ethics clearance through a University 8

of Waterloo Research Ethics Committee. 9

SUMMARY OF THE 2015 CANADIAN SURVEY FINDINGS 10

The following is a highly summarized overview of the survey responses in tabular and/or graphical 11

format. For all tables, “no answer” indicates that no answer was provided by the agency. For 12

number of tables, the percentages do not add to 100 percent because agency provided multiple 13

answers. The list respondents to the 2015 Canadian WMA survey is provided in Table 2. 14

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TABLE 2 Summary of the Survey Respondents 16

No. Organization City Province

1 Alberta Transportation Edmonton Alberta

2 British Columbia Ministry of

Transportation and Infrastructure

Victoria British

Columbia

3 The City of Calgary Calgary Alberta

4 Manitoba

Infrastructure and Transportation

Winnipeg Manitoba

5 Ministry of Transportation Ontario Downsview Ontario

6 Nova Scotia Transportation and

Infrastructure Renewal

Halifax Nova Scotia

7 Ministry of Highway and Infrastructure, Saskatchewan Saskatoon Saskatchewan

8 Transports Quebec Quebec City Quebec

9 Halifax Regional Municipality Halifax Nova Scotia

10 Government of Yukon Highway and Public Works Whitehorse Yukon

11 New Brunswick Department of Transportation and

Infrastructure

Fredericton New Brunswick

As noted in Table 3 the first usage of warm mix technology in Canada dates back to 2006, 17

while majority of the agencies started using WMA in 2009. Currently, majority of the provincial 18

agencies indicated routine use of warm mix technology in considerable amount of tonnage, as 19

illustrated in Figures 1 and 2 respectively. In survey revealed that more than half of the respondents 20

(64%) consider green concepts (i.e. GHG, reduction) in design and management decision making. 21

The usage of WMA technology is specified as an option for 73 % of agencies, while it is a 22

requirement for the remaining 27 percent. 23

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Varamini, Tighe 7

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TABLE 3 First Usage of WMA technology in Canada 2

Year Response

2006 9 %

2007 9 %

2008 27 %

2009 45 %

No Answer 8 %

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FIGURE 1 Warm Mix Asphalt Usage in Canada. 6

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FIGURE 2 Warm Mix Asphalt tonnage placed to date in Canada. 10

Varamini, Tighe 8

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Table 4 provides the list of most commonly used warm mix additives and technologies 2

used by agencies and cities across Canada. In addition to Table 4, other technologies were 3

indicated by respondents including Ecomat (Sintra-Colas product), Evotherm (M1, TE, 2000), and 4

Chemoran CWM, ALmix Foaming system, and Meeker Foaming system. 5

Almost 91% of respondents have used warm mix with dense-graded type of asphalt 6

mixtures, which is mostly designed by Marshall method of design. Superpave method is the 7

second most common design method used for warm mix asphalt. 8

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TABLE 4 Which of the following WMA additives do you use more often? 10

Additive Response

Accu-Shear™ -

Advera® WMA 18%

Aquablack™ -

Aspha-Min® 9%

Cecabase® RT 36%

Double Barrel Green® 45%

Evotherm® 3G. 82%

Evotherm® DAT 45%

Low Energy Asphalt (LEA) -

Rediset®, 18%

Rediset™ WMX 9%

REVIX™ -

Sasobit® 18%

Shell Thiopave™ -

SonneWarmix™ 27%

Terex® -

TLA-X Warm Mix -

Ultrafoam GX™ 27%

WAM Foam® -

Other Additives 17%

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Majority of respondents indicated mandatory use of anti-stripping agents with warm mix 12

technology, if laboratory test results indicate presence of moisture damage (73%); while 18% of 13

agencies require the use of anti-stripping agents when employing aggregates with a history of 14

moisture susceptibility. Furthermore, 18% of agencies indicated that there are warm mix additives 15

known to have anti-stripping properties, and because of this, use of anti-stripping agents may not 16

be required. Being asked if they can provide name of anti-stripping agents that are commonly used 17

for their projects, 64% of the agencies replied, the agencies named at least one of the following 18

anti-stripping agent names: 19

Hydrated Lime 20

Zycosoil 21

AD-Here LOF 6500 and AD-Here 77-00 22

Morlife 5000 23

Indulin 814A and Redicote C2914 24

Varamini, Tighe 9

75 percent of agencies stated that they have a set of specification or guidelines for the use 1

of WMA. Furthermore, 64 percent of respondents indicated that evaluation of WMA moisture 2

sensitivity is based primarily on Tensile Strength Ratio (TSR) using the AASHTO T 283, 9% of 3

respondents preferred the Hamburg Wheel Tracking Test (AASHTO T 324), 9% Asphalt 4

Pavement Analyzer (APA) (AASHTO TP 63), and 9% the Immersion-Compression Test 5

(AASHTO T 165). About 27% of respondents had no requirement for moisture sensitivity testing. 6

Also, respondents were asked if they can provide testing criteria for WMA moisture damage. 9 7

percent of respondents stated they have no criteria while 45% provided no answer. The criteria 8

provided by the remaining 45% of the respondents are as follow: 9

AASHTO T283, require a TSR of 73% or greater with visual assessment by the 10

Department representative 11

AASHTO T283, require a TSR of 75% or greater for Superpave mixtures, and 80% or 12

greater for Stone Mastic Asphalt (SMA) mixtures. 13

AASHTO T283, require a TSR of 80% or greater with visual assessment by the 14

Department representative 15

Lottman completed on Hot Mix Asphalt (HMA), if no additive required for HMA, no 16

additive will be require for WMA. 17

AASHTO T 165, Minimum Index of Retained Stability after immersion in water at 18

60°C (140°F) for 24 hours of 85% and 75% for different classes of pavement. 19

The laboratory and field performance of WMA has been documented by 75% of the 20

respondents. Moreover, the vast majority of agencies (91%) indicated that no premature failures or 21

distresses had been observed for any WMA projects/trials. However, one agency (9%) observed 22

appearance of thermal cracking in WMA pavements. 23

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COMPARISON OF THE 2015 CANADIAN AND THE 2010 UNITED STATES SURVEYS 25

In 2010, a survey of the U.S. Departments of Transportation (DOTs) and other agencies was 26

conducted at the beginning of NCHRP project 09-49 with main objective of documenting the 27

performance of existing WMA pavements across the United States with emphasis on moisture 28

susceptibility (16). The survey included responses from 35 agencies out of 52 state highway 29

agencies, in which 40 percent of the responding state DOTs indicated routine use of WMA, as 30

illustrated in Figure 3. In compare to the results of the 2015 Canadian survey, results suggest that 31

WMA is being used by Canadian agencies more routinely. 32

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FIGURE 3 WMA use in the United States (16) 3

Table 6 compares the results of this survey with the 2015 Canadian survey. It should be noted that 4

the symbol of N/A means that the question was not included in the survey. 5

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TABLE 5 Comparison of the 2015 Canadian Survey with the 2010 U.S. Survey 7

2015 Canadian

Survey

2010 U.S.

Survey

Usage of WMA Asphalt

Routinely

Rarely (or in trial projects)

Never Used

73%

18%

9%

40%

54%

6%

Options of Using WMA Technology

Requirement

Allow as option

Allow as a separate bid item

No Answer

Do not know

Does not allow

27%

73%

-

-

N/A

N/A

6%

73%

6%

N/A

3%

12%

Specification or Guidelines for Use of WMA Technologies

Yes

No

75%

25%

76%

24%

Type of WMA Technologies

Accu-Shear™

Advera® WMA

Aquablack™

Aspha-Min®

Cecabase® RT

Double Barrel Green®

Evotherm® 3G.

Evotherm® DAT

Low Energy Asphalt (LEA)

-

18%

-

9%

36%

45%

82%

45%

-

3%

9%

8%

N/A

N/A

N/A

4%

16%

N/A

Varamini, Tighe 11

Rediset®,

Rediset™ WMX

REVIX™

Sasobit®

Shell Thiopave™

SonneWarmix™

Terex®

TLA-X Warm Mix

Ultrafoam GX™

WAM Foam®

Other Additives

18%

9%

-

18%

-

27%

-

-

27%

-

17%

N/A

4%

2%

12%

2%

2%

9%

N/A

5%

3%

4%

Require the Use of Anti-Stripping with WMA

If there is a history of moisture problems with the aggregate

in the mixture

Combination of moisture susceptible aggregate and moisture

laboratory results

if laboratory test results (i.e. Tensile Strength Ratio (TSR))

indicate presence of moisture susceptibility

NO

18%

N/A

73%

18%

12%

30%

6%

52%

Moisture Susceptibility Test Methods

NO

Modified Lottman Test (AASHTO T 283)

Hamburg Wheel Tracking Test (AASHTO T324)

Asphalt Pavement Analyzer (APA - AASHTO TP063)

Immersion-Compression test (AASHTO T 165)

No Answer

Other

27%

64%

9%

9%

9%

9%

N/A

10%

61%

17%

5%

5%

N/A

2%

Any Premature Failures or Distresses

No

Thermal Cracking

Compaction

91%

9%

N/A

91%

3%

6%

CONCLUSION AND FUTURE STEPS 1

This paper has presented an overview of the current Canadian state-of-the-practice warm mix 2

asphalt based on a survey prepared by the CPATT at the University of Waterloo. A comparison of 3

this survey with the most recent U.S. survey on WMA pavements with emphasis on moisture 4

susceptibility is also presented. 5

The Canadian survey results indicated that majority of the provincial agencies use of 6

warm mix technology on routine bases in considerable amount of tonnage. Usage of WMA 7

technology is specified as an option for most of agencies, which could facilitate fair competition 8

and purchasing of WMA technologies, and provide the asphalt industry with the incentive and 9

opportunity to invest and build confidence in WMA. 10

The evaluation of moisture susceptibility of WMA is based primarily on Tensile Strength 11

Ratio (TSR) using the AASHTO T 283. Majority of respondents indicated mandatory use of 12

anti-stripping agents with warm mix technology, if laboratory test results indicate presence of 13

moisture damage. 14

There are number of agencies that require the use of anti-stripping agents when 15

employing aggregates with a history of moisture susceptibility. Finally, the vast majority of 16

agencies indicated that no premature failures or distresses had been observed for any WMA 17

Varamini, Tighe 12

projects/trials to date. 1

Going forward, CPATT’s research team will be closely working with Ministry of 2

Transportation Ontario (MTO) on assessing different conditioning and aging protocols and 3

thresholds for different empirical and mechanistic standard laboratory tests used to evaluate 4

moisture sensitivity of WMA. This would help in better determining and modeling 5

moisture-induced damage in asphalt pavements. 6

ACKNOWLEDGEMENTS 7

The authors of this paper gratefully acknowledge the respondents for participating in this survey. We 8

would also like to acknowledge Ministry of Transportation Ontario for providing funding for this study. 9

Appreciation is also extended to the Norman W McLeod Chair in Sustainable Engineering. 10

REFERENCES 11

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Testing Procedures for HMA Moisture Susceptibility. Washington, D.C, 2007.

3. Solaimanian, M., J. Harvey, M. Tahmoressi, and V. Tandon. Test Methods for Determination of

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4. Santucci, L. A.T. Moisture Sensitivity of Asphalt Pavements: Introduction and Seminar Objectives.

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5. Warm Mix Technologies and Research. U. S. Department of Transportation Federal Highway

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Test for Moisture-Induced Damage with Superpave Volumetric Mix Design. Washington, D.C., 2000.

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Moisture-Induced Damage (NCHRP web-only document 166). Washington, DC, 2010.

14. Kandhal, P. a.I.R. Premature Failure of Asphalt Overlays from Stripping: Case Histories. 2002.

15. Mogawer, W.S., A.J. Austerman, and H.U. Bahia. Evaluating the Effect of Warm-Mix Asphalt

Technologies on Moisture Characteristics of Asphalt Binders and Mixtures. Washington, DC., 2011.

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

E.S. Park. Evaluation of the Moisture Susceptibility of WMA Technologies (NCHRP Report No. 763).

Washington, DC, 2014.

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