AN APPROACH TO EXAMINE THERMAL FATIGUE IN ASPHALT CONCRETE

Amy L. Epps

Abstract

Thermal cracking in asphalt concrete pavements manifests from a single drop in

temperature to an extreme low (low temperature cracking) or from a series of repeated large

temperature fluctuations with low temperarures above the fracture temperature of the asphalt·

aggregate mixture (thermal fatigue) , The research described presents an approach to examine

mixture resistance to thermal fatigue and applies this approach 10 evaluate urunodified and

crumb-rubber modified (eRM) mixrures. A slow frequency beam fatigue test was used to

measure mixture resistance in a controlled strain mooe, with strain levels selected to simulate

thermal stress levels induced under average and extreme environmental conditions in harsh

climates like the intermountain west of the United States. Selection afthese stress levels was

based on mixture fracture temperatures and results from an analysis of the interaction between

asphah concrete pavements and the selected environment.

Resuhs from a limited laboratory experiment illustrated that the approach presented can

be used to measure the finite capacity of both modified and unmodified mixtures for thermal

fiucruations coupled with low temperatures. According to these results, CRM modification

improved mixture resistance to thennal fatigue under average environmental conditions in the

harsh climate of the intermountain west of the United States. Limited testing indicated that

!hennal stress level affected the perfonnance of modified mixtures with a gap-graded aggregate

and Ihese gap-graded modified mixtures sustained a greater nwnber ofthennal cycles prior to

failure than dense-graded mixtures under the selected average environmental conditions. Further

development of this approach to directly measure resistance to thermal fatigue is encouraged for

expanded testing programs with more mixture and environmental variables. Both short-term and

long-term oven aging is recommended to simulate field ronditions under which thermal fatigue

is likely 10 occur, and Ihe use of a controlled stress fatigue lest for comparison of resul ts is

suggested.

Key Words: Thennal Fatigue, Crumb-Rubber Modifier(CRM), Beam Fatigue Test

lulrodudioo

1

Many areas of the Uni ted Slates experience large daily temperature fluctuations coupled

with extreme low temperatures during the winter and high temperatures and solar radiation thaI

promote asphalt hardening during the summer. These conditions may calise transverse cracking

problems in asphalt concrete pavements due to thennal fatigue. Extensive cracking results in a

deterioration in ride quality; allows destructive substances, such as air and water, to enter the

pavement structure; and reduces pavement life, requiring frequent maintenance and rehabili tation

activities to restore safe and efficient routes for moving people and goods. In the literature

thermal fatigue is described as one mechanism causing thermal cracking, a primary form of

distress in asphalt concrete pavements (I, 2, 3, 4). This mode of cracking is caused by a series of

repeated temperature nucrnations, with temperatures above the fracture temperature of the

asphalt-aggregate mixture. The second mode of thermal cracking is low temperature cracking,

resulting from a single drop in temperature to an extreme low below the fracture temperature of

the asphalt-aggregate mixture. A complete evaluation of mixture resistance to both types of

thermal cracking was recently completed. but this paper focuses on an approach to directly

measure mixture resistance to thermal fatigue (5).

Thermal fatigue failure is hypothesized to result from repeated tensile stresses induced by

temperature nuctualions in the pavement as temperature decreases and contraction is restrained.

Aging of the asphalt-aggregate mixture contributes to the level of stress induced. Both rapid

short-term aging during plant mixing and construction and slower long-term aging in the field

stiffen the mixture and increase the stress induced on cooling. When the effect of thermal

cycling exceeds the mixture fatigue resistance, transverse cracks result from the maximwn stress

in the longitudinal direction of the pavement. To minimize this type of cracking and extend

pavement life, resistant aspha1t-ag~gate mixtures are selected based on their thermal and

mechanical properties and the environment where they will be placed.

3

In this research, mixture resistance to thermal fatigue is measured in laooratory tests

under appropriate conditions that simulate environmental demand on the pavement. This

approach facilitates the search for mixtures that perform satisfactorily under the coupled

conditions oflarge daily temperature fluctuations and extreme low temperatures. Some modified

mixtures may meet the criteria for adequate performance in these extreme climates. The addition

of crumb-rubber modifier (CRM), manufactured from scrap tires, to the asphalt binder contained

in asphalt concrete pavements has been suggested as a partial remedy to thwart the onset and

extent of thermal fatigue failure . A modified binder formed by adding CRM 10 a base asphalt

cement using the wet process lends enhanced material properties to asphalt-aggregate mixtures,

increasing their resistance to induced tensile stresses. For equivalent changes in temperature,

CRM modified mixtures sustain lower induced thermal stresses than conventional mixtures due

to reduced stiffucsses as compared to corresponding unmodified mixtures (6). The durability of

these modified mixtures is also improved as a result of increased binder film thicknesses on the

aggregate, reducing the rate of oxidative aging and decreasing the potential for stripping (7).

In the research described in this paper, an approach for measuring mixture resistance to

thermal fatigue is introduced and applied to unmodified and CRM modified asphalt-aggregate

mixtures. A description of this approach follows the next section swnmarizing past efforts to

measure mixture resistance to thermal fatigue. The experimental design and materials used in

the limited laboratory testing program are described, and test results and analysis are presented.

Conclusions and reconunendations complete the paper.

4 Background

Initial efforts to understand the factors associated with thermal cracking were highlighted

in a 1966 symposium, and early research focused on low temperature cracking (8). Resistance of

asphalt concrete to thermal fatigue alone or in combination with low temperature cracking was

also examined in a few studies prior to the Strategic Highway Research Program (SHRP) in the

late 1980's and early 1990·s. Vinson, lanoo, and Haas (2) and lanoo, Bayer, and Walsh (9)

reviewed research efforts preceding the extensive SHRP program that measured thermal stress

and predicted thermal cracking. The SHRP program produced mixture tests and analysis tools

capable of predicting resistance to [ow temperature cracking and the combination ofbolh forms

oftherrnal cracking. Recent research has utilized these tools to examine thermal fatigue in

asphalt concrete and develop an analysis system (or predicting performance in terms of both

types of thermal cracking. This section describes previous efforts to study thermal fatigue or a

combination ofthennal fatigue and low temperature cracking. An evaluation of these efforts is

also provided.

Tht rmal Ftsligut

Examination of the possibility of a second fonn of thermal cracking began in the \970's

in response to severe transverse cracking in West Texas, where pavements are nol subjected to

extreme low temperatwes. A series of reports (10, II , 12, 13) present the envirorunental

conditions in West Texas, the thermal activity of base course materials ill freeze-thaw cycles, and

a prediction model for estimating crack spacing from material properties. Thermal susceptibility

of the base course was identified as the damage mechanism causing transverse cracking in some

of the asphalt pavements in this area. A study by Epps and Anderson (14), including field

observations in West Texas coupled with laboratory testing and modeling with the COLD

program (IS), indicated that properties oflhe asphalt concrete as well as the base material

influence transverse cracking in this area. In addition, they considered hardening of the binder

from aging as a possible indicator of susceptibility to this type of cracking. Sugawara and

Moriyoshi (16) also conducted laboratory tests on mixtures subjected to thennal cycling until

failure. Fatigue failures were noted in tests with the minimum temperature close to the mixture

fracture temperature, and mixtures with harder asphalts sustained fewer cycles before failure.

Lytton and Sharunugham (4) and Lytton, Shanmugham, and Garren (17) initialed

research based on fracture mechanics to predict thermal fatigue life. Building on the work by

Shahin and McCullough (3. 18), they developed a modella predict the occurrence ofthermai

fatigue cracking caused by temperature cycling below 25C. The THERM program supports this

model that calculates the number of cycles to failure, three cumulative damage functions, and

crack frequency or spacing. Thermal fatigue life is determined according to the following

equation based on the rale of crack growth defined by Paris and Erdogan (19):

• J

do N f ~ 1 , c . A C, K yo

5

where ~is the number ofthennal cycles to failure, de is the incremental growth of crack depth c

from a change in temperature, h is the thickness of the asphalt concrete layer. Co is the initial

crack depth.,1/( is the change in stress intensity factor at the crack tip from a change in

temperature, and A and n are fracture parameters. The effect of aging is also incorporated into

the model based on equations presented by Benson (20).

Maj idzadeh, Buranrom. and Karakomzian (21) have developed other fracture mechanics­

based approaches. Abdulshafi and Majidzadeh (22) proposed the use of the energy release rate,

JIO to characterize asphalt concrete in a prediction offatigue life, and Little and Mahboub (23)

used this same parameter to evaluate low temperarure fracture potential of binders in asphalt­

aggregate mixtures. Abdulshafi and Kalosb (24) used another energy release rate parameter, the

Co.·line integral, in a study ofload-induced fatigue and suggested its use to study thennal fatigue .

Cyclic changes in temperature are also possible with the Thermal Stress Restrained

Specimen Test (TSRST) developed during SHRP. Jackson and Vinson (25) used this test with

thennal cycling. Based on a limited experiment, they concluded that thermal fatigue is not a

viable mode of distress in asphalt concrete mixtures in the absence of environmental aging.

6

Thermal Patigufllfnd Low TemperQture Cracking

Limiting values for binder temperature susceptibility and binder stiffuess were

historically recommeooerllo minimize themul cracking in either fonn prior to the development

of empirical and mechanistic approaches for predicting mixture resistance to both low

tempnature cracking and thermal fatigue (26). Empirical approaches based primarily on binder

pro~ies included regression equations developed in Canada to estimate transverse crack

spacing and a measure of cracking intensity (27, 28). These are limited in application and only

provide a relative means of rating different mixtures thai are similar to those used in developing

the equations. Mixture response characteristics and thermal stress predictions are nol included in

these approaches.

Experimental methods to measure mixture resistance to both low temperature cracking

and !henna! fatigue were developed in the late 1980's and 1990's at the Cold Regions Research

and Engineering Laboratory (CRREL) of the United States Army Corps of Eng in em (9). The

environmentaJ system associated with the CRREL Thermal Stress Test (CfST) is capable of

generating a wide range of conditions, including cooling rates between 3 and 27C per hr and a

low temperature of -60C. Limited thermal cycling experiments conducted with the erST did

not validate the hypothesis of thermal cracking by thennal fatigue.

EITorts to model mixture resistance to both forms of thennal cracking bf:gan with the

work of Shahin and McCullough (3, 18). The computer program Te-I supports their model that

considers low temperature cracking and thermal fatigue separately and adds the two effects to

predict overall thennal cracking. In this model, a phenomenological approach to thennal fatigue

is used to estimate the number ofthennal cycles to failure. These researchers indicated thaI

temperature cycling stimulates a constant strain fatigue distress, and the relationship between

strain and thennal fatigue life is analogous to the conventional traffic load-induced fatigue

function:

7 where Nfis the average number of thermal cycles to failure, £ is the strain level, and A and B are

fatigue constants. Variability in material and mixture properties and aging are acrounled for in

the model, and a cumulative damage hypothesis is used to determine the amount of cracking due

to thermal fatigue.

A thennal cracking analysis system was developed during SHRP in response 10 a change

in focus from phenomenological approaches \0 more mechanics·based approaches that account

for crack propagation and predict crack spacing with lime. Both types ofthennal cracking are

included in the analysis, and the two effects are nol separated. The analysis system contains five

major components. and the relationships between these components are illustrated in Figure I.

This system is described by Hiltunen and Roque (I, 29) and Buttlar and Roque (30). The

resulting performam:e prediction model uses material properties measured with the Indirect

Tensile Test (IDn as input. This test simulates the tensile stress stale caused by thermal changes

in the field by loading cylindrical specimens (I 52·nun diameter by 5 I-mm) across a diameter

within a controlled temperature chamber. The lOT is conducted in (wo phases (31). The first

phase utilizes short-term creep tests at multiple temperatures to determine the viscoelastic

properties of the mixture needed to predict thermal stress development Results from the tensile

strength test conducted in the second phase are used in conjunction with the viscoelastic

propenies to calculate the fracture properties of the mixture that control the rate of crack

development IDT specimens have been oven-aged to simulate short-term aging during

production and construction (3\). Long-term aging in the field is not considered in the modeL

The resulting prediction of thermal crack spacing with lime is based on a calculated depth of a

local, a\'mge crack and an asswned normal distribution of crack depths (I).

Evaluation a/Past Efforts

Allhough previous research efforts have improved the understanding of the interaction

between asphalt pavements and the envirorunent, at present there is not universal acceptance of

thermal fatigue as a distress mechanism causing thermal cracking. In examining the hypothesis

of this mechanism of failure, thermal fatigue must be isolated from low temperature cracking.

8 As a result, only those approaches thai separate the effects of the two different [onns of thermal

cracking are recommended to explore the phenomenon of thermal fatigue. An advantage of

direct measurement of mixture response to thermal cycling is the absence of necessary

asswnplions of material behavior required in mechanics-based approaches. Previous laboratory

testing programs employing direct measurement of mixture response have produced mixed

results. Jackson and Vinson (25) indicated thai thermal fatigue is not a viable distress mode in

the absence of environmental aging, but Sugawara and Moriyoshi (16) suggested thai mixtures

do have a finite capacity for thermal fluctuat ions with low temperatures greater than but close 10

the mixture fracture temperatwe. Janoo, Bayer, and Walsh (9) also conducted a limited

experiment with direct measurement of response 10 thennal cycling and were not able 10 validate

failure by thennal fatigue. The approach described in the following section provides another

method to measure mixture response to conditions selected to simulate thennal Slresses induced

from daily lempenture fluctuations in extreme climates.

Measurement of Thermal Fatigue Resistance

A standard test method for evaluating mixture resistance to thermal fatigue does not exist.

In this experiment, a load-induced slow-cycle beam fatigue test was selected to measure actual

mixture response to nuctuations in strain that simulate changes in induced thermal stresses

caused by daily temperature variations. This same test is used to measure mixture resistance to

traffic-load induced fatigue when conducted at a higher frequency (10Hz). This test was chosen

because failure by thermal fatigue is similar to failure by load-induced fatigue, with daily

temperature cycles equivalent to traffic-induced loading of the pavement.

The beam fatigue test subjected rectangular beam specimens (64- by 51 - by 38 1-mm) to

flexural fatigue using four-point loading (Figure 2) (32). Specimens were subjected to a

sinusoidal variation in strain until failure. Strain levels were selected to represent induced

thermal stresses caused by temperature fluctuations. At failure, defined as a reduction in

stiffness to 50 percent of its initial value, the nwnber of cycles was recorded !is the mixture

response to thermal fatigue.

9

The test was conducted al one temperature (4C), with thennal stresses caused by field

temperature fl uctuations simulated by a change in strain. Using the flexural stiffness of each

mixrure, this selected strain was calculated from a representative variation in thermal stress

occurring from daily lemperarure changes. As the lest proceeds io I conllolltd strain mode, the

stress will decrease with the sliffiless, but strain levels weee dctenttined from thennal stress

levels selected by the process described in the next section. An average thennal stress level of

1.72 MPa for unmodified mixtures and 1.03 MPa for modified mixtures was selected to simulate

average winter conditions in the intermountain west of the United States. Extreme thermal stress

levels of2.4\ MPa for unmodified mixtures and 1.72 MPa for modified mixtures were used to

represent extreme conditions in this region. Although pavement temperatures vary over a period

of24 hours, frequency of loading in the thermal fatigue test was increased 10 achieve a

reasonable lime for each test The frequency selected was 0.05 Hz, a slow-cyc\e fatigue test

when compared wi th lraditionalload-induced fatigue tests conducted at 10 Hz.

Elpt riment

A limited laboratory experiment was designed and completed to examine an approach

different than those ~ in previous efforts to measure mixture resistance to thermal fatigue.

The mixture variables considered include CRM content and aggregate gradation. Modified

mixtures contained 15% CRM, and no CRM (0%) was added to unmodified mixtures. Two

gradations (gap and dense) of the same aggregate source were used. The binder content for each

mixture was an optimwn content as determined by a specific mix design methodology that

incorporates reliability (5). The optimwn binder contents (by dry weight ofaggregale) were 7

percent and 5 percent fo r modified and urunodified mix\W"eS, respectively. In addition 10 a single

aggregate source, only one base asphalt cement was used and the CRM size and chemistry were

held constant. Codes fo r each mixture variable are as follows:

Mixture Variable

CRM Content

Aggregate Gradation

Value

o percent (unmodified)

15 percent (modified)

Gap-graded

Dense-graded

10

Code

0

15

G

0

Combining these variables and us ing the codes described, the following three mixtures were used

in the experiment: GO,GI5,andDI5.

Environmental variables were also considered.. All tests were perfonned at a single test

temperature (4C), but two strain levels were used to simulate average and extreme thenna! stress

levels in the intennountain of the United Slates. Different stress levels in each class of

environmental conditions (average and extreme) were selected for unmodified and modified

mixtures based on an analysis of the interaction between the environment and asphalt concrete

pavements (5). An overview of this analysis follows.

To aid in the selection ofthennal stress levels, the COLD program was used to examine

hourly changes in thennal stress and mixture tensile strength with hourly fl uctuations in

temperature over a short (2o.day) period of time during the winter of 199()..91 in Winnemucca,

Nevada (15). This site in the intermountain wesl of the United States was selected because large

daily temperature fluctuations and extreme low temperatures are common in this region and

conducive to thennal fatigue. Inputs 10 the COLD program included a description of the

pavement structure and its thennal properties, climate data at the selected site. and relationships

characterizing the temperature dependence of mixture stiffuess and tensile strength. The

assumed pavement structure and properties of each layer are shown in Figure 3.

Required climate data included daily maximum and minimum air temperatures and total

daily solar insolation values. The two extreme temperatures were obtained from the Surface

Airways CD-ROM manufactured by Earthlnfo. Inc. and input for the time period from December

\I 14, 1990 through January 2, 1991 (33). Output of the COLD program was only collected for the

last 15 days o[this lime period to ensw-e a minimum innuence of assumed initial conditions.

Other required lemperarure information included assumed daily limes for minimum and

maximum air temperature, initial and final air temperatures for the analysis period, and an initial

temperature profile for the pavement structure (5). Radiation values representing total daily solar

insolation were also input [or the 2O-day study period. These values were obtained based on the

latitude ofWiMemucca, Nevada, using modified values ofllie output of part of the Climatic­

Material-Structural (eMS) program (34). Modification procedures suggested by Deacon

accounted for atmosphere, angle of ground surface, and sunshine (35). Other required radiation

information included average sunrise and sunset times for the study period.

To chancterize the effect of temperature on mixture stiffuess and tensile strength, Shell

nomographs were used with binder properties measured after accelerated aging in both the

Rolling Thin Film Oven Test (RTFOT) and the Pressure Aging Vessel (PAV) (simulating both

sbort·lerm and long-term field aging), an asswned time ofloading (r=10) seconds for estimating

mixture sliffuess, and measured (r-5 seconds) tensile strength values from the Indirect Tensile

Test (IDT) (5, 3 1,36, 37, 38). Measured binder properties are discussed in the next section of

this paper.

The aged state of the binder and the specified times of loading were selected based on a

sensitivity analysis of the effect of these inputs on the output of the COLD program (5). This

analysis explored time of loading (I) values of7200 seconds and 10 seconds for use in estimating

mixture sliffuess and values of 5 seconds and 245 seconds for use in estimating mixture tensile

strength. The longer times of loading were recommended in the original COLD program

literature (15). The shorter time of loading for estimating mixture stiffitess and tensile strength,

respectively, was used to calibrate the COLO program with U. S. data from Utah and represent

the cross head speed used in the Indirect Tensile Test (IDT) (31 , 39). Aging was considered by

using properties of the binder in the unaged condition, after a thin-film oven lest (equivalent to

short-term aging of the mixture), and after short· term and pressure aging (equivalent to long-term

aging of the mixture).

12

Results of the sensitivity analysis indicated a substantial effed of aging on the COLD

output while both the lime ofloading used to estimate mixture stiffness and the time ofloading

used to estimate mixture tensile strength had linle effect with all other variables held constant.

For each COLD run using the longer time of loading for estimating mixture stiffness (7200

seconds), however, no thermal cracking problems were predicted. This result was unreasonable,

as cracking is predicted based on mixture resistance measured in the Thermal Stress Restrained

Specimen Test (TSRSn and extreme temperature recorded al Winnemucca (5, 31), The use of

the shorter time of loading for the tensile strength oflhe mixture (5 seconds) produced

reasonable results consistent with the measured trend oflensile strength versus temperature (5),

These results led to an assumption thai estimating thermal stresses after Doth short-term and

long-term aging of the binder is more appropriate in terms of in-situ conditions and a

recommendation of the use of the selected times ofloading based on more realistic cracking

behavior and strength values for the asphalt-aggregate mixture in the assumed pavement

structure (S).

Using measured binder properties and the selected times ofloading, the effect of

temperature on both mixture stiffness and tensile strength was estimated for mixtures GO and

015 (Table I). Mixture DIS was not analyzed, as measured tensile strength data were not

available. In estimating the necessary relationships, 3SSwoptions as to !.he effect of aging on ring

and ball softening point and the penetration index (PI) for the umnodified binder in mixture GO

were made based on data for a similar binder measured for three aging conditions (5, 37, 40). In

estimating the mixture stiffness versus temperature relationship for mixture 0 IS, E* values at the

selected lime ofloading (1=10 seconds) for the corresponding modified binder were obtained by

multiplying shear stiffness data (0*) from the Dynamic Shear Rheometer (DSR) test by a factor

of three (assuming Poisson's ratio'" 0.5) (3 \).

Figure 4 illustrates the COLD output for the gap-graded mixture without CRM (GO), and

Figure 5 shows the output for the gap-graded mixture with IS percent CRM (015). Positive

induced stresses indicate tensile stress in the pavement. These figures also include the predicted

13

Table 1 Effect of Temperature 00 Stiffness (S.J and Tensile Strength

PAV residue 1=10 sec for stiffness estimation measured tensile slreruzth (1''''5 sec)

MiIture Tempenlure (C) S .. (MPa) Tensile Strength (MPa)

·40 4.0' \0· -.

·30 3. 1'104 ...

·20 2.2'11t 3.46 GO

·10 0.97' 10' 3.05

0 0.35*1(t 2.66

10 O.ll ' l(f _.

-40 3.9'10' ...

·30 2.3' \(f ...

·20 1.3'104 2.57 GIS

· 10 0.69'10' 2.41

0 0.34'10' 1.86

I 10 O.IO' lIt ... ,

air and pavement temperatures for Winnemucca, Nevada. For half of the stud'y period

(December 25, 1990 through January 2, 1991), comparison of the mixture tensile strength and

the induced thennal stresses shown illustrate the possibi li cy ofl arge fluctlJations in air

temperature without failure by the mechanism associated with low temperature cracking (Figures

4 and 5). While the predicted tensile strength for mixture GO is only slightly larger (3.18 MPa on

average) than the tensi le strength for mixture G 15 (2.36 MFa on average), the estimated tensile

stress for GO is considerably larger (peaking at 9.14 MPa compared with a peak of 5.94 MPa for

01 5). This difference in predicted tensile srress is expected, as the crumb· rubber mixture (01 S)

is more elastic at cold temperatures than the corresponding unmodified mixture (GO).

14 Using these results and measured tensile strength values at OC, two thermal stress levels

to simulate in the thermal fatigue test were selected for unmodified mixtures (GO) and two

thermal stress levels were selected for both modified mixtures (01 S, 015) based on the COLD

output for mixture GIS. For each class of environmental conditions (average and extreme)

defined subsequently, different thermal stress levels were chosen for the tv.'o mixtures types due

to differences in mixture response to thermal fluctuation (induced stress) and extreme low

temperatures (tensile strength). With measured mixture stiffnesses from frequency sweeps, these

stress levels were converted 10 strain levels for testing.

Two classes of envirorunental conditions (average and extreme) in the intermountain west

of the United Slates were defined based on the results oftbe COLD analysis and used in the

selection oftltennal stress levels. Extreme winter conditions in this region over an eleven-year

period occurred during the time under investigation (December 19, 1990 through January 2,

1991) (5). A large pavement temperature fluclUation of22C was recorded, and this condition

was defined as the extreme case. Average winter conditions over the same period of time were

defined as a 14C Ouctuation in pavementlemperature with the additional condition ofa daily low

temperature below - 29C.

Thermal stress varied approximately 6.9 MPa in the extreme case (22C change in

temperature) for the urunodified mixture (GO) and 4.\ MPa in the extreme case for the modified

mixture (GIS) (Figw-es 4 and 5). For the average case, the stress varies approximately 2.4 MPa

for the tmmodified mixture (GO) and 1.4 MPa for the modified mixture (GIS) (Figures 4 and 5).

Thermal stress levels were nol sel equal to the thermal stresses output from the COLD program

for each class of envirorunental conditions due to limitations in mixture tensile strength and the

desire to measure mixture resistance to more than one thennal cycle. With the tensile strength at

OC of these mixtures measured as 2.66 MPa (GO) and 1.86 MPa (G 15), stress levels to simulate

in the thermal fatigue test conducted at 4C were selected below these thresholds to ensure more

than one cyde prior to failure. As a result. an extreme level of2.41 MPa was chosen for

unmodified mixtures (GO), with an average level of 1.72 MPa selected for these same mixlUres.

The extreme level for both modified mixtures (G IS, DIS) was set equal to the average level for

Il unmodified mixtures (1.72 MFa), and an average level of 1.03 MPa was selected for all modified

mixrures.

The number of specimens tested at each selected stress level is shown in the

corresponding cell crlhe experimental design matrix (fable 2), All specimens were subjected to

short-term Dvec aging prior to compaction (0 simulate aging during production and construction.

The loose mixture was oven aged at a temperature of 135C for four hours (AASHTO PP2) (3\ ).

Long-term aging in the field was nol simulated in order to examine the possibility of mixture

failure due to thermal fatigue in the first few years of service in the field.

Table 2 Thermal FIUgue Experiment

Test: Slow Freouencv Beam Fatii!ue Test

Measured Mixture Response: Number ofThenna.l Cycles to Failure

Thermal Stress Level l Mixture Type

Average I Extreme I Average I Extreme I Unmodified Unmodified Modified Modified

Mixture 1.72 MPa 2.41 MPa 1.03 MPa 1.72 MPa

GO 2 3

Gil 2 2

Oil 2 2

Results from this limited experiment were used to demonstrate an approach to measure

mixture resistance to thennal fatigue and compare the resistance of unmodified and eRM modified mixtures to this form of distress. Following a description of the materials used to

fabricate the mixtures under investigation. the analysis section presents these results.

Materials

The three components of modified and unmodified asphalt-aggregate mixtures used in

this analysis are base asphalt cement, cnunb-rubber modifier (CRM), and aggregate. General

descriptions of each component are given in this section, and selected material properties are

shown in rabies]. 4, and 5.

Bas~ Asphalt Cement

16

SHRP Materials Reference Library (MRL) asphalt cement ABL-3 was selected [or this

experiment. SHRP Superpave specification tests and standard penetration (ASTM OS) and

viscosity tests (ASTM D2170, D2171) were performed, and Table 3 presents selected properties

of the unmodified binder, including the resulting SHRP Sup~ave grade (31, 36, 41 , 42),

Crumb-Rublur Modifier (eRM)

One sowte of fine CRM was selected for this experiment to facilitate ease of specimen

preparation and limit the number of variables under investigation. Properties for this CRM

manufactured by Rouse Rubber Industries, Inc. arc shown in Table 4 (43).

Modifl~d Bilfdt r

All of the new binder specification tests developed during SHRP were perfonned on the CRM

modified binder produced by blending 15 percent CRM (by total weight of binder) with base

asphalt cement ABL-3 (31,41). The blending protocol included preheating the base asphalt

cement for one hour at 15OC, adding the CRM at 15 percent by tolal weight of binder, and

stirring the two components with a propeller blade at 11 00-1200 rpm for one hour at 175C (44,

45). Initial binder tests indicated thai ABL-3 when combined with CRM using the wet process

exhibits improved properties as compared to unmodified ABL-3 (46). It was also observed Ihat

I) Table 3 Base Aspblll Cemeu( Properties 42

MRL ~"'It Codt ABL·)

Traditional AsDhalt Gnde AC·10

Carbo){ylic Acid Content (mo1eslliler) <0,023

III"" h.1

Penetration@25C 100 R, 5 see (0.1 mm) 9{)

Viscoslty @6OC 300 mm HI vacuum (Poises) 1200

Kinemaric Visc05i t~_@...I3SC (cSt) ]1'

Flash Point (Cl 268

Dynamic Shear (G-' sin 5)@S8C to radfsec (kPa) 1.30

Dynamic Shear (G-/sin o)@64e, 10 radfsec (kPa) 0.62

Roll" i...ll!in Film Oven Residue rShort·Term A~in "l

Mau Loss (oercent) 0.5)

Dynamic Shear (G-/sin 01 @SSe, 10 radfsec~) 3.28

Dynamic Shear (G' /sin 5)@64C, 10 radfsec (kPa) 1.51

"m~' A';" V",", ;d,dL"",·T,,,,, A,;"I

ily>umkSh", (G' ,;, 6)@ llC iO nd/"" (MP.) 6.13

ic Shear (G· sin 5)@16C 10 mdfsec (MPa) 4.33

Dynamic Shear (G' sin o)@ 19C. 10 radfsec (MPa) 2.96

C,"" SI;/fn,~ (S) (ii) .240, 60 "" 100 , (MP.) J91

C,,,pSri/fn,~(S)@·18C 60", lOO~ 18)

m·val11~24C 60 sec 100 II 0.27

m-vallle (iil-18C 60 sec 100 R 0.33

PO·Grade PG58·28

Table 4 CRM Properties (43)

Sieve Analysis (Screen) Percent Passing

0.06 nun 100

0.09 nun 100

0. 12 nun 9'

0. 15mm 88

0.075 mm SO

Specific Gravity U SO

18

over time and under elevated temperatures, the high acid conlent of ABL·3 may cause the CJU...1

to deteriorate by some type of physical-chemical reaction, thus altering the binder properties and

possibly reducing the benefits gained from CRM. To mitigate this potential damaging effecl of

high temperatures, modified binders were stored at OC in Ihis experiment (47). Table 5 presents

measured properties for the modified binder, including the resulting SHRP Superpave grade of

each binder.

Aggregfl.tt

Two gradations of one corrunonly used, readily available local mineral aggregate source

were selected to evaluate modified and unmodified mixture response. The selected clean

aggregate source was SHRP MRL aggregate RB, a crushed granite with rough surface texture

and angular shape. The two selected gradations include a California gap gradation and a typical

California dense gradation (Figure 6) (48, 49).

Results IUd Analysis

Using the beam fatigue test at a slow frequency (0.05 Hz), resistance to thermal fatigue

was measured in terms of number of cycles to failure for each mixture in the experimental design

(Table 2) at strain levels simulating the indicated average or extreme thermal stress levels.

Individual test results are shown in Table 6.

At equivalent numerical thermal stress levels (average for GO and extreme for G 15 and

DIS), both modified mixtures (G I 5 and 015) exhibited improved performance in terms of the

number of thermal cycles to fai lure. As expected, at average stress levels modified mixtures

resisted more thennal cycles before failure as compared to the number of thermal cycles 10

failure at extreme stress levels. For the unmodified mixture (GO), the number of cycles to failure

appears approximately constant regardless ofthennal stress level. The selected stress levels may

19

Table 5 Modified Binder Properties

Base Asphalt Cement ABL-J

CRM (percent by total weight of binder) 15

Unaged~

Flash Point (C) 254

Dynamic Shear (Go/sin &)@64e, ]0 rad/sec (kPa) 4.68

Dynamic Shear (O-'sin 1i) @76C, ]0 rad/sec (kPa) 1.34

Dynamic Shur (Go/sin 1i) @82C, 10 rad/sec (kPa) 0.76

RoHing Thin Ei!m Qym ~ (Sb!!ri-Tenn tutin&l

Mass Loss (percent) 0.5J

Dynamic Shear (Go/sin 1i)@64e, 10 rad/sec (kPa) 11.60

Dynamic Shear (G' /sin O)@76C. 10 rad/sec (kPa) 4.03

Dynamic Shear (Oo/sin O)@82C, 10 rad/sec (!cPa) 2.40

Dynamic Shear (Go/sin o)@88e, 10 rad/sec (kPa) \.49

Ile~~ure 6ging Vessel ~ (I,,!!ng-Iellll.6.iiD.&l

Dynamic Shear (G ' sin o)@ IOC, 10 rad/sec (MPa) 5.49

Dynamic Shear(O ' sin o)@ I3C, 10 rad/sec (MPa) 4.01

Cretp Stiffness (S)@ -24C, 60 sec, 100 g (MPa) 198

Cretp Stiffness (S)@ -18C, 60 sec, 100 g (MPa) 98

Creep Stiffness (S)@-12C, 60 sec, 100 g (MPa) ---

m-value@-24C,60sec, 100 g 0.28

m-value@-18C,6Ostc,loog 0.33

m-value@-12C, 60 sec, 100 g ---PG-Grade PG76-28

20 nol be different enough to discriminate the effect on mixture response. The results in Table 6

show a pronounced effect of aggregate gradation on modified mixture response at the average

thermal stress level, with gap-graded mixtures outperforming dense-graded mixtures. At the

extreme thermal stress level for modified mixtures, there appears to be no effect of gradation on

mixture resistance 10 thennal fatigue.

' i;: ~~" a .. .... "c'. ' . I I

I Thermal 1# Cycles

Binder Content Stress to ('1G by dry weigbt Specimen D/. Air Voids Level Failure

MiIture ID --'~ =:&k ~ GO 5.0 2B 7.5

GO 5.0 3A I. u

i a U GO 5.0 2A ~ 2.41JI;EL GO 5.0 6A 5.5 2~ j 8.4: GO 5.0 6B 6.9 ~ -w.= u ~ --w.-

~ ~

~ =; -fo¥J 7.0 IB 7.3 7.0 3A 6.5 ~

u u

ti I- M

~ il5 7. g I- il5 7. 6.5 .~

=! u SJ a 91 0 15 7.0 IA 6.0 ~(A") ~ ....ill 0 15 7.0 2A 7.1 9.75

" ~ ~~ a M ji-tlt ~ 7.0 IB 5.7 1.72 (Ext) 7.0 2B 7.2 HExt)

=i~ u ~ a l.l L",I

21 The effects of each mixture and envirorunental variable on mixture resistance to thermal

fatigue were explored further in a statistical analysis of the test results. With the assumption that

the natural logarithm of the number ofthennal cycles to failure is normally distributed, F-Iests

and I-tests were conducted for each pair of mixtures (Table 7). F-tests were conducted to test the

null hypothesis that the variances of the two sets of data arc equal. Wilh the additional

assumption of equal variances (the null hypothesis of the F-Iests cannot be rejected for all pairs

of mixtures), I·tests were conducted between each pair of mixtures 10 lest the null hypothesis that

the means of lIle two sets of data are equal. A \0 percent significance level (a = 0. 10) was used

for each test. A summary of the results of all statistical tests is given in Table 7.

Table 7 Thermal Fatigue Test Statistical Analysis Results (Reject or Cannot Reject Null Hypothesis)

fa :z: 0.10, Null Hypotheses: UI;;U2 ror I-tes t, 0'1:;(J2 ror F-testl Mblure I Milture 2 Lo(NJ

(fhermal Stress Level) (Thermal Stress Level) I-Iesl F-test

GO (Average) GO (Extreme) Cannot Cannot Reiect Reiect

GIS (Average) GIS (Extreme) Reject Cannot Re"ect

DIS (Average) DIS (Extreme) Cannot Cannot Reiect Reiect

GO (Average) GIS (Extreme) Reject Cannot Reiect

GO (Average) GIS (Average) Reject Cannot Reiect

GO (Extreme) GIS (Extreme) Cannot Cannot Reiect Relect

GI5 (Average) 0 15 (Average) Reject Cannot Reiect

GIS (Extreme) DIS (Extreme) Cannot Cannot Relect Reiect

The statistical analysis indicates that CRM has a significant (a:().lO) effect on mixture

resistance to thermal fatigue at the average thermal stress level. At equivalent numerical stress

levels (average for GO and extreme for GIS), the effect of CRM modification was also

significant. lmproved performance due to modification was not validated at the extreme thermal

22 stress level, although this effect of modification is unclear because unmodified mixtures did not

perfonn statistically different when tested at the two different stress levels. Modified mixtures

with the dense-graded aggregate also did not ~rfonn significantly different when tested at the

two stress levels, and no effect of aggregate gradation was found althe extreme stress level. The

effect of aggregate gradation allhe average stress level was significant, and modified mixtures

with the gap-graded aggregate showed statistically different performance when tested al the two

stress levels.

Results from this limited laboratory experiment indicated that the approach presented can

be used to measure the finite capacity of both modified and UMlOdified mixtures for thermal

fluctuations coupled with low temperatures. According to these results, CRM modification

improved mixture resistance to thenna! fatigue under average environmental conditions in the

intennountain west of the United States. Data measured under testing conditions selected from a

logical and rational process illustrated that the phenomenon ofthennal fatigue may contribute 10

transverse cracking in pavements, especially in harsh climates.

Specimens used in this experiment were not long-term aged, and modification was shown

to improve performance under average envirorunental conditions in a harsh climate. Modified

mixtures are predicted to resist aging better than their unmodified counterparts (6, 7). Evidence

of improved aging characteristics is illustrated with dynamic shear test results shown in Tables 3

and 5. A comparison oftest results for unaged binders at 64C and long-term aged binders at 13C

showed the increase in shear modulus caused by aging for unmodified binders was much greater

than the increase for modified binders. Fatigue results for long-term aged specimens are

therefore expected to emphasize improvements in performance for modified mixtures to a greater

extent than the results presented in this section. Based on a rough comparison of environmental

demand in the intermountain west of the United States and mixture resistance as measured in this

experiment, both unmodified and modified mixtures provide satisfactory resistance to thennal

fatigue at high levels of reliability (950/.) in the first few years of service and thermal fatigue

fai lure is not expected at early ages (5). ~ a result, it is recommended in this approach that

23 specimens are long-term oven aged (LTOA) in addition to short-term oven aged (STOA) prior \0

testing to simulate field conditions under which thennal fatigue: is likely to occur.

CooclusioDS and RecommendalioDS

AIl approach to measure mixture resistance 10 thermal fatigue was described and

demonstrated through the selection cflesting conditions and the results of a limited laboratory

experiment. A slow frequency beam fatigue test was introduced in this approach, and this test

was used to evaluate unmodified and CRM modified mixture resistance to thennal cycling.

Analysis of the results from this limited laboratory c:xperimenlled to the following conclusions

and recommendations:

1. A slow frequency beam fatigue test Can be used in a controlled strain mode to

measure mixture resistance to thermal fatigue if the strain levels are carefully selected

\0 simulate large temperature fluctuations coupled with low temperatures in a harsh

climate. Based on the results of a limited laboratory experiment using the approach

presented, asphalt-aggregate mixtures have a finite capacity for repeated large thermal

Ouctuations at relatively low temperarures. These results indicate that the

phenomenon of thermal fatigue may connibute to transverse cracking in pavements.

2. Knowledge was gained in terms of the differences in thermal behavior between

unmodified and CRM modified asphalt-aggregate mixtures. Limited experimental

results reported herein lend validation to the hypothesis that for some base asphalt

cements the addition ofCRM may result in improved mixture performance as

compared to their unmodified counterparts when subjected to thermal cycling under

average envirorunental conditions in a harsh climate. Envirorunental benefits may

also be realized by reusing scrap tires and reducing the solid waste stream.

24 3. Based on the: mix design process, modified mixtures contained 7 percent binder (by

dry weight of aggregate) and unmodified mixtures contained 5 percent binder.

Increased binder oontents in modified mixtures may have contributed 10 improved

performance in terms of resistance 10 thermal fatigue as measllred in the laboratory

under average cnvirorunenlal conditions in a hmh climate. Improved durability and

resistance \0 aging is also expected for the modified mixtures in fi eld applications.

4. Further development of the approach used in the limited laboratory experiment

described is suggested. An evaluation of the use of a controlled stress fatigue test is

recommended. A controlled stress test may more accurately simulate field

conditions, as thermal stress fluctuates in the pavement as temperature cbanges, nol

thermal strain. Deformation is restrained in the field resulting in induced thermal

stress. In addition., long-term oven aging (LTOA) is recommended in addition to

short-term oven aging (STOA) for specimens prior to testing, as thermal fatigue is not

expected to occur in the lint few years of pavement service.

5. An expanded laboratory testing program is reconunended to further explore the

efTects of aggregate gradation and CRM modification on mixture resistance to

thermal fatigue. The effect of aggregate gradation on mixture resistance to this type

of distress was not completely examined in the limited experiment described due to

budget and time constraints and the assumption that the effect of the binder will

dominate mixture response. As result, testing of urunodified dense-graded mixtures is

recommended. As the binder propcnies are expected to control resistance to thennal

distress, mixtures with difTerent base asphalt cements should be included in the

recommended expanded testing program. Different base asphalt cements may also

have different propenies when combined with CRM due to the compatibility of the

two materials.

RefcrtD(ts

(\) HiltWlcn, D., and R. Roque, "A Mechanics-Based Prediction Model for Thennal

Cracking of Asphaltic Concrete Pavements", Journal of the Association of Asphalt

Paving Techn%gisls, Vol. 63, pp. 81-1 13 (199~).

25

(2) Vinson. T., V . 1anoo, and R. Haas, Summary Report on Low Temperature and Thermal

Falfgue Cracking, SHRP·A/IR·9()..OOI, 1989, Washington, O. C.: Strategic Highway

Research Program, National Research Council.

(3) Shahin, M., and B. F. McCullough, "Damage Model for Predicting Temperature

Cracking in Flexible Pavements", Transportation Research Record 521, pp. 30-46

(1974).

(4) Lytton. R., and U. Shanmugham, "Analysis and Design ofPavemenls to Resist Thomal

Cracking Using Fracture Mechanics", Proceedings of the 51h International Conferenu

on the Struc/ural Design of Asphalt Pavements, Vol. I, pp. 818·839 (1982).

(5) Epps, A., Thennal Behavior of Crumb· Rubber Modified Asphalt Concrete Mixtures,

UCB·ITS·DS·97·2, 1997, Universi ty of California, Berkeley: Institute ofTransportation

Srudies DiSSeI1ation Series.

(6) Heitzman, M., State of the Practice · Design and C01l5truction of Asphalt Paving

Materials with Crumb Rubber Modifier, 1992, Washington, D.C.: Federal Highway

Administration.

(7) Flynn, L, "Jury Remains QuI on Asphall-Rubbcr Usc", Roads &: Bridgu, December,

1992, pp. 42·50.

(8) Monismith. C., Chairman, "Non-Traffi c Load Associated Cracking of Asphalt

Pavements, Symposium", Proceedings of the Association of Asphalt P(H'ing

Technologists Technical SeJSiOIU , Vol. 35, pp. 239-357 (1966).

26

(9) Janoo, V., 1. Bayer, Jr., and M. Walsh, 'Thermal Slress Measuremenls in Asphalt

Concrele, CRREL Report 93-\0, 1993, Hanover, New Hampshire: U.S. Army Corps of

Engineers, Cold Regions Research aJ'ld Engineering Laboratory.

(10) Carpenter, S., R. Lytton, and 1. Epps, Environmentol Faclors Relevant /0 Povemenl

Cracking in West Texas, Research Report 18·1, 1974, College Station. Texas: Texas

Transportation Institute.

(11) Carpenter, S., and R. Lytton, Thermol Activity 0/ Base Course Maleriol Relaltd /0

Pavement Crocking, Research Report 18·2, 1975, College Slation, Texas: Texas

Transportation Institute.

(12) Chang, H., R. Lytton, and S. Carpenter, Prediction of Thermal Rejlection Cracking in

West Texas, Research Report 18·3, 1976, Ccllege Station, Texas: Texas Transportation

Institute.

(13) Carpenter, S., and R. Lytton, 11rermal Pavement Cracking in West Texas, Research

Report 18·4, 1977. College Station, Texas: Texas Transportation Institute.

(14) Anderson, K., and J. Epps, "Asphalt Concrete Factors Related to Pavement Cracking in

West Texas", Proceedings of the Association of Asphalt Paving Techl1%gists Technical

Sessions, Vol. 52, pp. 151 ·1 97 (1983).

(15) Finn. F., C. Saraf, R. Kulkarni, K. Nai r, W. Smith, and A. Abdullah, '1'he UseofDi strcss

Prediction Subsystems for the Design of Pavement Structures", Proceedings of the ~Ih

27 Internalional Conference on the Structural Design of Asphalt Pavements, Vol. I, pp. 3-38

(1977).

(16) Sugawara, T., and A. Moriyoshi, "Thennal Fracture of Bituminous Mixtures",

Proceedings of Paving in Cold Arw Mini-Workshop, 1984, pp. 291·320.

(17) Lynon, R., U. Shanmugham, and B. Garrett, Design of Asphalt Pavemenu for Thermal

Fatigue Cracking, Research Report 284·4, 1983. College Station, Texas: Texas

Transportation Institute.

(! 8) Shahin, M .• and 8. F. McCullough, Prediction of Low-Temperature and Thermol·Faliguc

Cracking in Flexible Pavements , Research Report 123·14, 1972, Austin, Texas: Center

for Highway Research.

(19) Paris, P., and F. Erdogan, "A Critical Analysis of Crack Propagation Laws", Transactions

of Ihe American Auociarion of Mechanical Engineers Journal of B{Jlic Engineering

Series D 85, No. 4 (December), pp. 528-534 (1963).

(20) Benson, P., to ..... Temperature Transvers~ Cracking of Asphalt U)f!CTete Pavements in

Central and West Tuas, Research Report 17S-2F, 1976, College Station, Texas: Texas

Transportation Institute.

(21) Majidzadeh, K., C. Buranrom, and M. Karakomzian, Applications of FraClure Mechanics

for Improved Design of Bitl/minom Concrete, FHWA Report No. 76-91, 1976,

Washington, D. C.: Federal Highway Administration.

(22) Abdulshafi, A., and K. Majidzadeh, "J·integral and Cyclic Plasticity Approach to Fatigue

and Fracture of Asphaltic Mixtures", rransp0r/alion Research Record 1034, pp. 112-123

(198l).

(23) Unle, D., and K. Mahboub, "Engineering Properties ofFirsl Generation Plasticized

Sulfur Binders and Low Temperature Fracture Evaluation of Plasticized Sulfur Paving

Mixtures", Transportation Research Record 1034, pp. 103-111 (1985).

28

(24) Abdulshafi, A" and K. Kaloush, Modifiers for Asphalt Concrele, ESL-TR·88·29, 1988,

Air Forte Engineering and Services Cenler.

(25) Jackson, N. M., and T. Vinson, "Analysis orlnennal Fatigue Distress of Asphalt

Concrete Pavements", Tromporla/ion Research Record 1545. pp. 43-49 (\996),

(26) Asphalt Institute, Design Techniques /0 Minimize Low-Temperature Asphalt Povemenl

Transverse Cracking, RR-8 1-1 , 1981 , Lexington, Kentucky: Asphalt Institute.

(27) Haas, R.t F. Meyer, G. Assaf, and H. Lee. "A Comprehensive Study of Cold Climate

Airport Pavement Cracking", Proceedings of 'he Association of Asphalt Paving

TechnologU/l Technical Sessums, Vol. 56, pp. 198-245 (1987).

(28) Fromm, H., and W. Phang, "A Study ofTransverse Cracking of Bituminous Pavements",

Proceedings of the Association of Asphalt Paving Technologists Technical Sessions, Vol.

41 , pp. J8J-42J (1972).

(29) Hiltunen, D., and R. Roque, ''The Use ofTime-Temperature Superposition to

FiIDdamentally Characterize Asphaltic Concrete Mixtures at Low Temperatures",

Engineering Properties of Asphalt Mixtures and the Refarionship to Performance, ASTM

STP 265, 1994, Philadelphia: American Society for Testing and Materials.

(30) Buttlar, W., and R Roque, "Development and Evaluation ofthe Strategic Highway

Research Program Measurement and Analysis System for Indirect Tensile Testing at Low

Temperatures", Transportation Research Record 1454, pp. \63-171 (1994).

(3\) American Association of State Highway and Transportation Officials (AASHTO),

AASHTO Provisional Slandards, June Edition, 1998, Washington, D. C.: American

Association of State Highway and Transportation Officials.

(32) University ofCalifomia. Berkeley, Pavement Research Center, "Procedure for Fatigue

Beam Test" (Unpublished).

(33) Suiface Airways [CD-ROM], 1993, Boulder, Colorado: Earthlnfo, Inc.

(34) Dempsey, B., W. Herlache, and A. Patel, A Climatic-Mareriaf-SlIuclllra/ Pavement

Analysis Program (CMS4), June 5, 1986, University of Illinois at Urbana-Champaign,

29

(35) Deacon, 1. "Validation, Cal ibration, and Documentation of eMS Model", Memo to Carl

Monismith. September 24, 1995.

(36) American Society for Testing and Materials (ASTM), 1997 Annual Book of ASTM

Standards, yot. 04.03: Road and PaYing Materials; Pavement Managemem

Technologies, 1997, Philadelphia: American Society for Testing and Materials.

(37) Van der Poel, C., "A General System Describing the Visco-Elastic Properties of Bitumen

and Its Relation \0 Routine Test Data", Journal of Applied Chemistry, Vol. 4, pp. 221 -

236(1954).

(38) Heukelom, W., "Observations on the Rheology and Fracture of Bitumens and Asphalt

Mixes", Proceedings of the Association of Asphalt Paving Technologists Technical

SlmiollS, Vol. 35, pp. 358-399 (1966).

(39) FiM, F., C. Saraf, and W. Smith, Developmenr of Pavement Structural Subsystenu,

NCHRP Report 291 , 1986, Washington, D. C.: l'!ational Cooperative Highway Research

Program.

(40) American Society for Testing and Materials (ASTM), 1997 Annual Book of ASTU

Standards , Yolo 04.04: Roofing, Waler·Proofing. and Bituminous Materials, 1997,

Philadelphia: American Society (or Testing and Materials.

(41) The Asphalt Institute, Performance Graded Asphalt Binder Specificotion and Tesling.

Superpave Series No. I (SP·I), Lexington, Kentucky: The Asphalt Institute.

(42) MRL Data Sheet for MRL Asphalts, SHRP Materials Reference Library.

(43) eRM Data Sheet, Stock GF-80, Rouse Rubber Industries, Inc., Vicksburg, Mississippi.

(44) Asphalt Mixing Protocol, Western Research Institute, September 5,1995.

(45) Mixing Procedure for SBS Modified Asphalt (or Paving Applications, EniChem

Elastomers Americas, Inc., 1995.

(46) Tauer, J.t Western Research Institute, Conversation with the author, Apri12J, 1996.

30

(47) Tauer, I., Western Research institute, Conversation with the author, November 15, 1995.

(48) Hicks, R. G., 1. Lundy, R. Leahy, D. Hanson, and 1. Epps, Crumb Rubber Modifim

(eRM) in Asphalt PavemenlJ: Summary oJ Practices in Arizona, Ollifomia, and Florida ,

FHWA-SA-95-0S6, 1995, Washington, D.C.: Federal Highway Administration.

(49) Harvey, 1., I. Deacon, B. Tui, and C. L. Monismith, "Fatigue Performance of Asphalt

Concrete Mixes and Its Relationship to Asphalt Concrete Pavement Performance in

California", 1995, Prepared for California Department ofTransportation by the Asphalt

Research Program, CAUm Program, Insti tute ofTransportation Studies, University of

C.lifornia at Berkeley.

~

0 ~ - " " .-,~

o u E ~ <u

r3 " "-~ u -, .'8

~ i5~

u I ., u '8 c: '" u "_ ~ E 8. u

" ~ i'l '8 , a:1X:::t ~

5

--.t "§ 'V L-ij'l

'-' E::;: " o ~ " u ';: .2 "~ "'"'

-" ~ - u ~ - ~ .-~ " " , ~ Co "gv_ -~ -

• :; '0 • • " t u

Specimen ClfJllp R~.cl ion Ddleclion

MUM cmmI

wl l VDT

Rtto:lioa

Figure 2 Schematic of Thermal Fatigue Test (32)

General Pavement StJucture Properties

DRAWING NOT TO SCALE

0.20m Asphalt COllCrete

061m Granular Base

284 m Subgndt

Mll imum Allowable Coav«lion Coefficient Emissi¥ily Factor Absorptivity FilC\Of

Temperature SlrUI;ture Begins Pretzing Temperature Sb'UCture is Partially Frozen

Thermal Conductivity (unfrozen. hOlen)

Heat Capacity (unfroun, hOlen) Unit Weight Moisture PoilSOll's Ratio COCfflCicol of Thermal Ex~nsion

Dry Density Thermal Conductivity (unfrozen)

(frozen) Heat CapKilY (unfrOlen)

(frozen) Moisture I. Frozen

Dry Den~ity Thenna! Conductivity (unfrozen)

(frozen) He.! Capacity (unfrozen)

(frozen) Moisture

" frozen

Constant Deep Ground Temperature

6"10" Ilhr'ml'K 0.85 0.90 ·2e .4C

5000 Jlbr ' m' K 920 Jr..g ' K 2420 kglm) 21. by wt solids 0.35 0.1XXXI21 per C

2160 kgfm) 4700 1/hr'm' K 6850 Jlhr ' m' K 1700 llkg' K 1300Jr..g'K 10% by wt solids 80.0

1920 kglm) 4000 J/hr ' m' K 7190 J/hr ' m' K 2lOO JIk, ' K lSOOJlkS ' K 251. by .... \ solids 90.0

---------------.. _-- ----------.-. __ .. _------------------------------------------------------

Figure 3 Pavement Structure and Properties

iii a 10 • - 0 ~ e -10 > • ~ .. -20 cz:: ~ -30 o E -40 • • "< !- -50

a ~ .. -- -~~ '; cz:: '::0

.11 .. • ~ 7 - 5 - 3 ~ • \ • -\ • u; -3

12119190 12121 /90 12123/90 12125190 12127190 12129/90 1213 1/90

Doy

112/91

1- ~ M ixture Tensile Strength ( 10, S) • Induced Tens ile Stress (1~

Figure 4 C OLD Output for Mixture G O L oog-Term Aged Binder

+-- AirTemp

Pavement Temp

Outputs of COL D program shown with conditions used to estlmatc inputs (A, B) given in legend

A- time o f loading (sec) for esti mating m ilc.ture sti ffness vs. temperature relatlOnsh.p

H- time ofloadin.: (sec) l .... r eSlimatm.: m.x tu re tenSile s tren.:!!'! V I>. lempc~ture

rela tIOnshIp

"fa .­!" ::: ;; = ~ . 0: • o ~ " . -- . < ....

o:~ 0-~

~ ~ · "~ = - .. tnVlIol-

10 o

- 10 - 20 -30 -40 - --

" t~_~--~ __ . -----7 5 · .-==6

" " • • 3 1

~~ -I -3

lZf19/90 1Zf21 /90 12/23/90 12/25/90 12/27/90 12/29/90 12/31190 112/91

Da

- ~- MiJtture Tensile Strength (10, 5) _lnduced Tensile Stress (10, 5)

Figul'"e 5 COLD Output rol'" Mb:tul'"e G15 Long-Tel'"m Aged Biudel'"

-+-- Air Temp

Pavemenl Temp

Outp uts of COLD program shown with conditions used to estimate inpuu (A, B) g iven in legend

A-time of loading (sec) ror estimating mixture stiffness vs. temperature relationship

B-time of loading (sec) for estimating m ixture tensile strength v • . temperature relationship

o N

--.",

g

k,..

"-.. , " ,

,

\

o N

0

0

o 0 0

-E E -

,~ '" • • ,. '"

~I 0: 0 '

'; • '! ,;

0 1 :!. • ,

~ , ,2 u .. 0 , ~ • • • ()

• ;; ~ • • ~ ~

<

- ~

0 ~ -c , ,9 • I] ~

0 ~ • 0 '

t