Construction and Building Materials 27 (2012) 45–53

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Construction and Building Materials

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Field and laboratory performance comparison for asphalt mixtureswith different moisture conditioning systems

Erol Iskender a,⇑, Atakan Aksoy b

a Karadeniz Technical University, Of Faculty of Technology, Civil Engineering Department, 61830 Trabzon, Turkeyb Avrasya University, Civil Engineering Department, 61010 Trabzon, Turkey

a r t i c l e i n f o a b s t r a c t

Article history:Received 28 April 2011Received in revised form 4 August 2011Accepted 7 August 2011Available online 28 September 2011

Keywords:Conditioning systemsField performanceMoisture damageAsphalt concreteMarshall methodIndirect tensile testIndirect tensile strength testRepeated creep test

0950-0618/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.08.019

⇑ Corresponding author.E-mail address: eroliskender@gmail.com (E. Iskend

The purpose of this study is to compare laboratory and field performances for dense graded asphalt mix-tures. Control road pavement section was constructed in Black Sea Coast Highway. Marshall identicalcontrol samples produced in laboratory and core samples taken from wearing courses before the trafficopened were used. Three different moisture conditioning methods were applied to control laboratory andcore samples. Mechanical properties of samples were evaluated with indirect tension, indirect tensionstrength and repeated creep tests. Indirect tensile strength test results for laboratory mixtures werefound 1.22 and 1.30 times more in accordance with field samples at 10 �C and 20 �C respectively. Mar-shall samples gave higher resilient modulus for all control and conditioned mixtures. Repeated creep testresults also proved the difference between laboratory and field sample performance. Laboratory samplesprotected their structural integrity along with the test duration and did not showed tertiary creep. It isconcluded from this study that laboratory samples state expressly higher performance according tothe core field samples.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The difference between laboratory mix design methods is notonly the result of the evaluation procedure but is also the conse-quence of the compaction technique used. The goal of a mix de-sign procedure is to combine aggregates and a binder in aproportion that is able to satisfy a desired level of performance.Realistic procedures for evaluating the strength of bituminousmixtures are therefore quite important. There are several factorsthat affect the strength of bituminous mixtures; one of them isthe method of forming a realistic test specimen in the laboratorythat represents the structure of the paving mixture when it isplaced in the field. Duplicating the composition of a field mix-ture in the laboratory presents some problems, but they areminor compared to producing in the laboratory a specimen ofthe mixture that truly represents the mixture as it exists inthe field [1].

Ideally, the mixtures to be tested should be prepared and com-pacted to as close to the field condition as possible, so that they canbe representative of the mixtures to be produced and put in ser-vice. The properties of the mixtures to be determined should begood indicators of performance of the mixtures in service, so that

ll rights reserved.

er).

these properties can be used to determine the acceptability ofthe mixtures and to select the optimum mix design to be used [2].

Environmental factors such as temperature, air, and water canhave a profound effect on the durability of asphalt concrete mix-tures. In mild climatic conditions where good-quality aggregatesand asphalt cement are available, the major contribution to thedeterioration may be traffic loading, and the resultant distressmanifests as fatigue cracking, rutting (permanent deformation),and raveling. However, when a severe climate is in question, thesestresses increase with poor materials, under inadequate control,with traffic as well as with water which are key elements in thedegradation of asphalt concrete pavements. Water causes loss ofadhesion at the bitumen–aggregate interface. This premature fail-ure of adhesion is commonly referred to as stripping in asphaltconcrete pavements. The strength is impaired since the mixtureceases to act as a coherent structural unit. Loss of adhesion renderscohesive resistance of the interstitial bitumen body useless. Watermay enter the interface through diffusion across bitumen films andaccess directly in partially coated aggregate. Water can cause strip-ping in five different mechanisms such as detachment, displace-ment, spontaneous emulsification, pore pressure, and hydraulicscour [3].

Asphalt pavement failure is a complicated phenomenon. It is aresult of cumulative damage in different pavement layers. Theinfluence of moisture on hot-mix asphalt (HMA) stripping is diffi-cult to characterize due to the presence of many factors affecting

Table 2Aggregate specific gravities (g/cm3).

Grain-size fraction Apparent specific gravity Bulk specific gravity

Coarse aggregate 2.894 2.832Fine aggregate 2.889 2.751Filler aggregate 2.910 –Aggregate mixture 2.893 2.803

Table 3The results of tests performed on asphalt cement (AC 50-70).

Properties Test method Unit Value

Specific gravity (25 �C) ASTM D-70 g/cm3 1.019Softening point (�C) ASTM D36-76 �C 52Flash point (Cleveland) ASTM D-92 �C 210Penetration (25 �C) ASTM D-5 0.1 mm 67Ductility (25 �C) ASTM D-113 cm 100+

0

10

20

30

40

50

60

70

80

90

100

0,01 0,10 1,00 10,00 100,00

Sieve Size, mm

Perc

enta

ge P

assi

ng, %

Fig. 1. Aggregate distribution on gradation chart.

Table 4Summary of Marshall design results.

Design parameters Values Board in Turkey

46 E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53

this damage. One of the major problems affecting the performanceof hot-mix asphalt is stripping. Many studies indicated that asphaltbinder chemistry, aggregate mineralogy, aggregate surface texture,and the interaction between asphalt and aggregate significantlyaffect moisture susceptibility. The large numbers of differentaggregate mineralogy and the different types of asphalt bindersused across the world, coupled with varied environmental condi-tions, traffic, and construction practices, have made testing to pre-dict accurately hot-mix asphalt moisture susceptibility a difficulttask [4].

So far, a number of test procedures have been developed toevaluate the moisture destruction potential of HMA. However,with pavement performance prediction, these tests do not confirmthe effects of moisture on material properties, hence, they need tobe developed to estimate the behavior of the mixtures in resistingrutting, fatigue, and thermal cracking when subjected to moistureunder different traffic levels. Resistance of compacted bituminousmixtures to moisture induced destruction or AASHTO T283 is thestandard method used to predict the effect of moisture destructionin HMA. AASHTO T283 has also been recommended by StrategicHighway Research Program (SHRP) to evaluate the water sensitiv-ity of HMA within the Superpave volumetric mixtures designsystem [5]. Indirect tensile strength ratios of asphalt paving spec-imens were found to be less than the Marshall stability ratios incontext with the stripping interrogation [6].

Numerous test procedures have been developed to evaluateHMA stripping interrogation in the laboratory. The most com-monly used procedures include the boiling test, tensile strengthratio (TSR), static immersion, Lottman, modified Lottman, andRoot–Tunnicliff tests. However, several disadvantages are associ-ated with the current test methods, and the effectiveness of theseprocedures has been questioned [7].

The purpose of this study is to compare performance of labora-tory and field asphalt mixtures and to evaluate stripping problemin context with the ratios. With this purpose a trial section of wear-ing course in Black Sea Coastal Region was constructed. Rollercompaction was made and many identical core samples were ob-tained. Also identical samples were produced in laboratory withMarshall method (ASTM D1559). With the different moisture con-ditioning systems performance comparisons were done.

Min. Max.

Bulk specific gravity, Gmb 2.510 – –Marshall stability (kg) 1530 900 –Air voids, Pa (%) 4 3 5Void filled with asphalt, Vf (%) 72 75 85Flow, F, 1/100 in. 3.2 2 4Filler/bitumen 1.17 – 1.5Asphalt cement, Wa 5.15

2. Materials

Used test materials and experimental procedures in this study were following.Aggregate combination and asphalt cement were used. Aggregate combination wasobtained from the Sularbasi rock quarry. Various engineering properties of coarse–fine aggregate were given in Tables 1 and 2. 50–70 penetration grade asphaltcement was used. Test results for bituminous binder are presented in Table 3.Gradation curve are represented in Fig. 1.

Three types of moisture conditioning systems were applied. Damage mecha-nisms were applied to half of the samples. Two different moisture conditioning sys-tems were selected. At the last conditioning first and second damage models werecome together and third conditioning model was developed. In the first condition-ing conditioned samples were kept in 60 �C water for 72 h. In the second systemsamples were located in �15 �C freezer for 72 h with water bath and after sampleswere kept in water at room temperature. Plastic bags were used. These processes

Table 1Engineering properties of the used aggregate.

Properties Test method Value

L.A. Abrasion (%) ASTM C-131 9.6Flakiness (%) BS 812 (part 105) 14.7Stripping resistance (%) ASTM D-1664 30–35Water absorption (%) ASTM C-127 0.85Soundness in NaSO4 (%) ASTM C-88 4.06Polished stone value BS 812 (part 114) 0.60Plasticity index for sandy aggregate TS 1900 Non-plastic

were also repeated as three steps. Control and conditioned asphalt briquettes forboth laboratory and field samples were used. Performance comparison was realizedwith test results that belong to laboratory and field samples.

Design parameters obtained with the ASTM D1559 Marshall method. Optimalmixture parameters were presented in Table 4 according to the test.

Properties of the used samples in experimental stages were illustrated inTables 5 and 6. Table 5 shows laboratory samples while Table 6 gives field cores.

3. Test methods

3.1. Repeated creep test

Repeated creep tests (RCT) were applied to laboratory and fieldcompacted identical samples. RCT test parameters were given inTable 7. Repeated creep test is an indicator of the permanent defor-mation properties of asphalt pavement materials with a few thou-sand of load pulses on laboratory or field samples. Permanent

Table 5Properties of the laboratory produced samples.

Sample number Average height (mm) Practical density (g/cm3) Max. T. density (g/cm3) Air voids (%) VMA (%) VFA (%)

1 60.7 2.522 2.618 3.7 14.4 74.72 59.6 2.532 2.618 3.3 14.1 76.73 60.3 2.516 2.618 3.9 14.6 73.54 59.7 2.520 2.618 3.7 14.5 74.35 60.1 2.514 2.618 4.0 14.7 72.96 60.5 2.509 2.618 4.2 14.9 72.07 60.2 2.532 2.618 3.3 14.1 76.78 60.5 2.518 2.618 3.8 14.6 73.99 60.0 2.522 2.618 3.7 14.4 74.6

10 60.7 2.527 2.618 3.5 14.3 75.611 59.7 2.525 2.618 3.6 14.3 75.212 60.6 2.519 2.618 3.8 14.5 74.013 60.8 2.526 2.618 3.5 14.3 75.514 60.7 2.524 2.618 3.6 14.4 75.015 60.7 2.525 2.618 3.6 14.3 75.216 60.3 2.519 2.618 3.8 14.5 74.117 60.3 2.512 2.618 4.0 14.8 72.718 60.2 2.522 2.618 3.7 14.4 74.619 59.7 2.519 2.618 3.8 14.5 74.020 60.9 2.525 2.618 3.6 14.3 75.221 60.1 2.517 2.618 3.9 14.6 73.622 60.1 2.507 2.618 4.2 14.9 71.623 60.5 2.520 2.618 3.7 14.5 74.224 59.8 2.516 2.618 3.9 14.7 73.325 60.0 2.528 2.618 3.4 14.2 75.926 60.6 2.523 2.618 3.6 14.4 74.827 60.1 2.526 2.618 3.5 14.3 75.528 60.3 2.530 2.618 3.4 14.2 76.329 60.3 2.528 2.618 3.4 14.2 76.030 59.3 2.525 2.618 3.5 14.3 75.331 60.3 2.530 2.618 3.4 14.2 76.232 59.3 2.529 2.618 3.4 14.2 76.133 59.9 2.523 2.618 3.6 14.4 74.934 59.9 2.523 2.618 3.6 14.4 74.935 60.1 2.519 2.618 3.8 14.6 73.936 60.7 2.518 2.618 3.8 14.6 73.837 61.8 2.533 2.618 3.2 14.1 76.938 60.8 2.528 2.618 3.4 14.2 75.939 60.6 2.530 2.618 3.4 14.2 76.340 61.1 2.517 2.618 3.9 14.6 73.6

E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53 47

deformations are saved during test pulses [9,10]. Tertiary deforma-tion phase can be obtained with the RCT [9]. RCT tests were studiedin NAT tester as it shown in Fig. 2.

Creep deformations at 40 �C test temperature for laboratoryproduced and field core samples were given in Table 8. RCT wasapplied on both unconditioned and three different moisture condi-tioning systems. Deformations were presented for only somepulses. (see Figs. 3 and 4).

Laboratory Marshall samples do not give tertiary deformationregion for any samples. Unlike this all field core samples showstertiary deformation process. Before the RCT tests end all field sam-ples lost their structural integrity and destructed. Average perma-nent deformations for different mixtures were illustrated in Fig. 5.

Field core samples gave much higher creep deformations thanthe laboratory samples. Unconditioned lab and field samplesshows similar deformation planes but with the water conditioningdifference between lab and field deformations is large. It was con-cluded that moisture effects were found as an effectual factor forrutting phenomenon. Moisture conditioning for lab samples donot changed dramatically RCT deformations. In addition to thisintervals between conditioned field samples were found largerand obtained much higher deformations. As far as conditioningtype creep deformations for field samples were concerned creepdeformations could have been nine times higher than the labora-tory samples.

It is known from the literature that for the purpose of designingasphalt pavement mixtures results obtained from laboratory and

field can reveal substantial differences. In context with themechanical properties higher performance levels can be found inlaboratory design with Marshall method than the real field condi-tion as a result of compaction and angularity effects. During servicelife of pavement especially in first service condition higher voidcontent can contribute moisture damage problem and also plasticdeformation [11–14].

It was shown that LCPC compactor shows good correlation withthe real field roller. Field roller compacted samples showed higherpermanent deformation than the LCPC compactor. It is thoughtthat higher void contents can be concerned in highway pavements.Laboratory prepared samples for both compacted cylindricallysamples (Marshall compaction) and slabs (wheel tracking compac-tors) gives higher rut resistance because of the compaction simula-tion differences [15].

The Marshall mixture design method is simple and inexpensiveto use. Due to its widespread use throughout the world, a lot ofexperience has been gained in the use of this method. Results ofthe Marshall stability test are somewhat related the performanceof the asphalt mixture. The Marshall stability is related to the ten-sile strength, while a high Marshall flow is related to low resistanceto rutting of the asphalt mixture. The disadvantage of the Marshallmixture design method is that the aggregate orientation in thecompacted Marshall specimens is not representative of that inthe field-compacted mixtures. The aggregates in the Marshallcompacted specimens tend to get crushed at high compaction lev-els [2].

Table 6Properties of core samples obtained from field.

Sample number Average height (mm) Practical density (g/cm3) Max. T. density (g/cm3) Air voids (%) VMA (%) VFA (%)

1 66.7 2.478 2.618 5.35 15.9 66.42 62.4 2.474 2.618 5.51 16.1 65.73 62.7 2.486 2.618 5.03 15.6 67.94 60.5 2.486 2.618 5.03 15.6 67.85 51.3 2.472 2.618 5.58 16.1 65.46 52.3 2.471 2.618 5.62 16.2 65.27 65.9 2.488 2.618 4.95 15.6 68.28 52.0 2.479 2.618 5.31 15.9 66.69 54.9 2.477 2.618 5.38 16.0 66.3

10 57.4 2.482 2.618 5.20 15.8 67.111 48.5 2.480 2.618 5.26 15.9 66.812 61.4 2.470 2.618 5.63 16.2 65.213 53.0 2.488 2.618 4.95 15.6 68.214 56.3 2.479 2.618 5.32 15.9 66.615 57.9 2.471 2.618 5.63 16.2 65.216 62.9 2.477 2.618 5.36 15.9 66.317 49.7 2.488 2.618 4.97 15.6 68.118 52.5 2.471 2.618 5.59 16.2 65.419 60.0 2.488 2.618 4.98 15.6 68.120 55.1 2.482 2.618 5.18 15.8 67.221 61.7 2.473 2.618 5.51 16.1 65.722 62.0 2.487 2.618 5.01 15.6 67.923 56.1 2.488 2.618 4.97 15.6 68.124 67.9 2.478 2.618 5.34 15.9 66.525 52.6 2.470 2.618 5.66 16.2 65.126 54.0 2.471 2.618 5.59 16.2 65.427 60.3 2.489 2.618 4.94 15.6 68.328 56.3 2.474 2.618 5.48 16.0 65.929 50.5 2.482 2.618 5.20 15.8 67.130 55.4 2.486 2.618 5.05 15.7 67.831 54.5 2.481 2.618 5.21 15.8 67.032 44.1 2.488 2.618 4.97 15.6 68.133 53.1 2.480 2.618 5.27 15.9 66.834 66.1 2.479 2.618 5.32 15.9 66.535 56.1 2.479 2.618 5.29 15.9 66.736 56.9 2.483 2.618 5.14 15.7 67.437 61.6 2.485 2.618 5.06 15.7 67.738 55.4 2.487 2.618 5.01 15.6 68.039 60.5 2.484 2.618 5.10 15.7 67.540 66.8 2.485 2.618 5.07 15.7 67.7

Table 7Repeated creep test parameters.

Test parameters Values

Temperature 40 �CConditioning stress 10 kPaConditioning stress time 1 minConditioning stress rest time 1 minTest stress 100 kPaLoading period 1000 msTime loaded 500 msTime unloaded 500 msPulse number 64,800 (18 h)Resting time 15 min

Actuator

Load cell

Fig. 2. Nottingham asphalt tester (NAT) repeated creep test apparatus [8].

48 E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53

The Marshall mix procedure is empirical and suffers the limita-tion of accuracy in determining full effects of variations in environ-mental and loading conditions, and material properties and typeson the pavement performance. It cannot identify the mixes withhigh degree of shear susceptibility. In addition, the impact methodof compaction in the Marshall mixing method does not simulatedensification that occurs under traffic in a real pavement [16].

3.2. Indirect tension strength test

Indirect tension strength tests were studied for low tempera-ture cracking resistance at 10 �C and 20 �C test temperatures for

both control and three different conditioning systems. Table 9,Fig. 6 and Fig. 7 summarize test results.

Depending upon Table 9 and Fig. 6 laboratory samples for bothcontrol and conditioned types show higher cracking resistance fortwo different temperatures. At 10 �C test temperature laboratorycontrol samples gives 23.54 kN and field cores is 20.39 kN byaverage. These values were obtained respectively 21.24 kN and17.91 kN for water immersion conditioning (first conditioning)while in the second freeze- and thaw- conditioning in turn in order22.52 kN and 18.07 kN. In addition to this third conditioning

Table 8RCT test creep deformations at various load pulses application for laboratory and field core samples.

Number of pulses Sample numbers and permanent deformation values (10�6 in./in.)

33 34 35 36 37 38 39 40

Lab samples 1 563 1597 272 2966 2446 1061 320 10171000 3267 5626 5533 6360 6823 5043 7904 4666

10,000 4692 7417 13,048 7366 9641 7779 17,774 793619,952 5277 8194 17,940 7794 12,270 10,482 26,241 11,71130,045 5711 8804 22,887 8091 16,790 15,194 39,046 21,15039,810 6079 9349 29,126 8361 26,641 27,021 45,251 60,98050,118 6453 9901 38,737 8584 58,984 53,351 45,251 60,98064,730 6949 10,680 59,172 8864 58,984 53,351 45,251 60,980

Field samples 1 126 211 459 231 871 273 334 4481000 2289 3059 4495 2880 5304 3833 3837 5511

10,000 3427 4006 5358 3692 6215 4767 4763 669619,952 3726 4257 5587 3918 6469 5017 5044 700830,045 3899 4382 5716 4096 6622 5156 5199 717939,810 4044 4460 5806 4195 6732 5256 5296 730250,118 4140 4537 5896 4264 6831 5365 5383 738864,730 4227 4605 5965 4373 6928 5435 5481 7531

0

2000

4000

6000

8000

0 20000 40000 60000

Perm

anen

t def

orm

atio

n (1

0-6 in

/in)

Number of pulses

33 35 37 3934 36 38 40

Fig. 3. RCT curves for laboratory produced samples.

0

20000

40000

60000

80000

0 20000 40000 60000

Perm

anen

t def

orm

atio

n (1

0-6 in

/in)

Number of pulses

33 35 37 3934 36 38 40

Fig. 4. RCT curves for field core samples.

0

10000

20000

30000

40000

50000

60000

0 20000 40000 60000

Perm

anen

t def

orm

atio

n (1

0-6 in

/in)

Number of pulses

Lab. Uncond.

Lab. Cond.1

Lab. Cond.2

Lab. Cond.3

Field Uncond.

Field Cond.1

Field Cond.2

Field Cond.3

Fig. 5. RCT graphs for laboratory and field samples.

E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53 49

system gives 15.99 kN and 11.84 kN for mixtures. Resemble this at20 �C test temperature laboratory control samples gives 17.23 kNand field cores is 14.36 kN by average. These values were obtainedrespectively 16.90 kN and 12.77 kN for water immersion condi-tioning (first conditioning) while in the second freeze- and thaw-

conditioning in turn in order 16.30 kN and 12.04 kN. In additionto this third conditioning system gives 14.72 kN and 10.91 kN formixtures.

Average indirect tension strengths were found as 20.82 kN and17.05 kN respectively control and conditioned types at 10 �C testtemperature and 16.29 kN and 12.52 kN at 20 �C test temperature.Marshall laboratory samples exposure higher cracking resistanceas 1.22 more times than the field core samples at 10 �C tempera-ture and 1.30 more times at 20 �C temperature. For two tempera-tures conditioning lab samples reflect higher resistance. With theincreasing of temperature from 10 �C temperature to 20 �C tensionstrengths of the mixtures decreased. Tension strengths decreasedwith conditionings. At 10 �C and 20 �C test temperatures controlsamples have the biggest resistance value. This would further im-ply that lab Marshall mixtures appear to be capable of withstand-ing larger tensile strains prior to cracking (internal resistance).

The tensile strength of the mixtures was presented. As it seen,tensile strength decreased from the unconditioned to conditionedspecimens for all mixtures, implying the presence of damage inthe mixtures. Mixtures with anti-strip additive generally exhibitedless decrease than mixtures without anti-strip additive after condi-tioning. However, an increase in the CAA level could not result inincrease in tensile strength [7].

Table 9Indirect tension strength test results (kN).

Conditioning types Sample number Laboratory samples Field samples Sample number Laboratory samples Field samples

10 �C 20 �C

Unconditioned 7 23.30 22.46 19 19.39 13.928 22.97 19.53 20 14.90 14.469 24.35 19.17 21 17.39 14.71

Average 23.54 20.39 Average 17.23 14.36

Cond. 1 10 22.59 16.66 22 16.85 12.1711 21.08 18.58 23 17.57 11.4012 20.04 18.50 24 16.29 14.73

Average 21.24 17.91 Average 16.90 12.77

Cond. 2 1 22.94 17.36 13 15.90 11.312 22.54 18.22 14 16.60 12.133 22.08 18.64 15 16.40 12.67

Average 22.52 18.07 Average 16.30 12.04

Cond. 3 4 16.71 13.59 16 14.10 11.875 15.88 10.88 17 14.83 10.066 15.39 11.05 18 15.24 10.80

Average 15.99 11.84 Average 14.72 10.91

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Uncond. Cond. 1 Cond. 2 Cond. 3 Uncond. Cond. 1 Cond. 2 Cond. 3

C°02C°01

Indi

rect

tens

ion

stre

ngth

(kN

)

Temperature & Sample Number

Laboratory samples

Field samples

Fig. 6. Indirect tension strength test results for laboratory and core samples.

0

5

10

15

20

25

Unc

ond.

Con

d. 1

Con

d. 2

Con

d. 3

Unc

ond.

Con

d. 1

Con

d. 2

Con

d. 3

10°C 20°C

Indi

rect

tens

ion

stre

ngth

(kN

)

Temperature

Laboratory samplesField samples

Fig. 7. Average indirect tension strength values.

Table 10Tensile strength ratios of mixtures.

Test temp. Conditioning types Indirect tensile strength ratio

Laboratory samples Field samples

10 �C Cond. 1 0.90 0.89Cond. 2 0.95 0.88Cond. 3 0.68 0.58

20 �C Cond. 1 0.98 0.88Cond. 2 0.94 0.83Cond. 3 0.85 0.76

50 E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53

Indirect tension strength ratios can be used as an indicator ofmoisture damage potential. Conditioned strength is divided to con-trol strength and ratio is calculated. Generally 0.70 as an accept-able value is allowable value. Higher ratios are thought asacceptable mixtures [6]. Tensile strength ratios were illustratedin Table 10. Only one ratio was found below 0.70 for third

Table 11Indirect tensile test results for lab and field core samples (A–B: resilient modulus from orthorhombic sections).

Sample number Laboratory samples (20 �C) Field samples (20 �C) Laboratory samples (40 �C) Field samples (40 �C)

40 ms 60 ms 80 ms 40 ms 60 ms 80 ms 40 ms 60 ms 80 ms 40 ms 60 ms 80 ms

Uncond. 25A 11,645 9764 10,130 8029 7795 7141 2492 1942 1634 1354 1219 104325B 9580 9945 9769 9052 7840 7861 2490 1786 1596 1414 1176 99426A 11,577 10,958 9690 8196 7753 7345 2047 1617 1364 1652 1228 82426B 7384 7597 7806 8712 7950 7934 1939 1498 1270 2530 1136 861

Average 10,047 9566 9349 8497 7835 7570 2242 1711 1466 1737 1190 930

Cond. 1 27A 7424 7124 6595 5392 4894 4111 1951 1587 1351 1217 1138 109427B 8237 8045 7622 5633 4918 4331 1819 1418 1205 1260 1163 120928A 7656 7676 7639 5645 5422 4626 2289 1790 1543 1224 1170 95128B 8206 7587 5605 5839 5543 4826 1883 1530 1320 1395 1038 931

Average 7881 7608 6865 5627 5194 4474 1986 1581 1355 1274 1127 1046

Cond. 2 29A 11,000 7673 7285 6408 5722 6033 1976 1535 1313 1456 945 87529B 8512 7955 7514 6928 5939 5103 2136 1688 1456 1193 1075 103930A 9239 9001 8483 6931 6021 5787 2371 1763 1454 1399 1174 107930B 8575 8636 8219 7452 6337 5078 2224 1699 1424 1410 1255 1229

Average 9332 8316 7875 6930 6005 5500 2177 1671 1412 1364 1112 1056

Cond. 3 31A 7169 6811 6323 6171 4918 4357 1805 1427 1222 1042 918 77431B 7481 5903 5789 5257 4545 4011 1747 1330 1325 1123 864 83332A 7142 6539 6188 4676 4329 3964 1792 1539 1224 1025 858 93132B 6361 6332 5892 4819 4987 4611 1813 1472 1129 1014 993 842

Average 7038 6396 6048 5231 4695 4236 1789 1442 1225 1051 908 845

0

2500

5000

7500

10000

12500

15000

25A

25B

26A

26B

27A

27B

28A

28B

29A

29B

30A

30B

31A

31B

32A

32B

Res

ilien

t Mod

ulus

(M

Pa)

Sample Number

40ms-20°C 60ms-20°C 80ms-20°C 40ms-40°C 60ms-40°C 80ms-40°C

Fig. 8. Resilient modulus values for laboratory samples.

0

2500

5000

7500

10000

12500

15000

25A

25B

26A

26B

27A

27B

28A

28B

29A

29B

30A

30B

31A

31B

32A

32B

Res

ilien

t Mod

ulus

(M

Pa)

Sample Number

40ms-20°C 60ms-20°C 80ms-20°C

40ms-40°C 60ms-40°C 80ms-40°C

Fig. 9. Resilient modulus values for field core samples.

E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53 51

0

2000

4000

6000

8000

10000

Lab. Field Lab. Field Lab. Field Lab. Field Lab. Field Lab. Field

40ms 60ms 80ms 40ms 60ms 80ms

40°C20°C

Res

ilien

t Mod

ulus

(M

Pa)

Temperature & Rise Time

Uncond.

Cond. 1

Cond. 2

Cond. 3

Fig. 10. Average resilient modulus values for laboratory and field samples.

Table 12Resilient modulus ratios for laboratory and field samples.

Temp. (�C) Rise time (ms) Laboratory samples Field samples

Cond. 1/uncond. Cond. 2/uncond. Cond. 3/uncond. Cond. 1/uncond. Cond. 2/uncond. Cond. 3/uncond.

20 40 0.78 0.93 0.70 0.66 0.82 0.6260 0.80 0.87 0.67 0.66 0.77 0.6080 0.73 0.84 0.65 0.59 0.73 0.56

40 40 0.89 0.97 0.80 0.73 0.79 0.6160 0.92 0.98 0.84 0.95 0.94 0.7680 0.92 0.96 0.84 1.12 1.13 0.91

52 E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53

conditioning at 10 �C. Laboratory samples gave higher ratios thanfield samples. Laboratory mixtures proved less strippingpropensity.

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

40ms 60ms 80ms 40ms 60ms 80ms

20°C 40°C

Res

ilien

t Mod

ulus

Rat

io

Temperature & Rise Time

Lab. Cond. 1 Lab. Cond. 2Lab. Cond. 3 Field Cond. 1Field Cond. 2 Field Cond. 3

Fig. 11. Resilient modulus ratio for laboratory and field samples.

3.3. Indirect tensile test

Resilient modulus of asphalt mixtures, measured in the indirecttensile mode (ASTM D4123), is the most popular form of stress–strain measurement used to evaluate elastic properties. The resil-iency modulus along with other information is then used as inputto the elastic theories model to generate an optimum thickness de-sign. Therefore the effectiveness of the thickness design procedureis directly related to the accuracy and precision in measuring theresiliency modulus of the asphalt mixture. The accuracy and preci-sion are also important in areas where resilient modulus is used toas an index for evaluating stripping, fatigue and low temperaturecracking of asphalt mixtures [17]. Indirect tensile tests were ap-plied for both conventional and modified mixtures. Variations oftemperatures in the experiments were used as 20 �C and 40 �C.Poisson ratio was selected as 0.35. Pulse and conditioning periodwere designed as 2000 ms. Applied load was 1000 N. Rise timesare 40 ms, 60 ms, 80 ms.

Indirect tensile test results for laboratory and field sampleswere presented in Table 11 and Figs. 8 and 9.

Resilient modulus values were found as harmonious for40–60–80 ms rises ratios for selected 20 �C and 40 �C testtemperatures.

Average resilient modulus values for different mixtures weresummarized in Fig. 10. Temperature and loaded time was found in-versely proportional relation with resilient modulus. Control sam-ples always give highest modulus. Lower modulus was calculatedwith conditioned samples. Lowest modulus was found in condi-tioning 3.

Resilient modulus of different mixtures was studied. Resilientmodulus for all mixtures decreased after conditioning scheme[7]. When examined averages of resilient modulus for controland conditioned mixtures modulus values were calculated8026 MPa for laboratory and 5983 MPa for field mixtures at20 �C. Correlatively modulus values were calculated 1671 MPa forlaboratory and 1137 MPa for field mixtures at 40 �C. Temperatureeffect was shown as more effectual factor than the loading condi-tions on resilient modulus variation. Because of the higher resilientmodulus for laboratory mixtures it is thought that laboratory mix-tures have higher load spreading capacity and higher resistance torutting according to the field mixtures.

Table 12 shows resilient modulus ratios for laboratory and fieldsamples. At 20 �C test temperature (moderate) laboratory samples

E. Iskender, A. Aksoy / Construction and Building Materials 27 (2012) 45–53 53

gives higher ratios than the field samples in context with rise times(40–60–80 ms) for different moisture conditionings. As a result ofhigher ratios laboratory samples have clearly higher strippingresistance. At 40 �C test temperature (high) laboratory samples re-veal also higher ratios than the field ones for 40 ms. Unlike thisfield samples show a controversial result at the 40 �C for 60–80 ms. It is thought that this result stem from the high temperatureand high rise times. With the resilient modulus concept (ASTMD4123) moisture resistance can be evaluated more truly at themoderate temperature conditions for example 20 �C test tempera-ture according to Fig. 11.

4. Conclusions

Performance evaluation between Marshall laboratory samplesand field core samples was realized in this research. It is possibleto conclude below considerations from this study.

� Indirect tensile strength test results for laboratory mixtureswere found 1.22 and 1.30 times more in accordance with fieldsamples at 10 �C and 20 �C respectively. Indirect tensilestrength was found lower with the moisture conditioning. Atthe end of third conditioning both laboratory and field samplesgave lower values than the 0.70 acceptable criteria.� Marshall samples gave higher resilient modulus for all control

and conditioned mixtures. Resilient modulus results for labora-tory mixtures were found 1.34 and 1.47 times more in accor-dance with field samples at 20 �C and 40 �C respectively.Marshall samples have higher load spreading capacity but thisdifference is a result of Marshall compaction type and disadvan-tages of similarity to real field condition.� Temperature effect was found more effectual factor on resilient

modulus according to the stress loading conditions and waterdamage conditioning.� Repeated creep test results also proved the difference between

laboratory and field sample performance. Laboratory samplesprotected their structural integrity during test duration anddid not showed tertiary creep. Unlike this field core samples loststructural resistance and scattered. All field samples showedtertiary creep in repeated creep tests.� With the resilient modulus concept (ASTM D4123) moisture

resistance can be evaluated more truly at the moderate temper-ature conditions for example 20 �C test temperature.

Acknowledgements

This investigation is a part of the research supported byKaradeniz Technical University Scientific Research Fund. Theauthors would like to thank Karadeniz Technical UniversityResearch Fund for providing the opportunity to perform this study.Dogus Construction is also gratefully acknowledged for their labo-ratory facilities and opportunities.

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