1-s2.0-S0360132306002903-main

8/13/2019 1-s2.0-S0360132306002903-main

1/8

Building and Environment 42 (2007) 36213628

Effect of asphalt lm thickness on the moisture sensitivity characteristicsof hot-mix asphalt

Burak Sengoz a, , Emine Agar b

a Faculty of Engineering, Department of Civil Engineering, Dokuz Eylul University, 35160, Izmir, Turkeyb Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey

Received 13 October 2006; received in revised form 13 October 2006; accepted 13 October 2006

Abstract

Temperature, air and water are the common factors that profoundly affect the durability of asphalt concrete mixtures. In mild weatherconditions, distresses such as permanent deformation, fatigue cracking can be encountered on the pavements due to trafc loading. Butwhen a severe climate is in question, these stresses increase in poor materials; under inadequate control; with trafc as well as with waterwhich are key elements in the degradation of asphalt concrete pavements. Many variables affect the amount of water damage in asphaltconcrete layer. Among them, mixture design properties such as air void level, permeability, asphalt content and asphalt lm thickness arethe ones that must be investigated carefully.

This study is aimed to determine the relationship between the various asphalt lm thicknesses and the susceptibility characteristics towater of hot mix asphalt (HMA) so that an optimum asphalt lm thickness that minimizes the moisture damage of HMA can beobtained. For this purpose, the modied Lottman Test (AASHTO T283) is performed on the Superpave Gyratory compacted specimensthat contain 5 different asphalt lm thicknesses. A good correlation between the asphalt lm thickness and the modied Lottman testresults as well as an optimum asphalt lm thickness of 9.510.5 mm is obtained.r 2006 Elsevier Ltd. All rights reserved.

Keywords: Asphalt lm thickness; Moisture susceptibility; Water damage; Stripping

1. Introduction

Many highway agencies have been experiencing pre-mature failures that diminish the performance and servicelife of the pavements. One of the major causes of prematurepavement failure is the moisture damage of the asphaltconcrete layer. However, the causes of the increase inpavement distress because of moisture susceptibility have

not been conclusively identied. Researchers suggest thatchanges in asphalt binders, decreases in asphalt bindercontent to satisfy rutting associated with increases intrafc, changes in aggregate quality, increased widespreaduse of selected design features and poor quality control areprimarily responsible for increased water sensitivity pro-blems [1,2].

Moisture damage in the asphalt concrete pavement occursdue to the loss of adhesion (stripping) or loss of cohesion (i.e.softening of asphalt that weakens the bond between asphaltand aggregate). The stripping of asphalt from the aggregatesresults in the reduction of strength of asphalt concretemixture [2]. The reduction in strength may contribute to thedevelopment of various forms of pavement deterioration suchas rutting, raveling, cracking [3].

Many variables affect the amount of the moisturedamage which occurs in an asphalt concrete mixture. Thecharacteristics of aggregate and asphalt concrete mixtureproperties in terms of permeability, air voids and asphaltlm thicknesses are probably the most important factors[4]. Researchers have carried out laboratory experimentsrelated to the effect permeability, air voids and aggregategradation on the moisture susceptibility of asphalt concretemixtures [1,4,5], however no experimental study has beenconducted for evaluating the effect of asphalt lm thicknesson the water damage of hot-mix asphalt (HMA).

ARTICLE IN PRESS

www.elsevier.com/locate/buildenv

0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved.doi: 10.1016/j.buildenv.2006.10.006

Corresponding author. Tel.: +90 232412 7072; fax: +90232 4127253.E-mail address: [email protected] (B. Sengoz).
http://www.elsevier.com/locate/buildenvhttp://localhost/var/www/apps/conversion/tmp/scratch_9/dx.doi.org/10.1016/j.buildenv.2006.10.006mailto:[email protected]:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_9/dx.doi.org/10.1016/j.buildenv.2006.10.006http://www.elsevier.com/locate/buildenv

8/13/2019 1-s2.0-S0360132306002903-main

2/8

The objectives of this study are to conduct the modiedLottman Test (AASHTO T 283) on the SuperpaveGyratory compacted samples that contain different asphaltlm thicknesses so as to obtain optimum asphalt lmthickness. In this way, relationship between the asphalt lmthickness and the moisture susceptibility of hot-mix asphalt

(HMA) can be determined.

2. Factors affecting moisture susceptibility of asphaltconcrete pavement

Moisture damage in asphalt concrete pavement isaffected by many factors. The type of aggregate, bothcoarse and ne, must be examined carefully in evaluatingthe water damage of the mixture. Some aggregates such asgranite, gravel and other siliceous type materials aresensitive to moisture and are prone to stripping whenincorporated in asphalt concrete. Other aggregates such aslimestone are less susceptible to moisture damage [6]. Insome cases, the majority of the stripping takes place in thecoarse aggregate portion of the mixture. In some cases, thene aggregate is more moisture sensitive and moststripping occurs in that part of the mixture.

The second factor is the type of source of crude oil andrening process which is used to manufacture the asphaltcement. Most asphalt cements are relatively inert in regardto moisture damage. The asphalt cements, from one toanother; do not show much difference in the degree of stripping. In other words, the source of asphalt cement ismuch less dominant than the type of aggregate [7].

The third factor is the asphalt concrete mixture proper-

ties. The air void level and the permeability of the mixture,which are inuenced by the degree of compaction, asphaltcement and the aggregate gradation, are important sincethey control the level of water saturation and drainage. Athigh air void contents, above 6%, a given mixture cansuffer a considerable degree of moisture damage. Exceptionis made for open graded mixtures where air void levels of 15%25% allow water to drain [8].

The asphalt lm thickness has also an inuence on themoisture susceptibility characteristics of HMA because itaffects durability of the mixture. Thick lms which areassociated with black exible mixtures are known to bedurable. On the other hand, thin lms which are associatedwith brownish, brittle mixtures tend to crack and ravelexcessively thus shortening the service life of the pavement.Mixtures with thick asphalt lm are less susceptible towater damage than the mixtures with thin asphalt lm sincevery little quantities of water can move through the mixturethat contains thick asphalt lm thicknesses [8,9].

Environmental conditions and trafc affect the amountof stripping which happens in a particular mixture. Moremoisture damage typically occurs in areas where there areconsiderable amount of rain and/or snowfall. Both the typeof trafc and the volume are important variables. As thetrafc becomes heavier and as the truck volume increases,the amount of stripping becomes greater [9].

The summary of the factors that affect the amount of moisture damage are given in Table 1 .

3. Materials

3.1. Aggregate

The Superpave mixtures are produced with limestoneaggregate from Redland Genstars Frederick Marylandquarry. Although asphalt mixtures prepared with limestoneaggregate are less susceptible to moisture damage, thereason for the utilization of limestone aggregate is tosimulate the real pavement conditions in Turkey, wheremost of the asphalt pavements are constructed usinglimestone aggregate. In order to nd out the properties of the aggregate used the sieve analysis, specic gravity, LosAngeles abrasion resistance test, sodium sulfate soundnesstest, ne aggregate angularity test, fractured faces, sandequivalent and at and elongated particles tests wereconducted on each aggregate group. The results of thesetests conducted on aggregate groups and specicationlimits corresponding to each test method are presented in

ARTICLE IN PRESS

Table 1Factors which inuence moisture damage [3]

1. Aggregate Aggregate composition

J Degree of acidityJ Surface chemistryJ Types of mineralsJ Source of aggregate

Physical characteristicsJ AngularityJ Surface roughnessJ Surface areaJ GradationJ PorosityJ Permeability

Dust and clay coatings Moisture content Resistance to degradation

2. Asphalt Chemical composition Hardness Crude source and rening process

3. Mixture design and construction Air voids level and compaction Permeability and drainage Film thickness

4. Environment Temperature Freeze-thaw cycles Dampness and pavement age

5. Trak6. Anti-stripping additives properties

B. Sengoz, E. Agar / Building and Environment 42 (2007) 362136283622

8/13/2019 1-s2.0-S0360132306002903-main

3/8

Table 2 . As seen from Table 2 , all results obtained fromexperiments are within Superpave Specication limits.

After determining the properties of aggregate groups,mixture ratios were chosen based on the Superpaveconsensus aggregate criteria related to control points andrestricted zones for 12.5 mm nominal sized aggregate. Fourstockpile proportion and nal gradation is presented inTable 3 .

3.2. Asphalt cement

The asphalt cement used in each of the Superpavemixtures is an unmodied PG 64-22 obtained from thePaulsboro, New Jersey Terminal of the Citgo AsphaltRening Company. An extensive testing program isperformed to characterize the rheological properties of the asphalt cement using both conventional and Superpavetests. Table 4 summarizes the results of the tests conductedon PG 64-22 asphalt cement. The tests carried out (given inTable 4 ) complying with the Superpave requirements andSpecications. As seen from Table 4 , all results obtainedfrom the experiments are within the Superpave Specica-tion limits.

4. Experimental

After the properties of the aggregate and the asphaltcement were determined, the surface area of the aggregate

was calculated by multiplying the surface area factors givenin MS-2. [10], by the gradation values presented in Table 3 .The surface area factors are presented in Table 5 . Thesurface area factors used to calculate asphalt lm thickness(given in Table 5 ) are also adopted in Superpave DesignMethod. For the aggregate gradation used, the surface areawas calculated to be 5.1827 m 2/kg. This value was used inthe calculation of asphalt content corresponding to theasphalt lm thicknesses chosen in the study.

In this study asphalt paving mixtures were prepared ateach of the following ve effective asphalt lm thicknesses:4.9, 5.8, 7.7, 9.6 and 11.4 mm. The utilization of thesethicknesses are based on the Shell Bitumen Handbookwhich states that the average asphalt lm thickness inHMA ranges from 5 to 15 m [11]. The required asphaltcontents corresponding to 4.9, 5.8, 7.7, 9.6 and 11.4 mm

asphalt lm thicknesses were calculated as 3.08%, 3.58%,4.56%, 5.5% and 6.45% taking the percentage of asphalt(unmodied PG 64-22) absorption for limestone aggregateinto consideration.

The Modied Lottman Test (AASHTO T283) was thenperformed on the asphalt specimens prepared by using thecalculated asphalt contents mentioned above.

The aim of the modied Lottman Test is to evaluatesusceptibility characteristics of the mixture to waterdamage. This test is performed by compacting specimensto an air void level of 7% 7 1%. Three specimens areselected as a control and tested without moisture con-ditioning; and three more are selected to be conditioned bysaturating with water (55%80% saturation level) followedby a freeze cycle ( 18 1 C for 16 h) and subsequently havinga warm-water soaking cycle (60 1 C water bath for 24 h).The specimens are then tested for indirect tensilestrength (ITS) by loading the specimens at a constant rate(50mm./min vertical deformation at 25 1 C) and the forcerequired to break the specimen is measured. The indirecttensile strength (ITS) of the conditioned specimens iscompared to the control specimens in order to determinethe tensile strength ratio (TSR).

In this study, specimens were sorted into two subsets(both control and conditioned) of three specimens eachso that average air voids of two subsets are equal.

ARTICLE IN PRESS

Table 2Results of experiments conducted on aggregate groups

Test 7# 8# 10# Washed 10# Specication Spec. Limits

Bulk specic gravity 2.701 2.700 2.586 2.663 AASHTO T84/T85 Surface saturated SG. 2.717 2.710 2.646 2.687 AASHTO T84/T85 Apparent SG 2.736 2.730 2.729 2.729 AASHTO T84/T85 Absorption (%) 0.4 0.4 0.9 0.9 AASHTO T84/T85 Los angeles abrasion (%) 26 26 AASHTO T96 45% (max)Sodium sulfate soundness 0.1 0.1 1.2 1.2 AASHTO T104 1020% (max)Fine aggregate angularity 45.6 45.6 AASHTO TP33 40% (min.)Fractured faces (%) 100 100 100 100 PTM 621 Sand equivalent . 89 89 AASHTO T176 40% (min.)Flat and elongated particles 7.5 9.7 ASTM D4791 10% (max.)

Table 3Stockpile proportions and nal 12.5 mm gradation

Sieve no (mm) Passing %

19.0 10012.5 97

9.5 874.75 582.36 351.18 210.600 130.300 90.150 80.075 6.1

B. Sengoz, E. Agar / Building and Environment 42 (2007) 36213628 3623

8/13/2019 1-s2.0-S0360132306002903-main

4/8

The specimens were prepared to give target air void contentlevel of 7%. A Superpave Gyratory Compactor was usedfor this purpose. The total number of specimens testedwere 5 (asphalt lm thickness)*2 (control and conditionedspecimen)*3 (replicates) 30. The ow chart of theexperimental study and design parameters are presentedin Fig. 1 and Table 6 respectively.

5. Results and discussion

The ITS test results of control and conditioned speci-mens which are a part of the modied Lottman test aregiven in Tables 7 and 8 respectively.

In order to see the effect of the asphalt lm thickness onthe moisture susceptibility characteristics of the samplesand to determine the optimum asphalt lm thickness,asphalt lm thicknesses were plotted against the values of ITS for both control and conditioned specimens.

The concept of power regression analysis was used as atool to t the observed data to the curve, which quantiesthe relationship between the independent and the depen-

dent variables. The independent variable is the asphalt lmthickness whereas the dependent variables whose valueswere given in Tables 7 and 8 were the ITS test results forthe control and the conditioned specimens. Fig. 2 showsthe relationship between the asphalt lm thickness and theITS test results of specimens.

Regression analysis leads to power functions in the dataas modeled by the following equations:

ITS control 8097 :4 h 1:0026 R 2 0:99 (1)

ITS cond 5453 :5 h 0:8694 R 2 0:98 (2)

where ITS control is the Indirect tensile strength of controlspecimens, kpa, ITS cond the Indirect tensile strength of conditioned specimens, kpa, h the Asphalt lm thickness,mm, R2 the Determination of coefcient.

A fairly good relationship was obtained between theasphalt lm thickness and the ITS of control andconditioned specimens both of which were compacted with7% air voids. Although the database is small, the very highvalue of R 2 (determination of coefcient) indicates that theinvestigated functions exactly represent the relationshipbetween the asphalt lm thickness and the ITS of speci-mens. It should be noted the mentioned functions are onlyvalid between the asphalt thicknesses of 512 mm.

It can be seen in Fig. 2 that the slope of the curvebecomes steeper as the lm thickness falls below a value of about 9.510.5 mm. This indicates that the asphalt pavingmixture becomes more susceptible to water damage with adecrease in the asphalt lm thickness below about9.510.5 mm. Therefore, it can be concluded that, the9.510.5 mm asphalt lm thickness can be accepted as anoptimum asphalt lm thickness that minimizes themoisture damage of HMA.

The ITS of the conditioned specimens was compared tothe control specimens in order to determine the tensile

ARTICLE IN PRESS

Table 4Results of the experiments conducted on PG 64-22 asphalt

Condition Test Specication Results Specication limits

Unaged asphaltSpecic gravity (25 1 C) AASHTO T228 1.021 Viscosity, 135 1 C ASTM D4402 0.420 Pa.s Viscosity 165 1 C ASTM D4402 0.114 Pa.s Dynamic shear rheometer ( G */sin d ) , 10 rad/sec., 64 1 C AASHTO TP5 1.260 kPa 1.00 kPa (min)(Indicator to resistance to permanent deformation)

RTFO aged residueMass change AASHTO T240 0.14% Dynamic shear rheometer ( G */sin d ), 10 rad/s., 64 1 C AASHTO TP5 2.516 kPa 2.200 kPa (min)(Indicator to resistance to permanent deformation)

PAV aged residueDynamic shear rheometer ( G */sin d ), 10 rad/s., 25 1 C AASHTO TP5 4154 kPa 5000 kPa (max)(Indicator to fatigue cracking)Bending beam Rheometer 60 s, 12 1 C AASHTO TP1 209 MPa 300 Mpa (max)(Indicator to low temperature cracking)m value 60s., 12 1 C AASHTO TP1 0.342 0.300 (min.)

Table 5Surface area factors

Sieve no (mm) Surface area factor

19.0 0.4112.5 0.41

9.5 0.414.75 0.412.36 0.821.18 1.640.600 2.87

0.300 6.140.150 12.290.075 32.77


8/13/2019 1-s2.0-S0360132306002903-main

5/8

strength ratio (TSR) which is calculated with the followingequation:

TSR S 2S 1

(3)

where S 1 is the Average indirect tensile strength of controlspecimen, S 2 the Average indirect tensile strength of conditioned specimen.

The results are presented in Table 9 .TSR values were then drawn corresponding to each

asphalt lm thickness that is given in Fig. 3 .Power regression gave an acceptable model for the

relationship between the asphalt lm thickness and TSR

values presented below:

TSR 0:6735 h 0:1332 R2 0:92 (4)

The very high value of R2 indicates that the abovefunction represents the relationship between the asphaltlm thickness and TSR values of specimens.

Table 9 and Fig. 3 show that as the asphalt lm thicknessincreases, the TSR values increase as well. This indicatesthat the resistance of asphalt mixtures to the detrimentaleffect of water decrease with increase in asphalt lmthickness.

6. Conclusions and recommendations

Moisture damage in asphalt mixtures is a complexmechanism which is not well understood and has manyinteracting factors. The effect of the asphalt lm thicknesson the moisture damage in HMA is one of the factors andhas not been investigated. Therefore the main objective of the study is to evaluate moisture susceptibility character-istics of HMA in terms of asphalt lm thickness and thefollowing conclusions can be drawn:

The relationship between the asphalt lm thickness andthe ITS of control and conditioned specimens as well as

ARTICLE IN PRESS

Preparation of asphalt concrete mixturesusing five different asphalt film thickness

Loose mix curing at 60 C for 16 hours

Short term aging of loose mixture at 135

C for 2 hours

Compaction

Application of partial vacuum in order todetermine level of saturation between

Indirect TensileStrength Test on

control specimens(S1)

Freezing procedure of compacted specimen at

-18 C for 16 hours

Thawing procedure of compacted specimen at

60 C for 24 hours

Indirect Tensile StrengthTest on conditioned

specimens(S2)

Tensile Strength Ratio (TSR)=S 2/S1

Fig. 1. The ow chart of the modied Lottman Test (AASHTO T283).

Table 6Design parameters

Type of asphalt Unmodied PG 64-22

Type of aggregate Lime stone aggregateAsphalt lm thickness ( mm) 4.9, 5.8, 7.7, 9.6, 11.4Specimen conditions Control and conditionedTarget air void level (%) 7Tests performed Indirect tensile strength at 25 1 CReplicates 3


8/13/2019 1-s2.0-S0360132306002903-main

6/8

8/13/2019 1-s2.0-S0360132306002903-main

7/8

References

[1] Epps JA, Sebeally PE, Penerande J, Maher MR, Hand JA.Compatibility of a test for moisture induced damage with SuperpaveVolumetric Mix Design, National Cooperative Highway ResearchProgram, Report No: 444, Washington DC, 2000.

[2] Tandon V, Vemuri N, Nazarian S. Evaluation of environmentalconditioning system for predicting moisture susceptibility of asphalt

concrete mixtures, Transportation Research Board, 75th AnnualMeeting, Washington DC, 1996.

[3] Solaimanian M, Kennedy TW, Elmore WE. Long term evaluation of stripping and moisture damage in asphalt pavements treated withlime and anti-stripping agents. Texas Department of Transportation,Report No: CTR 0-1286-1F, Center of Transportation Research,

University of Texas at Austin, 1993.

ARTICLE IN PRESS

ITScontrol = 8097.4h -1.0026

R2 = 0.99

ITScond. = 5453.5h -0.8694

R2 = 0.98

500

700

900

1100

1300

1500

1700

1900

4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12Asphalt Film Thickness (micronmeter)

A v e r a g e

I n d i r e c

t T e n s

i l e

S t r e n g

h t ( k p a

)

Indirect Tensile Str. of conditioned SpecimensIndirect Tensile Str. of control SpecimensRegression line between asphalt film thickness and ITS of control specimensRegression line between asphalt film thickness and ITS of conditioned specimens

Fig. 2. Relationship between the asphalt lm thickness and the indirect strength test results of the control and conditioned specimens.

Table 9Tensile strenght ratios (TSR) correponding to the asphalt lm thicknesses

Asphalt lm thickness ( mm) TSR ( S 2/S 1)

4.9 0.835.8 0.847.7 0.909.6 0.91

11.4 0.92

TSR = 0.6735h 0.1332

R2 = 0.92

0.82

0.84

0.86

0.88

0.90

0.92

0.94

4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12Asphalt Film Thickness (micronmeter)

T S R

V a

l u e

TSR valuesof compacted specimensRegressionline between asphaltfilm thickness and TSRvalues of specimens

Fig. 3. Relationship between the asphalt lm thickness and the indirect tensile strength ratio (TSR).


8/13/2019 1-s2.0-S0360132306002903-main

8/8

[4] Kennedy TW. Laboratory tests for water susceptibility. Proceedingsof the Annual Meeting of Texas Hot mix Asphalt PavementAssociation, Report No: FHWA-DP 39-36, 1982. p. 160189.

[5] Graf EG. Factors affecting moisture susceptibility of asphalt concretemixtures. Association of Asphalt Paving Technologists 1986;55:176204.

[6] Proctor J. Marginal and low quality moisture susceptible aggregatesin bituminous mixtures Final report, Colorado Department of

Highways, Report No:CDOH-SBM-R-82-S, 1984.[7] Mullins TE. Affect of hot asphalt on anti-strip. A paper presented atthe annual meeting of Western Cooperative Test Group, Montana,1983.

[8] Stuart KD. Moisture damage in asphalt mixtures-a state of artreport, Federal Highway Administration, 1990.

[9] Scherocman JA, Mesch KA, Proctor J. The effect of multiple freezethaw cycle conditioning on the moisture damage in asphalt concretemixture. Association of Asphalt Paving Technologists 1986;55:21327.

[10] The Asphalt Institute, Mix design methods for asphalt concrete and

other hot mix types, The Asphalt Institute, MS-2, Sixth edition,1993.[11] Whiteoak D, Read JM. The Shell bitumen handbook. London:

Published by Thomas Telford Services Ltd; 2003.

ARTICLE IN PRESS


Documents

1-s2.0-S0360132306002903-main