Fatigue and rutting performance of lime-modified hot-mix asphalt mixtures

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  • mgu,ngreort

    Hot-mix asphalt

    ffecsinin efatihodt teonnce

    provinas beeven tof its abage reysico-creduce

    ture has been repeatedly shown to be benecial, the benet of limein a volumetric mix design, which may or may not change the opti-mum asphalt binder content, has still not been demonstrated.

    The primary objective of this study was to use advanced testsand analysis methods to investigate the effect of lime on the fun-damental behaviour of asphalt concrete in such areas as fatiguecracking, stripping resistance, and rutting performance for various

    procedure [3,4].Optimum asphalt contents of 5.6% and 5.3% for the control and Lsub mixtures,

    respectively, were determined from the mix design based on Table 2. The Super-pave volumetric criteria were met for both mixtures. Table 2 refers to the voidsin mineral aggregate (VMA) and the volume of voids lled with asphalt (VFA).

    Performance testing was conducted for lime-modied HMA mixtures with theoptimum asphalt content. All test specimens were compacted by a Superpave gyra-tory compactor to a height of 178 mm and a diameter of 150 mm. To obtain spec-imens of uniform quality and air void distribution, they were cut and cored tocylindrical specimens with dimensions of 100 mm in diameter and 150 mm inheight for the dynamic modulus test and TRLPD test, and 75 mm in diameter and150 mm or 140 mm in height for the constant crosshead test. The details of this pro-cess can be found elsewhere [5,6].

    Corresponding author.

    Construction and Building Materials 25 (2011) 42024209

    Contents lists availab

    B

    evE-mail addresses: smundyna@gmail.com, smun@seoultech.ac.kr (S. Mun).mum asphalt content by lling voids. It also improves thestability and fatigue resistance via dispersion of tiny particlesthroughout the mixture to stop cracks. In addition, it can have anactive ller effect that reduces age hardening and moisture suscep-tibility by a chemical reaction with the asphalt mixture. Moisturedamage can occur when the bond between the asphalt cementand the aggregate breaks down due to the action of moisture onthe interface of the asphaltaggregate system and when the binderis separated from the aggregate surface.

    Even though the use of hydrated lime in asphalt concrete mix-

    2. Materials and specimen fabrication

    Table 1 shows the target gradation for the selected mixture. The mixing temper-ature was 150 C, and the compaction temperature was 143 C. Hydrated lime wasadded to the HMA mixture using one of the dry introduction techniques [2]. In thismethod, hydrated lime (1% by aggregate weight) was substituted for a portion ofthe baghouse nes. Mix designs for the unmodied HMA mixture (referred to asthe control mixture) and the lime-modied HMA mixture (referred to as the Lsubmixture) were developed following the standard Superpave volumetric mix design1. Introduction

    The use of mineral ller for imhot-mix asphalt (HMA) mixtures hHydrated lime, in particular, has proor ller for HMA mixtures because otigue performance and moisture damreacts with asphalt mixtures in a phert ller, hydrated lime physically0950-0618/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.04.059g the performance ofn demonstrated [1,2].be a superior additiveility to improve the fa-sistance. Hydrated limehemical manner. As in-s the volumetric opti-

    volumetric optimum asphalt content levels. This paper summa-rises ndings based on the performance evaluation of differentmixtures.

    The outline of the paper is as follows. Section 2 contains the de-tails of the materials and specimen fabrication. Section 3 describesthe test setup and methods used to determine the material param-eters. Section 4 presents the results of the testing and performanceevaluation. Section 5 contains the concluding remarks andsummary.Continuum damageDynamic modulus

    of various mixtures with respect to the fatigue damage and rutting performance. 2011 Elsevier Ltd. All rights reserved.Fatigue and rutting performance of lime-

    Sangyum Lee a, Sungho Mun b,, Y. Richard Kim caRoad Management Division, Seoul Metropolitan Government, Deoksugung-gil 15, Jung-b School of Civil Engineering, Seoul National University of Science & Technology, 172 GocDepartment of Civil, Construction and Environmental Engineering, Campus Box 7908, N

    a r t i c l e i n f o

    Article history:Received 31 December 2010Received in revised form 10 March 2011Accepted 22 April 2011Available online 25 May 2011

    Keywords:Lime-modied asphaltViscoelasticity

    a b s t r a c t

    This paper describes the easphalt binder evaluated uthe effective stress vs. straated in this study includedaged states. The test metcharacterization, the direcload permanent deformatithe demonstration of adva

    Construction and

    journal homepage: www.elsll rights reserved.t of lime on composite hot-mix asphalt (HMA) mixtures of aggregate andg viscoelastic continuum damage analysis, which is based on predictingquations and microcrack growth. The performance characteristics evalu-gue cracking and rutting resistance in both moisture-damaged and undam-s used in this evaluation were the dynamic modulus test for stiffnessnsion test for fatigue cracking characterization, and the triaxial repeated-test for rutting characterization. The main contribution of this paper isd test methods and models that can be used to evaluate the performanceodied hot-mix asphalt mixtures

    Seoul 100-110, South Koreaung-2 Dong, Nowon-Gu, Seoul 139-743, South Koreah Carolina State University, Raleigh, NC 27695-7908, USA

    le at ScienceDirect

    uilding Materials

    ier .com/locate /conbui ldmat

  • Both tensile and compressive loading protocols were used with

    ldinga closed-loop servo-hydraulic testing machine composed of a uni-versal testing machine (UTM-25; IPC Global, Boronia, Australia)and a loading frame (MTS 810) equipped with either a 25-kN or8.9-kN load cell, depending on the nature of the test. Measure-After obtaining specimens of the appropriate dimensions, air void measure-ments were conducted using the CoreLok method [6], and specimens were storedfor a maximum of two weeks until testing took place. During storage, specimenswere sealed in bags and placed in an unlit cabinet to reduce aging effects.

    3. Test setup and methods

    Table 1Gradation used for control mixture.

    Sieve size % Passing

    3/400 (19 mm) 100.01/200 (12.5 mm) 99.23/800 (9.5 mm) 95.3#4 (4.75 mm) 77.5#8 (2.36 mm) 59.2#16 (1.18 mm) 45.1#30 (0.600 mm) 32.5#50 (0.300 mm) 19.9#100 (0.150 mm) 12.1#200 (0.075 mm) 6.4Pan 0.0

    Table 2Volumetric mix design results.

    Property Control Lsub Criteria

    Optimum % AC 5.6 5.3 n/a% Air voids 3.9 3.9 n/aVMA 16.2% 15.7% 15% minVFA 75.7% 75.1% 6580%Passing #200 6.4 6.3 4.08.0Dust portion 1.28 1.30 0.61.4

    S. Lee et al. / Construction and Buiments of axial deformation, load, and crosshead movement forall tests were obtained via a data acquisition system consisting ofa National Instruments 16-bit data acquisition card and Labviewsoftware. In all the tests conducted during this study, axial mea-surements were taken at 90 intervals over the middle 100 mmof the specimen with loose-core linear variable differential trans-formers (IPC Global).

    The purpose of the moisture conditioning process was to intro-duce a certain amount of moisture damage in the specimen prior tofatigue testing. Three parameters were controlled in the pre-condi-tioning process (moisture saturation before conditioning): mois-ture content (saturation level), conditioning temperature, andconditioning duration. Of these three parameters, the conditioningtemperature had the most signicant effect on the moisture resis-tance of the asphalt mixes, followed by the conditioning durationand the moisture content.

    Multiple-freezethaw (FT)-cycle conditioning was conductedin accordance with AASHTO T-283 [7]. Because the fatigue testmethod used in this study was different from that in AASHTO T-283, the conditioning procedure was adjusted for appropriate sat-uration levels and post-conditioning temperatures.

    A greater number of air voids in asphalt pavement generally in-creases the permeability and permits more water to penetrate. Inother words, the permeability of asphalt mixtures is proportionalto air void content when the properties and the structure of theaggregate are otherwise similar. In this study, all the mixtureshad the same aggregate and structure with a 4% air voids; this isless than the 7% air voids used for the tensile strength ratio testing.Due to the small air void percentage, the test required three timeslonger than the maximum 10 min specied in AASHTO T-283.

    The preconditioned (saturated) specimens were subjected tothree multiple-FT cycles that consisted of freezing at 18 C for24 h followed by thawing at 60 C for 24 h. The conditioned spec-imens were stabilised in a water bath at 25 C for 2 h. This proce-dure was not part of the AASHTO T-283 test but used to minimizethe weight creep of the specimens. All conditioned specimens weredried to a certain level of saturation using a core dryer to minimizethe effects of different saturation levels. Because setting up theconstant crosshead strain rate test took 18 h, the specimens werewrapped in plastic lm (Paralm) to avoid the evaporation of themoisture until the test setup was complete. The test saturation le-vel (post-conditioning) was determined based on the testing setuptime. Table 3 shows the saturation levels for pre-conditioning andpost-conditioning.

    The moisture-conditioned specimens were then subjected tothe same performance tests used for the dry specimens, includingthe dynamic modulus test, triaxial repeated-load permanent defor-mation (TRLPD) test, and constant crosshead-rate direct tensiontest.

    3.1. Dynamic modulus tests

    The dynamic modulus test was performed in load-controlledmode under axial compression (zero maximum stress) generallyfollowing the protocol given in AASHTO TP-62 [8], as shown inFig. 1a. Tests were completed for all mixtures at 10, 10, 35,and 54.4 C and at frequencies of 25, 10, 5, 1, 0.5, 0.1, 0.05, and0.01 Hz. Load levels were determined by a trial-and-error processto ensure that the resulting strain amplitudes remained between50 and 70 microstrains. Based on the work of other researchers,this criterion was judged appropriate to ensure accurate linear vis-coelastic characterization [9,10].

    3.2. TRLPD tests

    TRLPD or ow number tests (Fig. 1b) were performed to as-sess the rutting potential of the asphalt concrete mixtures fol-lowing the protocol presented in NCHRP Report 465 [3]. Usingthis procedure, the specimen was subjected to a deviatoric hav-ersine stress pulse for 0.1 s and then allowed to rest for 0.9 s. Forthe mixtures presented here, only a single conning stress of138 kPa, temperature of 54.4 C, and deviatoric stress level of827 kPa were examined. This test protocol is one of the proposedsimple performance tests used to ensure the satisfactory perfor-mance of Superpave mixtures in rutting. Note that due to limitedavailability of material, the TRLPD test was conducted on thesame specimens that were used for the dynamic modulus (|E|)test. That is, the TRLPD test was performed after allowing thespecimen subjected to the |E| test to restabilise. This was possi-ble because the |E| test is nondestructive.

    3.3. Constant crosshead-rate direct tension tests

    Constant crosshead-rate tests were performed by applying aconstant rate of deformation over the complete loading train asshown in Fig. 1c. Because each component in the loading train(e.g., machine ram and load cell) deformed slightly, the on-specimen displacement rate or strain rate was not constant [11].The tests were conducted at 5 C and at multiple rates (0.000055,0.000030, and 0.000021 s1) for the purpose of viscoelastic contin-uum damage (VECD) characterization. These rates were fast

    Materials 25 (2011) 42024209 4203enough not to cause any signicant plastic or viscoplastic deforma-tions during loading. Constant crosshead rate monotonic directtension tests were used to generate the damage characteristic

  • 2 58.33 58.6

    ldingAvg. 58.7Table 3Level of saturation for moisture-conditioned procedure.

    Test type Saturation level (%)

    Mix Control

    Stage Pre-conditioned

    Dynamic modulus test 1 56.02 60.23 58.3Avg. 58.2

    Direct tension test 1 59.1

    4204 S. Lee et al. / Construction and Buicurve, which represents the fundamental resistance of a mixture todamage, based on the VECD model and Schaperys work potentialtheory [12].

    3.4. Determination of pseudo stiffness C(S)

    The VECD model and the constant crosshead rate monotonic di-rect tension test method were used to evaluate the fatigue crackingperformance of HMA mixtures. The VECD model requires the dy-namic modulus and damage characteristic curve to predict theHMA cracking performance.

    On the simplest level, the VECD model considers a damagedbody with some stiffness as an undamaged body with reducedstiffness. The VECD model thus quanties the amount of damagethat has occurred in the sample and determines the impact of thisdamage on the material behaviour. An internal state variable Sbased on Schaperys work potential theory [12] was used to quan-

    LVDT

    (b)(a)

    (c)

    Fig. 1. Testing setups: (a) dynamic modulus test, (b) triaxial repeateLsub

    Post-conditioned Pre-conditioned Post-conditioned

    33.3 56.7 38.434.8 57.6 38.037.3 54.2 37.935.1 56.2 38.133.7 59.5 37.135.7 60.1 36.635.6 60.3 38.035.0 60.0 37.2

    Materials 25 (2011) 42024209tify the damage in the material. The relationship between S and thematerial integrity is referred to as the damage characteristic curve,or the C vs. S curve, which is discussed below.

    Schapery [12] developed a theory using the method of thermo-dynamics of irreversible processes to describe the mechanicalbehaviour of elastic composite materials with growing damage.The work potential theory contains three fundamental elements:

    Strain energy density function; W Weij; Sm; 1

    Stressstrain relationship; rij @W@eij

    and 2

    Damage evolution law; @W@Sm

    @Ws@Sm

    ; 3

    where rij and eij are stress and strain tensors, respectively; Sm rep-resents the internal state variables; and Ws =Ws(Sm) is the

    LVDT

    LVDT

    d-load permanent deformation test, and (c) direct tension test.

  • 4.1. Dynamic modulus test results

    The TRLPD tests were conducted for 10,000 cycles without theoccurrence of tertiary ow. The TRLPD test results shown inFig. 5 indicate the benets of lime modication: lower volumetricoptimum asphalt content (e.g., 5.3%) and more resistance to ruttingpotential. Fig. 6 shows that the increase in the permanent straindue to moisture conditioning was much greater in the control mix-ture than in the Lsub mixture, demonstrating the benecial effectof lime on moisture damage in terms of permanent deformation.

    Note that due to the lack of available materials, the TRLPDtests were conducted on the same specimens used for the |E|tests. A certain level of densication occurred even though the

    ldingdissipated energy due to structural changes. Using Schaperys elas-ticviscoelastic correspondence principle and the rate-type damageevolution law [1215], the physi...

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