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Laboratory Performance Evaluation of Modified AsphaltMixtures for Inchon Airport PavementsHyun-Jong Lee a , Jo S. Daniel b & Y. Richard Kim ca Department of Civil Engineering, Kangnung National University, Kangnung, Kangwondo,210-702, Koreab Graduate Research Assistant Department of Civil Engineering, North Carolina StateUniversityc Associate Professor Department of Civil Engineering, North Carolina State UniversityRaleigh, P.O. Box 7908, NC, 27695-7908Version of record first published: 01 Feb 2007.

To cite this article: Hyun-Jong Lee , Jo S. Daniel & Y. Richard Kim (2000): Laboratory Performance Evaluation of ModifiedAsphalt Mixtures for Inchon Airport Pavements, International Journal of Pavement Engineering, 1:2, 151-169

To link to this article: http://dx.doi.org/10.1080/10298430008901703

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Laboratory Performance Evaluation of Modified Asphalt Mixtures for Inchon Airport Pavements

HYUN-JONG LEE"*, JO S. DANIEL^ and Y. RICHARD KIM'^ "Deparrmenr rf Civil Engineerirlg Kangnun~ Narional University Kangnung. Kangwondo 210-702, Korea. b~radlcore Research Assisronr Deparrmenr of Civil Engineering Norrh Carolina Stare University and CAssociare Professor RO. Box 7908 Depann~enr of Civil E~rgineering Norrh Carolina Stare Universiry Raleigh. N C 27695-7908

(Received January 19. 1998; Infinal form July 29. 1999)

In this paper, fatigue and rutting characteristics of various modified and unmodified mixtures are evaluated using uniaxial tension and triaxial compression cyclic tests, respectively. The fatigue and healing behavior of the mixes is presented by means of the viscoelastic, contin- uum damage (VCD) model previously developed by the authors. Since the VCD model takes the same form as the classical, strain-based fatigue model, the coefficients in the classical model are described in terms of fundamental material properties and test conditions in the VCD model. The explicit form of the VCD model and different performance data from all the mixes are used to investigate the effects of the material properties on the fatigue life and microdamage healing potential of asphalt concrete. Structural analysis based on the multi-lay- ered elastic theory is conducted to compare the fatigue lives of the various mixes in pavement systems.

A simple permanent deformation model that correlates vertical pernlanent strain and number of applied loads is used in representing the data from the triaxial compression tests at different confining pressures. The modified mixtures demonstrate better rutting resistance as expected, although the ranking among the modified mixtures changes depending on the con- fining pressure. The role of additive at high temperatures and different gradations and binder contents used in the modified mixtures seem to explain these observations.

Keywords: Modified Asphalt Mixtures, Fatigue, Healing, Rutting. Viscoelasticity. Damage

INTRODUCTION though the materials and environmental conditions of Yong Jong-Do pavements are different from those

The Korean Airport Construction Authority plans to used in developing the FAA design equations. Dae- build an international airport a t YongJong-Do, Korea. bon Engineering Corp. (DEC) was charged to build Pavements in the airport are designed based on the and evaluate test pavement sections to verify the FAA airport pavement thickness design method even thickness designs and has developed a comprehensive

* Phone: 82-391-640-2419 FAX: 82-391-640-2244 E-mail: hlee@knusun.kangnung.ac.kr t Phone: 919-515-7758 FAX: 919-515-7908 E-mail: kim@eos.ncsu.edu

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HYUN-JONG LEE et a/.

plan to instrument these pavements with sensors to mcuurc pavcnicnt responses (stresses, strains, and dcforniations) under simulated loading conditions.

As n part of this work, laboratory fatigue and per- mancnt dcformntion modcls were applied to the vari- ous modilicd and unmodified mixtures used in the ficld tcst pavement project. The principal objectives of thc work conducted at North Carolina State Uni- vcrsity wcrc: (I) to determine the viscoelastic mate- rial propcrtics of the asphalt mixtures at varying loading frcqucncics; and (2) to evaluate the fatigue and rutting pcrformance of the different asphalt mix- turcs. Evcntually, the laboratory prediction models wcrc used to provide information on performance ranking of these mixtures in terms of fatigue and rut- ting.

Thcrc arc scvcn diffcrent asphalt mixtures used in thc construction of the test sections, five mixtures for thc surface course and two for the base course. The materials for the surface course include a conven- tional dcnsc graded asphalt mixture, Stone Matrix Asphalt, and asphalt mixtures modified with Latex (SBR), SBS, and Gilsonite (hereafter called S19, SMA, SBR, SBS, and GIL mixtures, respectively). The two materials used for the asphalt concrete base coursc arc a conventional asphalt base course and asphalt ~nodificd with Chemcrete (hereafter called 025 and CHE mixtures, respcctively).

Uniaxial tensile creep tests were performed to mcasurc viscoelastic material properties of each mix- turc. Rclaxation modulus and dynamic modulus were predicted from the creep data using theory of linear viscoclasticity. Uniaxial tensile fatigue tests were conducted on the seven asphalt mixtures to evaluate fatigue pcrformance. A mechanistic fatigue perform- ancc prediction model proposed by Lee and Kim ( 19983, 1998b). and Lee el al. (1 998) was used to esti- mate the fatigue lives of the mixtures. Rutting per- formance was evaluated for five surface course materials by performing triaxial compression tests. A typical permanent deformation model was adopted in this study to model the permanent deformation of the mixtures.

PERFORMANCE PREDICTION MODELS

Fatigue Prediction Models

The two main approaches in the fatigue characteriza- tion of asphalt mixtures are phenomenologically and mechanistically based approaches. One of the most commonly used phenomenological fatigue models relates the initial response (such as tensile strain) of an asphalt mixture to the fatigue life:

where

Nf = number of cycles to failure, ~g = initial strain response, and a, b = regression coefficients.

This phenomenological model is simple to use because only the mixture response at the initial stage of fatigue testing needs to be measured. This model does not account for how damage evolves throughout the fatigue life, and hence it is only valid for a given set of loading conditions (Dijk and Visser 1997) and may need additional means to account for complex damage under realistic loading conditions (e.g., multi-level loading, rest periods, etc.).

Recently, a uniaxial constitutive model of nonaging asphalt-aggregate mixtures has been developed by the authors (Kim et al. 1997, Lee and Kim 1998a, 1998b). It employs the elastic-viscoelastic correspondence principle (Schapery 1984) and Schapery's work potential theory (Schapery 1990) to model the mechanical behavior of asphalt concrete under cyclic loading with rest periods. It was proven by the labora- tory experimental study that this model was able to predict hysteretic stress-strain behavior of asphalt concrete under different loading histories (monotonic and cyclic), varying rates of loading, different modes-of-loading (controlled-stress and control- led-strain), various stresslstrain amplitudes, and ran- dom rest periods.

Based on the constitutive model described above, Lee et al. (1999) developed a simplified fatigue per- formance prediction model as follows:

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EVALUATION OF MODIFIED ASPHALTS

CI 16: : Pseudo Stiffness (SR)

FIGURE I Pseudo Stiffness and Pseudo Strain Energy Density Function

where Nf,Tol,l = number of load repetitions to failure with multiple rest periods, Nf,w/oRP = number of load repetitions to failure without any rest, Nf . i = increase in Nf due to the ith rest period, and M = total number of rest periods.

To determine the explicit form of Nf equation in (2). the following damage evolution law applicable to viscoelastic media (Schapery 1990, Park et al. 1996) was used:

where S, = internal state variables (ISVs) representing any structural changes in the system, N = number of applied loads, 1.v: =maximum value of pseudo strain energy

density function in the N ' ~ cycle, a, = material constants, and

m = 1 , 2 , 3 ,..., M. Equation (3) is similar in form to a crack growth

law in fracture mechanics for viscoelastic materials. For a cyclic loading condition under the control-

led-strain mode, the maximum pseudo strain energy density function was proposed to be a function of the peak pseudo strain and an ISV as follows (Lee and Kim 1998b, Lee et al. 1999):

where I = initial pseudo stiffness, CI = C l o + Cll ( s ~ ) ~ ~ ~ = damage function,

R EN = peak pseudo strain in the N ' ~ cycle,

= uniaxial pseudo strain (5) Figure I shows a typical stress-pseudo strain curve

under a cyclic load. As shown in this figure. the

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154 HYUN-JONG LEE CI a/.

pseudo stiffness, denoted by sR, is defined as the slope of the stress-pseudo strain loop (i.e., n N / ; ). Thc pseudo stiffness decreases as cyclic loading con- tinucs due to fatigue damage in the system, which is rcprcscntcd by the function C I . The S t in Equation (4) is thc first ISV representing the fatigue damage growth in the system.

The NI. equation without rest periods may be obtnincd by integrating Equation (3) after the substi- tuting in Equations (4) and (5):

where

11 = slope of the creep compliance versus time curve in log-log scales,

C I I , C I 2 =damage coefficients to be determined from experiments, S I f = the value of damage parameter at failure. EO = tcnsilc strain amplitude, T = loading frequency, and I E * ~ =dynamic modulus.

The Nl.,v,uRP is a function of damage evolution ch:~rncteristics of the material ( C I I and CI2), viscoe- lastic nia~erial propenies (n and I E* I), fatigue test conditions ( E ~ and 0, and a failure criterion (St&

The major difference between the fatigue model in Equation (6) and the phenomenological fatigue model in Equation ( I ) is that all the coefficients in the fatigue model in Equation (6) are represented by engi- neering parameters except the coefficients C I 1 and CI2 . These regression coefficients are necessary to model the nonlinear behavior of the material as it is undergoing damage. Pavement engineers may be able to use the fatigue model in Equation (6) as a tool to sclcct or design more fatigue resistant asphalt mix- turcs by investigating ways of changing the parame-

ters in ways that improve the fatigue life of the mixture.

Similarly, Lee et al. (1999) proposed the following equation for determining the increase in fatigue life due to a rest period:

where

p3 = l+(l-C32)a3, C, = CZO + CZ1 ( s ~ ) ~ ~ ~ = increase in pseudo

stiffness during the rest period, C3!, C32 = damage coefficients after rest periods to be obtained from experiments,

a2 , a3 = material constants to be obtained from experiments,

SSe = a value of damage parameter S3 when sR = s:: 7 ~2 =pseudo stiffness immediately before the rest period, and S: =pseudo stiffness immediately after the rest period.

Detailed steps involved in ;he development of the fatigue models in Equations (6) and (7) can be found in Lee et al. (1999). Substituting Equations (6) and (7) into Equation (2) gives the final equation:

In this study, both phenomenological and viscoe- lastic continuum damage models are applied to the fatigue characterization of asphalt mixtures.

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EVALUATION OF MODIFIED ASPHALTS 155

Permanent Deformation Model 'The permanent deformation is composed of two

In the last two decades, permanent deformation (rut- ting) has been one of the major traffic associated fail- ure modes in asphalt concrete pavements. Especially with increases in axle load, load repetition, tire pres- sure, and asphalt concrete thickness, a methodology to predict permanent deformation and mitigate poten- tial safety problems associated with this distress is needed (Sousa et al. 1990).

The layer-strain predictive methodology and vis- coelastic procedure have commonly been used to pre- dict the amount of rutting in a multi-layered asphalt pavement system (Sousa et al. 1990). The layer-strain method consists of predicting rut depths using perma- nent deformation characteristics determined from lab- oratory tests together with an analysis procedure for the pavement structure using either linear or nonlinear elastic theory. The general principle of this method was first proposed by Barksdale (1972) and Romain (1972). One of the major advantages of the viscoelas- tic approach is that moving wheel loads can be con- sidered in conjunction with time-dependent material properties to define the state of stress and strain at particular points in the pavement structure. Material properties can be defined either in terms of models consisting of finite numbers of Maxwell andlor Kel- vin elements in various arrangements. Detailed infor- mation on the layer-strain and viscoelastic methods is well reviewed by Sousa et al. (1990).

Since rutt...