2013 Session: 599

• Laboratory Validation of Healing-Based Fatigue Endurance Limit for Hot-Mix Asphalt
  Abstract: One of the main requirements of designing perpetual pavements is to determine the endurance limit of Hot Mix Asphalt (HMA). The endurance limit, as applied to HMA and flexible pavement design, is the strain or stress level below which the HMA would endure indefinite fatigue load repetitions and the pavement would not experience bottom-up fatigue cracking. The purpose of this study is to validate the endurance limit for HMA using laboratory beam fatigue tests. A rational procedure was developed to determine the endurance limit of HMA due to healing that occurs during the rest periods between loading cycles. Relating healing to endurance limit makes this procedure unique compared to previous research projects that investigated these concepts separately. An extensive laboratory testing program, including 468 beam fatigue tests, was conducted according to AASHTO T321-03 test procedure as a part of the NCHRP 9-44A project. Six factors that affect the fatigue response of HMA were evaluated: binder grade, binder content, air voids, test temperature, rest period and applied strain. The endurance limit was determined when no accumulated damage occurred indicating complete healing during the rest period after each load application. A threshold rest period of about 5 seconds for a load duration of 0.1 seconds was obtained beyond which no more healing is gained. HMA exhibits endurance limits ranging from 37 micro-strains to 246 micro-strains depending on mixture properties and environmental conditions. The results of this study can be used to design perpetual pavements that can sustain a large number of loads if traffic volumes and vehicle weights are controlled.
  Authors: Souliman, Mena I.; Zeiada, Waleed Abdelaziz; Mamlouk, Michael S.; Kaloush, Kamil E.
  Authors: Souliman, Mena I.; Zeiada, Waleed Abdelaziz; Mamlouk, Michael S.; Kaloush, Kamil E.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-0691
• Mechanistic Modeling of Fracture in Asphalt Mixtures Under Compressive Loading
  Abstract: When an asphalt mixture is subjected to a destructive compressive load, it experiences the primary, secondary and tertiary deformation stages. Studies in the literature focused on the plastic deformation in the primary and secondary stages, such as the prediction of flow number, which is the initiation of the tertiary stage. However, little effort has been reported on the mechanistic modeling of the damage that occurs in the tertiary stage. The objective of this study is to mechanistically characterize the damage in the tertiary stage. The preliminary study illustrated that the deformation during the tertiary flow was principally caused by the growth of cracks which was signaled by the increase of the phase angle. The strain caused by the crack growth is the viscofracture strain which can be obtained by performing strain decomposition in the destructive compressive test. The viscofracture strain is employed in this study to mechanistically characterize the time dependent fracture (viscofracture) of asphalt mixtures in compression. By using dissipated pseudo strain energy balance principle, damage density and true stress are determined and both increase with load cycles in the tertiary stage. The increased true stress yields extra viscoplastic strain, which is the reason why the permanent deformation is accelerated by the occurrence of the cracks. To characterize the evolution of the viscofracture, a pseudo J-integral Paris’ law in terms of damage density is proposed and the material constants in the Paris’ law are determined, which can be employed to predict the fracture of asphalt mixtures in compression.
  Authors: Zhang, Yuqing; Luo, Rong; Lytton, Robert Leonard
  Authors: Zhang, Yuqing; Luo, Rong; Lytton, Robert Leonard
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-1824
• Constitutive Modeling of Cyclic Viscoplastic Response of Asphalt Concrete
  Abstract: Rutting (i.e. permanent deformation) is the most important distress that asphalt concrete pavements are prone to at high temperatures. However, it is shown that the available classical viscoplastic theories are incapable of properly predicting the permanent deformation of asphalt concrete materials at high temperatures subjected to cyclic loading conditions. To remedy this issue, a physically-based viscoplastic hardening-relaxation model is proposed. This model considers the changes in the microstructure during the rest period. This evolution of the microstructure during the rest period causes the induced hardening stress to relax and recover which affects the viscoplastic properties of asphalt concrete before and after the rest period is applied. A memory surface is introduced as the general criterion for the evolution of the hardening-relaxation mechanism. The memory surface possesses a state variable memorizing the history of the viscoplastic deformation during the loading history. The proposed viscoplastic hardening-relaxation model is coupled to the Schapery’s viscoelastic model (VE) and classical Perzyna’s viscoplastic model (VP) and is validated against an extensive experimental data including repeated creep-recovery tests at different stress levels, confinements, loading times, and rest periods. It is shown that the proposed model reasonably predicts the cyclic viscoplastic response of asphalt concrete materials at high temperatures.
  Authors: Darabi, Masoud K.; Abu Al-Rub, Rashid K.; Masad, Eyad A.; Little, Dallas N.
  Authors: Darabi, Masoud K.; Abu Al-Rub, Rashid K.; Masad, Eyad A.; Little, Dallas N.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-1839
• Development of a Calibration Testing Protocol for the Permanent Deformation Model of Asphalt Concrete
  Abstract: Recent permanent deformation modeling research at North Carolina State University has resulted in the so-called shift model, which is capable of expressing the permanent strain growth of asphalt concrete as a function of deviatoric stress, load time, and temperature, based on the time-temperature superposition and time-stress superposition principles. This paper presents an efficient calibration test protocol for the shift model, as well as verification of the model. The proposed test protocol is comprised of triaxial stress sweep (TSS) tests and a reference test. The TSS test is suggested to reduce the number of tests required by applying three deviatoric stresses within one test. Each TSS test is performed at three temperatures: high (TH), intermediate (TI) and low (TL). The reference test is a triaxial repeated load permanent deformation (TRLPD) test conducted at TH only. The shift model is calibrated for the polymer-modified dense-graded NY9.5B mix, and the calibrated model is applied successfully to predict strain growth for the composite tests at the three study temperatures and for random load tests at TH. The calibration testing procedure is optimized for the asphalt mixture performance tester (AMPT). The TSS tests take approximately 2.9 hours at TH and 1.5 hours at TI and TL. Thus, the proposed test protocol requires about a day to complete one set of calibration tests. Within two to three days of testing, depending on the number of replicates, the calibrated shift model is capable of predicting permanent strain growth for different temperatures, load times, and deviatoric stresses.
  Authors: Choi, Yeong-Tae; Kim, Y. Richard
  Authors: Choi, Yeong-Tae; Kim, Y. Richard
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-2555
• Characterization of Hot-Mix Asphalt Permanent Deformation: Flow Number Test and Fn Index Concept
  Abstract: Permanent deformation (PD), or rutting, is one of the common distresses occurring in hot-mix asphalt (HMA) pavements. As part of the HMA mix- and structural-design processes to optimize field performance, various laboratory tests, including the Hamburg wheel tracking test (HWTT) and flow number (FN), have been developed to characterize the HMA mix rutting resistance. With this background, this study was conducted to explore the potential of routinely using the FN test to characterize the PD response of different types of Texas HMA mixes as a supplement to the HWTT. Towards this goal, a new PD parameter¡ªthe FN Index¡ªwas developed to differentiate and screen the HMA mixes. The research methodology incorporated a two-phase approach, namely: (1) laboratory testing and (2) field performance monitoring of selected HMA mixes under conventional traffic loading on in-service highways. Overall, the findings indicated that the FN Index, computed from the FN test data, has ability to statistically differentiate the HMA mixes evaluated as well as promising potential to supplement the HWTT for routine HMA mix-design and screening. In addition, the FN test method has a practically reasonable test time (about 3 hours per specimen) and is cost-effective. However, the inability to readily test field cores and the need for field validation with long-term performance data remain some of the key challenges to be addressed with the FN test.
  Authors: Walubita, Lubinda F.; Zhang, Jun; Haggerty, Brett; Leidy, Joe; Alvarez, Allex E.; Hu, Xiaodi; Scullion, Tom
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-1541
• X-Ray CT-Based Three-Dimensional Microstructural Modeling of Asphalt Concrete
  Abstract: This paper presents a three-dimensional (3D) microstructural computational modeling framework based on X-ray CT images to predict the thermo-mechanical response of asphalt concrete. 3D microstructures for dense-graded asphalt concrete (DSG) and stone matrix asphalt (SMA) are generated and contain two phases: aggregate and matrix. The aggregate phase is considered as an elastic material and the matrix phase is modeled as a thermo-viscoelastic, thermo-viscoplastic, and thermo-damage material. The reconstructed 3D microstructures are used in simulating uniaxial and repeated creep recovery tests to obtain stress-strain response and damage propagation, and to investigate the effect of strain rate, temperature, and loading type. Consequently, the behavior of two types of asphalt concrete (DSG and SMA) are investigated and compared. The presented results show that the proposed framework is capable to effectively predict the overall thermal mechanical response of asphalt concrete and can be useful to compare the behavior of different types of asphalt concrete. Therefore, the X-ray based microstructural modeling framework can be used to understand how the constituents in microscopic level of asphalt concrete affect the behavior in macroscopic level of asphalt concrete. Moreover, guidelines for design of asphalt concrete to have better performance can be provided by such proposed framework.
  Authors: You, Taesun; Abu Al-Rub, Rashid K.; Masad, Eyad A.; Little, Dallas N.
  Authors: You, Taesun; Abu Al-Rub, Rashid K.; Masad, Eyad A.; Little, Dallas N.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-3013
• Modeling Water Vapor Diffusion in Pavement and Its Influence on Fatigue Crack Growth of Fine Aggregate Mixture
  Abstract: This paper describes two key objectives: the first objective is to develop a method of predicting and quantifying the amount of water that can enter into a pavement system by vapor transport; the second objective is to identify to which extent the fatigue crack growth of pavement would result from such moisture accumulation. To fulfill these two objectives, a diffusion model was first established to illustrate the wetting process of the surface asphalt layer due to the vapor migration from subgrade soil into the upper layer. Secondly, in order to quantify the degree of moisture damage induced by water vapor diffusion, fine aggregate mixture (FAM) specimens were fabricated and conditioned at different levels of relative humidity (RH) in closed vacuum desiccators that allows little temperature fluctuation. Moreover, the moisture conditioned specimens were tested using a newly developed repeated direct tension (RDT) test method to evaluate the fatigue crack growth. The RDT test greatly reduced the stress state complexity within the specimens by evenly distributing stress over the cross section area of the cylindrical specimen. Compared to the previous torsional test, the newly proposed test protocol was more efficient in characterizing the moisture susceptibility of the asphalt mixture. A major finding in this paper is that the higher level of RH in as asphalt surface layer will induce significantly higher crack growth rates.
  Authors: tong, yunwei; Luo, Rong; Lytton, Robert Leonard
  Authors: tong, yunwei; Luo, Rong; Lytton, Robert Leonard
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-3102
• Endurance Limit for Hot-Mix Asphalt Based on Healing-Damage Balance Criterion Using Viscoelastic Continuum Damage Analysis
  Abstract: Fatigue endurance limit (FEL) is a key parameter for designing perpetual pavements to mitigate bottom-up fatigue cracking. This study was conducted as part of the National Cooperative Highway Research Program (NCHRP) Project 9-44A to develop a framework and mathematical methodology to determine the FEL using the uniaxial fatigue test. In this unique procedure, the FEL is defined as the allowable tensile strains at which a balance takes place between the fatigue damage during loading, and the healing during the rest periods between loading pulses. The viscoelastic continuum damage model was used to isolate time dependent damage and healing in hot mix asphalt from that due to fatigue. The laboratory testing program consisted of dynamic modulus testing to estimate the viscoelastic properties of the asphalt mixtures, and uniaxial fatigue test experiment conducted with and without rest periods. Five factors that affect the fatigue and healing behavior of asphalt mixtures were evaluated: asphalt content, air voids, temperature, rest period and tensile strain. Based on the test results, a Pseudo Stiffness Ratio (PSR) regression model was developed that is a function of the five factors and the number of loading cycles. The FEL was defined when PSR is equal to 1.0 (net damage is equal to zero). The determined FEL values were rational compared to historical literature ranges. The results from the sensitivity analysis showed rational relationships between the FEL and investigated factors.
  Authors: Zeiada, Waleed Abdelaziz; Souliman, Mena I.; Kaloush, Kamil E.; Mamlouk, Michael S.
  Authors: Zeiada, Waleed Abdelaziz; Souliman, Mena I.; Kaloush, Kamil E.; Mamlouk, Michael S.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-4507
• Approach for Quantifying Effect of Binder Oxidative Aging on Viscoelastic Properties of Asphalt Mixtures
  Abstract: Due to the noted influence of oxidative aging on the mixture properties and pavement performance, it is becoming imperative to have a more complete understanding of the influence of asphalt binder aging on the viscoelastic behavior of asphalt mixtures. This study proposes a new approach to correlate the oxidative aging of asphalt binder in terms of carbonyl functional groups to the viscoelastic behavior of asphalt mixtures in terms of a continuous relaxation spectrum. The asphalt mixture complex modulus, E*, and the carbonyl area, CA, for the recovered asphalt binder were measured for mixtures subjected to varying durations of long-term aging in the laboratory. The continuous relaxation spectrum was obtained analytically from the 2S2P1D model of complex modulus of asphalt mixture through the inverse Fourier-Laplace transform approach. A consistent horizontal shift in the continuous relaxation spectrum was observed for all mixtures with the increase in aging duration. However, the shape and the amount of shifting of the spectra were mixture dependent. In particular, mixtures with higher asphalt binder absorption exhibited the largest shift in the continuous spectra for both unmodified and polymer-modified asphalt mixtures. Good correlations were observed between the carbonyl in asphalt binder and the continuous relaxation spectrum parameters of the asphalt mixture. Such relationships should permit the incorporation of long-term oxidative aging directly into the constitutive equation utilized in pavement response analyses.
  Authors: Alavi, Mohammad Zia; Hajj, Elie Y; Morian, Nathan
  Authors: Alavi, Mohammad Zia; Hajj, Elie Y; Morian, Nathan
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-4560
• Mechanistic-Based Approach to Evaluate Rutting Susceptibility of Hot-Mix Asphalt Mixtures Using Dynamic Triaxial Testing
  Abstract: The performance of an asphalt pavement is significantly impacted by the properties of the asphalt mixture, pavement structure, and the imposed environmental and traffic loading conditions. In particular, hot mix asphalt (HMA) mixtures are believed to have a critical combination of temperature and traffic loading rate which will result in excessive permanent deformation. This study presents a new approach to assess the rutting susceptibility of HMA mixtures under a given set of traffic loads and environmental conditions. The approach consists of evaluating asphalt mixtures using the repeated load triaxial (RLT) test at field representative testing conditions to determine the critical temperature of the HMA beyond which the mix becomes unstable. An HMA was considered appropriate for a specific project location if the determined critical temperature was greater than the effective asphalt pavement temperature for rutting determined using the Mechanistic-Empirical Pavement Design Guide (MEPDG) software. Predictive equations that account for the actual project characteristics such as climate conditions, material characteristics, operational speed, and traffic loading were developed in this study to estimate the effective asphalt pavement temperature. Nine HMA mixtures, each of which were associated with a specific project that has performed well in rutting, were characterized and analyzed for rutting behavior. The critical temperature for each HMA was obtained using RLT results and actual field performance. Flow number criteria as a function of traffic level were also developed for the HMA mixtures. The proposed approach was validated using three additional mixtures from Nevada and two mixtures from the WesTrack accelerated test facility. Good agreement between laboratory results and field performance was achieved.
  Authors: Ulloa Calderon, Alvaro Esteban; Hajj, Elie Y; Sebaaly, Peter E.
  Authors: Ulloa Calderon, Alvaro Esteban; Hajj, Elie Y; Sebaaly, Peter E.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-4599
• Effect of Confinement Pressure on the Nonlinear-Viscoelastic Response of Asphalt Concrete at High Temperatures
  Abstract: Asphalt concrete materials exhibit the nonlinear viscoelastic responses at high stress/strain levels. The traffic loading induces multi-axial stress states within the asphalt concrete pavement structure. Therefore, it is imperative to characterize the nonlinear viscoelastic responses of asphalt concrete under the realistic stress states since these nonlinearities significantly affect the rutting and fatigue damage performance of pavements. Schapery¡¯s (1) nonlinear viscoelastic model has been used extensively by several researchers to characterize the nonlinearity of asphalt concrete materials. However, the available methods for characterizing the viscoelastic nonlinearity are mostly based on the simple uniaxial creep-recovery tests.In this paper, the nonlinear viscoelastic properties of asphalt concrete materials are characterized considering the effects of confinement pressure on the variation of the nonlinear parameters. Dynamic modulus test is used to obtain the linear viscoelastic properties and the time-temperature shift factors. Cyclic creep-recovery tests are performed at high temperature (55¢ªC) and at different confinement levels to characterize the nonlinear viscoelastic responses. The effects of confinement levels and the triaxiality ratio on the variation of the nonlinear viscoelastic parameters are investigated. The analyses show that the confinement pressure and the triaxiality ratio have substantial effects on the nonlinear strain response of the asphalt concrete. The significance of these nonlinear parameters on the complex response of asphalt concrete subjected to different loading conditions is discussed.
  Authors: Rahmani, Eisa; Abu Al-Rub, Rashid K.; Darabi, Masoud K.; Kassem, Emad; Masad, Eyad A.; Little, Dallas N.
  Authors: Rahmani, Eisa; Abu Al-Rub, Rashid K.; Darabi, Masoud K.; Kassem, Emad; Masad, Eyad A.; Little, Dallas N.
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-4735
• Permanent Deformation Charcterization of Asphalt Mixtures Using Incremental Repeated Load Testing
  Abstract: Currently, flow number (FN) test is being used for measuring permanent deformation resistance of asphalt mixtures. The provisional AASHTO TP 79-10 test method specifies the requirements of the FN test; however, there are undefined levels of test parameters, such as temperature, axial stress, and confinement, which have not been addressed. Furthermore, flow number criteria that can reliably discriminate between various mixtures have not been established. In addition, as the asphalt industry continues to develop more sophisticated mixtures, a single FN value is not adequate to capture the true complexity of the asphalt mixtures. These and other shortcomings of the FN test reduce its effectiveness for evaluating high temperature performance of asphalt mixtures. A new high temperature test for evaluation of rutting susceptibility of asphalt mixtures is being proposed. The new test referred to as Incremental Repeated Load Permanent Deformation Test is conducted at one temperature and multiple stresses in four increments, whereas only takes 33 minutes to complete. The property of the test is the strain per cycle at the end of each test increment (minimum strain rate= MSR). A master curve is developed by plotting the MSR values versus a combined temperature-stress parameter. The MSR master curve characterizes the high temperature response of asphalt mixtures at any stress and temperature. The MSR master curve has both laboratory and field applications. The laboratory applications are to evaluate mixture design and to rank various mixtures. The laboratory applications are to predict rut depth and to estimate allowable traffic levels.
  Authors: Azari, Haleh; Mohseni, Alaeddin
  Authors: Azari, Haleh; Mohseni, Alaeddin
  Year: 2013
  Document Type: Paper
  Subject: Materials
  Session: 599
  Paper Number: 13-5160
• Mechanistic Modeling of Fracture in Asphalt Mixtures Under Compressive Loading
  Authors: Zhang, Yuqing
  Authors: Zhang, Yuqing
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-1824
• Endurance Limit for Hot-Mix Asphalt Based on Healing-Damage Balance Criterion Using Viscoelastic Continuum Damage Analysis
  Authors: Zeiada, Waleed
  Authors: Zeiada, Waleed
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-4507
• Mechanistic-Based Approach to Evaluate Rutting Susceptibility of Hot-Mix Asphalt Mixtures Using Dynamic Triaxial Testing
  Authors: Hajj, Elie
  Authors: Hajj, Elie
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-4599
• Approach for Quantifying Effect of Binder Oxidative Aging on Viscoelastic Properties of Asphalt Mixtures
  Authors: Alavi, Mohammad Zia
  Authors: Alavi, Mohammad Zia
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-4560
• Laboratory Validation of Healing-Based Fatigue Endurance Limit for Hot-Mix Asphalt
  Authors: Souliman, Mena
  Authors: Souliman, Mena
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-0691
• Approach for Quantifying Effect of Binder Oxidative Aging on Viscoelastic Properties of Asphalt Mixtures
  Authors: Hajj, Elie
  Authors: Hajj, Elie
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-4560
• Modeling Water Vapor Diffusion in Pavement and Its Influence on Fatigue Crack Growth of Fine Aggregate Mixture
  Authors: tong, yunwei
  Authors: tong, yunwei
  Year: 2013
  Document Type: Presentation; Poster
  Subject: Materials
  Session: 599
  Paper Number: 13-3102