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Rice husk ash (RHA) has been considered as a suitable cement mineral additive. A key issue in the study of RHA blended cement is to evaluate the contribution of RHA to hydration kinetics. Although numerous methods have been given to assess the hydration degree of blended cement, there are still some controversial aspects, such as the effect of temperature is not well considered. Therefore, this study aims at developing a method for evaluating the hydration degree of blended cement which can consider the influence of temperature. The key of this method is to adopt a hydration kinetic model of nonevaporable water (NEW) to determine the ultimate NEW content of blended cement when it is completely hydrated. In the hydration kinetic model, the Arrhenius equation is introduced to reflect the relationship between hydration rate and temperature, and the inversion phenomenon between ultimate NEW and temperature is considered simultaneously. Furthermore, the hydration process of portland cement pastes containing RHA (two types of RHA: RHA-1 from the factory and RHA-2 by controlled combustion) is analyzed by this assessment method. It is found that the effect of temperature on RHA cement is similar to that of ordinary Portland cement (OPC), which has an inversion phenomenon between hydration degree and temperature. Under the same temperature, the hydration degree of RHA cements is lower than that of OPC, while the difference in hydration degree gradually decreases with the progress of hydration. Moreover, according to the fitting results of the model when m = 3, the addition of RHA could reduce the apparent activation energy (Ea) of blended cement, the Ea values of OPC, RHA-1 cement and RHA-2 cement are 37.64 kJ/mol, 35.39 kJ/mol and 34.18 kJ/mol, respectively.
Xue Luo; Xunli Jiang; Qi Chen; Zhiyi Huang. An assessment method of hydration degree of Rice husk ash blended cement considering temperature effect. Construction and Building Materials 2021, 304, 124534 .
AMA StyleXue Luo, Xunli Jiang, Qi Chen, Zhiyi Huang. An assessment method of hydration degree of Rice husk ash blended cement considering temperature effect. Construction and Building Materials. 2021; 304 ():124534.
Chicago/Turabian StyleXue Luo; Xunli Jiang; Qi Chen; Zhiyi Huang. 2021. "An assessment method of hydration degree of Rice husk ash blended cement considering temperature effect." Construction and Building Materials 304, no. : 124534.
Soft soils are usually treated to mitigate their engineering problems, such as excessive deformation, and stabilization is one of most popular treatments. Although there are many creep models to characterize the deformation behaviors of soil, there still exist demands for a balance between model accuracy and practical application. Therefore, this paper aims at developing a Mechanistic-Empirical creep model (MEC) for unsaturated soft and stabilized soils. The model considers the stress dependence and incorporates moisture sensitivity using matric suction and shear strength parameters. This formulation is intended to predict the soil creep deformation under arbitrary water content and arbitrary stress conditions. The results show that the MEC model is in good agreement with the experimental data with very high R-squared values. In addition, the model is compared with the other classical creep models for unsaturated soils. While the classical creep models require a different set of parameters when the water content is changed, the MEC model only needs one set of parameters for different stress levels and moisture conditions, which provides significant facilitation for implementation. Finally, a finite element simulation analysis of subgrade soil foundation is performed for different loading levels and moisture conditions. The MEC model is utilized to predict the creep behavior of subgrade soils. Under the same load and moisture level, the deformation of soft soil is largest, followed by lime soil and RHA–lime-stabilized soil, respectively.
Xunli Jiang; Zhiyi Huang; Xue Luo. An Improved Mechanistic-Empirical Creep Model for Unsaturated Soft and Stabilized Soils. Materials 2021, 14, 4146 .
AMA StyleXunli Jiang, Zhiyi Huang, Xue Luo. An Improved Mechanistic-Empirical Creep Model for Unsaturated Soft and Stabilized Soils. Materials. 2021; 14 (15):4146.
Chicago/Turabian StyleXunli Jiang; Zhiyi Huang; Xue Luo. 2021. "An Improved Mechanistic-Empirical Creep Model for Unsaturated Soft and Stabilized Soils." Materials 14, no. 15: 4146.
Fatigue cracking of viscoelastic asphalt composite materials is one of the major distresses in asphalt pavements. To quantify the weakening effect of the fatigue cracks on the mechanical properties of the viscoelastic asphalt composite materials, this study takes an asphalt-filler composite system as an example, and micromechanics models are proposed by combining Eshbely’s equivalent inclusion theory and Mori-Tanaka approach. Dynamic shear rheometer (DSR) tests are performed on the viscoelastic asphalt-filler composite systems with two volumetric contents of inclusion (10% and 27%) at different frequencies (0.1–100 Hz), temperatures (15℃, 20℃, 25℃) and strain levels (0.01%-0.1% for nondestructive DSR tests; 5%, 6%, 7% for destructive DSR tests). Results show that the predicted shear modulus results by a modified viscoelastic strengthening coefficient (VSC) model match with the test results at both low and high filler contents. Then a viscoelastic strengthening coefficient with fatigue cracks (VSC-f) model is proved being capable of accurately predicting the shear modulus for the viscoelastic asphalt-filler composite systems at different strain levels, temperatures, filler contents and damage levels. Both the VSC and the VSC-f model are derived to be dependent of loading frequency, temperature and filler content, but independent of strain level.
Hui Li; Xue Luo; Fuquan Ma; Yuqing Zhang. Micromechanics modeling of viscoelastic asphalt-filler composite system with and without fatigue cracks. Materials & Design 2021, 209, 109983 .
AMA StyleHui Li, Xue Luo, Fuquan Ma, Yuqing Zhang. Micromechanics modeling of viscoelastic asphalt-filler composite system with and without fatigue cracks. Materials & Design. 2021; 209 ():109983.
Chicago/Turabian StyleHui Li; Xue Luo; Fuquan Ma; Yuqing Zhang. 2021. "Micromechanics modeling of viscoelastic asphalt-filler composite system with and without fatigue cracks." Materials & Design 209, no. : 109983.
This study has investigated the impact of graphene oxide (GO) in enhancing the performance properties of an asphalt binder. The control asphalt binder (60/70 PEN) was blended with GO in contents of 0%, 0.5%, 1%, 1.5%, 2%, and 2.5%. The permanent deformation behavior of the modified asphalt binders was evaluated based on the zero shear viscosity (ZSV) parameter through a steady shear test approach. Superpave fatigue test and the linear amplitude sweep (LAS) method were used to evaluate the fatigue behavior of the binders. A bending beam rheometer (BBR) test was conducted to evaluate the low-temperature cracking behavior. Furthermore, the storage stability of the binders was investigated using a separation test. The results of the ZSV test showed that GO considerably enhanced the steady shear viscosity and ZSV value, showing a significant contribution of the GO to the deformation resistance; moreover, GO modification changed the asphalt binder’s behavior from Newtonian to shear-thinning flow. A notable improvement in fatigue life was observed with the addition of GO to the binder based on the LAS test results and Superpave fatigue parameter. The BBR test results revealed that compared to the control asphalt, the GO-modified binders showed lower creep stiffness (S) and higher creep rate (m-value), indicating increased cracking resistance at low temperatures. Finally, the GO-modified asphalt binders exhibited good storage stability under high temperatures.
Abbas Adnan; Chaofeng Lü; Xue Luo; Jinchang Wang. Impact of Graphene Oxide on Zero Shear Viscosity, Fatigue Life and Low-Temperature Properties of Asphalt Binder. Materials 2021, 14, 3073 .
AMA StyleAbbas Adnan, Chaofeng Lü, Xue Luo, Jinchang Wang. Impact of Graphene Oxide on Zero Shear Viscosity, Fatigue Life and Low-Temperature Properties of Asphalt Binder. Materials. 2021; 14 (11):3073.
Chicago/Turabian StyleAbbas Adnan; Chaofeng Lü; Xue Luo; Jinchang Wang. 2021. "Impact of Graphene Oxide on Zero Shear Viscosity, Fatigue Life and Low-Temperature Properties of Asphalt Binder." Materials 14, no. 11: 3073.
Construction and demolition (C&D) waste is generated for 100 billion tonnes per annum globally, which has caused underground water contamination and farmland occupation when disposing the C&D waste by landfilling. The C&D waste materials have been recycled and used as an alternative to virgin mineral aggregates in pavement construction. This study aims at proposing a convenient method to estimate resilient modulus of cement-treated C&D waste materials when used in pavement base layer based on material performance-related properties and using discrete element simulation tests. Two kinds of materials are investigated, they're blends of two C&D waste materials, crushed bricks (CB) and recycled concrete aggregate (RCA). Fundamental property experiments were carried out on the aggregates to evaluate the engineering performance. Unconfined compress strength (UCS) tests were conducted on cement-treated materials to analyze the effect of curing duration and cement content on UCS. The numerical resilient modulus (Mr) tests by the discrete element method (DEM) were conducted to evaluate the resilient performance of C&D waste. The simulation results were verified with the lab measurements. Test results showed that the test materials have a high water absorption and a low durability. The minimum cement content was determined as 5% to satisfy the strength requirement of 4 MPa according to the national standards. Mr increases with confining pressure. Performance-related properties (UCS, γd, E50) were proposed to build their correlations with k values of the resilient modulus model, which are formulated to predict the k values. The values of Mr predicted by the performance-relatedproperties were consistent to the DEM modeled ones.
Xue Luo; Ganggui Liu; Yao Zhang; Tao Meng; Liangtong Zhan. Estimation of resilient modulus of cement-treated construction and demolition waste with performance-related properties. Construction and Building Materials 2021, 283, 122107 .
AMA StyleXue Luo, Ganggui Liu, Yao Zhang, Tao Meng, Liangtong Zhan. Estimation of resilient modulus of cement-treated construction and demolition waste with performance-related properties. Construction and Building Materials. 2021; 283 ():122107.
Chicago/Turabian StyleXue Luo; Ganggui Liu; Yao Zhang; Tao Meng; Liangtong Zhan. 2021. "Estimation of resilient modulus of cement-treated construction and demolition waste with performance-related properties." Construction and Building Materials 283, no. : 122107.
This study aims to propose a kinetics-based model of fatigue crack growth rate coupling with temperature, strain level and damage degree for bituminous materials. The fatigue crack length is calculated by an energy-based mechanistic (EBM) approach, and kinetic parameters characterizing the fatigue crack growth rate are determined based on an Arrhenius equation. Results show that the logarithm of the fatigue crack growth rate is linear to the inverse of absolute temperature, and cracking activation energy is independent of strain level and damage degree. Besides, the proposed kinetics-based model can predict fatigue crack growth rate at arbitrary temperature, strain level and damage degree of bituminous materials.
Hui Li; Xue Luo; Yuqing Zhang. A kinetics-based model of fatigue crack growth rate in bituminous material. International Journal of Fatigue 2021, 148, 106185 .
AMA StyleHui Li, Xue Luo, Yuqing Zhang. A kinetics-based model of fatigue crack growth rate in bituminous material. International Journal of Fatigue. 2021; 148 ():106185.
Chicago/Turabian StyleHui Li; Xue Luo; Yuqing Zhang. 2021. "A kinetics-based model of fatigue crack growth rate in bituminous material." International Journal of Fatigue 148, no. : 106185.
An equivalent relationship between stationary dynamic load and moving vehicular load is of necessity and importance for the fact that pavement responses from nondestructive testing devices with high speeds are usually validated with responses from falling weight deflectometer (FWD), which applies stationary dynamic loads to pavements. Also, two-dimensional (2D) axisymmetric finite element (FE) models with statinary dynamic loads are still popular to represent pavements in service conditions for their less storage space and computational time compared with three-dimensional (3D) FE models. This study aims to provide a methodology using the FE model updating implemented with artificial intelligence algorithms to obtain equivalent stationary dynamic loads applied in 2D axisymmetric FE pavement models for moving vehicular loads applied in 3D FE pavement models. The 2D axisymmetric FE models can eventually provide similar results as 3D FE models but with higher efficiency. Besides, obtained equivalent relationship is independent of structural and material properties such as layer thickness and moduli. This finding significantly extends the application of this equivalent relationship. Furthermore, techniques applied in this study can be used as references for problems in pavement materials and structures such as the model updating, model equivalency, and model optimization.
Yong Deng; Yazhou Zhang; Xue Luo; Robert L. Lytton. Development of equivalent stationary dynamic loads for moving vehicular loads using artificial intelligence-based finite element model updating. Engineering with Computers 2021, 1 -20.
AMA StyleYong Deng, Yazhou Zhang, Xue Luo, Robert L. Lytton. Development of equivalent stationary dynamic loads for moving vehicular loads using artificial intelligence-based finite element model updating. Engineering with Computers. 2021; ():1-20.
Chicago/Turabian StyleYong Deng; Yazhou Zhang; Xue Luo; Robert L. Lytton. 2021. "Development of equivalent stationary dynamic loads for moving vehicular loads using artificial intelligence-based finite element model updating." Engineering with Computers , no. : 1-20.
Fatigue damage of engineering materials severely affects the serviceability of their structures. It is impracticable to accurately predict fatigue damage process of engineering materials due to the variability of material properties, microstructure heterogeneity and others. This study aims to track the entire fatigue damage process of viscoelastic materials by coupling the variability with the fatigue damage mechanism. A typical viscoelastic material, asphalt binder, widely used in pavement engineering is selected for investigation in this study. A pseudo J-integral Paris' law model and probability theory are combined to establish a stochastic fatigue damage model for viscoelastic materials. Results show that the damage density can be determined by the apparent shear modulus and true shear modulus. The damage evolution rate is a function of material parameters (Paris’ law coefficients), apparent shear modulus, apparent shear strain amplitude and apparent phase angle. Then, a cumulative distribution function of loading time (TCDF) and damage density exceedance probability (DDEP) are derived and experimentally verified. Next, the stochastic fatigue damage model is proposed, which can track the entire fatigue damage process for viscoelastic materials, and it depends on the damage density, material parameters and variability parameters. The variability of minor damage can be used to predict the variability of severe damage based on the stochastic fatigue damage model.
Hui Li; Xue Luo; Yuqing Zhang; Rongqiao Xu. Stochastic fatigue damage in viscoelastic materials using probabilistic pseudo J-integral Paris' law. Engineering Fracture Mechanics 2021, 245, 107566 .
AMA StyleHui Li, Xue Luo, Yuqing Zhang, Rongqiao Xu. Stochastic fatigue damage in viscoelastic materials using probabilistic pseudo J-integral Paris' law. Engineering Fracture Mechanics. 2021; 245 ():107566.
Chicago/Turabian StyleHui Li; Xue Luo; Yuqing Zhang; Rongqiao Xu. 2021. "Stochastic fatigue damage in viscoelastic materials using probabilistic pseudo J-integral Paris' law." Engineering Fracture Mechanics 245, no. : 107566.
This paper aims to provide a methodology in determining the deterioration conditions of flexible pavements using the Long‐Term Pavement Performance (LTPP) database and artificial intelligence (AI)‐based finite element (FE) model updating. A new term quantifying the effects of the aging and load repetitions on the modulus gradient of the asphalt layer was defined. The modulus gradient change was captured by a two‐step calibration process. The proposed method combines the laboratory and field tests on the characterizations of the material properties and structural behaviors. Furthermore, it considers the effects of the environmental and loading conditions on the pavement behaviors and the gap between the laboratory and field tests on the same material characterizations. In this paper, the equivalent frequency in the asphalt layer for typical falling weight deflectometer (FWD) load was determined using the AI‐based FE model updating as well. This paper extends the applications of the FE model updating in the pavement structures and discusses the performance of the modulus as an indicator of the pavement condition.
Yong Deng; Xue Luo; Yazhou Zhang; Shengxin Cai; Kai Huang; Xijun Shi; Robert L. Lytton. Determination of flexible pavement deterioration conditions using Long‐Term Pavement Performance database and artificial intelligence‐based finite element model updating. Structural Control and Health Monitoring 2020, 28, 1 .
AMA StyleYong Deng, Xue Luo, Yazhou Zhang, Shengxin Cai, Kai Huang, Xijun Shi, Robert L. Lytton. Determination of flexible pavement deterioration conditions using Long‐Term Pavement Performance database and artificial intelligence‐based finite element model updating. Structural Control and Health Monitoring. 2020; 28 (2):1.
Chicago/Turabian StyleYong Deng; Xue Luo; Yazhou Zhang; Shengxin Cai; Kai Huang; Xijun Shi; Robert L. Lytton. 2020. "Determination of flexible pavement deterioration conditions using Long‐Term Pavement Performance database and artificial intelligence‐based finite element model updating." Structural Control and Health Monitoring 28, no. 2: 1.
The aims of this study are to determine the complex Poisson’s ratio of asphalt mixtures based on linear viscoelastic theory and to evaluate the effect of the complex Poisson’s ratio on critical responses of asphalt pavements using finite element (FE) models. Direct tension tests were conducted on field core specimens, and horizontal and axial strains at the top and bottom of the field cores were recorded with loading time. The elastic–viscoelastic correspondence principle was utilized to compute the complex Poisson’s ratio including the magnitude and phase angle with loading frequency. It is shown that the magnitude and phase angle were time, temperature and aging dependent. To better illustrate the effect of the complex Poisson’s ratio on asphalt pavement responses, FE models with user-defined materials were developed to compute and compare pavement responses at critical locations with a constant Poisson’s ratio and a complex Poisson’s ratio. Besides, the effect of the aging time on the complex Poisson’s ratio was evaluated from pavement responses. The differences between these cases were highlighted, which indicated the importance of using the complex Poisson’s ratio in pavement design and performance evaluation.
Meng Ling; Yong Deng; Yao Zhang; Xue Luo; Robert L. Lytton. Evaluation of complex Poisson’s ratio of aged asphalt field cores using direct tension test and finite element simulation. Construction and Building Materials 2020, 261, 120329 .
AMA StyleMeng Ling, Yong Deng, Yao Zhang, Xue Luo, Robert L. Lytton. Evaluation of complex Poisson’s ratio of aged asphalt field cores using direct tension test and finite element simulation. Construction and Building Materials. 2020; 261 ():120329.
Chicago/Turabian StyleMeng Ling; Yong Deng; Yao Zhang; Xue Luo; Robert L. Lytton. 2020. "Evaluation of complex Poisson’s ratio of aged asphalt field cores using direct tension test and finite element simulation." Construction and Building Materials 261, no. : 120329.
With the development and application of highway-speed nondestructive testing (NDT) devices, a reliable method to evaluate the current level of deterioration of pavements from the measured results is necessary to provide comprehensive and timely maintenance and rehabilitation decisions for pavements. The objective of this study is to evaluate the deterioration conditions of flexible pavements from their deflection profiles under the moving loads. The deterioration is due primarily to the development and growth of microcracks in flexible pavement materials and is commonly called the “crack initiation” phase. This phase is characterized and represented by changes in the dynamic modulus and the phase angle. To simulate a flexible pavement under moving loads, a three-dimensional (3D) finite element (FE) model and its equivalent two-dimensional (2D) axisymmetric FE model are constructed using a commercial FE software and the technique of artificial intelligence (AI). The deflection profiles of the pavement model are analyzed and the time lag between the load and deflection peaks is used to define a new term named “lag angle” to represent the structural response of the flexible pavement under the moving loads. It is also found the lag angle is closely related to the degree of deterioration of the pavement, the speed of the moving load, the structural and material properties of the pavement, which reveals a promising application of the lag angle in the evaluation of flexible pavements using highway-speed NDT devices.
Yong Deng; Xue Luo; Yazhou Zhang; Robert L. Lytton. Evaluation of flexible pavement deterioration conditions using deflection profiles under moving loads. Transportation Geotechnics 2020, 26, 100434 .
AMA StyleYong Deng, Xue Luo, Yazhou Zhang, Robert L. Lytton. Evaluation of flexible pavement deterioration conditions using deflection profiles under moving loads. Transportation Geotechnics. 2020; 26 ():100434.
Chicago/Turabian StyleYong Deng; Xue Luo; Yazhou Zhang; Robert L. Lytton. 2020. "Evaluation of flexible pavement deterioration conditions using deflection profiles under moving loads." Transportation Geotechnics 26, no. : 100434.
The modulus gradient of asphalt concrete (AC) layers is an important feature of flexible pavements. The variation of the modulus with depth results from the synthetical effect of material properties, the service time of pavements, loading and environmental conditions. Since the modulus gradient directly affects critical responses and performance of pavements, the determination of the modulus gradient of AC layers is necessary for the evaluation, maintenance and rehabilitation of flexible pavements. This paper aims to propose a method to obtain layer moduli of flexible pavements at different loading frequencies, which include a power function describing the modulus gradient of AC layers. The method utilizes results from a typical nondestructive test in the field applying the falling weight deflectometer and techniques of the fast Fourier transform, finite element model updating, kriging model and artificial intelligence. The method is validated by comparing layer moduli obtained from the proposed method and other backcalculation softwares.
Yong Deng; Xue Luo; Yazhou Zhang; Robert L. Lytton. Determination of complex modulus gradients of flexible pavements using falling weight deflectometer and artificial intelligence. Materials and Structures 2020, 53, 1 -17.
AMA StyleYong Deng, Xue Luo, Yazhou Zhang, Robert L. Lytton. Determination of complex modulus gradients of flexible pavements using falling weight deflectometer and artificial intelligence. Materials and Structures. 2020; 53 (4):1-17.
Chicago/Turabian StyleYong Deng; Xue Luo; Yazhou Zhang; Robert L. Lytton. 2020. "Determination of complex modulus gradients of flexible pavements using falling weight deflectometer and artificial intelligence." Materials and Structures 53, no. 4: 1-17.
The article "A new short-term aging model for asphalt binders based on rheological activation energy", written by "Derun Zhang, Bjorn Birgisson, Xue Luo, Ibrahim Onifade", was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 24 June 2019 without open access.
Derun Zhang; Bjorn Birgisson; Xue Luo; Ibrahim Onifade. Correction to: A new short-term aging model for asphalt binders based on rheological activation energy. Materials and Structures 2020, 53, 1 -1.
AMA StyleDerun Zhang, Bjorn Birgisson, Xue Luo, Ibrahim Onifade. Correction to: A new short-term aging model for asphalt binders based on rheological activation energy. Materials and Structures. 2020; 53 (4):1-1.
Chicago/Turabian StyleDerun Zhang; Bjorn Birgisson; Xue Luo; Ibrahim Onifade. 2020. "Correction to: A new short-term aging model for asphalt binders based on rheological activation energy." Materials and Structures 53, no. 4: 1-1.
The cohesive cracking within asphalt binders has a significant influence on fatigue cracking resistance of asphalt pavements. To more clearly understand the mechanism and accurately characterize the process of the cohesive cracking occurring within the asphalt binder, an energy-based mechanistic (EBM) approach is applied to determine crack length and the pseudo J-integral is adopted to calculate crack growth rate in this study. First, a critical strain level separating nonlinear viscoelasticity from damage is determined based on a statistical analysis approach, and the result indicates that 0.7% is a critical nonlinear strain level for unmodified asphalt binder. Then, the crack length of asphalt binders is derived based on a torque equilibrium equation and two energy balance equations, as well as crack length is measured and verified based on an image processing method. It is found that contact regions in cracked area of the asphalt binder are formed when performing a strain-controlled rotational shear load. The contact regions have two stages, which first increase to the peak and then decrease with the increase of loading time. Next, the crack growth rate is formulated based on the pseudo J-integral Paris’ law equation considering nonlinear viscoelasticity. A linear relationship between the crack growth rate and the function of material properties (such as shear modulus, phase angle) in double logarithmic scales is proven and experimentally verified. In addition, the Paris’ law parameters (n and A) associated with crack growth rate are determined. Results show that they are independent on strain levels and temperatures. For example, six values of n of the unmodified asphalt binder are approximately equal to 1.10 at 5%, 6%, 7% strain levels when test temperatures are 15°C and 20°C. They are inherent material properties for the asphalt binder.
Hui Li; Xue Luo; Weizhuo Yan; Yuqing Zhang. Energy-based mechanistic approach for crack growth characterization of asphalt binder. Mechanics of Materials 2020, 148, 103462 .
AMA StyleHui Li, Xue Luo, Weizhuo Yan, Yuqing Zhang. Energy-based mechanistic approach for crack growth characterization of asphalt binder. Mechanics of Materials. 2020; 148 ():103462.
Chicago/Turabian StyleHui Li; Xue Luo; Weizhuo Yan; Yuqing Zhang. 2020. "Energy-based mechanistic approach for crack growth characterization of asphalt binder." Mechanics of Materials 148, no. : 103462.
The dynamic modulus (|Em*|) of asphalt mixtures is one of most fundamental mechanical parameters used in flexible pavement design, which has been extensively estimated through various predictive models. However, most of existing dynamic modulus predictive models does not fit well for the purpose of the Level 3 (the lowest input level) flexible pavement design in the current AASHTOWare Pavement ME Design due to the following major deficiencies: (1) lacking physical significance; (2) providing poor prediction accuracy; and (3) requiring laboratory testing to obtain key model parameters. To address these deficiencies, this paper is aimed to develop a new model on the basis of the law of mixtures. First, a large database is collected and revised for the new model development. Two exiting law of mixture models are then evaluated in terms of the mode prediction accuracy, and neither of them provided satisfactory prediction results. A new model is subsequently developed, which involves using a parallel form to represent the contribution of each of three phases (asphalt, aggregate and air void) to the |Em*| as well as utilizing a standard sigmoid function to characterize the mechanical response of asphalt mixture. Statistical analysis shows that the new model has comparable prediction performance with traditional Witczak models, but with significantly lower number of input variables and relatively higher model quality. Supplemental data collected from laboratory tests and independent literature sources finally validate that the new model has the capability to provide an accurate prediction of |Em*| with an R2 value up to 0.90. In these regards, the new model is believed to be a good candidate for the |Em*| prediction of asphalt mixtures for a reliable Level-3 flexible pavement design.
Derun Zhang; Bjorn Birgisson; Xue Luo. A new dynamic modulus predictive model for asphalt mixtures based on the law of mixtures. Construction and Building Materials 2020, 255, 119348 .
AMA StyleDerun Zhang, Bjorn Birgisson, Xue Luo. A new dynamic modulus predictive model for asphalt mixtures based on the law of mixtures. Construction and Building Materials. 2020; 255 ():119348.
Chicago/Turabian StyleDerun Zhang; Bjorn Birgisson; Xue Luo. 2020. "A new dynamic modulus predictive model for asphalt mixtures based on the law of mixtures." Construction and Building Materials 255, no. : 119348.
The recovery of asphalt mixtures during rest periods is a key factor that affects the performance and service life of asphalt pavements in addition to the loading period. However, much less attention has been paid to the unloading periods in terms of laboratory characterization and numerical modeling. Thus, this study is intended to develop a coupled mechanical and kinetic approach to accurately characterize and simulate the recovery phase of asphalt mixtures. For the unloading period, a kinetics-based recovery model is proposed, which consists of two periods (fast-rate period and constant-rate period) with the kinetic parameters like the recovery activation energy and pre-exponential factors. In addition, a generalized Maxwell model is proposed to characterize the change of the recovery modulus predicted by the kinetics-based recovery model, which would facilitate the implementation in the numerical simulation process. For the loading period, an improved constitutive model is developed for the damage process of asphalt mixtures based on the relation between the pseudo strain and damage density. The proposed models are then applied to laboratory tests and finite element modeling on different asphalt mixtures with two types of binders, three aging periods, two air void contents, and nondestructive and destructive loading conditions. The laboratory results show that the kinetic parameters like the recovery/healing activation energy are good indictors of recovery/healing capacity of asphalt mixtures. The numerical simulations demonstrate that the output responses match very well with the measured values under both the nondestructive and destructive loading conditions, which verify the accuracy of the proposed approaches.
Xue Luo; Fuquan Ma; Bjorn Birgisson; Zhiyi Huang. Coupled mechanical and kinetic modeling of recovery in asphalt mixtures. Construction and Building Materials 2020, 254, 118889 .
AMA StyleXue Luo, Fuquan Ma, Bjorn Birgisson, Zhiyi Huang. Coupled mechanical and kinetic modeling of recovery in asphalt mixtures. Construction and Building Materials. 2020; 254 ():118889.
Chicago/Turabian StyleXue Luo; Fuquan Ma; Bjorn Birgisson; Zhiyi Huang. 2020. "Coupled mechanical and kinetic modeling of recovery in asphalt mixtures." Construction and Building Materials 254, no. : 118889.
Permanent deformation is a long-term irrecoverable depression accumulated in the wheel path when the flexible pavement is subjected to heavy loads at high temperature, which can be simulated using the vertically loaded wheel test (VLWT) in the laboratory. The objective of this study is to develop a new approach to analyze the vertically loaded wheel test results based on the elastic-viscoelastic correspondence principle. The energy-based pseudo variables are proposed to perform rutting evaluation of asphalt mixtures in the VLWT. Four types of styrene-butadienestyrene modified asphalt mixtures were prepared to conduct the undamaged compressive dynamic modulus test at different temperatures. Then the master curves of dynamic modulus for these mixtures were converted to get the relaxation modulus. The innovative VLWT for four types of two-layer structure with different asphalt mixture combinations were performed to investigate the rutting development. After that, a new mechanical-empirical rutting prediction model was introduced to predict the rutting development for each layer in the two-layer structure. The energy-based pseudo variables including pseudo strain, pseudo strain rate and dissipated pseudo strain energy (DPSE) were introduced to correlate with the rutting resistance. The results show that the developed mechanical-empirical rutting prediction model is proficient in capturing the rutting development of a two-layer structure of asphalt mixtures measured by a vertically loaded wheel tester. The rutting contributions of the top and bottom layers can be separated using this model. Compared with the total strain, the pseudo strain which removes the viscoelastic effect, is more accurate to evaluate the permanent deformation in a cyclic loading condition. The DPSE increases with the increase of loading cycles and rut depth. Two typical stages with an inflection point can be observed from the test results which indicate that the faster to reach the inflection point, the better rutting performance will be achieved.
Yao Zhang; Xue Luo; Yong Deng; Shuguang Hou; Xijun Shi; Robert L. Lytton. Evaluation of rutting potential of flexible pavement structures using energy-based pseudo variables. Construction and Building Materials 2020, 247, 118391 .
AMA StyleYao Zhang, Xue Luo, Yong Deng, Shuguang Hou, Xijun Shi, Robert L. Lytton. Evaluation of rutting potential of flexible pavement structures using energy-based pseudo variables. Construction and Building Materials. 2020; 247 ():118391.
Chicago/Turabian StyleYao Zhang; Xue Luo; Yong Deng; Shuguang Hou; Xijun Shi; Robert L. Lytton. 2020. "Evaluation of rutting potential of flexible pavement structures using energy-based pseudo variables." Construction and Building Materials 247, no. : 118391.
The recovery property of asphalt binders plays an important role in the performance and service life of asphalt pavements. Since the internal stress is the driving force for the recovery of asphalt binders, the accurate measurement of the internal stress is full of significance. Based on this rationale, this paper aims to measure the internal stress of asphalt binders using a creep and step-loading recovery (CSR) test and characterizing the recovery behaviors by the internal stress. One base asphalt binder and one styrene–butadiene–styrene (SBS)-modified binder are selected in this study. The key elements of the CSR test are carefully designed and its accuracy is verified in three aspects, including the loading conditions, the effect of disturbance by step-loads, and accuracy of measured internal stress. Then, a kinetics-based recovery model is proposed to evaluate and predict the recovery properties of asphalt binders from its causal relationship. The constant-rate recovery activation energy indicates a major difference with nondestructive and destructive loading conditions, while the fast-rate recovery activation energy keeps almost constant regardless of the loading conditions. After that, the healing activation energy is calculated by using the kinetics-based recovery model and the results indicate that SBS modified asphalt binder shows better healing abilities than a base binder.
Fuquan Ma; Xue Luo; Zhiyi Huang; Jinchang Wang. Characterization of Recovery in Asphalt Binders. Materials 2020, 13, 920 .
AMA StyleFuquan Ma, Xue Luo, Zhiyi Huang, Jinchang Wang. Characterization of Recovery in Asphalt Binders. Materials. 2020; 13 (4):920.
Chicago/Turabian StyleFuquan Ma; Xue Luo; Zhiyi Huang; Jinchang Wang. 2020. "Characterization of Recovery in Asphalt Binders." Materials 13, no. 4: 920.
Promotion of healing of asphalt mixtures is significant to enhance the resiliency and extend the service life of asphalt pavements. Extensive laboratory measurements of effects of healing and field observations have proven its impact. Many approaches have been developed to explain and model healing of asphalt mixtures based on its mechanisms and/or mechanical features. However, due to the complexity caused by the co-existence of several coordinated rate processes during healing, there are still unclear aspects in terms of mechanisms and appropriate representation of each rate process. Target this issue, this study proposes to investigate healing of asphalt mixtures using kinetic and thermodynamic quantities and formulations, aiming at clarifying the relationships among the coordinated processes involved in healing and developing an approach to predict the rate of each process. Healing is found to contain two coordinated rate processes: free energy change and bond restoration. Healing rate is proportional to the rates of these two processes, and the healing activation energy is the product of the activation energy of the free energy change and that of the bond restoration. In order to calculate each activation energy and rate constant, the recoverable strain energy (RSE) and recoverable pseudo strain energy (RPSE) measured in the rest time of a creep and step-loading recovery (CSR) test are used. The RPSE in the intact material and the surface energy constitute the total free energy change for healing. A three-parameter model is proposed to simulate a rate process like the change of the RSE or free energy change with time, and a dimensionless logarithmic rate is defined to obtain a representative change rate. This representative rate is ideal to be used as the rate constant in the Arrhenius equation to compute the activation energy. The activation energies for viscoelastic recovery, healing, free energy change, and bond restoration are determined for two types of asphalt mixtures at unaged and aged states. The relations between different activation energies are clarified so as the relationships among different rate processes. Furthermore, the healing activation energy obtained from this kinetic approach is proven to be the same as that calculated using the damage density from a mechanistic approach. A method to generate a damage density-based healing curve at any rest time at any temperature using just energy measurements is proposed in this study.
Xue Luo; Bjorn Birgisson; Robert L. Lytton. Kinetics of healing of asphalt mixtures. Journal of Cleaner Production 2019, 252, 119790 .
AMA StyleXue Luo, Bjorn Birgisson, Robert L. Lytton. Kinetics of healing of asphalt mixtures. Journal of Cleaner Production. 2019; 252 ():119790.
Chicago/Turabian StyleXue Luo; Bjorn Birgisson; Robert L. Lytton. 2019. "Kinetics of healing of asphalt mixtures." Journal of Cleaner Production 252, no. : 119790.
With increased awareness of environmental protection, the output of traditional curing agents such as cement and lime is less and less, so it is urgent to develop new curing agents with high efficiency and environmental benefits. Thus, this study aims at investigating the application of rice husk ash (RHA) from agricultural waste to the soft soil stabilization. A series of tests are conducted to analyze the strength development process and soil–water characteristics of rice husk ash–lime (RHA–lime) stabilized soils. The results of the strength tests showed that by increasing the content of RHA, the unconfined compressive strength (UCS) and splitting strength of stabilized soils increased first and then decreased. The effective shear strength indexes of the three soil types (soft soil, lime-stabilized soil, and RHA–lime soil) are measured and compared. It is found that RHA can effectively improve the shear resistance and water resistance of stabilized soil. The results of methylene blue test demonstrated that RHA can also promote the reduction of the specific surface area and swelling potential energy of lime-stabilized soil. In addition, the influence of RHA on mineral composition and morphology change in stabilized soils is studied at the microscopic level. The X-ray diffraction tests and scanning electron microscope (SEM) tests showed that strength development and change of soil–water properties of RHA–lime stabilized soil are attributed to enhanced cohesion by cementation and pores filling with agglomerated mineral.
Xunli Jiang; Zhiyi Huang; Fuquan Ma; Xue Luo; Ma; Luo. Analysis of Strength Development and Soil–Water Characteristics of Rice Husk Ash–Lime Stabilized Soft Soil. Materials 2019, 12, 3873 .
AMA StyleXunli Jiang, Zhiyi Huang, Fuquan Ma, Xue Luo, Ma, Luo. Analysis of Strength Development and Soil–Water Characteristics of Rice Husk Ash–Lime Stabilized Soft Soil. Materials. 2019; 12 (23):3873.
Chicago/Turabian StyleXunli Jiang; Zhiyi Huang; Fuquan Ma; Xue Luo; Ma; Luo. 2019. "Analysis of Strength Development and Soil–Water Characteristics of Rice Husk Ash–Lime Stabilized Soft Soil." Materials 12, no. 23: 3873.