Uniaxial Compression Creep Tests Research Articles

Research on the mesoscopic viscoelastic property of semi-flexible pavement mixture based on discrete element simulation

Semi-flexible pavement (SFP) mixture is a relatively new pavement material that combines the characteristics of the flexibility of asphalt mixtures and the rigidity of cement concrete. In this research, the discrete element method was used to reveal the viscoelastic mechanical behavior mechanism of the SFP mixture at a mesoscopic scale. First, the influence of the matrix asphalt mixture air voids on the viscoelastic performance of the SFP mixture was studied through laboratory tests to clarify its basic macroscopic mechanical properties. The results showed that the SFP mixture combines good high and low temperature performances when the air void is 25%. Then, the discrete element simulation software PFC3D was applied to establish an SFP mixture model, and the simulation of the dynamic modulus test and uniaxial compression creep test was conducted to study the mesoscopic mechanical composition and force evolution. The results demonstrated that when subjected to dynamic loading, each constituent inside the SFP mixture is subjected to compressive forces, most of which are borne by the internal contact of aggregate-aggregate, while the tensile forces are mainly borne by the contacts of asphalt mortar-asphalt mortar, cement stone-cement stone, and aggregate-asphalt mortar. When subjected to a constant static loading, the value order of the contact force in the SFP mixture is: aggregate-aggregate > cement stone-cement stone > aggregate-asphalt mortar > asphalt mortar-cement stone > cement stone-aggregate > asphalt mortar-asphalt mortar. As the creep progresses, the contact force of aggregate-aggregate increases slightly; the contact forces of cement stone-cement stone, aggregate-asphalt mortar, and cement stone-aggregate decrease slightly; and the contact forces of asphalt mortar-asphalt mortar and asphalt mortar-cement stone decrease rapidly.

Multi-scale creep analysis of river sand and manufactured sand concrete considering the influence of ITZ

This paper investigated the multi-scale prediction of long-term creep in river sand (RS) concrete and manufactured sand (MS) concrete and analyzed the effect of the interfacial transition zone (ITZ) around the aggregate on the creep properties of concrete. Uniaxial compressive creep tests were conducted on the concrete for a duration of 360 d. The creep kinetic properties of the paste matrix and ITZ were obtained by microindentation test. The properties of ITZ were determined by the backscattered electron (BSE) image threshold segmentation technique and the Lu & Torquato model. Finally, the predicted concrete creep modulus was obtained through the calculation of creep homogenization, and the accuracy of multi-scale creep prediction when considering different ITZ cases was discussed. The results show that under the same water-binder ratio, the thickness of ITZ around MS was larger, the creep modulus was smaller and the volume fraction was larger compared with that of ITZ around RS. In the multi-scale homogenization calculation of the concrete long-term creep, the prediction accuracy of the computational model increased with the raised of the considered ITZ types. The prediction accuracy obtained when all ITZs were considered was improved by more than 46.3% compared to that when no ITZs were considered.

Modified Burgers model of creep behavior of grouting-reinforced body and its long-term effect on tunnel operation

Grouting has been widely employed to mitigate geohazards in underground projects (e.g., the tunnel). However, few studies have focused on the effects of the creep behavior of a grouting-reinforced body on the stability of tunnel operation. In this study, the curtain grouting-reinforced Nanshibi tunnel was adopted as an example to explore this issue. More specifically, uniaxial compressive creep tests were firstly performed to study the time-dependent behavior (i.e., the creep behavior) of the grouted specimen. Then, the improved nonlinear Burgers model was proposed to characterize the observed creep behavior of the grouted specimen. Finally, a numerical simulation of the tunnel operation post grouting was conducted using the newly-proposed nonlinear Burgers model. The following results were obtained: (1) The creep behavior of the grouted specimen under different loadings undergoes three stages: decaying creep, steady creep, and accelerated creep. The steady creep rate is attributed to the homogeneity of the grouting-reinforced body. (2) The nonlinear Burgers model can reasonably quantify the creep behavior of the grouting-reinforced body. (3) The creep behavior of the grouting circle of the tunnel has a significant influence on the tunnel deformation and thus the lining safety. More specifically, the tunnel deformation exhibits nonlinear growth and mainly occurs at the vault and inverted arch. Furthermore, owing to the shape of the lining structure, the arch spring is most vulnerable to cracking under the eccentric tension state. The improved creep model is proved to more accurately predict the structural deformation of a curtain grouting-reinforced tunnel. As such, it can help devise grouted-tunnel maintenance strategies for long-term safety.

A Core Damage Constitutive Model for the Time-Dependent Creep and Relaxation Behavior of Coal

The creep and stress relaxation behaviors of coal are common in coal mining. The unified constitutive model is suitable to describe and predict both the creep and relaxation evolution characteristics of rocks. The generalized Kelvin model is the core element for traditional and improved component models to reflect both the nonlinear creep and relaxation. In this paper, an improved core damage model, which could both reflect the creep and stress relaxation in relation to the damage evolution, was established based on a comparison of the traditional and improved component models, and the responding constitutive equations (creep and stress relaxation equation) at constant stress/strain were deduced. Then, the core damage model was validated to the uniaxial compressive multistage creep and stress relaxation test results of coal, showing that the model curves had great accordance with the experimental data. Moreover, the model comparisons on accuracy, parameter meaning, and popularization among the core damage model, hardening-damage model, and the fractional derivative model were further discussed. The results showed that the parameters in the core damage model had clear and brief physical significances. The core damage model was also popularized to depict the time-dependent behaviors of other rocks, showing great accuracy.

Three-dimensional finite element analysis for structural parameters of asphalt pavement: A combined laboratory and field accelerated testing approach

To solve the issues that material parameters measured under specific laboratory conditions are extremely different from the actual pavement, a method of structural parameters correction in semi-rigid base asphalt pavement combining numerical simulations, laboratory tests, and accelerated pavement testing (APT) was proposed. The dynamic modulus and the uniaxial static compression creep tests were conducted to explore the effect of temperature, size, and fatigue. Then, these factors were coupled to the modified Burgers model that can reflect the creep law of the whole process. A constitutive model reflecting the real parameters of the pavement was subsequently constructed with the ABAQUS user-defined material (UMAT) subroutine. Experimental results illustrated it was verified that the modified subroutine has good feasibility both in single-layer and multi-layer materials from the actual pavement. Furthermore, simulated results also showed excellent agreement with field-tested findings. Finally, the rutting deformation curves and the demarcation points of each stage were obtained, which could guide the rutting prediction and maintenance decision of semi-rigid asphalt pavement.

Laboratory Study and Simulation Analysis on Anticrack Properties of Open-Graded Friction Course Based on Creep Tests

Cracking is a common early disease of asphalt pavements. To evaluate the temperature shrinkage cracking resistance of an open-graded friction course (OGFC), the viscoelastic parameters of an OGFC mixture at different temperatures were obtained by uniaxial compression creep tests. According to the viscoelastic parameters, numerical models of the creep, relaxation, and temperature shrinkage cracking of an OGFC were established. Subsequently, the reliability of the numerical model was verified based on the creep test results and the extensive Maxwell model. The crack initiation temperature of the OGFC mixture at different cooling rates was analyzed by combining indirect tensile strength and temperature shrinkage stress. The results showed that the simulation results were close to the model results, and the average errors of the simulation results for creep compliance and relaxation modulus did not exceed 7.18% and 1.83%, respectively. The faster the cooling was, the greater the temperature shrinkage stress and the higher the crack initiation temperature were. The crack initiation temperature of the OGFC at a cooling rate of 20°C/h was about −3.5°C. This research provides a reference for quickly obtaining the crack initiation temperature of asphalt mixtures at different cooling rates.

Multiphase modeling of the effect of external loading on the shrinkage of concrete and its consequences for modeling tensile creep

Multiphase modeling is a powerful framework for the simulation of the early-age and long-term behavior of concrete. Nevertheless, state-of-the-art multiphase models do not capture the experimentally observed instantaneous change in internal relative humidity upon external loading, which also manifests in the lack of predicting load-induced shrinkage. The approach presented in this publication is a step to overcome this deficiency. It is based on a poromechanical multiphase model for coupled creep and shrinkage of concrete, which is enhanced by a strong hygro-mechanical coupling, introduced via a load-dependent desorption isotherm. The enhanced model is evaluated for sealed and drying uniaxial compressive and tensile creep tests. Instantaneous changes in internal relative humidity upon loading are recovered by the enhanced model. In compression, the influence on the mechanical response is small. In contrast, the representation of tensile creep is significantly improved by considering load-induced shrinkage.

High-precision molding simulation prediction of glass lens profile for a new lanthanide optical glass

Precision glass lens molding (PGLM) is a recently developed method for fabricating glass optical components with high precision in large volumes. Lanthanum optical glasses are extensively used as optical materials owing to their superior optical properties, such as high refractive index, low dispersion, and high transparency. However, the transformation temperature of currently available high refractive index glass is generally above 650 °C and poses a challenge in manufacturing ultra-hard molds, durable coatings, and high-temperature molding equipment using PGLM. In this study, a preparation method for obtaining high refractive index, low -melting -point lanthanide optical glass (B-ZLaT198) used in PGLM was developed to reduce the transformation temperature. The developed method also characterizes the glass refractive indices and thermal-mechanical properties. To achieve the high-precision prediction of a molding shape in a simulation, a viscoelastic constitutive model of glass was established based on a micro-deformation uniaxial compression creep test. Moreover, by solving the Tool-Narayanasway-Moynihan model parameters based on the specific heat capacity fitting of optical glass at different heating and cooling rates, the input parameters of the structural relaxation model (SRM) for simulation prediction of aspheric glass lens profile deviation in the annealing stage were obtained. Finally, the profile deviation of the aspheric lens was predicted using a finite element model simulation. The results showed that the simulation’s predicted profile of an aspheric lens using the SRM model was in good agreement with that of experimental molding profile. In addition, using the SRM provided a higher prediction accuracy than that of the thermal expansion model in the annealing stage. Adopting the SRM was necessary for the annealing simulations of molding pressing and also verified the accuracy of the proposed viscoelastic characterization method for calculating the thermomechanical parameters of optical glasses.

Experimental Study on the Mechanical and Permeability Properties of Lining Concrete Under Different Complex Stress Paths

A promising large-scale energy storage is underground compressed air energy storage (CAES) in lined rock caverns. To ensure the safety and stability of storage caverns because of the influence of periodic injection during production, it is crucial to understand the mechanical behavior of lining concrete under different complex stress paths. In this study, three types of uniaxial compressive fatigue test and uniaxial creep test were conducted on concrete. The following conclusions were obtained from the results. 1) The irreversible deformation after the interval was larger than that before the interval in the discontinuous multi-step cyclic loading (DMCL) test. 2) Loading velocity significantly influenced concrete fatigue, and the irreversible deformation in the cycle of low loading velocity was greater than that in the cycle of high loading velocity. 3) The residual strain increased with an increase in stress level. 4) The creep strain increased with an increase in stress level during the multi-step creep loading test; the fractional derivative results were more consistent with the experimental results. 5) The permeability of concrete increased rapidly under the influence of an external force when the stress level exceeded 0.73.

Nonlinear creep model of salt rock used for displacement prediction of salt cavern gas storage

To explore the creep response and unloading rebound effect of salt rock, uniaxial compression creep and unloading rebound tests are performed at different axial stresses on salt rock specimens. The test results indicate that the instantaneous strain generated by salt rock mainly contributes by unrecoverable instantaneous plastic strain under a higher axial stress, and the creep strain mainly consists of unrecoverable visco-plastic creep strain. The ratio of visco-plastic creep strain to the total creep strain gradually increases with increases in time and axial stress. A hardening viscous body and a damage viscous body are proposed to describe the hardening effect and damage effect of rock during the creep process. Subsequently, a new five-component nonlinear creep model is established by connecting the two viscous bodies with the conventional elastic body and Kelvin model in series. The creep and unloading rebound test data of salt rock are utilized to testify the reasonability of the nonlinear creep model. The results indicate that the theoretical curves of the nonlinear creep model exhibit good coherence to the test data in the creep and unloading stages. Based on the secondary development platform of the FLAC3D software, the nonlinear creep model is redeveloped to obtain the computer application program. Thus, the creep and unloading rebound test of salt rock is simulated using the secondary development program of the nonlinear creep model. In general, the results from the numerical simulation and creep and unloading rebound test of salt rock are in good agreement, and this proves the accuracy of the secondary development program of the nonlinear creep model. Finally, the computer application program of the model is utilized to predict the surrounding rock deformation of a salt cavern gas storage during operation.

Improved Maxwell Model Describing the Whole Creep Process of Salt Rock and its Programming

Based on the creep test results of salt rock, three stages of changes in the viscosity coefficient with time during the creep process of salt rock were delimited from the perspective of creep rate, namely, gradually increased stage, basically unchanged stage and gradually decreased stage. According to this variation, a nonlinear dashpot was proposed, and its viscosity coefficient was assumed as a function of creep time. Then, the dashpot in the Maxwell model was replaced by this nonlinear dashpot to establish an improved Maxwell model that can describe the whole creep process of rock. The rationality of the improved Maxwell model was verified based on the uniaxial compression creep test results of salt rock and the triaxial compression creep test results of coal. Comparisons of the theoretical curves of the model and test results show good agreement between them, and the model can describe the three stages of the whole creep process of rock with a unified expression, thereby overcoming the shortcomings of the traditional mechanical model that requires segmentation processing. Based on the secondary development platform of the FLAC[Formula: see text] software, the secondary development of the improved Maxwell model was achieved by using VC++ 6.0 development environment, and the computer application program of the model was obtained. Then, the secondary development program of the model was used to simulate the uniaxial compression creep test of salt rock and the triaxial compression creep test of coal. In general, the numerical simulation results are in good agreement with the test results, proving the correctness of the secondary development calculation program of the model.

Experimental study of creep Poisson ratio of hydraulic concrete under multi-age loading-unloading conditions

Elastic creep theory, which is widely used in concrete dam engineering, assumes that the elastic Poisson ratio and the creep Poisson ratio equal the effective creep Poisson ratio. However, differences in creep test conditions and stress state make this assumption controversial. To accurately clarify the Poisson effect of hydraulic concrete, uniaxial compression creep tests with four loading ages (3d, 14d, 28d, and 60d) and conventional triaxial compression creep tests with three loading ages (14d, 28d, and 60d) are conducted under unified test conditions. And high-precision creep data of transverse and longitudinal for multi-age loading and unloading are obtained. We then denoise the creep data by using a Savitzky-Golay filter. Furthermore, based on the denoised creep data, we calculate the Poisson ratio at each stage for uniaxial compression and conventional triaxial compression. Finally, we compare and analyze the Poisson ratio of each stage in different stress states. The results show that the creep tests have the same noise when conducted under the same test conditions, and the optimal denoising by the Savitzky-Golay filter is obtained with parameters W (window width) = 9 and N (polynomial order) = 6. Under different stress states, the elastic Poisson ratio, creep Poisson ratio and effective creep Poisson ratio are not equal to each other, and the elastic Poisson ratio is greater than the creep Poisson ratio. In addition, under the conventional triaxial stress state, the effective creep (creep recovery) Poisson ratio in each direction is different, which indicates that the creep (creep recovery) in each direction is dependent under multi-axial stress state.

Viscoelastic Damage Characteristics of Asphalt Mixtures Using Fractional Rheology.

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage; however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

A two-scale method to rapidly characterize the logarithmic basic creep of concrete by coupling microindentation and uniaxial compression creep test

A recent survey has showed the prediction of the long-term deflection of existing concrete bridges after several decades is a great challange in civil engineering. The crux is to predict the creep deflection of a concrete structure after several decades from laboratory tests carried out over few months. This work aims at combining microindentation tests and as short as possible Uniaxial Compression Creep Test (UCCT) to characterize the modulus C and the characteristic time τch of the compliance function of basic creep used in modern design codes.First, concrete samples made of cement paste, mortar and concrete with a water-to-cement ratio of 0.6 were cured and loaded in sealed condition at a age of 90 days under UCCT for a duration of 1 year. A convergence study showed that the duration of UCCT which is needed to accurately estimate the characteristic time τch and creep modulus C is about 30 days and 300 days, respectively. Then, the creep modulus C was measured by microindentation tests on the cement paste and homogenized at the scale of mortar and concrete by micromechanics. Finally, the compliance creep function obtained by the proposed two-scale method was compared to experimental results which are available in open literature and other ones of existing design models, such as the model code 2010 and the well-established B4 model. As main result, the proposed simplified method which combines short (2-month) UCCT and rapid microindentation tests showed to be practical and accurate to characterize the basic creep compliance function of concrete.

Creep Characteristics of Different Saturated States of Red Sandstone after Freeze-Thaw Cycles

To investigate the creep mechanical characteristics of rocks in different saturated states after freeze-thaw cycles, samples with different saturations (30%, 50%, 70%, 90%, and 100%) were selected for nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and uniaxial compression creep tests. The internal microscopic damage of the rock sample and mechanical characteristics under long-term loading are analyzed after the action of freeze-thaw cycles. The test results show that, as the saturation increases, the T2 spectrum distribution shifts to the right. The spectrum area gradually increases as the porosity increases. The critical saturation of freeze-thaw damage occurs when the saturation increases from 70% to 90%. It can be seen from the SEM image that the number of pores inside the rock samples gradually increases with increases in saturation, leading to the appearance of cracks. Under long-term loading, the saturation has a significant influence on the time-efficiency characteristics of sandstone freeze-thaw. As the saturation increases, the creep deformation gradually increases. After reaching 70%, the axial creep strain increases significantly. The rate of creep is accelerated, the creep failure stress is reduced, and the creep time under the last level of stress is significantly increased. A modified viscous-plastic body is connected in series to the basic Burgers model, the freeze-thaw-damage viscous element is introduced, and the creep parameters are fitted using test data. The results will provide a reference for long-term antifreeze design for rock engineering in cold areas.

Experimental Investigations on Creep Behavior of Coal under Combined Compression and Shear Loading

The creep behavior of rock has received much attention for analyzing the long-term response and stability of underground rock engineering structures. Numerous studies have been carried out on the creep properties of various rocks under pure compression conditions. However, little attention has been paid to the creep behavior of rocks in a combined compression-shear loading state. In this work, a novel combined compression and shear test (C-CAST) system was used to carry out inclined uniaxial compression tests and creep tests for various inclination angles (0°, 5°, 10°, and 15°). The results revealed that the peak strength of the coal decreased with the inclination angle of the specimen, which could provide the basis for setting up a creep test scheme. Multistage compression-shear creep tests were carried out on specimens with different inclination angles. Based on the analysis of the creep test data, the creep behavior of the coal in a combined compression-shear state was studied. It was found that the specimen inclination affected the time-dependent deformation, long-term strength (LTS), and time to failure. Compared with the specimen under pure compression, the inclination specimens tend to produce large shear strain with time, while they were more prone to shear failure. The reduction of the long-term strength was closely associated with the increase of the specimen inclination angle when the angle was more than 5°. Moreover, the ratio of the peak strength to the LTS was not affected by the specimen inclination, which is considered an inherent characteristic. We anticipate that the results obtained will assist in pillar design and long-term stability analysis.

Effects of moisture content and tillage methods on creep properties of paddy soil.

The rheological properties parameters of paddy soil affect the interaction between the tillage tools and soil, thus influencing the operation quality and power consumption. In order to study the effects of tillage methods and moisture content on the rheological properties parameters of paddy soil in the middle and lower reaches of the Yangtze River, uniaxial compression creep tests of paddy soils with four moisture contents under no tillage (moisture contents: 26.71%, 24.52%, 23.26%, 21.28%) and plough tillage (moisture contents: 26.77%, 25.55%, 23.40%, 20.56%) were carried out using a TMS-PRO texture analyzer. The creep properties curves obtained from the tests, and the rheological constitutive equation of paddy soil under compression was established by Burgers viscoelastic model. Respectively, the quantitative change rules of creep properties of paddy soil with different moisture contents under different tillage methods and the correlation between these parameters were explored. The results showed that the moisture content under the three-year plough tillage and no tillage methods had significant influence on the rheological properties parameters of paddy soil (P < 0.05). The instantaneous elastic modulus, delay elastic modulus, and viscosity coefficient of the two paddy soils (no tillage and plough tillage soils) decreased with the increase of moisture content. However, the variation rules of relaxation time and delay viscosity coefficient with moisture content differed between these two paddy soils. Specifically, the strain rate of the two paddy soils decreased as moisture content decreased, where the total strain combines elastic strain, viscous strain, and viscoelastic strain. The initial strain rate and steady strain rate of the plough tillage paddy soils were lower than that of the no tillage paddy soils. The established creep model equation could be used to obtain viscoelastic rheological parameters of paddy soil in a wide range. The fitting equations between rheological parameters and moisture content were introduced into Burgers model, and the coupling equations between creep deformation and moisture content and time were derived, which could be used to predict the creep properties and deformation behavior of paddy soil in a certain range of no tillage and ploughed field. Overall, this study has a certain theoretical significance for the development and improvement of paddy soil rheology theory, and can also provide theoretical basis and technical support for the research of agricultural machinery design optimization, field water, soil conservation, soil tillage and compaction related simulation analysis in the middle and lower reaches of the Yangtze River.

A novel nonlinear creep model based on damage characteristics of mudstone strength parameters.

Mudstone interlayer is a weak layer in rock engineering. When it is subjected to continuous stress higher than its damage threshold, due to the dislocation of particles in mudstone crystals and the expansion of cracks, mudstone strength is gradually damaged and deteriorated and the strain gradually increases, thus accelerating the phenomenon of creep damage. In order to describe the characteristics of the whole process of mudstone aging deformation, based on the damage evolution of strength parameters (cohesion and internal friction coefficient) with stress and time in mudstone creep tests, a novel damage nonlinear viscoelastoplastic body (D-NVPB) is proposed through improving traditional plastic element. D-NVPB describes the nonlinear characteristics of the accelerated creep stage of mudstone. With the element combination method, D-NVPB is connected with the Burgers model in series to form a new nonlinear damage creep model (D-NVEP model). The analysis results of creep characteristics theoretically verified the rationality of the model in describing the instantaneous elasticity, viscoelasticity, and nonlinear viscoplastic characteristics of the complete creep curve of mudstone. With the data obtained in the uniaxial compression creep test of mudstone under the action of a stress level of 14 MPa, based on the Levenberg-Marquardt nonlinear least squares method, the fitting calculation was performed through piecewise fitting and overall fitting. The correlation coefficient was 0.9909, which verified the applicability of the model. The obtained model parameters by the identification were used to predict the mudstone creep curve under the stress levels of 13 MPa and 15 MPa. The good prediction results further verified the feasibility of the model. Compared with the traditional creep model, the D-NVEP model can better describe the nonlinear characteristics of the accelerated creep stage and quantitatively display the strength damage evolution process of rock in the creep failure process.

Performance Deterioration of Asphalt Mixture under Chloride Salt Erosion

In order to ensure smooth traffic and driving safety, deicing salt or snow melting agents are usually adopted to solve the problem of traffic jams and prevent pavement surfaces from freezing. The objective of this present study is to investigate the performance deterioration evaluation of asphalt mixture under the chloride salt erosion environment. Five chloride salt solution concentrations were designed and the uniaxial static compression creep test, low-temperature IDT test, freeze-thaw splitting test, and freeze-thaw cycle test were carried out for asphalt mixtures (AC-16) soaked in chloride salt solution. Results showed that with the increase in chloride salt solution concentration, the high-temperature stability, low-temperature crack resistance, and water stability of the asphalt mixture decreases. Moreover, the high-temperature stability, low-temperature crack resistance, and water stability of the asphalt mixture show a decreasing trend under different chloride salt solution concentrations following the negative cubic polynomial function. Based on the viscoelastic analysis, chloride salt solution could reduce the ability of the asphalt mixture to resist instantaneous elastic deformation and permanent deformation, and this influence will become more obvious with the increase in chloride salt solution concentration. In addition, the salt freeze-thaw cycle test indicated that in the early stage of freeze-thaw cycles, the splitting tensile strength of the asphalt mixture decreases rapidly, then tends to be flat, and then decreases rapidly. This study explores the performance damage law of asphalt mixture under salt corrosion, and the analysis results of this study could provide some references for the chloride salt dosage in the snow melting project while spreading deicing salt.

A Nonlinear Fractional Viscoelastic-Plastic Creep Model of Asphalt Mixture.

The mechanical behavior of asphalt mixture under high stresses presents nonlinear viscoelasticity and permanent deformation. In this paper, a nonlinear fractional viscoelastic plastic (NFVEP) creep model for asphalt mixture is proposed based on the Nishihara model, with a Koeller spring-pot replacing the Newton dashpot. The NFVEP model considers the instantaneous elasticity, viscoelasticity with damage and time-hardening viscoplasticity with damage concurrently, and the viscoelastic response is modeled by fractional derivative viscoelasticity. To verify the model, uniaxial compressive creep tests under various stresses ranging from 0.4 MPa to 0.8 MPa were carried out at room temperature. The NFVEP model predictions are in good agreement with the experiments. The comparison with the modified Nishihara model and the Burgers model reveals the advantages of the NFVEP model. The results show that the NFVEP model, with the same set of parameters, can not only describe the primary and steady-state creep stages of asphalt mixture under low stress levels but also the whole creep process, including the tertiary creep stage, of asphalt mixture under high stress levels.