Deformation Of Asphalt Mixtures Research Articles

Analysis of skeleton contact stability of graded aggregates system and its effect on slip creep properties of asphalt mixture

Geometric characteristics are the essential properties of aggregates, which form the gradation skeleton through contact effect among aggregates and further affect the deformation characteristics of asphalt mixture. In this investigation, the skeleton contact stability of graded aggregate system was evaluated and the slip creep properties of asphalt mixture were analyzed from the geometric characteristics of aggregates. First, the skeleton stability index (SSI) was constructed with the geometric characteristics of aggregates based on the idea of variable weight, and the effectiveness of SSI in representing the skeleton contact stability was verified by the maximum slip force (Fm). Secondly, the interface slip creep test of asphalt mixtures were performed, a quantitative model with three-stage of creep deformation was put forward to calculate the deformation in each stage, and the migration creep rate (SM), steady-state creep rate (SS) and creep life (FT) were proposed to characterize the slip creep properties of asphalt mixture. Finally, the effect of skeleton contact stability of graded aggregate system on the slip creep properties of asphalt mixture was analyzed. The results indicate that SSI has a good correlation with Fm, which can effectively characterize the skeleton contact stability of graded aggregate system, and a larger SSImeans a bigger skeleton contact stability. According to the deformation mechanism, the deformation behavior of asphalt mixture was divided into instantaneous elasticity, migration creep, steady-state creep and creep failure stage. Among them, SMdetermines the deformation level of asphalt mixture, SSreflects the deformation potential of asphalt mixture, and FT embodies the creep length of asphalt mixture. In migration creep stage, the slippage of aggregate induces asphalt mortar to flow; while in steady-state creep stage, the flow of asphalt mortar drives the aggregate to slip. The aggregate slippage and asphalt mortar flow promote and superimpose each other, resulting in the deformation of asphalt mixture.

Developing a load-temperature master curve for the permanent deformation of asphalt mixtures by the power function model

The multiple repeated load test, consisting of 189 test conditions from different combinations of three test temperatures, three confining stresses, three loading frequencies and seven vertical stresses, was developed to obtain the permanent deformation parameters. Three asphalt mixtures with different asphalt binder types were designed to conduct this multiple repeated load test. A linear fitting process was applied to each increment to obtain the slopes of cumulative strain growth. A multiple linear regression method was utilized to analyse the effects of different test conditions on the permanent deformation characteristics of asphalt mixtures. A power function model was proposed to establish the load-temperature master-curve of the slope versus reduced vertical stress. Results show that neat asphalt mixtures have the largest slope distribution, followed by PG 70–22 mixtures and PG 76–22 mixtures. Based on the multiple linear regression methods, higher vertical stress, higher temperature, lower confining stress, and lower loading frequency could increase the slope of permanent deformation growth from strongly to weakly. Fitting parameters α and β from the power function model could be utilized to rank the rutting resistance of different asphalt mixtures. The shifted parameters were divided into temperature part, confining stress part, loading frequency part and vertical stress part. The slope of cumulative strain growth under varying test conditions could be successfully shifted to a power function model, which could be used to predict the rutting resistance of asphalt mixtures under a broad range of test conditions.

Investigating the creep response of asphalt mixtures under waveform loading

The objective of this study was to examine the effect of waveform loading, truck speed levels and varying load pulse duration on the permanent deformation of asphalt mixture. The effect of vehicle speed and axle configuration was converted to pulse period using the length of total space influence domain divided by speed of the vehicle. Same effect was reproduced in uniaxial repeated load permanent deformation test by computing the pulse width and pulse period to evaluate the response of asphalt mixtures. Test was conducted at a single stress level and two temperature levels. Open-graded and dense-graded asphalt mixtures were prepared using two crushing mechanisms (single-stage and two-stage crushed aggregates). The study revealed that pulse duration and axle type related to any waveform have a significant influence on the permanent deformation of the asphalt mixtures as pulse duration depends on the speed of a vehicle and its axle configuration. The two-stage crushed material performed better in the laboratory as compared to the single-stage crushed material, which is in line with the previous study. Statistical analysis revealed that artificial neural network (ANN) can better predict the permanent deformation in asphalt mixtures than other techniques. However, as the data become more complex, ANN’s ability to predict with more accuracy reduces.

High-temperature creep behavior characterization of asphalt mixture based on micromechanical modeling and virtual test

The high-temperature creep behavior of asphalt mixture was investigated based on micromechanical modeling and virtual test by using three-dimensional discrete element method (DEM). A user-defined micromechanical model of asphalt mixture was established after analyzing the irregular shape and gradation of coarse aggregates, the viscoelastic property of asphalt mastic, and the random distribution of air voids within the asphalt mixture. Virtual uniaxial static creep test at 60 °C was conducted by using Particle Flow Code in three dimensions (PFC3D) and was validated by laboratory test. Based on virtual creep test, the micromechanical characteristics between aggregates, within asphalt mastic, and between aggregate and asphalt mastic were analyzed for the asphalt mixture. It is proved that the virtual test based on the micromechanical model can efficiently predict the creep deformation of asphalt mixture. And the high-temperature behavior of asphalt mixture was characterized from micromechanical perspective.

Virtual Uniaxial Creep Testing Method of Asphalt Mixture

AbstractThis paper presents a virtual uniaxial creep testing method. Different gradations were selected, and the X-ray CT was used to scan the asphalt specimens non-destructively in order to predict the deformation of asphalt mixture and verify the feasibility of the proposed method. Moreover, the finely distributed information of asphalt mixture microstructure, including aggregates, sand mastic and air voids, were captured. The 3D virtual specimen reflecting the real microscale distribution of asphalt mixture was created according to the developed 3D reconstruction theory and algorithm. Considering the Burgers visco-elastic consecutive relations of sand mastic, the visco-elastic state of sand mastic was transformed to the Prony parameters identified by finite element by using the Boltzmann superposition principle and Laplace theory. Finally, the virtual uniaxial creep testing was conducted. Results show that the predicted deformations agree well with the testing results. The proposed virtual uniaxial cre...

Effect of Asphalt Mortar Composition on Dynamic Response of Asphalt Mixture

To investigate the effect of mortar composition on visco-elastic response of asphalt mixture, The Asphalt Mixture Performance Test (SPT) was conducted on several asphalt mixtures for different ratios of filler to asphalt (F/A) , fiber dosage and proportion of cement instead of mineral powder. The effect of F/A, fiber dosage and and proportion of cement replacement on visco-elastic mechanical parameters (dynamic modulus and phase angle) of asphalt mixtures are analyzed. The results indicate that the dynamic modulus of asphalt mixtures increases first and then decreases with the increases in F/A and fiber dosage. And the more significant differences in these dynamic moduli appear at the higher the load frequency. The asphalt mixture with the lowest F/A has the biggest phase angle, and the difference in the phase angles of those asphalt mixtures is not significant. The changes of phase angle have a close relationship with the load frequency. The resistance to permanent deformation of asphalt mixture can be greatly enhanced by adding fiber. The effect of cement instead of mineral powder on the viscoelastic property of asphalt mixture is relatively small, while the resistance to high-temperature deformation of asphalt mixture can be improved to some extent.

Modelling of permanent strain of asphalt concrete using the ESSO model

The objective of this paper is to present the work to improve the ESSO model used for the prediction of permanent deformation of asphalt mixtures. The ESSO model was first presented in the early 1970s and their formalism is based on intrinsic responses of asphalt mixture samples under cyclic compression tests subjected to critical environmental conditions (stresses, temperature and frequencies) in the context of permanent deformation. To simplify this model, we have integrated the time–temperature superposition principle to eliminate one constants of the ESSO model. With this modification, six experimental tests are now needed instead of nine. Finally, this article presents a new approach to define the ESSO constants. This approach proves to be more representative of the laboratory test used to characterise the ESSO parameters.

A New “Mix-confined” Repeated Load Test for Evaluating Permanent Deformation of Asphalt Mixture

Existing tests for evaluating the permanent deformation of an asphalt mixture have many problems, such as the fixed confining pressure for repeated load triaxial tests (RLTTs). The main objectives of this paper are to develop a new “mix-confined” test and to compare the accuracy and sensitivity of this test with those of RLTTs. A new mix-confined repeated load test (MCRLT) is developed to measure the permanent deformation of two types of test specimens, including field cores extracted from asphalt pavement and lab-mixed specimens. The accuracy and sensitivity of the MCRLT are compared with those of an RLTT. The results show that during the MCRLT the test specimen can provide some (but not enough) confining pressure itself (so-called mix-confined). MCRLTs have slightly higher accuracy and lower sensitivity than RLTTs. The MCRLT can be a good alternative to the RLTT for evaluating the permanent deformation of asphalt mixtures, especially when there is no RLTT equipment available.

Comparative Study of Different Form of Asphalt Mixture Viscoelastic Rheological Model

In this paper, based on the essential attribute of the asphalt mixture, the characteristics of the asphalt mixture creep deformation were analyzed. With the comparison of the theoretical and experimental results, the advantages and disadvantages of the common rheological models used as the reaction of asphalt mixture creep characteristics were studied. The characteristics of of the asphalt mixture deformation have been analyzed. For the accurate response of nonlinear viscous elasticity model of asphalt mixtures must be a reasonable combination of the characterization of deformation characteristics of various components, this paper reveals the rheological deformation of asphalt mixture of components and parts of correspondence with the proper models. Finally, the experimental data were given to verify the correctness of the proposed model.

Research on Permanent Deformation of Asphalt Mixture by Triaxial Repeated Load Test

AbstractTriaxial repeated load permanent deformation tests of AC13F, AC13C, AC16 and AC20 under interim haversine loading were conducted. The flow number was selected as an evaluation index to investigate the influences of asphalt mixture characteristic including gradation, asphalt content, air voids, stress and temperature on the high-temperature performance of asphalt mixture. It is indicated that (1) flow number of AC16 is the highest, then is that of AC13C, but the AC13F and AC20 have the smaller ones; (2) with asphalt content increases by 0.5%, the flow number decreases by 20%∼30%; (3) with air voids increases from 4% to 7%, the flow number also decreases by about 50%; (4) the flow number also decreases with smaller decrease range at the higher stress and temperature; and (5) the flow numbers of asphalt mixtures are very small at the extreme stress and temperature, and the difference among them is inconspicuous which could not be used to distinguish high-temperature performance of the asphalt mixture...

Permanent Deformation Model Based on Shear Properties of Asphalt Mixtures

A permanent deformation model of asphalt concrete based on shear properties is developed and calibrated. This model is extended and improved from previous work with the use of laboratory test results. Triaxial compressive strength and repeated-load permanent deformation (RLPD) tests on three types of asphalt mixtures are performed at various loads and temperatures to correlate the shear properties of asphalt mixtures with rutting performance. Test results indicate that the cohesion and friction angle of a given asphalt mixture decrease with increased temperature. Also, the results of RLPD tests indicate that loading and environmental conditions such as deviatoric stress, confining pressure, test temperature, and load frequency significantly affect the permanent deformation of asphalt mixtures and must be incorporated into the prediction model. Three versions of the permanent deformation model based on different input levels are proposed and verified by the test data. Then, the model is calibrated by an accelerated pavement testing data set conducted on a typical pavement structure at various temperatures. The proposed model can successfully predict the permanent deformation of various asphalt mixtures under a wide range of loading and temperature conditions without changing model coefficients.

Effects of Asphalt Mixture Properties on Permanent Deformation Response

The hot-mix asphalt (HMA) rutting prediction model in the Mechanistic-Empirical Pavement Design Guide (MEPDG) uses a relationship that includes the effects of mix characteristics only through the resilient strain, which in turn is a function of the dynamic modulus (|E*|) of the mix. However, increasing evidence suggests that the use of |E*| alone may be insufficient to characterize completely the permanent deformation behavior of HMA. In addition to effects already considered by the MEPDG model with |E*|, the effects of mix characteristics on permanent deformation are analyzed with the use of the results of repetitive axial permanent deformation tests from laboratory-compacted HMA specimens. Results of multiple linear regression analysis indicate that binder type, effective binder content, and air void content have significant effects on model parameters for permanent deformation. The potential effects of mix characteristics on these parameters are analyzed with the use of the MEPDG model and an HMA pavement section with four levels of compaction. Scenarios in which the mixture characteristics are incorporated solely by means of |E*| are compared with scenarios in which the effects of air void content and asphalt content are incorporated into the rutting prediction model by adjusting its parameters according to relationships established in the laboratory. Empirical laboratory evidence supports the hypotheses that, regardless of mixture properties, universal values for permanent deformation model parameters do not fully account for mixture-specific contributions to rutting and that other mix characteristics (e.g., air void content) may be needed to supplement |E*| for the appropriate characterization of the permanent deformation of asphalt mixtures.

A mechanical model for three-phase permanent deformation of asphalt mixture under repeated load

On basis of the Burgers model, a new model consisting of modified dashpot and Van Der Poel model was derived from rheological and viscoelastic theory. Subsequently, triaxial repeated load permanent deformation tests of AC16 asphalt mixtures were conducted to validate this new developed model. Parameters of new developed model were obtained by a nonlinear regression analysis of test data, and then permanent strains and flow number of each mixture were calculated. The experimental results prove that the new developed model can well describe three phases permanent deformation of asphalt mixture under repeated load and it can be used for pavement mechanical analysis and rutting prediction.

Analysis of Asphalt Pavement Rut Based on Elastic-viscoplastic Theory

The elastic-viscoplastic theory was applied to research the permanent deformation of asphalt mixture, and a creep model was adopted for its good agreement with actual result. ABAQUS, the finite element modeling technique, were employed to simulate and investi- gate rut of the asphalt pavements with flexible base, and then the results were validated according to the circular track test. It is indicated that, rut increases fast in the early stage, but slow in later stage; pavement rut consists chiefly of absolute rut, and lateral upheaval only ac- counts for 15% -30% ; deformation rate increases as the depth increases and achieves the largest value at the depth of 8 cm then it de- creases gradually; pavement absolute rut is composed primarily of rut of the layer within the depths of 4 cm and 20 cm, especially within the depths of 4 cm and 12 cm.In addition,pavement ruts were simulated under different loads,and the axle load conversion indices were obtained by the rut equivalent method.For the adopted structures,the index is 5.9.

Homogeneous test specimens from gyratory compaction

This paper presents a study on the production of homogeneous test specimens using gyratory compaction that was performed as part of a research that is currently being conducted at the Delft University of Technology on permanent deformation of asphalt mixtures. The main aim of this study was to establish suitable gyratory compactor protocols for preparation of homogeneous test specimens compacted to a reference density that was obtained using the Marshall mix design. The mixtures considered in this study included porous, stone mastic and dense asphalt concrete mixtures. The compaction homogeneity of the gyratory compacted specimens was investigated using coring methods and X-ray tomography. The study concluded that due to the non-homogeneous compaction within gyratory compacted specimens it was necessary to core test specimens from the inner part of gyratory compacted specimens and that it was not possible to use the number of gyrations as a compaction control parameter.

STUDY ON DEFORMATION CHARACTERISTICS OF ASPHALT MIXTURE WITH STEEL GRIDS EMBEDDED

The present paper deals with investigations conducted on deformation of asphalt mixture in road pavements. Since loads are constantly applied to pavements in a certain direction by passing cars, the wheel tracking tester was modified so that the wheel loads were applied in one direction only. It has been pointed out that deformations are more likely to occur under loads applied in a single direction. Burial of steel strips joined together in a grid in the asphalt mixture was proposed as a method of reducing the deformation. The test results indicate that the burial of steel grids is a most effective way of reducing the deformation.