Response Of Asphalt Pavement Research Articles

Application of semi-analytical finite element method to analyze asphalt pavement response under heavy traffic loads

Abstract Accurate assessment of the impact of heavy traffic loads on asphalt pavements requires a computational model which is able to calculate the response of the pavement fast and precisely. Currently the most finite element analysis programs based on traditional methods have various limitations. A specific program SAFEM was developed based on a semi-analytical finite element method to overcome the problems. It is a three-dimensional FE program that requires only a two-dimensional mesh by incorporating the semi-analytical method using Fourier series in the third dimension. The computational accuracy and efficiency of the program was verified by analytical verification previously. The experimental verification is carried out in this paper and the results show that the SAFEM is able to predict the mechanical responses of the asphalt pavement. Using the program SAFEM, the impact of heavy traffic loads was analyzed in terms of stress and strain distribution, surface deflection and fatigue life. The results indicate that if the asphalt pavement is subjected to the heavy traffic load more, the thicknesses and stiffness of the pavement structural layers should be increased adequately in order to support the surface deflection. The compressive stress in asphalt binder course is relatively large and increases more significantly compared with that in the other asphalt layers when the axle load becomes larger. With comparison of the predicted fatigue life, the increase of the axle load will lead to the destruction of the asphalt pavement extremely easily.

Effects of Material Cross-anisotropy on the Mechanical Responses of Asphalt Pavements

Granular road materials have been experimentally demonstrated to be cross-anisotropic. This paper explores the mechanical behavior of asphalt pavements with cross-anisotropic unbound aggregate layers (UAB)/subgrade through three-dimensional (3D) finite-element (FE) simulation. The analysis results indicate that (1) the cross-anisotropy of UAB has significant effects on the critical stresses and strains at critical depths; (2) the cross-anisotropy of subgrade has considerable effects on the surface deflection and the vertical strain at the top of the subgrade. Subsequent pavement performance predictions indicate that cross-anisotropy of UAB has great negative effect on pavement life in terms of fatigue cracking and rutting potential. Therefore, the cross-anisotropy of UAB and subgrade layer should be considered in the mechanical analysis of asphalt pavements.

Advanced evaluation of asphalt mortar for induction healing purposes

Induction heating technique is an innovative asphalt pavement maintenance method that is applied to inductive asphalt concrete mixes in order to prevent the formation of macro-cracks by increasing locally the temperature of asphalt. The development of asphalt mixes with improved electrical and thermal properties is crucial in terms of producing induction healed mixes. This paper studies the induction healing capacity of asphalt mixes without aggregates as the part of asphalt concrete where inductive particles are dispersed notably contributing to the final response of asphalt pavements. Special attention was given to the characterization of inductive asphalt mixes using experimental techniques and numerical methods. The research reported in this paper is divided into two parts. In the first part, the impact of iron powder as filler-sized inductive particle on the rheological performance of asphalt-filler systems was studied. The mechanical response, the induction heating and healing capacity of asphalt mortar by adding iron powder and steel fibers was evaluated as well. In the second part, the utilization of advanced finite-element analyses for the assessment of the induction heating potential of inductive asphalt mortar with steel fibers are presented. The influential factors of induction mechanism in asphalt mixes are also described. The experimental and numerical findings of this research provided an optimization method for the design of induction healed asphalt concrete mixes and the development of necessary equipment that will enable the implementation of induction technology for healing of asphalt concrete mixes.

Comparative Study of Asphalt Pavement Responses under FWD and Moving Vehicular Loading

AbstractThis study aimed to compare pavement responses caused by impulsive dynamic loading and moving vehicular loading using mechanistic pavement analysis. Finite-element (FE) models were developed to simulate falling weight deflectometer (FWD) loading with axisymmetric FE models and to simulate moving vehicular loading with three-dimensional (3D) FE models. Two flexible pavement structures with different asphalt layer thicknesses and temperature profiles were considered in the analysis. The FE models simulated dynamic impulse loading during FWD testing and moving tire loading patterns with 3D tire-pavement contact stresses. It was found that the pulse durations of compressive stresses in the asphalt layer were significantly affected by speed and pavement depth in what can be described as an exponential relationship. However, pulse duration was found to be pavement-dependent, and the quantitative relationship between pulse duration and speed and depth could only be developed for each individual pavement ...

Viscoelastic Nonlinear Multilayered Model for Asphalt Pavements

AbstractFlexible pavements are multilayer structures, typically with a viscoelastic asphalt layer followed by nonlinear unbound/bound layers. Conventionally, multilayered elastic analysis is performed to obtain the response of flexible pavements for design and inverse analyses; however, assuming asphalt pavement to be a linear elastic material is an oversimplification of its actual behavior. It is well known that the responses of asphalt pavements are both rate and temperature dependent. In the present work, a computationally efficient model has been developed to analyze flexible pavements, considering the top layer of linear viscoelastic asphalt concrete (AC), followed by a stress-dependent (nonlinear) base layer, and an elastic subgrade. Constitutive equations are formulated for layered viscoelastic–nonlinear axisymmetric systems. It is shown that the developed model can be used to simulate pavement response under stationary or transient loading. A comparison between the model responses and results obta...

Analysis of measured strain response of asphalt pavements and relevant prediction models

In order to investigate the actual strain response of asphalt pavement under real condition, three types of asphalt pavement sections with typical surface structures are built. The effects of axle configuration, axle load, speed and testing temperature on strain response of asphalt pavement were analysed through in situ dynamic loading. Experimental results indicate that the strain response at the bottom of the asphalt surface layer increases with increasing axle load and temperature, but decreases with the rise of speed. On the other hand, the temperature exerts different influence levels on pavement sections with different structures. It is also concluded that the tandem axle load could lead to a greater strain response than that of single axle load. Applying the analysis of variance, the effects of pavement surface temperature, axle load, speed and their double interactions are studied as well. Finally, the paper proposes prediction models of the strain response at the bottom of asphalt layer by means of multivariate regression analysis.

Design of Thin Surfaced Asphalt Pavements

Thin flexible pavements are widely used worldwide in scarcely populated areas. However, this kind of pavement structure is not widely used in Germany. As a result, no M-E design procedure exists. Recently, a research project aiming to understand the response of thin asphalt pavements under design conditions in Germany showed that the durability of pavements with less than 50 mm asphalt thickness proved to be satisfactory; provided that the design is performed considering the non-linear behaviour of the UGM's in the base course. It was concluded that granular materials in the vicinity of the load must be modelled using non-linear stress dependent models. The paper presents an M-E design approach for thin surfaced asphalt pavements.

Dynamic viscoelastic response of an instrumented asphalt pavement under various axles with non-uniform stress distribution

This paper is presented to analyse the instrumented asphalt pavement responses with infinite element boundaries under moving non-uniform distribution tyre–pavement contact stresses. The 3-D finite element model and implicit dynamic analysis were used to simulate the instrumented pavement. The asphalt layer was modelled as a viscoelastic material and the Prony series was used in the viscoelastic material model. The viscoelastic parameters were obtained from creep compliance experiments at various temperatures and converted to relaxation parameters. The interface binding conditions between asphalt layers were analysed and determined from field measurements. A non-traditional loading assumption was used to represent the non-uniform distribution of tyre–pavement contact stresses along longitudinal and transverse directions. It was found that the asphalt layers were not well bonded, which may result from thermal conditions in the pavement. With infinite element boundaries and moving non-uniform stress distribution, the pavement responses obtained by calculations and measurements under different vehicle loading conditions (vehicle with two single axles and vehicle with a single axle plus a tandem axle) were compared and its characteristics were analysed. Good agreements were achieved. The critical responses under different loading conditions such as strains at the bottom of the asphalt binder course and asphalt base course obtained from both calculations and measurements were identified. The results also show that the strain interference effect is significant between axles and this effect is more serious as the pavement depth increases.

Evaluation of interlayer bonding condition on structural response characteristics of asphalt pavement using finite element analysis and full-scale field tests

This study was primarily focused on evaluating the effect of different interlayer bonding conditions on change in critical responses for real pavements related to performance and service life using the results from the finite element analysis (FEA) and full-scale field tests. The current lack of thorough understanding and mechanistic characterization of the interlayer bonding behavior that enables to accurately simulate the change in structural responses of pavement system is probably the greatest deficiency in our ability to properly evaluate the effect of interlayer bonding condition for asphalt pavements. Also, most of the pavement models previously introduced assumed either full-bond or no-bond condition which is not a realistic interlayer condition for pavements in the field. Therefore, there is a need to develop improved model to accurately predict the change in pavement critical responses for real pavement system due to the different interlayer bonding conditions. Results indicated that the pavement model developed was capable of accurately predicting the change in pavement critical responses due to the different interlayer bonding conditions and the predicted values were matched well with those measured from the full-scale field test. Also, it was found that a good interlayer bonding condition can positively affect the strain responses of asphalt pavement that results in potential structural benefits for enhanced pavement performance. Based on the comparative observations between analytical and experimental results, it was confirmed that the interlayer bonding condition plays a significant role on structural response characteristics of layered flexible pavement system and therefore the pavement service life.

Dynamic backcalculation of asphalt pavement layer properties using spectral element method

The response analysis mode of asphalt pavement plays a critical role in properly interpreting falling weight deflectometer (FWD) test results and obtaining reasonable backcalculated layer properties. This study uses the spectral element method (SEM) to analyse the dynamic viscoelastic response of asphalt pavement subjected to FWD loading. The modified Havriliak–Negami (MHN) mode is used to characterise the mechanical properties of asphalt concrete (AC). The MHN model can accurately characterise the viscoelastic and damping behaviour of AC with much fewer number of model coefficients (only five) than the widely used Prony series representation, which makes the model well suited for the dynamic response analysis and backcalculation of layer properties. A computer code is developed to implement the SEM procedure and the results are in good agreement with finite element analysis. The dynamic and quasi-static viscoelastic responses are compared and the results show that the inertia and damping behaviour greatly influences the surface deflection of asphalt pavement under FWD loading, especially for pavements with cemented treated base. Therefore, it is important to consider the dynamic effects in interpreting FWD data. The SEM method is used as the forward analysis engine to backcalculate field FWD data, and the results show that the proposed approach is able to well simulate the deflection history at the pavement surface. The layer properties backcalculated from dynamic viscoelastic analysis are significantly different from those obtained from the traditional backcalculation procedure based on the layered elastic theory.

Random Dynamic Response Analysis of Asphalt Pavement Based on the Vehicle-Pavement Interaction

In order to analyze the dynamic response of asphalt pavement under vehicle load, the random characteristic of pavement roughness was considered and the vehicle was simplified into 1/2 model with four freedom degrees when establishing the dynamic load model. Then the sequence of the random dynamic load coefficient was obtained by developing a MATLAB program based on the incremental Newmark-β method. Based on the plane strain assumption, a two-dimensional layered finite element model of asphalt pavement was established by ABAQUS software. Then the dynamic load coefficient was used to modify tire pressure that would be applied on the ABAQUS model. Then dynamic response rule of the model and how it was effected by vehicle speed were studied under random load. The results show that under the condition of random load, dynamic response of the pavement structure exhibiting a fluctuation trend as vehicle speed increases and the dynamic response characteristics of each point is different.

Measured Dynamic Response of Asphalt Pavement under FWD Load

To study the real dynamic response regularity of asphalt pavement structure under dynamic load, a road test was conducted for three types of typical asphalt pavement. Dynamic and static deflection basins were established. The characteristics of the dynamic deflection basin were studied. The set-in dynamic strain sensors at the bottom of the surface layer collected the dynamic strain response under falling weight deflectometer (FWD) load. Results show that the static deflection basin is deeper than the dynamic deflection basin, but the range of the latter is larger than that of the former. The characteristics of the two deflection basins differ. The change trends of dynamic response with an increase in FWD load reflect nonlinear characteristics. The dynamic strain of three typical asphalt pavements at the bottom of the surface layer does not induce fatigue failure in the pavement structure. The longitudinal strain is larger than the lateral strain. Different prediction models on dynamic strain on the basis of dynamic deflection basin parameters are established.

Accurate determination of near-surface responses of asphalt pavements

Accurate determination of structural responses plays a critical role in a mechanistic-empirical pavement design. A new distress model, top-down fatigue cracking, has been incorporated in the newly developed Mechanistic-Empirical Pavement Design Guide. The critical response for top-down cracking is the horizontal tensile stress or strain at the pavement surface. However, the poor convergence of analytical layered elastic solutions in the vicinity of the pavement surface may result in large errors in response results. This study uses the Lucas algorithm to effectively solve this problem. The algorithm converts the complicated oscillating behaviour of the product of Bessel functions to regular oscillations by separating the integrand into high- and low-frequency components. Thus, extrapolation techniques can be effectively applied to accelerate the convergence. A computer code is developed to implement the proposed procedure. The computer code is verified against the boundary conditions and finite element results. It is also compared to other layered elastic programs. The results show that the proposed procedure can accurately determine the near-surface responses of asphalt pavements.

Modulus evolution of asphalt pavement based on full-scale accelerated pavement testing with Mobile Load Simulator 66

A full-scale accelerated pavement testing was conducted with Mobile Load Simulator 66 in Chongming Island, Shanghai, to study the performance response of a semi-rigid base asphalt pavement with fine-sand subgrade designed for the G40 construction. As an index sensitive to temperature and load, three different moduli including the seismic modulus, field falling weight deflectometer back-calculation modulus and interior material testing system resilient modulus were all measured during and after the test. The modulus evolution of asphalt pavement with the loading applications, rutting, strain and temperature, and the comparison of three methods for measuring modulus were analysed. There exists a modulus gradient from top to bottom, which can be considered in the pavement design or fatigue life prediction. Because of the strain level differences, the seismic modulus was the largest, followed by back-calculation and resilient modulus; the development of seismic and back-calculation modulus better reflected the anti-deformation changes.

Stochastic Identification of Linear-Viscoelastic Models of Aged and Unaged Asphalt Mixtures

The behavior of asphalt mixtures is typically described using linear viscoelastic models at low-strain applications. The time and temperature dependency of asphalt mixture properties is described by forming a master curve that includes three components: time-temperature shift factors, and storage and loss moduli (or compliances). Mathematical models are needed to describe the master curve, which are used in calculating asphalt pavement responses to load and also to compare the overall properties of various mixtures at a wide range of temperatures. This paper proposes a rigorous approach to mathematically describe the master curves using stochastic identification techniques. These techniques have the advantage over current deterministic methods in their ability to account for the uncertainty associated with the constructed models, which could be contributed to variation in the material properties of the asphalt mixture phases as well as their spatial distribution, measurement errors, modeling errors, and inadequate available information. Consequently, uncertainty can be accounted for in the analysis and design of asphalt pavements. The stochastic approach is used successfully in this paper to identify the linear viscoelastic master curve for asphalt mixtures that have been aged to different time durations.

Coupled hydro-mechanical response of saturated asphalt pavement under moving traffic load

Based on the Boit's theory, the governing equation was established to account for the response of moisture pavement. The analytical solutions were obtained through the expansion of Fourier series. Furthermore, the effects of parameters (i.e. hydraulic conductivity, traffic load velocity, drainage boundary and solid modulus) on dynamic response were investigated in terms of water-induced damage of pavement. Compared with the dry–elastic pavement, the negative normal stress in saturated asphalt pavement is concentrated beneath the traffic load, which may be a reason for a damage phenomenon in asphalt pavement. Hydraulic conductivity anisotropy plays a significant role in influencing the physical fields. Between vertical and horizontal hydraulic conductivity, the physical field almost depends on vertical hydraulic conductivity rather than horizontal hydraulic conductivity which just affects the horizontal pore-water velocity obviously. Moreover, the drained boundary evidently influences the seepage field of surface course with high permeability.

Modulus Back-Calculation Based on FWD Dynamic Deflection Basin for Semi-Rigid Base Asphalt Pavement

To study semi-rigid base asphalt pavement response characteristics, two structural APT test roads of cement stabilized aggregate and lime fly-ash stabilized aggregate were constructed, and accelerated loading test was developed. After certain number of wheel loads (70,000 times) pavement deflection basin parameters were detected by using the falling weight deflectometer, then modulus of each pavement layer was back-calculated, dynamic response was analyzed. Studies have shown that the modulus of semi-rigid base decay faster, and with decreasing thickness of the semi-rigid base, the greater the rate of decay of modulus; cement stabilized aggregate decay rate is greater than that of lime fly-ash stabilized aggregate.

Impact of cross-anisotropy on embedded sensor stress–strain and pavement damage

The effects of cross-anisotropy on asphalt pavement responses and damage are investigated in this study. As a part of this investigation, a dynamic Finite Element Model (FEM) of a pavement section at interstate I-40 (Mile Post 141) in New Mexico is developed in ABAQUS. This section has recently been instrumented with strain gauges, moisture probes and pressure cells. The dynamic FEM has been simulated to determine pavement responses under Falling Weight Deflectometer (FWD) and truckload. Pavement response (i.e. stress, strain and deflection) from the instrumented section are then compared to the FEM predicted values. To study the effect, a total of five combinations of cross-anisotropy are considered. The first combination considers cross-anisotropy of modulus in every layers of the pavement. The rest of the combinations considers it in each of the individual layers such as surface (Hot Mix Asphalt (HMA)), base (Granular aggregate), sub-base (PPC) and subgrade (Fine soil), respectively. Time-deflection histories, stress and strain are predicted from the FEM under FWD and truckload. Results show that predicted deflections, stress and strain are highly sensitive to HMA and all layer cross-anisotropy. In these cases, predicted deflections, stress and strain increase with a decrease in n-value, defined by the ratio of horizontal to vertical modulus of elasticity. The effect of cross-anisotropy in base, sub-base and subgrade is not as significant as the former two cases. Pavement damage is also determined using the tensile strain at the bottom of surface (HMA) layer. It is observed that damage increases with decrease in n-value. This effect is pronounced in HMA and all layer cross-anisotropy among the five combinations of cross-anisotropy. Finally, it is recommended to include this effect in the mechanistic analysis to improve the pavement design and evaluation.

Viscoelastic Response Solutions of Multilayered Asphalt Pavements

This study proposes a procedure for determining the viscoelastic responses of multilayered asphalt pavements. A computer code is developed to determine the elastic responses of pavements subjected to uniform circular pressures according to the layered elastic theory. The results from the code were successfully verified. The viscoelastic behavior of asphalt concrete is characterized using a complex modulus model. Relaxation of asphalt concrete is obtained by replacing the corresponding variables in the complex modulus model and substituting the elastic solution to obtain the step response function in the transformed domain. The time-domain response is solved through numerical transform inversion and is then expressed in the form of an exponential series with the relationship between the exponential series coefficients and the step responses at zero and infinite time being satisfied. The response as a result of an arbitrary loading history is solved using an incremental formulation of the convolution integral, taking advantage of the exponential series representation of the step response function. A discrete formulation of the linear superposition principle is used to solve the response under a moving load. The computer code developed for elastic analysis is extended to implement the viscoelastic analysis procedure and the results are in good agreement with those obtained from finite-element analyses. The procedure developed in this study provides an effective tool for pavement analysis and design.

Dynamic model and criteria indices of semi-rigid base asphalt pavement

This paper presents a dynamic model of asphalt pavement by considering the characteristics of moving tyre load, visco-elastic performance of material and layered system of pavement. The pavement is defined as an infinite layered system with the tyre load moving at a constant speed, and asphalt concrete (AC) is characterised as a kind of visco-elastic material. Using the spectrum analysis method, a complex tyre load is decomposed into a series of harmonic loads. Based on the frequency characteristics of a linear system, a universal formulation pattern for differential visco-elastic constitutive relations is provided. And then, a model is set up to analyse the dynamic response of asphalt pavement under moving harmonic load, and then to extend to the arbitrary moving load according to the superposition principle of a linear system. The dynamic responses of seven typical semi-rigid base asphalt pavements are analysed using the model. Analysis results indicate that the tensional strain at the bottom of the AC layer and the vertical compression strain at the top of the roadbed are not suitable for key indices of the semi-rigid base asphalt pavement. The shearing strain at the bottom of the AC layer can be taken as a key index to evaluate the fatigue performance, and the vertical compression strain at the top of the pavement surface can be taken as a key index to evaluate pavement rutting, and the vertical shearing strain at the top of pavement surface can be taken as a key index to evaluate top–down crack.