Predict Pavement Response Research Articles

Constitutive modelling and systematic evaluation of asphalt concrete’s viscoelastic tension-compression asymmetry effect on pavement performance

ABSTRACT Asphalt concrete (AC) exhibits significant tension-compression (TC) asymmetry, which is currently not considered in pavement design. This study develops a novel temperature-dependent dual viscoelastic model to quantitatively capture the viscoelastic behaviour of AC. Unlike the conventional viscoelastic constitutive model, the proposed model decomposes strain into tensile and compressive components to characterise AC’s TC asymmetry. Additionally, a systematic modelling framework with intrinsic TC asymmetry is developed for the first time to predict the response of pavement under moving tire load. The results illustrate that implementing the proposed dual viscoelastic model enlarges both the vertical deformation of pavements and the tensile and shear strains in the AC layers, bringing it closer to the realistic scenario compared to the conventional model that only considers compression properties. Furthermore, high temperatures and low vehicular speeds exacerbate the substantial effects of AC’s TC asymmetry on asphalt pavement. This study provides a valuable method to capture AC’s TC asymmetry and predict pavement response more accurately, giving better insight into pavement response and enhancing pavement design and maintenance.

Comparative evaluation of mitigation methods for traffic-induced reflective cracking in airport composite pavement

Composite pavement provides an effective and quick solution to restore structural and functional capacity of airfield pavement. However, discontinuities of concrete slabs cause initiation and propagation of reflective cracking in asphalt overlay. This study aims to evaluate and compare the effectiveness of mitigation methods for traffic-induced reflective cracking in airport composite pavements. Finite element (FE) models were developed and validated to predict pavement responses under heavy weight deflectometer (HWD) and aircraft tire loading. The load transfer efficiency (LTE) of existing rigid pavement were evaluated under common deterioration scenarios like base erosion and concrete damage. The crack potential was indicated by pseudo J-integral considering stress intensity factors (SIFs) of different fracture modes. The results show that thicker asphalt overlay, stress absorbing interlayer, and increase of LTE can help mitigate reflective cracking. Increasing 51-mm overlay (from 76 mm to 127 mm) and applying 25-mm interlayer show the similar reduction in reflective cracking fracture potential by about 35% at early crack stage. However, applying interlayer has more benefit on cost effectiveness and pavement elevation control. On the other hand, dowel bar retrofit and base treatment can improve LTE and thus reduce the crack potential at early crack stage of 76-mm overlay by 40% on doweled pavement and 60% on un-doweled pavement, respectively.

SIMPLIFIED MECHANISTIC – EMPIRICAL ANALYSIS OF FLEXIBLE PAVEMENT

Pavement stress-strain analysis is an ideal tool for analytical modelling of pavement behaviour and thus, constitutes an integral part of pavement design and performance evaluation. It is the fundamental basis for the mechanistic design theory. Predicting pavement response by simplified procedure analysis by relying on equivalency factors using axle load spectrum which is obtained from Weigh-In-Motion (WIM) data is aimed for this study. The framework for computing the structural response of the standard axle group loads on a pavement structure by using a layered elastic computer program and calculation of pavement responses for axle load distribution for different axle groups and axle types by using the theoretical analysis. From the study, the summary of the obtained results are as follows: (1) axle load distribution was developed for the four considered axle configurations; (2) Single axle with single tyre has the greatest destructive impact followed by the tridem axle with dual tyres (TRDT) and next by TADT. The least destructive axle group type is the Single Axle with Dual tyre SADT.The predicted pavement response by theoretical analysis indicates that the critical tensile strains obtained results are all greater than the critical vertical strains. At the heaviest axle load, from 70KN, for both SAST and SADT; from 140KN for TADT; and from 210KN, the critical strains have the greatest magnitude by SAST and followed by SADT and next by TADT. The least critical tensile strain is from the TRDT.

Field and numerical investigation of full depth reclamation with Portland cement in Georgia

The Full Depth Reclamation (FDR) technique has recently become a popular rehabilitation method to reconstruct old flexible pavement. Pulverized existing roadway materials are blended with stabilizing agents such as foamed asphalt and Portland cement to form a stiff base course for the new pavement. In Georgia, Portland cement is commonly used as a stabilizing agent for FDR stabilization. One of the challenges in FDR stabilization projects is to achieve uniform stiffness throughout the stabilized layer. FDR mix design often specifies a fixed rate of stabilizing agent, which could generate a range of FDR strengths due to the inherent variability in the existing pavement. Stiffness variation in the stabilized base should be minimized for optimum long-term pavement performance. This study investigates the influence of the variability in the FDR base layer stiffness on pavement performance. A series of field and laboratory tests were performed on a pavement reconstruction project in Georgia to assess variability. Tests included Unconfined Compressive Strength (UCS) tests and deflection tests with a Light Weight Deflectometer (LWD) and Falling Weight Deflectometer (FWD). Mechanistic sensitivity analyses were performed based on the field and laboratory test results to investigate the effect of variability in FDR properties on pavement performance. The results indicate both the FDR base thickness and strength have a significant influence on the predicted pavement responses. Findings presented here will be of interest to pavement engineers involved in the design and performance modeling of FDR pavement.

Developing Machine-Learning Models to Predict Airfield Pavement Responses

Aviation promotes trade and tourism by connecting regions, people, and countries. Having a functional and efficient airport pavement network is important to improve aviation traffic and to provide safer mobility to almost 800 million passengers travelling in the U.S. per year. The Federal Aviation Administration has initiated and actively been participating in many projects to further advance pavement design and performance to meet user requirements. To accomplish that, quantitative data are needed; such data may be collected from the pavement response to gear and environment loading. In this study, responses from four instrumented taxiway concrete slabs at John F. Kennedy International Airport were analyzed. The collected data were used to develop machine-learning (ML) based prediction models to compute the temperature, curling and bending strains within pavement. The ML models were developed using the support vector machine (SVM) algorithm. The results showed that SVM based ML models can predict pavement responses with a high accuracy and low computation time. Furthermore, in the case of feeding more data from various airports, ML models have proven to be a promising technique for pavement analysis engine for future airport pavement design frameworks. This study also produces recommendations for future data collection projects to have well-designed databases for data-driven models development.

A mechanistic-empirical approach to quantify the influence of geogrid on the performance of flexible pavement structures

The objective of this study was to develop a methodology for quantifying the influence of geogrid on the performance of flexible pavement structures in a manner that would allow incorporation into Pavement Mechanistic-Empirical (ME) Design. The finite element technique was used to develop the geogrid-reinforced flexible pavement structure models, which focused on the characterization of the lateral confinement and vertical membrane effect of geogrid. A full-scale Soil Tank test was conducted to assess the validity of the developed geogrid-reinforced models by comparing the model predicted pavement responses (i.e., surface deflections, tensile strain at the bottom of asphalt concrete, and vertical stress distributions) to those tank test measurements. In general, the developed finite element models were capable of accurately predicting the responses of geogrid-reinforced and unreinforced pavement structures. It was found that the placement of geogrid increases the stiffness of base course and significantly reduces the vertical stresses around the geogrid layer, but cannot effectively reduce the tensile strain at the bottom of asphalt concrete. This indicated that the geogrid reinforcement is beneficial for reducing the rutting damage in base course and subgrade, but not effective in prolonging the fatigue life of flexible pavement. To quantify the influence of geogrid, the geogrid-reinforced flexible pavement structure was equivalent to an unreinforced flexible pavement structure with the modified material properties, which was based on a pavement response equivalency approach. The determined modified material properties was then input into Pavement ME Design software to predict the performance of geogrid-reinforced flexible pavement structures. Two case studies were conducted to predict the performance of two geogrid-reinforced pavement sections that were identified from the Long-Term Pavement Performance (LTPP) database. The predicted performance results (i.e., rutting depth and fatigue cracking area) were coincident with those field measurements, which validated the prediction accuracy of the proposed approach.

Efficient surrogate method for predicting pavement response to various tire configurations

A computationally efficient surrogate model was developed based on artificial neural networks (ANN) to investigate the effect of the new generation of wide-base tires on pavement responses. Non-uniform tire contact stress measurements were obtained using a stress-in-motion instrument. The measured 3-D contact stresses were applied on two extreme 3-D flexible pavement finite element models representing low-volume (thin) and high-volume (thick) roads. Eleven critical pavement responses were modeled at two different material properties input levels--detailed and simplified--depending on data availability. The results rendered by the ANN surrogate models were highly accurate with average prediction error less than 5 % and R-square values higher than 0.95. In addition, two sensitivity analyses were performed to investigate the variables effect on pavement responses. It was found that the type of tire (wide-base vs. dual tire assembly) is more influential than the inflation pressure on pavement responses. However, the tire inflation pressure seemed to have a significant effect on near-surface responses. The developed models were incorporated into a tool to assist designers and engineers in investigating the effect of the pavement responses of wide-base versus dual tire assembly under typical loading conditions and pavement structures.

Analytical evaluation of load movement on flexible pavement and selection of optimum neural network algorithm

Nowadays, Finite Element Method (FEM) is used to predict pavement responses, which presents accurate results, considering all determinative parameters, including dynamic loading, crack, non-linear elastic and viscoelastic behaviours, damping and etc. On the other hand, due to the type of loads and the material properties, pavement analysis requires a lot of time. This paper describes the use of Artificial Neural Networks (ANNs) as pavement structural analysis tools for the rapid and accurate prediction of longitudinal strains at the bottom of asphalt layer of flexible pavements subjected to moving loads. A back propagation neural network of three layers is employed. Results indicate that ANN predicts the pavement strain with high accuracy. It is also demonstrated that ANN is an excellent method that can reduce time consumed and can be used as an important tool in evaluating the pavement responses.

Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model

Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.

An analytical procedure for strain response prediction of flexible pavement

The bottom-up fatigue damage in flexible pavements is typically assessed through the tensile strains at the bottom of the asphalt layer. The fatigue damage is then correlated using a calibration factor to the fatigue cracking. Therefore, the success of any pavement design depends on the accuracy and efficiency of employed mechanistic parameters, such as stress and strain. A procedure that can accurately and rapidly predict pavement strain response when traffic and environmental data are provided is desirable. In this study, an analytical procedure was developed to predict pavement response using a mixed pool of tensile strains from instrumentation and 3D FE simulation. Statistical features make the developed procedure powerful and efficient such that the strain responses due to every individual axle pass can be predicted. A demonstration example of predicting tensile strains under multiple-axle loading conditions is provided to facilitate application of the procedure to other data-sets. The maximum difference of 9 microstrain in response implies a reasonable accuracy of the analytical procedure. As demonstrated by using a full-depth flexible pavement section, the analytical procedure is effective and of immediate assistance to experimentally compare design alternatives.

Field evaluation and analysis of flexible pavement structural responses under dynamic loads

This study investigates the structural responses of flexible pavements at the Center for Pavement and Transportation Technology (CPATT) test track located at Waterloo, Ontario, Canada. A comprehensive field testing program was performed to examine flexible pavement responses to a variety of loading conditions. Tests were completed using six tire types: 11R22.5, 275/80R22.5, 295/75R22.5, and 285/70R22.5 dual tires, and 455/55R22.5 and 445/50R22.5 wide-base tires, and tire inflation pressures that ranged between 482 to 827 kPa. A two-dimensional finite element model was developed using MichPave software to predict pavement responses. A simplified method was proposed to characterize HMA properties using the laboratory dynamic modulus test. The developed model simulations approximated the field measured responses to all loading configurations.

Review on the Use of Instrumented Pavement Test Data in Validating Flexible Pavement Mechanistic Load Response Models

For designing pavement structures effectively and efficiently designers are moving from the old empirical design approach to the new Mechanistic Empirical (M-E) pavement design procedure. In M-E design, the pavement responses in terms of stresses and strains have greater influence on the performance prediction. Many theoretical equations were developed by researchers in the past fifty years to predict pavement responses under different loading conditions. The overall accuracy of the models are in question while considering unbound base materials, behaviour of hot-mix asphalt and dynamic moving loads applied by traffic. Despite this, layered elastic model continue to be the state-of-the practice for most pavement design and analysis applications. To make sure that the accurate pavement response model is being used in the M-E design, this mechanistic load response model has to be validated with measured pavement responses under traffic or applied loads. In this regard, instrumented pavement testing facilities play an important role in validating the mechanistic load response models by measuring the pavement responses from the field through proper instrumentation and comparing them with theoretical responses. In this paper, a detailed review and analysis on the major research works conducted in Europe and United States over the past fifty years on flexible pavements starting from the TRRL study in 1962 to the recent research at the NCAT Test Track to use the instrumented pavement test data to validate the load response model and their outcome is presented along with the efforts needed to increase the model accuracy.

Comparisons of Measured and Predicted Pavement Strain in Full-Scale Accelerated Pavement Testing

In this paper, the measured and predicted responses between a full-scale accelerated pavement test facility and that from a three-dimensional (3D) finite element model were compared using the measured 3D tire contact stresses. The objective was to predict pavement response in asphalt mixture layers using the measured 3D tire contact stresses and compare with the measured transverse strains in August and November. To carry out this objective, the transverse strains within asphalt layers were measured and the corresponding strains were predicted by 3D finite element analysis. Additionally, a layered elastic analysis, the BISAR program, was used to predict the corresponding field measurements. The predicted transverse strains by 3D finite element analysis were matched reasonably with the measured strains.

Dynamic Analysis of Thin Asphalt Pavements by Using Cross-Anisotropic Stress-Dependent Properties for Granular Layer

A three-dimensional (3-D) finite element (FE) model was developed to investigate the dynamic responses of thin, flexible pavement under impulsive loading similar to a falling weight deflectometer test. The FE model simulated the hot-mix asphalt (HMA) surface layer as a linear viscoelastic material and considered the cross-anisotropic stress dependent modulus for the unbound base layer. Implicit dynamic analysis was used to consider the effect of inertia on pavement structural responses. Using two thin-pavement structures of different HMA layer thicknesses, 76 and 127 mm, the study analyzed the effects of cross-anisotropic stress-dependent aggregate base modulus and dynamic analysis on pavement responses, including surface deflection, tensile strain at the bottom of the HMA layer, deviator stress in the base layer, and compressive strain on top of the subgrade. Results showed that use of the cross-anisotropic stress-dependent modulus for the unbound base layer resulted in greater predicted pavement responses and, hence, less estimated pavement life for rutting and fatigue cracking. It was found that as the thickness of HMA surface layer or the ratio of horizontal modulus to vertical modulus decreases, the effects of stress dependency and cross anisotropy become more significant. Analysis-predicted surface deflections were compared to field-measured values and they were in agreement when the stress dependency and cross anisotropy of the base layer and subgrade were considered.

Validation of a Three-Dimensional Finite Element Model using Airfield Pavement Multiple Wheel Load Responses

ABSTRACT Various highway vehicle axle/wheel arrangements and aircraft gear configurations adopted nowadays to accommodate increasing load levels impact flexible pavement response and performance in accordance with different multiple wheel loading scenarios. As the demand for heavier wheel loads and number of load applications continually increases, it is essential to properly characterize the nonlinear behavior of the pavement subgrade and unbound aggregate base/subbase layers. This paper focuses on the validation of a recently developed three-dimensional (3D) nonlinear finite element (FE) model using the measured responses of airfield flexible pavement test sections trafficked under 4-wheel and 6-wheel aircraft gear configurations. For this purpose, realistic nonlinear, stress-dependent pavement subgrade and base/subbase resilient modulus models were employed in a programmed User MATerial (UMAT) subroutine of the general purpose ABAQUSTM FE program. The predicted pavement responses matched closely with the displacements and stresses measured in the field and the FE model could be reasonably applied to the design of airfield pavements serving multiple wheel gear loads when the nonlinear pavement geomaterials were considered. In addition, comparisons made between the single wheel superposition and the full 3D loading results proved the need and importance of 3D FE nonlinear analyses of thinly surfaced flexible pavements to properly consider both the stress dependent modulus behavior and the implications of multiple wheel loads and their interaction.

Analytical Approach to Predicting Temperature Fields in Multilayered Pavement Systems

An accurate and rapid estimation of the pavement temperature field is desired to better predict pavement responses and for pavement system design. In this paper, an innovative method to derive the theoretical solution of an axisymmetric temperature field in a multilayered pavement system is presented. The multilayered pavement system was modeled as a two-dimensional heat transfer problem. The temperature at any location (r,z) and any time t in an N -layer pavement system can be calculated by using the derived analytical solution. The Hankel integral transform with respect to the radial coordinate is utilized in the derivation of the solution. The interpolatory trigonometric polynomials based on discrete Fourier transform are used to fit the measured air temperatures and solar radiation intensities during a day, which are essential components in the boundary condition for the underlying heat transfer problem. A FORTRAN program was coded to implement this analytical solution. Measured field temperature resu...

Effects of Tire Inflation Pressure and Load on Predicted Pavement Strains

In this paper, effects of tire loads and inflation pressures on predicted pavement responses were presented. The objective was to study the effect of increased tire loads and tire inflation pressures on predicted transverse strains and vertical strains at the different pavement layers and material properties. A 3 dimensional (3D) tire contact stresses for 6 different tires were interpolated from the database of the measured tire contact stresses. The shape of measured tire contact stresses is dependent on tire loading conditions. The results show that the predicted values were different near the asphalt concrete (AC) layer by increased tire inflation pressure. Under the increased tire load, the predicted values were different at the base and subgrade layer. From statistical analysis, predicted transverse strains at the bottom of asphalt layer and vertical strains at the top of subgrade are affected by different AC thicknesses, AC moduli, and subgrade moduli.

Effects of Tire Types on Predicted Pavement Service Life

ABSTRACT In this paper, comparisons are presented of the predicted pavement response from three-dimensional (3D) finite element (FE) and layered elastic programs. The objective was to study effect of different tire types on pavement lives. Authors used available contact pressure measurements on four tires to predict pavement response using a 3D finite element program. The results show that the predicted pavement fatigue life based on horizontal strains at the bottom of asphalt layer is different by tire types and analysis methods while the predicted rutting life based on vertical strains at the top of subgrade layer shows no significant difference.

Evaluation of Long-Term Performance of Pavement Drainage Layers on I-469 in Indiana

Subsurface drainage is important for long-term pavement performance. Rational procedures to analyze and evaluate the design, reliability, and effectiveness of subsurface drainage systems are needed in order for their use to be recommended with confidence. Three pavement subdrainage test sections were constructed in 1995 on the eastbound driving lane of I-469 in Indiana, at the northern junction with I-69, between Stations 150+05 and 173+40. Presented are the original laboratory characterization and mechanistic evaluation for permanent deformation and stability of the test sections employing finite element analysis. Triaxial tests were conducted on all pavement layers of the sections. Falling weight deflectome-ter evaluations in 1995 and 1998 are also presented. Such measurements are not available after 1998 because compliance with Indiana Department of Transportation safety regulations is required at that location. Finite element analyses were conducted by using laboratory-measured material properties to predict pavement response to falling weight deflec-tometer loads, compare predicted and measured deflections, examine layer shear stability for shear stress and strength, and predict rutting. Long-term pavement performance indicators up until 2007 (including international roughness index and ground penetration radar), after 12 years of heavy truck traffic, are also presented. Finite element analysis predicted very well the deflections measured by the falling weight deflectometer and accumulated rutting of the three test sections. Comparisons of shear stresses and strengths indicated that the sections were stable. All long-term evaluations indicated that all drainage layers in the study sections have performed their function adequately and protected the subgrade.

Dynamic Analysis and in Situ Validation of Perpetual Pavement Response to Vehicular Loading

A three-dimensional (3-D) finite element (FE) model was developed to predict pavement responses to vehicular loading. The model incorporates measured tire-pavement contact stresses, continuous moving wheel loading, and hot-mix asphalt (HMA) viscoelastic characteristics. The model was fine-tuned using implicit-dynamic analysis and validated using pavement response from accelerated loading. Two tire configurations (dual-tire assembly and wide-base 455 tire) and three full-depth flexible pavement designs (HMA 152 mm, 254 mm, and 420 mm) were used in both FE modeling and accelerated loading tests. The predicted and calculated strain responses at the bottom of HMA were in agreement. Most important, the study shows that vertical shear strain in the upper 76 to 100 mm of the pavement surface is critical for thick pavement and is influenced by the 3-D tire-pavement contact stresses under each tire rib. However, the tensile strain at the bottom of HMA is affected mainly by the total wheel load. The vertical shear strain is responsible for near-surface fatigue cracking as well as HMA primary rutting. Top-down cracking could result from the local vertical shear strain in the upper 25 mm of the HMA where the effect of tire-pavement tangential stresses are the highest. In addition, the study concluded that wide-base tires cause higher longitudinal tensile strain at the bottom of HMA and compressive strain at the top of subgrade, where those responses are highly affected by the total wheel load. However, wide-base tires were found to cause less vertical shear strains near the surface than dual-tire assembly loading regardless of HMA thicknesses.