Multilayer Pavement Research Articles

New analytical solution of flow and heat refraction problem in multilayer pavement

The paper covers a new analytical solution of a flow and refraction problem in a multilayer pavement. The solution includes conditions of internal and external exchange as well as cyclic temperature and heat flux changes. Solution of a problem of heat conduction in a multilayer system showed a significant influence of coefficients introduced by the authors on the temperature and thermal stresses field in structure of a multilayer pavement. The coefficients were: diffusivity, thermal matching of layers and thermal refraction of layers. It was found that solar radiation is very important climatic factor acting directly on the upper layer of pavement, causing an increase in temperatures and creation of an additional temperature gradient in a multilayer pavement. It is shown that temperature field in a multilayer pavement depends significantly on geometry of layers structure, thermal characteristics of upper and lower layers expressed by Biot and Fourier numbers, colour of a surface course, humidity, velocity of wind etc., which are expressed by value of an external heat transfer coefficient. Moreover, an original example of analysis of an influence of pavement layer and subgrade parameters as well as climatic conditions on the temperature field in three different pavement structures, is shown. Results of the presented analysis can be directly applied in roads and airstrips pavements design.

Adherence in a pavement rehabilitated with a polymeric grid used as interlayer

A polymeric grid was placed between layers of a pavement with the aim of preventing the reflection of cracks from the base material to the upper layer. Results explain why the usual faults that occur in rehabilitated pavements: (i) chemical modifications of geosynthetic polypropylene determined by FTIR lead to changes in its melting point; (ii) the discontinuity or continuity of the interface observed by SEM depends on the application temperature of the asphalt mix and (iii) the adherence obtained in laboratory tests correlates perfectly with the quoted chemical modifications of geosynthetic polypropylene and the structure of interface in multilayer pavements.

NUMERICAL SIMULATION OF RIGID PAVEMENT BEHAVIOR TO NON-DESTUCTIVE IMPULSE RESPONSE TESTING

The Impulse Response (IR) technique is a stress wave method that measures the structure’s response to stress waves generated by an impact source. When applied to rigid pavements, the measured response contains complex information on the dynamic pavement properties that is primarily used in detection of voids or loss of support, and softening of the subgrade. The dynamic response of the pavement system is assumed to be similar to that of a single degree of freedom (SDOF) system. This assumption is useful for practical purposes but introduces inconsistencies and uncertainties in the data interpretation because it oversimplifies a complex dynamic problem. Results of a Finite Element parametric study analysis conducted to identify key factors that influence rigid pavement response during Impulse Response (IR) testing are presented. A dynamic modal analysis of a multilayer rigid pavement, assuming viscoelastic and elastic linear material properties, indicates that the mobility spectra from IR testing is predominantly influenced by the properties of the surface layer and the subgrade. The presence of voids beneath a rigid pavement results in increased mobility and less damped behavior of the pavement. The validity of the SDOF assumption in void detection in the reduction of field IR data is also examined.

Prediction of Asphalt Pavement Temperature Profile with Finite Control Volume Method

The accurate prediction of the pavement temperature profile and history is critical for the calculation of the viscoelastic response of asphalt concrete pavements under traffic and thermal loadings. An accurate prediction is also essential in the estimation of the asphalt binder oxi-dative aging. A sound alternative approach is proposed to predict the pavement temperature profile with the finite control volume method in a fully implicit scheme. The model for the finite control volume method provides a fundamental and clear understanding of the heat energy balance, including the incoming and outgoing thermal energies, in addition to the dissipated heat in the system. Also, the variability in the materials’ thermal properties in a multilayered pavement structure can be remedied by assigning appropriate thermal properties to each control volume or cell. The fully implicit scheme improved the time efficiency of the calculation significantly. Moreover, enhancements were made by defining the accurate heat balance equations for the pavement surface and the bottom boundary conditions. With reliable meteorological data, solar radiation, and monthly variable pavement surface radiation properties, accurate prediction of the pavement temperature profile was made possible as validated by comparison with field measurements. Consequently, Windows-compatible software has been developed on the basis of the proposed model, which is capable of effectively predicting the pavement temperature profile and history.

Field performance and numerical modeling of multi-layer pavement system subject to blast load

In this paper, a new multi-layer pavement system subject to blast load was developed. This multi-layer pavement system consisted of Asphalt Concrete (AC) layer reinforced with Geogrid (GST), followed by High Strength Concrete (HSC) layer and then Engineered Cementitious Composites (ECC) layer, taking into account their relative advantages in terms of strength and relative ductility. A series of field blast test was conducted to evaluate the behavior of the new multi-layer pavement in the field condition. Two pavement slabs were cast and tested. One is a normal concrete pavement, as control, and the other is the new multi-layer pavement. It was found that the new multi-layer pavement performed better than conventional pavement system when subjected to blast load. At the same time, a 3D finite element numerical modeling is employed to evaluate the dynamic behavior of the normal concrete pavement and the new multi-layer pavement system subject to blast load. For this modeling, a 3D dynamic numerical model using LSDYNA with appropriate material models and suitable boundary conditions are developed. Actual measurements from the field blast test were used as a validation for the numerical model developed. It was shown that the results from numerical model and field blast test measurements compared very well in terms of damage pattern, crater diameter, acceleration and total pressure cell readings. It is also observed that the new multi-layer pavement system had better blast resistance than conventional pavement system. The developed 3D numerical model using LSDYNA seems to be able to model the real behavior of the pavement subjected to blast load.

HISTOPATHOLOGICAL ECTOCERVIX EPITHELIUM CHANGES IN PATIENTS WITH HPV-INFECTION

Aim. To study the histopathological changes in ectocervix epithelium among patients with HPV-infection. Materials and methods. The object of the study – 105 women aged 25 to 39 with PCR-diagnosed HPV-infection. Patients underwent standard gynecological investigation and widened colposcopy with a target (colposcopically oriented) uterine cervix biopsy. Biopsy material was subjected to histological investigation using the generally accepted histological methods. Statistical analysis was performed with the program package Biostat. For the purpose of assessing significance of differences between distribution of qualitative signs in the studied samples, χ 2 criterion and Z criterion were used. Results. Patients with HPV-infection had some morphological variants of changes in uterine cervix mucosa that depends on presence and degree of multilayer pavement epithelium dysplasia. It was established that while CIN is progressing, expression of such HPV-infection signs as manifestation of koilocytosis and hyper-and parakeratosis is reduced. Besides, there is a tendency to chronization of inflammatory changes in uterine cervix lamina as CIN degree is growing. As CIN degree is growing, there is increase in cervical glandular intraepithelial neoplasia degree (CGIN). Conclusion. As a result of histological investigation of biopsy material taken from HPV-infected patients with uterine cervix pathology, regularities of changes in the character of reactive ectocervix processes connected with CIN progressing were established.

Thermal and hydraulic analysis of multilayered asphalt pavements as active solar collectors

The fulfillment of current environmental aims like reducing fossil fuel consumption or greenhouse gas emissions entails the development of new technologies that enable the use of cleaner, cheaper and renewable energies. Furthermore, the need to improve energy efficiency in buildings encourages scientists and engineers to find new ways of harvesting energy for later uses.The use of asphalt pavements as active solar collectors is introduced in this article. Several authors have studied the use of roads as an energy source before. However, a new technology is presented in which a multilayered pavement with a highly porous middle layer is used instead of a solar collector with an embedded pipe network. These collectors are fully integrated within the road infrastructure and may offer low cost solar energy for water heating.The paper includes a brief comment on the state-of-the-art. Then, a broad methodology is presented in which data, materials and procedures needed to run the tests are fully described. Finally, the results of the laboratory tests are stated and discussed.The prototype used in the laboratory provided excellent thermal efficiency. However, these good results contrast with the low flow rate levels registered during the tests. Thus, although this technology seems to be very promising, new experimental tests should be performed before an effective application is possible.

Analytical Approach to Predict Temperature Profile in a Multilayered Pavement System Based on Measured Surface Temperature Data

This paper presents an algorithm to predict one-dimensional (1D) temperature profiles in a multilayered pavement system on the basis of measured surface temperature data. The model inputs are pavement layer thicknesses, thermal conductivity and diffusivity of layer materials, average initial pavement temperatures along pavement depths, and measured pavement surface temperature data. The main mathematical tools employed in deriving the analytical solution of pavement layer temperature predictions are the Laplace transform and numerical inverse Laplace transform. Measured in situ temperature data from a two-layer flexible pavement system demonstrate that the derived analytical solution generates reasonable temperature profiles in the asphalt concrete layer. The main advantages of the proposed algorithm are that it can rapidly predict the pavement temperature profile when the thermal conductivity and diffusivity values of the layer material are selected and the surface temperature data are measured at end points of each equally spaced time interval. Climatic data, such as air temperature, solar radiation intensity, and wind speed, are not needed to implement this algorithm. This algorithm can be applied to assist field engineers in estimating temperature profiles in a multilayered pavement system for the period during which falling weight deflectometer (FWD) tests are performed.

Analysis of Stress and Displacement Field in Flexible Layered Pavement Based on Boundary Element Method

AbstractIn order to study the stress and the displacement of the flexible multi-layered elastic pavement under various loads distributed in arbitrary shape, the boundary element method for the flexible layered pavement was presented using the fundamental solutions multi-layered solids for the analysis. With combination of the generalized Kelvin fundamental solution and the boundary element method, the boundary integral equation was established for the boundary value problem of the flexible layered pavement to explain the singular integral appearing in the kernel function. The method, which does not involve integral of layered material’s interface, can be used to solve the stress and the displacement of the multi-layered elastic media under various loads distributed in arbitrary shape. The analytical result shows that the present method is of higher precision and can be used for analysis of the flexible pavement which mechanical parameters change along the depth because of using the generalized Kelvin fund...

Innovative Algorithm to Solve Axisymmetric Displacement and Stress Fields in Multilayered Pavement Systems

This paper presents an innovative algorithm to calculate the displacement and stress fields within a multilayered pavement system using layered elastic theory and Hankel and Laplace integral transforms. In particular, a recurrence relationship, which links the Hankel transform of displacements and stresses at any point P(r,z) within a multilayered pavement system with those at the surface point, Q(r,0), is systematically derived. The Hankel transforms of displacements and stresses at any point within a multilayered pavement system can be explicitly determined using the derived recurrence relationships, and the subsequent inverse Hankel transforms give the displacements and stresses at the point of interest. Theoretical and computational verification of the proposed algorithm justify its correctness. The proposed algorithm does not use a numerical linear system solver employed in the traditional approach to solve the axisymmetric problems in multilayered pavement systems. Because of the explicitly derived ...

FINITE ELEMENT BASED ADAPTIVE NEURO‐FUZZY INFERENCE TECHNIQUE FOR PARAMETER IDENTIFICATION OF MULTI‐LAYERED TRANSPORTATION STRUCTURES

During the service life of a pavement, it is often required to conduct Non-destructive tests (NDTs) to evaluate its structural condition and bearing capacity and to detect damage resulting from the repeated traffic and environmental loading. Among several currently used NDT methods, the Falling Weight Deflectometer (FWD) is the most commonly used pavement NDT method applied by many transportation agencies all over the world. Non-destructive testing of pavements using FWD is typically accompanied by the prediction of the Young’s modulus of each layer of the pavement structure through an inverse analysis of the acquired FWD deflection data. The predicted pavement layer modulus is both an indicator of the structural condition of the layer as well as a required input for conducting mechanistic-based pavement structural analysis and design. Numerous methodologies have been proposed for backcalculating the mechanical properties of pavement structures from NDT data. This paper discusses the development of an Adaptive-Network-based Fuzzy Inference System (ANFIS) combined with Finite Element Modeling (FEM) for the inverse analysis of the multi-layered flexible pavement structures subjected to dynamic loading.

Evaluation of Structural Integrity of Asphalt Pavement System from FWD Test Data Considering Modeling Errors

This study examines the structural integrity assessment technique used for the asphalt pavement system that considers the modeling errors introduced by material uncertainties. To this end, the artificial neural network is utilized to estimate the elastic modulus of soil layers by using the measured deflection data from the Falling Weight Deflectometer test. A wave analysis program for a multi-layered pavement system is developed based on the spectral element method for more accurate and faster calculation. The developed program is applied for the numerical simulation of the Falling Weight Deflectometer tests, specifically for the reliability analysis and the generation of training and testing patterns for the neural network. The effects of uncertainties in the material properties for modeling a given pavement system such as Poisson ratio and layer thickness are intensively investigated using the Monte Carlo Simulation. Results reveal that the amplitude of impact loads is most significant, followed by the layer thickness and the Poisson ratio, which are more significant on the max deflections than other parameters. The evaluation capability of the neural network is also investigated when the input data is corrupted by the modeling errors. It is found that the estimation results can be significantly deviated due to the modeling errors. To reduce the effect of the modeling error, (to improve the robustness of the algorithm), we proposed an alternative scheme in order to generate the training patterns taking into consideration any modeling errors. The study then concludes that the estimation results can be improved by using the proposed training patterns from an extensive numerical simulation study.

Analysis of High Temperature Fluctuations on Asphalt Pavement of Cement Concrete Bridge

Abstract In this study a 2-D finite element model of a multilayered pavement structure of a cement concrete bridge was developed to calculate the temperature fluctuations in summer due to thermal environmental conditions for 1 week. The different specific heat capacity and absorptivity factors of the asphalt layers were considered. The results indicate that the surface temperature’s fluctuation of the pavement is similar to the outside atmosphere temperature; the maximum temperature and temperature gradient of asphalt pavement decreased gradually from the top down; the larger the specific heat capacity is, the less the maximum surface temperature becomes; the larger the absorptivity factor of asphalt pavement is, the higher the maximum surface temperature becomes. It is concluded that 2-D finite element analysis proved to be an interesting tool to simulate the transient behavior of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at different levels of bituminous layers with good accuracy, which can provide engineers some guidance on the rutting resistance.

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...

Surface wave testing of pavements.

Pavements are constructed using several layers of materials, and their durability depends on the quality of all of these strata. It is, therefore, valuable to be able to determine the properties of the layers nondestructively. A method is presented for evaluating the thickness and stiffness of multilayered pavement structures from guided waves measured at the surface. In this type of layered structure, the interaction of leaky Lamb waves in the embedded layers generates surface waves corresponding only to certain portions of the guided wave dispersion curves and branches measurable at the pavement surface. To resolve the different mode branches, the wavefield is measured at the surface by using a light hammer as the source and an accelerometer as receiver, generating a synthetic receiver array. The recorded data are transformed to a phase velocity spectrum, which is then inverted to give the layer properties using a global inversion algorithm. The theoretical background along with experimental results of the application to nondestructive testing of pavements will be presented. Ongoing research on noncontact air-coupled measurements is also demonstrated. This opens up the possibility for faster on-the-fly surface wave testing of pavement layers, since surface contact is no longer required.

Statistical investigation of two different interlayer shear test methods

The performance of multi-layered pavement systems strongly depends on interlayer bonding. In order to evaluate this parameter, some countries have developed their own test method. However, different devices generally provide different results due to the test conditions. In this article, the statistical investigation of two interlayer shear test methods is shown considering different asphalt materials and different specimen preparation techniques. Both test methods provided comparable results showing the same ranking in interlayer shear stress for different test conditions and the same level of precision in terms of scatter of the results. Moreover, the repeatability limit was found to be dependent on the test method, the pavement material and the compaction technique. It is worth noting that this extensive experimental investigation paves the way for the incoming European Standardization process involving the two shear test methods.

Thickness Measurement of Thin Pavement Layers Using Time-Frequency Analysis of Ground Penetrating Radar Data

Accurate knowledge of pavement layer thickness can provide important information to determine the quality of newly constructed pavements, and to estimate the remaining service life of pavements. Ground penetrating radar (GPR) is one of current technologies for determining pavement layer thickness. However, the estimation of the thickness of very thin pavement layers is not satisfied by the use of commercial impulse GPR. Hence, a thickness measurement approach for very thin layer of multilayered pavement structures is introduced. The technique presented in the present work is based on the evaluation of the instantaneous bandwidth of GPR receiving signals by means of S-transform. One unique feature of the current technique is that it only requires common impulse GPR system operated at relatively low frequency. The algorithms were tested on simulation as well as experimental data. Specific challenges on dispersion effect in dissipative media and random noise effects were also discussed and addressed.

Seed Modulus Generation Algorithm for Backcalculation of Flexible Pavement Moduli

The seed moduli chosen for backcalculation analysis of multilayer flexible pavements can have significant impacts on the performance of backcalculation software and, sometimes, the final solutions of the backcalculated moduli. Practically all backcalculation programs provide internally generated seed moduli for backcalculation analysis. However, as the internally generated seed moduli do not always produce satisfactory results, the use of user-input seed moduli is generally encouraged. With the aim of providing useful guidance in the choice of seed moduli, a seed modulus generation algorithm, 2L-BACK, for multilayer flexible pavements based on a closed-form modulus backcalculation solution for two-layer flexible pavement structures was developed. The proposed algorithm does not require any subjective judgment by the user. An evaluation analysis of the effectiveness of the proposed procedure is presented by the use of two types of backcalculation software, MICHBACK and EVERCALC, and is based on measured an...

Analytical Study of Effects of Truck Tire Pressure on Pavements with Measured Tire–Pavement Contact Stress Data

Truck tire inflation pressure plays an important role in the tire–pavement interaction process. As a conventional approximation method in many pavement studies, tire–pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and to be simply equal to the tire pressure. However, recent studies have demonstrated that the tire–pavement contact stress is far from uniformly distributed. Measured tire–pavement contact stress data were input into an elastic multilayer pavement analysis program to compute pavement immediate responses. Two asphalt concrete pavement structures, a thick pavement and a thin pavement, were investigated. Major pavement responses at locations in the pavement structures were computed with the measured tire–pavement contact stress data and were compared with the conventional method. The computation results showed that the conventional method tends to underestimate pavement responses at low tire pressures and to overestimate pavement responses at high tire pressures. A two-way analysis of variance model was used to compare the pavement responses to identify the effects of truck tire pressure on immediate pavement responses. Statistical analysis found that tire pressure was significantly related to tensile strains at the bottom of the asphalt concrete layer and stresses near the pavement surface for both the thick and thin pavement structures. However, tire pressure effects on vertical strain at the top of the subgrade were minor, especially in the thick pavement.

Predicting Asphalt Pavement Temperature with a Three-Dimensional Finite Element Method

A three-dimensional (3D) finite element (FE) model was developed to calculate the temperature of a pavement located in northeast Portugal. A case study was developed to validate the model. Input data to the model were the hourly values for solar radiation and temperature and mean daily values of wind speed obtained from a meteorological station. The thermal response of a multilayered pavement structure was modeled with a transient thermal analysis for 4 months (December 2003 to April 2004), and the analysis was initiated with the full-depth constant initial temperature obtained from field measurements. During these 4 months, the pavement temperature was measured at a new pavement section, located in IP4 main road, near Braganca, in northern Portugal. At this location, seven thermocouples were installed in the asphalt concrete layers at seven different depths. These pavement data were used to validate this simulation model by a comparison of model calculated data with measured pavement temperatures. The 3D FE analysis proved to be an interesting tool to simulate the transient behavior of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at different levels of bituminous layers with good accuracy.