Asphalt Layer Thickness Research Articles

Rutting of Rubberized Gap-Graded and Polymer-Modified Dense-Graded Asphalt Overlays in Composite Pavements

The rutting performance of polymer-modified dense-graded and rubberized gap-graded asphalt mixes used in composite pavement was evaluated with full-scale accelerated pavement testing with the heavy vehicle simulator (HVS) and laboratory test results. The effect of asphalt layer thickness on measured surface deformation for both mix types was also investigated for recommendations for future design. In addition, the progression of the rutting failure mechanism for both mix types was evaluated with transverse cross sections measured with a laser profilometer at various HVS load repetitions. The polymer-modified dense-graded mix performed better than the rubberized gap-graded mix under both laboratory and HVS testing. The greater shear movement of the rubberized gap-graded mix under HVS loading caused larger humps, which consequently increased the maximum deformation and resulted in earlier failure. Larger aggregate size and denser gradation for the polymer-modified dense-graded mix resulted in more efficient dissipation of shear stresses and created greater permanent deformation resistance.

Performance of Asphalt Mixture Used for Asphalt Treated Base of Perpetual Pavements

This paper presents the results of laboratory and performance tests for an asphalt treated base (ATB) and mixes developed in this study for perpetual asphalt pavements. Laboratory tests for the mixes included moisture susceptibility, wheel tracking and fatigue tests. The results of performance test indicated that the resistances of the high content binder ATB against moisture and fatigue damage were better than those of the lower one. It was also found from the full scale test sections that the tensile strain values at the bottom of the asphalt layer for the ATB sections were low when the asphalt layer thicknesses of the ATB sections were not thicker than those of the conventional sections. All the tensile strain values measured from the ATB sections were within the fatigue endurance limit of 70 microstrain which is the fatigue criterion of a perpetual asphalt pavement.

Design Factors Affecting the Initial Roughness of Asphalt Pavements

Past studies have shown that initial pavement roughness greatly affects future pavement roughness and roughness progression rate. Highway agencies typically use incentives/disincentives to control the initial roughness of pavements. However, the current blanket specifications do not account for inherent factors that affect initial roughness, such as design factors. In other words, pavements are designed to have different initial roughness. This study analyzes the design factors affecting the initial roughness of asphalt-surfaced pavements. An initial international roughness index (IRI) of 442 asphalt-surfaced pavements constructed from 2000 to 2004 was analyzed based on analysis of covariates. The factors considered in this study include hot mix asphalt (HMA) layer thickness, project location (urban vs. rural), base type, HMA mix classification, and pavement length. The statistically significant factors affecting initial pavement roughness were identified and discussed. These factors can be taken into account to develop specifications for initial roughness of asphalt pavements.

Shear Stress Analysis of Long-Span Steel Bridge Deck Asphalt Pavement Using FEM

Asphalt pavements have been widely used to protect the steel bridge deck against moisture and provide good riding quality. However, various types of distresses especially rutting have been observed frequently in bridge deck asphalt layers. Therefore it is necessary to understand the mechanics behavior of asphalt layer in the steel bridge deck. In this paper, finite element model for bridge deck with asphalt layers have been setup. Then shear stresses have been analyzed in the various cases using finite element method. The results show that the most disadvantage position locates above the diaphragm plate outer side. The shear stress between layers decreases with the increase of the asphalt layer thickness, the peak shear stress increases either. The thin surface layer has its advantage with the requirement of the minimum paving thickness if bonding properly. Comparison with the common pavement structure, the maximum shear stress in the bridge deck pavement could be affected by the type of loading more significant.

Sublayer-thickness inversion of asphalt layer from ground penetrating radar data

A new technique for measuring the permittivity and sublayer thickness of asphalt layer from air-launched ground penetrating radar (GPR) data is presented. This technique involves three major steps: (1) estimation of the time delay of echoes by means of independent component analysis, (2) determination of the permittivity of each sublayer by pattern search method and (3) calculation of the thickness of the individual layers. Numerical simulations show that the overlapped GPR echoes can be separated even if the surface sublayer is quite thin and the low dielectric contrast between sublayers is present. Analysis of field test data of a commonly used impulse GPR is introduced.

Geogrid mechanism in low-volume flexible pavements: accelerated testing of full-scale heavily instrumented pavement sections

This study uses full-scale accelerated testing to provide new insight into the effectiveness of geogrids on the performance of low-volume flexible pavements. Although several previous studies reported that geogrids improve pavement performance by enhancing its structural capacity and reducing distress potential, this study goes further to quantify the effectiveness of geogrids, specify the mechanism of the reinforcement they provide and identify the optimum placement of geogrid in low-volume flexible pavements. Full-scale, low-volume flexible pavement sections were constructed on weak subgrade (California bearing ratio = 4%) and heavily instrumented with 170 sensors. The pavement was divided into three cells with each cell having three sections. The granular base and hot-mix asphalt layer thicknesses varied, and each cell had at least one control and one geogrid-reinforced pavement section. The instruments were embedded to measure stress, strain, deflection, moisture, pore-water pressure and temperature and were used to monitor pavement response to a moving load using the Accelerated Transportation Loading ASsembly (ATLAS). The testing programme was divided into two parts: response testing and performance testing. The response testing considered tyre configuration, loading, inflation pressure, speed and travelling offset. The performance testing considered number of passes to failure. This paper presents the various pavement responses to different loading configurations and pavement performances when a repetitive moving dual-tyre assembly at 8 km/h and 44 kN was applied. Based on the performance testing and visual observation of the pavement cross sections after excavation, the reinforced sections showed reduced rutting and delayed surface cracking compared to the control sections. Specifically, the pavements' measured response showed that geogrid-reinforced pavement sections exhibited less vertical pressure and less vertical deflection in the subgrade when tested at a low speed. Therefore, the study's most notable conclusion is that geogrid reinforcement reduces the horizontal movement of the granular material, especially in the longitudinal direction. The study also concludes the following about geogrid placement: (1) for a relatively thick granular base layer, placing the geogrid in the upper one-third of the base reduces the shear strains in the longitudinal and transverse directions. (2) For weaker pavements, the geogrid reinforcement at the base–subgrade interface reduces the vertical deflection. In the second case, the effectiveness of geogrid shall be compared to the increase in pavement structure or using other geosynthetic materials such as geotextiles.

Dynamic Viscoelastic Analysis of Asphalt Pavements using a Finite Element Formulation

ABSTRACT This paper studies the effect of time and load rate on the structural response of asphalt pavements when the surface layer is a linear viscoelastic material. A finite element incremental algorithm for dynamic analysis of viscoelastic solids is presented, where the stresses are computed using a hereditary integral in which the relaxation modulus is described by a Prony-Dirichlet series. The stresses are integrated in a semi-analytical form, whereas the dynamic equilibrium equations are integrated by the Trapezoidal Rule. Different pulse loads are considered and the viscoelastic responses of different asphalt layer thicknesses are compared. Several performance indicators typically utilized in pavement design are studied, particularly those at the surface layer, i.e., tensile stress and strain, shear strain, and surface deflection.

A study of the Hot-Mix Asphalt layer thickness reduction when applied over lateritic soils cement base in airfield

In tropical region, in upper layers, soils having red or yellow coloration are generally found and are denominated lateritic soils. They are rich in aluminum hydroxides and ferric hydrates that give an elevated mechanic resistance. When the lateritic soils are used as a construction material in the structural pavement, the exceptional mechanical characteristic reduced the cost over 50% when associated with the sub-base and base layers, or over 25% when the lateritic soil is treated with cement. In São Paulo State, it was made more than ten thousands kilometers of roads where the base or sub-base was made using lateritic soils or lateritic soils treated with cement. In this study, it is showed, through Finite Element Method, a critical analysis of the sub-base and base of airfield pavement using lateritic soils cement base course and Hot-Mix Asphalt thickness surface less than recommended for critical area in according to Federal Aviation Administration (1996). Considering the results, it is possible to propose a reduction of thickness Hot-Mix Asphalt layer, resulting in a reduction of the final cost of implantation of hundreds of airfields in South America.

Numerical Simulation of Temperature Stress on Asphalt Pavement of Concrete Bridge Deck in Cold Region

Flexible pavement plays an important role in the primary concrete bridges at present. However, climate environment, to which pavement is exposed, significantly impact pavement stability and long-term performance. Especially, low temperature cracking of asphalt pavement in cold region is a common existing problem. In order to improve the pavement’s crack resistance it is necessary to predict the temperature stress distribution within the asphalt layers. A two-dimensional finite element model of a concrete bridge in thermal and thermal-structural couple analysis is developed to predict temperature and temperature stress variation of asphalt layers in cold region. The temperature stress variation is analyzed at seasonal temperature, different cooling rate and the different thickness of asphalt layers. The model considers a set of primary thermal environmental conditions. Ultimately, the model is aimed at providing pavement engineers with an efficient computational tool that attempts to increase the prediction accuracy of temperature in asphaltic pavement of cold region for more reliable pavement design.

Mechanical properties of asphalt pavement structure in highway tunnel

A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles. The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer, the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the asphalt layer were calculated. The influencing factors such as double-wheel weight; asphalt layer thickness; base course stiffness modulus and thickness; and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.

Long-Term Performance of Chemically Modified Subgrade Soils in Indiana

Chemical modification of soils with lime in Indiana is widely used to improve the workability and compactability of weak subgrade soils. Although the modification process is primarily aimed at construction expediency, additional effects such as long-term improvement of stiffness or strength by pozzolanic and carbonation cementation processes of the treated soils have been expected but have not been quantified. Because of a lack of confidence in the long-term performance of the chemically modified soils, their enhanced stiffness has not been taken into account in pavement design, leading to a conservative design of the asphalt or concrete pavement layers. Six roads that have been in service for 5 to 11 years were selected to conduct field tests. The selection was performed considering (a) location of road project in Indiana, (b) class of road, (c) year when chemical treatment was done, (d) type of chemical modifier used, (e) type of pavement, (f) availability of geotechnical information for postconstruction evaluation, and (g) traffic and safety control for field testing. The results from the field tests show that the long-term stiffness or strength of subgrades that were chemically treated 5 to 11 years ago is 4 to 11 times higher than that of natural sub-grades. This finding suggests that the enhanced stiffness of the chemically modified subgrade could be accounted for in pavement design, which would lead to a reduction of the thickness of asphalt or concrete pavement layers.

Geogrid in Flexible Pavements

Full-scale accelerated testing was used to provide new insight into quantifying the effectiveness of geogrids on low-volume flexible pavement performance. Although several previous studies report that geogrids improve pavement performance by enhancing structural capacity and reducing distress potential, the new study addresses how to maximize the benefits and cost-effectiveness of geogrid. To perform full-scale testing, three cells of flexible pavements, each having three pavement sections, were constructed. The granular base and hot-mix asphalt (HMA) layer thicknesses varied, and each cell had at least one control and one geogrid-reinforced pavement section. Instruments were embedded during construction to measure stress, strain, deflection, moisture, pore-water pressure, and temperature and were used to monitor pavement response to moving load. A moving dual-tire at 8 km/h and 44 kN was used to apply accelerated traffic loading. The performance of the various pavement sections when exposed to accelerated loading is presented. On the basis of pavement measured response as well as visual observation of the pavement cross section after excavation, the study showed that geogrid is very effective in reducing the horizontal shear deformation of the aggregate layer, especially in the traffic direction. Hence, the effectiveness of geogrid is clear for aggregate base layers with thicknesses ranging from 203 to 457 mm, and geogrid is expected to show similar effectiveness for greater base thickness given that thin HMA layer is used. The study also found that the optimal geogrid location in a thin aggregate layer is at the unbound aggregate-subgrade interface. For a thicker base layer, it is optimal to install a single geogrid at the upper third of the layer; the addition of another geogrid at the subgrade-base layer interface may be needed for stability.

Development of a Simplified Design Procedure for Determining Layer Thickness in Long-Life Pavements

This study is a part of the research for developing the technologies of long-life pavements having a design life of more than 40 years. The objective of this study was to develop a simplified design procedure for determining the layer thickness needed for long-life pavements. High modulus asphalt binder for the intermediate layer was introduced and applied in this procedure. To develop the models for predicting the critical pavement responses, a synthetic database was established through use of a finite element program with various combinations of layer thickness and modulus. The synthetic database includes structural and material information, surface deflection, and critical pavement responses. From the developed synthetic database, this paper suggests the minimum layer thickness and modulus value—based on the concept of limited strain level—for long-life pavements. This study also determined experimentally the fatigue endurance limit of asphalt mixtures used in this study. A long-life pavement should have an intermediate layer with a thickness greater than 175 mm (6.89 in.), and an asphalt mix with a modulus greater than 3.5 GPa (507 ksi) should be used. Measured strain values from the accelerated pavement testing and field test sections have been used to validate the proposed design procedure. The validation study has shown that the use of a high modulus asphalt mix is capable of reducing the tensile strain at the bottom of the asphalt concrete layer and layer thickness significantly. The validation study has also shown that the proposed procedure can predict the measured strain values from the test sections within an acceptable level.

EFFECT OF SURFACE CRACKING ON RESPONSES OF FLEXIBLE PAVEMENTS STRUCTURE

Pavement cracking is a major factor of failure in sof pavements structure, In spit of this, seldom intention has be en considered how is the pavement structure has been affected when surface cracking a re presented and/or progressed. On the other hand, higher costs are presented for m aintenance and repair. Generaly, pavement surface conditions in terms of pavement su rface cracks, rutting, roughness and pit-holes are the main factors used to establis h criteria for pavement maintenance and repair. Structural adequacy factor of the pavem ent is usualy neglected. The accurate decision making processes for maintenance and repair works must be done not only due to functional conditions, but also due to structural conditions. Finite element analysis is used in this research p aper using the ANSYS-10 program. SOLID45, and SOLID185 elements represent u nbounded layers, and asphalt cement layers respectively to evaluate the stresses in a flexible pavement system under different conditions. These conditions were: (1) Th e vertical load of a single wheel was modeled as uniform pressure placed directly at the edge of the transverse crack. (2) The effects of seasonal differentiation of the pave ment material properties during winter and summer. and (3) Various crack depthes wh ich represent 25% , 50%, 75% and 100% of the asphalt layer thicknesses are also, considered in the analysis. The horizontal normal stresses along the top and bottom of the AC layer, and vertical stresses at selected points in the base has been in vestigated. Comparisons of stresses finally were made for all scases. It is found that the presence of crack in the AC layer significantly increases both the vertical stresses and the horizontal stresses in the AC layer which i ndicate a greater potential for tensile stresses outside the tire treads than in the middle of the treads. With the wheel load located at the edge of transverse crack there is considerable change in the values of horizontal and vertical normal stresses in the a sphalt pavement layers. Seasonal variation has significant effect on the normal stre sses values, where the maximum horizontal tension stresses (σyy ) is higher in winter than that in summer with abo ut 66% . Finally, it is recommended that at crack depth rati o (CDR) 50% pavement must be rehabilitated to prevent initiation of new crack s or rutting of asphalt pavement surface. In other side the winter season is consid ered the critical for initiation of cracking, as summer season is considered critical f or rutting occurrence.

Performance evaluation of high modulus asphalt mixtures for long life asphalt pavements

This paper describes the results of laboratory and full scale performance tests for a high modulus asphalt binder (HMAB) and mixes (HMAM) developed in this study for long life asphalt pavements. Various binder tests were first conducted on the HMAB and test results showed that the stiffness of the HMAB was significantly increased compared to the conventional binder without changing the low temperature properties of the binder. Laboratory tests for the mixes included dynamic modulus, moisture susceptibility, wheel tracking and fatigue tests. Dynamic modulus test results showed that the modulus of the HMAM was 50% higher than those of the conventional mix at the high temperatures. The results of performance test indicated that the resistances of the HMAM against moisture, rutting, and fatigue damage were better than those of the conventional mix. It was also found from the full scale test sections that the tensile strain values at the bottom of the asphalt layer for the HMAM sections were lower than those of the conventional mix sections although the asphalt layer thicknesses of the HMAM sections were thinner than those of the conventional sections. All the tensile strain values measured from the HMAM sections were within the fatigue endurance limit of 70 microstrain which is the fatigue criterion of a long life asphalt pavement. Similar to the wheel tracking test results, the rut depth occurred in the thick HMAM test section was two times smaller than the conventional pavement section.

Viscoelastic continuum damage finite element modeling of asphalt pavements for fatigue cracking evaluation

This paper documents the findings from the study of fatigue cracking mechanisms in asphalt pavements using the finite element program (VECD-FEP++) that employs the viscoelastic continuum damage model for the asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables into account, such as asphalt layer thickness, layer stiffness, pressure distribution under loading, and load level applied on the pavement surface. The cracking mechanisms in various pavement structures under different loading conditions are studied by monitoring a damage contour. Preferred conditions for top-down cracking were identified using the results from this parametric study. The conjoined damage contours in thicker pavements suggest that the through-the-thickness crack may develop as the bottom-up and top-down cracks propagate simultaneously and coalesce together, supporting observations from field cores and raising the question of the validity of traditional fatigue performance models that account for the growth of the bottom-up cracking only.

Modulus Testing in Indirect Tension Mode

ABSTRACT In 2004, a new European standard (NF EN 12697-26), the object of which is the measurement of stiffness modulus, appeared. It includes five annexes corresponding to five different testing methods, in particular modulus testing in indirect tension (IDT) mode. Given that a typical asphalt layer thickness is about a few centimeters and that coring is the most effective method for obtaining specimens from actual pavements, the IDT testing of cores is bound to become very practical for routine use. Notwithstanding this fact, IDT testing is still of little use in French public and private sector laboratories and, moreover, little information is available in the technical literature concerning the comparison between stiffness modulus data obtained in uniaxial direct tension or tension-compression and in biaxial indirect tension. This paper provides rational understanding, based on principles of linear viscoelasticity in particular, of the moduli commonly used for structural evaluation of asphalt mixtures: complex, secant and resilient moduli. The assumptions and limitations of these moduli are discussed. The pros and cons of the adopted testing and analysis methods are evaluated. A simple and direct relationship was found and exemplified between stiffness moduli obtained either in uniaxial direct tension/tension-compression mode or in biaxial indirect tension mode.

Capacitance sounding: a new geophysical method for asphalt pavement quality evaluation

A capacitance sounding method has been proposed and developed for evaluation of the actual thickness and dielectric permittivity of asphalt pavement. The method is based on the continuous measurements of the electrical capacitance between two electrodes in real time. One of them is grounded within the soil immediately adjacent to the side of the road. Another one (sensing electrode) is mounted on a motor-driven positioner to obtain the capacitance measurements at multiple locations along the direction perpendicular to asphalt surface. The principle of the method is to vary the clearance of the sensing electrode to sound the 1D structure of the pavement beneath that electrode. A distinguished feature of the proposed technology is that the measured signal depends only on the thickness and the permittivity of the asphalt layer. All underlying layers do not affect the capacitance readings. A set of capacitance values versus sensing electrode positions is considered as a sounding curve. Software tools were created for solving forward and inverse problems of the capacitance sounding. An unknown thickness and permittivity are derived from a real-time inversion of the data obtained. Upon completing the inversion, an operator can move the assembling with the second electrode across the asphalt surface to the next sounding site. The capacitance sounding method proved to have a good lateral resolution: the dielectric permittivity values and the asphalt layer thickness are accurately detected over distances of 40 cm from a measuring point. An extensive feasibility study of capacitance sounding using both mathematical modeling and field measurements has been carried out. As a result, portable, low-frequency equipment has been designed and created. Asphalt layer thickness and the dielectric permittivity measurements were carried out on a high-traffic highway. The comparison of field trial results with core sampling analysis demonstrated the efficiency of the proposed method.

Fatigue Cracking Mechanisms in Asphalt Pavements with Viscoelastic Continuum Damage Finite-Element Program

A study of fatigue-cracking mechanisms in asphalt pavements used the finite-element program VECD-FEP++. This program employs the viscoelastic continuum damage model for the asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables, such as asphalt layer thickness, layer stiffness, pressure distribution under loading, and load level applied on the pavement surface, into account. The cracking mechanisms in various pavement structures under different loading conditions are studied by monitoring a damage contour. Preferred conditions for top-down cracking were identified with the results from this parametric study. The conjoined damage contours in thicker pavements suggest that a through-the-thickness crack may develop as the bottom-up and top-down cracks propagate simultaneously and coalesce; that idea supports observations from field cores and raises the question of the validity of traditional fatigue performance models that account for the growth of the bottom-up cracking only.

Finite Element Studies of Asphalt Concrete Pavement Reinforced with Geogrid

Many geotechnical applications are becoming more sophisticated and solutions derived from simplistic procedure are no longer reasonable or solutions do not exist. This paper describes two-dimensional finite element studies that analyzed the behavior of reinforced asphalt pavement under plane strain conditions and subject to monotonic loading. The asphalt material and soils were expressed using triangular elements of elastoplastic behavior that obeys Mohr–Coulomb criteria with associated and nonassociated flow rules. The geogrid was modeled using a one-dimensional linear elastic bar element. The finite element procedure was validated by comparing the results of analysis with the results obtained from a series of model tests. The load–settlement relationships, settlement profile, and strains in the geogrid were compared. The failure load obtained by assuming subgrade foundation with nonassociated flow rule was smaller than that of associated flow rule. There was only minor difference between the results obtained from the associated and nonassociated plastic models. The finite element procedure was capable of determining most measured quantities satisfactorily except the tensile strain in the geogrid, which was assumed linear elastic. The effects of the stiffness of geogrid reinforcement, thickness of asphalt layer, and strength of subgrade foundation were also investigated. The finite element procedure is a versatile tool for enhanced design of reinforced pavement systems.