Asphalt Layer Thickness Research Articles

Evaluating pavement management treatment selection utilising continuous deflection measurements in flexible pavements

The objective of this study was to develop a new structural index based on rolling wheel deflectometer (RWD) deflection data to describe pavement structural capacity and to improve pavement management treatment selection. To achieve this objective, pavement conditions including surface cracking, rutting, roughness and asphalt layer thicknesses were categorised and sorted according to their AC layer thickness and divided into various subgroups. The cumulative distribution function of the new RWD index in each subgroup was generated so that various percentiles were calculated and used to define the boundary between structural and functional rehabilitation. Results showed that the Louisiana criteria may recommend structural rehabilitation for pavements with sound pavement structure (Type I error) and functional rehabilitation to pavements with weak pavement structure (Type II error). Therefore, the state pavement management system should consider both pavement structural indices and surface distress indices currently available when making recommendations for pavement preservation and rehabilitation. RWD testing technology and indices derived from its data are one of the most promising candidates to fulfil this need.

Numerical Analysis of Concrete Block Pavements and Comparison of its Settlement with Asphalt Concrete Pavements using Finite Element Method

Regarding time consuming properties and complex intervention of layers and different materials, it is better to replace laboratory based design and analysis of pavements with quick and powerful software including finite element, finite reduction software and etc. Using finite element software ABAQUS, at first, the paper investigated effects of changes of concrete block thickness in vertical stress and it was validated with experimental results. Also, using this software, effect of asphalt concrete thickness change was studied in vertical strain. And finally, results of finite element model were validated, using experimental data. Regarding that finite element analysis is suitable for crust environments and concrete block pavement does not have such environment, this research tends to compare these two types of pavements, using mathematical equations to analyze settlement. To do this, first, two models were analyzed, one for concrete block pavement and the other one for asphalt concrete pavement. Subgrade and base layers' models were the same in geometrical point of view and types of materials, but thickness of asphalt and concrete block pavement layers and bedding sand changed, alternatively and based on the obtained relations and diagrams, there has been a chance to equate indices of these two types of pavements.

Laboratory and Field Study on Compaction Quality of an Asphalt Pavement

Compaction of hot mix asphalt (HMA) layer is a process of densification through the application of vibratory, dead weight and/or pneumatic tires compactors. These processes are employed independently or in combination, depending on factors such as type of asphalt mix, layer thickness, and weather conditions, to achieve desired density of HMA pavement layers. Appropriate compaction (desired density) of the asphalt mixture is one of the important factors that influence long term performance of an asphalt pavement. During the compaction of HMA layer using vibratory rollers, the applied load and vibration energy cause reorientation and interlocking of asphalt coated aggregates resulting in increase in density. Good compaction is necessary for achieving target specifications such as required density of asphalt layers, stiffness, or volumetric properties of the asphalt mix. These specifications are designed to maximize the resistance of the pavement to deformation, cracking, raveling, moisture damage, and rutting. In the United States of America, target specifications for quality control and assurance of asphalt pavements are usually given in terms of the density of roadway cores extracted from the completed pavement. This paper investigates the level of compaction (in terms of density), that is achievable both in the laboratory and in the field. Compaction quality as a function of compaction time/roller passes and pavement thickness is studied. In addition, the uniformity of compaction over the entire length of the pavement, and the variation in density laterally across the pavement are examined during pavement construction in the field. The results of this study provide insight into the compaction quality that can be achieved during construction. Such information would is helpful for a successful design and the implementation of emerging technologies such as Intelligent Compaction.

Diseño de pavimentos urbanos por retrocalculo según guía AASHTO 93 mediante la utilización del deflectómetro liviano de impacto

One of the uses of a Falling Weight Deflectomer is to determine the overlay thickness throughout backcalculation according to the AASHTO93 guide, which is widely used. This is achieved by the generation of deflections on the old asphalt layer, allowing different asphalt layer thickness in each a part of a road.An analog application to determine the asphalt layer thickness is predictable if the deflection is caused above the base, regarding this there has been several successful experiences worldwide. This application could be helpful in urban street paving given the heterogeneity of the subgrade, the materials, the compaction process, and etcetera. However, the FWD is a high cost device and this makes it difficult to apply, especially because some paving works are not large enough to afford it.Recently similar devices have appeared in the region and they could be a reasonable alternative, such as the Light Weight Deflectometer. The LEMaC,RoadInvestigationCenterfrom the National Technological University ofLa Plata(Buenos Aires–Argentina), regarding the situation described has made an analysis in that sense.At the international level, various initiatives have been developed but they all arrive at a correlation constant, which according to the elastic layers theory would not be recommendable. Models of correlation should be developed instead.A research project was developed in the LEMaC, in order to obtain those correlation models. This was done throughout the use of LWD carried out on road test surfaces and laboratory tests, which are presented with their determination coefficients.

Comparison of Fatigue Damage, Healing, and Endurance Limit with Beam and Uniaxial Fatigue Tests

The concept of an endurance limit assumes a strain value below which the net fatigue damage that occurs during a load cycle is zero. The fact that real traffic loads are separated by rest periods may allow for partial or full healing of the microcracks, which can affect this endurance limit. If the asphalt layer thickness is controlled to keep strains below the endurance limit, the fatigue life of the pavement can be extended considerably. In the study reported in this paper, it was hypothesized that the endurance limit in asphalt concrete developed from the interaction and balance of damage and healing during a load cycle. This hypothesis formed the basis of the testing and analysis program, which evaluated the effects of air voids, asphalt content, rest periods, and temperature on the endurance limit. Two types of fatigue tests were conducted: beam (flexural) and uniaxial. A regression model also was developed on the basis of the results of each test and used to obtain the endurance limit values. This paper compares fatigue damage, healing, and endurance limit results from the two tests under similar conditions. The comparison shows that the beam fatigue test yields less overall fatigue damage and less healing than the uniaxial fatigue test. Beam fatigue yields 8 to 14 times longer fatigue lives, while uniaxial fatigue yields higher healing (10.4 times for the only available case). Because damage and healing combined to govern the endurance limit, the two tests produced close values in which the overall uniaxial endurance limit values were 12% less than the beam fatigue endurance limit values.

Decision of National and Provincial Highway Asphalt Pavement Structure Based on Value Engineering

It is important that decision of asphalt pavement structure requires overall considerations of the performance and financial investment. To have asphalt pavement structure fulfilling good reliability, the asphalt pavement structure decision was researched based on value engineering theory. According to the national and provincial highway investigation data in Shandong Province during the last decade, the asphalt pavement performance attenuation rules of traffic levels and asphalt layer thicknesses were developed, and then the road performance evaluation method was presented. In addition, the initial investments, the costs of road maintenance, and middle-scale repair in a period were analyzed. For the light traffic and medium traffic example, using the value engineering method, the pavement performance and costs of which thickness varies from 6 cm to 10 cm were calculated and compared. It was concluded that value engineering was an effective method in deciding the asphalt pavement structure.

Measurements of the stiffness and thickness of the pavement asphalt layer using the enhanced resonance search method.

Enhanced resonance search (ERS) is a nondestructive testing method that has been created to evaluate the quality of a pavement by means of a special instrument called the pavement integrity scanner (PiScanner). This technique can be used to assess the thickness of the road pavement structure and the profile of shear wave velocity by using the principle of surface wave and body wave propagation. In this study, the ERS technique was used to determine the actual thickness of the asphaltic pavement surface layer, while the shear wave velocities obtained were used to determine its dynamic elastic modulus. A total of fifteen locations were identified and the results were then compared with the specifications of the Malaysian PWD, MDD UKM, and IKRAM. It was found that the value of the elastic modulus of materials is between 3929 MPa and 17726 MPa. A comparison of the average thickness of the samples with the design thickness of MDD UKM showed a difference of 20 to 60%. Thickness of the asphalt surface layer followed the specifications of Malaysian PWD and MDD UKM, while some of the values of stiffness obtained are higher than the standard.

The Interrelationship between Indirect Resilient Modulus and Dynamic Modulus for Dense Graded Hot Mix Asphalt

Permanent deformation is one of the most important types of distress in flexible pavement. Currently and based on the Australian Mechanistic-Empirical Pavement Design Procedure, the indirect tensile test (IDT) is conducted in New Zealand in order to determine the asphalt modulus. This test is carried out on a 100 mm diameter by 50 mm height specimen. However, the current Simple Performance Test (SPT) procedure requires the dynamic modulus to be obtained from the axial compression test performed on 100 mm diameter by 150 mm height specimen. One issue related to the axial compression test is that it is often impossible to obtain this size specimen from actual pavement since a typical asphalt layer thickness is less than 150 mm in New Zealand. Therefore, IDT becomes more appropriate for existing pavement evaluation due to its privilege of testing on cored size specimens. The objective of this research is to perform an experimental and analytical study on the dynamic modulus parameters derived from the aforementioned test methods to improve design accuracy. In this research, two common types of asphalt cement are tested at three different air void percentages. Graphical and statistical comparisons of results from the axial compression and IDT test methods are presented in order to assess their interrelationships. The findings show that, the dynamic modulus determined form IDT test is in good agreement with that form axial compression tests. Based on the statistical analysis, more than 90% of data showed complete similarity for the dynamic modulus calculated from these two tests.

Analysis on Shear Stresses of Asphalt Layers on Lean Concrete Base

Since it exist a significant difference in stiffness between asphalt surface and lean concrete base layer,the probability of shearing failure increase.In this paper,a typical structure of asphalt pavement with lean concrete base is established,selecting smooth state as the interfacial contact condition.BISAR3.0 is used to calculate stresses in the multilayered elastic system.Results display that the thickness of asphalt layer and the load condition have an enormous influence on shear stresses,while surface modulus,the modulus and thickness of base layer do not much affect the shear stresses in surface.

Orthogonal Analysis on Responses Indexes of Asphalt Pavement

The asphalt layer thickness, base thickness, the modulus of the asphalt layer, base modulus and subgrade modulus are selected as the responses indexes of asphalt. The level of each factor corresponding parameters and test results table are established by orthogonal analysis for four-level table of five factors. This paper took the Shell Designing Software BISAR 3.0 as calculation tool to get the three-dimensional response results of the different kinds of asphalt pavement. Based on results, the course bottom tensile strain of the asphalt layer, subgrade compressive strain and maximum shear stress of asphalt pavement are analyzed by intuitive analysis, variance analysis, and sensitivity analysis. It is found that the sensitivity analysis is a more accurate analysis of the factors of the factor in the level of assessment indicators. Response to the degree of influence of various factors on the pavement mechanics, pavement structure design and material design should be selected according to road type of damage specifications. In accordance with the sensitivity analysis of the impact of factors based on balanced other design specifications.

Impact of Traffic Overload on Road Pavement Performance

Traffic on a road pavement is characterized by a large number of different vehicle types, and these can be considered in pavement design by using truck factors to transform the damage they apply to the pavement to the damage that would be applied by a standard axle. The truck factors to convert trucks into standard axles or the load equivalent factors to convert axles into standard axles are defined by considering the average loads for each axle. This process includes the vehicles that travel with axle loads above the maximum legal limit. There are also a substantial number of overloaded vehicles in terms of total vehicle weight. These axles/vehicles cause significant damage to the pavements, increasing the pavement construction and rehabilitation cost. Thus, this paper investigates the impact of overloaded vehicles on road pavements by studying the truck factors for different vehicle cases applied to a set of pavements composed of five different asphalt layer thicknesses and five different subgrade stiffness moduli. The study revealed that the presence of overloaded vehicles can increase pavement costs by more than 100% compared to the cost of the same vehicles with legal loads.

Effects of high modulus asphalt binders on performance of typical asphalt pavement structures

Several factors related to the performance of high modulus asphalt binders (HMABs) in pavement engineering were studied: stiffness, elastic recovery, asphalt layer thickness reduction, workability and thermal cracking resistance. Results showed that HMABs had higher stiffness and elasticity than neat binder. The asphalt layers thickness could be significantly reduced by replacing neat binder with HMABs. The coarse aggregate absorption method provided reasonable means to estimate mixing temperature for HMABs. The application of HMABs where the low design temperature of the pavement is lower than −16°C should be with caution based on the low temperature performance grades of HMABs.

Structural Design and Sensitivity Analysis of Semi-Rigid Pavement of a Motorway

This paper presents application of mechanistic-empirical methods in design of semi-rigid pavement for a section of a motorway in Poland. The stage construction was assumed. Three fatigue criteria were applied in the design. For asphalt fatigue cracking and subgrade soil the criteria from the Asphalt Institute (USA) were applied. For fatigue cracking of cement stabilized bases the Dempsey (USA) and De Beer (South Africa) criteria were applied. Software BISAR was used. Additional study was carried out to find the sensitivity of design thickness of asphalt layer related to several design factors. The most significant factors were (a) load transfer through shrinkage and reflective cracks, (b) high summer temperature which causes decrease of asphalt layers stiffness and increase of tensile stresses in cement stabilized bases, and (c) the effect of overloaded vehicles.

Importance of Nonlinear Anisotropic Modeling of Granular Base for Predicting Maximum Viscoelastic Pavement Responses under Moving Vehicular Loading

AbstractThis paper explains the importance of using a nonlinear anisotropic three-dimensional (3D) finite-element (FE) pavement model to simulate the granular base layer and predict viscoelastic pavement responses under moving vehicular loading. The FE model was built using the general-purpose FE software ABAQUS, and a user material subroutine was developed to implement the constitutive model of granular material using a modified Newton-Raphson approach with secant stiffness. The FE model utilizes implicit dynamic analysis and simulates the vehicular loading as a moving load with 3D contact stresses at the tire-pavement interface. The analysis results indicate that it is important to consider the viscoelastic nature of the asphalt layer and the moving load for accurately capturing the nonlinear granular base modulus in the mechanistic pavement model. The modulus distribution in the granular base layer is affected not only by wheel load and pavement structure (such as asphalt layer thickness and subgrade s...

Thermal Effect Mechanism on Composite Pavement Consisted of Asphalt Surface Overlay and Concrete Layer

Composite pavement consisted of flexible asphalt surface overlay and rigid concrete base layer has come up. Though it occupies advantages of asphalt and concrete pavements, still there are problems containing thermal cracking, rutting deformation and pothole which result from the out-sync shrinkage of temperature. Therefore, influence of temperature on the composite pavement structure has been analyzed with methods of theoretical analysis and numerical simulation. And results indicate that the thickness of asphalt layer in some sense determines the influence extent of temperature and worst case happens at the concrete joints, which means that the optimal asphalt (Here, the best choice of asphalt thickness equals 16cm) and suitable joints should be designed.

Comparison of the Pavement Layers Thickness Measured by Georadar and Conventional Methods – Examples From Croatia

Thickness of the pavement structure layers represents an important data for the implementation into the database of roads already constructed, during the pavement strengthening design, particularly if the appraisal of the bearing capacity of the pavement structure is done by means of the Falling Weight Deflectometer, during reconstruction of pavements or during control of the newly constructed roads. If reconstruction is carried out by procedures of recycling of the existing pavement the details about the thickness of asphalt layers are important not only when determining the depth of the intervention but also when designing asphalt mixture. During quality control of the newly constructed road sections the Ground Penetrating Radar (GPR, georadar) can be used as the instrument for fast and efficient determination of the thickness of layers. Measuring is done at speeds that approx correspond to the speeds of traffic flow, so that disturbance of traffic is minimum, whereby the safety of participants in traffic and measuring personnel is increased. The paper presents several examples of determining the thickness of layers of road pavement structures by the non-destructive GPR method. The obtained results were compared to conventional methods of determining thicknesses that are used in Croatia, i.e. coring or data obtained by surveying methods during construction of the pavement structural layers. Measurements were done on completely new and existing roads of different age having the asphalt pavement.

Effects of overlay designs on reliability of flexible pavements

Management of flexible pavements requires timely application of preventive maintenance and rehabilitation actions such as overlays. These actions are an integral part of a design strategy that minimises the use of recourses over the pavement's life-cycle. The objective of this paper is to develop a reliability model for flexible pavements that accounts for the effects of overlay designs. In this paper, the pavement responses are determined by the linear theory of elasticity for the system of pavement layers, while the pavement reliability is represented as a series system of two failure criteria: fatigue cracking and rutting. To illustrate the developed model, a numerical study is presented. Sensitivity and importance measures are computed for the parameters and the random variables included in the limit state functions. The sensitivity measures suggest that the initial asphalt layer thickness and the sub-grade stiffness are the critical predictors of the pavement performance after application of a structural overlay.

Establishing Effective Linear Temperature Gradients for Ultrathin Bonded Concrete Overlays on Asphalt Pavements

The effective linear temperature gradient is a significant input needed to characterize the effects of environmental loadings when available pavement design procedures are used for bonded concrete overlays on asphalt (BCOA), also known as thin or ultrathin whitetopping. Establishing such an input is challenging and therefore has not been well guided in current BCOA design procedures across the country. Guidance is provided on suitable values for the effective equivalent linear temperature gradient (EELTG) that can be used in the design of ultrathin BCOAs. The EELTG is expressed as a function of the climatic conditions, geographical location, and design features of the BCOA: longitude, latitude, elevation, annual mean percentage of sunshine, overlay panel size, 28-day modulus of rupture for the portland cement concrete, and thickness of the hot-mix asphalt layer. Typical values for the annual mean percentage of sunshine are recommended to facilitate implementation of the proposed guideline in the current design procedures.

Impact of Wide-Base Tires on Pavements: Results from Instrumentation Measurements and Modeling Analysis

Wide-base tire technology can reduce vehicle fuel consumption and greenhouse gas emissions because there is less rolling resistance at the tire–pavement interface. This study investigated the impact of wide-base tires on two typical flexible pavement structures—full-depth and thin asphalt pavements—through accelerated pavement testing and advanced finite element modeling. Three tire configurations (dual, the first-generation 425, and the new generation 455 wide-base tires) and various pavement sections with different asphalt layer and granular base layer thicknesses were considered. In particular, the advanced modeling simulated realistic tire–pavement interaction and considered appropriate material properties for each pavement layer. It was evident from this study that, of the three possibilities, the wide-base 425 tire configuration caused the greatest pavement damage. The wide-base 455 tire was found to cause greater bottom-up fatigue cracking and increased potential for subgrade rutting than the dual-tire assembly on most tested sections except the thin pavement section with the thickest granular base layer. However, the impact of wide-base tires on fatigue cracking and subgrade rutting potential became less significant with a stronger pavement structure. The finite element modeling results indicated that, compared with the dual-tire assembly, the wide-base 455 tire resulted in similar or less primary rutting potential in thin asphalt pavements and less near-surface cracking potential in thick asphalt pavements.

Influence of Tire–Pavement Stress Distribution, Shape, and Braking on Performance Predictions for Asphalt Pavement

Advances in computing power and more realistic laboratory characterization of properties of pavement layers have resulted in a rational approach to predicting the performance of hot-mix asphalt (HMA) mixtures that takes into account pavement temperature, complex contact stress distributions, and rate of loading. A study was conducted to evaluate the effect of tire–pavement contact stress distribution and braking on flexible pavement responses while also considering moving loads and viscoelastic properties of the asphalt layer. The computed pavement responses were used to predict rut depth and bottom-up fatigue cracking in the asphalt layer following the Mechanistic–Empirical Pavement Design Guide approach for computation of pavement distresses. The comprehensive study used three pavement sections and laboratory-measured mixture properties for the HMA layer. The data for measured nonuniform contact stresses showed a much larger contact area and substantial variation in contact stress distribution than did the conventional uniform conditions often assumed in pavement analyses. Regardless of the asphalt layer thickness, mixture type, and braking condition, all three uniform contact stress distributions (circular, square, and elliptical) overestimated the maximum vertical strains and thus HMA rut depth by as much as 71% compared with those from a nonuniform contact stress distribution. For the nonbraking condition, an increase of 34% to 71% in HMA rut depth was observed for the uniform stress distributions compared with the nonuniform stress distributions. The HMA rut depth was three to four times larger for the pavements subjected to braking condition regardless of the type and shape of the tire–pavement contact stress distribution. Numbers of cycles to fatigue failure in nonbraking conditions for the uniform contact stress distributions were within 15% of those determined for the nonuniform stress distributions. Braking further increased the failure limit to as much as 27%, an indication of the importance of accounting for braking in pavement performance analyses.