AC Layer Research Articles

Fatigue Cracking Behaviour and Characteristics of Flexible Pavement Subjected to Freight Coal-Truck Loading

Fatigue cracking is one of the varieties of flexible pavement distress caused by frequent traffic loads, and it is also a sign of structural collapse. Using finite element methods, numerical simulations were conducted to evaluate the strain changes that occur throughout the process of flexible pavement cracking. Several flexible pavement configurations with various thickness and different material properties of AC layer were developed, and several loading conditions in terms of the axle load, the speed, and the loading cycles of the freight truck were modelled. The numerical modelling showed that the greatest horizontal tensile strain in the 1stAC layer (surface course) is at the surface-centre of the pavement structure, which is predicted to be prone to top-down cracks. In other side, the greatest horizontal tensile strain in the 2ndAC layer (base course) is at the bottom-below of the tire tread, which is predicted to be vulnerable to bottom-up cracks. The outcomes of this study added to the knowledge gathered from previous studies, especially regarding the critical locations within the AC layer with the greatest magnitude of horizontal tensilestrain and their potency to experience either the top-down cracking or bottom-up cracking, as well as related to the effect of slowing the truck speed and increasing both the truck’s hauling load and loading cycles on the fatigue life of asphalt concrete layer. Future research needs to be done to evaluate the balance between both permanent deformation behaviour of the AC layer and to determine the optimum flexible pavement configurations.

ANALISIS KONDISI PERKERASAN JALAN DENGAN METODE BINA MARGA DAN PAVEMENT CONDITION INDEX (PCI)

Highways are one of the infrastructures to accelerate the growth and development of an area, especially the Klungkung Regency. Due to the age of the road pavement plan, the road service level will decrease. If this condition is left unchecked, it will worsen the condition of the pavement layers and the costs required will increase. Therefore, it is necessary to analyze the road damage so that later it can determine the maintenance and handling program. In writing this analysis using qualitative methods, data on road damage conditions was carried out by visual surveys, on the Kutapang-Maos road section, with the length of the road being observed along 1,200 km from km 0+000 - km 1+200. The categories of types of damage reviewed are cracking, patches and holes, surface hardness, grooves, and subsidence. While the existing condition of the pavement width is 3 meters, the pavement thickness is 5 cm with the AC layer, and the last overlay was carried out in 2009. The condition of the road shoulders is 1.5 – 2 meters wide with a grassy surface. In the analysis of the types of damage raveling, alligator cracking, patching, longitudinal and transverse cracking, shoving, potholes, ruts, and grade depressions with the Bina Marga method analysis, the priority order value is 8 while the PCI method analysis gets the road condition value is 6, meaning the road is included in moderate condition level (Fair) and the order of priority is 9 so that the appropriate alternative type of maintenance is a routine maintenance program. The form of handling the damage is with Burtu, Burda, and Lapen, while the costs required are Rp. 27,702,395.00-

Performance analysis of subgrade in asphaltic rail track design and Indonesia’s existing ballasted track

AbstractDue to subgrade-related concerns, the performance of Indonesia’s ballasted track continues to be significant impediments for the Indonesian railway stakeholders’ intention to increase the speed of passenger train operations. This study aims to examine the vertical compressive stress in the subgrade of Indonesia’s ballasted track and two asphaltic rail track designs, asphaltic overlayment and asphaltic underlayment, under various cyclic loading conditions based on three different train speeds, 120 (low speed), 240 (medium speed), and 360 kph (high speed). The AC layer thicknesses for each asphaltic rail track design are as follows: 0.1, 0.2, 0.3, and 0.4 m for asphaltic underlayment, and 0.075, 0.15, 0.225, and 0.3 m for asphaltic overlayment. 2D finite element models and simulations were used to capture and predict the subgrade’s vertical compressive stress performance. The most obvious finding to emerge from this study is that the asphaltic overlayment track has a greater capacity for transmitting and decreasing stresses from the top structure to subgrade layer than the asphaltic underlayment track and the Indonesia’ ballasted track, respectively. This research can shed light on the prospective application of asphaltic rail track to the Indonesian rail network for the faster passenger trains operation.

Mechanical properties of coarse asphalt Mixture-Paved trackbed under High-Speed moving train loads

The long-term stability of the substructure is a critical guarantee for the safety and ride comfort of high-speed railway (HSR) operations. The asphalt mixture-paved trackbed (APT) can not only play a favorable role in preventing and draining water on the top of the subgrade but also be beneficial to the gradual change of vertical stiffness between layers. This paper determines a coarse but dense-graded asphalt mixture suitable for the APT and numerically analyzes the mechanical properties of APT under high-speed moving train loads. The results indicate that the SBS-modified asphalt mixture (SBS-25) with the optimum asphalt content (OAC) of 4.2 % is more appropriate than the crumb rubber-modified asphalt mixture (CRMA-25) for the APT. The dynamic stress in the subgrade of APT is significantly determined by the conditions of the AC layer. Meanwhile, the vibration attenuation of APT is directly related to temperature change. Compared with the traditional ballastless track, the vibration acceleration of APT with trackbed thickness of 300 mm reduces by 20.1 % at 20 ℃ while only reducing by 1.7 % at 40℃. Moreover, the greater the structural stiffness of the APT, the stronger the control on dynamic deformation of each layer in the subgrade, and the influence on the formation is weaker than that on the bottom layer of the subgrade. The findings hopefully contribute to the APT substructure design; however, further verification of real engineering still needs to be conducted by field or full-scale tests.

Evaluating the performance of inverted pavement structure using the accelerated pavement test (APT)

• Full-scale inverted pavement was investigated. • Accelerated pavement test was applied to the inverted pavement. • Rutting performance between inverted and conventional pavements was compared. • Inverted pavement structure outperformed the conventional flexible pavement. Inverted pavement is considered an unconventional type of flexible pavement structure. In this pavement structure, an unbound aggregate base (UAB) with a low initial modulus is sandwiched (layered) between two stiffer layers, a thinner asphalt concrete layer (AC) and a cement-treated base layer (CTB). This paper presents a comparison study of the rutting performance (permanent deformation) between conventional and inverted pavement structures. In addition, the inverted pavements with different thicknesses of UAB and CTB were studied. The accelerated pavement test (APT) method was conducted on a full-scale pavement consisting of two inverted pavement lanes and one typical three-layer conventional flexible pavement lane as the control section for performance comparison. Significant permanent deformation was observed in all three pavement lanes after the completion of 100,000 passes of APT. Comparisons of the measured total deformations showed that the inverted pavement structure outperformed the conventional pavement. Furthermore, the inverted pavement with a thicker CTB layer exhibited less deformation compared with the inverted pavement with a thicker UAB layer. The stiffness of the UAB layer of the inverted pavement increased with the loading passes. A stiffer UAB could provide a cushion for the thin AC layer, resulting in less deformation in the AC surface compared with that of the conventional pavement. Furthermore, the loading on the pavement surface had a larger affected area in the inverted pavement structure. Based on the overall pavement conditions, the inverted pavement can be regarded as a promising alternative to the conventional flexible pavement, and the asphalt mixture layer thickness can be reduced during the construction.

Asphalt Layer Cracking Behavior and Thickness Control of Continuously Reinforced Concrete and Asphalt Concrete Composite Pavement

Based on thermal–mechanical coupling simulation analysis and physical engineering tracking observation, the mechanical behavior and response of a continuously reinforced concrete and asphalt concrete (CRC + AC) composite pavement layer were analyzed, and the causes of cracking on the surface and bottom of the asphalt layer were revealed. Studies have shown that under normal driving conditions, the AC layer, which is usually in the position of the wheel load gap and wheel load side, more easily generates a longitudinal “corresponding crack”. Compared to normal driving, longitudinal cracks are generated more easily inside of the curve, and transverse cracks occur more easily on poor stadia curves. When the AC layer thickness is less than 8 cm, the AC layer is more prone to bottom-up cracking, and it is more prone to top-down cracking when it is more than 8 cm thick. Comprehensively considering the tensile stress, shear stress, and the thickness of the AC layer, it is recommended that the suitable thickness range of the AC layer is 8 cm~14 cm. The calculated results show good agreement with the physical engineering investigation. The research results can provide a theoretical and scientific basis for cracking control and the rational design of a CRC + AC composite pavement layer.

Numerical Analysis of Top-Down Crack in AC Layer of Continuous Reinforced Composite Pavement under Multifactor Coupling

Numerical Analysis of Top-Down Crack in AC Layer of Continuous Reinforced Composite Pavement under Multifactor Coupling

Field investigation and numerical analysis of an inverted pavement system in Tennessee, USA

Inverted pavement system has been introduced for many years with field investigations, laboratory studies and numerical simulation works. Field investigations of inverted pavement structures have not been widely conducted and are very limited in the USA. This study presents a comprehensive field study on a full-scale inverted pavement as well as a conventional control pavement section constructed in Tennessee, USA. A combination of multiple non-destructive testing (NDT) methods, including ground penetration radar (GPR), Benkelman beam test, 3D road profiling test by laser crack measurement system (LCMS), and falling weight deflectometer (FWD) tests were utilized to assess the actual thickness, structural capacity and surface conditions of the pavement structures. The road surface profiling test results showed that the inverted pavement outperformed the conventional section in roughness, cracking and rutting conditions. Deflection Basin Parameters (DBPs) such as surface curvature index (SCI), base damage index (BDI), base curvature index (BCI) and W7 (7th sensor’s value of FWD) values were compared to study the layers’ condition of the inverted and conventional pavement sections. In addition, a preliminary simulation analysis by a Finite Element Method (FEM) model was conducted to compare the performance of inverted and conventional pavement sections under FWD load. The simulation results showed that the inverted pavement structure could reduce the potential of crack initiation and propagation due to smaller tensile stress at the bottom of the asphalt concrete layer (AC). Also, the smaller deflection was measured at the top of subgrade soil (SG), which reduced the total deflection of the inverted pavement structure. Furthermore, the cement-treated base (CTB)-constrained unbound aggregate base (UAB) acted as a cushion to relieve the tension from CTB and support the AC layer. The stress-dependent property of UAB in the inverted pavement contributed to the performance and ductility of inverted pavement but had little influence on the conventional pavement.

Stress-strain characteristics and service life of conventional and asphaltic underlayment track under heavy load Babaranjang trains traffic

Abstract A more durable rail track structure is fundamental in the railway industry, allowing the government to operate the train with higher speed and axle load. That means more passengers and better quality of railroads travel, thereby reducing the maintenance costs and ensuring passengers’ comfort and safety. The effect of a sub-ballast and asphalt layer thickness and freight train traffic with low operational speed on mechanical behavior and design life of conventional track and asphaltic underlayment track, are presented in this paper. One of the significant findings to emerge from this study is that an AC layer with minimum thickness of 0.20 m is required in the asphalt underlayment track application for Indonesian railway infrastructure to facilitate Babaranjang freight trains with up to 50% more tonnage. The evidence from this study also suggests that the asphalt underlayment track with 0.20 m thick of AC layer that contains grade PG70-28 binder could be beneficial to be applied in Indonesian railway system so that the rail track could be constructed with less volume of works than the regular Indonesia's conventional track with 0.40 m of sub-ballast layer.

Influence of Modulus of Base Layer on The Strain Distribution for Asphalt Pavement

In order to investigate the influence of modulus of the base layer on the strain distribution for asphalt pavement, the modulus ratio of the base layer and the AC layer (Rm) is introduced as a controlled variable when keeping modulus of the AC layer as a constant in this paper. Then, a three-layered pavement structure is selected as an analytical model, which consists of an AC layer with the constant modulus and a base layer with the variable modulus covering the subgrade. A three dimensional (3D) finite element model was established to estimate the strains along the horizontal and vertical direction in the AC layer under different Rm. The results show that Rm will change the distribution of the horizontal strains along the depth in the AC layer; the increase of Rm could reduce the maximum tensile strain in the AC layer, but its effect is limited; the maximum tensile strain in the AC layer does not necessarily occur at the bottom, but gradually rises to the middle with the increase of Rm. Rm could significantly decline the bottom strain in the AC layer, and there is a certain difference between the bottom and the maximum strain when Rm is greater than or equal to one, which will enlarge with increasing Rm. Rm could change the depth of the neutral axis in the AC layer, and the second neutral axis will appear at the bottom of the AC layer under a sufficiently large Rm. The average vertical compressive strain in the AC layer will significantly enlarge with the increase of Rm.

Characterizing the fatigue cracking behaviors of OGFC pavements using the overlay tester

The objective of this study was to evaluate the fatigue performance of the composite specimens combined by OGFC and the underlying dense-graded layer (OGFC-AC) by conducting overlay tester (OT) tests. Other two types of specimens, including single layer OGFC13 and single layer AC20, were fabricated to make comparable analysis with OGFC-AC composites. For OGFC-AC specimens, the effects of tack coat application rate and contaminations (soil and oil) were quantificationally explored. Peak tensile stress, cracking rate index (CRI), and dissipated energy were obtained and analyzed. Meanwhile, the damage propagation during the fatigue tests were analyzed using a damage factor. Results indicated that the peak tensile stresses of OGFC-AC composites were somewhere between OGFC13 and AC20. Contaminations would attenuate the peak tensile stress. There existed a power exponential relation between dissipated energy and the load cycle. CRI and damage factor presented the same development law in demonstrating that the fatigue cracking resistance of OGFC13 was superior, followed by AC20, and the performance of OGFC-AC was inferior. The results of CRI and damage factor showed that an optimum tack coat application rate (0.4 kg/m2) existed at which the OGFC-AC composites presented the least cracking potential. The contamination of soil partially increased the cracking resistance, which was probably due to the fact that some sand particles in soil increased the friction and interlock effect between OGFC and the AC layer.

FDTD Simulation for Moisture Asphalt Pavement Thickness and Density Estimation Utilizing Ground Penetrating Radar

Ground penetrating radar (GPR) has the potential to estimate the thickness and density of asphalt pavement during compaction. However, the surface moisture sprayed by the compactor interferes with the accuracy of data collection significantly. This study proposed an approach based on the extended common midpoint (XCMP) method to minimize the effect of surface moisture. Both the numerical simulation of finite-difference time-domain (FDTD) and laboratory experiments were carried out to study the effect of the surface moisture on the GPR signal. Then, three FDTD models with different incident angles of GPR signal were established, and the difference of time intervals obtained from dry and moisture pavements with each model was studied to propose a proper antennas installation mode. Finally, the thickness and density estimated using the proposed method and surface reflection method were compared to validate the accuracy of the proposed approach. The results show that: 1) FDTD models were verified to simulate the interaction of GPR signal with moisture pavement effectively; 2) the time interval of the GPR signal between the surface and bottom of AC layer increased as the thin wet layer dielectric constant grew, and remained unaffected by the electric conductivity of the thin wet layer; 3) the average error of thickness and density predicted utilizing the proposed method were less than 1.3% and 2.4%, respectively, undercomplicated compaction conditions. This study notes that compaction monitoring in real time could benefit from the proposed method.

Evaluation of the effects of transverse cracking on the falling weight deflectometer data of asphalt pavements

ABSTRACT This study aims to investigate the effects of transverse cracking on the deflections of asphalt pavements. 3D finite element models were developed to simulate various intact and cracked asphalt pavements. The deflections of intact and cracked pavements under falling weight deflectometer (FWD) loading were computed and compared. In most cases analyzed, the deflections of cracked pavements are greater than those of intact pavements. For pavements with thermal cracking, the deflections can be 12% and 25% greater than those of intact pavements for cement treated base (CTB) and granular base (GB), respectively. For pavements with reflective cracking, the deflections of cracked pavements can be 98% greater than those of intact pavements, and the deflection decreases sharply across the reflective crack and in some cases it can even increase with increasing distance from the loading center. Crack location and width mainly affect the deflections on the loaded side of crack. Both thermal and reflective cracking have greater influences on the deflections of pavement with a thicker AC layer and a weaker subgrade. The effects of reflective cracking on the deflections are significantly greater than thermal cracking. LTE30–60cm is recommended as a deflection index to distinguish reflective cracking from thermal cracking.

Novel double‐layer DC/AC railway traction power supply system with renewable integration

Back-to-back converter based railway traction power supply system (TPSS) can eliminate neutral sections in the traction side and improve power quality in the grid side, but it still has some drawbacks such as low reliability, difficulty in accepting large-capacity renewable energy, and power mismatches. In this study, a double-layer DC/AC TPSS with renewable integration is proposed to address these challenges and to improve system performance. The proposed topology breaks the limit of back-to-back structure and enables more flexible free energy flow. A top-down system design method is proposed in this study. Firstly, the characteristics of the proposed TPSS for integration with renewable power are described and compared with the traditional back-to-back topology. Secondly, a DC droop controller and a AC droop controller are designed for DC layer grid and AC layer grid, respectively, to control the power flow in each layer. The traditional AC droop control is based on the inductive transmission impedance, but the resistance of traction transmission line cannot be ignored. Thus, a modified droop control strategy with the consideration of line resistance is also proposed in this study. Subsequently, the voltage control strategy for the single modular multilevel converter is designed to track the reference signal from the upper droop controller. Finally, a general double-layer DC/AC TPSS is designed from bottom to top, and the simulation results confirm that the proposed TPSS with renewable integration is capable of delivering desirable performance.

A planning framework for AC-DC bilayer microgrids

This paper proposes a novel stochastic planning framework for bilayer microgrids (BμGs), which facilitates the integration of different types (AC and DC) of loads and distributed generations (DGs). In contrast to the conventional μG configurations that adopt single layer, the bilayer configuration has an AC layer in addition to a DC layer, where all the AC/DC loads and DGs are connected directly to the corresponding AC/DC layer. The interconnection between the AC and DC layers is achieved through one or more interlinking converters (ICs). Depending on the types, locations, and specifications of the μG loads and DGs, the planning framework allows each node to be a universal node that can include two buses (AC and DC) or a single bus (AC or DC). The network wiring can also be universal (AC, DC, or both) to facilitate the connection between the system nodes. The framework determines the optimal BμG configuration that minimizes the system total costs by providing the following decisions: the AC-layer connection; the DC-layer connection; and the number, locations and sizes of the ICs. Two case studies have been implemented and solved using different μG configurations to demonstrate the effectiveness of the proposed framework and the benefits of the BμG.

Artificial neural network back-calculation of flexible pavements with sensitivity analysis using Garson’s and connection weights algorithms

The primary objective of this research was to develop a model to accurately predict the modulus of flexible pavement layers from surface deflections measured using the falling weight deflectometer (FWD) device. To do so, a synthetic dataset consisting of 10,000 flexible pavements was created using the layered elastic theory. The developed dataset contained the moduli values for different pavement sections, and deflections at known distances from the load center. Next, the moduli of different asphalt pavement layers consisting of a surface course, base course, and subgrade were calculated using the Artificial Neural Network (ANN) methodology through backcalculation. The inputs for the neural network are thicknesses and deflection values at seven distances from the load center. The outputs are the moduli for different layers. The optimum neural network consists of two hidden layers and has a general architecture of 9-36-18-3. The transfer function is sigmoid for hidden layers and linear for the output layer. Results indicate that the ANN model can predict the modulus of different layers accurately with a coefficient of determination (R2) of more than 0.999 in all cases. For validation, the results from the developed model were compared with typical backcalculation software of ISSEM4, MODCOMP, MODULUS, WESDEF, and BAKFAA as well as 386 LTPP sections. Moreover, an analysis was conducted to assess the contribution of inputs in moduli prediction for each of the pavement layers using the Garson algorithm and the Connection Weight methods. It was concluded that the results from the latter method are in better agreement with the theories. Finally, the significance of different input variables was assessed using an indirect method by excluding each from the analysis and checking of the model predictability power. It was concluded that in order of significance, the base layer thickness, 1st geophone deflection, and the AC layer thickness are the variables that their exclusion causes large errors.

Effect of reclaimed asphalt pavement in granular base layers on predicted pavement performance in Egypt

This research presents the prediction of pavement performance constructed with base layer consisting of reclaimed asphalt pavement (RAP)/virgin aggregate blends. The prediction was made by the Multi-Layer Elastic Analysis software (KENLAYER) in terms of horizontal tensile strain at the bottom of AC layer and the vertical resilient strain at critical locations within the pavement system. The dynamic modulus |E*| for the hot mix asphalt was estimated by using the quality-related specifications software considering three different climatic conditions and two levels of design speeds. Finally, total pavement rutting and fatigue cracking were determined using the critical strains computed by the Multi-Layer Elastic Analysis along with the Mechanistic Empirical Pavement Design Guide performance models and transfer functions. In general, the RAP blends showed superior/comparable performance compared to natural aggregates for the application in base/subbase layers for the Egyptian conditions. The effect of the rate of loading and climate conditions was significant on both asphalt concrete layer fatigue cracking and rutting.

Investigation of accuracy of pavement mechanistic empirical prediction performance by incorporating Level 1 inputs

Abstract The recently developed AASHTOWare pavement mechanistic empirical (M-E) design requires advanced characterization of pavement materials. In particular, M-E Level 1 analysis requires materials input parameters to be obtained from the laboratory test results. In cooperation with the New Mexico Department of Transportation (NMDOT), six pavement sites were selected to compare M-E Level 1 predicted performances from laboratory tested data with the field performances. Pavement materials such as subgrade, base, asphalt concrete, binder, aggregate, etc., were collected from these pavements sites during construction. Laboratory dynamic modulus, fatigue endurance limit (FEL), dynamic shear rheometer, and resilient modulus tests were conducted on the collected materials. Using these parameters, pavement sections, as constructed, were modeled and analyzed in M-E at Levels 1, 2 and 3. The predicted distress quantities for international roughness index (IRI) and rutting were compared with the field collected data as well as among the three design levels. The analysis results demonstrated that M-E overpredicts IRI and rutting in the pavement compared to the field performance. It was also observed that Level 1 showed the lowest rutting, whereas the maximum rutting was found at Level 2. The dynamic modulus of AC layer was underpredicted at Levels 2 and 3 resulting in higher rutting and IRI.

Evaluating Dynamic Modulus for Indiana Mechanistic-Empirical Pavement Design Guide Practice

After the implementation of the Mechanistic-Empirical Pavement Design Guide (MEPDG) in Indiana, an overall evaluation of the stiffness characteristics of local AC mixtures and the ability of level III MEPDG predictive equations to estimate dynamic modulus (E*) with local mixtures was required. Therefore, the primary objectives of this study were to identify significant differences among Indiana asphalt mixtures, to evaluate the performance of commonly used E* predictive models, and to assess the influence of level III E* input on the pavement design life of typical pavement structures. It was found that Indiana mixtures do not show extensive variability among mixtures having the same nominal maximum aggregate size. When conducting a statistical analysis to group asphalt mixtures having similar characteristics, few mixtures were left out of the groups. In general, it was observed that mixtures having Ndes equal to 75, showed the lowest E* values along the entire frequency range. The Witczak 1-37A showed the most accurate and less biased E* predictions for Indiana mixtures. It showed the highest R2, and the least deviation from the measured E* values. However, predicted E* input values produced higher levels of pavement distress compared with measured E* values, indicating general overprediction. Besides, using level III (predictive) rather than level I (measured) E* input values can influence the pavement thickness design due to the functional performance (i.e., the International Roughness Index (IRI)). When a structural performance (i.e., bottom-up cracking) was taken into consideration, no influence of the E* input type on the design AC layer thickness was observed.

One‐Pot Synthesis of CuS Nanoflower‐Decorated Active Carbon Layer for High‐Performance Asymmetric Supercapacitors

AbstractCopper sulfide‐active carbon (CuS‐AC) with a three‐dimensional (3D) porous structure is fabricated based on AC‐supported CuS nanosheets by using a solvothermal method and used in a high‐performance asymmetric supercapacitor devices to enhance the specific capacitance, cycling stability, and energy density. The CuS nanosheets form an array on the AC layer, and the two kinds of materials are ideally combined, leading to increased conductivity and enlarged electroactive surface area of the electrode materials. Moreover, the 3D CuS‐AC porous structure exhibited excellent electrochemical energy storage properties with large specific capacitance (247 F g−1 at a current density of 0.5 A g−1), high energy density (24.88 Wh kg−1 at the power density of 800 W kg−1), and good long‐term cycling stability (92% capacitance retention after 5000 cycles). This superior electrochemical performance can be ascribed to the high pseudocapacitance of CuS and large surface area from AC. The experimental results indicate that the hierarchical nanostructure design of CuS grown on AC exhibits considerable potential for supercapacitor applications.