Asphalt Pavement Layers Research Articles

The Effects of Asphalt Migration on the Dynamic Modulus of Asphalt Mixture

Asphalt migration is one of the significant detrimental effects on asphalt pavement performance. In order to simulate the state after the occurrence of asphalt migration amid asphalt pavement layers and further investigate the effects of asphalt migration on the dynamic modulus of asphalt mixture, samples with different asphalt contents layers were firstly separated into the upper and lower half portions and then compacted together. By conducting the dynamic modulus test with the Superpave Simple Performance Tester (SPT), the variation laws of the dynamic modulus (|E*|) and the phase angle (δ) at different testing temperatures and loading frequencies were analyzed in this paper. Further, the dynamic modulus and the stiffness parameter (|E*|/sinδ) at the loading frequency of 10 Hz and testing temperature of 50 °C were illustrated. Simultaneously, the master curves of the dynamic modulus and phase angle of asphalt mixtures under different testing conditions were constructed to better investigate the effects of asphalt migration on the dynamic modulus by means of Williams–Landel–Ferry (WLF) equation and Sigmoidal function. Results show that, after the asphalt migration, the dynamic modulus of asphalt mixtures increase with the increasing loading frequency while they decrease with the increasing testing temperature; the dynamic modulus and the stiffness parameter are the highest when asphalt mixtures have the optimum asphalt content layers, and then decrease with the incremental difference of asphalt content in the upper and lower half portions. Besides this, different from the master curves of dynamic modulus, the master curves of phase angle firstly increase with the increase of loading frequency to the highest point and then decrease with the further increase of loading frequency and are not as smooth as that of dynamic modulus. It can be concluded that the asphalt migration has compromised the mixture’s mechanical structure, and the more asphalt migrates, the weaker the mechanical properties of asphalt mixture will be. Additionally, based on the shift factors and master curves in the time–temperature superposition principle (TTSP), the effects of asphalt migration on the dynamic modulus and the variation laws of the dynamic modulus of asphalt mixture after the occurrence of asphalt migration can be better construed at the quantitative level.

Fiber Optics Sensors in Asphalt Pavement: State-of-the-Art Review

Pavement design is essentially and usually a structural long-term evaluation process which is needed to ensure that traffic loads are efficiently distributed at all levels of the total road structure. Furthermore, to get a complete analysis of its durability behavior, long-term monitoring should be facilitated, not only from the top by falling weight deflectometer (FWD) or core drilling but preferably from inside the structure and at exactly the same positions during a long-time interval. Considering that it is very hard to devise an efficient method to determine realistic in-situ mechanical properties of pavements, the determination of strain at the bottom of asphalt pavement layers through non-destructive tests is of a great interest. As it is known, fiber Bragg grating (FBG) sensors are the most promising candidates to effectively replace conventional strain gauges for a long-term monitoring application in a harsh environment. The main goals of this paper are to compile an overview of the recent developments worldwide in the application of fiber optics sensors (FOS) in asphalt pavement monitoring systems; to find out if those systems provide repeatable and suitable results for a long-term monitoring; if there are certain solutions to validate an inverse modelling approach based on the results of FWD and FOS.

Influence of tack coat on reflective cracking propagation in semi-rigid base asphalt pavement

Asphalt tack coat, which is usually used to ensure a bond between asphalt pavement layers, has a significant effect on mechanics response in asphalt pavement during traffic loading and temperature loading. In this paper, the tack coat is applied between asphalt overlay and semi-rigid base to investigate its influence on reflective crack in asphalt pavement. Cohesive zone model (CZM) in contact property is employed to simulate tack coat. Moreover, extended finite element method (XFEM) is utilized to analyze the reflective cracking propagation. In addition, the combined loads of temperature and moving traffic are applied on the asphalt pavement. The mechanical response, crack temperature and reflective cracking propagation are investigated in semi-rigid base asphalt pavement. Results indicate that maximal tensile stress at crack tip increases with the increase of tack coat modulus while crack propagates. However, the maximal tensile stress at pavement surface decreases with the increase of tack coat modulus while crack propagates. A decrease in tack coat modulus results in a gradual increase in temperature differences of crack initiation and crack completion. Hence, decrease of tack coat modulus between asphalt overlay and semi-rigid base can improve resistance of reflective crack in asphalt pavement.

Study on Dynamic Response Characteristics of Saturated Asphalt Pavement under Multi-Field Coupling.

To study the dynamic response of saturated asphalt pavement under moving load and temperature load, 3-D finite element models for asphalt pavements with hydro-mechanical coupling and thermal-hydro-mechanical coupling were built based on the porous media theory and Biot theory. First, the asphalt pavement structure was considered as an ideal saturated fluid–solid biphasic porous medium. Following this, the spatial distribution and the change law of the pore-water pressure with time, the transverse stress, and the vertical displacement response of the asphalt pavement under different speeds, loading times, and temperatures were investigated. The simulation results show that both the curves of the effective stress and the pore-water pressure versus the external loads have similar patterns. The damage of the asphalt membrane is mainly caused by the cyclic effect of positive and negative pore-water pressure. Moreover, the peak value of pore-water pressure is affected by the loading rate and the loading time, and both have positive exponential effects on the pore-water pressure. In addition, the transverse stress of the upper layer pavement is deeply affected by the temperature load, which is more likely to cause as transverse crack in the pavement, resulting in the formation of temperature cracks on the road surface. The vertical stress at the middle point in the upper layer of the saturated asphalt pavement, under the action of the temperature load and the driving load, shows a single peak.

Integrated predictive artificial neural network fatigue endurance limit model for asphalt concrete pavements

Asphalt endurance limit is a strain value if experienced by asphalt pavement layer, no accumulated damage will occur and is directly related to asphalt healing. Therefore, if the pavement experiences this value of strain, or lower, no fatigue damage would accumulate within that pavement section. Beam fatigue test data conducted under the NCHRP Project 9-44A were extracted and utilized to create an artificial neural network predictive model (ANN) to determine the endurance limit strain values for conventional asphalt concrete pavements. The developed ANN model architecture as well as how to utilize it to predict the endurance limit were demonstrated and discussed in detail. Also, a stand-alone equation that is capable in the prediction of the endurance limit strain value, separate from the ANN model environment, was derived utilizing the eclectic extraction approach. The model training and validation data included 934 beam fatigue laboratory data points, as extracted from NCHRP Project 9-44A report. The developed model was able to determine the endurance limit strain value as a function of the stiffness ratio, number of cycles to failure, initial stiffness and rest period, and had a reasonable coefficient of determination (R2) value, which indicates the reliability of both the developed ANN model and the stand-alone equation. Furthermore, a correlation between the endurance limit strain values, as predicted utilizing the generated regression model under the NCHRP project 944-A, and the endurance limit strain values predicted utilizing the stand-alone ANN derived equation was found with a high R2 value.

Phosphogypsum, tropical soil and cement mixtures for asphalt pavements under wet and dry environmental conditions

Phosphogypsum (PG), a by-product of phosphoric acid, is sensitive to the variation in water content. Therefore, this paper aims to investigate the use of hemihydrate PG (HH) mixed with a fine lateritic soil (S) and cement (C) considering the mechanical and durability characteristics in wet and dry cycles. This study investigated hemihydrate PG (HH) produced in the laboratory using a thermal treatment process aiming its application in mixtures for asphalt pavement layers. The mixtures of soil with different contents of HH and cement were obtained based on previous studies and physical-chemical designs. The natural soil and mixtures were characterized by laboratory tests and compacted at a fixed energy and time after moistening (from 5–25 min). In order to carry out the durability tests, the mixtures were cured for 7 days in a wet chamber and then 12 cycles of wetting, drying and brushing were applied. Unconfined compression tests were performed after a 7-days curing process with and without immersion and after durability tests with 1, 6 and 12 cycles. The resilient modulus was found by dynamic triaxial testing for different curing times (0, 7 and 28 days) in a wet chamber. Scanning electron microscopy images were obtained to improve understanding on the changes in the behavior of the samples. Solubility tests were also performed considering soil and water quality. It is possible to conclude that the mixtures demonstrate technical viability for pavements, but solutions related to solubility must be considered to avoid environmental problems.

Research on Mesoscopic Response of Asphalt Pavement Structure under Vibration Load

The various damages of asphalt pavement are closely related to the mesomechanical gradual behavior of asphalt materials, and it is very important to study the mesoscopic response under vibration loading in order to reveal the failure mechanism of asphalt pavement. The semisinusoidal vertical load is applied to the subgrade‐surface discrete element model in this paper, and we use the model to analyze the evolution behavior of microcrack generation and expansion processes, stress distribution and stress transfer, and displacement field in various structural layers of asphalt pavement. The results show that the number of cracks increases rapidly on both sides of the vibration load, the rut is generated due to repeated load on the wheel, the asphalt mixture has bulging phenomenon on both sides of the rut and formed macroscopic cracks at the ridge, the microcracks extend mainly along the weak joints of the edges of the coarse aggregate and the asphalt cement, the number of microcracks increases slowly at the initial stage of the vibration load, the microcracks increase sharply until macroscopic cracks appear with the vibration load increases, the direction of compressive stress extends parallel to the microcrack, and the direction of tensile stress extends perpendicular to the microcracks inside the asphalt pavement. The results show that the discrete element method can not only obtain the stress and displacement of each structural layer, but also reveal the microcrack gradual behavior between particle flows.

Fatigue performance of interface bonding between asphalt pavement layers using four-point shear test set-up

This paper aims to study the fatigue performance of interface bonding between asphalt pavement layers. To fulfill this objective, a four-point shear test (4PST) set-up was developed, and a series of fatigue tests were conducted on composite asphalt beam samples made up of stone mastic asphalt (SMA) and asphalt concrete (AC) mixtures. The combined effect of test temperature (3 levels), normal pressure (6 levels), loading frequency (5 levels), and shear stress (6 levels) with single tack coat type and application rate were considered for evaluation. Two interface failure criteria were successfully adopted in this study, and high correlation was relatively found between the fatigue test results and the corresponding fatigue life criteria. Findings of this study revealed that firstly, both the interface fatigue life and shear stiffness increased at all temperatures with increasing normal stress. Secondly, with increasing loading frequency, the interface fatigue life increased at each temperature. Thirdly, shear stiffness decreased with increasing shear stress for each temperature; the decrease was more pronounced at lower temperatures. Power laws were also proposed to characterize interface fatigue life at each temperature. Finally, the results of the analysis of variance (ANOVA) indicated that unlike the fatigue life, all factors had a significant effect on the shear stiffness. A multiple regression model was established successfully to predict the initial shear stiffness.

Analysis of Strain Law of Structural Layer of Semi-rigid Base Asphalt Pavement with Graded Crushed Rock

Based on the long-life test road project of Yunluo expressway in Guangdong province, the strain law of the semi-rigid asphalt pavement with graded crushed rock was analyzed and studied. Firstly, the ANSYS finite element analysis model was established according to the structure of Yunluo long-life test road, and the strain data of corresponding points were extracted according to the strain arrangement scheme of Yunluo test road. Secondly, FWD was used as the loading device, and the strain data of different points of the corresponding structure layer were obtained according to the test scheme of the long-life test road of Yunluo. Finally, through the analysis of the theory and the measured strain data, the strain law of the semi-rigid base asphalt pavement with graded gravel rock was obtained. To grasp the mechanical response law of this type of asphalt pavement structure, it would provide useful help for the design, construction and maintenance of the semi-rigid base asphalt pavement structure with the graded crushed rock.

Principal component analysis-based predictive modeling and optimization of permanent deformation in asphalt pavement: elimination of correlated inputs and extrapolation in modeling

Permanent deformation in asphalt pavement is a function of material properties, loading, environmental conditions, and structural design (e.g., thickness of pavement layers). Because of the large number of effective variables and their nonlinear interrelationships, it is not easy to develop a predictive model for permanent deformation. In this study, a laboratory database containing accumulated strain values (output) and material properties (inputs) from several asphalt pavements has been used to develop a predictive model for permanent deformation. We first show that the inputs are highly correlated, then principal component analysis (PCA) is used to compute a set of orthogonal pseudo-inputs. Two predictive models based on the pseudo-inputs were developed using linear regression analysis and artificial neural networks (ANN) and are compared using statistical analysis. Extrapolation using empirical predictive models is highly risky and discouraged by experienced practitioners, so to guard against extrapolation, a method is developed to determine an input hyper-space. The above-developed model, along with an n-dimensional hyper-space, provides sufficient information for supporting an optimization algorithm for finding the minimum accumulated strain. An asphalt pavement design with accumulated strain value of 1772 micro-strain (0.02 in. in a 10-in.-thick asphalt pavement layer) is obtained by solving the optimization problem and the design parameters meet flexible pavement design specifications. The proposed framework is able to generate accurate predictive models when the original inputs are highly correlated and able to map to an optimal point in the fitted input space.

Assessing the Bond Strength of Hot Mix Asphalt Pavement for Wearing and Binder Courses

This study investigated the use of a shear box device to measure the bond condition between two layers of hot mix asphalt pavement: the wearing course and the binder course. The wearing course analysed was a Malaysian dense-graded asphaltic concrete mixture of nominal maximum aggregate 10 mm in size (AC10), which was applied over the binder course of another dense-graded asphaltic concrete mixture, AC28. A range of bond conditions was investigated by selecting various asphalt emulsions, application rates, and wearing course thicknesses based on the Malaysian standards of specification. Test results showed that interface shear strength increased as tack coat application rates and wearing course thicknesses increased. Among the tested asphalt emulsion types, a modified asphalt emulsion called RS2KL provided the highest shear resistance. Findings also show that a binder's complex shear modulus elastic portion (G*/sinδ) can affect interface shear strength for thin mixes at low rates of tack coat application.

Artificial neural network-based prediction of field permeability of hot mix asphalt pavement layers

ABSTRACT Field permeability of Hot Mix Asphalt (HMA) needs to be controlled to prevent excessive ingress of water into asphalt pavements, which leads to premature failure. Existing literature shows scatter in the prediction of field permeability values and relationships between factors affecting permeability are complex and are not known precisely. The objective of this paper is to present the analysis and modelling of field permeability of HMA with artificial neural networks (ANN). Permeability data from field testing at five sites, along with materials and mix data are presented. Preliminary statistical analysis to identify correlations and significant factors were conducted. A three-layer ANN was built and trained with part of the data and it was validated and also tested on two separate sets of data. The performance results indicated excellent prediction ability of the neural network. Experiments were conducted to improve the model, and the relative importance of the different factors was evaluated. Gradation and air voids were identified as two of the primary factors affecting field permeability. It is recommended that ANNs be considered to be used on a regular basis for predicting field permeability, particularly because field permeability tests are processes that require a considerable amount of time and resources.

An investigation on the interface bond strength of geosynthetic-reinforced asphalt concrete using Leutner shear test

The application of geosynthetics between the cracked asphalt pavement layer and new asphalt layers to retard reflective cracking has gained interest in the past decades. The performance of the interlayer system depends on its capacity to bond between the old and newly laid overlay layers. This study is taken up to evaluate the interlayer bond strength between the asphalt pavement layers that is reinforced with a geosynthetic product impregnated with asphalt as a tack coat material. Three geosynthetic reinforcement materials made of coir, jute, and glasgrid are used for the bond strength evaluation. The strength of the unreinforced (UR) interface samples are also evaluated for comparison. A trial pavement section was constructed to obtain the reinforced and unreinforced samples for the current research work. The main objective is to study the effects of these geosynthetic products at different temperatures on the interface shear strength behaviour of the reinforced asphaltic concrete layer. Leutner shear tests are employed for the estimation of the shear strength of these samples. The tests are performed at five different temperatures, −10, 0, 10, 20 and 30 °C to understand the thermal effects on the composite interface in the pavement. The shear tests conducted at a strain rate of 50 mm/min shows an increase in strength by 10–15% with change in temperature from −10 to 10 °C followed by 80% reduction in strength up to 30 °C. It is observed that the shear strength of the geosynthetic-reinforced interface samples reduces by 20–50% compared to the unreinforced samples depending upon the type of geosynthetic material. This paper proposes an equation to predict the Leutner shear strength at any temperature varying from −10 to 30 at the studied range of strain rates knowing the peak shear modulus of unreinforced samples at −10 °C and the reduction factor for the geosynthetic interlayer.

Fiber Bragg Grating Sensors in Three Asphalt Pavement Layers

In the present study, a new approach to the installation of fiber Bragg grating (FBG) sensors in three asphalt pavement layers (the surface layer and both base layers) was implemented for the first time in Belgium. Fiber Bragg grating sensors (FBGs) are diagnostic tools that accurately and efficiently monitor in situ structural behavior. However, nowadays, this technology is not commonly used in asphalt due to its application restrictions under installation and service conditions. FBGs are fragile and break easily under loading. Therefore, there is a need for suitable protection of FBG sensors if they are to be installed during the rough construction process and exposed to heavy-duty loading afterwards. The main objective of the present study is to show the FBG results only for the initial construction process, and, if successful, to continue studying this FBG monitoring system and to plan the next research step by adjusting the system for its application in heavy-duty pavements. Two approaches to FBG installation in three asphalt layers (placed at the bottom of each layer) were tested in the present study: (1) installation of FBGs in prefabricated asphalt specimens in the base layer, directly on the base, and (2) installation of FBGs on the surface of the previously constructed asphalt layer. Both innovative approaches allow the implementation of FBGs without sawing the whole layer into two parts. The obtained results proved a survival rate of 100% for the FBGs. It can be concluded that these new described methods of FBG installation—using a cross-section configuration to carry out strain measurements in two directions (transverse and longitudinal)—can be applied for the monitoring of heavy-duty pavements, while providing the possibility to further re-evaluate current pavement design methods used in Flanders (Belgium).

Quick heating method of asphalt pavement in hot in-place recycling

To improve the heating rate of asphalt pavement in Hot In-Place Recycling (HIR), a quick heating method was proposed. Considering input heat flux, the thermal capacity and thermal resistance of asphalt pavement materials, a novel heat transfer model was established based on energy conservation law. Time-dependent heating temperature field distributions of various heating methods were calculated with Euler formulation, and numerical simulation results from the heating transfer model were validated by measured results. The results indicate that one-way continuous heating method (OCHM) leads to an obvious temperature gradient along the depth direction at the upper layer of asphalt pavement, and the heating speed is too slow when the temperature at the bottom of the upper layer reaches 100 °C. However, the heating speed is increased using another reciprocating intermittent heating method (RIHM). The surface temperature is changed periodicity, and the operation is too complex to control all the peak temperatures at 180 °C, which leads to the aging or charring of asphalt binder. Finally, a new constant temperature heating method (CTHM) was proposed and the ideal heat flux curve was obtained. With CTHM, the surface temperature of asphalt pavement is always kept 180 °C to ensure the heating quality by adjusting the input heat flux. Especially, the heating speed with CTHM is the fastest compared with OCHM and RIHM.

Study the Using of Reed Mats in Asphalt Pavement Layers

During the service life, the asphalt pavement layers subjected to various detrimental types of distresses such as permanent deformation, fatigue, stripping and shoving which lead to the complete failure of the pavement. In Iraq roads the permanent deformation (rutting) is the importance distresses which cause impact on the highway performance and reducing the service life of the pavement. The research aims to utilize locally available materials and environment friendly as reinforcement layer. The program of this research include preparing asphalt mixes represent surface layer by using locally available materials and using the reinforcement layer which made of reed. The permanent deformation test has been done with three temperatures (40˚C, 50˚C and 60˚C) and four locations of the reed mats. The test results of the wheel- Track for the rutting measurement showed that the rut depth decrease in reinforcement layers as compared with unreinforcement layers for all temperature testing. The reed netting embedded bottom and middle of wearing layer has the best amount of improvement (75%, 84% and 85%).

Incorporation of GPR data into genetic algorithms for assessing recycled pavements

The current paper outlines the necessity to incorporate Ground Penetrating Radar (GPR) during assessment procedures in order to increase the accuracy of backcalculated results through the increased accuracy provided for test location thickness data. The focus is on the assessment of a pavement that has undergone full depth reclamation with foamed asphalt (FDR-FA). The examined pavement structure was rebuilt and in operation for a total of five years at which point a scheduled monitoring program was undertaken. The monitoring of the investigated section was carried out in-situ by both Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR) measurements and the asphalt pavement layers moduli were estimated utilizing genetic algorithms and evaluated. GPR data was vital for the investigation as the coring data along the section exhibited an increased variability along the test section. Results of the investigation are found in the paper and they indicate increased accuracy from the inclusion of GPR data and point to the long term sustainability of the FDR-FA process.

Application of Microcracking Technology at the Grassroots Level in Rapid Repair

The technical characteristics combined with the pre-crack at home and abroad present the early strength of grassroots without the material repair technology.However, the grassroots space mesh microcracks must be implemented in the early period of heavy traffic, and widely related transverse cracks reflective of asphalt pavement cracking probability, which decreases asphalt pavement status, are also improved; a finite element method was analyzed to simulate the ideal type of crack between the two kinds of mechanical asphalt pavement crack under the form of responses, and the surface layer of microcracking technology life asphalt pavement is calculated. This study found that the microfracturing technique reduced the life of the asphalt surface to some extent. However, to solve the problems of the conventional repair techniques for readily reflective cracks and to achieve a rapid restoration of the technical requirements, a microcracking technology rapid repair in the grassroots has indicated a certain feasibility.Considering that crack forms are drawn, the fatigue life of the asphalt surface, the definition and control of the size of the cracks in the construction, and other related issues require further studies under actual crack forms.

Characterization of Interface Bonding in Asphalt Pavement Layers Based on Direct Shear Tests with Vertical Loading

AbstractThe interface bonding condition between asphalt concrete layers is unquestioned as one of the significant factors influencing pavement performance. In order to research the interface charac...

Dynamic characteristics of 100% cold recycled asphalt mixture using asphalt emulsion and cement

This paper aims at investigating the dynamic characteristics of 100% cold recycled asphalt mixture using asphalt emulsion (CRME) and cement. Firstly, dynamic modulus and phase angle of CRME are studied at different curing times. Then, creep and relaxation of CRME are also studied to determine its response at service condition with higher temperature. Lastly, fatigue life of CRME is evaluated in pavement structure and the fracture interface microstructure of CRME is observed by Scanning Electron Microscopy (SEM). The results indicate that CRME is a viscoelastic material and has time-temperature dependence effect both in its early-stage and fully cured stage. The viscoelastic of CRME is significantly weaker than that of HMA. CRME can be depicted by Burgers model and has excellent ability to resist permanent deformation at 60 °C. Fatigue life of CRME is only 1/5-1/10 of ordinary asphalt mixture at high strain, but which still meets the requirement for special heavy traffic (>25,000,000 cycle/track) in road structure. The difference of CRME and HMA in dynamic properties and fatigue life is explained by its internal microstructure. This research may help to better understand the materials property of CRME and benefit to the application of CRME in higher layer of asphalt pavement.