In most of developing countries across the world, pavement design is still based on an empirical approach that may result in premature failure or overdesigned pavements. A shift from an empirical to a semi-mechanistic or mechanistic approach is the need of modern time. In this regard, computational tools such as finite element (FE) are being successfully utilized to gain deeper insights because such tools have allowed researchers to study the complex behaviour of bituminous concrete (BC) materials. It is well recognized that BC material typically exhibits viscoelastic/visco-elasto-plastic behaviour depending on applied loading (including temperature) conditions. However, due to the complexity of the whole procedure yet many pavement design tools consider them as pure elastic material. The aim of this research is to develop FEM based simple and practical framework to evaluate the structural response of BC material with viscoelastic material characterization which can be an effective tool to predict field behaviour with commonly available pavement material tests. Such a framework will be helpful in analysing variations in the critical response of BC pavement with varied traffic loads and ambient temperatures. The framework provides a relatively simple procedure to obtain the viscoelastic parameters of BC mix with a creep compliance test conducted at different temperatures. It was concluded that Creep compliance data if pre-smoothened by the Power law model reduces mathematical optimization issues to some extent. Furthermore, with the obtained parameters, a 3-dimensional FE model was developed to obtain sensitivity to critical stresses, strains, and vertical deformations at desired conditions. Material characterization of unbound granular layers was evaluated through resilient modulus based on empirical relations. Analysis was carried out taking into consideration the traffic load, contact pressure, mix type, air-void, and temperature variation.

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Inconsistencies between performance data from laboratory-prepared and field samples have been widely reported. These inconsistencies often result in inaccurate condition prediction, which leads to inefficient maintenance planning. Traditional pavement management systems (PMS) do not have the appropriate means (e.g., mechanistic solutions, extensive data handling facilities, etc.) to consider these data inconsistencies. With the growing demand for sustainable materials, there is a need for more self-learning systems that could quickly transfer laboratory-based information to field-based information inside the PMS. The article aims to present a future-ready machine learning-based framework for analyzing the differences between laboratory and field-prepared samples. Developed on the basis of data obtained from field and laboratory data, the gradient-boosting decision trees-based framework was able to establish a good relationship between laboratory performance and field performance (R2test > 80 for all models). At the same time, the framework could also show more complex relationships that are often not considered in practice.@en

The ever-growing need to build roads to meet the necessary transportation demands is challenging, especially for developing countries. Low-volume roads (LVRs) are usually the backbone of catalyzing economic growth in these countries. With impediments surrounding Petroleum bitumen (price fluctuations) and environmental concerns, scientists are putting their effort into finding an alternative. The presented research is an attempt to check if Natural asphalt can be used as a full or partial replacement of the Petroleum bitumen. To the best of the authors' knowledge, only limited studies have focused on characterizing and understanding the engineering properties of Natural asphalt. The available techniques do not provide reliable information to the road authorities and hence they are discouraged from using it in practice. Particularly for countries, where the Natural asphalt source is available, the overall dependence on importing the Bitumen could be substantially reduced. Empirical and experience-based design criteria may not be sufficient as the standards were never developed for such materials, hence, a scientific approach is required before bringing it into practice. In this research, Natural asphalt sourced from different locations in Nigeria was assessed. Before performing the mixture level tests using Marshall and Cantabro design methods, the rheological and fatigue properties of the extracted Natural bitumen were examined in the laboratory. In the design of the experiment, various percentages of Natural asphalt were added between 0 % and 20 % by total mix weight; implying that the remaining required fraction of binder was fulfilled by the addition of petroleum bitumen. By using a ranking system (supported by statistics), an optimal design of mixture was obtained which was used in the field (exposed to normal traffic) at 30 different sections.

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The relationship between real-world traffic and pavement raveling is unclear and subject to ongoing debates. This research proposes a novel approach that extends beyond traditional correlation analyses to explore causal mechanisms between mixed traffic and raveling. This approach incorporates the causal discovery method, and is applied to five Dutch porous asphalt (PA) highway sites that have substantial data sets. Findings indicate a nonlinear relationship between traffic volume and raveling, with road age emerging as a shared contributor. The results also suggest that the degree to which different vehicle types contribute as a causal factor for raveling varies with carriageway configurations and lane characteristics. This underlines the need for targeted maintenance strategies. Challenges remain due to confounding correlations among traffic variables, necessitating further development of causal discovery models. This study may not conclusively resolve the debate on to what extent traffic contributes to raveling, but we argue we provide sufficient evidence against rejecting this hypothesis.

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In the context of climate change and global warming, the attention on the environmental cost of pavements is increasing. To scientifically quantify the environmental cost of pavements, accurate prediction of rolling resistance and fuel consumption is important. In this paper, a comprehensive review on rolling resistance of asphalt pavements and its environmental impact was presented. At first, the commonly used definitions of rolling resistance and texture characterisation methods of pavement surface were introduced. Then, the influence of different factors on rolling resistance was discussed. Next, the measuring and modelling approaches of rolling resistance were reviewed. At last, methods which can be used to predict fuel consumption and environmental impact were presented. It was found that an ideal approach for texture characterisation of pavement surface is to make use of the entire wavelength spectrum of road profiles and consider the enveloping curve of tire treads. Furthermore, the fact that rolling resistance can be influenced by different factors introduces difficulties in accurate measurement and modelling of rolling resistance. Moreover, testing methods and conditions have a significant effect on the empirical modelling of rolling resistance, while it is difficult and time-consuming to consider all the energy loss in the computational modelling of rolling resistance. In addition, the prediction of fuel consumption and environmental impact highly depends on the formulating methods and measuring conditions. The work presented in this paper will help to gain more insight into rolling resistance and its environmental impact, which ultimately promotes the construction of environmentally friendly pavements.

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A critical review of lab and field measurement methodologies, harmonization in measuring techniques, and modelling of skid resistance of asphalt concrete pavement have been provided. Although several past studies have provided literature review on general topics of skid resistance, to the best of the author's knowledge, none of them have compressively covered the topic considering the status & requirements of developing nations. There has been significant development in speed with the improvement in computational facilities. In modern times, with the improvement in infrastructure quality in developing nations, permitted speeds have also drastically increased. To avoid skid-related accidents, it is important to develop good practices in maintaining sufficient skid resistance. The requirements and the availability of technology might be significantly different in developing nations. The suitability and limitations of various methods used for capturing the skid characteristics of the surface have been outlined. The harmonization in skid resistance measurement using laboratory and field-testing methods has been summarized. Correlation analysis of various in-situ and laboratory test data has been made to maintain a better harmony of measurement either in the field or in the laboratory. In the subsequent sections, progress in the modelling approach (analytical to numerical) has been discussed in brief. Computational capabilities of an analytical and numerical modelling approach for predicting pavement skid resistance characteristics have been reviewed. These models have been developed to consider complex attributes of tire pavement interactions like hydroplaning, temperature rise in the tire, mix morphology, tire inflation, and vehicle acceleration and deceleration for predicting skid resistance. These attributes of skid resistance have been discussed in detail and presented a basic overview of the model development process which is missing in past review studies. Few recent studies on skid resistance measurement and modelling to highlight the use of new technology and improvements over conventional techniques have been presented in the manuscript which has not been reviewed earlier. Critical factors affecting the skid resistance model like hydroplaning, tire-related parameters, temperature, and surface texture have been highlighted in this manuscript. Few key research directions have been suggested as the scope of future study to predict a more reliable skid resistance model.

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The demand for alternative bitumen which could fully/partially replace Petroleum sourced bitumen for pavement construction is globally increasing. The increase in demand can be associated with several factors: depletion in crude oil resources, advances in crude oil refining processes, increased demand for highway infrastructure, and regional transportation-environmental policies. Since the production of Petroleum bitumen consumes energy and generates emissions, there is an effort to decrease harmful emissions which has inspired researchers to look for so-called "green alternatives". Natural bitumen could be considered a green alternative as it is a mixture of bitumen and mineral matter present naturally on earth, mainly if the Natural bitumen can be transported easily to the construction site. This paper reviews the state-of-the-art information on pavement construction using Natural bitumen from laboratory and field perspectives. The Physico-chemical properties, rheological properties and field behaviour of asphalts pavements containing Natural bitumen were assessed. Many road authorities would hesitate to utilise Natural bitumen for pavement applications due to a lack of available data, knowledge and a systematic research study. To the best of the authors’ knowledge, there is no comprehensive literature review article on Natural bitumen. Thus, the presented article aims to comprehensively review Natural bitumen resources and their types, Physico-chemical properties, application in pavement constructions, and reported field performances. At the end of the paper, future research challenges, future recommendations and a methodological framework is proposed.

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Understanding the relationship between pavement raveling and traffic characteristics is important to pavement management and maintenance planning. In this work, we propose a framework to empirically quantify this relationship. It consists of an alignment method to tackle the inconsistent spatial-temporal scales of the raveling and traffic measurements and we propose spatial-temporal maps to qualitatively analyze and compare the data. A non-parametric correlation is done on the aligned raveling and traffic flow data. This framework is applied to five study areas in the Dutch highway network. The correlation analysis of the study areas provides empirical evidence to a commonly held theory that traffic flow has effects on raveling. Categorizing the correlation by lanes indicates that the raveling is homogeneous in the through or auxiliary lanes, and the severe raveled sections are parallel to the road discontinuity, suggesting the potential effect of mandatory lane changing on raveling development. The proposed framework can be employed in empirical raveling models that predict raveling based on traffic and other factors.@en

Membranes of sufficient bonding characteristics could improve the integrity of the multi-layer structures on orthotropic steel deck bridges (OSBDs), enhancing thus the structural response of these systems and, ultimately, their service life. In this research, full-scale experiments were performed at the LINTRACK accelerated pavement testing facility of the Delft University of Technology to evaluate the performance of two surfacing systems commonly used in the Netherlands, giving emphasis on assessing the interface response of membranes with the surrounding materials. Results indicated that the tensile strains remain almost uniform at the top of porous asphalt, in both transverse and longitudinal directions, as no appreciable loss in stress-carrying capabilities was seen even at the end of the testing program. The sections exhibited similar behaviour in terms of strains, with some differences in strains indicating the impacts of membranes at interfaces. The importance of membranes of the desired bonding characteristics was also reflected by the relative displacement measurements. The relative interlayer slip had been higher in the transverse direction than the longitudinal one, with slightly higher displacements in one of the test sections. Overall, no cracking was observed on either section, and the current findings support the use of membranes between surfacing layers on OSBDs.

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First, porous asphalt (PA) pavement possesses a lower strength and lifetime compared to typical dense-grade asphalt mixtures due to its large empty space structure. Second, PA pavements' fatigue life and durability are affected significantly by climate factors; the two most critical factors being aging conditions and moisture actions. Third, because of the environmental concerns connected with producing or repairing asphalt pavements using only virgin materials, studies have recommended reusing reclaimed asphalt pavement (RAP) materials. On the other hand, their use in road pavement is negative to the fatigue performance of asphalt pavements, especially PA. Therefore, modifying PA mixtures containing RAP to address the mentioned issues is necessary. Researchers have found that modifying asphalt mixes using nanotechnology is one of the more effective methods. The four-point bending beam fatigue test is one of the most dependable tests to assess the fatigue performance of asphalt mixtures, and evaluating the fatigue resistance of nano-modified PA mixes containing RAP under laboratory conditions by performing this test is essential. This study aims to investigate the fatigue behavior of different compounds of PA mixtures modified with nano zinc oxide (NZ) (0%, 2%, 4%, 6%, and 8%) containing various contents of RAP materials (0%, 25%, and 50%) under normal, long-term aging, and freeze-thaw (F-T) cycle conditions. Moreover, the self-healing capability of these PA samples was evaluated using this test by performing two 24-h recovery periods following the first and second loading. It can be inferred from the result that although adding RAP and inducting long-term aging and moisture-damaged conditions negatively influenced PA mixes' fatigue lives, incorporating NZ caused increases in these values by averages of 114%. Besides, results indicated that applied rest periods were observed to significantly impact PA specimens' self-healing capability, resulting in longer fatigue life for them. On average, conventional and NZ-modified PA mixes with/without RAP could recover up to 32 and 48% of their fatigue resistance in all conditions.

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The structural evaluation of existing pavements forms the basis for formulating cost-effective maintenance and rehabilitation strategies. A promising tool for pavement structural evaluation at network level is the Traffic Speed Deflectometer (TSD) test. However, the application of the TSD test is hindered by the lack of a robust and efficient parameter identification technique. To solve this problem, a theoretical model for the TSD test is first formulated. Then, a minimisation algorithm which works best with the theoretical TSD model for parameter identification is selected. Finally, the performance of this combination in processing field TSD measurements is studied. The results show that the modified Levenberg-Marquardt algorithm using all the 9 detection points is most suitable to be combined with the theoretical TSD model for parameter identification, which gives a promising parameter identification technique for TSD tests of pavements. The presented work contributes to the development of technologies for pavement structural evaluation.

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The existing sources of fresh aggregates are depleting due to the boom in large infrastructure projects. Therefore, this demand necessitates the pursuit of substitute materials and technologies. Foamed bituminous mix (FBM) prepared using reclaimed asphalt pavement (RAP) is one of the alternative solutions that will not only reduce the demand for fresh aggregates but may also minimize the carbon emission during the production of the mix as FBM is a cold mix technique. Therefore, in the present study, an attempt has been made to develop the cold bituminous mix using RAP and foamed bitumen. In this regard, the mix is prepared using fresh and by varying RAP content from 70% to 100%. The influence of RAP on the tensile strength ratio of the foamed bituminous mix is evaluated. Further, resistance against the moisture damage is also determined by assessing the variation in the resilient modulus of the specimen subjected to soaking conditioning. Test results describe that FBM prepared using RAP material exhibits better resilient modulus and less moisture susceptible than the mix prepared using 100% fresh aggregates. Based on the limited laboratory studies it can be concluded that RAP material considerably improves the resistance of the FBM against the moisture damage as compare to fresh aggregates.

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Present article reviews the early and recent developments in skid resistance measurement techniques at asphalt concrete pavement. Suitability and limitations of various methods used for capturing skid characteristics of the surface has been outlined. The harmonization of laboratory and field-testing methods has been summarized briefly. Harmonization is agreement of test outcomes reported from field as well as laboratory. Correlation analysis of various in-situ and laboratory test data has been made to maintain the better harmony of measurement either in field or in laboratory. Measurement of skid resistance in field is time consuming, labor intensive and requires use of costly, advanced and sophisticated instruments. Lab measurement lags in accuracy and still needs improvement in design and working methodology which compelled researchers for looking into modelling as an alternative option. In the subsequent sections, progress in modelling approach (analytical to numerical) has been discussed in brief. Analytical and numerical solutions of asphalt concrete pavement for modelling skid resistance have been reviewed and emphasis for choosing a particular solution has been justified on the basis of accuracy as well as efficacy of the output model. Critical factors affecting skid resistance model like hydroplaning, tire related parameters, temperature, surface texture has been highlighted in this manuscript. Skid data obtained from any model whether it is analytical or numerical, needs to be validated against field measurement or some established data. Validation of skid resistance model using field test and experimentally derived equations in various research studies has been summarized in later section of this article. Few key research directions have been suggested as scope of future study so as to predict a more reliable skid resistance model (1) For predicting dynamic frictional properties with higher accuracy at tire pavement interface, tire pavement interaction modelling still needs improvement considering all field constraints (2) Influence of surface texture, hydroplaning, temperature and pavement ageing needs to be studied in depth for modelling skid resistance as these are critical parameters & contributes significantly.

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Micromechanics, which can be used to relate the properties of a composite to the properties of individual constituents, is considered a good approach to understanding the fundamental mechanisms behind the behavior of asphalt materials. Compared with the semi-empirical and numerical micromechanical models, analytical micromechanical models do not need calibration factors. In addition, they can provide analytical solutions on the basis of a series of assumptions. Using these models, researchers have separated the effects of different stiffening mechanisms (i.e., the volume-filling reinforcement, the physicochemical reinforcement, and the particle-contact reinforcement) for mastic. However, similar research work has not been conducted for asphalt mixtures and, moreover, the characteristics of the particle-contact reinforcement have not been deeply analyzed by researchers. Therefore, this paper aims to understand the stiffness of asphalt mixture through micromechanics. The focus of this study was on porous asphalt mixture where particle-contact reinforcement plays an important role in its behavior. The stiffening effects of different mechanisms were separated using analytical micromechanical models. The effects of temperature/frequency and the properties of the matrix phase on the stiffening effect of the particle-contact reinforcement were analyzed.@en

Asphalt mixtures with high porosities (known as porous asphalt (PA) mixes) are becoming a popular choice among road authorities as it provides better skid resistance while also reducing tire-pavement noises. Towards the design and manufacture of PA mix pavement, the evaluation of the mechanical properties of PA mixes is of great importance. To predict the mechanical properties of PA mixes, micromechanical models have been considered as an effective tool. In most research studies, continuum-based micromechanical models, i.e. the Self-consistent model, the Mori-Tanaka model, etc. are widely used to predict the stiffness of asphalt mixtures. However, the limitation of these models is that they cannot describe the characteristics of individual particles and thus they cannot provide accurate predictions. On the other hand, the discrete-based micromechanical model (DBMM) which simulates a granular material as an assembly of bonded particles seems to be a promising alternative. Limited research studies have focused on studying the utilization and the applicability of this model for asphalt mixes. Therefore, this paper aims to propose a framework to use DBMM and to evaluate its performance in estimating a PA mix's stiffness. Based on the obtained results, both the merits and limitations of this model were highlighted.

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The paper aims to simulate the micromechanical behavior of asphalt mixtures during the compaction process using the Discrete Element Method (DEM). The interactions between the components of a Porous Asphalt (PA) mixture were represented using an Elastic Viscoelastic Contact Model (EVCM), which is a user-defined model implemented in EDEM software, developed based on linear elastic and Burger's viscoelastic constitutive equations. The macroscale parameters of asphalt mortar were characterized using the nonlinear regression analysis of master curves obtained from Dynamic Shear Rheometer (DSR) tests. The verification process of EVCM successfully indicated that the computations trends fall within the range of expected values for the typical asphalt mixture material. Further, a Superpave Gyratory Compaction (SGC) test was carried out and the obtained sample was scanned using X-ray Computed Tomography (X-ray CT) to capture the air void distributions. The DEM was utilized where digital samples were established to simulate the overall process of laboratory and field compaction. The simulation results showed that the model provided a comparable prediction of responses and demonstrated the capability of SGC to fabricate a representative sample. The influence of temperature on the asphalt compaction process was explored and the results implied that temperature decreasing adversely affects the compactability and dramatically increases the demanded compaction efforts which are consistent with the law of viscoelasticity. On the contrary, when the temperature is high, the asphalt binder becomes too fluid and roller loads will simply displace, or “shove” the mat rather than compact it. Tracking the change in the air voids proportion indicates that the motion of aggregates is rather compound. The aggregates flowed vertically downwards in line with the compacting orientation while moved horizontally outwards away from the center. The results demonstrated that the model effectively simulated the compaction process, the developed model, and can be considered as a useful tool. All in all, the findings confirm that the concept is technically practicable, affording the model a tremendous potential to help researchers understand the microstructural phases of asphalt mixture during the compaction.

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A non-destructive testing method suitable for network-level pavement structural evaluation is the traffic speed deflectometer (TSD) test. However, the analysis of TSD measurements still needs a proper parameter back-calculation procedure, which requires an accurate and efficient forward calculation model. As a first step to solving this issue, a nonlinear spectral element model which can simulate TSD tests of asphalt pavements is developed. The model is used to investigate the characteristics and parameter sensitivity of the response of asphalt pavements caused by the TSD loading. The results indicate that the vertical deflection curve along the direction of movement observed on the asphalt pavement surface is slightly asymmetric, and the maximum deflection appears behind the centre of the loading area. In addition, the slope curve of vertical deflection is highly sensitive to the magnitude of the applied force, the moduli of the base layer and subgrade, and the thicknesses of the asphalt layer and base layer. Furthermore, the slope curve is relatively sensitive to the glassy modulus of the asphalt layer. Because of its good predictive capability and high computational efficiency, the proposed model has the desired characteristics to be used as the computational kernel for parameter back-calculation procedures of TSD measurements.

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The mechanical properties of asphalt mixture are always required for the evaluation of the durability of pavements. In order to obtain these properties without conducting expensive laboratory tests and using calibrated empirical models, research studies have been carried out to develop micromechanics-based models. Continuum-based micromechanical models (CBMM), which are developed based on continuum mechanics, have increasingly been utilized to estimate the mechanical properties of asphalt materials based on the fundamental properties of individual constituents. These analytical models are expected to provide reliable predictions without the need for extensive computational facilities. Although the utilization of CBMM has been presented by several past studies, most of the studies do not provide a concise and critical review of these models. Therefore, in this paper, a complete review of CBMM was presented. Commonly used CBMM were introduced in detail and their advantages and disadvantages were discussed and compared. Comprehensive summaries and critical discussions about their current utilization and limitations for predicting the mechanical properties of asphalt materials were given. Further modifications and new development for addressing the limitations were extensively described and discussed. In the end, research challenges were highlighted and future recommendations from different perspectives were proposed.

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Micromechanical modelling has been widely used to predict the properties of asphalt mixes. In comparison to numerical micromechanical models, analytical micromechanical models have the benefits of consuming much less time and facilities. The most commonly used analytical micromechanical models are the Eshelby-based micromechanical models. However, without the consideration of particles’ interactions, these models fail to accurately predict the properties of asphalt mixes, especially at high temperatures. In porous asphalt (PA) mixes, due to the formation of an interconnected aggregate network, the particles’ interactions under a compressive loading condition at high temperatures mainly refer to the packing effects. In order to describe the behavior of packed aggregates in PA mixes, Walton’s model which predicts the effective moduli of a pack of spherical particles is possible to be a suitable way. However, to the best of authors’ knowledge, this model has not been utilized for asphalt mixes. Therefore, this paper aims to investigate the application of Walton’s model for predicting the properties of PA mixes at high temperatures.@en