Journal of Transportation Engineering, Part B: Pavements

Flexible pavements are subjected to loading stresses and resulting strains dependent on the existing environmental conditions. Distresses in the form of rutting and cracking occur in pavements due to progressive damage accumulation caused by repeated traffic-induced stresses/strains. For the accurate design of pavements, a knowledge of in-place strain is necessary to calibrate the laboratory obtained models. In the form of traffic loading and response sensors and weather instruments, pavement instrumentation plays a critical role in bridging the gap between theory and practice in pavement design. The commonly used instruments consist of weigh in motion (WIM) sensors, multidepth deflectometer (MDD), asphalt strain gauges, soil compression gauges, and earth pressure cells. Weather instruments consist of anemometers, thermocouples, and pyranometer. This paper presents a review of state-of-the-art instruments, basic principles, and working mechanisms with examples. The needs for successful instrumentation programs, including the provision of rugged sensors and protections, triggering of sensors with the WIM, and collation of data for successful analysis, are discussed. Concepts of the Wheatstone bridge, pressure cells, and linear variable differential transformers (LVDT) for the various sensors are presented. The principles and working mechanisms of anemometer, pyranometer, and thermocouples are discussed for weather sensors.

The ability of a Traffic Speed Deflectometer (TSD) to detect joint movement on a rigid pavement was investigated. Based on a mathematical model of a moving vehicle on a concrete pavement, a method of calculating the joint displacement from a TSD measurement was developed. The joint displacement indicator was tested in practice on a concrete highway in northern Germany. Short-term repeatability, day-to-day repeatability, and reproducibility between two different TSD vehicles were evaluated based on the measurements. It was found that the TSD is able to consistently find movement at the same joints, and that the magnitude of the movement has a high short-term repeatability. Day-to-day repeatability and reproducibility between vehicles was lower due to temperature effects in the concrete slabs. However, also for these cases, there was a high level of consistency in the detected joints. Based on the distance between successive joints, a method of identifying potential locations of transverse cracks was developed. Finally, a way of quantifying joint movement in terms of spatially averaged quantities is presented.

This paper studies the merits of applying liquified polyethylene (PE) as a modifier for bitumen. Chemical recycling of PE is often incomplete and generates some amount of waste “PE oil”. The viscoelasticity and chemical characteristics of bitumen modified with PE oil were examined using dynamic shear rheometry, infrared spectroscopy, and adhesion measurements in comparison and in conjunction with bitumen modified with wax, which is one of the most common additives in warm-mix bitumen. The study found that PE oil softens bitumen without severely increasing the creep compliance or viscoelastic damping properties. Wax-modified bitumen showed enrichment of crystallized alkanes at the free bitumen surface that negatively impacted adhesion and interface healing. The introduction of PE oil to wax-modified bitumen did not appreciably decrease the fraction of crystallized wax. Thus, PE oil may not be effective as an additive for warm-mix wax-modified bitumen. However, the PE oil showed potential in protecting bitumen against ultraviolet (UV) aging, and it is worth further exploration as an anti-aging agent, or as a rejuvenator for reclaimed asphalt pavement. The outcomes of this study promote plastic recycling by presenting the merits of applications of liquefied waste PE in the design and engineering of bituminous composites.

Automatic and rapid detection of pavement cracks is one of the important tasks for the highway department. This study proposed an improved model of you only look once (YOLO) V5 integrated with the vision transformer (ViT) that can calculate the attention weights of image regions and form a new feature map with weights. The ViT module was added to the neck of YOLO V5 to improve the speed and accuracy of the model. 1944 asphalt pavement images were collected for testing. The test results showed that the proposed model obtained high accuracy and speed for longitudinal, transverse, and fatigue cracks and was capable of real-time detection. The ViT-improved YOLO V5m obtained 0.872 in mAP(0.5), and the detection time for a single image is 11.9 ms. The study also investigated the pavement crack detection performance of the models in a rainfall environment. All models did not have satisfying detection capabilities in rainfall conditions, but the developed YOLO V5 had better performance.

Ideal mixing between the asphalt and rejuvenator is the key to ensure the performance of the recycled asphalt mixture in hot in-place recycling. In this paper, the undetermined temperature and thermal parameters in the finite-element (FE) model of pavement were back calculated by the backward method of regression. The temperature field of the recycled asphalt layer after paving was obtained by FE simulation, and was applied to set the temperature in the subsequent molecular dynamics (MD) simulation. Molecular models of virgin asphalt, aged asphalt, and the representative rejuvenator components were applied to establish a three-layer model. New indicators were defined to analyze the interdiffusion between the virgin asphalt, aged asphalt, and rejuvenator, and the microstructure, interdiffusion, and interaction states between the asphalt and rejuvenator in the asphalt miscibility zone were analyzed. Results show that the parameter transferring from the macro FE simulated temperature field to the micro temperature setting of MD model is feasible. There is an obvious difference between the temperature fields on the surface and the inside hot in-place recycled asphalt layer during the cooling process, which causes different interaction and interdiffusion states between the asphalt and rejuvenator as well as the uneven performance of the recycled asphalt mixture. The effects of chain and aromatic rejuvenator on different interdiffusion and interaction indicators are different, so the combination of the two could have a better rejuvenation effect. The results can offer reference in aspects including prescreening the recycling temperature, the proportion of rejuvenator, virgin asphalt and aged asphalt, the rejuvenator component composition, and other parameters in hot in-place recycling.

Bitumen is a complex hydrocarbon material that is used as a binder for the construction of road pavements. Asphalt pavements are frequently exposed to high temperatures that result in the aging of bitumen. This investigation reports the effect of aging on the chemical properties, mechanical properties, and thermal stability of bitumen. Pressure ageing vessel (PAV) was used to study the long-term aging of the bitumen. Characterization of binders was carried out using conventional testing, rheological measurements with a dynamic shear rheometer (DSR), and chemical study by SARA analysis, Fourier transform infrared spectroscopy (FTIR) analysis, and thermal stability analysis through thermogravimetric analysis (TGA) and dynamic scanning calorimeter (DSC) tests. Results presented that aging significantly affects the rheological, chemical, and thermal properties of bitumen. The aging of bitumen increased asphaltenes, resins, and decreased aromatics, saturates which increased the colloidal instability index (CII). A maximum increase in CII was observed after 20 h of PAV aging with a comparatively insignificant increase after 60 h of PAV aging. TGA results indicated that the unaged binder was most thermal sensitive, whereas 60 h PAV aged binder showed the least thermal sensitivity up to 550°C but lost maximum mass at 800°C. The endothermic DSC curve indicated that weight loss was due to evaporation up to 550°C, whereas a maximum mass loss at 800°C could be due to decomposition of asphaltene fraction as also verified from FTIR results. Aging increased the carbonyl index, and the rate of formation of carbonyl group was high for 20 h aged binder. Furthermore, strong increasing and decreasing correlations between different parameters of rheological, chemical, and thermal properties were observed.

Mechanical responses and damage behaviors of asphalt pavement are closely associated with the mesostructure characteristics of the asphalt mixture. The aim of this research was to investigate the effect of the different mesostructure characteristics of asphalt mixtures on pavement damage behavior through a multiscale finite-element (FE) analysis method. A two-dimensional (2D) random aggregate generation algorithm was used to construct the mesostructures of asphalt mixtures with different characteristics, including aggregate distribution uniformity, shape, volume fraction, and size range. Bilinear cohesive elements were used to model damage initiation within asphalt pavement. Also, the nonuniformity coefficient (NUC) was applied to evaluate the uniformity of aggregate distribution within asphalt pavement. The results indicated that the NUC could well characterize the uniformity of coarse aggregate distribution in pavement, and the damage initiation zone became larger as the NUC increased. Compared with regular aggregates, irregular shape aggregates led to more damage initiation in asphalt pavement. For regular shape aggregates, the damage initiation zone became smaller as the aggregate shape approached the circle. In addition, the decrease of aggregate size and volume fraction could increase the possibility of “top-down” cracking of pavement.

Cracking in flexible pavements is one of the most prevalent forms of distress. Two types of cracking ubiquitous to most regions are fatigue or alligator cracking, and thermal or low-temperature cracking. Cracking characteristics of a flexible pavement depend on a combination of factors that include the structural design of the pavement, asphalt mixture properties, component material properties, and construction quality. The cracking resistance of asphalt mixtures used in flexible pavements may be improved by use of asphalt binders with properties that are suitable to the application. Asphalt binder relies on its stiffness, tensile strength, ductility, and ability to relax to resist cracking due to repeated loading or changes in temperature. In current performance grade specifications of asphalt binders, cracking resistance is primarily characterized by asphalt rheology. Over the years, several researchers have considered this to be a gap. Several studies have been conducted to close this gap by considering various properties including strength and ductility. This study focuses on ductility of asphalt binders as measured by the poker-chip test to resist cracking. Field performance data measured on several pavement sections in Texas were compared with ductility of asphalt binders recovered from field cores. This study finds the poker-chip test to be a promising means of measuring ductility as well as characterizing ability of asphalt binders to resist fatigue and thermal cracking.

Abstract

The heating temperature field of asphalt pavement is a key factor affecting the quality of pavement heat-in-place recycling (HIR). Using the heat transfer characteristics of HIR, a three-dimensional heat transfer model was simplified into a one-dimensional heat transfer model along the depth direction. A temperature sensor was installed on the site to monitor the temperature change of the asphalt pavement at different depths under different heating powers, and the actual temperature and heat transfer model were highly compatible. Through this model, the influence of heater running speed and heater heat flux density on the temperature field of the asphalt pavement heated by infrared radiation (IR) was calculated by the finite differential method, and an optimal combination of heating is proposed. In accordance with construction continuity and minimum energy consumption principles, at the $3.0–3.5\mathrm{m}/\min$ recommended running speed of the heating machine, the asphalt at a depth of 4 cm satisfied the temperature demand, but the asphalt on the road surface was prone to heat aging. The heating effect of the constant temperature variable power heating (CTVP) is ideal, but the continuous change in heating power increases the difficulty of construction. Constant temperature discrete power heating (CTDP) divides the ideal heat flux density curve into several stages according to the length of the heating plate in the heater, increasing the feasibility of constant temperature heating in engineering and reducing energy consumption.

Practical Applications

The mileage of roads in some countries has basically satisfied the needs of national development, and the research focus of road workers has gradually shifted from building new roads to the renovation and maintenance of existing roads. In order to meet the purposes of convenient transportation and environmental protection at the same time, construction optimization must be carried out in the process of road renovation and maintenance to ensure that energy is not wasted during the construction process, and the relevant requirements of construction specifications are met. At present, high proportion of paved roads throughout the world have asphalt pavement. HIR has gradually become a popular maintenance method in order to save resources. In this method, the heating temperature field of the original asphalt pavement plays a key role in the construction quality, and the temperature field is affected by many factors, such as the running speed of the heater and the heat flux density of the heater during the heating process. This study mainly considers the foregoing two factors, combined with the actual situation of the project, in order to find a heating method with excellent heating effects and simple construction. The heating effect of the pavement is further optimized, improving the quality of the project, while saving energy and reducing the project cost.

Poor condition of roads is a major factor for traffic accidents and damage to vehicles. A significant portion of car accidents is attributed to severe three-dimensional (3D) pavement distresses such as potholes, ruttings, and ravelings. Insufficient road condition assessment is responsible for the poor condition of roads. To inspect the condition of the pavement surfaces more frequently and efficiently, an inexpensive data acquisition system was developed that consists of a consumer-grade RGB-D sensor and an edge computing device that can be mounted on vehicles and collect data while driving vehicles. The RGB-D sensor is used for collecting two-dimensional (2D) color images and corresponding 3D depth data, and the lightweight edge computing device is used to control the RGB-D sensor and store the collected data. An RGB-D pavement surface data set is generated. Furthermore, encoder-decoder deep convolutional neural networks (DCNNs) consisting of one or two encoders, and one decoder trained on heterogeneous RGB-D pavement surface data are used for pothole segmentation. Comprehensive experiments using different depth encoding techniques and data fusion methods including data- and feature-level fusion were performed to investigate the efficacy of defect detection using DCNNs. Experimental results demonstrate that the feature-level RGB-D data fusion based on the surface normal encoding of depth data outperform other approaches in terms of segmentation accuracy, where the mean intersection over union (IoU) over 10-fold cross-validation of 0.82 is achieved that shows a 7.7% improvement compared with a network trained only on RGB data. In addition, this study explores the efficacy of indirectly using depth information for pothole detection when depth data are not available. Additionally, the semantic segmentation results were utilized to quantify the severity level of the potholes assisting in maintenance decision-making. The result from these comprehensive experiments using an RGB-D pavement surface data set gathered through the proposed data acquisition system is a stepping stone for opportunistic data collection and processing through crowdsourcing and Internet of Things in future smart cities for effective road assessment. Finally, suggestions about the improvement of the proposed system are discussed.

The existing research on pavement mechanics was rarely conducted from the perspective of the spatial stress state. In this research, by utilizing analytical solutions, a three-dimensional space calculation program for asphalt pavement was developed to study the spatial distributions of the stress state and damage risk of the pavement structure. First, this study selected various types of pavement structures to analyze the spatial distribution of the stress state. The results indicated that the important influence factors are the order and quantity of asphalt-bound material, chemically stabilized material, and granular material in the structure. In contrast, the thicknesses of these materials have a limited effect. Then, the stress states of the asphalt pavements in winter and summer were compared. The results demonstrated that the tensile region bulges upward at low temperatures, and the structure is more inclined to experience tension and compression simultaneously. In addition, the failure criterion suitable for asphalt mixture materials was applied, and a strength conversion coefficient between different temperatures was proposed to calculate the damage situations of asphalt mixture layers. Three-dimensional images were generated to display the differences in the dangerous positions and damage forms for different structural types and temperature conditions.