A Review on the Application of 3D Printing Technology in Pavement Maintenance

To examine the application and significance of 3D printing technology in pavement maintenance engineering, a review of the current developments in principles, types, materials, and equipment for 3D printing was conducted. A comparison and analysis of traditional methods and 3D printing for asphalt pavement maintenance led to an investigation of 3D asphalt printing technologies and equipment. As a result, the following suggestions and conclusions are proposed: 3D printing technology can increase the level of automation and standardization of pavement maintenance engineering, leading to effective improvements in worker safety, climate adaptability, repair accuracy, etc. For on-site repair of cracks and minor potholes, utilizing material extrusion technology a mobile 3D asphalt printing robot with a screw extrusion device can be used for accuracy and flexibility. For efficient repair of varying cracks, material jetting technology with a UAV equipped with a 3D printing air-feeding device can be employed

DexPro:A Bytecode Level Code Protection System for Android Applications

Unauthorized code modification through reverse engineering is a major concern for Android application developers. Code reverse engineering is often used by adversaries to remove the copyright protection or advertisements from the app, or to inject malicious code into the program. By making the program difficult to analyze, code obfuscation is a potential solution to the problem. However, there is currently little work on applying code obfuscation to compiled Android bytecode. This paper presents DexPro, a novel bytecode level code obfuscation system for Android applications. Unlike prior approaches, our method performs on the Android Dex bytecode and does not require access to high-level program source or modification of the compiler or the VM. Our approach leverages the fact all except floating operands in Dex are stored in a 32-bit register to pack two 32-bit operands into a 64-bit operand. In this way, any attempt to decompile the bytecode will result in incorrect information. Meanwhile, our approach obfuscates the program control flow by inserting opaque predicates before the return instruction of a function call, which makes it harder for the attacker to trace calls to protected functions. Experimental results show that our approach can deter sophisticate reverse engineering and code analysis tools, and the overhead of runtime and memory footprint is comparable to existing code obfuscation methods

Lab assessment and discrete element modeling of asphalt mixture during compaction with elongated and flat coarse aggregates

© 2018 Superpave gyratory compactor (SGC) is usually used for analysis of volumetric properties of asphalt mixture, evaluation of mixture densification properties, estimation of sensitivity to aggregates’ shapes, field quality control and other testing purposes. The specimens produced by SGC very closely simulate the density, aggregate orientation and structural characteristics of asphalt mixture on actual pavement. Aggregates make up the major volume or mass of asphalt mixture, and their shapes significantly impact both the structural and mechanical performance of mixtures. The objectives of this study were to analyze the influences of selected coarse aggregates on asphalt mixture compaction through lab testing and modeling. First, coarse aggregates were classified into five types, and testing samples were produced with designed percentages of different types. Second, images of selected coarse aggregates were obtained by 3D scanning and saved in STL (Stereolithography) files. Finally, the air void curves and results of discrete element modeling (DEM) were used to evaluate the influences of selected coarse aggregate shapes on asphalt mixture compaction. It was found that the asphalt mixtures with 100% angular or 100% fractured coarse aggregates were easier to compact compared with asphalt mixtures of hybrid coarse aggregates in a SGC test. Results also clearly indicated that the larger percentage of elongated and flat aggregates, with a 3:1 ratio, results in worse compactability of asphalt mixtures under laboratory conditions, and the influences of flat aggregates were greater than that of elongated. Therefore, special attention should be paid to asphalt mixtures with a large percentage of elongated or flat aggregates

Characterization and evaluation of morphological features for aggregate in asphalt mixture: A review

The objective of this paper is to review the current characterization and evaluation methods and introduce emerging technologies of aggregate morphologies in asphalt mixture through conventional tests and imaging techniques that would be possibly applied to analyze and evaluate the morphological features of particles. The current evaluating-characterizing method is defined as a procedure that has been shown by experience or research to obtain satisfying results, that is established or proposed as a standard suitable for general application. This review first identified the methods based on laboratory tests to characterize and evaluate the morphologies of the aggregate particle. Then, an attempt was made to study the existing methodologies from different points of view, accompanied by extensive comparisons on three categories of imaging techniques-early imaging techniques, dynamic imaging techniques, and static imaging techniques to facilitate further research studies. Additionally, the evaluation parameters of aggregate morphologies based on image technologies were represented. Finally, a comparative evaluation between different conventional testing methods and different imaging techniques through basic tools, application conditions, advantages, and disadvantages were conducted. This review concluded with some recommendations and conclusions in terms of morphological characterization and evaluation of aggregates in the asphalt mixture to materials selection during the mixture design and construction

Sustainable Recycling Techniques of Pavement Materials

Innovative sustainable techniques for transportation infrastructure enhancement have been proposed in recent decades [...

Aggregate morphological characterization with 3D optical scanner versus X-ray computed tomography

In quantifying the morphological features of aggregate, X-ray computed tomography (CT) is one of the most popularly used approaches for capturing aggregate images that is considered accurate and reliable. In this study, however, a three-dimensional (3D) optical scanner was also employed to characterize aggregate morphology in addition to X-ray CT. The major objective is to validate the accuracy of the optical scanner-based image analysis method through a comparative study of the optical scanning and X-ray CT results. Four types of aggregate particles were selected, and their aggregate images were obtained through those two methods. Second, the scanned aggregate images were saved in STereoLithography (STL) files and analyzed. Then the differences in the morphological features of aggregate obtained from these two methods were quantified and evaluated. Through this study, it was found that even though there were relatively large differences in special aggregate particles (flat or elongated aggregates), the 3D optical scanner was comparable with the X-ray CT in the overall quality of the morphological characteristics of aggregate. Furthermore, differences between the two scanning technologies are dependent on particle shape and surface features. Aggregate particles with sharp angles or rich surface features may induce larger differences

Using discrete element models to track movement of coarse aggregates during compaction of asphalt mixture

The objective of this study is to analyze the movement characteristic of differently-shaped compositions in the Superpave Gyratory Compactor (SGC) test through tracking coarse aggregates and the numerical simulation of Discrete Element Method (DEM). First, the coarse aggregates were classified into five shape types (rounded, fractured, angular, elongated and flat) and scanned by a 3D scanner. Second, seven groups of asphalt mixtures with different combination types of hybrid, 100%fractured, 100%angular, 80%fractured + 20%rounded, 60%fractured + 40%rounded, 80%fractured + 20%elongated, and 80%fractured + 20%flat groups were simulated by Particle Flow Code (PFC) Version 5. Third, numerical simulations were conducted to analyze the SGC test process and the movement paths of differently-shaped coarse aggregates were obtained. Finally, statistical analysis on the results from the modeling test were used to study the movement characteristics of asphalt mixtures with differently-shaped aggregate compositions. Through this study, it was found that: (1) there were three main stages of particle movement in the SGC test; (2) the ratio of vertical displacement was obviously larger than that of horizontal displacement, while the variation of vertical rotation was obviously smaller than that of horizontal rotation in asphalt mixtures with differently-shaped compositions; (3) the rounded, elongated and flat coarse aggregates have greater influence on horizontal displacement compared with vertical displacement, but have adverse effects on particle rotations during the compaction process; (4) the effects of elongated coarse aggregates on particle movement were larger than those of flat coarse aggregates, but the flat coarse aggregates have more influence on particle rotation for the variations of horizontal and vertical rotational angles

3D printed rubber modified asphalt as sustainable material in pavement maintenance

The application of 3D asphalt printing technology can be used to effectively improve the automation level and reduce the construction risk in pavement maintenance. In order to prepare and optimize 3D printed asphalt with good high-temperature performance and printability by sustainable utilization of waste rubber powder, the conventional properties and printability of rubber modified 3D printed asphalt (R-3DPA) were analyzed according to the basic properties and printing tests. The results were used to determine the optimal mesh and content of crumb rubber and additive content of C9 petroleum resin. Then, the thermal storability and high temperature rheological property of R-3DPA were studied by phase separation test and dynamic shear rheological test. Fourier transform infrared spectroscopy and fluorescence microscopy were used to analyze the modification mechanism of R-3DPA. The printing temperature and speed were determined by a 3D printing test. The results show that R-3DPA has good viscosity, elasticity, compatibility, high-temperature rutting resistance, and printability with 80 mesh and 18 % of crumb rubber and 4 % of C9 petroleum resin. Physical blending occurred, and C9 petroleum resin can play an effective compatibilization role in R-3DPA. The recommended printing temperature and speed R-3DPA are 150–160 °C and 1 cm/s

Development of a new asphalt mixture containing reacted and activated rubber and reclaimed asphalt pavement via Superpave mix design and Marshall mix design

Reacted and Activated Rubber (RAR) is one of the pre-treated crumb rubber technologies. It has been developed as a new approach to produce crumb rubber modified asphalt mixture in the field. However, most of the previous studies are limited to the Marshall design method to obtain the optimum asphalt content. Further, none of these studies tried to add reclaimed asphalt pavement (RAP) to the RAR modified asphalt mixtures. The objective of this study was to conduct a Superpave mix design for determining the optimum asphalt content of asphalt mixture with RAR and RAP, and analyze the performance of RAR modified binder and mixture through a series of laboratory tests. Performance Grade (PG) 58-28 binder was used for this study. Both the Superpave mix design method and the Marshall mix design method selected the optimum asphalt binder content as 11.0% by weight of the mixture, where the virgin binder content was 6.6% and the RAR content was 4.4%. In general, the test results were favorable in rutting resistance performance and moisture resistance. The designed RAR modified mixtures will be used to construct trial sections in early August 2018 in Kalamazoo, Michigan

Determining aggregate grain size using discrete-element models of sieve analysis

The grain size of aggregate particles is crucial to the mixture gradation of discrete-element (DE) models when realistic aggregate shapes are simulated. The objective of this study was to answer the question of how to determine the grain size of aggregates using DE models based on virtual sieving analysis. First, virtual sieving analysis models were developed with prolate ellipsoid, oblate ellipsoid, and cubic-shaped particles, and virtual sieving was performed under three vibration patterns, namely, vertical, horizontal, and hybrid vibration. The influence and efficiency of the vibration patterns were analyzed based on the results of the virtual sieving analysis. Then, the virtual sieving analysis was conducted with realistic aggregate shapes. By analyzing the test results, the shape sieving factor (Ssf) was derived and was used to calculate the grain size of individual particles. For further validation, the grain size (Gs) of selected aggregates was measured by lab manual measurement and virtual sieving analysis, separately. Then the test results were analyzed and compared. The main findings from this study include the following: (1) vibration patterns had significant impacts on the results of the virtual sieving analysis, and vertical vibration is recommended for virtual sieving analysis; (2) particle shapes had important impacts on the results of the virtual sieving analysis, and it was determined that aggregates with cubic shapes are relatively difficult to pass through the sieve meshes; (3) most particles can pass through smaller sieve apertures than their equivalent-volume spheres; (4) the approach to virtual sieving analysis developed in this study was validated by lab sieving tests, and the shape sieving factor (Ssf) derived from the virtual sieving analysis can be used to generate DE models with more accurate gradation