SGC Tests for Influence of Material Composition on Compaction Characteristic of Asphalt Mixtures
Compaction characteristic of the surface layer asphalt mixture (13-type gradation mixture) was studied using Superpave gyratory compactor (SGC) simulative compaction tests. Based on analysis of densification curve of gyratory compaction, influence rules of the contents of mineral aggregates of all sizes and asphalt on compaction characteristic of asphalt mixtures were obtained. SGC Tests show that, for the mixture with a bigger content of asphalt, its density increases faster, that there is an optimal amount of fine aggregates for optimal compaction and that an appropriate amount of mineral powder will improve workability of mixtures, but overmuch mineral powder will make mixtures dry and hard. Conclusions based on SGC tests can provide basis for how to adjust material composition for improving compaction performance of asphalt mixtures, and for the designed asphalt mixture, its compaction performance can be predicted through these conclusions, which also contributes to the choice of compaction schemes.
Lab assessment and discrete element modeling of asphalt mixture during compaction with elongated and flat coarse aggregates
Abstract 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.
Diversity of Electrospinning Approach for Vascular Implants: Multilayered Tubular Scaffolds
Abstract The biomimetics of biological structures found in nature remains one of the most promising approaches to engineer functional tissues from natural or synthetic biocompatible materials for the replacement of damaged or injured parts of the human body. Recently, medical therapeutic regimes have advanced into a new era, overcoming the known mechanical and biological variances that occur when using autologous or synthetic grafts. Basically, the core concept of tissue biofabrication, commonly referred to as tissue engineering, is to find out the favorable cellular microenvironments to grow a living tissue prior to clinical uses. In fact, the ability of stem cells to regenerate is controlled via signaling pathways (growth factors) and supporting materials (scaffolds) that guide the cellular activities. After the first successful experiments to fabricate polymer fibers from their solutions, Cooley proposed the use of an electric field a century ago (Cooley (US 692:631, 1902 ). The electrospinning technique has been continually developed as a fruitful polymer processing technique to draw ultrafine nonwoven fibers. Electrospun polymer fibers have been used for a wide range of technical and biotechnical applications such as filtration, organic solar cells, tissue engineering, and drug releasing implants. In this regard, this review begins with an overview about the various spinning approaches for the fabrication of polymer fibers as well as the basic principles of electrospinning process. In addition, this review will highlight vascular bypass surgery and, in particular, the needs for vascular tissue engineering. Finally, the review includes some of the latest attempts to improve the mechanical and biological properties of electrospun polymeric fibers and summarizes the challenges and prospects for the future. Lay Summary However, vascular defects are treated successfully via bypass surgical bypass grafting using autologous or synthetic vessels. The small-diameter vessels (less than 6) are often associated with high failure rate. This review reports some of the recent features that should be highlighted to fabricate an ideal graft for small-diameter vascular grafts. The review introduces multilayered conduits as an alternative approach to overcome the known mechanical and biological mismatches of single layered vascular grafts of electrospun polymers.