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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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12 pages, 5638 KiB  
Article
Corrosion of Steel Rebars in Anoxic Environments. Part II: Pit Growth Rate and Mechanical Strength
by Elena Garcia, Julio Torres, Nuria Rebolledo, Raul Arrabal and Javier Sanchez
Materials 2021, 14(10), 2547; https://doi.org/10.3390/ma14102547 - 14 May 2021
Cited by 6 | Viewed by 2210
Abstract
Reinforced concrete may corrode in anoxic environments such as offshore structures. Under such conditions the reinforcement fails to passivate completely, irrespective of chloride content, and the corrosion taking place locally induces the growth of discrete pits. This study characterised such pits and simulated [...] Read more.
Reinforced concrete may corrode in anoxic environments such as offshore structures. Under such conditions the reinforcement fails to passivate completely, irrespective of chloride content, and the corrosion taking place locally induces the growth of discrete pits. This study characterised such pits and simulated their growth from experimentally determined electrochemical parameters. Pit morphology was assessed with an optical profilometer. A finite element model was developed to simulate pit growth based on electrochemical parameters for different cathode areas. The model was able to predict long-term pit growth by deformed geometry set up. Simulations showed that pit growth-related corrosion tends to maximise as cathode area declines, which lower the pitting factor. The mechanical strength developed by the passive and prestressed rebar throughout its service life was also estimated. Passive rebar strength may drop by nearly 20% over 100 years, whilst in the presence of cracking from the base of the pit steel strength may decline by over 40%. Full article
(This article belongs to the Special Issue Durability and Safety of Concrete Structures)
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12 pages, 3874 KiB  
Article
Molecular Dynamics Investigation of the Deformation Mechanism of Gold with Variations in Mold Profiles during Nanoimprinting
by Abhaysinh Gaikwad and Salil Desai
Materials 2021, 14(10), 2548; https://doi.org/10.3390/ma14102548 - 14 May 2021
Cited by 17 | Viewed by 2315
Abstract
Understanding the deformation behavior during nanoimprint lithography is crucial for high resolution patterning. Molecular dynamics modeling was implemented to investigate the effect of different mold profiles (cylindrical, rectangular, and spherical) on the von Mises stress, lattice dislocations, and material deformation. Relatively higher von [...] Read more.
Understanding the deformation behavior during nanoimprint lithography is crucial for high resolution patterning. Molecular dynamics modeling was implemented to investigate the effect of different mold profiles (cylindrical, rectangular, and spherical) on the von Mises stress, lattice dislocations, and material deformation. Relatively higher von Mises stress (1.08 × 107 Pa) was observed for the spherical mold profile compared to the rectangular and cylindrical profiles due to the larger surface area of contact during the mold penetration stage of NIL. Substantial increases in the von Mises stress were observed for all the mold geometries during the mold penetration stage. The von Mises stresses had a reduction in the relaxation and mold retrieval stages based on the rearrangement of the gold atoms. The lattice dislocation during the deformation process revealed the formation of the BCC structure which further reverted to the FCC structure after the mold retrieval. The polyhedral template matching (PTM) method was used to explain the retention of the FCC structure and subsequent ductile behavior of the substrate. The cylindrical mold had the lowest percentage spring back in both of the orthogonal directions and thus replicated the mold profile with high-fidelity as compared to the spherical and rectangular molds. The findings of this research can aid the design of molds for several applications. Full article
(This article belongs to the Special Issue Microstructure and Mechanics of Metallic Materials)
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12 pages, 2602 KiB  
Article
Simultaneous Micro-Structuring and Surface Smoothing of Additive Manufactured Parts Using DLIP Technique and Its Influence on the Wetting Behaviour
by Florian Kuisat, Fabian Ränke, Fernando Lasagni and Andrés Fabián Lasagni
Materials 2021, 14(10), 2563; https://doi.org/10.3390/ma14102563 - 14 May 2021
Cited by 7 | Viewed by 2730
Abstract
It is well known that the surface topography of a part can affect its function as well as its mechanical performance. In this context, we report on the surface modification of additive manufactured components made of Titanium 64 and Scalmalloy®, using [...] Read more.
It is well known that the surface topography of a part can affect its function as well as its mechanical performance. In this context, we report on the surface modification of additive manufactured components made of Titanium 64 and Scalmalloy®, using Direct Laser Interference Patterning technique. In our experiments, a nanosecond-pulsed near-infrared laser source with a pulse duration of 10 ns was used. By varying the process parameters, periodic structures with different depths and associated roughness values are produced. Additionally, the influence of the resultant morphological characteristics on the wettability behaviour of the fabricated textures is investigated by means of contact angle measurements. The results demonstrated a reduction of the surface roughness of the additive manufactured parts (in the order of some tens of micrometres) and simultaneously the production of well-defined micro-patterns (in the micrometre range), which allow the wettability of the surfaces from 26° and 16° up to 93° and 131° to be tuned for Titanium 6Al 4V and Al-Mg-Sc (Scalmalloy®), respectively. Full article
(This article belongs to the Special Issue Laser Applications in Micromachining and Surface Functionalization of Materials)
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11 pages, 3686 KiB  
Article
Novel Cold Crucible Ultrasonic Atomization Powder Production Method for 3D Printing
by Łukasz Żrodowski, Rafał Wróblewski, Tomasz Choma, Bartosz Morończyk, Mateusz Ostrysz, Marcin Leonowicz, Wojciech Łacisz, Piotr Błyskun, Jan S. Wróbel, Grzegorz Cieślak, Bartłomiej Wysocki, Cezary Żrodowski and Karolina Pomian
Materials 2021, 14(10), 2541; https://doi.org/10.3390/ma14102541 - 13 May 2021
Cited by 34 | Viewed by 6817
Abstract
A new powder production method has been developed to speed up the search for novel alloys for additive manufacturing. The technique involves an ultrasonically agitated cold crucible installed at the top of a 20 kHz ultrasonic sonotrode. The material is melted with an [...] Read more.
A new powder production method has been developed to speed up the search for novel alloys for additive manufacturing. The technique involves an ultrasonically agitated cold crucible installed at the top of a 20 kHz ultrasonic sonotrode. The material is melted with an electric arc and undergoes pulverization with standing wave vibrations. Several different alloys in various forms, including noble and metallic glass alloys, were chosen to test the process. The atomized particles showed exceptional sphericity, while powder output suitable for additive manufacturing reached up to 60%. The AMZ4 metallic glass powder remained amorphous below the 50 μm fraction, while tungsten addition led to crystallization in each fraction. Minor contamination and high Mn and Zn evaporation, especially in the finest particles, was observed in atomized powders. The innovative ultrasonic atomization method appears as a promising tool for material scientists to develop powders with tailored chemical composition, size and structure. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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26 pages, 19088 KiB  
Article
Foundation Piles—A New Feature for Concrete 3D Printers
by Marcin Hoffmann, Krzysztof Żarkiewicz, Adam Zieliński, Szymon Skibicki and Łukasz Marchewka
Materials 2021, 14(10), 2545; https://doi.org/10.3390/ma14102545 - 13 May 2021
Cited by 16 | Viewed by 6842
Abstract
Foundation piles that are made by concrete 3D printers constitute a new alternative way of founding buildings constructed using incremental technology. We are currently observing very rapid development of incremental technology for the construction industry. The systems that are used for 3D printing [...] Read more.
Foundation piles that are made by concrete 3D printers constitute a new alternative way of founding buildings constructed using incremental technology. We are currently observing very rapid development of incremental technology for the construction industry. The systems that are used for 3D printing with the application of construction materials make it possible to form permanent formwork for strip foundations, construct load-bearing walls and partition walls, and prefabricate elements, such as stairs, lintels, and ceilings. 3D printing systems do not offer soil reinforcement by making piles. The paper presents the possibility of making concrete foundation piles in laboratory conditions using a concrete 3D printer. The paper shows the tools and procedure for pile pumping. An experiment for measuring pile bearing capacity is described and an example of a pile deployment model under a foundation is described. The results of the tests and analytical calculations have shown that the displacement piles demonstrate less settlement when compared to the analysed shallow foundation. The authors indicate that it is possible to replace the shallow foundation with a series of piles combined with a printed wall without locally widening it. This type of foundation can be used for the foundation of low-rise buildings, such as detached houses. Estimated calculations have shown that the possibility of making foundation piles by a 3D printer will reduce the cost of making foundations by shortening the time of execution of works and reducing the consumption of construction materials. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication (Second Volume))
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18 pages, 8347 KiB  
Article
Combined Manufacturing Process of Copper Electrodes for Micro Texturing Applications (AMSME)
by Carlos J. Sánchez, Pedro M. Hernández, María D. Martínez, María D. Marrero and Jorge Salguero
Materials 2021, 14(10), 2497; https://doi.org/10.3390/ma14102497 - 12 May 2021
Cited by 4 | Viewed by 2550
Abstract
Surface texturing has brought significant improvements in the functional properties of parts and components. Sinker electro discharge machining (SEDM) is one of the processes which generates great texturing results at different scale. An electrode is needed to reproduce the geometry to be textured. [...] Read more.
Surface texturing has brought significant improvements in the functional properties of parts and components. Sinker electro discharge machining (SEDM) is one of the processes which generates great texturing results at different scale. An electrode is needed to reproduce the geometry to be textured. Some geometries are difficult or impossible to achieve on an electrode using conventional and even unconventional machining methods. This work sets out the advances made in the manufacturing of copper electrodes for electro erosion by additive manufacturing, and their subsequent application to the functional texturing of Al-Cu UNS A92024-T3 alloy. A combined procedure of digital light processing (DLP) additive manufacturing, sputtering and micro-electroforming (AMSME), has been used to produce electrodes. Also, a specific laboratory equipment has been developed to reproduce details on a microscopic scale. Shells with outgoing spherical geometries pattern have been manufactured. AMSME process has shown ability to copper electrodes manufacturing. A highly detailed surface on a micrometric scale have been achieved. Copper shells with minimum thickness close to 300 µm have been tested in sinker electro discharge machining (SEDM) and have been shown very good performance in surface finishing operations. The method has shown great potential for use in surfaces texturing. Full article
(This article belongs to the Special Issue Improving Alloy Material Performance: Alloy design, Structural Modification and Advanced Processing)
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20 pages, 4473 KiB  
Article
Novel Approaches to the Design of an Ultra-Fast Magnetorheological Valve for Semi-Active Control
by Zbyněk Strecker, Filip Jeniš, Michal Kubík, Ondřej Macháček and Seung-Bok Choi
Materials 2021, 14(10), 2500; https://doi.org/10.3390/ma14102500 - 12 May 2021
Cited by 29 | Viewed by 3260
Abstract
This article presents a list of suitable techniques and materials leading to the design of an ultra-fast magnetorheological (MR) valve. Two approaches for achieving the short response time are proposed: (a) by means of material, and (b) by means of the shape. Within [...] Read more.
This article presents a list of suitable techniques and materials leading to the design of an ultra-fast magnetorheological (MR) valve. Two approaches for achieving the short response time are proposed: (a) by means of material, and (b) by means of the shape. Within the shape approach, the revolutionary technique of 3D metal printing using a selective laser melting (SLM) method was tested. The suitability of the materials and techniques is addressed based on the length of the response time, which is determined by the FEM. The simulation results determine the response time of the magnetic flux density on the step signal of the current. Subsequently, the response time is verified by the measurement of the simple magnetorheological valve. The following materials were tested: martensitic stainless steel AISI 420A (X20Cr13), cutting steel 11SMn30, pure iron for SLM, Sintex SMC STX prototyping material, ferrite N87, and Vacoflux 50. A special technique involving grooves was used for preventing eddy currents on materials with a high electrical conductivity. The simulation and experimental results indicate that a response time shorter than 2.5 ms can be achieved using materials such as Sintex SMC prototyping, ferrite N87, and grooved variants of metal pistons. Full article
(This article belongs to the Special Issue Electrorheological and Magnetorheological Performance in Materials Science)
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10 pages, 9086 KiB  
Article
Repair of a Cracked Historic Maryan Bell by Gas Welding
by Dariusz Bartocha and Czesław Baron
Materials 2021, 14(10), 2504; https://doi.org/10.3390/ma14102504 - 12 May 2021
Cited by 1 | Viewed by 1975
Abstract
In this article, the range of works connected with the repair of a historical Maryan bell from 1639 are presented. The first attempts to repair damaged bells occurred in the 1930s in Poland. However, this process was stopped because of extensive technological difficulties. [...] Read more.
In this article, the range of works connected with the repair of a historical Maryan bell from 1639 are presented. The first attempts to repair damaged bells occurred in the 1930s in Poland. However, this process was stopped because of extensive technological difficulties. Welding and soldering-welding were the basic methods. There is one difference between these two methods—connecting surfaces are melted during the welding process but only heated until the melting temperature of the material added to the connection (that is the solder) during the soldering-welding process. It was important to heat the bell to the proper temperature during welding. Uneven heating causes the enlargement of existing cracks or the appearance of new ones, or even the complete destruction of the bell. Nowadays, a method of even heating using a special heating mat has been devised. Thanks to this method it is possible to control the heating and cooling process. The most important task during the whole operation of bell welding was obtaining the original sound. During this research, the chemical composition was examined to prepare a welding rod with a suitable chemical composition. After the repair process, an analysis of the sound of the bell was conducted. It was shown that the repair of bells is possible when correct thermal parameters are used. The most highly recommended technique for repairing bells is gas welding. Full article
(This article belongs to the Special Issue Novel Material and Technological Solutions in Foundry Engineering)
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24 pages, 1410 KiB  
Article
Correlation between Defects and Technical Wear of Materials Used in Traditional Construction
by Jarosław Konior and Mariusz Rejment
Materials 2021, 14(10), 2482; https://doi.org/10.3390/ma14102482 - 11 May 2021
Cited by 8 | Viewed by 2366
Abstract
The degree of technical wear of old buildings, which are made of basic materials (cement, concrete, steel, timber, plaster, brick) using traditional technology, is expressed by the size and intensity of damage to their elements. The topic of the research concerns old residential [...] Read more.
The degree of technical wear of old buildings, which are made of basic materials (cement, concrete, steel, timber, plaster, brick) using traditional technology, is expressed by the size and intensity of damage to their elements. The topic of the research concerns old residential buildings from the turn of the 19th and 20th centuries, which are located in the downtown district of Wroclaw, Poland. The descriptive analysis and the analysis of the definitions of defects that occur in the elements of residential buildings, which were performed as random analyzes, do not allow defects to be considered as measurable variables at a level of visual investigation. The major drawback of the method that is used by experts when assessing the technical condition of civil engineering buildings is that it does not numerically express the magnitude (strength) of the defects. Therefore, an attempt was made to numerically express the relationship (if such a relationship exists) between the occurred defects of buildings and the extent of their technical wear process. When calculating the strength of this relationship, the method of determining the point biserial correlation coefficient for the measurable property and the dichotomous property was used. It was found that the direction of the relation is right-hand for all the tested building elements, but the strength of the correlation between the detected defects and technical wear shows a considerable span and depends on the conditions of the apartment house’s maintenance. As a rule, damage caused by water penetration and moisture penetration always shows correlations of at least moderate strength. Full article
(This article belongs to the Special Issue Advanced Construction Materials and Processes in Poland)
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12 pages, 14179 KiB  
Article
The Using of Concrete Wash Water from Ready Mixed Concrete Plants in Cement Systems
by Danutė Vaičiukynienė, Aras Kantautas, Simona Tučkutė, Fallon Manhanga, Eugenijus Janavičius, Ernestas Ivanauskas, Žymantas Rudžionis and Aloyzas Gaudutis
Materials 2021, 14(10), 2483; https://doi.org/10.3390/ma14102483 - 11 May 2021
Cited by 11 | Viewed by 2619
Abstract
Concrete plants accumulate large amounts of concrete wash water. This water, which pH is highly alkaline, has a negative impact on the environment. Its reuse in fresh concrete slightly reduces its mechanical properties. The combination of concrete wash water and zeolitic by-product led [...] Read more.
Concrete plants accumulate large amounts of concrete wash water. This water, which pH is highly alkaline, has a negative impact on the environment. Its reuse in fresh concrete slightly reduces its mechanical properties. The combination of concrete wash water and zeolitic by-product led to an increase of 4.6% in the compressive strength at 7 days hydration and up to 30% at 28 days hydration. The same combination led to the denser microstructure compared to the samples made with concrete wash water. This could be explained by the pozzolanic reaction of the zeolitic by-product. The complex chemical reactions of cement, zeolitic by-product, and fines presented in the concrete wash water occurred. Therefore, it was suggested the reusing method of concrete wash water together with zeolitic by-product in the fresh concrete mixtures by substituting some amount of tap water with concrete wash water. In this way, the consumption of tap water is possible to reduce in cement systems. Full article
(This article belongs to the Special Issue Research on Novel Sustainable Binders, Concretes and Composites)
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26 pages, 5425 KiB  
Article
Effects of Amorphous Poly Alpha Olefin (APAO) and Polyphosphoric Acid (PPA) on the Rheological Properties, Compatibility and Stability of Asphalt Binder
by Xiaoguang Pei and Weiyu Fan
Materials 2021, 14(9), 2458; https://doi.org/10.3390/ma14092458 - 10 May 2021
Cited by 12 | Viewed by 3446
Abstract
High production costs and poor storage stability have become important constraints in the manufacture of modified asphalt binder. To simplify the production process and reduce the production cost, amorphous poly alpha olefin (APAO) and polyphosphoric acid (PPA) were applied to prepare highly stable [...] Read more.
High production costs and poor storage stability have become important constraints in the manufacture of modified asphalt binder. To simplify the production process and reduce the production cost, amorphous poly alpha olefin (APAO) and polyphosphoric acid (PPA) were applied to prepare highly stable modified asphalt binder. The influence of APAO/PPA on the temperature sensitivity, rheological property, storage stability, compatibility and microstructure of neat binder were studied by rotational viscosity (RV), dynamic shear rheometer (DSR), bending beam rheometer (BBR) and Fourier transform infrared (FTIR) spectroscopy. The results show that the incorporation of APAO/PPA reduced the temperature sensitivity of neat binder. The combined effect of APAO/PPA contributed to the improvement in deformation resistance, which was evidenced by the increase in failure temperature and percent recovery. However, the compound modification of APAO/PPA decreased the binder’s low-temperature performance. APAO strengthened the fatigue resistance of the binder, while PPA reduced the anti-fatigue performance. Composite modified asphalt binder with superior storage stability could be prepared, which was confirmed by the desired Cole–Cole plots and fluorescence imaging. Furthermore, chemical and physical reactions occurred during the APAO/PPA modification process. Overall, 2 wt.% (weight percentage) APAO and 1.5 wt.% PPA are recommended for the production of modified asphalt binder with remarkable rheological performance and storage stability. Full article
(This article belongs to the Special Issue Research and Development of Modified Building Materials)
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15 pages, 3572 KiB  
Article
Microstructure, Texture and Mechanical Properties in Aluminum Produced by Friction-Assisted Lateral Extrusion
by Viet Q. Vu, Laszlo S. Toth, Yan Beygelzimer and Yajun Zhao
Materials 2021, 14(9), 2465; https://doi.org/10.3390/ma14092465 - 10 May 2021
Cited by 16 | Viewed by 3361
Abstract
The Friction-Assisted Lateral Extrusion Process (FALEP) is a severe plastic deformation (SPD) technique for producing metal sheets from bulk metal or powder in one single deformation step at room temperature. In the present work, aluminum Al-1050 was deformed by FALEP. Then, its microstructure [...] Read more.
The Friction-Assisted Lateral Extrusion Process (FALEP) is a severe plastic deformation (SPD) technique for producing metal sheets from bulk metal or powder in one single deformation step at room temperature. In the present work, aluminum Al-1050 was deformed by FALEP. Then, its microstructure was examined by EBSD; the crystallographic texture by X-ray; material strength, ductility, and the Lankford parameter by tensile testing; the latter also by polycrystal plasticity simulations. It is shown that the microstructure was highly refined, with the grain size reduced more than 160 times down to 600 nm under the imposed shear strain of 20. The obtained texture was a characteristic simple shear texture with a shear plane nearly parallel to the plane of the sheet. The yield and ultimate strengths increased by about 10 times and three times, respectively. The Lankford parameter was 1.28, which is very high for aluminum, and due to the specific shear texture, unusual in a sheet. All these exceptional characteristics of Al-1050 were obtained thanks to the efficiency of the FALEP SPD process, which is a promising candidate for industrial applications. Full article
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18 pages, 4257 KiB  
Article
Cavitated Charcoal—An Innovative Method for Affecting the Biochemical Properties of Soil
by Krzysztof Gondek, Monika Mierzwa-Hersztek, Wojciech Grzymała, Tomasz Głąb and Tomasz Bajda
Materials 2021, 14(9), 2466; https://doi.org/10.3390/ma14092466 - 10 May 2021
Cited by 4 | Viewed by 2384
Abstract
Thermal biomass transformation products are considered to be one of the best materials for improving soil properties. The aim of the study was to assess the effect of charcoal after cavitation on the chemical and biochemical properties of soil. The study was carried [...] Read more.
Thermal biomass transformation products are considered to be one of the best materials for improving soil properties. The aim of the study was to assess the effect of charcoal after cavitation on the chemical and biochemical properties of soil. The study was carried out with a 10% aqueous charcoal mixture that was introduced into loamy sand and clay at rates of 1.76%, 3.5%, 7.0%, and 14.0%. The effect of the application of cavitated charcoal was tested on Sorghum saccharatum (L.). Soil and plant material was collected to determine chemical and biochemical properties. The application of cavitated charcoal reduced the acidification of both soils. The highest rate (14.0%) of cavitated charcoal increased the content of soil total carbon (CTot) by 197% in the loamy sand compared to CTot in the control treatments, 19% for clay soil, respectively. The application of cavitated charcoal did not significantly change the total content of heavy metals. Regardless of the element and the soil used, the application of cavitated charcoal reduced the content of the CaCl2-extracted forms of heavy metals. Following the application of cavitated charcoal, the loamy sand soil presented an even lower content of the most mobile forms of the studied elements. It should also be noted that regardless of the soil texture, mobile forms of the elements decreased with the increased cavitated charcoal rate. The results of dehydrogenase and urease activity indicated the low metabolic activity of the microbial population in the soils, especially with the relatively high rates (7.0% and 14.0%) of cavitated charcoal. However, the cavitated charcoal used in the study showed a significant, positive effect on the amount of biomass S. saccharatum (L.), and its application significantly reduced the heavy metal content in the biomass of S. saccharatum (L.). Full article
(This article belongs to the Special Issue Functionalized Mineral Materials in Environmental and Civil Engineering, Ceramics, Foundry and Metals)
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12 pages, 3549 KiB  
Article
Additive Manufacturing-Based In Situ Consolidation of Continuous Carbon Fibre-Reinforced Polycarbonate
by Andreas Borowski, Christian Vogel, Thomas Behnisch, Vinzenz Geske, Maik Gude and Niels Modler
Materials 2021, 14(9), 2450; https://doi.org/10.3390/ma14092450 - 9 May 2021
Cited by 17 | Viewed by 4070
Abstract
Continuous carbon fibre-reinforced thermoplastic composites have convincing anisotropic properties, which can be used to strengthen structural components in a local, variable and efficient way. In this study, an additive manufacturing (AM) process is introduced to fabricate in situ consolidated continuous fibre-reinforced polycarbonate. Specimens [...] Read more.
Continuous carbon fibre-reinforced thermoplastic composites have convincing anisotropic properties, which can be used to strengthen structural components in a local, variable and efficient way. In this study, an additive manufacturing (AM) process is introduced to fabricate in situ consolidated continuous fibre-reinforced polycarbonate. Specimens with three different nozzle temperatures were in situ consolidated and tested in a three-point bending test. Computed tomography (CT) is used for a detailed analysis of the local material structure and resulting material porosity, thus the results can be put into context with process parameters. In addition, a highly curved test structure was fabricated that demonstrates the limits of the process and dependent fibre strand folding behaviours. These experimental investigations present the potential and the challenges of additive manufacturing-based in situ consolidated continuous fibre-reinforced polycarbonate. Full article
(This article belongs to the Special Issue Additive Manufacturing Materials and Their Applications)
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19 pages, 13685 KiB  
Article
Influence of the Fly Ash Material Inoculants on the Tensile and Impact Characteristics of the Aluminum AA 5083/7.5SiC Composites
by Santhosh Nagaraja, Kempaiah Ujjaini Nagegowda, Anand Kumar V, Sagr Alamri, Asif Afzal, Deepak Thakur, Abdul Razak Kaladgi, Satyam Panchal and Ahamed Saleel C
Materials 2021, 14(9), 2452; https://doi.org/10.3390/ma14092452 - 9 May 2021
Cited by 57 | Viewed by 3646
Abstract
The choice of suitable inoculants in the grain refinement process and subsequent enhancement of the characteristics of the composites developed is an important materials research topic, having wide scope. In this regard, the present work is aimed at finding the appropriate composition and [...] Read more.
The choice of suitable inoculants in the grain refinement process and subsequent enhancement of the characteristics of the composites developed is an important materials research topic, having wide scope. In this regard, the present work is aimed at finding the appropriate composition and size of fly ash as inoculants for grain refinement of the aluminum AA 5083 composites. Fly ash particles, which are by products of the combustion process in thermal power plants, contributing to the large-scale pollution and landfills can be effectively utilized as inoculants and interatomic lubricants in the composite matrix–reinforcement subspaces synthesized in the inert atmosphere using ultrasonic assisted stir casting setup. Thus, the work involves the study of the influence of percentage and size of the fly ash dispersions on the tensile and impact strength characteristics of the aluminum AA 5083/7.5SiC composites. The C type of fly ash with the particle size in the series of 40–75 µm, 76–100 µm, and 101–125 µm and weight % in the series of 0.5, 1, 1.5, 2, and 2.5 are selected for the work. The influence of fly ash as distinct material inoculants for the grain refinement has worked out well with the increase in the ultimate tensile strength, yield strength, and impact strength of the composites, with the fly ash as material inoculants up to 2 wt. % beyond which the tensile and impact characteristics decrease due to the micro coring and segregation. This is evident from the microstructural observations for the composite specimens. Moreover, the role of fly ash as material inoculants is distinctly identified with the X-Ray Diffraction (XRD) for the phase and grain growth epitaxy and the Energy Dispersive Spectroscopy (EDS) for analyzing the characteristic X-Rays of the fly ash particles as inoculant agents in the energy spectrum. Full article
(This article belongs to the Special Issue Functional Materials, Machine Learning, and Optimization)
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24 pages, 13858 KiB  
Article
The Mechanical Properties and Damage Evolution of UHPC Reinforced with Glass Fibers and High-Performance Polypropylene Fibers
by Jiayuan He, Weizhen Chen, Boshan Zhang, Jiangjiang Yu and Hang Liu
Materials 2021, 14(9), 2455; https://doi.org/10.3390/ma14092455 - 9 May 2021
Cited by 36 | Viewed by 4645
Abstract
Due to the sharp and corrosion-prone features of steel fibers, there is a demand for ultra-high-performance concrete (UHPC) reinforced with nonmetallic fibers. In this paper, glass fiber (GF) and the high-performance polypropylene (HPP) fiber were selected to prepare UHPC, and the effects of [...] Read more.
Due to the sharp and corrosion-prone features of steel fibers, there is a demand for ultra-high-performance concrete (UHPC) reinforced with nonmetallic fibers. In this paper, glass fiber (GF) and the high-performance polypropylene (HPP) fiber were selected to prepare UHPC, and the effects of different fibers on the compressive, tensile and bending properties of UHPC were investigated, experimentally and numerically. Then, the damage evolution of UHPC was further studied numerically, adopting the concrete damaged plasticity (CDP) model. The difference between the simulation values and experimental values was within 5.0%, verifying the reliability of the numerical model. The results indicate that 2.0% fiber content in UHPC provides better mechanical properties. In addition, the glass fiber was more significant in strengthening the effect. Compared with HPP-UHPC, the compressive, tensile and flexural strength of GF-UHPC increased by about 20%, 30% and 40%, respectively. However, the flexural toughness indexes I5, I10 and I20 of HPP-UHPC were about 1.2, 2.0 and 3.8 times those of GF-UHPC, respectively, showing that the toughening effect of the HPP fiber is better. Full article
(This article belongs to the Special Issue High Performance of Fiber Reinforced Cementitious Composites)
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14 pages, 2959 KiB  
Article
Improving Indoor Air Quality by Using Sheep Wool Thermal Insulation
by Andreea Hegyi, Cezar Bulacu, Henriette Szilagyi, Adrian-Victor Lăzărescu, Vasile Meiţă, Petrică Vizureanu and Mihaela Sandu
Materials 2021, 14(9), 2443; https://doi.org/10.3390/ma14092443 - 8 May 2021
Cited by 16 | Viewed by 4681
Abstract
Currently, the need to ensure adequate quality of air inside the living space but also the thermal efficiency of buildings is pressing. This paper presents the capacity of sheep wool heat-insulating mattresses to simultaneously provide these needs, cumulatively analyzing efficiency indicators for thermal [...] Read more.
Currently, the need to ensure adequate quality of air inside the living space but also the thermal efficiency of buildings is pressing. This paper presents the capacity of sheep wool heat-insulating mattresses to simultaneously provide these needs, cumulatively analyzing efficiency indicators for thermal insulation and indicators of improving air quality. Thus, the values obtained for the coefficient of thermal conductivity, and its resistance to heat transfer, demonstrate the suitability of their use for thermal insulation. The results of the permeability to water vapor characteristics on the sorption/desorption of water, air, demonstrate the ability to control the humidity of the indoor air and the results on the reduction of the concentration of formaldehyde, demonstrating their contribution to the growth of the quality of the air, and to reduce the risk of disease in the population. Full article
(This article belongs to the Special Issue Obtaining and Characterization of New Materials, Volume II)
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18 pages, 3839 KiB  
Article
Effect of Cathodic Protection on Reinforced Concrete with Fly Ash Using Electrochemical Noise
by Jorge García-Contreras, Citlalli Gaona-Tiburcio, Irene López-Cazares, Guillermo Sanchéz-Díaz, Juan Carlos Ibarra Castillo, Jesús Jáquez-Muñoz, Demetrio Nieves-Mendoza, Erick Maldonado-Bandala, Javier Olguín-Coca, Luis Daimir López-León and Facundo Almeraya-Calderón
Materials 2021, 14(9), 2438; https://doi.org/10.3390/ma14092438 - 7 May 2021
Cited by 10 | Viewed by 3460
Abstract
Corrosion of steel reinforcement is the major factor that limits the durability and serviceability performance of reinforced concrete structures. Impressed current cathodic protection (ICCP) is a widely used method to protect steel reinforcements against corrosion. This research aimed to study the effect of [...] Read more.
Corrosion of steel reinforcement is the major factor that limits the durability and serviceability performance of reinforced concrete structures. Impressed current cathodic protection (ICCP) is a widely used method to protect steel reinforcements against corrosion. This research aimed to study the effect of cathodic protection on reinforced concrete with fly ash using electrochemical noise (EN). Two types of reinforced concrete mixtures were manufactured; 100% Ordinary Portland Cement (OCP) and replacing 15% of cement using fly ash (OCPFA). The specimens were under-designed protected conditions (−1000 ≤ E ≤ −850 mV vs. Ag/AgCl) and cathodic overprotection (E < −1000 mV vs. Ag/AgCl) by impressed current, and specimens concrete were immersed in a 3.5 wt.% sodium chloride (NaCl) Solution. The analysis of electrochemical noise-time series showed that the mixtures microstructure influenced the corrosion process. Transients of uniform corrosion were observed in the specimens elaborated with (OPC), unlike those elaborated with (OPCFA). This phenomenon marked the difference in the concrete matrix’s hydration products, preventing Cl− ions flow and showing passive current and potential transients in most specimens. Full article
(This article belongs to the Special Issue Corrosion in Concrete: Inhibitors and Coatings)
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16 pages, 4352 KiB  
Article
A New Method for Compaction Quality Evaluation of Asphalt Mixtures with the Intelligent Aggregate (IA)
by Chen Zhang and Hainian Wang
Materials 2021, 14(9), 2422; https://doi.org/10.3390/ma14092422 - 6 May 2021
Cited by 5 | Viewed by 2264
Abstract
To provide a new method for the evaluation of the compaction quality of asphalt mixture, a real-time data acquisition and processing system (RDAPS) for the motion state of aggregate with a small volume and high precision is developed. The system consists of an [...] Read more.
To provide a new method for the evaluation of the compaction quality of asphalt mixture, a real-time data acquisition and processing system (RDAPS) for the motion state of aggregate with a small volume and high precision is developed. The system consists of an intelligent aggregate (IA), analysis software and hardware equipment. The performance of the IA was tested by regarding data sensitivity, high-temperature resistance, and mechanical properties. A new evaluation method was proposed for evaluating the compaction quality of AC-25 and SMA-25 asphalt mixtures based on an IA. The results show that the best transmission baud rate for the IA was 9600 bps, and the corresponding signal transmission distance was 380 m. Only one IA was needed to complete the state data collection for the aggregate within the asphalt mixture in a circular area, with the IA layout point as the center of the circle and a radius of 5 m. The IA conducted reliable data transmission up to 200 °C; however, its compressive strength decreased with increasing temperature until reaching stability. Traditional aggregate could be replaced by an IA to withstand external forces and internal load transfer. Embedding an IA into AC-25 or SMA-25 asphalt mixtures did not have a significant impact on the original mechanical properties of the mixture. The effect of the gradation type of the asphalt mixture on the IA motion state was not significant. When the compaction degree met the specification requirements, the motion data of the IA did not reach a stable state, and the interlocking effect between aggregates in the asphalt mixture could be further optimized. An evaluation method is proposed based on the IA for the compaction quality of AC-25 and SMA-25 asphalt mixtures with the compaction degree as the main index and the spatial attitude angle and spatial acceleration of the IA as the auxiliary indexes. Full article
(This article belongs to the Special Issue Structural Health Monitoring for Civil Engineering Materials)
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26 pages, 4943 KiB  
Article
Life-Cycle Assessment of Alkali-Activated Materials Incorporating Industrial Byproducts
by Iman Faridmehr, Moncef L. Nehdi, Mehdi Nikoo, Ghasan Fahim Huseien and Togay Ozbakkaloglu
Materials 2021, 14(9), 2401; https://doi.org/10.3390/ma14092401 - 5 May 2021
Cited by 44 | Viewed by 4100
Abstract
Eco-friendly and sustainable materials that are cost-effective, while having a reduced carbon footprint and energy consumption, are in great demand by the construction industry worldwide. Accordingly, alkali-activated materials (AAM) composed primarily of industrial byproducts have emerged as more desirable alternatives to ordinary Portland [...] Read more.
Eco-friendly and sustainable materials that are cost-effective, while having a reduced carbon footprint and energy consumption, are in great demand by the construction industry worldwide. Accordingly, alkali-activated materials (AAM) composed primarily of industrial byproducts have emerged as more desirable alternatives to ordinary Portland cement (OPC)-based concrete. Hence, this study investigates the cradle-to-gate life-cycle assessment (LCA) of ternary blended alkali-activated mortars made with industrial byproducts. Moreover, the embodied energy (EE), which represents an important parameter in cradle-to-gate life-cycle analysis, was investigated for 42 AAM mixtures. The boundary of the cradle-to-gate system was extended to include the mechanical and durability properties of AAMs on the basis of performance criteria. Using the experimental test database thus developed, an optimized artificial neural network (ANN) combined with the cuckoo optimization algorithm (COA) was developed to estimate the CO2 emissions and EE of AAMs. Considering the lack of systematic research on the cradle-to-gate LCA of AAMs in the literature, the results of this research provide new insights into the assessment of the environmental impact of AAM made with industrial byproducts. The final weight and bias values of the AAN model can be used to design AAM mixtures with targeted mechanical properties and CO2 emission considering desired amounts of industrial byproduct utilization in the mixture. Full article
(This article belongs to the Special Issue Advanced Cement and Concrete Composites)
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17 pages, 2685 KiB  
Article
High UV and Sunlight Photocatalytic Performance of Porous ZnO Nanostructures Synthesized by a Facile and Fast Microwave Hydrothermal Method
by Sofia Henriques Ferreira, Maria Morais, Daniela Nunes, Maria João Oliveira, Ana Rovisco, Ana Pimentel, Hugo Águas, Elvira Fortunato and Rodrigo Martins
Materials 2021, 14(9), 2385; https://doi.org/10.3390/ma14092385 - 4 May 2021
Cited by 65 | Viewed by 5127
Abstract
The degradation of organic pollutants in wastewaters assisted by oxide semiconductor nanostructures has been the focus of many research groups over the last decades, along with the synthesis of these nanomaterials by simple, eco-friendly, fast, and cost-effective processes. In this work, porous zinc [...] Read more.
The degradation of organic pollutants in wastewaters assisted by oxide semiconductor nanostructures has been the focus of many research groups over the last decades, along with the synthesis of these nanomaterials by simple, eco-friendly, fast, and cost-effective processes. In this work, porous zinc oxide (ZnO) nanostructures were successfully synthesized via a microwave hydrothermal process. A layered zinc hydroxide carbonate (LZHC) precursor was obtained after 15 min of synthesis and submitted to different calcination temperatures to convert it into porous ZnO nanostructures. The influence of the calcination temperature (300, 500, and 700 °C) on the morphological, structural, and optical properties of the ZnO nanostructureswas investigated. All ZnO samples were tested as photocatalysts in the degradation of rhodamine B (RhB) under UV irradiation and natural sunlight. All samples showed enhanced photocatalytic activity under both light sources, with RhB being practically degraded within 60 min in both situations. The porous ZnO obtained at 700 °C showed the greatest photocatalytic activity due to its high crystallinity, with a degradation rate of 0.091 and 0.084 min−1 for UV light and sunlight, respectively. These results are a very important step towards the use of oxide semiconductors in the degradation of water pollutants mediated by natural sunlight. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications)
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14 pages, 2789 KiB  
Article
Analyses of Influence on Chromium Coating after Grinding from the View of Final Microstructure and Microhardness in the Surface Layer
by Nataša Náprstková, Martin Novák, Martin Marek, Karel Šramhauser, Jan Sviantek, Dana Stančeková and Miroslava Ťavodová
Materials 2021, 14(9), 2396; https://doi.org/10.3390/ma14092396 - 4 May 2021
Cited by 3 | Viewed by 2131
Abstract
The article deals with the analysis of chromium layer grinding on a steel substrate, where this issue was addressed with regard to the requirements of the manufacturing sector, specifically in the aerospace industry. The experimental samples were chromium-plated and ground under different cutting [...] Read more.
The article deals with the analysis of chromium layer grinding on a steel substrate, where this issue was addressed with regard to the requirements of the manufacturing sector, specifically in the aerospace industry. The experimental samples were chromium-plated and ground under different cutting conditions by the grooving method of grinding. Two types of grinding wheels for grinding were used, grinding wheel based on SG (solgel) a grinding wheel based on SiC. The resulting microstructure and microhardness in the machined layer were evaluated with using of confocal laser microscopy, inverted materials microscopy, and hardness testing. Based on the results, recommendations were made regarding a suitable approach to grinding the chromium coating. We used a confocal laser microscope and hardness tester for the evaluation of presented values. It was found that, on the base of analyses values, with both grinding wheel and using cutting conditions used, good results have been achieved. This could be stated, because the analysis of the samples microstructure after grinding for the given cutting conditions showed that it is possible that a small influence is completely acceptable from the point of the final product view and there are no major negative phenomena. Measurements of surface microhardness after grinding showed similar results for all samples. The SiC-based grinding wheel showed slightly better results, but both grinding wheels can be used without problems for the presented cutting conditions, and the presented cutting conditions with both grinding wheels can be recommended for the grinding of the given material. Full article
(This article belongs to the Special Issue Precision and Ultra-Precision Subtractive and Additive Manufacturing Processes of Alloys and Steels)
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25 pages, 19775 KiB  
Review
Progress on In Situ and Operando X-ray Imaging of Solidification Processes
by Shyamprasad Karagadde, Chu Lun Alex Leung and Peter D. Lee
Materials 2021, 14(9), 2374; https://doi.org/10.3390/ma14092374 - 2 May 2021
Cited by 27 | Viewed by 5535
Abstract
In this review, we present an overview of significant developments in the field of in situ and operando (ISO) X-ray imaging of solidification processes. The objective of this review is to emphasize the key challenges in developing and performing in situ X-ray imaging [...] Read more.
In this review, we present an overview of significant developments in the field of in situ and operando (ISO) X-ray imaging of solidification processes. The objective of this review is to emphasize the key challenges in developing and performing in situ X-ray imaging of solidification processes, as well as to highlight important contributions that have significantly advanced the understanding of various mechanisms pertaining to microstructural evolution, defects, and semi-solid deformation of metallic alloy systems. Likewise, some of the process modifications such as electromagnetic and ultra-sound melt treatments have also been described. Finally, a discussion on the recent breakthroughs in the emerging technology of additive manufacturing, and the challenges thereof, are presented. Full article
(This article belongs to the Section Materials Physics)
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15 pages, 2051 KiB  
Article
Advanced Photonic Thin Films for Solar Irradiation Tuneability Oriented to Greenhouse Applications
by M. Barragán Sánchez-Lanuza, Amador Menéndez-Velázquez, Antonio Peñas-Sanjuan, Francisco J. Navas-Martos, Isidoro Lillo-Bravo and José-María Delgado-Sánchez
Materials 2021, 14(9), 2357; https://doi.org/10.3390/ma14092357 - 1 May 2021
Cited by 23 | Viewed by 3816
Abstract
The world population is growing by 1 billion people every 10 years. There will come a time when there will be more people to feed but less land to grow food. Greenhouses can be the solution to this problem because they provide the [...] Read more.
The world population is growing by 1 billion people every 10 years. There will come a time when there will be more people to feed but less land to grow food. Greenhouses can be the solution to this problem because they provide the highest production yield per m2 and also use less water, provide food safety, and offer high quality. Photosynthetic active radiation (PAR) favors vegetable growth with a specific blue and red light ratio. Thus, increasing the amount of red light improves chlorophyll absorption and photosynthetic efficiency. In this article, we present a hybrid system that combines luminescent materials and photonic crystals for better management of the light reaching the greenhouse. The luminescent dyes considered herein are combined ensuring a Förster resonance energy transfer (FRET) nonradiative mechanism to enhance the absorption range. The designed photonic crystal maximizes reflections in the Near-Infrared (NIR) range, and therefore, thermal losses are minimized. Thus, by converting harmful or ineffective radiation for plant growth to the PAR region, we aim to demonstrate growth-condition enhancement for the different vegetables that have been used as a model. Full article
(This article belongs to the Special Issue Advanced Materials for Optical Applications and Devices)
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17 pages, 4449 KiB  
Article
Zn- and Ti-Doped SnO2 for Enhanced Electroreduction of Carbon Dioxide
by Katarzyna Bejtka, Nicolò B. D. Monti, Adriano Sacco, Micaela Castellino, Samuele Porro, M. Amin Farkhondehfal, Juqin Zeng, Candido F. Pirri and Angelica Chiodoni
Materials 2021, 14(9), 2354; https://doi.org/10.3390/ma14092354 - 1 May 2021
Cited by 12 | Viewed by 3650
Abstract
The electrocatalytic reduction of CO2 into useful fuels, exploiting rationally designed, inexpensive, active, and selective catalysts, produced through easy, quick, and scalable routes, represents a promising approach to face today’s climate challenges and energy crisis. This work presents a facile strategy for [...] Read more.
The electrocatalytic reduction of CO2 into useful fuels, exploiting rationally designed, inexpensive, active, and selective catalysts, produced through easy, quick, and scalable routes, represents a promising approach to face today’s climate challenges and energy crisis. This work presents a facile strategy for the preparation of doped SnO2 as an efficient electrocatalyst for the CO2 reduction reaction to formic acid and carbon monoxide. Zn or Ti doping was introduced into a mesoporous SnO2 matrix via wet impregnation and atomic layer deposition. It was found that doping of SnO2 generates an increased amount of oxygen vacancies, which are believed to contribute to the CO2 conversion efficiency, and among others, Zn wet impregnation resulted the most efficient process, as confirmed by X-ray photoelectron spectroscopy analysis. Electrochemical characterization and active surface area evaluation show an increase of availability of surface active sites. In particular, the introduction of Zn elemental doping results in enhanced performance for formic acid formation, in comparison to un-doped SnO2 and other doped SnO2 catalysts. At −0.99 V versus reversible hydrogen electrode, the total faradaic efficiency for CO2 conversion reaches 80%, while the partial current density is 10.3 mA cm−2. These represent a 10% and a threefold increases for faradaic efficiency and current density, respectively, with respect to the reference un-doped sample. The enhancement of these characteristics relates to the improved charge transfer and conductivity with respect to bare SnO2. Full article
(This article belongs to the Section Catalytic Materials)
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16 pages, 5573 KiB  
Article
Grouting below Subterranean Water: Erosional Stability Test
by Jiří Boštík, Lumír Miča, Ivailo Terzijski, Mirnela Džaferagić and Augustin Leiter
Materials 2021, 14(9), 2333; https://doi.org/10.3390/ma14092333 - 30 Apr 2021
Cited by 1 | Viewed by 2613
Abstract
The article is focused on the medium-term negative effect of groundwater on the underground grout elements. This is the physical–mechanical effect of groundwater, which is known as erosion. We conduct a laboratory verification of the erosional resistance of grout mixtures. A new test [...] Read more.
The article is focused on the medium-term negative effect of groundwater on the underground grout elements. This is the physical–mechanical effect of groundwater, which is known as erosion. We conduct a laboratory verification of the erosional resistance of grout mixtures. A new test apparatus was designed and developed, since there is no standardized method for testing at present. An erosion stability test of grout mixtures and the technical solutions of the apparatus for the test’s implementation are described. This apparatus was subsequently used for the experimental evaluation of the erosional stability of silicate grout mixtures. Grout mixtures with activated and non-activated bentonite are tested. The stabilizing effect of cellulose relative to erosion stability has been also investigated. The specimens of grout mixtures are exposed to flowing water stress for a certain period of time. The erosional stabilities of the grout mixtures are assessed on the basis of weight loss (WL) as a percentage of initial specimen weight. The lower the grout mixture weight loss, the higher its erosional stability and vice versa. Full article
(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)
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18 pages, 5411 KiB  
Article
Application of Novel Machine Learning Techniques for Predicting the Surface Chloride Concentration in Concrete Containing Waste Material
by Ayaz Ahmad, Furqan Farooq, Krzysztof Adam Ostrowski, Klaudia Śliwa-Wieczorek and Slawomir Czarnecki
Materials 2021, 14(9), 2297; https://doi.org/10.3390/ma14092297 - 29 Apr 2021
Cited by 98 | Viewed by 5162
Abstract
Structures located on the coast are subjected to the long-term influence of chloride ions, which cause the corrosion of steel reinforcements in concrete elements. This corrosion severely affects the performance of the elements and may shorten the lifespan of an entire structure. Even [...] Read more.
Structures located on the coast are subjected to the long-term influence of chloride ions, which cause the corrosion of steel reinforcements in concrete elements. This corrosion severely affects the performance of the elements and may shorten the lifespan of an entire structure. Even though experimental activities in laboratories might be a solution, they may also be problematic due to time and costs. Thus, the application of individual machine learning (ML) techniques has been investigated to predict surface chloride concentrations (Cc) in marine structures. For this purpose, the values of Cc in tidal, splash, and submerged zones were collected from an extensive literature survey and incorporated into the article. Gene expression programming (GEP), the decision tree (DT), and an artificial neural network (ANN) were used to predict the surface chloride concentrations, and the most accurate algorithm was then selected. The GEP model was the most accurate when compared to ANN and DT, which was confirmed by the high accuracy level of the K-fold cross-validation and linear correlation coefficient (R2), mean absolute error (MAE), mean square error (MSE), and root mean square error (RMSE) parameters. As is shown in the article, the proposed method is an effective and accurate way to predict the surface chloride concentration without the inconveniences of laboratory tests. Full article
(This article belongs to the Special Issue Artificial Intelligence for Cementitious Materials)
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20 pages, 4368 KiB  
Article
2D Dynamic Directional Amplification (DDA) in Phononic Metamaterials
by Moris Kalderon, Andreas Paradeisiotis and Ioannis Antoniadis
Materials 2021, 14(9), 2302; https://doi.org/10.3390/ma14092302 - 29 Apr 2021
Cited by 11 | Viewed by 2650
Abstract
Phononic structures with unit cells exhibiting Bragg scattering and local resonance present unique wave propagation properties at wavelengths well below the regime corresponding to bandgap generation based on spatial periodicity. However, both mechanisms show certain constraints in designing systems with wide bandgaps in [...] Read more.
Phononic structures with unit cells exhibiting Bragg scattering and local resonance present unique wave propagation properties at wavelengths well below the regime corresponding to bandgap generation based on spatial periodicity. However, both mechanisms show certain constraints in designing systems with wide bandgaps in the low-frequency range. To face the main practical challenges encountered in such cases, including heavy oscillating masses, a simple dynamic directional amplification (DDA) mechanism is proposed as the base of the phononic lattice. This amplifier is designed to present the same mass and use the same damping element as a reference two-dimensional (2D) phononic metamaterial. Thus, no increase in the structure mass or the viscous damping is needed. The proposed DDA can be realized by imposing kinematic constraints to the structure’s degrees of freedom (DoF), improving inertia and damping on the desired direction of motion. Analysis of the 2D lattice via Bloch’s theory is performed, and the corresponding dispersion relations are derived. The numerical results of an indicative case study show significant improvements and advantages over a conventional phononic structure, such as broader bandgaps and increased damping ratio. Finally, a conceptual design indicates the usage of the concept in potential applications, such as mechanical filters, sound and vibration isolators, and acoustic waveguides. Full article
(This article belongs to the Special Issue Advances in Acoustic Metamaterials)
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26 pages, 7982 KiB  
Article
Investigation of the Effect of Mixing Time on the Mechanical Properties of Alkali-Activated Cement Mixed with Fly Ash and Slag
by Taewan Kim and Choonghyun Kang
Materials 2021, 14(9), 2301; https://doi.org/10.3390/ma14092301 - 29 Apr 2021
Cited by 4 | Viewed by 2287
Abstract
This is an experiment on the effect of mixing time for alkali-activated cement (AAC) using a binder mixed with ground granulated blast furnace slag (slag) and fly ash (FA) in a ratio of 1:1 on the mechanical properties. The mixing method of ASTM [...] Read more.
This is an experiment on the effect of mixing time for alkali-activated cement (AAC) using a binder mixed with ground granulated blast furnace slag (slag) and fly ash (FA) in a ratio of 1:1 on the mechanical properties. The mixing method of ASTM C305 was used as the basic mixing method, and the following mixing method was changed. Simply adding the same mixing time and procedure, the difference in the order of mixing slag and FA, and controlling the amount of activator and mixed water were considered. As a result of the experiment, the addition of the same mixing time and procedure, pre-injection of slag, and high-alkali mixed water in which half of the activator and mixing water were mixed showed the highest mechanical properties and a dense pore structure. As a result, the design of a blending method that can promote the activation action of slag rather than FA at room temperature was effective in improving the mechanical properties of AAC. In addition, these blending factors showed a clearer effect as the concentration of the activator increased. Through the results of this experiment, it was shown that high-temperature curing, high fineness of the binder, or even changing the setting of the mixing method without the use of excessive activators can lead to an improvement of mechanical properties. Full article
(This article belongs to the Special Issue Low Carbon Cements)
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16 pages, 4384 KiB  
Article
Inactivating SARS-CoV-2 Using 275 nm UV-C LEDs through a Spherical Irradiation Box: Design, Characterization and Validation
by Nicola Trivellin, Matteo Buffolo, Francesco Onelia, Alberto Pizzolato, Marco Barbato, Viviana Teresa Orlandi, Claudia Del Vecchio, Fabrizio Dughiero, Enrico Zanoni, Gaudenzio Meneghesso, Andrea Crisanti and Matteo Meneghini
Materials 2021, 14(9), 2315; https://doi.org/10.3390/ma14092315 - 29 Apr 2021
Cited by 34 | Viewed by 4545
Abstract
We report on the design, characterization and validation of a spherical irradiation system for inactivating SARS-CoV-2, based on UV-C 275 nm LEDs. The system is designed to maximize irradiation intensity and uniformity and can be used for irradiating a volume of 18 L. [...] Read more.
We report on the design, characterization and validation of a spherical irradiation system for inactivating SARS-CoV-2, based on UV-C 275 nm LEDs. The system is designed to maximize irradiation intensity and uniformity and can be used for irradiating a volume of 18 L. To this aim: (i) several commercially available LEDs have been acquired and analyzed; (ii) a complete optical study has been carried out in order to optimize the efficacy of the system; (iii) the resulting prototype has been characterized optically and tested for the inactivation of SARS-CoV-2 for different exposure times, doses and surface types; (iv) the result achieved and the efficacy of the prototype have been compared with similar devices based on different technologies. Results indicate that a 99.9% inactivation can be reached after 1 min of treatment with a dose of 83.1 J/m2. Full article
(This article belongs to the Special Issue Advanced Materials for Biophotonics Applications)
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16 pages, 3501 KiB  
Article
Mechanical Properties and Durability of Rubberized and Glass Powder Modified Rubberized Concrete for Whitetopping Structures
by Audrius Grinys, Muthaiah Balamurugan, Algirdas Augonis and Ernestas Ivanauskas
Materials 2021, 14(9), 2321; https://doi.org/10.3390/ma14092321 - 29 Apr 2021
Cited by 35 | Viewed by 3205
Abstract
This paper analyzes concrete fine aggregate (sand) modification by scrap tire rubber particles-fine crumb rubber (FCR) and coarse crumb rubber (CCR) of fraction 0/1 mm. Such rubberized concrete to get better bonding properties were modified by car-boxylated styrene butadiene rubber (SBR) latex and [...] Read more.
This paper analyzes concrete fine aggregate (sand) modification by scrap tire rubber particles-fine crumb rubber (FCR) and coarse crumb rubber (CCR) of fraction 0/1 mm. Such rubberized concrete to get better bonding properties were modified by car-boxylated styrene butadiene rubber (SBR) latex and to gain the strength were modified by glass waste. The following tests—slump test, fresh concrete density, fresh concrete air content, compressive strength, flexural strength, fracture energy, freezing-thawing, porosity parameter, and scanning electron microscope—were conducted for rubberized concretes. From experiments, we can see that fresh concrete properties decreased when crumb rubber content has increased. Mostly it is related to crumb rubber (CR) lower specific gravity nature and higher fineness compared with changed fine aggregate-sand. In this research, we obtained a slight loss of compressive strength when CR was used in concrete However, these rubberized concretes with a small amount of rubber provided sufficient compressive strength results (greater than 50 MPa). Due to the pozzolanic reaction, we see that compressive strength results after 56 days in glass powder modified samples increased by 11–13% than 28 days com-pressive strengths, while at the same period control samples increased its compressive strength about 2.5%. Experiments have shown that the flexural strength of rubberized concrete with small amounts of CR increased by 3.4–15.8% compared to control mix, due the fact that rubber is an elastic material and it will absorb high energy and perform positive bending toughness. The test results indicated that CR can intercept the tensile stress in concrete and make the deformation more plastic. Fracturing of such conglomerate concrete is not brittle, there is no abrupt post-peak load drop and gradually continues after the maximum load is exceeded. Such concrete requires much higher fracture energy. It was obtained that FCR particles (lower than A300) will entrap more micropores content than coarse rubbers because due to their high specific area. Freezing-thawing results have confirmed that Kf values can be conveniently used to predict freeze-thaw resistance and durability of concrete. The test has shown that modification of concrete with 10 kg fine rubber waste will lead to similar mechanical and durability properties of concrete as was obtained in control concrete with 2 kg of prefabricated air bubbles. Full article
(This article belongs to the Special Issue Research on Novel Sustainable Binders, Concretes and Composites)
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22 pages, 10611 KiB  
Article
Building and Breaking Bonds by Homogenous Nucleation in Glass-Forming Melts Leading to Transitions in Three Liquid States
by Robert F. Tournier and Michael I. Ojovan
Materials 2021, 14(9), 2287; https://doi.org/10.3390/ma14092287 - 28 Apr 2021
Cited by 11 | Viewed by 2734
Abstract
The thermal history of melts leads to three liquid states above the melting temperatures Tm containing clusters—bound colloids with two opposite values of enthalpy +Δεlg × ΔHm and −Δεlg × ΔHm and zero. All colloid bonds disconnect at [...] Read more.
The thermal history of melts leads to three liquid states above the melting temperatures Tm containing clusters—bound colloids with two opposite values of enthalpy +Δεlg × ΔHm and −Δεlg × ΔHm and zero. All colloid bonds disconnect at Tn+ > Tm and give rise in congruent materials, through a first-order transition at TLL = Tn+, forming a homogeneous liquid, containing tiny superatoms, built by short-range order. In non-congruent materials, (Tn+) and (TLL) are separated, Tn+ being the temperature of a second order and TLL the temperature of a first-order phase transition. (Tn+) and (TLL) are predicted from the knowledge of solidus and liquidus temperatures using non-classical homogenous nucleation. The first-order transition at TLL gives rise by cooling to a new liquid state containing colloids. Each colloid is a superatom, melted by homogeneous disintegration of nuclei instead of surface melting, and with a Gibbs free energy equal to that of a liquid droplet containing the same magic atom number. Internal and external bond number of colloids increases at Tn+ or from Tn+ to Tg. These liquid enthalpies reveal the natural presence of colloid–colloid bonding and antibonding in glass-forming melts. The Mpemba effect and its inverse exist in all melts and is due to the presence of these three liquid states. Full article
(This article belongs to the Special Issue Glass Science and First-Order Transitions at a Turning Point)
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15 pages, 6206 KiB  
Article
Revealing the WEDM Process Parameters for the Machining of Pure and Heat-Treated Titanium (Ti-6Al-4V) Alloy
by Nitin Kumar Gupta, Nalin Somani, Chander Prakash, Ranjit Singh, Arminder Singh Walia, Sunpreet Singh and Catalin Iulian Pruncu
Materials 2021, 14(9), 2292; https://doi.org/10.3390/ma14092292 - 28 Apr 2021
Cited by 67 | Viewed by 3794
Abstract
Ti-6Al-4V is an alloy that has a high strength-to-weight ratio. It is known as an alpha-beta titanium alloy with excellent corrosion resistance. This alloy has a wide range of applications, e.g., in the aerospace and biomedical industries. Examples of alpha stabilizers are aluminum, [...] Read more.
Ti-6Al-4V is an alloy that has a high strength-to-weight ratio. It is known as an alpha-beta titanium alloy with excellent corrosion resistance. This alloy has a wide range of applications, e.g., in the aerospace and biomedical industries. Examples of alpha stabilizers are aluminum, oxygen, nitrogen, and carbon, which are added to titanium. Examples of beta stabilizers are titanium–iron, titanium–chromium, and titanium–manganese. Despite the exceptional properties, the processing of this titanium alloy is challenging when using conventional methods as it is quite a hard and tough material. Nonconventional methods are required to create intricate and complex geometries, which are difficult with the traditional methods. The present study focused on machining Ti-6Al-4V using wire electrical discharge machining (WEDM) and conducting numerous experiments to establish the machining parameters. The optimal setting of the machining parameters was predicted using a multiresponse optimization technique. Experiments were planned using the response surface methodology (RSM) technique and analysis of variance (ANOVA) was used to determine the significance and contribution of the input parameters to changes in the output characteristics (cutting speed and surface roughness). The cutting speed obtained during the processing of the annealed titanium alloy using WEDM was quite large as compared to the cutting speed obtained in the case of processing the pure, quenched, and hardened titanium alloys using WEDM. The maximum cutting speed obtained while processing the annealed titanium alloy was 1.75 mm/min. Full article
(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)
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15 pages, 3421 KiB  
Article
Theoretical and Experimental Identification of Frequency Characteristics and Control Signals of a Dynamic System in the Process of Turning
by Antoni Świć and Arkadiusz Gola
Materials 2021, 14(9), 2260; https://doi.org/10.3390/ma14092260 - 27 Apr 2021
Cited by 4 | Viewed by 2022
Abstract
The article presents the results of the experimental validation of the developed static, time and frequency characteristics under interference and longitudinal feed control of a dynamic system in the process of turning axisymmetric parts. The experiments were conducted on a test bench, consisting [...] Read more.
The article presents the results of the experimental validation of the developed static, time and frequency characteristics under interference and longitudinal feed control of a dynamic system in the process of turning axisymmetric parts. The experiments were conducted on a test bench, consisting of a 16B16P center lathe, a measuring system and a PC with a measurement card. The experiments were carried out to verify the assumptions of the baseline model of the turning process. As part of the study, we determined the static characteristics of the machining process, the time characteristics of the object under interference and under longitudinal feed rate control, and the frequency characteristics of the machine tool system under longitudinal feed rate control. During the experiments, we recorded the observed input and output signal curves and the observed characteristics of the interferences acting on the object, as well as the numerical values of the parameters of the equations describing the model, and in particular the gain of the elastic system, which is difficult to determine by analytical methods. The positive results of the experiments confirm the effectiveness of the proposed models and their usefulness for automation of machining processes. Full article
(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)
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14 pages, 7277 KiB  
Article
Omega Phase Formation in Ti–3wt.%Nb Alloy Induced by High-Pressure Torsion
by Anna Korneva, Boris Straumal, Askar Kilmametov, Alena Gornakova, Anna Wierzbicka-Miernik, Lidia Lityńska-Dobrzyńska, Robert Chulist, Łukasz Gondek, Grzegorz Cios and Paweł Zięba
Materials 2021, 14(9), 2262; https://doi.org/10.3390/ma14092262 - 27 Apr 2021
Cited by 8 | Viewed by 3054
Abstract
It is well known that severe plastic deformation not only leads to strong grain refinement and material strengthening but also can drive phase transformations. A study of the fundamentals of α → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys [...] Read more.
It is well known that severe plastic deformation not only leads to strong grain refinement and material strengthening but also can drive phase transformations. A study of the fundamentals of α → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Before HPT, a Ti–3wt.%Nb alloy was annealed at two different temperatures in order to obtain the α-phase state with different amounts of niobium. X-ray diffraction analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the characterisation of phase transitions and evolution of the microstructure. A small amount of the β-phase was found in the initial states, which completely transformed into the ω-phase during the HPT process. During HPT, strong grain refinement in the α-phase took place, as did partial transformation of the α- into the ω-phase. Therefore, two kinds of ω-phase, each with different chemical composition, were obtained after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the α-phase. It was also found that the transformation of the α-phase into the ω-phase depended on the Nb concentration in the α-Ti phase. The less Nb there was in the α-phase, the more of the α-phase was transformed into the ω-phase. Full article
(This article belongs to the Special Issue Feature Papers in Materials Physics)
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15 pages, 2639 KiB  
Article
Influence of Groundwater pH on Water Absorption and Waterproofness of Polymer Modified Bituminous Thick Coatings
by Barbara Francke and Maria Wichowska
Materials 2021, 14(9), 2272; https://doi.org/10.3390/ma14092272 - 27 Apr 2021
Cited by 4 | Viewed by 2340
Abstract
Polymer modified bituminous thick coatings are increasingly used in the construction industry to protect underground parts of buildings from groundwater. When assessing their durability, one vital issue related to their functional properties is the influence of water absorption on the waterproofness of the [...] Read more.
Polymer modified bituminous thick coatings are increasingly used in the construction industry to protect underground parts of buildings from groundwater. When assessing their durability, one vital issue related to their functional properties is the influence of water absorption on the waterproofness of the applied solution as a result of the action of groundwater with different pH values. As part of the research, the water absorption of the products in question was assessed using the method of total immersion in water with pH of 4.0, 7.0 and 7.5 as well as comparatively, as a result of one-way exposure to demineralized water under successively increasing pressure up to 0.5 MPa. The moisture susceptibility of the coatings was assessed both concerning the local surface damage and the continuous waterproofing coating. It was established that the coatings show the highest water absorption when the water pH is 4.0, which simulates the groundwater aggressiveness on construction products. It was proven that moisture absorbed by the coatings is retained within this layer and is not transferred to the substrate on which the coatings are laid. It was also found that water in contact with the tested coatings changes its reaction to alkaline, which can result in contamination of groundwater in the area of waterproofing coating. A modification of the method of assessing the water absorption of polymer modified bituminous thick coatings was proposed, taking into account their use in conditions of use. Full article
(This article belongs to the Special Issue Sustainability in Construction and Building Materials)
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15 pages, 7580 KiB  
Article
The Parameters Identification of High-Temperature Constitutive Model Based on Inverse Optimization Method and 3D Processing Map of Cr8 Alloy Steel
by Xuewen Chen, Tingting Lian, Bo Zhang, Yuqing Du, Kexue Du, Bingqi Liu, Zhipeng Li, Xuanhe Tian and Dong-Won Jung
Materials 2021, 14(9), 2216; https://doi.org/10.3390/ma14092216 - 26 Apr 2021
Cited by 5 | Viewed by 2491
Abstract
As a novel kind of cold roller steel, Cr8 alloy steel has the characteristics of high hardness, high wear resistance and good toughness, which can effectively prolong the service life of the roller that is an important part of the steel rolling mill. [...] Read more.
As a novel kind of cold roller steel, Cr8 alloy steel has the characteristics of high hardness, high wear resistance and good toughness, which can effectively prolong the service life of the roller that is an important part of the steel rolling mill. How to accurately define the constitutive model parameters of metal materials is the major problem, because it seriously affects the accuracy of numerical simulation results of the roller hot forming process. In the study of Cr8 alloy steel’s thermal deformation behavior of the present paper, the high temperature compression test was done on a Gleebel-1500D thermal/force simulation testing machine. A novel method of parameter identification was proposed based on inverse optimization. The Hansel–Spittel constitutive model was established by using the inverse optimization method. To carry out the verification on the accuracy of the established constitutive model, the predicted flow-stress of constitutive model was made a contrast to the experimental flow-stress, and the standard statistical parameters were also applied to further evaluation. The results showed a relatively high prediction accuracy of the Hansel–Spittel constitutive model based on the inverse optimization algorithm. Meanwhile, to obtain optimal parameters of Cr8 alloy steel in the thermal processing, 3D thermal processing maps concerning strain-rate, strain and temperature were built based on the dynamic material model. According to the 3D processing map, the most adequate thermal processing parameters of Cr8 alloy steel were obtianed as follows: strain 0.2–0.4, strain-rate 0.05–0.005 s−1, temperature 1100–1150 °C. Full article
(This article belongs to the Special Issue Recent Advances in Metal Forming Technology)
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14 pages, 8205 KiB  
Article
Metallographic Testing of 19th Century Steel in an Operating Water Tower
by Eugeniusz Hotała, Rajmund Ignatowicz and Maciej B. Lachowicz
Materials 2021, 14(9), 2204; https://doi.org/10.3390/ma14092204 - 25 Apr 2021
Cited by 2 | Viewed by 2681
Abstract
The world’s first steel structures were built towards the end of the 19th century. Some of them are still in use today, whereas others are maintained as precious technical heritage. In both cases, there may be a need to assess their technical condition [...] Read more.
The world’s first steel structures were built towards the end of the 19th century. Some of them are still in use today, whereas others are maintained as precious technical heritage. In both cases, there may be a need to assess their technical condition and carry out repairs and reinforcements, which requires an understanding of the properties of the steel used. The few studies that have been undertaken of such steel structures indicate that the properties depend on the history of use. This paper presents the results of metallographic tests of a steel tank in a water tower built in 1884 in Lower Silesia. The chemical composition was consistent with that of the puddled steel used in the 19th century. The carbon content showed significant segregation and ranged from 0.011% to 0.072% mass. As a consequence, a typical microstructure for low-carbon steels (ferritic) was observed, changing locally to ferritic-pearlitic. The tested steel contained a very high content of phosphorus and silicon. The microstructure with numerous slags favoured the formation of surface delamination caused by the corrosion processes. The degree of corrosion of the steel of the tank was also assessed, as well as the type of corrosion inside the tank. Corrosion was favoured by the oxygen concentration cell. The results of the research will be used to assess the potential for continuing tank use and the reinforcements that have been planned. The results presented will add to the somewhat limited research results available for steel dating back to the 19th century, which is still present in many building structures. Such a database is especially needed by those designing technical measures aimed at maintaining these historical structures in good technical condition. Full article
(This article belongs to the Special Issue Advanced Construction Materials and Processes in Poland)
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19 pages, 9896 KiB  
Article
Methodology for the Quality Control Process of Additive Manufacturing Products Made of Polymer Materials
by Grzegorz Budzik, Joanna Woźniak, Andrzej Paszkiewicz, Łukasz Przeszłowski, Tomasz Dziubek and Mariusz Dębski
Materials 2021, 14(9), 2202; https://doi.org/10.3390/ma14092202 - 25 Apr 2021
Cited by 47 | Viewed by 6206
Abstract
The objective of this publication is to present a quality control methodology for additive manufacturing products made of polymer materials, where the methodology varies depending on the intended use. The models presented in this paper are divided into those that are manufactured for [...] Read more.
The objective of this publication is to present a quality control methodology for additive manufacturing products made of polymer materials, where the methodology varies depending on the intended use. The models presented in this paper are divided into those that are manufactured for the purpose of visual presentation and those that directly serve the needs of the manufacturing process. The authors also a propose a comprehensive control system for the additive manufacturing process to meet the needs of Industry 4.0. Depending on the intended use of the models, the quality control process is divided into three stages: data control, manufacturing control, and post-processing control. Research models were made from the following materials: RGD 720 photopolymer resin (PolyJet method), ABS M30 thermoplastic (FDM method), E-Partial photopolymer resin (DLP method), PLA thermoplastic (FFF method), and ABS thermoplastic (MEM method). The applied measuring tools had an accuracy of at least an order of magnitude higher than that of the manufacturing technologies used. The results show that the PolyJet method is the most accurate, and the MEM method is the least accurate. The findings also confirm that the selection of materials, 3D printing methods, and measurement methods should always account not only for the specificity and purpose of the model but also for economic aspects, as not all products require high accuracy and durability. Full article
(This article belongs to the Special Issue Modeling, Simulation and Data Processing for Additive Manufacturing)
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14 pages, 4719 KiB  
Article
Inelastic Responses and Finite Element Predictions of Fiber Cementitious Composite and Concrete Columns
by Chang-Geun Cho and Sun-Ju Lee
Materials 2021, 14(9), 2180; https://doi.org/10.3390/ma14092180 - 24 Apr 2021
Cited by 2 | Viewed by 1718
Abstract
In this research, reinforced concrete (RC) and strain-hardening cementitious composite (SHCC) columns subjected to lateral loads combined with a constant load were investigated, both by experiments and predictions, with two distributed inelastic finite element models established by the stiffness and flexibility formulations. SHCC [...] Read more.
In this research, reinforced concrete (RC) and strain-hardening cementitious composite (SHCC) columns subjected to lateral loads combined with a constant load were investigated, both by experiments and predictions, with two distributed inelastic finite element models established by the stiffness and flexibility formulations. SHCC applied in the column plastic hinge region could not only enhance the lateral load and displacement capacities of columns but also offer effective advantages in the control of bending and shear cracks induced by multiple microcracks, the prevention of the spalling of cover concrete, and the resistance to buckling of steel bars. With the layered cross-sectional approach using constitutive laws of SHCC considering a proposed model of the post-cracked high-ductile tensile characteristics, as well as concrete and reinforcing steel bars, an inelastic beam-column finite element model was presented with a distributed flexibility formulation. In comparison with experiments concerning the RC and reinforced strain-hardening cementitious composite (R-SHCC) columns, the current flexibility method showed relatively accurate estimations in the lateral load and displacement responses of column systems as well as in localized nonlinear responses of cross-section as estimated in axial strains of longitudinal reinforcing steel bars. In comparison with the stiffness method, the current flexibility method gave more accurate solutions at both element and structural levels, as manifested in the experiments and analysis solutions. Full article
(This article belongs to the Special Issue Concrete Structures with Fiber-Reinforced Cementitious and Composite Materials)
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13 pages, 4038 KiB  
Article
Characterization of Open-Cell Sponges via Magnetic Resonance and X-ray Tomography
by Gabriele M. Cimmarusti, Abhishek Shastry, Matthieu N. Boone, Veerle Cnudde, Karl Braeckman, Anju D. M. Brooker, Eric S. J. Robles and Melanie M. Britton
Materials 2021, 14(9), 2187; https://doi.org/10.3390/ma14092187 - 24 Apr 2021
Cited by 2 | Viewed by 3128
Abstract
The applications of polymeric sponges are varied, ranging from cleaning and filtration to medical applications. The specific properties of polymeric foams, such as pore size and connectivity, are dependent on their constituent materials and production methods. Nuclear magnetic resonance imaging (MRI) and X-ray [...] Read more.
The applications of polymeric sponges are varied, ranging from cleaning and filtration to medical applications. The specific properties of polymeric foams, such as pore size and connectivity, are dependent on their constituent materials and production methods. Nuclear magnetic resonance imaging (MRI) and X-ray micro-computed tomography (µCT) offer complementary information about the structure and properties of porous media. In this study, we employed MRI, in combination with µCT, to characterize the structure of polymeric open-cell foam, and to determine how it changes upon compression, µCT was used to identify the morphology of the pores within sponge plugs, extracted from polyurethane open-cell sponges. MRI T2 relaxation maps and bulk T2 relaxation times measurements were performed for 7° dH water contained within the same polyurethane foams used for µCT. Magnetic resonance and µCT measurements were conducted on both uncompressed and 60% compressed sponge plugs. Compression was achieved using a graduated sample holder with plunger. A relationship between the average T2 relaxation time and maximum opening was observed, where smaller maximum openings were found to have a shorter T2 relaxation times. It was also found that upon compression, the average maximum opening of pores decreased. Average pore size ranges of 375–632 ± 1 µm, for uncompressed plugs, and 301–473 ± 1 µm, for compressed plugs, were observed. By determining maximum opening values and T2 relaxation times, it was observed that the pore structure varies between sponges within the same production batch, as well as even with a single sponge. Full article
(This article belongs to the Special Issue New Advances in Characterization of Cellular Materials)
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18 pages, 3912 KiB  
Article
Development of Impact-Echo Multitransducer Device for Automated Concrete Homogeneity Assessment
by Bartłomiej Sawicki, Tomasz Piotrowski and Andrzej Garbacz
Materials 2021, 14(9), 2144; https://doi.org/10.3390/ma14092144 - 23 Apr 2021
Cited by 3 | Viewed by 3047
Abstract
A combination of multiple nondestructive testing (NDT) methods speeds up the assessment of concrete and increases the precision. This is why the UIR-Scanner was developed at Warsaw University of Technology. The scanner uses an Impact-Echo (IE) method with a unique arrangement of multiple [...] Read more.
A combination of multiple nondestructive testing (NDT) methods speeds up the assessment of concrete and increases the precision. This is why the UIR-Scanner was developed at Warsaw University of Technology. The scanner uses an Impact-Echo (IE) method with a unique arrangement of multiple transducers. This paper presents the development of the IE module using numerical models validated with experimental testing. It was found that rectangular arrangement of four transducers with the impactor in the middle is optimal for quick scanning of area for faults and discontinuities, changing the method from punctual to volumetric. A numerical study of void detectability depending on its position with respect to the IE module is discussed as well. After confirmation of the findings of models using experimental tests, the module was implemented into the scanner. Full article
(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering (2nd Edition))
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10 pages, 2784 KiB  
Article
Reflective Quasi-Continuous Metasurface with Continuous Phase Control for Light Focusing
by Long Chen, Zhenglong Shao, Jia Liu and Dongliang Tang
Materials 2021, 14(9), 2147; https://doi.org/10.3390/ma14092147 - 23 Apr 2021
Cited by 6 | Viewed by 2415
Abstract
Benefitting from the arbitrary and flexible light modulation, metasurface has attracted extensive attention and been demonstrated in different applications. However, most reported metasurface-based devices were normally composed of discrete micro or nano structures, therefore the discretization precision limited the performance of the device, [...] Read more.
Benefitting from the arbitrary and flexible light modulation, metasurface has attracted extensive attention and been demonstrated in different applications. However, most reported metasurface-based devices were normally composed of discrete micro or nano structures, therefore the discretization precision limited the performance of the device, including the focusing efficiency, stray light suppression, and broadband performance. In this work, an all-metallic reflective metasurface consisting of numerous quasi-continuous nanostructures is proposed to realize high-efficiency and broadband focusing. The constructed quasi-continuous metasurface (QCMS) is then verified numerically through electromagnetic simulation, and the numerical results show a higher focusing efficiency and a better stray light suppression effect, compared to a binary-phase-based metalens. Through the same design strategy, a QCMS with the ability to overcome the diffraction limit can also be constructed, and a focal spot with the size of 0.8 times the diffraction limit can be achieved. We expect that this quasi-continuous structure could be utilized to construct other high-performance devices that require continuous phase controls, such as the beam deflector, orbital angle momentum generator, and self-accelerating beam generator. Full article
(This article belongs to the Special Issue Quasi-Continuous Metasurfaces for High-Performance Functional Electromagnetic Wave Devices)
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10 pages, 2418 KiB  
Article
Nanostructured Iron Sulfide/N, S Dual-Doped Carbon Nanotube-Graphene Composites as Efficient Electrocatalysts for Oxygen Reduction Reaction
by Gyu Sik Chae, Duck Hyun Youn and Jae Sung Lee
Materials 2021, 14(9), 2146; https://doi.org/10.3390/ma14092146 - 23 Apr 2021
Cited by 21 | Viewed by 3912
Abstract
Nanostructured FeS dispersed onto N, S dual-doped carbon nanotube–graphene composite support (FeS/N,S:CNT–GR) was prepared by a simple synthetic method. Annealing an ethanol slurry of Fe precursor, thiourea, carbon nanotube, and graphene oxide at 973 K under N2 atmosphere and subsequent acid treatment [...] Read more.
Nanostructured FeS dispersed onto N, S dual-doped carbon nanotube–graphene composite support (FeS/N,S:CNT–GR) was prepared by a simple synthetic method. Annealing an ethanol slurry of Fe precursor, thiourea, carbon nanotube, and graphene oxide at 973 K under N2 atmosphere and subsequent acid treatment produced FeS nanoparticles distributed onto the N, S-doped carbon nanotube–graphene support. The synthesized FeS/N,S:CNT–GR catalyst exhibited significantly enhanced electrochemical performance in the oxygen reduction reaction (ORR) compared with bare FeS, FeS/N,S:GR, and FeS/N,S:CNT with a small half-wave potential (0.827 V) in an alkaline electrolyte. The improved ORR performance, comparable to that of commercial Pt/C, could be attributed to synergy between the small FeS nanoparticles with a high activity and the N, S-doped carbon nanotube–graphene composite support providing high electrical conductivity, large surface area, and additional active sites. Full article
(This article belongs to the Special Issue Advances in Nanostructured Catalysts)
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16 pages, 2697 KiB  
Review
Research Hotspots and Development Trends on Recycled Construction Materials in Pavement Engineering: A Bibliometric Evaluation
by Yue Xiao, Qiankun Dong, Xiwen Chang, Peiqiang Cui and Gang Liu
Materials 2021, 14(9), 2170; https://doi.org/10.3390/ma14092170 - 23 Apr 2021
Cited by 6 | Viewed by 2501
Abstract
Road recycling technology is gradually becoming a research focus in road construction due to natural resource shortages. It is therefore necessary to carry out deep and extensive analysis of the huge amount of publications in the research area of recycling technology in road [...] Read more.
Road recycling technology is gradually becoming a research focus in road construction due to natural resource shortages. It is therefore necessary to carry out deep and extensive analysis of the huge amount of publications in the research area of recycling technology in road construction. Based on three databases (Web of Science, Compendex and Scopus) and VOSviewer visualization software, this study conducts a bibliometric analysis of the literature in the field of recycled construction materials in pavement engineering. The global research publications were reviewed to quantitatively identify the literature characteristics. A number of publications, document types, research areas and keywords were used to achieve the general statistics of this reviewed literature. H-index, publication number and citations per publication were used to evaluate the academic contributions by country, institution and journal. The results show that the most productive country and institution for publications are the USA and Chang’an University from China, respectively, followed by China and Wuhan University of Technology. In recent years, researchers have generally paid attention to two main approaches: the application of rubber modified asphalt and the performance enhancement of recycled pavement. Full article
(This article belongs to the Special Issue Silicate Solid Waste Recycling)
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13 pages, 7096 KiB  
Article
Magnetically Induced Transparency in Media with Helical Dichroic Structure
by Ashot H. Gevorgyan, Sergey S. Golik, Nikolay A. Vanyushkin, Ilya M. Efimov, Mushegh S. Rafayelyan, Hermine Gharagulyan, Tatevik M. Sarukhanyan, Meruzhan Z. Hautyunyan and Gvidon K. Matinyan
Materials 2021, 14(9), 2172; https://doi.org/10.3390/ma14092172 - 23 Apr 2021
Cited by 13 | Viewed by 2002
Abstract
In our paper, the magneto-optical properties of a dichroic cholesteric liquid crystal layer with large values of magneto-optical parameter g and low values of dielectric permittivity were investigated. The solutions of the dispersion equation and their peculiarities were investigated in detail. The specific [...] Read more.
In our paper, the magneto-optical properties of a dichroic cholesteric liquid crystal layer with large values of magneto-optical parameter g and low values of dielectric permittivity were investigated. The solutions of the dispersion equation and their peculiarities were investigated in detail. The specific properties of reflection, transmission, absorption, rotation, ellipticity spectra and also the spectra of ellipticity and azimuth of eigen polarization were investigated. The existence of a tunable linear and nonreciprocal transmission band was shown. Full article
(This article belongs to the Section Optical and Photonic Materials)
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14 pages, 40805 KiB  
Article
Approach of Pavement Surface Layer Degradation Caused by Tire Contact Using Semi-Analytical Model
by Edem Yawo Manyo, Benoit Picoux, Philippe Reynaud, Rémi Tautou, Daniel Nelias, Fatima Allou and Christophe Petit
Materials 2021, 14(9), 2117; https://doi.org/10.3390/ma14092117 - 22 Apr 2021
Cited by 7 | Viewed by 2132
Abstract
New methods of degradations on the pavement’s surface, such as top-down cracking and delamination, caused by the repeated passage of heavy vehicles led to questions about the impact of the contact between the tire and the pavement. In fact, to increase the service [...] Read more.
New methods of degradations on the pavement’s surface, such as top-down cracking and delamination, caused by the repeated passage of heavy vehicles led to questions about the impact of the contact between the tire and the pavement. In fact, to increase the service life of the structures, future road design methods must have a precise knowledge of the consequences of the contact parameters on the state of stress and deformation in the pavement. In this paper, tractive rolling contact under the effect of friction is modeled by Kalker’s theory using a semi-analytical method (SAM). A tire profile is performed thanks to a digitization by fringes or a photogrammetry technique. The effect of rolling on the main surface extension deformations is then highlighted to study top cracking. At the end of the SAM calculation, contact areas are closed to 200 μdef, exceeding the allowable micro-deformation limit for the initiation of cracking. In addition, results on the main strain directions also give information on the direction of cracking (initiation of longitudinal or transverse cracks). The cracking then becomes evident, leading to a reduced service life. Full article
(This article belongs to the Section Construction and Building Materials)
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17 pages, 86229 KiB  
Article
Use of Cement Suspension as an Alternative Matrix Material for Textile-Reinforced Concrete
by Richard Fürst, Eliška Fürst, Tomáš Vlach, Jakub Řepka, Marek Pokorný and Vladimír Mózer
Materials 2021, 14(9), 2127; https://doi.org/10.3390/ma14092127 - 22 Apr 2021
Cited by 4 | Viewed by 2897
Abstract
Textile-reinforced concrete (TRC) is a material consisting of high-performance concrete (HPC) and tensile reinforcement comprised of carbon roving with epoxy resin matrix. However, the problem of low epoxy resin resistance at higher temperatures persists. In this work, an alternative to the epoxy resin [...] Read more.
Textile-reinforced concrete (TRC) is a material consisting of high-performance concrete (HPC) and tensile reinforcement comprised of carbon roving with epoxy resin matrix. However, the problem of low epoxy resin resistance at higher temperatures persists. In this work, an alternative to the epoxy resin matrix, a non-combustible cement suspension (cement milk) which has proven stability at elevated temperatures, was evaluated. In the first part of the work, microscopic research was carried out to determine the distribution of particle sizes in the cement suspension. Subsequently, five series of plate samples differing in the type of cement and the method of textile reinforcement saturation were designed and prepared. Mechanical experiments (four-point bending tests) were carried out to verify the properties of each sample type. It was found that the highest efficiency of carbon roving saturation was achieved by using finer ground cement (CEM 52.5) and the pressure saturation method. Moreover, this solution also exhibited the best results in the four-point bending test. Finally, the use of CEM 52.5 in the cement matrix appears to be a feasible variant for TRC constructions that could overcome problems with its low temperature resistance. Full article
(This article belongs to the Special Issue Advanced Cement and Concrete Composites)
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17 pages, 2544 KiB  
Article
Chemical Modification of Agro-Industrial Waste-Based Bioadsorbents for Enhanced Removal of Zn(II) Ions from Aqueous Solutions
by David Castro, Nelly Ma. Rosas-Laverde, María Belén Aldás, Cristina E. Almeida-Naranjo, Víctor H. Guerrero and Alina Iuliana Pruna
Materials 2021, 14(9), 2134; https://doi.org/10.3390/ma14092134 - 22 Apr 2021
Cited by 42 | Viewed by 4336
Abstract
Contamination of water by heavy metals is a major environmental concern due to the potential ecological impact on human health and aquatic ecosystems. In this work, we studied the chemical modification of various fruit peels such as banana (BP), granadilla (GP), and orange [...] Read more.
Contamination of water by heavy metals is a major environmental concern due to the potential ecological impact on human health and aquatic ecosystems. In this work, we studied the chemical modification of various fruit peels such as banana (BP), granadilla (GP), and orange ones (OP) in order to obtain novel bio-adsorbents to improve the removal of Zn(II) ions from 50 mg·L−1 synthetic aqueous solutions. For this purpose, sodium hydroxide and calcium acetate were employed to modify the fruit peels. The moisture, extractives, lignin, hemicellulose, and cellulose contents of the raw materials were determined according to ASTM standards. The obtained bio-adsorbents were characterized by scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results showed the OP bio-adsorbents performed better, especially when the concentration of the modifier solutions increased, e.g., the OP particles modified using 0.8 M NaOH and Ca(CH3COO)2 solutions resulted in 97% removal of Zn(II) contaminating ions and reached a maximum adsorption capacity of 27.5 mg Zn per gram of bio-adsorbent. The adsorption processes were found to follow a pseudo-second order model. The error function sum of square error indicated the Freundlich isotherm (non-linear regression) as best fit model. The obtained results are particularly interesting for material selection in wastewater treatment technologies based on contaminant adsorption. Full article
(This article belongs to the Special Issue Low-Cost Water Treatment - New Materials and New Approaches)
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18 pages, 11163 KiB  
Article
Production of Hybrid Joints by Selective Laser Melting of Maraging Tool Steel 1.2709 on Conventionally Produced Parts of the Same Steel
by Ludmila Kučerová, Ivana Zetková, Štěpán Jeníček and Karolína Burdová
Materials 2021, 14(9), 2105; https://doi.org/10.3390/ma14092105 - 21 Apr 2021
Cited by 14 | Viewed by 2187
Abstract
Joining additively manufactured (AM) complex shaped parts to larger conventionally produced parts can lead to innovative product designs. Another alternative is direct deposition on a conventional semi-product. Therefore, similar joints of maraging tool steel 1.2709 were produced by AM deposition of powder of [...] Read more.
Joining additively manufactured (AM) complex shaped parts to larger conventionally produced parts can lead to innovative product designs. Another alternative is direct deposition on a conventional semi-product. Therefore, similar joints of maraging tool steel 1.2709 were produced by AM deposition of powder of this steel on a bulk conventionally manufactured steel part. The resulting hybrid parts were solution annealed and precipitation hardened. Solution annealing at 820 °C for 20 min was followed by furnace cooling. Precipitation hardening was performed at 490 °C for 6 h. The mechanical properties of the samples were characterised using tensile testing and hardness measurement across the joint. Metallographic analysis was also carried out. The tensile properties of the AM and conventionally produced steel after equivalent heat treatments were also determined as the reference values. The mechanical properties of the hybrid parts are close to the properties of both steels. The hybrid parts in the as-built condition had a tensile strength of 1029 MPa and a total elongation of 14%. Solution annealing did not change these properties significantly, except for yield strength, which decreased by approximately 150 MPa. After precipitation annealing, the strength was higher, 2011 MPa, and total elongation dropped to 5%. Full article
(This article belongs to the Special Issue Material Analysis of Additively Manufactured Metals)
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