Materials

19 pages, 6046 KB

Open AccessEditor’s ChoiceArticle

Understanding the Microstructure of Mortars for Cultural Heritage Using X-ray CT and MIP

by Valentina Brunello, Carmen Canevali, Cristina Corti, Tim De Kock, Laura Rampazzi, Sandro Recchia, Antonio Sansonetti, Cristina Tedeschi and Veerle Cnudde

Materials 2021, 14(20), 5939; https://doi.org/10.3390/ma14205939 - 10 Oct 2021

Cited by 15 | Viewed by 3492

Abstract

In this study, the microstructure of mock-up mortar specimens for a historic environment, composed of different mixtures, was studied using mercury intrusion porosity (MIP) and microcomputed tomography (µCT), highlighting the advantages and drawbacks of both techniques. Porosity, sphericity, and pores size distribution were [...] Read more.

In this study, the microstructure of mock-up mortar specimens for a historic environment, composed of different mixtures, was studied using mercury intrusion porosity (MIP) and microcomputed tomography (µCT), highlighting the advantages and drawbacks of both techniques. Porosity, sphericity, and pores size distribution were studied, evaluating changes according to mortar composition (aerial and hydraulic binders, quartz sand, and crushed limestone aggregate). The µCT results were rendered using 3D visualization software, which provides complementary information for the interpretation of the data obtained using 3D data-analysis software. Moreover, µCT contributes to the interpretation of MIP results of mortars. On the other hand, MIP showed significant ink-bottle effects in lime and cement mortars samples that should be taken into account when interpreting the results. Moreover, the MIP results highlighted how gypsum mortar samples display a porosity distribution that is best studied using this technique. This multi-analytical approach provides important insights into the interpretation of the porosimetric data obtained. This is crucial in the characterization of mortars and provides key information for the study of building materials and cultural heritage conservation. Full article

(This article belongs to the Special Issue Experiment and Computer Simulations with Concrete and Granular Materials)

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14 pages, 2986 KB

Open AccessEditor’s ChoiceArticle

Experimental Study on the Correlation between Crack Width and Crack Depth of RC Beams

by Yue Li, Juhui Zhang, Zhongguo Guan and Youliang Chen

Materials 2021, 14(20), 5950; https://doi.org/10.3390/ma14205950 - 10 Oct 2021

Cited by 10 | Viewed by 2746

Abstract

The depth of cracks propagating inside reinforcement concrete (RC) components is barely able to be detected by visual inspection. Without any help from facilities, crack width can provide us with a proper way to explore the depth of cracks developing. Therefore, this paper [...] Read more.

The depth of cracks propagating inside reinforcement concrete (RC) components is barely able to be detected by visual inspection. Without any help from facilities, crack width can provide us with a proper way to explore the depth of cracks developing. Therefore, this paper tried to explore the correlation between crack width on the surface and crack depth. A static loading test was conducted on eight RC beams, considering the variation of concrete strength, cover, and reinforcement ratio. The test results indicate that concrete strength has a certain impact on cracking load and the propagation of cracks is mainly related to reinforcement ratio. The linear changes in load and crack width can be found. Originally, crack depth markedly increased with loading, but when restricted by compression zone of concrete and the height of beams, crack depth stopped extending finally. The correlation between crack width and crack depth was analyzed by studying work phases of a cross-section and experimental data. The fitting function achieved in this paper was determined to be a good agreement between the theoretical and the experimental relationship. Full article

(This article belongs to the Section Construction and Building Materials)

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11 pages, 1752 KB

Open AccessEditor’s ChoiceArticle

Raman Spectroscopic Study of TiO₂ Nanoparticles’ Effects on the Hemoglobin State in Individual Red Blood Cells

by Elena Perevedentseva, Yu-Chung Lin, Artashes Karmenyan, Kuan-Ting Wu, Andrei Lugovtsov, Evgeny Shirshin, Alexander Priezzhev and Chia-Liang Cheng

Materials 2021, 14(20), 5920; https://doi.org/10.3390/ma14205920 - 9 Oct 2021

Cited by 24 | Viewed by 4759

Abstract

Titanium dioxide (TiO₂) is considered to be a nontoxic material and is widely used in a number of everyday products, such as sunscreen. TiO₂ nanoparticles (NP) are also considered as prospective agents for photodynamic therapy and drug delivery. These applications [...] Read more.

Titanium dioxide (TiO₂) is considered to be a nontoxic material and is widely used in a number of everyday products, such as sunscreen. TiO₂ nanoparticles (NP) are also considered as prospective agents for photodynamic therapy and drug delivery. These applications require an understanding of the potential effects of TiO₂ on the blood system and its components upon administration. In the presented work, we analyze the interaction of TiO₂ nanoparticles of different crystal phases (anatase and rutile) with individual rat Red Blood Cells (RBC) and the TiO₂ influence on the oxygenation state and functionality of RBC, estimated via analysis of Raman spectra of Hemoglobin (Hb) and their distribution along individual RBC. Raman spectral signals also allow localization of the TiO₂ NP on the RBC. No penetration of the NP inside RBC was observed; however, both kinds of TiO₂ NP adsorbed on the RBC membrane can affect the Hb state. Mechanisms involving the NP–membrane–Hb interaction, resulting in partial deoxygenation of Hb and TiO₂ photothermal effect on Hb under Raman laser excitation, are suggested. The possible influence on the safety of TiO₂ use in advanced medical application, especially on the safety and efficiency of photothermal therapy, is discussed. Full article

(This article belongs to the Special Issue Advanced Materials for Biophotonics Applications)

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16 pages, 4224 KB

Open AccessEditor’s ChoiceArticle

Novel Nano-Precursor Inhibiting Material for Improving Chloride Penetration Resistance of Concrete: Evaluation and Mechanism

by Ruixing Chen, Song Mu, Jiaping Liu, Jingshun Cai, Deqing Xie, Guangyan Liu and Zheng Guo

Materials 2021, 14(20), 5929; https://doi.org/10.3390/ma14205929 - 9 Oct 2021

Cited by 5 | Viewed by 2012

Abstract

Durability improvement is always important for steel–concrete structures exposed to chloride salt environment. The present research investigated the influence of a novel nano-precursor inhibiting material (NPI), organic carboxylic acid ammonium salt, on the mechanical and transport properties of concrete. The NPI caused a [...] Read more.

Durability improvement is always important for steel–concrete structures exposed to chloride salt environment. The present research investigated the influence of a novel nano-precursor inhibiting material (NPI), organic carboxylic acid ammonium salt, on the mechanical and transport properties of concrete. The NPI caused a slight reduction in the strength of concrete at later ages. NPI significantly decreased water absorption and slowed down the speed of water absorption of concrete. In addition, the NPI decreased the charge passed and the chloride migration coefficient, and the results of the natural chloride diffusion showed that the NPI decreased the chloride concentration and the chloride diffusion coefficient. The NPI effectively improved the resistance of chloride penetration into testing concrete. The improvement in the impermeability of concrete was ascribed to the incorporation with the NPI, which resulted in increasing the contact angle of cement pastes. The contact angle went up from 17.8° to 85.8° for 0% and 1.2% NPI, respectively, and cement pastes became less hydrophilic. Some small pore throats were unconnected. Besides, the NPI also optimized the pore size distribution of hardened cement paste. Full article

(This article belongs to the Section Construction and Building Materials)

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17 pages, 30836 KB

Open AccessEditor’s ChoiceArticle

Analysis of the Frequency of Acoustic Emission Events in Terms of the Assessment of the Reduction of Mechanical Parameters of Cellulose–Cement Composites

by Anna Adamczak-Bugno, Aleksandra Krampikowska and Grzegorz Świt

Materials 2021, 14(19), 5882; https://doi.org/10.3390/ma14195882 - 8 Oct 2021

Cited by 2 | Viewed by 2239

Abstract

The article proposes the application of the acoustic emission method as a technique for the evaluation of mechanical parameters of cellulose–cement composites. The analysis focused on frequency values in a time series analysis of elements subject to three-point flexural stress. In the course [...] Read more.

The article proposes the application of the acoustic emission method as a technique for the evaluation of mechanical parameters of cellulose–cement composites. The analysis focused on frequency values in a time series analysis of elements subject to three-point flexural stress. In the course of a statistic analysis, it has been demonstrated that a significant reduction of the recorded frequency values is associated with a considerable reduction in strength. This allowed the authors to determine the range of frequencies related to the depreciation in the strength of an element. The tests were carried out on elements cut from a full-size cellulose–cement board. Samples exposed to potential operational factors (environmental and exceptional) were analysed. It was shown that the frequencies recorded before reaching the maximum load during bending of samples exposed to environmental factors (water and low temperature) were significantly different (were much lower) from the sounds emitted by elements subjected to exceptional factors (fire and high temperature). Considering the fact that the analysed frequencies of acoustic emission events occur before the maximum stresses in the material are reached and the elements are destroyed, this provides the basis for the use of the acoustic emission method to assess the condition of cellulose–cement composites in terms of lowering mechanical parameters by observing the frequency of events generated by the material during load action. It was found that generating by material frequencies above 300 kHz during bending does not result in a significant decrease in mechanical parameters. The emission of signals with frequencies ranging from 200 to 300 kHz indicate that there was a decline in strength exceeding 25% but less than 50%. The registration of signals with frequencies below 200 kHz indicates that the reduction in mechanical parameters was greater than 50%. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering (2nd Edition))

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12 pages, 5045 KB

Open AccessEditor’s ChoiceArticle

Corrosion Performance of Nano-TiO₂-Modified Concrete under a Dry–Wet Sulfate Environment

by Chao Xu, Hao-Hao Liao, You-Liang Chen, Xi Du, Bin Peng and Tomas Manuel Fernandez-Steeger

Materials 2021, 14(19), 5900; https://doi.org/10.3390/ma14195900 - 8 Oct 2021

Cited by 14 | Viewed by 2568

Abstract

This study compared the effects of the sulfate dry–wet cycle on the properties of ordinary concrete and nano-TiO₂-modified concrete, including the mass loss rate, ultrasonic wave velocity, compressive strength, and XRD characteristics. In addition, a series of compression simulations carried out [...] Read more.

This study compared the effects of the sulfate dry–wet cycle on the properties of ordinary concrete and nano-TiO₂-modified concrete, including the mass loss rate, ultrasonic wave velocity, compressive strength, and XRD characteristics. In addition, a series of compression simulations carried out using the PFC2D software are also presented for comparison. The results show the following: (1) with an increase in dry–wet cycles, the damage to the concrete gradually increased, and adding nano-TiO₂ into ordinary concrete can improve the material’s sulfate resistance; (2) after 50 sulfate dry–wet cycles, the mass loss rate of ordinary concrete was –3.744%, while that of nano-TiO₂-modified concrete was −1.363%; (3) the compressive strength of ordinary concrete was reduced from 41.53 to 25.12 MPa (a reduction of 39.51%), but the compressive strength of nano-TiO₂-modified concrete was reduced from 49.91 to 32.12 MPa (a reduction of 35.64%); (4) after a sulfate dry–wet cycle, the nano-TiO₂-modified concrete surface produced white crystalline products, considered to be ettringite based on the XRD analysis; (5) when considering the peak stress and strain of the concrete samples, the numerical results agreed well with the test results, indicating the reliability of the method. Full article

(This article belongs to the Special Issue Advanced Cement and Concrete Composites)

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16 pages, 2858 KB

Open AccessEditor’s ChoiceArticle

A Mass Balance Approach for Thermogravimetric Analysis in Pozzolanic Reactivity R³ Test and Effect of Drying Methods

by Kira Weise, Neven Ukrainczyk and Eduardus Koenders

Materials 2021, 14(19), 5859; https://doi.org/10.3390/ma14195859 - 7 Oct 2021

Cited by 21 | Viewed by 4254

Abstract

The reactivity of supplementary cementitious materials (SCMs) is a key issue in the sustainability of cement-based materials. In this study, the effect of drying with isopropanol and acetone as well as the interpretation of thermogravimetric data on the results of an R³ [...] Read more.

The reactivity of supplementary cementitious materials (SCMs) is a key issue in the sustainability of cement-based materials. In this study, the effect of drying with isopropanol and acetone as well as the interpretation of thermogravimetric data on the results of an R³ test for evaluation of the SCM pozzolanic reaction were investigated. R³ samples consisting of calcium hydroxide, potassium hydroxide, potassium sulphate, water, and SCM were prepared. Besides silica fume, three different types of calcined clays were investigated as SCMs. These were a relatively pure metakaolin, a quartz-rich metakaolin, and a mixed calcined clay, where the amount of other types of clays was two times higher than the kaolinite content. Thermogravimetric analysis (TGA) was carried out on seven-day-old samples dried with isopropanol and acetone to stop the reaction processes. Additional calorimetric measurement of the R³ samples was carried out for evaluation of the reaction kinetics. Results show that drying with isopropanol is more suitable for analysis of R³ samples compared to acetone. The use of acetone results in increased carbonation and TGA mass losses until 40 (isothermal drying for 30 min) and 105 °C (ramp heating), indicating that parts of the acetone remain in the sample, causing problems in the interpretation of TGA data. A mass balance approach was proposed to calculate calcium hydroxide consumption from TGA data, while also considering the amount of carbonates in the sample and TGA data corrections of original SCMs. With this approach, an improvement of the linear correlation of TGA results and heat release from calorimetric measurement was achieved. Full article

(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)

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15 pages, 3467 KB

Open AccessEditor’s ChoiceArticle

Calorimetric Studies of Alkali-Activated Blast-Furnace Slag Cements at Early Hydration Processes in the Temperature Range of 20–80 °C

by Aleksandr Usherov-Marshak, Danutė Vaičiukynienė, Pavel Krivenko and Girts Bumanis

Materials 2021, 14(19), 5872; https://doi.org/10.3390/ma14195872 - 7 Oct 2021

Cited by 8 | Viewed by 2296

Abstract

In the hydration process of inorganic cements, the analysis of calorimetric measurements is one of the possible ways to better understand hydration processes and to keep these processes under control. This study contains data from the study of thermokinetic processes in alkali-activated blast-furnace [...] Read more.

In the hydration process of inorganic cements, the analysis of calorimetric measurements is one of the possible ways to better understand hydration processes and to keep these processes under control. This study contains data from the study of thermokinetic processes in alkali-activated blast-furnace slag cements compared to ordinary Portland cement (OPC). The obtained results show that, in contrast to OPC, the heat release values cannot be considered as a characteristic of the activity of alkali-activated blast-furnace slag cements. In addition, it is concluded that in the case of OPC cements, cumulative heat release is a criterion for the selection of effective curing parameters, while in the case of alkali-activated blast-furnace slag cements, a higher heat rate (which increases sharply with increasing temperature from 20 to 40 °C) is a criterion. From the point of views of thermokinetics, the rate of heat release at temperatures up to 40 °C can be a qualitative criterion that allows to choose the parameters of heat curing of alkali-activated cement concretes. By introducing a crystallo-chemical hardening accelerator, such as Portland cement clinker, into the composition of alkali-activated blast-furnace slag cements, it is possible to accelerate the processes not only in the condensation-crystallization structure formation stage, but also in the dispersion-coagulation structure formation stage. Portland cement clinker increased the efficiency of thermal curing at relatively non-high temperatures. Full article

(This article belongs to the Special Issue Research on Novel Sustainable Binders, Concretes and Composites)

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18 pages, 13502 KB

Open AccessEditor’s ChoiceReview

Review of Organic Photorefractive Materials and Their Use for Updateable 3D Display

by Pierre-Alexandre Blanche, Jae-Won Ka and Nasser Peyghambarian

Materials 2021, 14(19), 5799; https://doi.org/10.3390/ma14195799 - 4 Oct 2021

Cited by 27 | Viewed by 5912

Abstract

Photorefractive materials are capable of reversibly changing their index of refraction upon illumination. That property allows them to dynamically record holograms, which is a key function for developing an updateable holographic 3D display. The transition from inorganic photorefractive crystals to organic polymers meant [...] Read more.

Photorefractive materials are capable of reversibly changing their index of refraction upon illumination. That property allows them to dynamically record holograms, which is a key function for developing an updateable holographic 3D display. The transition from inorganic photorefractive crystals to organic polymers meant that large display screens could be made. However, one essential figure of merit that needed to be worked out first was the sensitivity of the material that enables to record bright images in a short amount of time. In this review article, we describe how polymer engineering was able to overcome the problem of the material sensitivity. We highlight the importance of understanding the energy levels of the different species in order to optimize the efficiency and recording speed. We then discuss different photorefractive compounds and the reason for their particular figures of merit. Finally, we consider the technical choices taken to obtain an updateable 3D display using photorefractive polymer. By leveraging the unique properties of this holographic recording material, full color holograms were demonstrated, as well as refreshing rate of 100 hogels/second. Full article

(This article belongs to the Special Issue Photoactive Materials: Synthesis, Applications and Technology (Second Volume))

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15 pages, 10195 KB

Open AccessEditor’s ChoiceArticle

Cross-Functional Test to Explore the Determination Method of Meso-Parameters in the Discrete Element Model of Asphalt Mixtures

by Xingyu Yi, Huimin Chen, Houzhi Wang, Zhiyun Tang, Jun Yang and Haopeng Wang

Materials 2021, 14(19), 5786; https://doi.org/10.3390/ma14195786 - 3 Oct 2021

Cited by 15 | Viewed by 2416

Abstract

In order to obtain more accurate parameters required for the simulation of asphalt mixtures in the discrete element method (DEM), this study carried out a series of cross-functional asphalt mixture experiments to obtain the DEM simulation meso-parameters. By comparing the results of simulation [...] Read more.

In order to obtain more accurate parameters required for the simulation of asphalt mixtures in the discrete element method (DEM), this study carried out a series of cross-functional asphalt mixture experiments to obtain the DEM simulation meso-parameters. By comparing the results of simulation and actual experiments, a method to obtain the meso-parameters of the DEM simulation was proposed. In this method, the numerical aggregate profile was obtained by X-ray CT scanning and the 3D aggregate model was reconstructed in MIMICS. The linear contact parameters of the aggregate and the Burgers model parameters of the asphalt mastic were obtained by nanoindentation technology. The parameters of the parallel bonding model between the aggregate and mastic were determined by the macroscopic tensile adhesion test and shear bond test. The results showed that the meso-parameters obtained by the macroscopic experiment provide a basis for the calibration of DEM parameters to a certain extent. The trends in simulation results are similar to the macro test results. Therefore, the newly proposed method is feasible. Full article

(This article belongs to the Special Issue Advances in Asphalt Materials)

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17 pages, 5487 KB

Open AccessEditor’s ChoiceArticle

Application of Advanced Machine Learning Approaches to Predict the Compressive Strength of Concrete Containing Supplementary Cementitious Materials

by Waqas Ahmad, Ayaz Ahmad, Krzysztof Adam Ostrowski, Fahid Aslam, Panuwat Joyklad and Paulina Zajdel

Materials 2021, 14(19), 5762; https://doi.org/10.3390/ma14195762 - 2 Oct 2021

Cited by 112 | Viewed by 4564

Abstract

The casting and testing specimens for determining the mechanical properties of concrete is a time-consuming activity. This study employed supervised machine learning techniques, bagging, AdaBoost, gene expression programming, and decision tree to estimate the compressive strength of concrete containing supplementary cementitious materials (fly [...] Read more.

The casting and testing specimens for determining the mechanical properties of concrete is a time-consuming activity. This study employed supervised machine learning techniques, bagging, AdaBoost, gene expression programming, and decision tree to estimate the compressive strength of concrete containing supplementary cementitious materials (fly ash and blast furnace slag). The performance of the models was compared and assessed using the coefficient of determination (R²), mean absolute error, mean square error, and root mean square error. The performance of the model was further validated using the k-fold cross-validation approach. Compared to the other employed approaches, the bagging model was more effective in predicting results, with an R² value of 0.92. A sensitivity analysis was also prepared to determine the level of contribution of each parameter utilized to run the models. The use of machine learning (ML) techniques to predict the mechanical properties of concrete will be beneficial to the field of civil engineering because it will save time, effort, and resources. The proposed techniques are efficient to forecast the strength properties of concrete containing supplementary cementitious materials (SCM) and pave the way towards the intelligent design of concrete elements and structures. Full article

(This article belongs to the Special Issue Emerging Construction Materials for Sustainable Infrastructure)

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18 pages, 3267 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Recycled Aggregates Produced from Construction and Demolition Waste for Structural Concrete: Constituents, Properties and Production

by João Pacheco and Jorge de Brito

Materials 2021, 14(19), 5748; https://doi.org/10.3390/ma14195748 - 1 Oct 2021

Cited by 67 | Viewed by 5479

Abstract

This paper concerns the recovery of construction and demolition waste as coarse recycled aggregates for concrete. Coarse recycled aggregates may be used as a partial or total replacement of natural aggregates, contributing to the circular economy and minimizing landfill disposals as well as [...] Read more.

This paper concerns the recovery of construction and demolition waste as coarse recycled aggregates for concrete. Coarse recycled aggregates may be used as a partial or total replacement of natural aggregates, contributing to the circular economy and minimizing landfill disposals as well as the consumption of natural mineral resources. However, construction and demolition waste is a heterogeneous material with undefined quality and the processing of this waste into recycled aggregates needs to ensure that the recycled aggregates have suitable properties for concrete. This paper summarizes several aspects related to coarse recycled aggregates, specifically addressing: (i) the typical composition of construction and demolition waste; (ii) the influence of different types of constituents on the properties of recycled aggregates and recycled aggregate concrete; (iii) requirements for recycled aggregates to be used in concrete; and (iv) production methods of recycled aggregates. It is argued that coarse recycled aggregates are a suitable construction material with adequate quality, even when common equipment is used in their production and preliminary separation as a key operation for ensuring the quality of the aggregates is recommended. Full article

(This article belongs to the Special Issue Structural Concrete Material: New Trends for Eco-Efficiency and Performance)

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18 pages, 11069 KB

Open AccessEditor’s ChoiceArticle

Advanced Eco-Friendly Formulations of Guar Biopolymer-Based Textile Conditioners

by Evdokia K. Oikonomou and Jean-François Berret

Materials 2021, 14(19), 5749; https://doi.org/10.3390/ma14195749 - 1 Oct 2021

Cited by 6 | Viewed by 7623

Abstract

Fabric conditioners are household products used to impart softness and fragrance to textiles. They are colloidal dispersions of cationic double chain surfactants that self-assemble in vesicles. These surfactants are primarily derived from palm oil chemical modification. Reducing the content of these surfactants allows [...] Read more.

Fabric conditioners are household products used to impart softness and fragrance to textiles. They are colloidal dispersions of cationic double chain surfactants that self-assemble in vesicles. These surfactants are primarily derived from palm oil chemical modification. Reducing the content of these surfactants allows to obtain products with lower environmental impact. Such a reduction, without adverse effects on the characteristics of the softener and its performance, can be achieved by adding hydrophilic biopolymers. Here, we review the role of guar biopolymers modified with cationic or hydroxyl-propyl groups, on the physicochemical properties of the formulation. Electronic and optical microscopy, dynamic light scattering, X-ray scattering and rheology of vesicles dispersion in the absence and presence of guar biopolymers are analyzed. Finally, the deposition of the new formulation on cotton fabrics is examined through scanning electron microscopy and a new protocol based on fluorescent microscopy. With this methodology, it is possible to quantify the deposition of surfactants on cotton fibers. The results show that the approach followed here can facilitate the design of sustainable home-care products. Full article

(This article belongs to the Special Issue Hydrophilic Copolymers for Bioapplications or Water Remediation)

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18 pages, 8919 KB

Open AccessEditor’s ChoiceArticle

Empirical NOx Removal Analysis of Photocatalytic Construction Materials at Real-Scale

by Miyeon Kim, Hyunggeun Kim and Jinchul Park

Materials 2021, 14(19), 5717; https://doi.org/10.3390/ma14195717 - 30 Sep 2021

Cited by 6 | Viewed by 2696

Abstract

The NOx removal performance of photocatalytic construction materials is demonstrated using two experiments under indoor and outdoor environments: (1) A photoreactor test was conducted to assess the NO removal performance of construction materials (e.g., coatings, paints and shotcrete) using a modified ISO 22197-1 [...] Read more.

The NOx removal performance of photocatalytic construction materials is demonstrated using two experiments under indoor and outdoor environments: (1) A photoreactor test was conducted to assess the NO removal performance of construction materials (e.g., coatings, paints and shotcrete) using a modified ISO 22197-1 method; (2) A water washing test was conducted using two specimens enlarged to the size of actual building materials and artificially exposed to NOx in a laboratory to analyze NOx removal performance. For (1), the UV irradiation of the outdoor environment was analyzed and the experiment was conducted in an indoor laboratory under UV irradiation identical to that of the outdoor condition. Photoreactor tests were conducted on construction materials applied to actual buildings located in Seoul, South Korea. In (2), the enlarged specimen was used for a field experiment by applying a modified method from the ISO 22197-1 standard. On sunny days, the NOx removal performance (3.12–4.76 μmol/150 cm²·5 h) was twice as much as that of the ISO 22197-1 standard specification (2.03 μmol/150 cm²·5 h) in the real-world. The washing water test results indicated that general aqueous paint achieved a NOx removal of 3.88 μmol, whereas photocatalytic paint was superior to 14.13 μmol. Full article

(This article belongs to the Special Issue Sustainable Construction Materials: From Paste to Concrete)

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17 pages, 3552 KB

Open AccessEditor’s ChoiceArticle

Porosity of Calcium Silicate Hydrates Synthesized from Natural Rocks

by Raimundas Siauciunas, Giedrius Smalakys and Tadas Dambrauskas

Materials 2021, 14(19), 5592; https://doi.org/10.3390/ma14195592 - 26 Sep 2021

Cited by 6 | Viewed by 2026

Abstract

In this work, the suitability of natural raw materials with various modifications of SiO₂—granite sawing waste (quartz) and opoka (a mixture of cristobalite, tridymite, quartz, and an amorphous part)—for the 1.13 nm tobermorite and xonotlite synthesis is examined, and their specific [...] Read more.

In this work, the suitability of natural raw materials with various modifications of SiO₂—granite sawing waste (quartz) and opoka (a mixture of cristobalite, tridymite, quartz, and an amorphous part)—for the 1.13 nm tobermorite and xonotlite synthesis is examined, and their specific surface area, pore diameter and volume, and the predominant pores are determined. Hydrothermal syntheses were carried out at 200 °C for 12 and 72 h from mixtures with a molar ratio of CaO/SiO₂ = 1.0. X-ray diffraction analysis, simultaneous thermal analysis, and scanning electronic microscopy were used, which showed that in the lime–calcined opoka mixture the formation of crystalline calcium silicate hydrates takes place much faster than in the lime–granite sawing waste mixture. The high reactivity of amorphous SiO₂ results in the rapid formation of 1.13 nm tobermorite and xonotlite (12 h). According to Brunauer, Emmet and Taller (BET) analysis data, this product features a specific surface area of ~68 m²/g, a total pore volume of 245 × 10⁻³ cm³/g, and has dominating 1–2.5 nm and 5–20 nm diameter pores. This porosity of the material should provide good thermal insulation properties of the products made from it as no air convection occurs in the fine pores. Full article

(This article belongs to the Section Construction and Building Materials)

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20 pages, 6242 KB

Open AccessEditor’s ChoiceArticle

Structure Life Extension towards the Structural Integrity of Sukhoi Su-30MKM

by Arvinthan Venugopal, Roslina Mohammad, Md Fuad Shah Koslan, Ashaari Shafie, Alizarin Ali and Owi Eugene

Materials 2021, 14(19), 5562; https://doi.org/10.3390/ma14195562 - 25 Sep 2021

Cited by 5 | Viewed by 5814

Abstract

The airframe structures of most fighter aircraft in the Royal Malaysian Airforce have been in service for 10 to 20 years. The effect of fatigue loading, operating conditions, and environmental degradation has led to the structural integrity of the airframe being assessed for [...] Read more.

The airframe structures of most fighter aircraft in the Royal Malaysian Airforce have been in service for 10 to 20 years. The effect of fatigue loading, operating conditions, and environmental degradation has led to the structural integrity of the airframe being assessed for its airworthiness. Various NDT methods were used to determine the current condition of the aircraft structure after operation of beyond 10 years, and their outcomes are summarized. In addition, although there are six critical locations, the wing root was chosen since it has the highest possibility of fatigue failure. It was further analyzed using simulation analysis for fatigue life. This contributes to the development of the maintenance task card and ultimately assists in extending the service life of the fighter aircraft. Using the concept of either safe life or damage tolerance as its fatigue design philosophy, the RMAF has adopted the Aircraft Structural Integrity Program (ASIP) to monitor the structural integrity of its fighter aircraft. With the current budget constraints and structural life extension requirements, the RMAF has embarked on the non-destructive testing method and engineering analysis. The research outcome will enhance the ASIP for other aircraft platforms in the RMAF fleet for its structure life assessment or service life extension program. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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23 pages, 31986 KB

Open AccessEditor’s ChoiceArticle

Luminescence and Electrochemical Activity of New Unsymmetrical 3-Imino-1,8-naphthalimide Derivatives

by Sonia Kotowicz, Mateusz Korzec, Katarzyna Malarz, Aleksandra Krystkowska, Anna Mrozek-Wilczkiewicz, Sylwia Golba, Mariola Siwy, Sebastian Maćkowski and Ewa Schab-Balcerzak

Materials 2021, 14(19), 5504; https://doi.org/10.3390/ma14195504 - 23 Sep 2021

Cited by 6 | Viewed by 2864

Abstract

A new series of 1,8-naphtalimides containing an imine bond at the 3-position of the naphthalene ring was synthesized using ¹H, ¹³C NMR, FTIR, and elementary analysis. The impact of the substituent in the imine linkage on the selected properties and bioimaging [...] Read more.

A new series of 1,8-naphtalimides containing an imine bond at the 3-position of the naphthalene ring was synthesized using ¹H, ¹³C NMR, FTIR, and elementary analysis. The impact of the substituent in the imine linkage on the selected properties and bioimaging of the synthesized compounds was studied. They showed a melting temperature in the range of 120–164 °C and underwent thermal decomposition above 280 °C. Based on cyclic and differential pulse voltammetry, the electrochemical behavior of 1,8-naphtalimide derivatives was evaluated. The electrochemical reduction and oxidation processes were observed. The compounds were characterized by a low energy band gap (below 2.60 eV). Their photoluminescence activities were investigated in solution considering the solvent effect, in the aggregated and thin film, and a mixture of poly(N-vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (50:50 wt.%). They demonstrated low emissions due to photoinduced electron transport (PET) occurring in the solution and aggregation, which caused photoluminescence quenching. Some of them exhibited light emission as thin films. They emitted light in the range of 495 to 535 nm, with photoluminescence quantum yield at 4%. Despite the significant overlapping of its absorption range with emission of the PVK:PBD, incomplete Förster energy transfer from the matrix to the luminophore was found. Moreover, its luminescence ability induced by external voltage was tested in the diode with guest–host configuration. The possibility of compound hydrolysis due to the presence of the imine bond was also discussed, which could be of importance in biological studies that evaluate 3-imino-1,8-naphatalimides as imaging tools and fluorescent materials for diagnostic applications and molecular bioimaging. Full article

(This article belongs to the Special Issue Recent Advances of Luminescent Materials and Devices in Optics and Photonics)

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11 pages, 6695 KB

Open AccessEditor’s ChoiceArticle

Temperature Effects in an Acousto-Optic Modulator of Terahertz Radiation Based on Liquefied SF₆ Gas

by Pavel A. Nikitin, Vasily V. Gerasimov and Ildus S. Khasanov

Materials 2021, 14(19), 5519; https://doi.org/10.3390/ma14195519 - 23 Sep 2021

Cited by 7 | Viewed by 2766

Abstract

The acousto-optic (AO) diffraction of terahertz (THz) radiation in liquefied sulfur hexafluoride (SF

_{6}

) was investigated in various temperature regimes. It was found that with the increase in the temperature from +10 to +23

^{°}

C, the efficiency of the AO diffraction [...] Read more.

The acousto-optic (AO) diffraction of terahertz (THz) radiation in liquefied sulfur hexafluoride (SF

_{6}

) was investigated in various temperature regimes. It was found that with the increase in the temperature from +10 to +23

^{°}

C, the efficiency of the AO diffraction became one order higher at the same amplitude of the driving electrical signal. At the same time, the efficiency of the AO diffraction per 1 W of the sound power as well as the angular bandwidth of the efficient AO interaction were temperature independent within the measurement error. Increase of the resonant sound frequency with decreasing temperature and strong narrowing of the sound frequency bandwidth of the efficient AO interaction were detected. Full article

(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)

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20 pages, 4984 KB

Open AccessEditor’s ChoiceArticle

Service Life Evaluation for RC Sewer Structure Repaired with Bacteria Mixed Coating: Through Probabilistic and Deterministic Method

by Hyun-Sub Yoon, Keun-Hyeok Yang, Kwang-Myong Lee and Seung-Jun Kwon

Materials 2021, 14(18), 5424; https://doi.org/10.3390/ma14185424 - 19 Sep 2021

Cited by 9 | Viewed by 2158

Abstract

Since a concrete structure exposed to a sulfate environment is subject to surface ion ingress that yields cracking due to concrete swelling, its service life evaluation with an engineering modeling is very important. In this paper, cementitious repair materials containing bacteria, Rhodobacter capsulatus, [...] Read more.

Since a concrete structure exposed to a sulfate environment is subject to surface ion ingress that yields cracking due to concrete swelling, its service life evaluation with an engineering modeling is very important. In this paper, cementitious repair materials containing bacteria, Rhodobacter capsulatus, and porous spores for immobilization were developed, and the service life of RC (Reinforced Concrete) structures with a developed bacteria-coating was evaluated through deterministic and probabilistic methods. Design parameters such protective coating thickness, diffusion coefficient, surface roughness, and exterior sulfate ion concentration were considered, and the service life was evaluated with the changing mean and coefficient of variation (COV) of each factor. From service life evaluation, more conservative results were evaluated with the probabilistic method than the deterministic method, and as a result of the analysis, coating thickness and surface roughness were derived as key design parameters for ensuring service life. In an environment exposed to an exterior sulfate concentration of 200 ppm, using the deterministic method, the service life was 17.3 years without repair, 19.7 years with normal repair mortar, and 29.6 years with the application of bacteria-coating. Additionally, when the probabilistic method is applied in the same environment, the service life was changed to 9.2–16.0 years, 10.5–18.2 years, and 15.4–27.4 years, respectively, depending on the variation of design parameters. The developed bacteria-coating technique showed a 1.47–1.50 times higher service life than the application of normal repair mortar, and the effect was much improved when it had a low COV of around 0.1. Full article

(This article belongs to the Special Issue Sustainable Construction Materials: From Paste to Concrete)

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13 pages, 5668 KB

Open AccessEditor’s ChoiceArticle

Helium Bubbles and Blistering in a Nanolayered Metal/Hydride Composite

by Caitlin A. Taylor, Eric Lang, Paul G. Kotula, Ronald Goeke, Clark S. Snow, Yongqiang Wang and Khalid Hattar

Materials 2021, 14(18), 5393; https://doi.org/10.3390/ma14185393 - 18 Sep 2021

Cited by 8 | Viewed by 3310

Abstract

Helium is insoluble in most metals and precipitates out to form nanoscale bubbles when the concentration is greater than 1 at.%, which can alter the material properties. Introducing controlled defects such as multilayer interfaces may offer some level of helium bubble management. This [...] Read more.

Helium is insoluble in most metals and precipitates out to form nanoscale bubbles when the concentration is greater than 1 at.%, which can alter the material properties. Introducing controlled defects such as multilayer interfaces may offer some level of helium bubble management. This study investigates the effects of multilayered composites on helium behavior in ion-implanted, multilayered ErD₂/Mo thin film composites. Following in-situ and ex-situ helium implantation, scanning and transmission electron microscopy showed the development of spherical helium bubbles within the matrix, but primarily at the layer interfaces. Bubble linkage and surface blistering is observed after high fluence ex-situ helium implantation. These results show the ability of metallic multilayers to alter helium bubble distributions even in the presence of a hydride layer, increasing the lifetime of materials in helium environments. Full article

(This article belongs to the Special Issue Radiation Damage in Materials: Coupled Extreme Environments)

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18 pages, 11816 KB

Open AccessEditor’s ChoiceArticle

Behavior of Biochar-Modified Cementitious Composites Exposed to High Temperatures

by Xu Yang, Run-Sheng Lin, Yi Han and Xiao-Yong Wang

Materials 2021, 14(18), 5414; https://doi.org/10.3390/ma14185414 - 18 Sep 2021

Cited by 21 | Viewed by 3292

Abstract

In this study, the effect of biochar on the high temperature resistance of cementitious paste was investigated using multiple experimental methods. The weight loss, cracks, residual compressive strength, and ultrasonic pulse velocity (UPV) of biochar cementitious paste with 2% and 5% biochar exposed [...] Read more.

In this study, the effect of biochar on the high temperature resistance of cementitious paste was investigated using multiple experimental methods. The weight loss, cracks, residual compressive strength, and ultrasonic pulse velocity (UPV) of biochar cementitious paste with 2% and 5% biochar exposed to 300, 550 and 900 °C were measured. The products and microstructures of biochar cementitious paste exposed to high temperatures were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The results showed that the cracks of specimens exposed to high temperatures decreased with increasing biochar content. The addition of 2% and 5% biochar increased the residual compressive strength of the specimens exposed to 300 °C and the relative residual compressive strength at 550 °C. As the exposure temperature increased, the addition of biochar compensated for the decreasing ultrasonic pulse velocity. The addition of biochar contributed to the release of free water and bound water, and reduced the vapor pressure of the specimen. The addition of biochar did not change the types of functional groups and crystalline phases of the products of cementitious materials exposed to high temperatures. Biochar particles were difficult to observe at 900 °C in scanning electron microscopy images. In summary, because biochar has internal pores, it can improve the high-temperature resistance of cement paste. Full article

(This article belongs to the Special Issue Carbon Peaking and Carbon Neutrality in the Cement-Based Materials)

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21 pages, 3743 KB

Open AccessEditor’s ChoiceArticle

Modification of Gold Zeolitic Supports for Catalytic Oxidation of Glucose to Gluconic Acid

by Adrian Walkowiak, Joanna Wolska, Anna Wojtaszek-Gurdak, Izabela Sobczak, Lukasz Wolski and Maria Ziolek

Materials 2021, 14(18), 5250; https://doi.org/10.3390/ma14185250 - 13 Sep 2021

Cited by 10 | Viewed by 3221

Abstract

Activity of gold supported catalysts strongly depends on the type and composition of support, which determine the size of Au nanoparticles (Au NPs), gold-support interaction influencing gold properties, interaction with the reactants and, in this way, the reaction pathway. The aim of this [...] Read more.

Activity of gold supported catalysts strongly depends on the type and composition of support, which determine the size of Au nanoparticles (Au NPs), gold-support interaction influencing gold properties, interaction with the reactants and, in this way, the reaction pathway. The aim of this study was to use two types of zeolites: the three dimensional HBeta and the layered two-dimensional MCM-36 as supports for gold, and modification of their properties towards the achievement of different properties in oxidation of glucose to gluconic acid with molecular oxygen and hydrogen peroxide. Such an approach allowed establishment of relationships between the activity of gold catalysts and different parameters such as Au NPs size, electronic properties of gold, structure and acidity of the supports. The zeolites were modified with (3-aminopropyl)-trimethoxysilane (APMS), which affected the support features and Au NPs properties. Moreover, the modification of the zeolite lattice with boron was applied to change the strength of the zeolite acidity. All modifications resulted in changes in glucose conversion, while maintaining high selectivity to gluconic acid. The most important findings include the differences in the reaction steps limiting the reaction rate depending on the nature of the oxidant applied (oxygen vs. H₂O₂), the important role of porosity of the zeolite supports, and accumulation of negative charge on Au NPs in catalytic oxidation of glucose. Full article

(This article belongs to the Special Issue Advanced Materials in Catalysis and Adsorption)

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11 pages, 1730 KB

Open AccessEditor’s ChoiceArticle

Reduction of Thermal Conductivity for Icosahedral Al-Cu-Fe Quasicrystal through Heavy Element Substitution

by Yoshiki Takagiwa, Ryota Maeda, Satoshi Ohhashi and An-Pang Tsai

Materials 2021, 14(18), 5238; https://doi.org/10.3390/ma14185238 - 12 Sep 2021

Cited by 5 | Viewed by 2696

Abstract

Icosahedral Al-Cu-Fe quasicrystal (QC) shows moderate electrical conductivity and low thermal conductivity, and both p- and n-type conduction can be controlled by tuning the sample composition, making it potentially suited for thermoelectric materials. In this work, we investigated the effect of introducing chemical [...] Read more.

Icosahedral Al-Cu-Fe quasicrystal (QC) shows moderate electrical conductivity and low thermal conductivity, and both p- and n-type conduction can be controlled by tuning the sample composition, making it potentially suited for thermoelectric materials. In this work, we investigated the effect of introducing chemical disorder through heavy element substitution on the thermal conductivity of Al-Cu-Fe QC. We substituted Au and Pt elements for Cu up to 3 at% in a composition of Al₆₃Cu₂₅Fe₁₂, i.e., Al₆₃Cu_25−x(Au,Pt)_xFe₁₂ (x = 0, 1, 2, 3). The substitutions of Au and Pt for Cu reduced the phonon thermal conductivity at 300 K (κ_ph,300K) by up to 17%. The reduction of κ_ph,300K is attributed to a decrease in the specific heat and phonon relaxation time through heavy element substitution. We found that increasing the Pt content reduced the specific heat at high temperatures, which may be caused by the locked state of phasons. The observed glass-like low values of κ_ph,300K (0.9–1.1 W m⁻¹ K⁻¹ at 300 K) for Al₆₃Cu_25−x(Au,Pt)_xFe₁₂ are close to the lower limit calculated using the Cahill model. Full article

(This article belongs to the Special Issue Advances in Thermoelectric Materials and Devices)

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17 pages, 2139 KB

Open AccessEditor’s ChoiceArticle

On Structural Rearrangements Near the Glass Transition Temperature in Amorphous Silica

by Michael I. Ojovan and Robert F. Tournier

Materials 2021, 14(18), 5235; https://doi.org/10.3390/ma14185235 - 11 Sep 2021

Cited by 35 | Viewed by 4117

Abstract

The formation of clusters was analyzed in a topologically disordered network of bonds of amorphous silica (SiO₂) based on the Angell model of broken bonds termed configurons. It was shown that a fractal-dimensional configuron phase was formed in the amorphous silica [...] Read more.

The formation of clusters was analyzed in a topologically disordered network of bonds of amorphous silica (SiO₂) based on the Angell model of broken bonds termed configurons. It was shown that a fractal-dimensional configuron phase was formed in the amorphous silica above the glass transition temperature T_g. The glass transition was described in terms of the concepts of configuron percolation theory (CPT) using the Kantor-Webman theorem, which states that the rigidity threshold of an elastic percolating network is identical to the percolation threshold. The account of configuron phase formation above T_g showed that (i) the glass transition was similar in nature to the second-order phase transformations within the Ehrenfest classification and that (ii) although being reversible, it occurred differently when heating through the glass–liquid transition to that when cooling down in the liquid phase via vitrification. In contrast to typical second-order transformations, such as the formation of ferromagnetic or superconducting phases when the more ordered phase is located below the transition threshold, the configuron phase was located above it. Full article

(This article belongs to the Section Materials Physics)

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35 pages, 6104 KB

Open AccessEditor’s ChoiceArticle

Removal of Aniline and Benzothiazole Wastewaters Using an Efficient MnO₂/GAC Catalyst in a Photocatalytic Fluidised Bed Reactor

by Cristian Ferreiro, Natalia Villota, José Ignacio Lombraña, María J. Rivero, Verónica Zúñiga and José Miguel Rituerto

Materials 2021, 14(18), 5207; https://doi.org/10.3390/ma14185207 - 10 Sep 2021

Cited by 2 | Viewed by 3569

Abstract

This work presents an efficient method for treating industrial wastewater containing aniline and benzothiazole, which are refractory to conventional treatments. A combination of heterogeneous photocatalysis operating in a fluidised bed reactor is studied in order to increase mass transfer and reduce reaction times. [...] Read more.

This work presents an efficient method for treating industrial wastewater containing aniline and benzothiazole, which are refractory to conventional treatments. A combination of heterogeneous photocatalysis operating in a fluidised bed reactor is studied in order to increase mass transfer and reduce reaction times. This process uses a manganese dioxide catalyst supported on granular activated carbon with environmentally friendly characteristics. The manganese dioxide composite is prepared by hydrothermal synthesis on carbon Hydrodarco^® 3000 with different active phase ratios. The support, the metal oxide, and the composite are characterised by performing Brunauer, Emmett, and Teller analysis, transmission electron microscopy, X-ray diffraction analysis, X-ray fluorescence analysis, UV–Vis spectroscopy by diffuse reflectance, and Fourier transform infrared spectroscopy in order to evaluate the influence of the metal oxide on the activated carbon. A composite of MnO₂/GAC (3.78% in phase α-MnO₂) is obtained, with a 9.4% increase in the specific surface of the initial GAC and a 12.79 nm crystal size. The effect of pH and catalyst load is studied. At a pH of 9.0 and a dose of 0.9 g L⁻¹, a high degradation of aniline and benzothiazole is obtained, with an 81.63% TOC mineralisation in 64.8 min. Full article

(This article belongs to the Special Issue Advanced Photocatalytic Materials for Water Treatment)

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22 pages, 1431 KB

Open AccessEditor’s ChoiceReview

Recent Advancements in Carbon Nano-Infused Cementitious Composites

by Eryk Goldmann, Marcin Górski and Barbara Klemczak

Materials 2021, 14(18), 5176; https://doi.org/10.3390/ma14185176 - 9 Sep 2021

Cited by 13 | Viewed by 2816

Abstract

A rising demand for efficient functional materials brings forth research challenges regarding improvements in existing materials. Carbon infused cementitious composites, regardless of being an important research topic worldwide, still present many questions concerning their functionality and properties. The paper aims to highlight the [...] Read more.

A rising demand for efficient functional materials brings forth research challenges regarding improvements in existing materials. Carbon infused cementitious composites, regardless of being an important research topic worldwide, still present many questions concerning their functionality and properties. The paper aims to highlight the most important materials used for cementitious composites, their properties, and their uses while also including the most relevant of the latest research in that area. Full article

(This article belongs to the Special Issue Smart Composite Materials for Self-Sensing and Self-Healing in Civil and Environmental Engineering)

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17 pages, 7278 KB

Open AccessEditor’s ChoiceArticle

Identification of Chemical Bonds and Microstructure of Hydrated Tricalcium Silicate (C₃S) by a Coupled Micro-Raman/BSE-EDS Evaluation

by Zheyu Zhu, Zhongping Wang, Yue Zhou, Yuting Chen and Kai Wu

Materials 2021, 14(18), 5144; https://doi.org/10.3390/ma14185144 - 8 Sep 2021

Cited by 10 | Viewed by 3127

Abstract

Identifying the phase evolution and revealing the chemical bonds of hydrated cements accurately is crucial to regulate the performance of cementitious materials. In this paper, a coupled Raman/BSE-EDS analysis was proposed to determine the chemical bonds of tricalcium silicate hydrates and the interface [...] Read more.

Identifying the phase evolution and revealing the chemical bonds of hydrated cements accurately is crucial to regulate the performance of cementitious materials. In this paper, a coupled Raman/BSE-EDS analysis was proposed to determine the chemical bonds of tricalcium silicate hydrates and the interface transition zone (ITZ) between inner C-S-H and anhydrates. The results show that the Raman/BSE-EDS method can accurately identify the chemical bonds of inner C-S-H and inner ITZ regions, which confirms the mixed structure of inner C-S-H and nano calcium hydroxide (CH). The inner ITZ shows a lattice change region with a thickness of 700–1000 nm, which can be attributed to the pre-disassembly process of C₃S crystal. The successful application of coupled Raman/BSE-EDS provides new insight into the hydration process and multi-structure features of traditional cementitious materials. Full article

(This article belongs to the Special Issue Corrosion, Properties and Characterization in Concrete)

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22 pages, 4518 KB

Open AccessEditor’s ChoiceArticle

Effect of Heat Treatments under High Isostatic Pressure on the Transport Critical Current Density at 4.2 K and 20 K in Doped and Undoped MgB₂ Wires

by Daniel Gajda, Andrzej J. Zaleski, Andrzej J. Morawski, Malgorzata Małecka, Konstantin Nenkov, Matt Rindfleisch, Md Shahriar A. Hossain and Tomasz Czujko

Materials 2021, 14(18), 5152; https://doi.org/10.3390/ma14185152 - 8 Sep 2021

Cited by 1 | Viewed by 2078

Abstract

Annealing undoped MgB₂ wires under high isostatic pressure (HIP) increases transport critical current density (J_tc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases J_tc by 25% in range [...] Read more.

Annealing undoped MgB₂ wires under high isostatic pressure (HIP) increases transport critical current density (J_tc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases J_tc by 25% in range magnetic fields from 2 T to 4 T and does not increase J_tc above 4 T at 20 K. Further research shows that a large amount of 10% SiC admixture and thermal treatment under a high isostatic pressure of 1 GPa significantly increases the J_tc by 40% at 4.2 K in magnetic fields above 6 T and reduces J_tc by one order at 20 K in MgB₂ wires. Additionally, our research showed that heat treatment under high isostatic pressure is more evident in wires with smaller diameters, as it greatly increases the density of MgB₂ material and the number of connections between grains compared to MgB₂ wires with larger diameters, but only during the Mg solid-state reaction. In addition, our study indicates that smaller wire diameters and high isostatic pressure do not lead to a higher density of MgB₂ material and more connections between grains during the liquid-state Mg reaction. Full article

(This article belongs to the Special Issue Challenges and Opportunities of Superconducting Materials for Future Applications)

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27 pages, 3501 KB

Open AccessEditor’s ChoiceReview

Review on the Integration of Microelectronics for E-Textile

by Abdella Ahmmed Simegnaw, Benny Malengier, Gideon Rotich, Melkie Getnet Tadesse and Lieva Van Langenhove

Materials 2021, 14(17), 5113; https://doi.org/10.3390/ma14175113 - 6 Sep 2021

Cited by 85 | Viewed by 8896

Abstract

Modern electronic textiles are moving towards flexible wearable textiles, so-called e-textiles that have micro-electronic elements embedded onto the textile fabric that can be used for varied classes of functionalities. There are different methods of integrating rigid microelectronic components into/onto textiles for the development [...] Read more.

Modern electronic textiles are moving towards flexible wearable textiles, so-called e-textiles that have micro-electronic elements embedded onto the textile fabric that can be used for varied classes of functionalities. There are different methods of integrating rigid microelectronic components into/onto textiles for the development of smart textiles, which include, but are not limited to, physical, mechanical, and chemical approaches. The integration systems must satisfy being flexible, lightweight, stretchable, and washable to offer a superior usability, comfortability, and non-intrusiveness. Furthermore, the resulting wearable garment needs to be breathable. In this review work, three levels of integration of the microelectronics into/onto the textile structures are discussed, the textile-adapted, the textile-integrated, and the textile-based integration. The textile-integrated and the textile-adapted e-textiles have failed to efficiently meet being flexible and washable. To overcome the above problems, researchers studied the integration of microelectronics into/onto textile at fiber or yarn level applying various mechanisms. Hence, a new method of integration, textile-based, has risen to the challenge due to the flexibility and washability advantages of the ultimate product. In general, the aim of this review is to provide a complete overview of the different interconnection methods of electronic components into/onto textile substrate. Full article

(This article belongs to the Special Issue Smart Textile Materials and Fabric-Based Wearable Devices)

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21 pages, 786 KB

Open AccessEditor’s ChoiceArticle

A Three-Phase Transport Model for High-Temperature Concrete Simulations Validated with X-ray CT Data

by Christoph Pohl, Vít Šmilauer and Jörg F. Unger

Materials 2021, 14(17), 5047; https://doi.org/10.3390/ma14175047 - 3 Sep 2021

Cited by 6 | Viewed by 2524

Abstract

Concrete exposure to high temperatures induces thermo-hygral phenomena, causing water phase changes, buildup of pore pressure and vulnerability to spalling. In order to predict these phenomena under various conditions, a three-phase transport model is proposed. The model is validated on X-ray CT data [...] Read more.

Concrete exposure to high temperatures induces thermo-hygral phenomena, causing water phase changes, buildup of pore pressure and vulnerability to spalling. In order to predict these phenomena under various conditions, a three-phase transport model is proposed. The model is validated on X-ray CT data up to 320 °C, showing good agreement of the temperature profiles and moisture changes. A dehydration description, traditionally derived from thermogravimetric analysis, was replaced by a formulation based on data from neutron radiography. In addition, treating porosity and dehydration evolution as independent processes, previous approaches do not fulfil the solid mass balance. As a consequence, a new formulation is proposed that introduces the porosity as an independent variable, ensuring the latter condition. Full article

(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)

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15 pages, 18496 KB

Open AccessEditor’s ChoiceArticle

Influence of Polypropylene Fibre Factor on Flowability and Mechanical Properties of Self-Compacting Geopolymer

by Bei-chen Pu, Bin Liu, Li Li, Wei Pang and Zhangrun Wan

Materials 2021, 14(17), 5025; https://doi.org/10.3390/ma14175025 - 2 Sep 2021

Cited by 12 | Viewed by 2523

Abstract

The possibility of using geopolymer instead of Portland cement could effectively reduce carbon dioxide emissions from cement manufacturing. Fibre-reinforced self-compacting geopolymers have great potential in civil engineering applications, such as chord member grouting for concrete-filled steel tubular truss beams. However, to the best [...] Read more.

The possibility of using geopolymer instead of Portland cement could effectively reduce carbon dioxide emissions from cement manufacturing. Fibre-reinforced self-compacting geopolymers have great potential in civil engineering applications, such as chord member grouting for concrete-filled steel tubular truss beams. However, to the best of the authors’ knowledge, the quantitative relationship between FF and the properties of the fibre-reinforced geopolymer has been rarely reported. In this research, 26 groups of mixtures were used to study the influence of the polypropylene fibre factor (FF) on the flowability and mechanical properties and also the compactness of the fibre-reinforced self-compacting geopolymer. At the same volume fraction, geopolymers with long fibres present worse flowability than those having short fibres due to the easier contacting of long fibres. By growing the FF the influence of fibre addition on the V-funnel flow rate is more significant than the slump spread. This can be ascribed to the consequence of fibre addition and friction by the V-funnel which estimates the restrained deformability. For FF lesser than critical factor Fc = 100, influence of fibres is negligible and fibres are far apart from each other and, thus, they cannot restrict cracking under load and transfer the load to improve the mechanical properties. For FF between the Fc = 100 and density factor Fd = 350, a noteworthy enhancement of mechanical properties was obtained and the geopolymer was still adequately workable to flow by weight of self, without any symbols of instability and fibre clumping. Under this condition, better fibre dispersal and reinforcing productivity can lead to better hardened properties. For FF higher than Fd = 350, fibres tend to come to be entwined together and form clumping resulting from the fibre balling, resulting in worse hardened properties. This research offers a sensible basis for the application of the workability regulator of the fresh properties of fibre-reinforced geopolymer as an operative way to basically obtain ideal mechanical properties. Full article

(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)

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15 pages, 4388 KB

Open AccessEditor’s ChoiceArticle

Compressive Creep and Shrinkage of High-Strength Concrete Based on Limestone Coarse Aggregate Applied to High-Rise Buildings

by Euichul Hwang, Gyuyong Kim, Kyungmo Koo, Hyungjae Moon, Gyeongcheol Choe, Dongkyun Suh and Jeongsoo Nam

Materials 2021, 14(17), 5026; https://doi.org/10.3390/ma14175026 - 2 Sep 2021

Cited by 12 | Viewed by 4272

Abstract

Concrete undergoes shrinkage regardless of the influence of external forces. The deformation of concrete is crucial for the structural stability of high-rise and large-scale buildings. In this study, the shrinkage and compressive creep of 70–90 MPa high-strength concrete used in high-rise buildings were [...] Read more.

Concrete undergoes shrinkage regardless of the influence of external forces. The deformation of concrete is crucial for the structural stability of high-rise and large-scale buildings. In this study, the shrinkage and compressive creep of 70–90 MPa high-strength concrete used in high-rise buildings were evaluated based on the curing conditions (sealed/unsealed), and the existing prediction models were examined. It was observed that the curing condition does not significantly affect the mechanical properties of high-strength concrete, but the use of limestone coarse aggregate increases the elastic modulus when compared to granite coarse aggregate. The autogenous shrinkage of high-strength concrete is greater than that of normal-strength concrete owing to self-desiccation, resulting in a large variation from the value predicted by the model. The drying shrinkage was observed to be similar to that predicted by the model. Compressive creep was affected by the curing conditions, compressive strength, loading level, and loading age. The compressive creep of high-strength concrete varied significantly from the prediction results of ACI 209; ACI 209 was modified based on the measured values. The shrinkage and compressive creep characteristics of high-strength concrete must be reflected to predict the deformation of an actual structure exposed to various conditions. Full article

(This article belongs to the Special Issue Research of Mechanical Behavior of Cement and Concrete Composites)

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13 pages, 5537 KB

Open AccessEditor’s ChoiceArticle

A FEM-Based Optimization Method for Driving Frequency of Contactless Magnetoelastic Torque Sensors in Steel Shafts

by Anna Ostaszewska-Liżewska, Michał Nowicki, Roman Szewczyk and Mika Malinen

Materials 2021, 14(17), 4996; https://doi.org/10.3390/ma14174996 - 1 Sep 2021

Cited by 6 | Viewed by 2809

Abstract

This paper presents a novel finite element method (FEM) of optimization for driving frequency in magneto-mechanical systems using contactless magnetoelastic torque sensors. The optimization technique is based on the generalization of the axial and shear stress dependence of the magnetic permeability tensor. This [...] Read more.

This paper presents a novel finite element method (FEM) of optimization for driving frequency in magneto-mechanical systems using contactless magnetoelastic torque sensors. The optimization technique is based on the generalization of the axial and shear stress dependence of the magnetic permeability tensor. This generalization creates a new possibility for the determination of the torque dependence of a permeability tensor based on measurements of the axial stress on the magnetization curve. Such a possibility of quantitative description of torque dependence of a magnetic permeability tensor has never before been presented. Results from the FEM-based modeling method were validated against a real magnetoelastic torque sensor. The sensitivity characteristics of the model and the real sensor show a maximum using a driving current of similar frequency. Consequently, the proposed method demonstrates the novel possibility of optimizing magnetoelastic sensors for automotive and industrial applications. Full article

(This article belongs to the Collection Magnetoelastic Materials)

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13 pages, 4619 KB

Open AccessEditor’s ChoiceArticle

Evaluation of PIRs Post-Fire Pull-Out Strength in Concrete Exposed to ISO 834-1 Fire

by Nagham Abdelrahman Alhajj Chehade, Amine Lahouar, Omar Al-Mansouri, Nicolas Pinoteau, Marco Abate, Sébastien Remond and Dashnor Hoxha

Materials 2021, 14(17), 4998; https://doi.org/10.3390/ma14174998 - 1 Sep 2021

Cited by 4 | Viewed by 2428

Abstract

Post-installed rebars (PIRs) using mortar can offer bond strength at ambient temperature equal or higher to that of cast-in place rebars. However, high temperatures have the effect of weakening the bond, typically governed by the chemical and physical properties of the mortar which [...] Read more.

Post-installed rebars (PIRs) using mortar can offer bond strength at ambient temperature equal or higher to that of cast-in place rebars. However, high temperatures have the effect of weakening the bond, typically governed by the chemical and physical properties of the mortar which is often sensitive to temperature increase. Therefore, the behavior of PIRs in a fire situation becomes vulnerable. Moreover, after exposure of PIRs to high temperature, the heat transfer continues during the post-fire phase, which might endanger the construction after a fire event. In order to evaluate the evolution of the pull-out capacity during fire, Pinoteau et al. have developed the bond resistance integration method (Pinoteau’s RIM) to predict the bond resistance value of a rebar subjected to various temperatures in accordance with the fire exposure curves. Therefore, accurate temperature profiles during the post-fire phase are needed to ensure a correct calculation of the post-fire behavior of the PIR connection. This paper presents 3D finite element thermal simulations of PIRs in concrete exposed to ISO 834-1 fire conditions then cooled with ambient air. Numerical thermal profiles are then compared to the experimental results (i.e., post-fire pull-out tests). The proposed model provides guidelines for conducting numerical simulations to determine the thermal entry data necessary for predicting thermal profiles in PIRs during heating and cooling phases. Then, the post-fire pull-out capacity of PIRs in concrete is calculated using Pinoteau’s RIM, and compared to experimental post-fire pull-out results. Full article

(This article belongs to the Special Issue Structural Concrete Material: New Trends for Eco-Efficiency and Performance)

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19 pages, 5164 KB

Open AccessEditor’s ChoiceArticle

Experimental Study on Solidification and Stabilization of Heavy-Metal-Contaminated Soil Using Cementitious Materials

by Xiaojun Li, Ruizhi Yang, Hao Li, Hao Yi and Hongjun Jing

Materials 2021, 14(17), 4999; https://doi.org/10.3390/ma14174999 - 1 Sep 2021

Cited by 20 | Viewed by 3230

Abstract

In order to solve the shortcomings of the traditional curing agent in the treatment of composite heavy-metal-contaminated soil with the solidification and stabilization method, a new type of cementing material A was used as a curing agent, and the Pb, Cd, Cu composite [...] Read more.

In order to solve the shortcomings of the traditional curing agent in the treatment of composite heavy-metal-contaminated soil with the solidification and stabilization method, a new type of cementing material A was used as a curing agent, and the Pb, Cd, Cu composite heavy-metal-contaminated soil was artificially prepared to carry out an experimental study on solidification and stabilization (SS) restoration by the mechanical properties test, leaching performance test, and microscopic test. The results show that in the range of test dosage, with the increase in the curing agent content, the unconfined compressive strength of the solidified body increased, and the resistance to deformation was enhanced. From the perspective of leaching characteristics, the new curing agent A had an excellent curing effect on the composite heavy-metal-contaminated soil. To achieve safe disposal, a curing agent content of 10% applies only for the soil heavily contaminated by heavy metals. The curing agent A could significantly reduce the content of acid-extractable heavy metals after solidifying the heavy metal Pb, Cd, and Cu composite contaminated soil and effectively converted it into a residue state. The solidified phase contained hydrated products such as calcium silicate hydrate (CSH) and ettringite (AFt). These hydrated products can inhibit the leaching performance of heavy metal ions through adsorption, encapsulation, and ion exchange. The study provides a feasible method and reference for the solidification, restoration, and resource utilization of heavy-metal-contaminated soil in the subgrade. Full article

(This article belongs to the Special Issue Materials, Structure, and Modeling for Smart and Resilient Roads)

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8 pages, 866 KB

Open AccessEditor’s ChoiceArticle

Pseudogap Isotope Effect as a Probe of Bipolaron Mechanism in High Temperature Superconductors

by Victor D. Lakhno

Materials 2021, 14(17), 4973; https://doi.org/10.3390/ma14174973 - 31 Aug 2021

Cited by 2 | Viewed by 2423

Abstract

A theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed. A temperature

T^{*}

of a transition from a pseudogap phase to a normal one is calculated. For the temperature of a transition to the [...] Read more.

A theory of a pseudogap phase of high-temperature superconductors where current carriers are translation invariant bipolarons is developed. A temperature

T^{*}

of a transition from a pseudogap phase to a normal one is calculated. For the temperature of a transition to the pseudogap phase, the isotope coefficient is found. It is shown that the results obtained, in particular, the possibility of negative values of the isotope coefficient, are consistent with the experiment. New experiments on the influence of the magnetic field on the isotope coefficient are proposed. Full article

(This article belongs to the Special Issue Advances in Superconducting Materials: Characterization, Properties and Applications)

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13 pages, 4290 KB

Open AccessEditor’s ChoiceArticle

Characterization of Sustainable Asphalt Mixtures Containing High Reclaimed Asphalt and Steel Slag

by Panos Georgiou and Andreas Loizos

Materials 2021, 14(17), 4938; https://doi.org/10.3390/ma14174938 - 30 Aug 2021

Cited by 19 | Viewed by 2613

Abstract

Policymakers are implementing the transition to a circular model in all economic sectors to drastically mitigate the effects of climate change. In this regard, the producers of paving products should promote the reuse and recycling of solid waste in the design of sustainable [...] Read more.

Policymakers are implementing the transition to a circular model in all economic sectors to drastically mitigate the effects of climate change. In this regard, the producers of paving products should promote the reuse and recycling of solid waste in the design of sustainable asphalt materials. This study evaluated the performance-based properties of three highly recycled mixtures for wearing courses of asphalt pavements containing steel slag and varying amounts (25, 40, and 50%) of fractionated reclaimed asphalt (RA). In addition, the mixtures incorporated a warm mix asphalt (WMA) organic additive to lower production temperatures compared to a reference hot mix asphalt (HMA). Based on the experimental results, the warm recycled asphalt mixtures show equivalent or better performance compared to HMA in terms of moisture susceptibility, stiffness, rutting and fracture resistance, and surface macrotexture. Therefore, the combined incorporation of RA and steel slag with WMA was proven to be an effective option in designing environmentally friendly and high-performance wearing course mixtures. Full article

(This article belongs to the Special Issue Long-Life and Circular Pavement Materials)

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40 pages, 2232 KB

Open AccessEditor’s ChoiceReview

A Review on Thermophotovoltaic Cell and Its Applications in Energy Conversion: Issues and Recommendations

by Mansur Mohammed Ali Gamel, Hui Jing Lee, Wan Emilin Suliza Wan Abdul Rashid, Pin Jern Ker, Lau Kuen Yau, Mahammad A. Hannan and Md. Zaini Jamaludin

Materials 2021, 14(17), 4944; https://doi.org/10.3390/ma14174944 - 30 Aug 2021

Cited by 78 | Viewed by 8523

Abstract

Generally, waste heat is redundantly released into the surrounding by anthropogenic activities without strategized planning. Consequently, urban heat islands and global warming chronically increases over time. Thermophotovoltaic (TPV) systems can be potentially deployed to harvest waste heat and recuperate energy to tackle this [...] Read more.

Generally, waste heat is redundantly released into the surrounding by anthropogenic activities without strategized planning. Consequently, urban heat islands and global warming chronically increases over time. Thermophotovoltaic (TPV) systems can be potentially deployed to harvest waste heat and recuperate energy to tackle this global issue with supplementary generation of electrical energy. This paper presents a critical review on two dominant types of semiconductor materials, namely gallium antimonide (GaSb) and indium gallium arsenide (InGaAs), as the potential candidates for TPV cells. The advantages and drawbacks of non-epitaxy and epitaxy growth methods are well-discussed based on different semiconductor materials. In addition, this paper critically examines and summarizes the electrical cell performance of TPV cells made of GaSb, InGaAs and other narrow bandgap semiconductor materials. The cell conversion efficiency improvement in terms of structural design and architectural optimization are also comprehensively analyzed and discussed. Lastly, the practical applications, current issues and challenges of TPV cells are critically reviewed and concluded with recommendations for future research. The highlighted insights of this review will contribute to the increase in effort towards development of future TPV systems with improved cell conversion efficiency. Full article

(This article belongs to the Special Issue Electronic and Optical Properties of Heterostructures)

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12 pages, 2952 KB

Open AccessEditor’s ChoiceArticle

Response and Deterioration Mechanism of Bitumen under Acid Rain Erosion

by Xuemei Zhang, Inge Hoff and Rabbira Garba Saba

Materials 2021, 14(17), 4911; https://doi.org/10.3390/ma14174911 - 29 Aug 2021

Cited by 12 | Viewed by 2644

Abstract

Acid rain as an important environmental issue has a negative impact on bitumen performance, thereby shortening the service life of asphalt pavements. Thus, this research aims to investigate the response of bitumen to acid rain and its deterioration mechanism. For this purpose, the [...] Read more.

Acid rain as an important environmental issue has a negative impact on bitumen performance, thereby shortening the service life of asphalt pavements. Thus, this research aims to investigate the response of bitumen to acid rain and its deterioration mechanism. For this purpose, the simulated acid rain was prepared to erode neat bitumen and short-term aged bitumen. The hydrogen ion concentration of the acid rain, and the morphological, physical, chemical, and rheological properties of the bitumen were evaluated by means of a pH meter, scanning electron microscopy, physical tests, Fourier transform infrared radiation with attenuated total reflectance, and dynamic shear rheometer. The results showed that bitumen properties were severely affected by acid rain, and the changes in bitumen properties were highly related to the erosion time, leading to a reduction in pH value by 0.2 of residual acid rain, rougher bitumen surface, and stiffer bitumen with more oxygen-containing functional groups and fewer carbonyl acid groups (around 10% decrement) after 90 days erosion. These changes contributed to two deterioration mechanisms: oxidation and dissolution of carbonyl acid. Oxidation and dissolution are, respectively, the dominant actions for neat bitumen and aged bitumen during the erosion process, which eventually leads to various responses to acid rain. Full article

(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)

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20 pages, 6931 KB

Open AccessEditor’s ChoiceArticle

Evaluation of the Protection Ability of a Magnesium Hydroxide Coating against the Bio-Corrosion of Concrete Sewer Pipes, by Using Short and Long Duration Accelerated Acid Spraying Tests

by Domna Merachtsaki, Eirini-Chrysanthi Tsardaka, Eleftherios Anastasiou and Anastasios Zouboulis

Materials 2021, 14(17), 4897; https://doi.org/10.3390/ma14174897 - 28 Aug 2021

Cited by 11 | Viewed by 2583

Abstract

The Microbiologically Induced Corrosion (MIC) of concrete sewer pipes is a commonly known problem that can lead to the destruction of the system, creating multiple public health issues and the need for costly repair investments. The present study focuses on the development of [...] Read more.

The Microbiologically Induced Corrosion (MIC) of concrete sewer pipes is a commonly known problem that can lead to the destruction of the system, creating multiple public health issues and the need for costly repair investments. The present study focuses on the development of a magnesium hydroxide coating, with optimized properties to protect concrete against MIC. The anti-corrosion properties of the respective coating were evaluated by using short and long duration accelerated sulfuric acid spraying tests. The coating presented satisfying adhesion ability, based on pull-off and Scanning Electron Microscopy (SEM) analysis measurements. The surface pH of the coated concrete was maintained at the alkaline region (i.e., >8.0) throughout the duration of all acid spraying tests. The consumption of the coating, due to the reaction (neutralization) with sulfuric acid, was confirmed by the respective mass and thickness measurements. The protection ability of this coating was also evaluated by recording the formation of gypsum (i.e., the main corrosion product of concrete) during the performed tests, by X-ray Diffraction (XRD) analysis and by the Attenuated Total Reflectance (ATR) measurements. Finally, a long duration acid spraying test was additionally used to evaluate the behavior of the coating, simulating better the conditions existing in a real sewer pipe, and the obtained results showed that this coating is capable of offering prolonged protection to the concrete substrate. Full article

(This article belongs to the Special Issue Corrosion in Concrete: Inhibitors and Coatings)

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25 pages, 55132 KB

Open AccessEditor’s ChoiceArticle

Improving Marine Concrete Performance Based on Multiple Criteria Using Early Portland Cement and Chemical Superplasticizer Admixture

by Taegyu Lee, Jaehyun Lee, Jaewook Jeong and Jaemin Jeong

Materials 2021, 14(17), 4903; https://doi.org/10.3390/ma14174903 - 28 Aug 2021

Cited by 9 | Viewed by 2868

Abstract

This study sought to examine the performance design of concrete mix proportions to ensure chloride resistance and early strength with respect to C35 (35 MPa), which is the minimum compressive strength class of concrete used in a marine environment. For the proposed concrete [...] Read more.

This study sought to examine the performance design of concrete mix proportions to ensure chloride resistance and early strength with respect to C35 (35 MPa), which is the minimum compressive strength class of concrete used in a marine environment. For the proposed concrete mixture, C24 (24 MPa) was selected and binders for concrete were manufactured using a blend of OPC (ordinary Portland cement), EPC (early Portland cement), and GGBS (ground granulated blast-furnace slag). The results of the experiment confirmed that the combined use of EPC and GGBS greatly improve the early-strength development and chloride resistance of concrete. An analysis revealed that the time for removal of forms can be reduced by 5–9 h from the aspect of early concrete strength. Moreover, in terms of construction productivity, EPC and GGBS were reduced by up to 16.39 h/cycle compared to other concretes. Regarding economic and environmental impacts, EPC and GGBS were more effective than C35 concrete. This study is significant as its findings help make it possible to examine the most economical concrete mix design in relation to strength development according to the application of EPC, GGBS, and PC-based admixtures. Full article

(This article belongs to the Special Issue Carbon Peaking and Carbon Neutrality in the Cement-Based Materials)

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21 pages, 39248 KB

Open AccessEditor’s ChoiceArticle

Application of Artificial Intelligence to Evaluate the Fresh Properties of Self-Consolidating Concrete

by Yuping Feng, Masoud Mohammadi, Lifeng Wang, Maria Rashidi and Peyman Mehrabi

Materials 2021, 14(17), 4885; https://doi.org/10.3390/ma14174885 - 27 Aug 2021

Cited by 74 | Viewed by 2902

Abstract

This paper numerically investigates the required superplasticizer (SP) demand for self-consolidating concrete (SCC) as a valuable information source to obtain a durable SCC. In this regard, an adaptive neuro-fuzzy inference system (ANFIS) is integrated with three metaheuristic algorithms to evaluate a dataset from [...] Read more.

This paper numerically investigates the required superplasticizer (SP) demand for self-consolidating concrete (SCC) as a valuable information source to obtain a durable SCC. In this regard, an adaptive neuro-fuzzy inference system (ANFIS) is integrated with three metaheuristic algorithms to evaluate a dataset from non-destructive tests. Hence, five different non-destructive testing methods, including J-ring test, V-funnel test, U-box test, 3 min slump value and 50 min slump (T50) value were performed. Then, three metaheuristic algorithms, namely particle swarm optimization (PSO), ant colony optimization (ACO) and differential evolution optimization (DEO), were considered to predict the SP demand of SCC mixtures. To compare the optimization algorithms, ANFIS parameters were kept constant (clusters = 10, train samples = 70% and test samples = 30%). The metaheuristic parameters were adjusted, and each algorithm was tuned to attain the best performance. In general, it was found that the ANFIS method is a good base to be combined with other optimization algorithms. The results indicated that hybrid algorithms (ANFIS-PSO, ANFIS-DEO and ANFIS-ACO) can be used as reliable prediction methods and considered as an alternative for experimental techniques. In order to perform a reliable analogy of the developed algorithms, three evaluation criteria were employed, including root mean square error (RMSE), Pearson correlation coefficient (r) and determination regression coefficient (R²). As a result, the ANFIS-PSO algorithm represented the most accurate prediction of SP demand with RMSE = 0.0633, r = 0.9387 and R² = 0.9871 in the testing phase. Full article

(This article belongs to the Special Issue Emerging Trends in Structural Health Monitoring)

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17 pages, 4401 KB

Open AccessEditor’s ChoiceArticle

Influence of Sand-Cement Ratio and Polycarboxylate Superplasticizer on the Basic Properties of Mortar Based on Water Film Thickness

by Zhao Zhang, Qingge Feng, Weiwei Zhu, Xianhao Lin, Kao Chen, Wuxiao Yin and Changhai Lu

Materials 2021, 14(17), 4850; https://doi.org/10.3390/ma14174850 - 26 Aug 2021

Cited by 11 | Viewed by 2785

Abstract

Previous studies demonstrated that water film thickness (WFT) is a key factor that affects the fluidity of mortar. Changes in the sand-cement (S/C) ratio and polycarboxylate superplasticizer (PCE) dosage will affect the WFT. In this study, several mortar samples with different S/C ratios [...] Read more.

Previous studies demonstrated that water film thickness (WFT) is a key factor that affects the fluidity of mortar. Changes in the sand-cement (S/C) ratio and polycarboxylate superplasticizer (PCE) dosage will affect the WFT. In this study, several mortar samples with different S/C ratios and different PCE dosages were prepared, and the basic properties of the mortar were measured. The results show that as the S/C ratio increases, the packing density of the mortar will decrease, the WFT will decrease, and the cohesiveness will increase, resulting in a decrease in the flow spread and strength of the mortar. When the PCE dosage is increased, the packing density of the mortar will increase, the WFT will increase, and the cohesiveness will decrease, which increases the flow spread of the mortar. When the water-cement (W/C) ratio is low, the S/C ratio has a significant effect on the strength, and the strength will increase with the increasing of the PCE dosage. When the W/C ratio is high, the strength of the mortar will be reduced once the PCE dosage exceeds the saturation value. In the case of different S/C ratios or different PCE dosages, the WFT can be used as a measure of mortar cohesiveness and flow spread. Full article

(This article belongs to the Special Issue Advances in Serviceability Analysis of Concrete Structures)

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19 pages, 4202 KB

Open AccessEditor’s ChoiceArticle

Effect of Boron and Water-to-Cement Ratio on the Performances of Laboratory Prepared Belite-Ye’elimite-Ferrite (BYF) Cements

by Raquel Pérez-Bravo, Alejandro Morales-Cantero, Margherita Bruscolini, Miguel A. G. Aranda, Isabel Santacruz and Angeles G. De la Torre

Materials 2021, 14(17), 4862; https://doi.org/10.3390/ma14174862 - 26 Aug 2021

Cited by 12 | Viewed by 2386

Abstract

The effect of superplasticiser, borax and the water-to-cement ratio on BYF hydration and mechanical strengths has been studied. Two laboratory-scale BYF cements—st-BYF (with β-C₂S and orthorhombic C₄A₃

\bar{S}

) and borax-activated B-BYF (with α’_H-C₂ [...] Read more.

The effect of superplasticiser, borax and the water-to-cement ratio on BYF hydration and mechanical strengths has been studied. Two laboratory-scale BYF cements—st-BYF (with β-C₂S and orthorhombic C₄A₃

\bar{S}

) and borax-activated B-BYF (with α’_H-C₂S and pseudo-cubic C₄A₃

\bar{S}

)—have been used, and both show similar particle size distribution. The addition of superplasticiser and externally added borax to BYF pastes has been optimised through rheological measurements. Optimised superplasticiser contents (0.3, 0.4 and 0.1 wt % for st-BYF, B-BYF and st-BYF with externally added 0.25 wt % B₂O₃, respectively) result in low viscosities yielding homogeneous mortars. The calorimetric study revealed that st-BYF is more reactive than B-BYF, as the values of heat released are 300–370 J/g and 190–210 J/g, respectively, after 7 days of hydration; this fact is independent of the water-to-cement ratio. These findings agree with the higher degree of hydration at 28 days of β-C₂S in st-BYF (from 45 to 60%) than α’_H-C₂S in B-BYF (~20 to 30%). The phase assemblage evolution has been determined by LXRPD coupled with the Rietveld method and MAS-NMR. The formation of stratlingite is favoured by increasing the w/c ratio in both systems. Finally, the optimisation of fresh BYF pastes jointly with the reduction of water-to-cement ratio to 0.40 have allowed the achieving of mortars with compressive strengths over 40 MPa at 7 days in all systems. Moreover, the st-BYF mortar, where borax was externally added, achieved more than 70 MPa after 28 days. The main conclusion of this work does not support Lafarge’s approach of adding boron/borax to the raw meal of BYF cements. This procedure stabilises the alpha belite polymorph, but its reactivity, in these systems, is lower and the associated mechanical strengths poorer. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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18 pages, 2322 KB

Open AccessEditor’s ChoiceArticle

Synthesis of Dimethyl Carbonate by Transesterification of Propylene Carbonate with Methanol on CeO₂-La₂O₃ Oxides Prepared by the Soft Template Method

by Maria Giorgia Cutrufello, Luciano Atzori, Daniela Meloni, Alessandra Piras, Delia Gazzoli and Elisabetta Rombi

Materials 2021, 14(17), 4802; https://doi.org/10.3390/ma14174802 - 24 Aug 2021

Cited by 7 | Viewed by 3416

Abstract

In this study, CeO₂, La₂O₃, and CeO₂-La₂O₃ mixed oxide catalysts with different Ce/La molar ratios were prepared by the soft template method and characterized by different techniques, including inductively coupled plasma atomic [...] Read more.

In this study, CeO₂, La₂O₃, and CeO₂-La₂O₃ mixed oxide catalysts with different Ce/La molar ratios were prepared by the soft template method and characterized by different techniques, including inductively coupled plasma atomic emission spectrometry, X-ray diffraction, N₂ physisorption, thermogravimetric analysis, and Raman and Fourier transform infrared spectroscopies. NH₃ and CO₂ adsorption microcalorimetry was also used for assessing the acid and base surface properties, respectively. The behavior of the oxides as catalysts for the dimethyl carbonate synthesis by the transesterification of propylene carbonate with methanol, at 160 °C under autogenic pressure, was studied in a stainless-steel batch reactor. The activity of the catalysts was found to increase with an increase in the basic sites density. The formation of dimethyl carbonate was favored on medium-strength and weak basic sites, while it underwent decomposition on the strong ones. Several parasitic reactions occurred during the transformation of propylene carbonate, depending on the basic and acidic features of the catalysts. A reaction pathway has been proposed on the basis of the components identified in the reaction mixture. Full article

(This article belongs to the Special Issue Oxide-Based Materials for Sustainable Catalytic Processes)

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11 pages, 10549 KB

Open AccessEditor’s ChoiceArticle

Direct One-Step Growth of Bimetallic Ni₂Mo₃N on Ni Foam as an Efficient Oxygen Evolution Electrocatalyst

by Sang Heon Park, Soon Hyung Kang and Duck Hyun Youn

Materials 2021, 14(16), 4768; https://doi.org/10.3390/ma14164768 - 23 Aug 2021

Cited by 16 | Viewed by 4082

Abstract

A simple and economical synthetic route for direct one-step growth of bimetallic Ni₂Mo₃N nanoparticles on Ni foam substrate (Ni₂Mo₃N/NF) and its catalytic performance during an oxygen evolution reaction (OER) are reported. The Ni₂Mo [...] Read more.

A simple and economical synthetic route for direct one-step growth of bimetallic Ni₂Mo₃N nanoparticles on Ni foam substrate (Ni₂Mo₃N/NF) and its catalytic performance during an oxygen evolution reaction (OER) are reported. The Ni₂Mo₃N/NF catalyst was obtained by annealing a mixture of a Mo precursor, Ni foam, and urea at 600 °C under N₂ flow using one-pot synthesis. Moreover, the Ni₂Mo₃N/NF exhibited high OER activity with low overpotential values (336.38 mV at 50 mA cm⁻² and 392.49 mV at 100 mA cm⁻²) and good stability for 5 h in Fe-purified alkaline electrolyte. The Ni₂Mo₃N nanoparticle surfaces converted into amorphous surface oxide species during the OER, which might be attributed to the OER activity. Full article

(This article belongs to the Special Issue Advances in Nanostructured Catalysts)

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33 pages, 4171 KB

Open AccessEditor’s ChoiceReview

A State-of-the-Art Review on Integral Transform Technique in Laser–Material Interaction: Fourier and Non-Fourier Heat Equations

by Mihai Oane, Muhammad Arif Mahmood and Andrei C. Popescu

Materials 2021, 14(16), 4733; https://doi.org/10.3390/ma14164733 - 22 Aug 2021

Cited by 18 | Viewed by 4009

Abstract

Heat equations can estimate the thermal distribution and phase transformation in real-time based on the operating conditions and material properties. Such wonderful features have enabled heat equations in various fields, including laser and electron beam processing. The integral transform technique (ITT) is a [...] Read more.

Heat equations can estimate the thermal distribution and phase transformation in real-time based on the operating conditions and material properties. Such wonderful features have enabled heat equations in various fields, including laser and electron beam processing. The integral transform technique (ITT) is a powerful general-purpose semi-analytical/numerical method that transforms partial differential equations into a coupled system of ordinary differential equations. Under this category, Fourier and non-Fourier heat equations can be implemented on both equilibrium and non-equilibrium thermo-dynamical processes, including a wide range of processes such as the Two-Temperature Model, ultra-fast laser irradiation, and biological processes. This review article focuses on heat equation models, including Fourier and non-Fourier heat equations. A comparison between Fourier and non-Fourier heat equations and their generalized solutions have been discussed. Various components of heat equations and their implementation in multiple processes have been illustrated. Besides, literature has been collected based on ITT implementation in various materials. Furthermore, a future outlook has been provided for Fourier and non-Fourier heat equations. It was found that the Fourier heat equation is simple to use but involves infinite speed heat propagation in comparison to the non-Fourier heat equation and can be linked with the Two-Temperature Model in a natural way. On the other hand, the non-Fourier heat equation is complex and involves various unknowns compared to the Fourier heat equation. Fourier and Non-Fourier heat equations have proved their reliability in the case of laser–metallic materials, electron beam–biological and –inorganic materials, laser–semiconducting materials, and laser–graphene material interactions. It has been identified that the material properties, electron–phonon relaxation time, and Eigen Values play an essential role in defining the precise results of Fourier and non-Fourier heat equations. In the case of laser–graphene interaction, a restriction has been identified from ITT. When computations are carried out for attosecond pulse durations, the laser wavelength approaches the nucleus-first electron separation distance, resulting in meaningless results. Full article

(This article belongs to the Special Issue Materials Thermal Behavior during Laser or Electron Beam Irradiation)

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29 pages, 7098 KB

Open AccessEditor’s ChoiceReview

Survey of Mechanical Properties of Geopolymer Concrete: A Comprehensive Review and Data Analysis

by Azad A. Mohammed, Hemn Unis Ahmed and Amir Mosavi

Materials 2021, 14(16), 4690; https://doi.org/10.3390/ma14164690 - 20 Aug 2021

Cited by 111 | Viewed by 7783

Abstract

Mechanical properties and data analysis for the prediction of different mechanical properties of geopolymer concrete (GPC) were investigated. A relatively large amount of test data from 126 past works was collected, analyzed, and correlation between different mechanical properties and compressive strength was investigated. [...] Read more.

Mechanical properties and data analysis for the prediction of different mechanical properties of geopolymer concrete (GPC) were investigated. A relatively large amount of test data from 126 past works was collected, analyzed, and correlation between different mechanical properties and compressive strength was investigated. Equations were proposed for the properties of splitting tensile strength, flexural strength, modulus of elasticity, Poisson’s ratio, and strain corresponding to peak compressive strength. The proposed equations were found accurate and can be used to prepare a state-of-art report on GPC. Based on data analysis, it was found that there is a chance to apply some past proposed equations for predicting different mechanical properties. CEB-FIP equations for the prediction of splitting tensile strength and strain corresponding to peak compressive stress were found to be accurate, while ACI 318 equations for splitting tensile and elastic modulus overestimates test data for GPC of low compressive strength. Full article

(This article belongs to the Special Issue Sustainability in Construction and Building Materials)

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23 pages, 7101 KB

Open AccessEditor’s ChoiceArticle

The Synergistic Effect of Ester-Ether Copolymerization Thixo-Tropic Superplasticizer and Nano-Clay on the Buildability of 3D Printable Cementitious Materials

by Yu Wang, Yaqing Jiang, Tinghong Pan and Kangting Yin

Materials 2021, 14(16), 4622; https://doi.org/10.3390/ma14164622 - 17 Aug 2021

Cited by 14 | Viewed by 2853

Abstract

The shape retention ability of materials deposited layer by layer is called buildability, which is an indispensable performance parameter for successful 3D printable cementitious materials (3DPC). This study investigated the synergistic effect of nano-clay (NC) and thixotropic superplasticizer (TP) on the buildability of [...] Read more.

The shape retention ability of materials deposited layer by layer is called buildability, which is an indispensable performance parameter for successful 3D printable cementitious materials (3DPC). This study investigated the synergistic effect of nano-clay (NC) and thixotropic superplasticizer (TP) on the buildability of 3DPC. The rheological parameters and static yield stress are characterized by the rheology testing, the green strength is measured by a self-made pressure tester, and the fluidity is tested by flow table. Results indicate that NC significantly increases the growth rate of static yield stress and green strength and TP can improve the initial rheological parameters and fluidity, which ensures the initial stiffness and workability of printed materials. The mixture with 7‰ (by mass of cementitious materials) NC and 3‰ TP obtains excellent extrudability and buildability, due to the synergistic effect of NC and TP. Based on the rheology testing and specific printing experiments, a printable window with 1.0 Pa/s~2.0 Pa/s of the rate of static yield stress evolution over time (RST) or 170 mm~200 mm of fluidity is established. This work provides theorical support for the control and evaluation of rheological properties in 3DPC. Full article

(This article belongs to the Special Issue Feature Papers in Construction and Building Materials)

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20 pages, 6173 KB

Open AccessEditor’s ChoiceReview

Magnetoelectric Memory Based on Ferromagnetic/Ferroelectric Multiferroic Heterostructure

by Jiawei Wang, Aitian Chen, Peisen Li and Sen Zhang

Materials 2021, 14(16), 4623; https://doi.org/10.3390/ma14164623 - 17 Aug 2021

Cited by 24 | Viewed by 5854

Abstract

Electric-field control of magnetism is significant for the next generation of large-capacity and low-power data storage technology. In this regard, the renaissance of a multiferroic compound provides an elegant platform owing to the coexistence and coupling of ferroelectric (FE) and magnetic orders. However, [...] Read more.

Electric-field control of magnetism is significant for the next generation of large-capacity and low-power data storage technology. In this regard, the renaissance of a multiferroic compound provides an elegant platform owing to the coexistence and coupling of ferroelectric (FE) and magnetic orders. However, the scarcity of single-phase multiferroics at room temperature spurs zealous research in pursuit of composite systems combining a ferromagnet with FE or piezoelectric materials. So far, electric-field control of magnetism has been achieved in the exchange-mediated, charge-mediated, and strain-mediated ferromagnetic (FM)/FE multiferroic heterostructures. Concerning the giant, nonvolatile, and reversible electric-field control of magnetism at room temperature, we first review the theoretical and representative experiments on the electric-field control of magnetism via strain coupling in the FM/FE multiferroic heterostructures, especially the CoFeB/PMN–PT [where PMN–PT denotes the (PbMn_1/3Nb_2/3O₃)_1−x-(PbTiO₃)_x] heterostructure. Then, the application in the prototype spintronic devices, i.e., spin valves and magnetic tunnel junctions, is introduced. The nonvolatile and reversible electric-field control of tunneling magnetoresistance without assistant magnetic field in the magnetic tunnel junction (MTJ)/FE architecture shows great promise for the future of data storage technology. We close by providing the main challenges of this and the different perspectives for straintronics and spintronics. Full article

(This article belongs to the Special Issue Advances in Magnetoelectric Materials and Devices)

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