Analysis of the Technical Feasibility of Sustainable Concrete Production Using Waste Foundry Sand as a Fine Aggregate.

Waste foundation sand (WFS) is one of the most abundant residues in the foundation industry. Currently, its annual production is estimated to be three million tons. This material has properties that make it an attractive candidate for implantation as an alternative constituent to a natural fine aggregate in concrete applications. This application can promote greater sustainability, as it would establish a noble destination for the waste generated in large quantities by the metallurgical industry in addition to reducing the exploitation of a natural resource widely used by the civil construction industry. Given this, the present study observed the test of three different proportions of replacement, 25, 50, and 100% by mass, of natural sand by WFS in concrete. To assess the feasibility of these replacements, several tests were carried out covering mechanical properties and aspects related to the durability of concrete. The results indicated a significant improvement in the mechanical performance, with a resistance gain of 25% in relation to the reference concrete. As for the modulus of elasticity, there was no significant variation. As for aspects related to durability, both the absorption test and the alkali aggregate reaction test did not show statistically significant disparity, which attests to the technical feasibility of using nonconcrete WFS.

Using Thermomechanical Properties to Reassess Particles' Dispersion in Nanostructured Polymers: Size vs. Content.

Nanoparticle-filled polymers (i.e., nanocomposites) can exhibit characteristics unattainable by the unfilled polymer, making them attractive to engineer structural composites. However, the transition of particulate fillers from the micron to the nanoscale requires a comprehensive understanding of how particle downsizing influences molecular interactions and organization across multiple length scales, ranging from chemical bonding to microstructural evolution. This work outlines the advancements described in the literature that have become relevant and have shaped today's understanding of the processing-structure-property relationships in polymer nanocomposites. The main inorganic and organic particles that have been incorporated into polymers are examined first. The commonly practiced methods for nanoparticle incorporation are then highlighted. The development in mechanical properties-such as tensile strength, storage modulus and glass transition temperature-in the selected epoxy matrix nanocomposites described in the literature was specifically reviewed and discussed. The significant effect of particle content, dispersion, size, and mean free path on thermomechanical properties, commonly expressed as a function of weight percentage (wt.%) of added particles, was found to be better explained as a function of particle crowding (number of particles and distance among them). From this work, it was possible to conclude that the dramatic effect of particle size for the same tiny amount of very small and well-dispersed particles brings evidence that particle size and the particle weight content should be downscaled together.

Characterization and in vivo toxicological evaluation of multi-walled carbon nanotubes: a low-dose repeated intratracheal administration study.

This study characterized and investigated the toxicity of two multi-walled carbon nanotubes (MWCNT) NM-401 and NM-403 at 60 and 180 µg after four repeated intratracheal instillations; follow-up times were 3, 7, 30, and 90 days after the last instillation. NM-401 was needle-like, long, and thick, while NM-403 was entangled, short, and thin. Both MWCNT types induced transient pulmonary and systemic alterations in renal function and oxidative lipid damage markers in recent times. Animals showed general toxicity in the immediate times after exposures, in addition to increased pulmonary LDH release at day 3. In further times, decreased liver and kidney relative weights were noted at higher MWCNT doses. Lung histological damages included pulmonary fibrosis, for both MWCNT types, similarly to asbestos; single liver and kidney histological alterations were present. Repeated instillations led to persistent pulmonary damage at low doses, and possibly the extrapulmonary effects may be associated with the consecutive exposures.

In-Plane Shear Strength of Single-Lap Co-Cured Joints of Self-Reinforced Polyethylene Composites.

The present study introduces the analysis of single-lap co-cured joints of thermoplastic self-reinforced composites made with reprocessed low-density polyethylene (LDPE) and reinforced by ultra-high-molecular-weight polyethylene (UHMWPE) fibers, along with a micromechanical analysis of its constituents. A set of optimal processing conditions for manufacturing these joints by hot-press is proposed through a design of experiment using the response surface method to maximize their in-plane shear strength by carrying tensile tests on co-cured tapes. Optimal processing conditions were found at 1 bar, 115 °C, and 300 s, yielding joints with 6.88 MPa of shear strength. The shear failure is generally preceded by multiple debonding-induced longitudinal cracks both inside and outside the joint due to accumulated transversal stress. This composite demonstrated to be an interesting structural material to be more widely applied in industry, possessing extremely elevated specific mechanical properties, progressive damage of co-cured joints (thus avoiding unannounced catastrophic failures) and ultimate recyclability.

Cerium Dioxide Particles to Tune Radiopacity of Dental Adhesives: Microstructural and Physico-Chemical Evaluation.

The insufficient radiopacity of dental adhesives applied under composite restorations makes the radiographic diagnosis of recurrent caries challenging. Consequently, the misdiagnosis may lead to unnecessary replacement of restorations. The aims of this study were to formulate experimental dental adhesives containing cerium dioxide (CeO2) and investigate the effects of different loadings of CeO2 on their radiopacity and degree of conversion for the first time. CeO2 was characterized by X-ray diffraction analysis, Fourier transforms infrared spectroscopy, and laser diffraction for particle size analysis. Experimental dental adhesives were formulated with CeO2 as the inorganic filler with loadings ranging from 0.36 to 5.76 vol.%. The unfilled adhesive was used as a control. The studied adhesives were evaluated for dispersion of CeO2 in the polymerized samples, degree of conversion, and radiopacity. CeO2 presented a monoclinic crystalline phase, peaks related to Ce-O bonding, and an average particle size of around 16 µm. CeO2 was dispersed in the adhesive, and the addition of these particles increased the adhesives' radiopacity (p < 0.05). There was a significant decrease in the degree of conversion with CeO2 loadings higher than 1.44 vol.%. However, all materials showed a similar degree of conversion in comparison to commercially available adhesives. CeO2 particles were investigated for the first time as a promising compound to improve the radiopacity of the dental adhesives.

Effect of nanostructured zirconium dioxide incorporation in an experimental adhesive resin.

OBJECTIVES: The aim of this study was to evaluate the influence of nanostructured zirconium dioxide incorporation in an experimental adhesive resin. METHODS: ZrO2 particles were characterized by X-ray diffraction (XRD), micro-Raman spectroscopy and Brunauer-Emmett-Teller (B.E.T). Experimental adhesive resins were formulated with 0, 0.5, 1, 4.8, and 9.1% ZrO2 in weight. The adhesives were evaluated based on degree of conversion (DC), radiopacity, softening in solvent and microtensile bond strength (µTBS) 24 h and after 1 year of aging. Mineral deposition at the hybrid layer was assessed with micro-Raman spectroscopy at the baseline and after 14 days. RESULTS: XRD showed monoclinic and tetragonal phases of ZrO2.particles. B.E.T data revealed a surface area of 37.41 m2/g, and typical chemical groups were shown on the Raman spectra. The addition of ZrO2 did not influence the radiopacity. The addition of 4.8% and 9.1 wt.% ZrO2 showed higher initial hardness with increased softening in solvent (P < 0.05) and promoted mineral deposition at the dentin interface. DC was significantly increased in the group with 1% ZrO2 (P < 0.05). The µTBS test showed difference on the group with 9.1 wt.% of ZrO2, with a significant reduction after aging. CONCLUSION: The incorporation of ZrO2 promoted mineral deposition on the adhesive interface and the addition of 1 wt.% caused a significant increase on the DC without compromising the other physicochemical characteristics, which may prove promising for the development of new dental adhesive systems. CLINICAL RELEVANCE: The mineral deposition on the hybrid layer can result in a longer stability of the adhesive, thus delaying the hydrolytic degradation.

The addition of nanostructured hydroxyapatite to an experimental adhesive resin.

OBJECTIVES: Was produced nanostructured hydroxyapatite (HAnano) and evaluated the influence of its incorporation in an adhesive resin. METHODS: HAnano was produced by a flame-based process and was characterized by scanning electron microscopy. The surface area, particle size, micro-Raman and cytotoxicity were evaluated. The organic phase was formulated by mixing 50 wt.% Bis-GMA, 25 wt.% TEGDMA, and 25 wt.% HEMA. HAnano was added at seven different concentrations: 0; 0.5; 1; 2; 5; 10 and 20 wt.%. Adhesive resins with hydroxyapatite incorporation were evaluated for their radiopacity, degree of conversion, flexural strength, softening in solvent and microshear bond strength. The data were analyzed by one-way ANOVA and Tukey's post hoc test (α=0.05), except for softening in solvent (paired t-test) and cytotoxicity (two-way ANOVA and Bonferroni). RESULTS: HAnano presented 15.096 m(2)/g of specific surface area and a mean size of 26.7 nm. The radiopacity values were not different from those of 1-mm aluminium. The degree of conversion ranged from 52.2 to 63.8%. The incorporation of HAnano did not influence the flexural strength, which ranged from 123.3 to 143.4MPa. The percentage of reduction of the microhardness after immersion in the solvent became lower as the HAnano concentration increased. The addition of 2% nanostructured hydroxyapatite resulted in a higher value of microshear bond strength than the control group (p<0.05). CONCLUSIONS: The incorporation of 2% of nanostructured hydroxyapatite into an adhesive resin presented the best results. CLINICAL SIGNIFICANCE: The incorporation of nanostructured hydroxyapatite increases the adhesive properties and may be a promising filler for adhesive resin.

Niobium pentoxide as a novel filler for dental adhesive resin.

OBJECTIVES: The purpose of this study was to develop an adhesive resin with incorporation of niobium pentoxide and evaluate its properties. METHODS: Niobium pentoxide was characterised by X-ray diffraction, surface area, particle size, micro-Raman, scanning electron microscopy and the effectiveness of silanisation process by Fourier Transform Infrared (FTIR). An experimental adhesive resin was formulated with 0, 5, 10 and 20wt% Nb(2)O(5). The formulated adhesive resins were evaluated based on microhardness, degree of conversion, radiopacity and interface (resin/dentine) characterisation by micro-Raman. RESULTS: The particles used in this study presented a monoclinic crystalline phase with typical chemical groups and micrometre mean size. Microhardness and radiopacity increased with higher amounts of Nb(2)O(5), and the particles were able to penetrate into the hybrid layers. CONCLUSIONS: Therefore, Nb(2)O(5) may be an alternative for polymer-based biomaterials. CLINICAL SIGNIFICANCE: Niobium pentoxide could be used to produce adhesive resins with enhanced properties.

Projeto, fabricação e avaliação de implantes craniofaciais personalizados: proposta de utilização de materiais combinados / Design, production and evaluation of customized craniofacial implants: an approach on the use of different materials

Um material adequado para a reconstrução óssea craniofacial deve ser simples de implantar, possuir forma adequada, resistência à fratura e à deformação similares ao osso original, ser eventualmente substituído por osso natural, ser largamente disponível e não possuir um custo muito elevado. Baseado no fato de que um material com todas estas características ainda não está disponível atualmente, torna-se importante buscar novos materiais, novas composições e novas conformações. Diferentes biomateriais são utilizados atualmente para cirurgias de reconstrução craniofacial, cada um apresentando suas vantagens e limitações. Entre eles destacam-se o titânio, o polimetilmetacrilato e os cimentos de fosfato de cálcio. O titânio apresenta difícil conformação; o polimetilmetacrilato polimeriza-se por meio de uma reação exotérmica, podendo causar necrose de tecidos adjacentes ao implante; o cimento de fosfato de cálcio, por sua vez apresenta certa fragilidade, característica de alguns materiais cerâmicos. Neste sentido, este estudo examinou diferentes materiais utilizados para reconstrução craniofacial e suas propriedades mecânicas quando submetidos a ensaios de flexão, como o polimetilmetacrilato, o cimento de fosfato de cálcio e o cimento de fosfato de cálcio reforçado com titânio. Foi verificada a melhoria de propriedades mecânicas do cimento de fosfato de cálcio quando reforçado com malha de titânio. Além disso, este estudo apresenta uma técnica para o projeto e fabricação de implantes craniofaciais personalizados utilizando cimento de fosfato de cálcio reforçado com titânio, validada através de quatro casos de indicação cirúrgica de reconstrução craniofacial.

A material suitable for craniofacial reconstruction must be easy to implant, have the appropriate shape, have the strength and deformation similar to the original bone, be eventually substituted for natural bone, be widely available and present affordable costs. As such as material, with all theses characteristics is still not available, it is important to search for new materials, new compositions and new design. Different biomaterials are used nowadays for craniofacial reconstruction surgeries, each one presenting its advantages and limitations. Among these materials are the titanium, the poli(methilmetacrilate) and the calcium phosphate cements. Titanium presents hard conformation; poli(methilmetacrilate)’s polymerization reaction is exothermic, which may cause necrosis of the adjacent tissues; calcium phosphate cement is brittle, an usual characteristic of ceramic materials. In this way, this study evaluated different materials used for craniofacial reconstruction and its mechanical properties when submitted to bending test, such as poli(methilmetacrilate), calcium phosphate cement and calcium phosphate cement reinforced with titanium. It was verified the improvement in the mechanical properties of the calcium phosphate cement when reinforced with titanium mesh. In addition, this study presents a method for design and manufacturing of customized craniofacial implants using calcium phosphate cement reinforced with titanium mesh, validated through four cases of craniofacial reconstruction surgery indication.

Electrostatic painting residues as an alternative raw material for red clay industry.

In this study, the viability of using electrostatic painting residues--paint sludge--as a raw material to the red clay industry was investigated. Red clay-based ceramic masses containing electrostatic paint residues were formulated during the study. The clays were obtained from the Rio do Rastro deposit, in Gravataí, and were of the standard formulation used in industry. Different ceramic mass formulations with additions of 0.5, 1.0, 2.5 and 5.0 wt.% electrostatic painting residue in addition to a formulation with no residue addition (standard formulation), were evaluated. The samples were uniaxially pressed in a double-effect press and were fired in an electric oven at 900, 950 and 1000 degrees C. The firing at constant temperature lasted 8 h, and heating rate was 150 K h(-1). After processing the samples were characterized in terms of their physical and mechanical properties. Environmental compatibility was also considered by the evaluation of gaseous emissions and leaching and solubilization tests according to the Brazilian standards NBR 10.005 and NBR 10.006, respectively. The results showed that it was possible to produce ceramic materials containing electrostatic painting residues within their formulations.

Método alternativo para fabricação de cabeça femoral cerâmica para próteses de quadril / Alternative manufacture method for ceramic femoral ball head applied in hip prostheses

O aumento da expectativa de vida da população e o crescente número de acidentes automobilísticos com lesões graves têm aumentado mundialmente o número de cirurgias de artroplastia total de quadril. A maior parte das cirurgias ortopédicas realizadas utiliza próteses com articulação cabeça/acetábulo tipo metal/polímero que tem demonstrado altos índices de falhas. A falha de um implante de quadril geralmente está associada ao processo de desgaste na articulação que libera partículas dos materiais envolvidos, causando reações biológicas de infecção e a perda de fixação do implante. Alumina tem sido utilizada com sucesso como cabeça femoral na indústria biomédica mundial. No entanto para a conformação de esferas cerâmicas, tem-se recorrido quase que sem exceção à prensagem isostática a quente, que exige alto custo em equipamentos e operação. Este estudo apresenta um processo alternativo de conformação de cabeças femorais cerâmicas. Este novo processo de fabricação de cabeças femorais cerâmicas para prótteses de quadril apresenta redução de custo considerável em comparação com a prensagem isostática a quente. O objetivo é apresentar um processo que permita chegar próximo ao formato final da peça. Isto traz como benefício redução de volume de material removido por desgaste e polimento promovendo aumento da produtividade. Aqui alguns critérios de seleção da alumina, complexidade do componente e viabilidade de execução foram abordados Neste trabalho foi possível a fabricação de componentes de quadril via processo de prensagem flutuante de duplo efeito. Os corpos cerâmicos obtidos apresentaram propriedades que satisfazem às exigências da norma ABNT NBR-ISO 6474 em termos de densificação, tamanho médio de grão e resistência mecânica.