Resumo em Inglês:

Abstract Alkali-activated binders represent a promising alternative for reducing the high carbon dioxide emissions associated with the cement industry. However, the influence of chemical admixtures on the workability of these materials remains insufficiently explored. This study aimed to evaluate the effect of surfactant admixtures on alkali-activated pastes composed of fly ash, basic oxygen furnace (BOF) steel slag, sodium hydroxide, and sodium silicate. Workability was assessed using the Kantro mini-slump test, alongside measurements of setting time and compressive strength. The polycarboxylate-based admixture (ADT1) and the sulfonated salt-based admixture (ADT2) improved the consistency of the material, with optimal dosages of 3% for ADT1 and 5% for ADT2, resulting in increases in mini-slump spread of 18% and 25%, respectively. The initial setting time was reduced by up to 50 minutes with the use of 5% ADT2, acting as an accelerator, while 3% of ADT1 presented a lower impact on setting time. However, compressive strength decreased by 33% with ADT1 and 27% with ADT2. Overall, ADT2 yielded better performance across all evaluated properties compared to ADT1.

Resumo em Inglês:

Abstract The construction sector faces increasing pressure to adopt sustainable practices and reduce reliance on non-renewable and high-impact materials. This study investigates the incorporation of carnauba fibers (CFs), an abundant lignocellulosic by-product of the wax extraction industry, as reinforcement in cement-based rendering mortars. Both untreated and Ca(OH)2-treated fibers were evaluated at volume fractions of 0.5%, 1.0%, and 1.5%. A comprehensive characterization of the fibers was conducted, including physical, mechanical, spectroscopic (FTIR), structural (XRD), and thermal (TGA) analyses, to assess the effects of alkali treatment on their morphology and performance. Results demonstrated that fiber addition led to significant improvements in fresh and hardened properties of the mortars. Treated CFs exhibited increased crystallinity and reduced hemicellulose and lignin content, promoting superior fiber-matrix bonding. In the fresh state, mortars with CFs showed decreased workability and air content, accompanied by increased water retention - particularly in treated formulations. In the hardened state, mortars reinforced with CFs displayed enhanced compressive strength, lower shrinkage, and reduced elastic modulus, indicating improved toughness and energy dissipation capacity. Tensile Bond Strength was notably improved by treated fibers, meeting technical standards for both internal and external applications. The findings underscore the technical viability and environmental relevance of incorporating treated carnauba fibers into cementitious mortars, offering a low-cost, renewable alternative to synthetic reinforcements. This work contributes to the circular economy by valorizing agricultural residues and aligns with global efforts towards sustainable construction materials.

Resumo em Inglês:

Abstract The reuse of mining wastes in ceramic production represents an important strategy for reducing environmental impacts while adding value to industrial by-products. Although black tourmaline has been explored in other ceramic and functional applications, its potential use in porcelain stoneware remains unexplored. In this context, the present study investigates the feasibility of incorporating black tourmaline-rich waste (WOS) as a partial substitute for feldspar in porcelain stoneware formulations, contributing to the sustainable management of mining residues. The waste was processed, characterized, and incorporated at levels ranging from 0 to 5 wt%, and the ceramic bodies were fired at 1150, 1175, and 1250ºC. Physical-mechanical properties, including linear shrinkage, water absorption, apparent porosity, flexural strength, and apparent density, were evaluated, complemented by SEM and XRD analyses. The results demonstrated that the waste is suitable as a ceramic raw material, with bodies containing higher waste contents fired at 1250ºC exhibiting properties compatible with the requirements of ISO 13006:2018, ISO 10545-3:2014, and ISO 10545-4:2014 for porcelain stoneware. These findings highlight the potential of black tourmaline-rich waste as an alternative raw material for high value-added ceramic applications and reinforce the role of traditional ceramics in advancing sustainable and circular production practices.

Resumo em Inglês:

Abstract This study presents an experimental and numerical investigation of the structural performance of masonry built with Extruded, Pressed, and Fired Ceramic Blocks (BCEPQ), an emerging class of units for structural masonry systems. Despite their potential advantages, the mechanical behavior of BCEPQ units assembled through dry interlocking remains largely unexplored. An extensive experimental program was conducted, including physical and mechanical characterization of the blocks, compressive testing of prisms and small walls, and full-field deformation measurements using Digital Image Correlation (DIC). The blocks exhibited a characteristic compressive strength of 4.86 MPa and water absorption of 22.83%, while prisms and small walls reached average compressive strengths of 1.66 MPa and 0.98 MPa, respectively, with brittle failure modes governed by stress concentration and interface effects. A three-dimensional finite element model was developed in ANSYS 2024 R1 using experimentally obtained properties and linear elastic assumptions. Numerical results reproduced the main trends observed experimentally, with an average discrepancy of approximately 20%, confirming the exploratory nature of the model. The study provides unprecedented experimental data on BCEPQ masonry, highlights structural limitations associated with mortarless assembly, and offers technical insights to support future improvements in block geometry, manufacturing processes, and computational modeling of ceramic masonry systems.

Resumo em Português:

Resumo Preocupações ambientais têm ganhado destaque devido à persistência de contaminantes orgânicos emergentes, como fármacos presentes em corpos d’água. Dentre os antidepressivos, a fluoxetina (FLX) é amplamente prescrita e se destaca por sua estabilidade à luz visível. Nesse contexto, a busca por métodos eficientes para a eliminação da FLX torna-se essencial para reduzir seu impacto nos ecossistemas. Este estudo avaliou estruturas porosas de ZnO, produzidas pela técnica de réplica, e submetidas à radiação UV em um reator fotoquímico, com o objetivo de analisar a fotodegradação da fluoxetina por processos oxidativos. Para a análise, foi utilizada cromatografia (HPLC UV-VIS). A presença do ZnO aumentou a taxa de remoção do fármaco em aproximadamente 20-30% nos primeiros 15 minutos de exposição, partindo de uma concentração de 10 mg/L, comparado à fotólise. Após 45 minutos, a fluoxetina foi completamente transformada em subprodutos, com comprovação do potencial de reuso dos corpos cerâmicos porosos obtidos.

Resumo em Inglês:

Abstract The use of waste materials for the production of construction materials is a sustainable alternative to their disposal, as well as a way of reducing the environmental impact of producing the materials. Geopolymer is a promising building material with attractive properties. Rice husk ash (RHA) is a potentially polluting waste material that, due to its properties, can be used to produce geopolymers. This study investigates the hardening behaviour of geopolymer mortars, incorporating up to 20 wt.% rice husk ash in the geopolymer formulations. After 28 days of curing, the samples were tested for mechanical and physical properties. Statistical analysis of the results revealed significant differences between the samples. In addition, the results showed an increase in the mechanical strength of the geopolymer mortars, reaching a value of 43.29 MPa with the simultaneous replacement of 20% metakaolin and sodium silicate with rice husk ash. The highest compressive strength reached 47.75 MPa, corresponding to an increase of 52.4% compared with the reference mixture.

Resumo em Inglês:

Abstract This study investigates the effect of incorporating eggshell ash (ESA) into 1:3 mortars and its influence on physical, mechanical, and microstructural properties. Mortars were prepared with 0%, 5%, and 10% ESA additions relative to cement weight. Characterization techniques included XRD, SEM, compressive and flexural strength tests, modulus of elasticity, and porosity analysis. Results demonstrated that 5% ESA enhanced early and 28-day compressive strength (31.34±1.14 MPa), reduced porosity (27.95%), and improved microstructure continuity, indicating nucleation and filler effects. In contrast, 10% ESA promoted excess Ca(OH)2 and ettringite formation, increasing heterogeneity and decreasing performance (26.61±1.80 MPa). XRD confirmed secondary phase formation, and SEM images corroborated matrix densification at optimal dosage. The findings suggest that ESA is a viable, eco-friendly additive, with 5% representing an optimal content that maximizes performance without compromising durability. Excess ESA (>10%) may impair mechanical behavior due to calcium oversaturation and porosity increase, highlighting the need for dosage control.

Resumo em Inglês:

Abstract Polycrystalline diamond (PCD) is widely used in cutting and drilling tools but faces challenges, including graphitization and environmental and health concerns related to its traditional binders, such as cobalt. This study explores the route to obtaining PCD composites using niobium and tantalum as alternative binders, evaluating composites with 15 wt% binder sintered via HPHT at 1650ºC, 1750ºC, and 1850ºC under 7.7 GPa. The starting powders and milled mixtures were characterized by XRD, particle size analysis, and SEM, while the sintered samples were subjected to densitometry and Brazilian disk compression tests. The samples containing tantalum showed higher densification and compressive strength than those containing niobium, and these properties increased with temperature. Low levels of graphitization were detected, but with negligible impacts on the properties analyzed, indicating these compositions through the HPHT route are promising and more sustainable alternatives to conventional PCD.

Resumo em Inglês:

Abstract Red ceramic production in the Pindaré Valley (Brazil) is affected by raw material variability linked to the geological transition between the Itapecuru and Barreiras formations. This study characterizes representative horizons of “fat” (high-plasticity) and “lean” (sandy) clays to support the shift from empirical practice to rational processing. Mineralogical analysis (XRD and FTIR) identified kaolinite as the predominant mineral, alongside illite, montmorillonite, and accessory phases, which dictate plasticity, sintering, and mechanical strength. Chemical and physical properties were evaluated via XRF, particle size analysis, Atterberg limits, TGA, and SEM. Technological tests on specimens fired at 950 and 1050ºC assessed water absorption, porosity, shrinkage, and flexural strength. Results revealed marked heterogeneity, with plasticity indices ranging from 13.25% to 39.24%. “Fat” clays exhibited higher strength (up to 29.79 MPa) and lower absorption, while “lean” clays provided superior dimensional stability. All samples met the requirements for bricks and roof tiles. The findings indicate that optimized blending of fat and lean fractions is key to enhancing industrial performance and overcoming the limitations of current empirical mixing methods.

Resumo em Inglês:

Abstract Additive manufacturing (AM) via vat photopolymerization (VPP) applied to alumina has emerged as a promising method for fabricating ceramic parts with complex geometries. Proper slurry formulation, comprising photosensitive resin, ceramic powder, and additives, is essential to ensure structural integrity and high densification after sintering. Solid loadings above 40% v/v are desirable, although they present rheological challenges. In this study, high-purity AKP-53 alumina (D50 = 0.17 µm) was employed; its high reactivity enables sintering at approximately 1400 °C but demands higher organic content due to its fine particle size. A ceramic suspension with over 40% v/v solids was formulated using n-methyl-2-pyrrolidone as the solvent. The resulting green bodies exhibited cohesion, no delamination, and high densification. As a proof of concept, an aircraft engine shroud was manufactured, validating the process for producing high-complexity structural ceramic components.

Resumo em Inglês:

Abstract This study proposes a new experimental methodology, called DCP (Degradation by Capillarity and Precipitation), to evaluate the durability of clayey soils stabilized with cement and lime in tropical environments. The method combines rainfall (artificial) and capillary suction, simulating environmental conditions more representative than traditional tests. Specimens with 6% and 10% binder stabilizer content were tested under four conditions: wetting-drying cycles, capillary rise, artificial rainfall, and the combined DCP condition. Indirect tensile strength tests were performed to assess mechanical response. Results show that the DCP methodology leads to different deterioration patterns and lower strength values, without direct correlation to mass or volume loss. This indicates that volumetric stability alone is insufficient to assess performance and that tropical environmental conditions significantly influence behavior. The DCP methodology complements traditional evaluations and improves predictions of long-term performance based on the geomechanical behavior of stabilized soils in road infrastructure and geotechnical applications.

Resumo em Português:

Resumo O objetivo desse trabalho foi verificar a possibilidade de aplicação da Terra de Shredder (TSH) e da Terra de Sucata (TS), geradas em usinas semi-integradas do setor siderúrgico durante o processo de fabricação do aço, como matérias-primas na composição da massa para a produção de placas cerâmicas que podem ser utilizadas como revestimento de pisos e paredes. Para tanto, foram analisados os comportamentos dos materiais, assim como sua interação com dois aditivos, denominados nesse estudo como Argila A e Argila B. Os corpos de prova foram submetidos a ensaios visando determinar a resistência mecânica à flexão, a retração linear e a absorção de água, e os resultados obtidos foram comparados com os valores estabelecidos em norma, desejáveis para placas cerâmicas. Existe um grande potencial para o uso das terras de sucata pela indústria cerâmica, pois as composições com 75% de terras de sucata (TSH + TS) e 25% de argilas proporcionaram cerâmicas que atendem aos valores normativos e àqueles encontrados na literatura, referentes ao módulo de ruptura à flexão (R > 20 MPa), à retração linear (RL < 10%), e à absorção de água (AA < 10%).

Resumo em Inglês:

Abstract This study developed and characterized photocatalytic coating mortars incorporating titanium dioxide (TiO2) and evaluated their efficiency in pollutant degradation and environmental impact. Mortar mixtures containing 0%, 2%, 4%, 6%, and 10% TiO2 by cement weight were analyzed with respect to structural, microstructural, and photocatalytic properties. Performance was assessed through methylene blue degradation under UV light, supported by UV-Vis spectrophotometry, SEM, and XRD analyses. The results showed that higher TiO2 concentrations enhanced photocatalytic efficiency, particularly in the degradation of organic compounds. It was concluded that the developed mortars exhibit strong potential for application on urban building facades, offering benefits such as self-cleaning capability, reduced maintenance costs, and improved air quality, thereby contributing to sustainability in the construction sector.

Resumo em Inglês:

Abstract This study aims to enhance porcelain’s physicochemical properties by adding glass powder as flux. Kaolinitic clay, sand, and glass powder were used to formulate six grades, fired between 1140-1260ºC for 2 h. Specimens were tested for shrinkage, mass loss, water absorption, density, porosity, and mechanical strength (three-point bending). Phases were identified by X-ray diffraction and compared with industrial porcelain. The incorporation of glass powder has enabled the reduction of the firing temperature, the enhancement of densification, the augmentation of mechanical properties, and the valorizations of glass waste. The grade with 20 wt% glass (P20) fired at 1220ºC (P20-122) showed the best results: 13% shrinkage, 3.93wt% mass loss, 0.2wt% water absorption, 0.4% porosity, density 2.4 g/cm3 (46.6%). Using glass powder not only improves porcelain quality but also contributes to recycling glass waste on an industrial scale.

Resumo em Inglês:

Abstract This work presents the synthesis and characterization of niobium pentoxide (Nb₂O₅) obtained by combustion reaction, as well as its application as a heterogeneous catalyst in the production of biodiesel via simultaneous transesterification and esterification reaction (TES). The choice of Nb2O5 is justified by the fact that it is a material with wide applications, as a catalyst for biodiesel production; few reports in the literature can be explored. The vast majority of natural Nb2O5 is extracted in Brazil, in the city of Araxá in Minas Gerais (MG) by the Brazilian Metallurgy and Mining Company (CBMM), as it holds 98.2% of the world’s reserves. The synthesis of Nb2O5 was carried out on a laboratory scale using urea as fuel and niobium ammonium oxalate as precursor. The material obtained was characterized by XRD, FTIR, DG, BET, and SEM, showing a polyphasic structure (T-orthorhombic and TT-pseudohexagonal), polydisperse particle size distribution, surface area of 14.59 m2·g, and predominance of mesopores with a mean diameter of 7.16 nm. Subsequently, Nb2O5 was applied as a catalyst in the production of biodiesel from soybean vegetable oil and residual frying oil, using ethanol and methanol. The conversions into ethyl and methyl esters, densities, and acidity values were analyzed and compared with the standards of the National Petroleum Agency (ANP). The highest conversions were observed for soybean oil using methanol (34.74±0.79%) and residual frying oil using methanol (42.54±1.09%). Although the parameters obtained were below regulatory requirements, the results demonstrated the potential of Nb2O5 as an efficient and low-cost catalyst. The production of biodiesel using alternative and renewable materials highlights the feasibility of applying Nb2O5 in sustainable processes, with the possibility of future optimizations in synthetic routes and reaction conditions.

Resumo em Inglês:

Abstract Mullite is an aluminosilicate of great technological importance, characterized by its high-performance refractory properties, which enable its use in both traditional and advanced applications. This review provides an overview of the crystalline structure of mullite, describes its nucleation process and kinetics, and explores synthesis strategies that enable its formation at lower temperatures, along with notable application examples reported in recent literature. Special attention is given to the use of iron ore tailings (IOTs) as a raw material for mullite production, highlighting an economically viable and environmentally friendly alternative that adds value to these materials. The paper further analyzes the synthesis methods employed and the mechanical properties of the resulting ceramics as a function of composition and IOTs content, as well as their potential applications, with particular emphasis on the construction sector.