Cimento sulfoaluminoso em ativação alcalina: caracterização e modelização de reações em sistemas híbridos

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Civil, Florianópolis, 2020.Esta pesquisa insere-se num contexto de elevada demanda por materiais ecoeficientes que permitam aplicações principalmente de ligantes com baixo teor de CO2. Ligantes de características híbridas podem ser desenvolvidos com a valorização de precursores de subprodutos industriais. O cimento sulfoaluminoso (CSA) se apresenta como um ligante ecoeficiente promissor, apresentando os principais compostos de ye?elimita, sulfato cálcico e belita que tem como principal produto de hidratação a etringita e AH3. A presença deste ligante em meios alcalinos pode afetar na estabilidade da formação da etringita. A ativação alcalina é composta por minerais aluminossilicatos e uma solução alcalina, os principais compostos de reação para resíduos contendo baixo teor de cálcio são os géis N-A-S-H. A originalidade desta pesquisa está na realização de caracterização da hidratação de composições híbridas entre cimentos sulfoaluminosos, comercializados na Europa, e diferentes resíduos (cinza volante, cinza pesada e lama vermelha) ativadas alcalinamente, visando identificar seus compostos formados nestes sistemas. Inicialmente foi avaliado o comportamento das fases mineralógicas do clínquer de CSA em diferentes fontes de sulfatos e do cimento em diferentes fontes de álcalis, analisando as fases da hidratação destas pastas, enquanto a segunda etapa avaliou a aplicação de cimentos híbridos compostos de cimento CSA e cinza volante, cinza pesada e lama vermelha, ativados. Por fim foram avaliadas as propriedades de argamassas híbridas binárias de cimento CSA com cinza pesada e lama vermelha. Ao utilizar álcalis na hidratação de cimento CSA foi observado aceleração de cinética para moderadas alcalinidades (0,1 M e 1 M), formando maiores conteúdos de etringita e AH3, responsáveis pelo aumento de resistência mecânica, já elevadas alcalinidades (4 M e 8 M) resultaram na formação de monosulfatos (fase-U) e tenardita, reduzindo a propriedade mecânica devido aumento de porosidade. Dentre os sais sólidos o silicato sódico contribuiu para aumento das resistências devido aumento de silicato na pasta, favorecendo formação de estratlingita, que resultou num maior preenchimento de poros do sistema. Para as pastas híbridas, 1 M de NaOH apresentou melhores resultados de aceleração de reações e ganho a longo prazo de resistência mecânica. Curas em temperaturas elevadas afetaram negativamente as resistências devido solubilização da etringita. Para todas as argamassas foram observadas baixa variação dimensional, mesmo com altas substituições (50% de resíduos). Substituições de 10% de resíduo apresentaram propriedades capilares similares a referência. Todas as amostras apresentaram ótima resistência à sulfatos, exceto argamassas produzidas com 50% de lama vermelha e ativadas com 1M de NaOH, devido rápida reatividade inicial provida pelo aumento de alumina fornecido pela lama vermelha. Os produtos híbridos de cimento sulfoaluminoso com resíduos elaborados neste trabalho apresentaram desempenho mecânico e durável similares ao do cimento sulfoaluminoso puro, com um maior apelo sustentável permitindo elevadas substituições de cimento por resíduos.Abstract: This research is inserted in a context of high demand for eco-efficient materials that allow applications mainly of binders with low CO2 content. Hybrid binders can be developed with the enhancement of precursors of industrial by-products. Calcium sulfoaluminate (CSA) cement is a promising eco-efficient binder. The main CSA phases are ye?elimite, calcium sulfate and belite whose main hydration product is ettringite and AH3. CSA in presence of alkaline media can affect the stability of the ettringite formation. Alkali activation is composed of aluminosilicate minerals and an alkaline solution, the main reaction product for aluminosilicate with low calcium content are N-A-S-H gels. The originality of this research is the characterization of the hydration of hybrid compositions of sulfoaluminate cement, commercialized in Europe, and different alkali activated residues (fly ash, bottom ash and red mud), aiming to identify its compounds formed in these systems. Initially, the mineralogical phases of CSA clinker in different sources of sulfates and cement in different sources of alkalis were evaluated, analyzing the hydration phases of the pastes. The second stage evaluated the application of hybrid cement composed of CSA cement and alkali activated fly ash, bottom ash and red mud. Finally, the properties of binary hybrid cement mortars with bottom ash and red mud were evaluated. When using alkalis to hydrate CSA cement, acceleration of kinetics for moderate alkalinities (0.1 M and 1 M), higher ettringite and AH3 formation was observed, increasing mechanical strength. For high alkalinity (4 M and 8 M) monosulfate (U-phase) and thenardite formation was observed, reducing mechanical strength due higher porosity. Among the solid salts, sodium silicate contributed to increase the strength due to the increase of silicate in the paste, favoring the formation of strätlingite, which resulted in a greater filling of pore of the system. For hybrid pastes, 1M NaOH presented better results in acceleration reactions and gain in long-term mechanical strength. Cures at elevated temperatures negatively affected the mechanical strength due to the ettringite solubilization. For all mortars, low dimensional variation was observed, even with high replacement (50% of residues). 10 % replacement presented similar capillary properties as reference. All samples showed excellent resistance to sulfates, except mortar produced with 50% of red mud and activated with 1M NaOH, due to the rapid initial reactivity provided by the increase in alumina. The hybrid products of sulfoaluminate cement with residues elaborated in this work presented similar mechanical and durability performance as pure sulfoaluminate cement. Hybrid products improve the sustainable appeal allowing high replacement of cement for residues

Desenvolvimento de argamassas autonivelantes com ativação alcalina de precursores residuais

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Civil, Florianópolis, 2016.Utilizar novas classes de ligantes cimentícios se faz recorrente atualmente, sendo os cimentos ativados alcalinamente, com valorização de percursores residuais, um tema que necessita de maiores pesquisas e investigações. Estes cimentos são formados a partir da ativação de minerais aluminossilicatos amorfos em soluções alcalinas. Resíduos industriais como cinza pesada (CZP) são utilizados como minerais aluminossilicatos em ativações alcalinas, motivando uma valorização dos mesmos. Para solução ativadora são difundidos os hidróxidos de sódio, potássio e silicatos solúveis. Nesta pesquisa foi realizado estudo de ativações alcalinas hibridas, em razão da baixa reatividade apresentada para ativações apenas para CZP, foram realizadas misturas binárias com cimento Portland (CP) nas proporções de 2,5, 5, 10 e 30% de substituição de CZP moída por 540? e calcinada a 600°C por CP e ternárias, substituindo na porcentagem de 10% de CP por cinza de casca de arroz (CCA) em 25, 50 e 75%. A cura foi feita em estufa a 80°C por 24 horas. Buscou-se obter composições que pudessem ser aplicadas em argamassas autonivelantes para uso em sistemas de revestimento de pisos. Para tanto, foram analisados os comportamentos de espalhamento em estado fresco das argamassas para a obtenção de um material autonivelante (espalhamento > 250 mm). No estado endurecido para as misturas binárias foi observado maiores resistências à tração na flexão e à compressão para maiores presenças de CP, amostra contendo 30% de CP obteve resistência de 7,53 MPa à tração e 33,5 MPa à compressão, entretanto o acréscimo de cimento acarretou em maiores perdas de trabalhabilidade e espalhamento. Foram realizadas análises por meio das técnicas de DRX e MEV, observando formação de géis N-A-S-H e (N,C)-A-S-H. Nas ternárias observou-se decréscimo de resistência à tração e à compressão para maiores substituições de CCA. Para todas as amostras constatou-se durabilidade similares as de argamassas comuns, havendo melhores resultados para ensaios de ataques ácidos, devido menores quantidades de cálcio. Houve menores valores de retração linear e empenamento de placas, absorção capilar e porosidade aberta para as ativações alcalinas quando comparadas a cimento Portland comum, havendo incremento da porosidade com o acréscimo da substituição de CP. Por fim, constatou-se a viabilidade na produção de produto autonivelante nas composições de ativações alcalinas híbridas binárias de CZP e CP, sendo a melhor mistura a contendo 10% de CP.<br>Abstract : Using new classes of cementitious binders is frequently today, the alkali-activated cements with residual precursors valorization is a topic that needs further research and investigation. These cements are formed from aluminosilicate minerals amorphous activated in an alkaline solution. Industrial waste, as bottom ash (CZP) are used as aluminosilicate minerals in alkaline activation, encouraging their valorization. Sodium and potassium hydroxides and sodium silicate are used as activating solution. This research was conducted of hybrid alkaline activation, due low reactivity presented from bottom ash, binary mixtures were made of bottom ash and Portland cement in proportions of 2.5%, 5%, 10% and 30% substitution of bottom ash grounded 450? and calcined 600°C of Portland cement, for ternary mixtures CP was replaced by rice husk ash (CCA) in proportions of 25%, 50% and 75% of Portland cement to rice husk ash, to the reference of binary 10% OPC (Ordinary Portland Cement). Curing was at 80°C for 24 hours. Was attempted to obtain compositions that could be applied in self-leveling mortars for coating systems. To this end, the spreading behavior were analyzed in the fresh mortar to obtain a self-leveling material (spreading > 250 mm). In the hardened state for binary mixtures was observed in greater tensile and compressive strength for higher CP amount, mortars with 30% CP obtained tensile resistance of 7,53 MPa and to compressive strength 33.5 MPa, however, the cement increasing resulted workability and spreading losses. Techniques SEM and XRD analyses were performed to observing the formation of N-A-S-H and (N,C)-A-S-H gels. In ternaries mixtures were observed resistance decrease with higher substitutions of CCA. For all samples were founded similar durability, with better results for acid attack test when compared with normal mortars, due lower amount of calcium. There were lower values of linear shrinkage, curling, capillary absorption and open porosity for alkaline activations compared to ordinary Portland cement, with increasing porosity with higher replacement of CP. Finally, it was viable the production of self-leveling products in the composition of binary hybrid alkaline activation of CZP600 and CP. The best mixture was the binary containing 10% CP

Development of Alkaline-Activated Self-Leveling Hybrid Mortar Ash-Based Composites

This study investigated the reactivity properties of self-leveling hybrid alkali-activated cements, such as ordinary Portland cement (OPC) and its residual precursors, coal bottom ash (BA), and rice husk ash (RHA). Due to the relatively low reactivity of BA, binary mixes were produced with OPC using contents of 2.5&ndash;30% in the treated BA samples. Furthermore, ternary mixes were prepared in proportions of 25%, 50%, and 75% with RHA as a replacement material for the OPC (mix with 90%:10% BA:OPC). For all of the mixes the spreading behaviors were fixed to obtain a self-levelling mortar, and dimensional changes, such as curling and shrinkage, were performed. Mortars with 30% OPC reached a compressive strength of 33.5 MPa and flexural strength of 7.53 MPa. A scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were used to indicate the formation of N-A-S-H and a (N,C)-A-S-H gel, similar to the gel with trace of calcium. The best performance was achieved when the binary mix produced 10% OPC. A hybrid mortar of OPS-BA presented 10 times lower susceptibility to curling than an OPC mortar. The results showed that both ashes reduced the shrinkage and curling phenomena

Development of self-compacting concretes using rice husk or fly ashes and different cement types

Abstract Self-compacting concretes (SCCs) are considered promising materials in the civil engineering field. Their main characteristic is the ability to compact only through gravitational force. Mineral additions such as rice husk ash (RHA) and fly ash (FA) are recommended to be used in SCCs during their mix designing, in order to increase fluidity and mechanical strength. These materials are also considered wastes from industry, without a certain destination, which contributes to environmental pollution. In this study, four mixtures of SCC were tested using RHA and FA with two different types of Portland cement, CEM CP IV and white CEM. For the fresh state tests, all of the SCCs mixtures showed satisfactory results. The SCCs with white CEM showed higher mechanical strength at 7 days than CEM CP IV. Analyzing the mineral additions, their use improved the mechanical strength of SCCs at 28 days, there is also observed a higher pozzolanic effect to RHA

Efecto del pH en la hidratación de cementos sulfoaluminosos-belíticos

Resumen del trabajo presentado a las I Jornadas de Jóvenes Científicos en Materiales de Construcción, celebradas en la Universidad Carlos III de Madrid del 18 al 19 de junio de 2018

Effect of alkaline salts on calcium sulfoaluminate cement hydration

This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (NaSO, NaCO, and NaSiO) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. NaSO induces cracking in the ≥28-d pastes due to posthardening gypsum and ettringite formation from the excess SO present. Anhydrite dissolves more rapidly in the presence of NaCO, prompting carbonation. NaSiO raises compressive strength and exhibits strätlingite as one of its reaction products.This study was partially supported by the Brazilian National Council for Scientific and Technological Development (CNPq) under projects 208380/2017‐5 and 151890/2020‐0, and CAPES. Financial support was also furnished by the Spanish Ministry of the Economy and Competitiveness and FEDER under research project BIA2016‐76466‐R and funding from BES‐2017‐082022. PhD. student Pilar Padilla‐Encinas thanks the Autonomous University of Madrid for the opportunity to complete her thesis in its Applied Chemistry program. The cement supplied by Heidelberg Cement Hispania is gratefully acknowledge

A Review of the Use of Natural Fibers in Cement Composites: Concepts, Applications and Brazilian History

The use of natural lignocellulosic fibers has become popular all over the world, as they are abundant, low-cost materials that favor a series of technological properties when used in cementitious composites. Due to its climate and geographic characteristics, Brazil has an abundant variety of natural fibers that have great potential for use in civil construction. The objective of this work is to present the main concepts about lignocellulosic fibers in cementitious composites, highlighting the innovation and advances in this topic in relation to countries such as Brazil, which has a worldwide prominence in the production of natural fibers. For this, some common characteristics of lignocellulosic fibers will be observed, such as their source, their proportion of natural polymers (biological structure of the fiber), their density and other mechanical characteristics. This information is compared with the mechanical characteristics of synthetic fibers to analyze the performance of composites reinforced with both types of fibers. Despite being inferior in tensile and flexural strength, composites made from vegetable fibers have an advantage in relation to their low density. The interface between the fiber and the composite matrix is what will define the final characteristics of the composite material. Due to this, different fibers (reinforcement materials) were analyzed in the literature in order to observe their characteristics in cementitious composites. Finally, the different surface treatments through which the fibers undergo will determine the fiber&ndash;matrix interface and the final characteristics of the cementitious composite