Navegando por Autor "Nunes, Vitor Alencar"

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    Compatibilidade e aderência entre argamassa de reparo álcali-ativada reforçada com fibra e substrato de concreto
    (Centro Federal de Educação Tecnológica de Minas Gerais, 2018-01-15) Nunes, Vitor Alencar; Borges, Paulo Henrique Ribeiro; Zanotti, Cristina; http://lattes.cnpq.br/2894639825694344; http://lattes.cnpq.br/5399317473703342; http://lattes.cnpq.br/5525081275110037; Borges, Paulo Henrique Ribeiro; Zanotti, Cristina; Ludvig, Peter; Gutiérrez, Ruby Méjia de
    O reparo de estruturas de concreto é uma tarefa complexa que requer um conhecimento especial de regulamentos e normas técnica de construção, mecanismo de deterioração, princípios e métodos de reparo, materiais de reparo, execução de trabalhos de reparo, inspeções, monitoramento e manutenção. Até o momento, as argamassas de reparo mais utilizadas se dividem em duas categorias, (i) as argamassas baseadas em ligantes inorgânicos (cimento Portland) e (ii) as baseadas em ligantes orgânicos (polímeros). Pesquisas recentes revelam uma terceira categoria de argamassas com alto potencial para serem utilizadas como reparo de concreto; as argamassas álcali-ativadas. Os materiais álcali-ativados (MAA) vêm sendo amplamente promovidos como um ligante mais verde para construções sustentáveis. Estes ligantes podem ser obtidos a partir da ativação alcalina de uma ampla variedade de aluminossilicatos para a produção de componentes endurecidos. Este estudo, portanto, visa avaliar a compatibilidade e a aderência entre argamassas álcali-ativadas reforçadas com fibra e um substrato de concreto. Diferentes formulações de MAA foram inicialmente estudadas, com base na ativação alcalina de metacaulim (MK) e de escória do alto-forno (BFS); suas propriedades mecânicas e seu módulo de elasticidade foram avaliados. Cinco formulações foram selecionadas para a produção de argamassas de reparo e aplicação sobre substratos de concreto. Uma fração 0,25% de fibra de PP foi utilizada para mitigar a retração em pequenas idades e aumentar aderência da argamassa. A aderência foi medida pelo ensaio de pull-off. Os comportamentos de fissuração e delaminação foram avaliados pelo mecanismo crack trapping . As propriedades físicas também foram estudadas: absorção de água, porosidade aparente e densidade aparente. Os resultados apresentaram uma boa compatibilidade e aderência entre as argamassas de reparo e o substrato. Resistências à aderência satisfatórias foram encontradas, atendendo os requisitos da norma de reparo BS EN 1504. O problema de delaminação foi observado apenas na argamassa com 100% de MK e o comportamento de fissuração foi típico de materiais frágeis. A formulação 80MK-20BFS com razão molar SiO2/Al2O3 de 3.0 e reforçada com fibra foi selecionada como a mais promissora para o uso em reparo de estruturas de concreto.
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    Compatibility and adhesion between fiberreinforced alkali-activated repair mortar and concrete substrate
    (Centro Federal de Educação Tecnológica de Minas Gerais, 2018-01-15) Nunes, Vitor Alencar; Borges, Paulo Henrique Ribeiro; Zanotti, Cristina; http://lattes.cnpq.br/2894639825694344; http://lattes.cnpq.br/5399317473703342; http://lattes.cnpq.br/5525081275110037; Borges, Paulo Henrique Ribeiro; Zanotti, Cristina; Ludvig, Péter; Mejía de Gutiérrez, Ruby
    Concrete repairing is a complex task that requires a special knowledge of technical building regulations and standards, deterioration mechanism and diagnosis, repair principles and methods, repair materials, execution of repair works, inspections, monitoring and maintenance. So far, most used patch repair mortars fall into two categories, (i) the mortars based on inorganic binders (Portland cement, PC) and (ii) those based on organic binders (polymers). Recent investigations reveal a third category of mortars with high potential to be used in the field of concrete repair, i.e. the alkali-activated based mortars. Alkali-activated materials (AAM) have been widely promoted as a greener binder for sustainable constructions. These binders can be generated from a wide range of aluminosilicate materials under alkaline conditions to produce a hardened component. This study, therefore, aims to evaluate the compatibility and the adhesion between a fiber-reinforced alkali-activated mortar and a concrete substrate. Different formulations of AAM were initially studied, based on the alkaline activation of metakaolin (MK) and blast furnace slag (BFS); their mechanical properties and modulus of elasticity were assessed. Five formulations were selected after this preliminary evaluation in order to produce the repair mortar and to apply onto concrete substrates. A volume fraction of 0.25% of PP fiber was used to mitigate the early-age shrinkage and to increase the adhesion bond of the repair mortar with the concrete substrate. The bond strength was evaluated by pull-off testing. The crack and delamination behaviour were assessed by four-point bending tests. Physical properties were also investigated: water absorption, apparent porosity and apparent density. Results showed a good compatibility and adhesion between alkali-activated repair mortars and the PC substrate. Satisfactory bond strengths were found meeting the required by the structure repair standard BS EN 1504. The delamination issue was observed only in 100 % MK-based mortars and the crack propagation behaviour was typical from brittle materials. The formulation 80MK-20BFS designed with SiO₂/Al₂O₃ molar ratio 3.0 and fiber-reinforced was selected as the most promising one to structural repair proposes.
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    Feasibility of steel slag as binder and aggregate in alkali-activated materials
    (Centro Federal de Educação Tecnológica de Minas Gerais, 2023-10-30) Nunes, Vitor Alencar; Borges, Paulo Henrique Ribeiro; Garcia, Carlos Thomas; http://lattes.cnpq.br/5399317473703342; http://lattes.cnpq.br/5525081275110037; Borges, Paulo Henrique Ribeiro; Garcia, Carlos Thomas; Ludvig, Peter; Gomes, João Paulo Castro; Blom, Johan; Aghajanian Sabbagh, Ali
    Steel slag (SS) is a solid waste generated during the steelmaking process, with annual generation of 270 million tons of SS worldwide. SS can be reused as an alternative raw material in several applications due to its chemical composition, mechanical and physical properties: in agriculture, soil stabilization, road construction and other building materials. However, the recovery rate for SS varies from 20 to 98%, depending on the country, which leads to an excessive stockpiling causing environmental harm and financial liability. So far, considerable quantities of SS are employed in road construction and internal recycling (steel making) but still with many restrictions. The construction sector appears as a potential consumer of large quantities of SS. However, the volumetric instability of SS may be an issue for application in Portland cement (PC) based products. An alternative reuse for the SS would be as raw material in the alkali-activated materials (AAM). AAM are alternative materials that could present better mechanical and durability performances; they also incorporate larger amounts of industrial wastes. This research investigated the feasibility of SS as binder and aggregate in AAM, by determining the optimum activation parameters and the pre-treatment process needed (wet-curing and carbonation). Mechanical, microstructural and durability properties were evaluated via a series of characterization methods, such as scanning electron microscopy (SEM), X-ray microtomography (μCT), mercury intrusion porosimetry (MIP) and autoclave expansion, among others. Results showed that SS has low reactivity but may be alkaliactivated as single binder. In fact, the best mechanical results (compressive strength up to 20 MPa) were achieved by using an activator with low Na2O concentration (4%) and intermediary silica modulus (1.50- 2.22). As aggregate, the wet curing as pre-treatment of the SS is highly recommended for AAM and PC matrices to control the delayed expansion of the former, producing sound materials after accelerated testing. In addition, the ITZ showed a gel phase (most likely resulting from the reaction of the SS aggregate in the alkaline system) which promoted the bond between aggregates and paste. On the other hand, the carbonation as pre-treatment of SS strongly affected the strength development at early ages of AAM mortars due to the formation of sodium carbonate in the activator. The AAM mortar designed with neat SS as binder and aggregate presented low mechanical strength (up to 5 MPa) and high porosity. Consequently, this mortar does not have sufficient mechanical strength to be evaluated in accelerated expansion testing. The findings of this research showed that the use of SS as raw material is very promising for AAM development.