EM - Escola de Minas

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Evaluation of the microstructure and micromechanics properties of structural mortars with addition of iron ore tailings.
(2023) Almada, Bruna Silva; Silva Neto, Gilberto Alves da; Prado, Dyala Fraga do; Aguilar, Maria Teresa Paulino de; Garcia, Dayana Cristina Silva; Silva, Guilherme Jorge Brigolini; Santos, White José dos
The Interfacial Transition Zone (ITZ) between the cement paste and aggregates is a region of great interest for concretes because it is the composites’ weakest region. ITZ presents a great amount of large calcium hydroxide and ettringite crystals, with the porosity being able to be up to 2.5 greater than that the rest of the paste. The microstructure, and consequently the ITZ, can be improved by mineral addition. These materials fill the pores in the composite, influence the hydration process and densify the matrix. Therefore, mineral additions, such as iron ore tailings (IOT), can modify microstructure of composites. There are few studies on the assessment of IOT heterogeneity on the microstructure and hardness of structural mortar. Thus, the present study analyzes the properties influences of four IOT types on the microstructure, porosity, and thickness of the structural mortars’ Interfacial Transition Zone (ITZ) with IOT addition, by different evaluation methods. The composites were characterized through the Scanning Electron Microscope by backscattered electrons (SEM-BSE), line scan by Energy Dispersive Spectroscopy and nanoindentation. Results presented that IOT improved particle packing and tended to reduce the ITZ. The IOT improved nucleation since it reduces the amount of anhydrous cement particles and increases the amount of calcium hydroxide particles in the cement matrix. The nanoindentation showed that IOT-added matrix presented greater hardness and indentation module. It can be concluded that the IOT heterogeneity may affect microstructural properties and that the methods presented can be good ways to evaluate the parameters.
Study of mechanical, durability and microstructural properties of cementitious composite with addition of different iron ore tailings from Brazil.
(2022) Almada, Bruna Silva; Melo, Henrique da Silva Silveira; Duarte, Marlo Souza; Aguilar, Maria Teresa Paulino de; Garcia, Dayana Cristina Silva; Silva, Guilherme Jorge Brigolini; Santos, White José dos
Brazil is the second-largest global iron ore producer in the world. Consequently, a large volume of iron ore tailings (IOTs) is generated, which is associated with environmental impacts. IOTs present potential to be used as an addition in cementitious compounds, however, few studies assess how the heterogeneity of this waste can limit its utilization as a building material. Thus, the present study aims to assess whether the heterogeneity of IOTs influences mechanical, durability, and microstructural properties when added to the cementitious composite. Four IOTs samples from different origins were collected and added to cementitious composite at 40% addition content. Composites’ mechanical (compressive strength and modulus of elasticity) and durability properties (water absorption, porosity, electrical resistivity, carbonation, and pH pore solution) were correlated to the microstructure of the IOTs. Results showed that the IOTs from different mines exhibited different physical properties and chemical/mineralogical compositions. Moreover, the higher the degree of ore processing, the lower the heterogeneity, iron content, and specific gravity. Although the IOT samples are heterogeneous, this type of tailing can be used as a filler addition in structural mortars. IOT addition tends to improve the mechanical and durability properties. Heterogeneity most significantly influenced the properties in the fresh state, durability, and microstructural properties. The microstructure of the cement matrix tends to be denser in the IOT-added with higher SSA and silica content. Was observed higher-porosity in regions close to the interfacial transition zone in the samples with coarser IOT.
Influence of the heterogeneity of waste from wet processing of ornamental stones on the performance of Portland cement composites.
(2020) Almada, Bruna Silva; Melo, Luciane de Souza; Dutra, Julia Baptistella; Bubani, Larissa Cardoso; Silva, Guilherme Jorge Brigolini; Santos, White José dos; Aguilar, Maria Teresa Paulino de
One of the difficulties of using some residues, such as those from stones beneficiation (cutting and polishing), is their heterogeneity. This study analyzes the influence of the heterogeneity of waste from wet processing of ornamental stones (marble, granite, slate, among others) on the performance of Portland cement composites when used at a 20% replacement of cement. The mechanical behavior (compressive strength, flexural strength, and elastic modulus) and durability parameters (porosity, water absorption, carbonation, and electrical resistivity) are analyzed. Results indicate that the waste can present considerable heterogeneity while maintaining composites properties, indicating little influence on their physicochemical properties. It can be inferred that the filler effect of the waste compensated to a certain extent the negative effects (the increase in w/c ratio and the reduction of important hydrates) due to reduced cement content, showing its viability as mineral addition, despite its heterogeneity.

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