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Navegando Dissertações e Teses (Mestrado e Doutorado) por Autor "Aghajanian Sabbagh, Ali"
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Item 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, AliSteel 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.