Doutorado em Engenharia Civil

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https://repositorio.cefetmg.br//handle/123456789/625

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Navegando Doutorado em Engenharia Civil por Autor "Blom, Johan"

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    Alkali-activated binders with reclaimed asphalt aggregates as a potential base layer of pavements
    (Centro Federal de Educação Tecnológica de Minas Gerais, 2022) Costa, Juliana Oliveira; Den Bregh, Wim Van; Blom, Johan; Bezerra, Augusto Cesar da Silva; Santos, Flávio Antônio dos; http://lattes.cnpq.br/0783179484317105; http://lattes.cnpq.br/5640767093177688; Van den bregh, Wim; Blom, Johan; Bezerra, Augusto Cesar da Silva; Santos, Flávio Antônio dos; Gomes, João Paulo de Castro; Rahier, Hubert
    The pavement infrastructure comprises 16.3 million kilometres worldwide, and the pavement-related industrial sectors are said to be responsible for 21% of the global Greenhouse Gas (GHG) emissions worldwide (Plati, 2019). Sustainable actions on materials for those pavement layers mostly consider replacing (i) natural aggregates (NA) with recycled ones and (ii) Portland cement (PC) used as binder/stabiliser with binders with a lower ecological footprint. This research investigates the possibility of incorporating recycled asphalt pavement (RAP) as an aggregate replacement and alkali-activated material (AAM) as Portland cement (PC) replacement in/for base layer materials. So far, most studies focused on the use of RAP and PC or supplementary cementitious materials. The combination of RAP with alkali-activated matrices may be an even more sustainable solution, given that not only the aggregate is recycled, but also PC is absent from the matrix. Properly designed AAMs are stronger and more durable than PC-based materials. It is, therefore, very likely that the employment of RAP in AAM will result in materials that achieve the minimum requirements for road applications. This research produced an alkali-activated material containing fine and/or coarse RAP aggregates (RAP-AAM) as a replacement for natural aggregates to be used as base layers of pavements. The main objective of this thesis is to determine whether AAM can incorporate high amounts of RAP and be used as pavement base layers without compromising mechanical and durability performance. During this research, two innovative characterization methods were used as an alternative to those often employed for Portland concrete. Firstly, the observation of the interfacial transition zone (ITZ) was improved by combining a laser scanning confocal microscope (LSCM) and a scanning electron microscope (SEM). The combination of both techniques permitted a better observation of the heterogeneous asphalt coating of the RAP particles, the presence of clusters, and cracks at the border and within the activated matrix. Secondly, the thesis proposes an alternative methodology to observe and quantify the shrinkage of RAP-AAM or any other cementitious materials by employing simplified optical imaging. Although this method only allows for the observation of total shrinkage, it is an almost inexpensive method that could give a clear indication of volume changes over time. The experimental data demonstrated that an ideal alkali-activated binder composition to produce RAP-AAM lean concrete would have 10% MK replacement (BFS vol%) and the activator would have 8% Na2O and Ms= 0 (i.e., activated with NaOH and no sodium silicate). This selection was based on the minimum activator amount required to reach the target compressive strength for a weak to medium lean concrete (5 to 10 MPa), while also minimizing the shrinkage effect. The durability assessment to freeze and thaw indicated similar performance for RAP-AAM and reference (RAP-PC). The findings of this research showed that RAP-AAM is a promising material for pavement base layers and more investigation is needed on long-term strength and durability.
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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.