Development of alkali-activated foamed materials combining both mining waste mud and expanded granulated cork

In Portugal, the significant amount of mine waste mud from tungsten mining operations has led to growing concerns about their ecological and environmental impacts such as the occupation of large areas of land, generation of powder and the contamination of surface and underground water. Furthermore, natural by-products in general, and natural cork particles in particular, have been used to manufacture new materials which not only provide good thermal insulation but also have a limited impact on the environment and a lower cost. Alkali-activated foamed materials have been introduced in the field of alkali-activated materials which have been produced from different raw and waste materials. It has been proposed as a new idea that involves the production of lightweight materials, thus combining the performance and the benefits of energy-saving (Carbon footprint) with the reduction of the cradle-to-gate emission obtained. Besides, in order to reduce the density of the alkali-activated materials holes or lightweight aggregates can be added for such purposes. Therefore, in this research, novel alkali-activated lightweight foamed materials (AALFM) from a combination of tungsten mine waste mud (TWM), waste glass (WG), and metakaolin (Mk) using alkali activators solution of Sodium Silicate (SS) and Sodium Hydroxide (SH) was developed and combined with natural expanded granulated cork (EGC) using aluminium powder (Al) as a foaming agent. The objective of this study is to develop a new alkali-activated foamed tungsten-based binder/mortar and to characterize the cork waste composite made from this binder/mortar and natural granulated aggregates (EG-Cork). Cork, which is the exterior bark of Quercus suber L., a natural, organic, and lightweight plant tissue with a high dimensional stability substance. Physical properties of tungsten-based alkali-activated binder/mortar such as bulk density, thermal conductivity and pore sizes distribution were provided. The formulations of the alkali-activated binders are based on a combination of tungsten waste mud (TWM), waste glass (WG), and metakaolin (Mk). The mechanical and thermal properties of alkali-activated foamed materials produced were then tested. The research work includes three main phases. The first part shows the feasibility to produce new improved lightweight foamed alkali-activated materials using Panasqueira tungsten waste mud (TWM) as major raw material incorporating expanded granulated cork (EGC). During this preliminary study, a series of mixes containing mining waste mud, milled waste glass, metakaolin and Ordinary Portland Cement, in different proportions, were prepared. The influence on porosity, density, and compressive strength of incorporating granulated expanded cork at different percentages was first studied with potential applications in artistic, architectural, and historical heritage restoration. The second part investigates the influence of different precursors’ particle sizes on the physical and mechanical properties, such as density, porosity, expansion volume, and pore size by image analysis. The design and development of tungsten-based alkali-activated foams (AAFs) were studied systematically. Moreover, the manufactured AAFs with enhanced compressive strength from non-calcined tungsten waste mud (raw material) by changing the precursor particle sizes showed results of the same level or even higher as other research results obtained with fly ash and MK. The third part of the research investigates the effect of the incorporation of expanded granulated cork (EGC) to produce alkali-activated lightweight foamed materials (AALFM) with thermal properties. The findings indicate that experimental research on different combinations of raw materials particularly tungsten mining waste mud (TMWM) contribute to the development of alkali-activated materials (AAMs) and alkali-activated foamed materials (AAFMs). These new improved materials can be used as building materials with enhanced properties such as compressive strength, density, thermal conductivity, and fire resistance. This doctoral research contributes to a sustainable development by promoting the complete recycling and use of mining wastes as construction materials.Em Portugal, a quantidade significativa de lamas residuais provenientes das operações de mineração de tungsténio, tem gerado preocupações crescentes relativamente aos impactos ecológicos e ambientais, tais como, ocupação de grandes áreas de terreno, libertação de poeiras, e a contaminação de águas superficiais e subterrâneas. Nesta pesquisa, um novo material espumoso leve obtido por ativação alcalina (AALFM) de lamas residuais da mina de tungsténio (TWM) foi desenvolvido, utilizando pó de alumínio (Al) como agente de formação de espuma e, ainda, combinado com cortiça granulada expandida natural (EGC). O trabalho de pesquisa comtemplou três fases principais. A primeira parte demonstra a viabilidade de produção de novos materiais expandidos ativados alcalinamente utilizando lamas residuais das minas de tungsténio da Panasqueira (TWM) como principal matéria-prima e, incorporando cortiça granulada expandida (EGC), com aplicações potenciais na restauração de património artístico, arquitetónico e histórico. Neste estudo preliminar, foram preparados conjuntos de misturas, contendo lamas residuais, resíduo de vidro moído, metacaulino e cimento Portland, em diferentes proporções. Em primeiro lugar, foi estudada a influência na porosidade, densidade e resistência à compressão da incorporação de cortiça expandida granulada em diferentes percentagens. A segunda parte investiga o projeto e o desenvolvimento de ligantes /argamassas espumosas ativadas alcalinamente com lamas das minas de tungsténio, utilizando três tamanhos de partícula de diferentes. As propriedades físicas e mecânicas, densidade, porosidade, volume de expansão e tamanho dos poros, foram estudados de forma sistemática. Além disso, foi também estudado o aprimoramento da resistência à compressão de espumas ativadas alcalinamente (AAFs), alterando os tamanhos das partículas precursoras. A terceira parte da investigação investiga o efeito da incorporação da cortiça granulada expandida (EGC) na produção de espumas leves ativadas alcalinamente (AALFM) nas suas propriedades térmicas. Os materiais espumosos ativados alcalinamente inserem-se no campo dos materiais obtidos por ativação alcalina, os quais têm sido produzidos a partir de diferentes matérias-primas e resíduos. Foi proposto como uma ideia nova que envolve a produção de materiais leves, combinando assim o desempenho e os benefícios da poupança de energia (pegada de carbono) com a redução da emissão “cradle-to-gate” obtida. Além disso, a fim de reduzir a densidade dos materiais ativados alcalinamente, podem ser adicionados orifícios ou agregados leves para esse fim. Os resultados dos estudos experimentais permitem desenvolver diferentes tipos de materiais, utilizando resíduos de minas como matéria-prima. Este novo material produzido pode ser usado como materiais de construção com propriedades aprimoradas, como resistência à compressão, densidade, condutividade térmica e resistência ao fogo. Esta investigação de doutoramento contribui para o desenvolvimento sustentável, promovendo a reciclagem completa e a utilização de resíduos de mineração como materiais de construção.This doctoral research work was conducted at the University of Beira Interior (UBI) and partially financed by the following grants: A Doctoral Incentive Grant (BID) – Santander-Totta/UBI research grants ‘‘Bolsa BID/ICI-FE/Santander Universidade – UBI/2017”; Portuguese national funds through FCT – Foundation for Science and Technology, IP, within the research unit C-MADE, Centre of Materials and Building Technologies (CIVE-Central Covilhã-4082), University of Beira Interior, Portugal and the European Commission Horizon2020, MARIE Skłodowska-CURIE Actions, Research, and Innovation Staff Exchange (RISE), - “REMINE- Reuse of Mining Waste into Innovative Geopolymeric-based Structural Panels, Precast, Ready Mixes and in-situ Applications”, project no. 645696, Coordinator: University of Beira Interior (PT), comprising three months secondments abroad at the company ALSITEK Limited (Ltd), Peterborough, United Kingdom (UK)

Mechanical, thermal insulation, thermal resistance and acoustic absorption properties of geopolymer foam concrete

This study reports the synthesis and characterization of geopolymer foam concrete (GFC). A Class F fly ash with partial slag substitution was used for GFC synthesis by mechanical mixing of preformed foam. The GFCs exhibited 28 d compressive strengths ranging from 3 to 48 MPa with demolded densities from 720 to 1600 kg/m3 (105 °C oven-dried densities from 585 to 1370 kg/m3), with the different densities achieved through alteration of the foam content. The thermal conductivity of GFCs was in the range 0.15-0.48 W/m K, showing better thermal insulation properties than normal Portland cement foam concrete at the same density and/or at the same strength. The GFC derived from alkali activation of fly ash as a sole precursor showed excellent strength retention after heating to temperatures from 100 to 800 °C, and the post-cooling compressive strength increased by as much as 100% after exposure at 800 °C due to densification and phase transformations. Partial substitution of slag for fly ash increased the strength of GFC at room temperature, but led to notable shrinkage and strength loss at high temperature. Thin GFC panels (20-25 mm) exhibited acoustic absorption coefficients of 0.7-1.0 at 40-150 Hz, and 0.1-0.3 at 800-1600 Hz

Assessing the suitability of fly ash geopolymers for high temperature applications

Geopolymers are an inorganic polymer synthesised from the dissolution and polycondensation of aluminosilicates in alkaline solutions under hydrothermal condition, yielding an amorphous, three-dimensional polymeric framework (Davidovits, 1991). They are a broad class of binding material with applications that range from conventional concrete to high tech, light weight composites for use in aviation. Geopolymers have also shown promise for use in high temperature applications, such as fire proof coatings, structural concrete in fire prone areas and thermal insulation for refractory type applications, due to their intrinsic thermal stability (Barbosa and MacKenzie, 2003a).This thesis reports on an investigation into the thermal performance of geopolymers synthesised from a range of fly ashes in order to assess their suitability for use in high temperature applications. Five fly ashes from Australian power stations with contrasting chemical properties were used in the study. Geopolymers were synthesised from each of the fly ashes using sodium silicate or sodium aluminate solutions in order to achieve a set range of Si:Al compositional ratios. Thermal analysis was conducted up to 1000 °C using a constant heat rate as well as a heating regime that simulated the conditions during a fire.The fly ashes were characterised in terms of elemental composition, phase composition, particle size, density and morphology prior to being used to synthesise geopolymers. It was determined that only a portion of each of the fly ashes was available for geopolymerisation and that the reactive Si:Al ratio (amorphous Si:Al ratio) varied greatly between the fly ashes. Collie and Port Augusta fly ashes had relatively low reactive Si:Al ratios (1.15 and 1.84, respectively) whereas Eraring, Tarong and Bayswater fly ashes had high Si:Al ratios (4.98, 8.84 and 7.49, respectively). All of the fly ashes had a predominantly spherical morphology, characteristic of fly ashes, though only the Collie and Port Augusta fly ashes had a significant portion of sub 5 μm particles.The thermo-physical, mechanical and micro-structural properties of the geopolymers made from each of the fly ashes are presented and the effect of the source fly ash characteristics on the hardened product is discussed. The results varied greatly with fly ash source and the most influential fly ash characteristic was the reactive Si:Al ratio. Fly ashes with a high reactive Si:Al ratio (≥5) were sodium aluminate activated and produced geopolymers with low to moderate as-cured compressive strengths but exhibited excellent dimensional stability during heating and greater compressive strengths after heating. Fly ashes with a low reactive Si:Al ratio (<2) were sodium silicate activated and produced geopolymers with high as-cured compressive strengths but exhibited poor dimensional stability during heating and greatly reduced compressive strengths after heating. All samples exhibited strength improving microstructural changes such as improved inter-particle bonding due to sintering after firing. However, the instability of non geopolymer phases during high temperature exposure led to strength losses in some samples depending on the type and composition of the activating solution.Geopolymers from three of the fly ashes were assessed for their performance upon exposure to a simulated fire. Solid and low density foamed variants (ρ ≈ 0.9 g cm-3, k ≈ 0.3 W m-1K-1) of the mixes were used for fire testing. Fire ratings of between 60 and 90 minutes for a sample thickness of 50 mm were achieved. The solid geopolymers exhibited better fire ratings than the low density geopolymers due to their higher water content (as they contained more of the hydrated geopolymer phase). Microstructural analysis of the fire tested samples indicated that the geopolymers were not significantly damaged by dehydration and the fire exposed side exhibited analogous changes to the samples that were gradually heated to 1000 °C.The results in this thesis indicate that fly ash geopolymers have great potential for utilisation in high temperature applications provided they are synthesised from a source material with suitable physical and compositional characteristics