Geopolímero é um material que possui boas propriedades físicas e químicas como resistência mecânica, resistência a ataque químico, material inerte depois de pronto, é de fácil obtenção, pois a sua base é uma argila, material abundante e de baixo custo. Muitos trabalhos são desenvolvidos com o geopolímero, como aplicações para pisos, cimentos, refratários, adesivos e isolamento acústico e térmico. O desenvolvimento do geopolímero é simples, são necessário um percussor que pode ser metacaulim ou argilas com quantidades aceitáveis de SiO2 e Al2O3, um ativador alcalino como NaOH, KOH ou silicato de sódio e aditivos se necessário para contribuir com algumas relações molares que devem ser atendidas para a formação do geoplímero. A formação do geopolímero ocorre através de reações de policondensação originando uma estrutura amorfa e até cristalina dependendo do processo. O uso de aditivos e agregados conferem características desejadas como melhor resistência mecânica, melhor capacidade de isolamento térmico ou acústico, melhor resistência química entre outros fatores. A execução foi a partir do metacaulim com o uso de NaOH e aditivos, a serragem e fibras de sisal ( algave sisalana ) para conferir maiores porosidades no geopolímero desenvolvido. O geopolímero desenvolvido gerou valores de resistência mecânica na ordem de 20 MPa em um tempo de cura de 11 dias, sua densidade variou de 1,0 a 2,5 g/ml, a porosidade volumétrica ficou na faixa de 25,0% a 47,0%, as concentrações utilizadas de NaOH foram entre 0,0 e 15,0 mol/Litro. Todos os dados foram compatíveis com dados verificados em literatura. / Geopolymer is a material that has good physical and chemical properties such as mechanical resistance, chemical etch resistance, inert material after ready, it is easy to obtain because its base is a clay, abundant material and low cost. Many jobs are developed with the geopolymer, such as floor applications, cements, refractories, adhesives and acoustic and thermal insulation. The development of the geopolymer is simple, a percussor is required which may be metakaolin or clays with acceptable amounts of SiO2 and Al2O3, an alkaline activator such as NaOH, KOH or sodium silicate and additives if necessary to contribute some molar ratios that must be met for the formation of the geoplímero. The formation of the geopolymer occurs through polycondensation reactions leading to an amorphous and even crystalline structure depending on the process. The use of additives and aggregates impart desired characteristics such as better mechanical strength, better thermal or acoustic insulation capacity, better chemical resistance among other factors. The execution was from metacaulim with the use of NaOH and additives, sawdust and sisal fibers (algae sisalana) to impart larger porosities in the developed geopolymer. The developed geopolymer generated values of mechanical strength in the order of 20 MPa in a cure time of 11 days, its density ranged from 1.0 to 2.5 gmL-1, the volumetric porosity was in the range of 25.0% to 47,0%, the concentrations of NaOH used were between 0.0 and 15.0 mol / Liter. All data were compatible with data verified in the literature.

Orientador: José Luiz Pinheiro Melges / Resumo: Atualmente, é vasta a quantidade de materiais estudados com potencial de substituir o cimento Portland em matrizes cimentícias, uma vez que a produção do mesmo é responsável pela emissão de grande quantidade de CO2, o que contribui drasticamente para o efeito estufa. Nesse contexto, os aglomerantes ativados alcalinamente são materiais que prometem qualidades similares ou superiores àqueles à base de cimento, porém produzidos com elementos menos agressivos ao meio ambiente. Neste trabalho, é realizado o estudo da aplicação de Cinza da Casca de Arroz (CCA) com Hidróxido de Sódio (NaOH) na produção de solução alcalina, para ativação do metacaulim, material este que já possui resultados positivos quando ativado com silicato de sódio, e outros ativadores obtidos comercialmente. A solução de CCA-NaOH é utilizada como substituta do silicato de sódio comercial, uma vez que, além de utilizar um resíduo em sua produção, dando a ele uma destinação adequada, observa-se uma significativa economia de energia, já que a produção de silicato de sódio demanda uma grande quantidade de energia para sua obtenção. Para que a solução de CCA-NaOH apresente potencial de ativar o metacaulim, é necessário manter tais materiais, por 24h em meio térmico, para que ocorra a dissolução da sílica do CCA. Utilizando-se a composição CCA-NaOH, foram elaborados 5 traços de argamassa com relações molares SiO2/NaOH iguais a 0.0; 0.4; 0.8; 1.2 e 1.6. Também foram elaborados outros 5 traços com as mesmas relações mo... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nowadays, the amount of studied materials with the potential to replace Portland cement in cementitious matrices is extensive, since its production is responsible for the emission of a large amount of CO2, which contributes drastically to the greenhouse effect. In this context, alkali-activated binders are materials that promise qualities similar or superior to those based on cement, but produced with elements that are less aggressive to the environment. In this work, Rice Husk Ash (RHA) with sodium hydroxide (NaOH) are used to produce an alkaline solution for the activation of metakaolin, which has already positive results when activated with sodium silicate or others commercially available activators. The RHA-NaOH solution is used as a substitute for commercial sodium silicate, once in addition to use a residue in its production, giving it an adequate disposal, it works with the fact of saving energy, since the production of silicate of sodium consumes a large amount of energy for its obtainment. In order for the RHA-NaOH solution to have the potential to activate metakaolin, it is necessary to keep such materials for 24 hours in a thermal container in order to dissolve the silica from the CCA. Using the RHA-NaOH solution, 5 mixtures of mortar were prepared with SiO2 / NaOH molar ratios equal to 0.0; 0.4, 0.8, 1.2 and 1.6. Another 5 mixtures were prepared with the same molar ratios, but this time using commercial sodium silicate for comparison purposes. It was observed the ... (Complete abstract click electronic access below) / Mestre

Concrete is the most common building material in the world and its use has been increasing during the last century as the need for construction projects has escalated. Traditionally, concrete uses Ordinary Portland Cement (OPC) as binder, water as the activator of cement and aggregate. Finding an appropriate replacement for traditional concrete is a desirable solution to obviate the environmental problems caused by cement production. The use of fly ash as a partial replacement for Portland cement is a method to maintain the properties of concrete and reduce the need for cement. Fly ash is a by-product from coal-fired power plants and is abundantly available. The percentage of cement replacement can be varied according to application and mix design. One of the potential materials to substitute for conventional concrete is geopolymer concrete (introduced by Davidovits in 1979). Geopolymer concrete is an inorganic alumino-silicate polymer synthesized from predominantly silicon, aluminum and byproduct materials such as fly ash. Geopolymer properties have been investigated for several years and it is still a major area of interest among researchers and industry partners as it does not contain cement and uses fly ash and alkali liquids as binders to produce a paste to consolidate aggregates. Furthermore, the aggregate comprises a substantial portion of concrete. Including coarse and fine aggregates it is normally obtained from natural sources. Fine aggregate in Australia is usually mined from sand quarries. As the demand for concrete production increases, more natural sand is needed. The need for fine aggregate should be addressed in an environmentally friendly manner, considering the diminishing sources of natural sand. Red sand is a by-product generated from the manufacture of alumina from bauxite by the Bayer process. / Previous studies on properties of red sand have shown that it has the potential to be used in concrete as a fine aggregate. While the use of red sand in traditional concrete has been investigated by some researchers, no research has been reported regarding the use of this by-product in manufacturing geopolymer concrete. This research looks into the replacement of natural sand fine aggregates with red sand in geopolymer concrete. Initially, an extensive series of mixtures was prepared and tested. The objective of the research was to identify the salient parameters affecting the properties of geopolymer concrete when natural sand is replaced by red sand. At the next stage, attempts were made to enhance the mechanical and durability features of red sand geopolymer concrete. The final stage consisted of testing red sand geopolymer concrete to find out the various properties of this novel construction material.

The use of Portland cement in concrete construction is under critical review due to high amount of carbon dioxide gas released to the atmosphere during the production of cement. In recent years, attempts to increase the utilization of fly ash to partially replace the use of Portland cement in concrete are gathering momentum. Most of this by-product material is currently dumped in landfills, creating a threat to the environment. Geopolymer concrete is a ‘new’ material that does not need the presence of Portland cement as a binder. Instead, the source of materials such as fly ash, that are rich in Silicon (Si) and Aluminium (Al), are activated by alkaline liquids to produce the binder. Hence concrete with no Portland cement. This thesis reports the details of development of the process of making fly ash-based geopolymer concrete. Due to the lack of knowledge and know-how of making of fly ashbased geopolymer concrete in the published literature, this study adopted a rigorous trial and error process to develop the technology of making, and to identify the salient parameters affecting the properties of fresh and hardened concrete. As far as possible, the technology that is currently in use to manufacture and testing of ordinary Portland cement concrete were used. Fly ash was chosen as the basic material to be activated by the geopolimerization process to be the concrete binder, to totally replace the use of Portland cement. The binder is the only difference to the ordinary Portland cement concrete. To activate the Silicon and Aluminium content in fly ash, a combination of sodium hydroxide solution and sodium silicate solution was used. Manufacturing process comprising material preparation, mixing, placing, compaction and curing is reported in the thesis. / Napthalene-based superplasticiser was found to be ii useful to improve the workability of fresh fly ash-based geopolymer concrete, as well as the addition of extra water. The main parameters affecting the compressive strength of hardened fly ash-based geopolymer concrete are the curing temperature and curing time, the molar H2O-to-Na2O ratio, and mixing time. Fresh fly ash-based geopolymer concrete has been able to remain workable up to at least 120 minutes without any sign of setting and without any degradation in the compressive strength. Providing a rest period for fresh concrete after casting before the start of curing up to five days increased the compressive strength of hardened concrete. The elastic properties of hardened fly ash-based geopolymer concrete, i,e. the modulus of elasticity, the Poisson’s ratio, and the indirect tensile strength, are similar to those of ordinary Portland cement concrete. The stress-strain relations of fly ash-based geopolymer concrete fit well with the expression developed for ordinary Portland cement concrete.

One technology that makes concrete without cement and does not have the associated carbon footprint is geopolymer concrete. This technology utilizes waste fly ash from power stations and mixes it with activating chemicals to form a binder with similar or better properties than cement. Not only does this technology directly reduce carbon emissions by replacing cement it also utilizes the waste bi-product from power stations and prevents it from going to landfill. Concrete is composed of coarse aggregates, sand and cementitious paste. It seemed possible to make geopolymer concrete from 100% waste. The aggregates would come from recycled concrete and hard brittle bottom ash from power stations, the sand would come from foundries and the fly ash binder would also come from the same power station as the bottom ash. All of these materials are waste and would all be dumped in landfill. Where would one find all these waste materials in one place? The industrial suburb of Kwinana outside Perth is home to a large number of industries producing all these wastes. To find products that have a specification that these materials would suit was a material with a relatively low specification, one such specification is the concrete masonry units’ specification. For this to be adopted the mix design would then have to be altered to a drier type mix without any slump. As recycling facilities do not make a range of products it was decided to crush the aggregates in the laboratory specifically for this research and to blend all the waste materials. Numerous combinations were blended, analysed and assessed to establish which blends would best suit the aims and scope of this research. Eventually three blends were selected that encompassed all the waste products. / To find the right mix design proved challenging as these masonry products generally require a mix to have zero slump. It was decided to test across all the known and analysed water to geopolymer solids ratios for each of the mixes and establish the best mix based on compressive strength, workability and slump A known mix design based on research into low calcium Class F geopolymer concrete, developed at Curtin University using natural aggregates, was applied to these selected recycled waste mix designs. The benefit was to be able to compare the results of this research to a known result. Flash setting, an unknown phenomenon in geopolymer concrete, did occur in the low water mixes, but in spite of this, geopolymer concrete was successfully manufactured. The compressive strengths were substantially lower than those of the design mix and more research is required in this regard, however an indirect relationship was observed between the amount of bottom ash and the compressive strength. The high degree of LOI (loss of ignition) in both ashes, porosity of recycled aggregates, angularity, degree of fineness of the fines and flash setting are all possible factors influencing the properties of the geopolymer concrete. More research is recommended in a number of these areas to be able to understand and develop this technology further in order to make this a practical and robust technology in the quest to find solutions to our warming planet and our changing climate.

Geopolymers (GPs) are a new class of inorganic polymers that have been considered as good candidate materials for many applications, including fire resistant and refractory panels, adhesives, and coatings, waste encapsulation material, etc. The aim of this study is to establish relationship between structural and mechanical properties of geopolymers with different chemical compositions. The metakaolin-based geopolymers were prepared by mechanically mixing metakaolin and alkaline silicate aqueous solutions to obtain samples with SiO2/Al2O3 molar ratio that ranges from 2.5 to 5, and Na/Al or K/Al atomic ratios equal to 1. Geopolymer samples were cured in a laboratory oven at 80°C and ambient pressure for different times in the sealed containers. Structural characterization of the samples with different chemical compositions was carried out using X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Nuclear Magnetic-Resonance (NMR) spectroscopy and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The mechanical characterization included Micro-indentation, Vickers indentation and fracture toughness measurement, as well as compressive testing. It was found that structure and mechanical properties of GPs depend on their chemical composition. The Na-GPs with ratio 3 have a highest compressive strength and Young‘s modulus of 39 MPa and 7.9 GPa, respectively. The results of mechanical testing are discussed in more detail in this thesis and linked to structural properties of processed geopolymers.

This research investigates complete recycling and utilization of waste concrete to produce new structural concrete through geopolymerization. The investigation was conducted through both macro-and micro/nano-scale studies. First the geopolymer paste synthesized using a mixture of waste concrete fines (WCF) and class F fly ash (FA) as the source material and a mixture of NaOH solution (N) and Na2SiO3 solution (SS) as the alkaline activating agent was studied. Various NaOH concentrations, SS/N ratios, and WCF contents were used to produce geopolymer paste specimens in order to study their effect on the properties of the geopolymer paste. Uniaxial compression tests were conducted to measure the strength of the geopolymer paste specimens. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), and Fourier transform infrared spectroscopy (FTIR) analyses were performed to investigate the micro/nano-structure, morphology and phase/surface elemental compositions of the geopolymer paste and the effect of calcium (Ca) on them. The results indicate that by using 10 M NaOH solution, SS/N of 2 and 50% WCF, the highest geopolymer paste strength can be obtained. Second, the interfacial transition zones (ITZs) between geopolymer (GP) and recycled aggregates (RA) were studied. Considering that RA consist of the stone particles and the attached paste/mortar from the original ordinary Portland cement (OPC) concrete, both the ITZs between GP and natural aggregate (NA) and those between GP and residual OPC paste/mortar (ROPM) were studied. For comparison, the ITZs between OPC paste and NA and those between OPC paste and ROPM were also investigated. 4-point bending tests were conducted to measure the bonding strength of the different types of ITZs at water to solid (W/S) ratio of 0.30, 0.35 and 0.40 for the geopolymer and OPC pastes after 7 and 14 days curing, respectively. SEM imaging was performed to investigate the microstructure of the ITZs. The results indicate that when NA is used, the bonding strength of both the GP-NA and OPC-NA ITZs decreases with higher water to solid (W/S) ratio. When ROPM is used, higher W/S ratio leads to smaller bonding strength for the GP-ROPM ITZ but greater bonding strength for the OPC-ROPM ITZ. Based on the measured bonding strength values for NA- and ROPM-based ITZs, the bonding strength of the GP-RA and OPC-RA ITZs was estimated by considering the average area coverage of ROPM on the RA surface. The GP-RA ITZ has the highest bonding strength among the different ITZs, implying the great potential for utilizing waste concrete (both the WCF and the RA) to produce geopolymer concrete. Third, based on the studies on geopolymer paste and ITZs, geopolymer concrete (GPC) was produced and studied using WCF and FA as the cementitious material and RA as the aggregate. For comparison, GPC using NA was also produced and studied at similar conditions. Various NaOH concentrations, SS/N ratios, and cement (WCF and FA) to aggregate (C/A) ratios were used to produce GPC specimens in order to study their effect on the behavior of GPC. The effect of water content and curing temperature on the initial setting time and 7-day unconfined compressive strength (UCS) of the GPC was also studied. The results show that the GPC produced from RA has higher UCS than the GPC from NA at both room curing temperature and 35°C curing temperature. Based on this study, it can be concluded that waste concrete can be completely recycled and used to produce new structural concrete based on the geopolymerization technology. Fourth, considering that the Si/Al and Na/Al ratios have great effect on the geopolymerization process and the properties of the final geopolymer product, a study was conducted on copper mine tailings (MT)-based geopolymer containing different amount of aluminum sludge (AS). The results indicate that by including AS and utilizing appropriate amount of NaOH, the UCS can be increased significantly. The main reason is because the addition of AS along with utilization of appropriate amount of NaOH makes both the Si/Al and Na/Al ratios reach the optimum values for geopolymerization, leading to higher degree of geopolymerization and more compact geopolymer microstructure. It is noted that although this study is not directly on waste concrete, it provides useful information for optimizing the design on complete recycling and utilization of waste concrete to produce new GPC. Finally, to better understand the effect of Ca on the geopolymerization process and the properties of geopolymer, molecular dynamics (MD) simulations were performed on geopolymer at different Ca contents. The molecular models at different Ca contents were constructed and uniaxial compression test was then performed on the numerical specimens. The results indicate that MD simulation is an effective tool for studying the effect of Ca on the properties of geopolymer at nano-scale.

The first part of the thesis investigates the enhancement of fly ash-based geopolymer with alkali pretreated sweet sorghum fiber. The unconfined compression, splitting tensile and flexural tests were conducted to investigate the mechanical properties of geopolymer composite. The results indicate that the inclusion of sweet sorghum fiber slightly decreases the unconfined compressive strength (UCS), however, the splitting tensile and flexural strengths as well as the post-peak toughness increase with the fiber content up to 2% and then decrease thereafter. A durability test program containing 10 wet/dry cycles was performed to evaluate the long-term performance of the geopolymer composite related to wet/dry cycling. The results indicate that both the UCS and the splitting tensile strength of the geopolymer composite progressively decrease with the number of wet/dry cycles. The second part of the thesis investigates the utilization of biopolymers to stabilize MT for dust control. First, a fall cone method was adopted to evaluate the Atterberg limits and undrained shear strength of MT stabilized with biopolymers. The results indicate that the inclusion of biopolymers increases both the liquid limit and the undriained shear strength of MT. Two new equations are proposed for predicting the undrained shear strength of MT based on liquid limit and water content, and liquidity index. Second, an experimental program including moisture retention, wind tunnel and surface strength tests was performed to evaluate the effectiveness of biopolymer stabilization for dust control. The results indicate that biopolymers are effective in enhancing the moisture retention capacity, improving the dust resistance, and increasing the surface strength of MT. Third, a durability test program containing 10 wet/dry cycles was applied to MT samples treated with biopolymer solutions of different concentrations. The results show that the dust resistance of MT samples progressively decreases with the number of wet/dry cycles. Finally, experimental and numerical studies on the unconfined compressive strength (UCS) of MT stabilized with biopolymer were carried out. It is found that inclusion of biopolymer into MT favors the increase of adhesion between MT particles and thus the increase of the UCS of MT.

Stricter greenhouse gas emission limits and renewable energy requirements are expected to further increase the worldwide practices of firing biomass and co-firing biomass with coal, which are both considered more sustainable energy sources than coal-only combustion. Reuse options for the by-products of these processes -biomass ash and co-fired fly ash -remain limited. Therefore, this research examines their use as supplementary cementitious materials (SCMs) in concrete and as precursors for alkali-activated geopolymers. Toward their potential use as an SCM, after characterizing these ashes assessing their compliance with ASTM C618 requirements, their impact on early-age hydration kinetics, rheology, setting time and permeability was assessed. Furthermore, the pozzolanic reactivity and the microstructural and hydrated phase development of the cement-ash samples were analyzed. The results show that a wood biomass ash sample was not satisfactory for use as an SCM. On the other hand, the findings demonstrate that co-fired fly ashes can significantly improve the strength and durability properties of concrete compared to ordinary portland cement, in part due to their pozzolanicity. Thus, it is recommended that the ASTM C618 standard be modified to permit co-fired fly ash sources that meet existing requirements and any additional requirements deemed necessary to ensure their satisfactory performance when used in concrete. Toward their potential use in geopolymers, this study characterized the early-age reaction kinetics and rheological behavior of these materials, showing that their exothermic reactivity, plastic viscosity and yield stress are significantly influenced by the activator solution chemistry and other characteristics of the ash. Two co-fired fly ashes were successfully polymerized, with compressive strengths generally highest for ashes activated with solutions with a molar ratio of SiO₂/(Na₂O + K₂O) = 1. The results show that geopolymerization is a viable beneficial reuse for these emerging by-products. Further characterization of these materials by scanning transmission X-ray microscopy analysis revealed the heterogeneity of the aluminosilicate phase composition of the co-fired fly ash geopolymer gel at the nano- to micro-scale.

Geopolymers are a relatively new class of material that has many broad applications, including use as a substitute for Ordinary Portland Cement (OPC), use in soil stabilisation, fire resistant panels, refractory cements, and inorganic adhesives. The synthetic alkali aluminosilicate structure of geopolymer results in a highly versatile material that can be synthesised en masse, cost competitively and from a wide varietyof aluminosilicate bearing raw materials. / Despite the commercial promise and technical viability of the technology, the fundamental understanding of the chemical structure and characteristics of geopolymeric materials, and to some degree the academic rigor of some aspects of the science related to geopolymers, leave a lot to be desired. In particular, the understanding of the effects of Si/Al ratio and alkali cation type on the molecular structure of the binder, and how these relate to the microstructure and mechanical and thermal properties are poorly understood. / The thesis explores the structure and characteristics of a systematic multi-dimensional matrix of geopolymers derived from metakaolin, a relatively pure aluminosilicate source. The thesis addresses the determination of the core molecular structure of geopolymers by solid-state NMR spectroscopy, and how this is altered by the nominal Si/Al ratio and alkali cation type. The chemical ordering is observed to reduce with Si/Al ratio and with inclusion of potassium over sodium. Most significantly, the presence of Al-O-Al linkages is identified for the first time in specimens with Si/Al ratios close to unity, by the application of 17O NMR techniques on geopolymers. The role of molecular structure and gel chemistry of geopolymers is elucidated, and links are drawn to understand the development of the microstructure and physical properties of the material. The thermal evolution of geopolymeric gels derived from metakaolin is investigated in terms of physical and structural development when exposed to temperatures up to 1000°C. The response of geopolymers to heating is characterised into four regions regardless of the extent of shrinkage or crystallisation. Several critical material performance relationships exist that are related to both the microstructure and chemical composition. / The thesis presents an updated structural model of geopolymers to include new insights obtained from application of solid-state NMR techniques and thermal analysis. The improvements in structural understanding described in the thesis have the potential to affect all aspects of geopolymer science.