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Guoping Zhang - One of the best experts on this subject based on the ideXlab platform.
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A multiscale investigation of reaction kinetics, phase formation, and mechanical properties of metakaolin Geopolymers
Cement & Concrete Composites, 2017Co-Authors: Mo Zhang, Mengxuan Zhao, Guoping Zhang, Tahar El-korchiAbstract:Abstract A multiscale study is presented of the reaction kinetics, phase formation, mechanical properties of metakaolin-based Geopolymers by varying Si/Al ratios of 1.2–2.2 and Na/Al ratios of 0.6–1.2. Macro- and nano-mechanical properties of geopolymer samples were determined by unconfined compression testing and grid nanoindentation technique, respectively. The latter, in combination with statistical deconvolution, also enables the extraction of generally 4 distinct phases together with their nanomechanical properties and volumetric fraction within the synthesized Geopolymers. Moreover, the reaction kinetics, phase formation (particularly geopolymer gel development), and mechanical property development were investigated by characterizing Geopolymers cured at the final setting time, 7, and 28 days. Phase formation was characterized by Fourier transform infrared spectroscopy (FTIR) via monitoring the evolution of the Si-O-T (T: Si or Al) and Al-O bonds. Results illustrate that the fraction of geopolymer gels dominantly governs the mechanical behavior, both of which increase with the Si/Al and Na/Al molar ratios, while the final setting time increases with the Si/Al ratio, but decreases with the Na/Al ratio. The chemical composition for the best mechanical performance of the studied Geopolymers is a Si/Al ratio of 1.7 and Na/Al ratio of 0.9. The relationships among geopolymer chemical compositions, geopolymer gel formation rate, and macromechanical properties are also discussed.
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synthesis factors affecting mechanical properties microstructure and chemical composition of red mud fly ash based Geopolymers
Fuel, 2014Co-Authors: Mo Zhang, Guoping Zhang, Tahar Elkorchi, Jianyu Liang, Mingjiang TaoAbstract:Abstract The influence of synthesis factors, including chemical composition of raw materials and curing conditions, on the microstructure and mechanical properties of Geopolymers synthesized from red mud (RM) and class F fly ash (FFA) was investigated. Mechanical properties, microstructure, mineralogy, and chemical composition of the resulting Geopolymers were characterized by unconfined compression testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX), respectively. Geopolymers were successfully synthesized at the ambient condition of 23 °C and 40–50% relative humidity (RH) with the 28-day unconfined compressive strength (UCS) ranging from 11.3 to 21.3 MPa. The formation of amorphous geopolymer gel was confirmed by XRD patterns, SEM images, and EDX spectra. This study suggests that a nominal Na/Al molar ratio in the range of 0.6–0.8 with a fixed nominal Si/Al molar ratio of 2 is a good starting point to synthesize geopolymer from RM and FFA. The ambient condition is also confirmed to be a practically feasible scheme for curing RM–FFA based Geopolymers, and exceptional mechanical properties can be obtained at a curing time period of up to 180 days.
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the strength and microstructure of two Geopolymers derived from metakaolin and red mud fly ash admixture a comparative study
Construction and Building Materials, 2012Co-Authors: Jian He, Jianhong Zhang, Yuzhen Yu, Guoping ZhangAbstract:Abstract The effects of source materials on the microstructure and mechanical properties were studied by comparing two types of Geopolymers synthesized from metakaolin, a non-waste material, and the admixture of two wastes, red mud and fly ash. Unconfined compression testing was conducted to assess their curing time and mechanical properties, while X-ray diffraction and scanning electron microscopy employed to examine geopolymerization reactions and the composition and microstructure of the end products. For a given Si/Al ratio, the metakaolin-derived geopolymer exhibits higher compressive strength than the waste-based one. Both Geopolymers contain a significant amount of voids and unreacted phases as inactive fillers within the geopolymer binder, resulting in complexity and variability in their mechanical behavior. The difference in strength and microstructure between the two Geopolymers is attributed to the different reactivity of source materials, percentage of nonreactive fillers, and alkalinity for geopolymerization reactions.
Arie Van Riessen - One of the best experts on this subject based on the ideXlab platform.
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Introduction to Geopolymers
SpringerBriefs in Materials, 2014Co-Authors: Les Vickers, Arie Van Riessen, William D.a. RickardAbstract:Geopolymers, also referred to as Aluminosilicate Inorganic Polymers (AIP) and Alkali Activated Cement (AAC) are based on alkali soluble aluminium and silicon precursors (aluminosilicates). Structural differences and resulting properties of Geopolymers can be explained by variation in the source silicon to aluminium amorphous molar ratio, alkali metal cation type and concentration, water content and curing regime amongst other variables in the geopolymer synthesis.
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Thermal Properties of Geopolymers
2014Co-Authors: Les Vickers, Arie Van Riessen, William D.a. RickardAbstract:The physics and testing methodology of thermal properties are introduced prior to a review of OPC and geopolymer thermal properties. The amorphous inorganic structure of the Geopolymers lends itself to good thermal resistance which leads to potential applications such as thermal insulation. Thermal expansion can generate destructive internal stresses when structural parts are heated and restrained from moving. The thermal expansion measuring techniques commonly utilised are dilatometry, interferometry and thermomechanical analysis (TMA). Thermal expansion measurements of metakaolin and fly ash based Geopolymers show several distinct regions as the temperature increases. The extent of these regions varies from system to system and the changes are attributed to dehydration, dehydroxylation, densification and crystallisation. Fillers and aggregates can be added to Geopolymers to reduce the thermal expansion of the composite and extend the usable temperature range. Thermal conductivity determination is required to assess Geopolymers’ suitability for potential applications in thermal barriers and construction structural members. The two approaches to measuring thermal conductivity: steady state and transient (non-steady state) techniques are compared. The microstructure of geopolymer profoundly influences thermal conductivity; particularly porosity which if increased leads to a reduction in thermal conductivity. The addition of aggregate influences the thermal conductivity of OPC and geopolymer concrete and at the same time decreases thermal durability due to mismatch of thermal conductivity between aggregate and matrix. Some Geopolymers with low initial strength have been shown to gain strength after exposure to high temperatures. It has been hypothesised that unreacted precursor levels can convert to geopolymer at high temperature and increase the strength. Once again the importance of the geopolymer microstructure is highlighted.
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Bayer-Geopolymers: An exploration of synergy between the alumina and geopolymer industries
Cement and Concrete Composites, 2013Co-Authors: Arie Van Riessen, E. Jamieson, Catherine S. Kealley, Robert D. Hart, Ross P WilliamsAbstract:Abstract Previously, caustic residues such as red mud and sodium oxalate have been used to provide filler and as a supplementary source of alkali for Geopolymers. However, rather than incorporation of dilute alkali residues within geopolymer precursors, a significant counter-intuitive approach is to synthesise Geopolymers using Bayer process liquors as a primary source of caustic sodium aluminate and to add locally available fly ash as a source of reactive silica and additional alumina. In addition to the potential for using significant quantities of industrial residues to manufacture Geopolymers, these relatively new cements have the ability to bind a range of contaminants. As the Bayer process could achieve significant process impurity removal by utilisation of plant liquor, synergy between the alumina and geopolymer industries could be achieved. Geopolymers with a Si/Al ratio of 2.3 and a Na/Al ratio of 0.8 were targeted. With only synthetic plant liquor as the alkali activator, Geopolymers with a mean compressive strength of 33 MPa were synthesised, while use of processed plant liquor resulted in compressive strengths of 43 MPa.
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costs and carbon emissions for geopolymer pastes in comparison to ordinary portland cement
Journal of Cleaner Production, 2011Co-Authors: Benjamin C Mclellan, Ross P Williams, Janine Lay, Arie Van Riessen, G D CorderAbstract:Abstract Geopolymer concrete is seen as a potential alternative to standard concrete, and an opportunity to convert a variety of waste streams into useful by-products. One key driver in geopolymer development is the desire to reduce greenhouse gas emissions from the production of concrete products. This paper presents an examination of the lifecycle cost and carbon impacts of Ordinary Portland Cement (OPC) and Geopolymers in an Australian context, with an identification of some key challenges for geopolymer development. The results of the examination show that there is wide variation in the calculated financial and environmental “cost” of Geopolymers, which can be beneficial or detrimental depending on the source location, the energy source and the mode of transport. Some case study geopolymer concrete mixes based on typical Australian feedstocks indicate potential for a 44–64% reduction in greenhouse gas emissions while the financial costs are 7% lower to 39% higher compared with OPC.
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thermo mechanical and microstructural characterisation of sodium poly sialate siloxo na pss Geopolymers
Journal of Materials Science, 2007Co-Authors: Arie Van RiessenAbstract:The thermo-mechanical and microstructural character of sodium-poly(sialate-siloxo) (Na-PSS) Geopolymers synthesised from dehydroxylated kaolinite (metakaolinite) have been investigated. Thermal analysis by means of TG–DTA showed a single endothermic peak at 135–140 °C due to dehydration (water evolution) from the geopolymer framework. Thermal expansion measurements show that geopolymer suffers 2% shrinkage below 250 °C and is then dimensionally stable up to 800 °C. The inclusion of aggregate (α-quartz or granite) was found to reduce the shrinkage by 1% although the presence of the quartz limits the working temperature range of the composite due a to disruptive phase change. Thermal conductivity and compressive strength of Na-PSS Geopolymers varied with change in chemical composition of the geopolymer as well as the amount and type of aggregate. Investigation of the microstructure by electron microscopy showed that the ratio of the starting materials influences the homogeneity of the geopolymer microstructure, which in turn leads to differences in thermal conductivity and compressive strength.
Xiang Shu - One of the best experts on this subject based on the ideXlab platform.
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mechanical and microstructural characterization of Geopolymers derived from red mud and fly ashes
Journal of Cleaner Production, 2018Co-Authors: Qingke Nie, Baoshan Huang, Xiang ShuAbstract:Abstract As a toxic industrial waste product, red mud causes severe environmental concern due to its strong alkalinity. In this study, red mud was systematically investigated for beneficial utilization as a raw material for geopolymer production. One type of red mud along with three types of fly ash were utilized to form Geopolymers as construction and building materials. Source materials were activated using two types of activator and cured at both ambient and elevated temperatures. The compressive strength, geopolymerization process, and microstructure of the Geopolymers were characterized in this study. The geopolymer derived from red mud and class C fly ash obtained a compressive strength of 15.2 MPa under ambient temperature curing at a significantly low NaOH concentration compared to the class F fly ash-based geopolymer. In contrast, the Geopolymers derived from red mud and class F fly ash were unable to obtain a serviceable strength when activated with the NaOH solution alone. Elevated temperature curing or using a composite activator proved to be solutions to this issue. This study indicated that the high alkalinity of red mud contributed to geopolymerization, but additional NaOH was necessary to achieve maximum compressive strength.
And Grant C Lukey - One of the best experts on this subject based on the ideXlab platform.
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effect of curing temperature and silicate concentration on fly ash based geopolymerization
Industrial & Engineering Chemistry Research, 2006Co-Authors: J S J Van Deventer, And Grant C Lukey, Hua XuAbstract:The development of the pore structure of Geopolymers synthesized from class F fly ash was studied using electron microscopy and porosimetry. Fly-ash-based geopolymer can be classified as a mesoporous aluminosilicate material, with a Si/Al composition varying from 1.51 to 2.24. The Si/Al composition and pore structure of fly-ash-based geopolymer vary depending on the curing temperature and the silicate ratio of the activating solutions (SiO2/M2O, M = Na or K). A higher Si/Al ratio and finer pores are obtained in Geopolymers synthesized at higher temperature and silicate ratios. Elevating the curing temperature increases the extent and rate of reaction, shown through an increase in mesopore volume, surface area, and an accelerated setting time. The kinetics appears to be temperature-controlled only before the material is hardened. Very high silicate ratios (SiO2/M2O ≥ 2.0) are also believed to slow the reactions. The pore structure of K-based geopolymer is more susceptible to change in temperature than that...
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effect of curing temperature and silicate concentration on fly ash based geopolymerization
Industrial & Engineering Chemistry Research, 2006Co-Authors: J S J Van Deventer, And Grant C LukeyAbstract:The development of the pore structure of Geopolymers synthesized from class F fly ash was studied using electron microscopy and porosimetry. Fly-ash-based geopolymer can be classified as a mesoporous aluminosilicate material, with a Si/Al composition varying from 1.51 to 2.24. The Si/Al composition and pore structure of fly-ash-based geopolymer vary depending on the curing temperature and the silicate ratio of the activating solutions (SiO2/M2O, M = Na or K). A higher Si/Al ratio and finer pores are obtained in Geopolymers synthesized at higher temperature and silicate ratios. Elevating the curing temperature increases the extent and rate of reaction, shown through an increase in mesopore volume, surface area, and an accelerated setting time. The kinetics appears to be temperature-controlled only before the material is hardened. Very high silicate ratios (SiO2/M2O ≥ 2.0) are also believed to slow the reactions. The pore structure of K-based geopolymer is more susceptible to change in temperature than that...
John L Provis - One of the best experts on this subject based on the ideXlab platform.
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The role of zinc in metakaolin-based Geopolymers
Cement and Concrete Research, 2020Co-Authors: Lei Wang, John L Provis, Daniel A. Geddes, Brant Walkley, Viktor Mechtcherine, Daniel C.w. TsangAbstract:Abstract Geopolymers are low-calcium, sustainable cementitious materials. The role of Zn, a known retardant used in Portland cement, in geopolymer systems is not well understood. This study scrutinises the effect of Zn on metakaolin-based geopolymer reaction mechanisms and kinetics, and investigates the incorporation mechanism of Zn in geopolymer gels. Isothermal calorimetry and X-ray diffraction analyses show that substitution of ZnO (20 mol% c.f. metakaolin) significantly hinders reaction, likely due to preferential formation of a Na/K-Zn containing phase. Solid-state nuclear magnetic resonance spectroscopy shows that Zn2+ partially substitutes for Na+/K+ in charge-balancing sites within the geopolymer gel. Setting time and leaching tests show that the retarding effect of Zn on reaction kinetics is significantly greater in Na-activated Geopolymers compared with K-activated Geopolymers, whereas Na-activated Geopolymers exhibit superior fixation capacity to Zn. A lab-scale experiment demonstrates that metakaolin-based Geopolymers are promising candidates for the stabilisation/solidification of Zn-rich hazardous waste.
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thermal activation of albite for the synthesis of one part mix Geopolymers
Journal of the American Ceramic Society, 2012Co-Authors: Dingwu Feng, John L ProvisAbstract:Precursors for the preparation of one-part Geopolymers are synthesized by thermal activation of albite with sodium hydroxide and sodium carbonate, then cooling and crushing the resulting product. Albite is stable under thermal treatment up to 1000°C, but is able to be converted to depolymerized, disordered, and X-ray amorphous geopolymer precursors in the presence of sodium hydroxide or sodium carbonate at elevated temperatures. The geopolymer precursors react with the addition of water (i.e., form a “one part geopolymer mix”), forming Geopolymers with acceptable compressive strength. One-part Geopolymers synthesized via thermal activation of albite with NaOH show a higher compressive strength than those produced with Na2CO3 at the same dosage. Some crystalline sodium-aluminosilicate hydrates (zeolites) are also formed in addition to geopolymer gel in the Geopolymers synthesized from albite activated by NaOH, compared to predominantly amorphous phases in the samples activated by Na2CO3. The activation of natural aluminosilicates including albite by thermal treatment with alkalis has great potential in the development of novel one-part mix Geopolymers.
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Thermal Activation of Albite for the Synthesis of One‐Part Mix Geopolymers
Journal of the American Ceramic Society, 2011Co-Authors: Dingwu Feng, John L ProvisAbstract:Precursors for the preparation of one-part Geopolymers are synthesized by thermal activation of albite with sodium hydroxide and sodium carbonate, then cooling and crushing the resulting product. Albite is stable under thermal treatment up to 1000°C, but is able to be converted to depolymerized, disordered, and X-ray amorphous geopolymer precursors in the presence of sodium hydroxide or sodium carbonate at elevated temperatures. The geopolymer precursors react with the addition of water (i.e., form a “one part geopolymer mix”), forming Geopolymers with acceptable compressive strength. One-part Geopolymers synthesized via thermal activation of albite with NaOH show a higher compressive strength than those produced with Na2CO3 at the same dosage. Some crystalline sodium-aluminosilicate hydrates (zeolites) are also formed in addition to geopolymer gel in the Geopolymers synthesized from albite activated by NaOH, compared to predominantly amorphous phases in the samples activated by Na2CO3. The activation of natural aluminosilicates including albite by thermal treatment with alkalis has great potential in the development of novel one-part mix Geopolymers.
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Geopolymers structure processing properties and industrial applications
2009Co-Authors: John L Provis, Jan Stephanus Jakob Van DeventerAbstract:Introduction to Geopolymers. Part 1 Geopolymer synthesis and characterisation: Fly ash glass chemistry and inorganic polymer cements Geopolymer precursor design Activating solution chemistry for Geopolymers Nanostructure/microstructure of metakaolin Geopolymers Nanostructure/microstructure of fly ash Geopolymers Geopolymer synthesis kinetics. Part 2 Manufacture and properties of Geopolymers: Accelerated ageing of Geopolymers Chemical durability of Geopolymers Life-cycle analysis of Geopolymers Engineering properties of geopolymer concrete Producing fire and heat-resistant Geopolymers Utilisation of mining wastes to produce geopolymer binders Utilisation of non-thermally activated clays in the production of Geopolymers Thermal properties of Geopolymers Utilisation of low-calcium slags to improve the strength and durability of Geopolymers. Part 3 Applications of Geopolymers: Commercialisation of Geopolymers for construction: Opportunities and obstacles Geopolymers for nuclear waste immobilization Immobilization of toxic waste in Geopolymers.
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1 – Introduction to Geopolymers
Geopolymers, 2009Co-Authors: John L Provis, J S J Van DeventerAbstract:: This introductory chapter provides a brief overview of some important aspects of geopolymer technology, in particular its historical development and the terminology by which Geopolymers are described. An introduction to geopolymer technology from a scientific viewpoint is also given. The scope of this review is confined to predominantly low-calcium materials, i.e. ‘traditional’ alkali-aluminosilicate Geopolymers, to the exclusion of alkali-activated slags and other related materials.