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Zuhua Zhang - One of the best experts on this subject based on the ideXlab platform.
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new selective dissolution process to quantify reaction extent and product stability in metakaolin based Geopolymers
Composites Part B-engineering, 2019Co-Authors: Zuhua Zhang, Brant Walkley, Marlon A Longhi, Erich D Rodriguez, Ana Paula Kirchheim, Hao WangAbstract:Abstract A selective dissolution process is developed that can quantify the amount of soluble material, Geopolymer gel and remnant unreacted precursor in metakaolin-based Geopolymer systems and determine the nanostructural features of the raw materials and Geopolymer gel components. The susceptibility of alkalis leachability from the alkaline aluminosilicate hydrate-type gel (N-A-S-H) produced during the Geopolymerization is not fully understood. This phenomenon led to deleterious processes from a microstructural, aesthetic and performance point of view. Geopolymers were synthesised using different contents and types of alkalis (M/Al = 0.50–0.83, where M represents Na or K), different contents of soluble silica in the activator (expressed as SiO2/M2O ratio of 1.0, 0.5 and 0.0), and curing temperatures (25 and 50 °C). The selective dissolution process is based on neutral dissolution at pH 7 to extract the soluble materials and acid dissolution using a strong acid at pH 0 to dissolve the Geopolymer gel, which provides for the first time a method to quantify the (i) soluble material, (ii) Geopolymer gel and (iii) unreacted material in Geopolymers. The soluble material provides a reliable indication of the materials that can be removed from the Geopolymers in a neutral pH environment and hence the potential for leaching and efflorescence, which is useful for durability prediction and service life. Quantification of remnant unreacted metakaolin determines the reactivity of the precursor and assesses the suitability of different synthesis conditions for varied applications. This work therefore provides a novel and widely applicable approach to determine the susceptibility of Geopolymer materials to leaching.
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efflorescence and subflorescence induced microstructural and mechanical evolution in fly ash based Geopolymers
Cement & Concrete Composites, 2018Co-Authors: John L Provis, Zuhua Zhang, Andrew Reid, Hao WangAbstract:This paper reports the effects of efflorescence on the microstructural and mechanical properties of fly ash-based Geopolymers. Geopolymer pastes manufactured by sodium hydroxide and sodium silicate activation of three Class F fly ashes exhibit varying efflorescence behaviour. The Geopolymer derived from sodium silicate activation of fine fly ash, which has a compact microstructure, shows a relatively slow efflorescence rate and low efflorescence potential. The efflorescence occurring on the surface of the Geopolymer specimens does not change their mineralogical characteristics. However, the compressive strength development and compressive modulus of Geopolymers can be affected through processes related to the loss of alkalis, and also to subflorescence. The phenomenon of subflorescence can be regarded as an extended efflorescence taking place under the surface of the material, leading to crystallisation pressure, which may exceed the tensile strength of hardened binders and generate structural damage.
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Geopolymer from kaolin in china an overview
Applied Clay Science, 2016Co-Authors: Zuhua Zhang, Chun Hui Zhou, Hao WangAbstract:Abstract The use of kaolin and calcined kaolin (metakaolin: MK) to manufacture Geopolymer has attracted worldwide interests. The aim of this paper is to present an overview on the progress of the Geopolymer research and development in China in the last 25 years. The works on Geopolymerisation mechanisms, microstructure development, properties and the application development of Geopolymers as green building material, thermal resistant material and advanced inorganic composites and ceramics are reviewed. Most of these works have been published, many of which are in Chinese, and have made significant contribution to the progress of Geopolymer science and technology, as a whole from a global view. The latest experimental results of efflorescence and phase transformation are discussed as two key issues regarding to the application of MK-based Geopolymers.
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the effects of phase changes on the bonding property of Geopolymer to hydrated cement
Construction and Building Materials, 2013Co-Authors: Huajun Zhu, Zuhua Zhang, Fenggan Deng, Yalong CaoAbstract:Abstract Using Geopolymers as bonding materials could be an alternative solution to the concrete repair. This study reports the effects of phase changes on the bonding property of Geopolymer to hydrated cement. A Geopolymer binder was prepared by activation of heated kaolin with sodium silicate solution, bonded with 28 days aged cement paste and cured under different conditions. The experimental results demonstrated that under the 20 °C air curing conditions, the bond strength achieved 1.3 MPa at 7 days and increased to 1.5 MPa at 28 days. While under the 80 °C steam and water curing conditions, the bond strength decreased by 31% and 37% respectively. The XRD, FTIR and SEM analysis of the Geopolymers and hydrated cement pastes show that the strength loss is due to two factors: (1) the increased porosity in cement paste due to the water loss and/or crystallization of C–S–Hs; and (2) the mineralogical change (crystallization) in Geopolymer binder which becomes more ordered structures. The increased porosity and the crystallization either in cement or Geopolymer generate local stress and weak regions at the interface. This study suggests that the stability of metakaolin-based Geopolymers should be taken into consideration when they are used as bonding or coating materials for concrete repair, particularly at the conditions with elevated temperatures.
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potential application of Geopolymers as protection coatings for marine concrete ii microstructure and anticorrosion mechanism
Applied Clay Science, 2010Co-Authors: Zuhua ZhangAbstract:The excellent anticorrosion property of Geopolymers in sea water and their efficient bonding to hardened cement paste did not only depend on the chemical compositions but were also influenced by the microstructure. This study presents an investigation into the interfaces between the Geopolymer and cement paste and mortar and the pore structure of Geopolymers by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and Brunauer–Emmett–Teller (BET) nitrogen adsorption. The interface between the Geopolymer and cement paste was compact and its chemical composition changed due to the reaction between the Geopolymer slurry and the surface of cement. Open pores in the Geopolymer synthesized with 90% metakaolin (MK) and 10% granulated blast furnace slag (GBFS) were < 15 nm in an average, thus much smaller than the average open pore size in ordinary Portland cement (OPC) paste. The compact microstructure of the Geopolymer made it difficult for sea water to penetrate. The amorphous aluminosilicate Geopolymeric gels, which were chemically stable in sea water or in air, provided a sustainable protection for marine concrete structures.
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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efflorescence and subflorescence induced microstructural and mechanical evolution in fly ash based Geopolymers
Cement & Concrete Composites, 2018Co-Authors: John L Provis, Zuhua Zhang, Andrew Reid, Hao WangAbstract:This paper reports the effects of efflorescence on the microstructural and mechanical properties of fly ash-based Geopolymers. Geopolymer pastes manufactured by sodium hydroxide and sodium silicate activation of three Class F fly ashes exhibit varying efflorescence behaviour. The Geopolymer derived from sodium silicate activation of fine fly ash, which has a compact microstructure, shows a relatively slow efflorescence rate and low efflorescence potential. The efflorescence occurring on the surface of the Geopolymer specimens does not change their mineralogical characteristics. However, the compressive strength development and compressive modulus of Geopolymers can be affected through processes related to the loss of alkalis, and also to subflorescence. The phenomenon of subflorescence can be regarded as an extended efflorescence taking place under the surface of the material, leading to crystallisation pressure, which may exceed the tensile strength of hardened binders and generate structural damage.
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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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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.
Mohd Mustafa Al Bakri Abdullah - One of the best experts on this subject based on the ideXlab platform.
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a review on durability performance of reinforcement bar in Geopolymer paste compare with its performance in ordinary portland cement paste
APPLIED PHYSICS OF CONDENSED MATTER (APCOM 2019), 2019Co-Authors: Nor Shida Dalila Mohd Azhar, Farah Farhana Zainal, Mohd Mustafa Al Bakri AbdullahAbstract:This paper presents the results of a study on the durability performance of the corrosion reinforcement bar in Geopolymer manufactured using metakaolin and fly ash. Durability can be defined as the ability of the material to withstand the surrounding environment without any significant deterioration during their service life such as weathering action, chemical attack, abrasion, compressive strength, sorptivity and water absorption. This review will be focussing on compressive strength, water absorption and porosity of the Geopolymer material. Geopolymer material is an alternative way to reduce carbon footprint as by using one tonne of Ordinary Portland Cement (OPC) will produce one tonne of carbon dioxide. Hence, metakaolin and fly ash Geopolymer has been used to reduce this problem. Both types of Geopolymers (metakaolin and fly ash) were synthesized with sodium silicate and potassium hydroxide solutions. The strength of the fly ash-based Geopolymer increased, however, the strength of the corresponding metakaolin-based Geopolymer decreased after similar exposure. The paper concludes that both types of Geopolymers still gave a better result compare to OPC.
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The effect of various molarities of NaOH solution on fly ash Geopolymer paste
2018Co-Authors: C.y. Heah, Y.m. Liew, Mohd Mustafa Al Bakri AbdullahAbstract:In the present work, a comparative study of the effect of the different molarities of sodium hydroxide (NaOH) on fly ash Geopolymer paste was investigated. The Geopolymer pastes were prepared by mixing fly ash with alkali activator (a mixture of sodium hydroxide and sodium silicate) at solid/liquid ratio of 2.5. The NaOH were used 6M, 8M, 10M, 12M and 14M with fixed sodium silicate/NaOH ratio of 2.5. The Geopolymers were cured at room temperature (29°C) for 24 hours and at 60°C for another 24 hours. The testing and analysis of the fly ash Geopolymers were performed after 28 days. The Geopolymer paste showed highest compressive strength (35MPa) with 8M of NaOH solution.
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Formation of one-part-mixing Geopolymers and Geopolymer ceramics from Geopolymer powder
Construction and Building Materials, 2017Co-Authors: Y.m. Liew, Nur Ain Jaya, Mohd Mustafa Al Bakri Abdullah, C.y. Heah, Soo Jin Tan, Kamarudin HussinAbstract:Abstract Geopolymer powder prepared through pre-curing and pulverization showed great potential to produce one-part-mixing Geopolymers as well as high flexural strength Geopolymer ceramics. The one-part-mixing Geopolymers were prepared by mixing Geopolymer powder with water while the Geopolymer ceramics were prepared by powder metallurgy and sintering. The one-part-mixing Geopolymers achieved a compressive strength of 10 MPa after 28 days with formation of Geopolymer precipitates in conjunction with zeolite phases. Despite the lower strength, they remained stable and did not disintegrate when immersed in water. Besides, the Geopolymer ceramics exhibited high flexural strength (90 MPa) after sintering at 1200 °C as result of nepheline formation.
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flood mud as Geopolymer precursor materials effect of flood mud alkaline activator and na2sio3 naoh ratios on compressive strength
Applied Mechanics and Materials, 2015Co-Authors: Mohd Mustafa Al Bakri Abdullah, Che Mohd Ruzaidi Ghazali, Kamarudin Hussin, Muhammad Faheem Mohd Tahir, Liew Yun Ming, Alida AbdullahAbstract:This paper investigates the potential and suitability of flood mud to be used in Geopolymer technique as construction materials. Flood mud was collected from Kelantan, Malaysia and crushed and sieved into powder form. Then, it was mixed with alkaline activator solution (mixture of NaOH and Na2SiO3 solutions) followed by curing process to produce flood mud Geopolymers. In addition, the effect of varying solids/liquid (S/L) and Na2SiO3/NaOH ratios on the compressive strength of flood mud Geopolymers were also investigated. The result showed that flood mud can be potentially used as precursor materials for Geopolymer formation with favorable strength. Optimum compressive strength (24.6 MPa) of Geopolymers based on flood mud was obtained at S/L = 1.25 and Na2SiO3/NaOH = 1.0.
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fly ash porous material using Geopolymerization process for high temperature exposure
International Journal of Molecular Sciences, 2012Co-Authors: Mohd Mustafa Al Bakri Abdullah, Che Mohd Ruzaidi Ghazali, Kamarudin Hussin, Liyana Jamaludin, Mohamed Bnhussain, Mohd Izzat AhmadAbstract:This paper presents the results of a study on the effect of temperature on Geopolymers manufactured using pozzolanic materials (fly ash). In this paper, we report on our investigation of the performance of porous Geopolymers made with fly ash after exposure to temperatures from 600 °C up to 1000 °C. The research methodology consisted of pozzolanic materials (fly ash) synthesized with a mixture of sodium hydroxide and sodium silicate solution as an alkaline activator. Foaming agent solution was added to Geopolymer paste. The Geopolymer paste samples were cured at 60 °C for one day and the Geopolymers samples were sintered from 600 °C to 1000 °C to evaluate strength loss due to thermal damage. We also studied their phase formation and microstructure. The heated Geopolymers samples were tested by compressive strength after three days. The results showed that the porous Geopolymers exhibited strength increases after temperature exposure.
Kamarudin Hussin - One of the best experts on this subject based on the ideXlab platform.
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Formation of one-part-mixing Geopolymers and Geopolymer ceramics from Geopolymer powder
Construction and Building Materials, 2017Co-Authors: Y.m. Liew, Nur Ain Jaya, Mohd Mustafa Al Bakri Abdullah, C.y. Heah, Soo Jin Tan, Kamarudin HussinAbstract:Abstract Geopolymer powder prepared through pre-curing and pulverization showed great potential to produce one-part-mixing Geopolymers as well as high flexural strength Geopolymer ceramics. The one-part-mixing Geopolymers were prepared by mixing Geopolymer powder with water while the Geopolymer ceramics were prepared by powder metallurgy and sintering. The one-part-mixing Geopolymers achieved a compressive strength of 10 MPa after 28 days with formation of Geopolymer precipitates in conjunction with zeolite phases. Despite the lower strength, they remained stable and did not disintegrate when immersed in water. Besides, the Geopolymer ceramics exhibited high flexural strength (90 MPa) after sintering at 1200 °C as result of nepheline formation.
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flood mud as Geopolymer precursor materials effect of flood mud alkaline activator and na2sio3 naoh ratios on compressive strength
Applied Mechanics and Materials, 2015Co-Authors: Mohd Mustafa Al Bakri Abdullah, Che Mohd Ruzaidi Ghazali, Kamarudin Hussin, Muhammad Faheem Mohd Tahir, Liew Yun Ming, Alida AbdullahAbstract:This paper investigates the potential and suitability of flood mud to be used in Geopolymer technique as construction materials. Flood mud was collected from Kelantan, Malaysia and crushed and sieved into powder form. Then, it was mixed with alkaline activator solution (mixture of NaOH and Na2SiO3 solutions) followed by curing process to produce flood mud Geopolymers. In addition, the effect of varying solids/liquid (S/L) and Na2SiO3/NaOH ratios on the compressive strength of flood mud Geopolymers were also investigated. The result showed that flood mud can be potentially used as precursor materials for Geopolymer formation with favorable strength. Optimum compressive strength (24.6 MPa) of Geopolymers based on flood mud was obtained at S/L = 1.25 and Na2SiO3/NaOH = 1.0.
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fly ash porous material using Geopolymerization process for high temperature exposure
International Journal of Molecular Sciences, 2012Co-Authors: Mohd Mustafa Al Bakri Abdullah, Che Mohd Ruzaidi Ghazali, Kamarudin Hussin, Liyana Jamaludin, Mohamed Bnhussain, Mohd Izzat AhmadAbstract:This paper presents the results of a study on the effect of temperature on Geopolymers manufactured using pozzolanic materials (fly ash). In this paper, we report on our investigation of the performance of porous Geopolymers made with fly ash after exposure to temperatures from 600 °C up to 1000 °C. The research methodology consisted of pozzolanic materials (fly ash) synthesized with a mixture of sodium hydroxide and sodium silicate solution as an alkaline activator. Foaming agent solution was added to Geopolymer paste. The Geopolymer paste samples were cured at 60 °C for one day and the Geopolymers samples were sintered from 600 °C to 1000 °C to evaluate strength loss due to thermal damage. We also studied their phase formation and microstructure. The heated Geopolymers samples were tested by compressive strength after three days. The results showed that the porous Geopolymers exhibited strength increases after temperature exposure.
Kang-hai Tan - One of the best experts on this subject based on the ideXlab platform.
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a critical review of Geopolymer properties for structural fire resistance applications
Construction and Building Materials, 2019Co-Authors: Mukund Lahoti, Kang-hai Tan, En-hua YangAbstract:Abstract Protection of structures from fire is of extreme importance. Geopolymer is a novel material that has wide-ranging applications, and this review article focuses on assessing the potential of Geopolymers towards enhancing the structural fire resistance by critically reviewing its properties subjected to elevated temperature exposure. The properties of Geopolymers are categorized into three scales, namely, micro-scale, meso-scale and macro-scale, and are discussed at length. It is noted that Geopolymers are chemically stable and do not undergo breakdown of chemical structure in contrary to OPC hydration products. Thermal deformations occurring in Geopolymers, which cause macro-cracking, are discussed. Compressive strength of Geopolymers is observed to be affected by microstructural changes (including crack formation, pore structure changes, densification, sintering, and melting) and phase composition changes (such as growth or destruction of crystals and transformations in Geopolymer paste). Geopolymer-based binders show inherently superior fire resistance as compared to Portland cement-based binders. However, it requires careful mix design, to achieve substantial chemical stability, low volume changes, strength endurance, and spalling resistance. Factors such as choice of precursor, use of aggregates, total alkali content in Geopolymer, water content, etc. are critical and should be controlled. The influence of these factors is discussed at length in this article. The current applications of Geopolymers for heat and fire resistance have also been briefly presented.
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effects of si al molar ratio on strength endurance and volume stability of metakaolin Geopolymers subject to elevated temperature
Ceramics International, 2017Co-Authors: Mukund Lahoti, En-hua Yang, Keng Khang Wong, Kang-hai TanAbstract:Abstract Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for Geopolymers has been reported in literature at a microscale. However, their performance at macroscale has not yet been systematically explored and the underlying mechanisms remain unexplained. In current study, effect of variation in Si/Al molar ratio on the meso- and macro-scale thermal stability of metakaolin Geopolymers has been comprehensively investigated to discover the underlying mechanisms governing the performance. Results show that all the Geopolymer samples experienced reduction in compressive strengths after exposure to high temperature up to 900 °C. Although, the Geopolymer mixes exhibited good chemical stability at microscale, they possessed poor volume stability at mesoscale with very high thermal shrinkage. It was observed that thermal shrinkage induced crack formation dominates the residual strength for Geopolymer mixes with Si/Al molar ratio ≤ 1.50, while densification of matrix is the governing factor of the residual strength for Geopolymer mixes with Si/Al molar ratio > 1.50. Re-crystallization of nepheline at high temperature adversely affect the strength by inducing expansion and cracking of the Geopolymer matrix. Geopolymer sample with Si/Al ratio 1.75 retained highest strength (6 MPa) because viscous sintering of Geopolymer mixes with high Si/Al ratio at temperature beyond 600 °C enables localized healing of micro-cracks and densification of matrix which favored compressive strength gain after exposure to 900 °C. At an even higher Si/Al of 2.0, foaming of unreacted silica upon heating can lead to expansion and cracking of the sample which reduce the strength. It was observed that due to high degree of cracking damage and low residual strength retention, it is essential to improve the macro-scale stability of metakaolin Geopolymers for structural fire resistance applications.