Geopolymer from kaolin in China: An overview

Zhang, Zuhua; Zhu, Huajun; Zhou, Chun Hui; Wang, Hao

doi:10.1016/j.clay.2015.04.023

Cited by 205 publications

(61 citation statements)

References 70 publications

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“…These materials were first discovered by Davidovits in 1975 [8]. The chemical processes behind the geopolymer structure formation are not fully understood, but there are simplified explanations of them [9]. Reactions that occur during geopolymerization can be summarized in three fundamental steps: a. Dissolution of aluminosilicate solids: Aluminosilicates that are found in pozzolanic solids are dissolved in alkali activators with a high pH.…”

Section: Introduction mentioning

confidence: 99%

Behaviour of Geopolymer Mortars after Exposure to Elevated Temperatures

Kaya

Uysal²,

Yılmaz

et al. 2018

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In this study it was investigated the behavior of class F fly ash based geopolymer mortars subjected to elevated temperatures. Geopolimer composites were prepared with CEN-sand, water, fly ash as the binder, nSiO2Na2O and NaOH mixture combination as alkali activator. After mixing fresh geopolymer mixture, prismatic specimens were prepared using 40 mm × 40 mm × 160 mm prism molds. After molding, fresh geopolymer mortar samples with their mold were subjected to heat curing at 50 °C, 60 °C, 70 °C, 80 °C, 90 °C and 100 °C temperature for 48 hours in an oven. After 48 hours initial heat curing, the hardened samples were taken out of their mold. Then, they were further cured by leaving them in laboratory environment at about 22 ± 2 °C temperature, until 28 days together with heat curing duration. At the end of 28 days, geopolymer mortar samples developed flexural strength values between 2,9 MPa and 8,51 MPa. Geopolymer mortar samples developed compressive strength values between 7,63 MPa and 50,64 MPa. High temperature experiments were conducted to observe behaviour of geopolymer mortars at elevated temperatures. The control cement mortar mixtures were also prepared and subjected to high temperature exposure in comparison to geopolymer mortar mixtures. Control cement mortars were cured at laboratory environment for 28 days without initial temperature curing. Control cement mortar mixtures and geopolymer mortar mixtures were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C and 800 °C temperature. The unit weight, ultrasonic pulse velocity, flexural and compressive strength of all mixtures were measured before and after high temperature exposure. Scanning electron microscope (SEM) images of the mixtures were taken and X-ray fluorescence (XRF) spectrometer analyses were carried out. It was observed that there was an increase in the flexural and compressive strengths of some geopolymer mortars after high temperature exposure. In general, geopolymer mortars exhibited better performance at elevated temperatures in comparison to control cement mortar mixture.

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Section: Introduction mentioning

confidence: 99%

Behaviour of Geopolymer Mortars after Exposure to Elevated Temperatures

Kaya

Uysal²,

Yılmaz

et al. 2018

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“…With respect to the mechanical properties of geopolymers, Table lists the compressive and bending strengths of the geopolymer samples N2C8 and N5C5, the latter of which is pictured in Figure . In contrast to typical geopolymers, the mechanical properties of these samples are not very impressive due to low sodium content. Most alkali‐activated geopolymers with excellent mechanical properties are based on high‐alkali compositions.…”

Section: Resultsmentioning

confidence: 71%

“…Geopolymers are aluminosilicate cement materials which are usually prepared by alkali hydroxide or alkali silicate activation of aluminosilicate sources such as coal fly ash, calcined kaolinite, slag, or red mud . As a reduced‐CO 2 cement material, geopolymers are actively being developed at present as a potential alternative to Portland‐based cements .…”

Section: Introductionmentioning

confidence: 99%

Sintering of metakaolin‐based Na/Ca‐geopolymers and their immobilization of Cs

et al. 2019

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Metakaolin‐based Na/Ca‐geopolymers with a designed composition close to feldspar were used as precursors of Cs immobilization form materials. The sintering behaviors of geopolymers and their sintered materials' immobilization of Cs ions were investigated; the results indicated that the major phases of sintered geopolymers are plagioclase feldspars and feldspathoid. With the addition of Cs to the geopolymers, Cs‐leucite phase and caesium silicates were formed at 1150°C and 1170°C, respectively. It was found that Cs addition can slightly decrease the sintering temperature of geopolymers and make the grains finer. In addition, in order to reduce the volatilization of Cs ions during sintering, sintering temperatures of Cs‐geopolymer were further decreased to 850°C by introducing B2O3. After the geopolymer and Cs‐geopolymer were sintered using a low‐temperature liquid‐phase process, they remained structurally plagioclase feldspars and feldspathoid. Leaching on Product Consistency Test indicates that the leaching concentrations of Cs‐geopolymer samples sintered at higher temperatures are lower than those of samples sintered at lower temperatures. Thus, the increased volatilization of Cs ions at the higher temperatures and the formation of Cs‐leucite phase and caesium silicates can lead to the decrease of leaching concentrations in leachates. Therefore, low sintering temperatures and the fabrication of Cs crystalline ceramics are the key factors toward improving the immobilization of Cs ions.

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“…This results in inconsistent geopolymer products. Regarding hazardous waste management, metakaolin may be a better raw material as it has more consistent chemical compositions than fly ash (Zhang et al 2016). However, metakaolin is a thermally treated product from kaolin, which is energy intensive, therefore using geopolymers obtained from metakaolin would not be a cost effective solution.…”

Section: The Characteristics Of the Source Materialsmentioning

confidence: 99%

Mechanisms of Heavy Metal Immobilisation using Geopolymerisation Techniques – A review

Gowripalan

2018

ACT

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Every year, substantial amount of waste materials containing toxic substances is produced throughout the world, which causes serious damage to the environment and poses threat to human health. Among available techniques of immobilisation of toxic elements in harmful by-products, geopolymerisation is considered as an effective approach to deal with many environmental issues. Geopolymer binders have long been recognised to have great potential in immobilisation of hazardous wastes due to its advantages over Portland cement based binders. A profound knowledge of how hazardous elements are immobilised by geopolymer binders is necessary for achieving effective waste management strategies. This paper provides some important aspects of geopolymer materials regarding the immobilisation mechanisms and factors influencing the immobilisation efficiency, which are necessary to carry out further research on addressing the hazardous waste immobilisation.

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Geopolymer from kaolin in China: An overview

Cited by 205 publications

References 70 publications

Behaviour of Geopolymer Mortars after Exposure to Elevated Temperatures

Behaviour of Geopolymer Mortars after Exposure to Elevated Temperatures

Sintering of metakaolin‐based Na/Ca‐geopolymers and their immobilization of Cs

Mechanisms of Heavy Metal Immobilisation using Geopolymerisation Techniques – A review

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