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Geopolymer Gels for Next-Generation Construction
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Geopolymer Gels for Next-Generation Construction

A special issue of Gels (ISSN 2310-2861).

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 46082

Special Issue Editors

Prof. Dr. Sumanta Das

E-Mail Website
Guest Editor
Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI 02881, USA
Interests: sustainable cementitious materials; microstructure and material modeling; materials design for sustainable and durable infrastructure
Dr. Sumeru Nayak

E-Mail Website
Guest Editor
Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI 02881, USA
Interests: multiscale and multiphysics material modeling; materials and structures; sustainable building materials

Special Issue Information

Dear Colleagues,

This Special Issue of Gels aims to provide a comprehensive collection of recent advances and developments in the domain of alkali-activated gels.  With a sustainable approach to building material development, alkali-activated binders displace the use of ordinary portland cement (OPC) for comparable performance in terms of mechanics and durability. Across the broad domain of alkali-activated binders, various industrial wastes or by-products such as fly ash, ground-granulated blast furnace slag and supplementary cementitious materials such as clay can reduce or replace OPC content. As a class of alkali-activated binders, geopolymers are based on fly ash or metakaolin. The hydration in such binders results in alkali aluminosilicate reaction products, in contrast to calcium (alumino) silicate gels resulting from OPC hydration. Specific topics include but are not limited to hydration kinetics, molecular and meso-scale simulations, synthesis of innovative gels, waste remediation and advanced additive manufacturing.

Prof. Dr. Sumanta Das
Dr. Sumeru Nayak
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Geopolymer gels
  • Hydration and strength development
  • Extrudability and viscosity
  • Synthesis and waste reuse
  • Advanced manufacturing and 3D printing

Published Papers (20 papers)

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15 pages, 3353 KiB  
Article
The Preparation Process and Hydration Mechanism of Steel Slag-Based Ultra-Fine Tailing Cementitious Filler
by Siqi Zhang, Bo Wu, Yutong Ren, Zeping Wu, Qian Li, Keqing Li, Minggen Zhang, Junhao Yu, Jialu Liu and Wen Ni
Gels 2023, 9(2), 82; https://doi.org/10.3390/gels9020082 - 18 Jan 2023
Cited by 3 | Viewed by 1324
Abstract
Steel slag, desulphurised ash, desulphurised gypsum and ultra-fine iron tailing sand are common industrial solid wastes with low utilisation rates. Herein, industrial solid wastes (steel slag, desulphurised gypsum and desulphurised ash) were used as the main raw materials to prepare a gelling material [...] Read more.
Steel slag, desulphurised ash, desulphurised gypsum and ultra-fine iron tailing sand are common industrial solid wastes with low utilisation rates. Herein, industrial solid wastes (steel slag, desulphurised gypsum and desulphurised ash) were used as the main raw materials to prepare a gelling material and ultra-fine tailing was used as an aggregate to prepare a new type of cementing filler for mine filling. The optimal composition of the cementing filler was 75% steel slag, 16.5% desulphurised gypsum, 8.75% desulphurised ash, 1:4 binders and tailing mass ration and 70% concentration. The compressive strength of the 28-day sample reached 1.24 MPa, meeting the mine-filling requirements, while that of the 90-day sample was 3.16 MPa. The microscopic analysis results showed that a small amount of C3A reacted with the sulphate in the desulphurised gypsum to form ettringite at the early stage of hydration after the steel slag was activated by the desulphurisation by-products. In addition, C2S produced hydrated calcium silicate gel in an alkaline environment. As hydration proceeded, the sulphite in the desulphurised ash was converted to provide sulphate for the later sustained reaction. Under the long-term joint action of alkali and sulphate, the reactive silica–oxygen tetrahedra and alumina–oxygen tetrahedra depolymerised and then polymerised, further promoting the hydration reaction to generate hydrated calcium silicate gel and ettringite. The low-carbon and low-cost filler studied in this paper represents a new methodology for the synergistic utilisation of multiple forms of solid waste. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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16 pages, 4215 KiB  
Article
Research on the Mechanical Properties and Microstructure of Modified Silt Sediment Geopolymer Materials
by Changming Li, Xiaoxiong Chai, Hui Liu, Haifeng Cheng, Dongyang Jia, Longfei Di, Songlin Qin and Yongbao Jin
Gels 2022, 8(12), 792; https://doi.org/10.3390/gels8120792 - 02 Dec 2022
Cited by 1 | Viewed by 1571
Abstract
The treatment of silted sediment in the river is a global problem. The accumulation of waste sediment will lead to an adverse impact on the environment. In this paper, the silted sediment was reused to produce geopolymer composite materials via alkali-activated gelling modification. [...] Read more.
The treatment of silted sediment in the river is a global problem. The accumulation of waste sediment will lead to an adverse impact on the environment. In this paper, the silted sediment was reused to produce geopolymer composite materials via alkali-activated gelling modification. The effects of the modifiers of sodium silicate solution, quicklime, and Na2SO4 admixture, and the dosage of the slag, fly ash, and silica fume admixture, and curing conditions and age, on the compressive strength and microstructure of the geopolymer-modified sediment materials were studied. The crystalline phase and hydration products of the modified sediment geopolymer composites were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), respectively. A compressive strength test was conducted to evaluate the mechanical properties of the composites. The results showed that the type and dosage of modifier, amount of mineral admixture additive, cure conditions, and cure age had significant effects on the mechanical properties of the composites. The effect of the addition of mineral admixture on the compressive strength of the modified sediment specimens was more noticeable than that of the modifier. The compressive strength of the geopolymer-modified specimens was greatly increased by the addition of mineral dopants. When 10 wt.% silica fume is added, the compressive strength reaches a maximum value of 33.25 MPa at 60 days. The SEM-EDS results show that the C-S-H gels and C-A-S-H gels were the main hydration products. The results indicate that river siltation sediment is an excellent raw material for geopolymer-modified materials. It is feasible to produce reliable and sustainable hydraulic engineering materials by using river sediment geopolymer-modified materials. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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17 pages, 4192 KiB  
Article
Mechanical Properties of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composites after High-Temperature Exposure
by Peng Zhang, Peishuo Zhang, Jingjiang Wu, Yong Zhang and Jinjun Guo
Gels 2022, 8(10), 662; https://doi.org/10.3390/gels8100662 - 17 Oct 2022
Cited by 8 | Viewed by 2228
Abstract
The mechanical properties of cementitious composites before and after exposure to high temperature are affected by calcium–silicate–hydrate (C–S–H) gels. To evaluate the effects of high temperature, plyvinyl alcohol (PVA) fiber content, and the cooling method on properties of cementitious composites, physical, mechanical, and [...] Read more.
The mechanical properties of cementitious composites before and after exposure to high temperature are affected by calcium–silicate–hydrate (C–S–H) gels. To evaluate the effects of high temperature, plyvinyl alcohol (PVA) fiber content, and the cooling method on properties of cementitious composites, physical, mechanical, and microscopic tests were performed in this study. The target temperatures were 25, 100, 200, 300, 400, 600, and 800 °C. The PVA fiber contents were 0.0, 0.3, 0.6, 0.9, 1.2, and 1.5 vol%. The high-temperature resistance of PVA fiber-reinforced cementitious composite (PVA-FRCC) specimens was investigated through changes in their appearance, mass loss, compressive strength, splitting tensile strength, flexural strength, and microstructure. The results showed that PVA fibers reduced the probability of explosion spalling in the PVA-FRCC specimens exposed to high temperatures. The mass loss rate of samples exposed to temperatures below 200 °C was small and lower than 5%, whereas a significant mass loss was observed at 200 °C to 800 °C. A small rise in the cubic compressive and splitting tensile strengths of samples was found at 400 °C and 300 °C, respectively. Below 400 °C, the fibers were beneficial to the mechanical strength of the PVA-FRCC specimens. Nevertheless, when the temperature was heated above 400 °C, melted fibers created many pores and channels, which caused a decrease in the strength of the specimens. The method of cooling with water could aggravate the damage to the cementitious composites exposed to temperatures above 200 °C. High temperature could lead to the decomposition of the C–S–H gels of the PVA-FRCC samples, which makes C–S–H gels lose their bonding ability. From the perspective of the microstructure, the structure of PVA-FRCC samples exposed to 600 °C and 800 °C became loose and the number of microcracks increased, which confirmed the reduction in macro-mechanical properties. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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19 pages, 4073 KiB  
Article
The Investigation of Compacting Cement Systems for Studying the Fundamental Process of Cement Gel Formation
by Alexey N. Beskopylny, Sergey A. Stel’makh, Evgenii M. Shcherban’, Levon R. Mailyan, Besarion Meskhi, Nikita Beskopylny, Diana El’shaeva and Maria Kotenko
Gels 2022, 8(9), 530; https://doi.org/10.3390/gels8090530 - 24 Aug 2022
Cited by 14 | Viewed by 1472
Abstract
Fundamental knowledge of the processes of cement gel formation for new generation concretes is a scientific deficit. Studies aimed at the formation of a cement gel for standard vibrated concrete research, and especially for centrifugally compacted concrete, are of interest because the structure [...] Read more.
Fundamental knowledge of the processes of cement gel formation for new generation concretes is a scientific deficit. Studies aimed at the formation of a cement gel for standard vibrated concrete research, and especially for centrifugally compacted concrete, are of interest because the structure of this concrete differs significantly from the structure of standard vibrated concrete. This article aims to study the fundamental dependencies of the theoretical and practical values that occur during compaction using vibration, as well as the centrifugal force of new emerging concrete structures. New theoretical findings about the processes of cement gel formation for three technologies were developed: vibrating, centrifuging, and vibrocentrifuging of concrete; the fundamental difference in gel formation has been determined, the main physical and chemical processes were described, and a significant effect of technology on the gel formation process was established. The influence of indirect characteristics based on the processes of cement gel formation, rheological properties of concrete mixtures, water squeezing processes, and the ratio between the liquid and solid phases in the mixture was evaluated. The process of formation of cement gel for centrifugally compacted cement systems was studied and graphical dependences were constructed, giving answers to the mechanism of interaction according to the principle “composition-rheological characteristics-structure-properties of concrete”. The quantitative aspect of the achieved result is expressed in the increase in the indicators demonstrated by centrifuged and especially vibrocentrifuged samples compared to vibrated ones. Additionally, in terms of strength indicators, vibrocentrifuged samples demonstrated an increase from 22% to 32%, depending on the type of strength, and the rheological characteristics of concrete mixes differed by 80% and 300% in terms of delamination. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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20 pages, 6929 KiB  
Article
Effects of Iron Minerals on the Compressive Strengths and Microstructural Properties of Metakaolin-Based Geopolymer Materials
by Dimace Lionel Vofo Ngnintedem, Marco Lampe, Hervé Kouamo Tchakouté and Claus Henning Rüscher
Gels 2022, 8(8), 525; https://doi.org/10.3390/gels8080525 - 22 Aug 2022
Cited by 8 | Viewed by 1544
Abstract
The current study aims to investigate the influence of iron minerals on the amorphous phase content, compressive strengths and the microstructural properties of the geopolymer materials. Geopolymer materials were prepared by the substitution of metakaolin by 10 and 20 wt.% of each iron [...] Read more.
The current study aims to investigate the influence of iron minerals on the amorphous phase content, compressive strengths and the microstructural properties of the geopolymer materials. Geopolymer materials were prepared by the substitution of metakaolin by 10 and 20 wt.% of each iron mineral sample. Sodium waterglass from rice husk ash was used as a hardener, and metakaolin was used as an aluminosilicate source. The X-ray patterns show that the iron minerals denoted FR and FB are associated with hematite and magnetite, respectively. FY contains goethite together with a significant content of kaolinite and quartz. It is observed in the XRD patterns and FTIR absorption spectra that the additions of hematite, magnetite and goethite remain largely unreacted in the geopolymer binder. The compressive strengths of the related geopolymer composites show some significant variations indicating certain effects for mechanical stability obtained: 10 wt.% replacement of metakaolin by hematite increased the compressive strength from 51.1 to 55.5 MPa, while 20 wt.% hematite caused a decrease to 44.9 MPa. Furthermore, 10 and 20 wt.% replacement with FB revealed decreased values 47.0 and 40.3 MPa, respectively. It was also found that 10 and 20 wt.% of FY caused lower values of 30.9 and 39.1 MPa, respectively. The micrographs of geopolymer materials present some voids and cracks. The denser matrix is related to a superior gel formation producing a better glue between the crystalline additions. The unsubstituted geopolymer sample provides with about 50% the highest X-ray-amorphous content, whereas the substituted samples range between 35 and 45%, indicating systematically smaller gel contents without any clear trend with the compressive strength variation, however. The strength dependencies reveal more complex interaction between the gel and crystalline additions. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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20 pages, 6908 KiB  
Article
A Study on the Cement Gel Formation Process during the Creation of Nanomodified High-Performance Concrete Based on Nanosilica
by Alexey N. Beskopylny, Sergey A. Stel’makh, Evgenii M. Shcherban’, Levon R. Mailyan, Besarion Meskhi, Valery Varavka, Nikita Beskopylny and Diana El’shaeva
Gels 2022, 8(6), 346; https://doi.org/10.3390/gels8060346 - 02 Jun 2022
Cited by 15 | Viewed by 2063
Abstract
One of the most science-intensive and developing areas is nano-modified concrete. Its characteristics of high-strength, high density, and improved structure, which is not only important at the stage of monitoring their performance, but also at the manufacturing stage, characterize high-performance concrete. The aim [...] Read more.
One of the most science-intensive and developing areas is nano-modified concrete. Its characteristics of high-strength, high density, and improved structure, which is not only important at the stage of monitoring their performance, but also at the manufacturing stage, characterize high-performance concrete. The aim of this study is to obtain new theoretical knowledge and experimental-applied dependencies arising from the “composition–microstructure–properties” ratio of high-strength concretes with a nano-modifying additive of the most effective type. The methods of laser granulometry and electron microscopy are applied. The existing concepts from the point of view of theory and practice about the processes of cement gel formation during the creation of nano-modified high-strength concretes with nano-modifying additives are developed. The most rational mode of the nano-modification of high-strength concretes is substantiated as follows: microsilica ground to nanosilica within 12 h. A complex nano-modifier containing nanosilica, superplasticizer, hyperplasticizer, and sodium sulfate was developed. The most effective combination of the four considered factors are: the content of nanosilica is 4% by weight of cement; the content of the superplasticizer additive is 1.4% by weight of cement; the content of the hyperplasticizer additive is 3% by weight of cement; and the water–cement ratio—0.33. The maximum difference of the strength characteristics in comparison with other combinations ranged from 45% to 57%. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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20 pages, 20815 KiB  
Article
Effect of Municipal Solid Waste Incineration Fly Ash on the Mechanical Properties and Microstructure of Geopolymer Concrete
by Mengya Niu, Peng Zhang, Jinjun Guo and Jia Wang
Gels 2022, 8(6), 341; https://doi.org/10.3390/gels8060341 - 30 May 2022
Cited by 13 | Viewed by 2086
Abstract
Geopolymers are environmentally friendly materials made from industrial solid waste with high silicon and aluminum contents, and municipal solid waste incineration fly ash (MFA) contains active ingredients such as Si, Al and Ca. According to this fact, a green and low-carbon geopolymer concrete [...] Read more.
Geopolymers are environmentally friendly materials made from industrial solid waste with high silicon and aluminum contents, and municipal solid waste incineration fly ash (MFA) contains active ingredients such as Si, Al and Ca. According to this fact, a green and low-carbon geopolymer concrete was prepared using MFA as a partial replacement for metakaolin in this study. The mechanical properties of the MFA geopolymer concrete (MFA-GPC) were investigated through a series of experiments, including a compressive strength test, splitting tensile strength test, elastic modulus test and three-point bending fracture test. The effect of the MFA replacement ratio on the microstructure of MFA-GPC was investigated by SEM test, XRD analysis and FTIR analysis. MFA replacement ratios incorporated in GPC were 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40% by replacing metakaolin with equal quality in this study. In addition, toxic leaching tests of MFA and MFA-GPC were performed by ICP-AES to evaluate the safety of MFA-GPC. The results indicated that the mechanical properties of MFA-GPC decreased with the increase of the MFA replacement ratio. Compared with the reference group of GPC without MFA, the maximum reduction rates of the cubic compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, initiation fracture toughness, unstable fracture toughness and fracture energy of MFA-GPC were 83%, 81%, 78%, 93%, 77%, 73% and 61%, respectively. The microstructure of MFA-GPC was porous and carbonized; however, the type of hydrated gel products was still a calcium silicoaluminate-based silicoaluminate gel. Moreover, the leaching content of heavy metals from MFA-GPC was lower than that of the standard limit. In general, the appropriate amount of MFA can be used to prepare GPC, and its mechanical properties can meet the engineering requirements, but the amount of MFA should not be too high. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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16 pages, 4622 KiB  
Article
Heat Treatment of Geopolymer Samples Obtained by Varying Concentration of Sodium Hydroxide as Constituent of Alkali Activator
by Ljiljana Kljajević, Miloš Nenadović, Marija Ivanović, Dušan Bučevac, Miljana Mirković, Nataša Mladenović Nikolić and Snežana Nenadović
Gels 2022, 8(6), 333; https://doi.org/10.3390/gels8060333 - 26 May 2022
Cited by 9 | Viewed by 2143
Abstract
In this paper, raw natural metakaolin (MK, Serbia) clay was used as a starting material for the synthesis of geopolymers for thermal treatment. Metakaolin was obtained by calcination of kaolin at 750 °C for 1 h while geopolymer samples were calcined at 900 [...] Read more.
In this paper, raw natural metakaolin (MK, Serbia) clay was used as a starting material for the synthesis of geopolymers for thermal treatment. Metakaolin was obtained by calcination of kaolin at 750 °C for 1 h while geopolymer samples were calcined at 900 °C, which is the key transition temperature. Metakaolin was activated by a solution of NaOH of various concentrations and sodium silicate. During the controlled heat treatment, the geopolymer samples began to melt slightly and coagulate locally. The high-temperature exposure of geopolymer samples (900 °C) caused a significant reduction in oxygen, and even more sodium, which led to the formation of a complex porous structure. As the concentration of NaOH (6 mol dm−3 and 8 mol dm−3) increased, new semi-crystalline phases of nepheline and sanidine were formed. Thermal properties were increasingly used to better understand and improve the properties of geopolymers at high temperatures. Temperature changes were monitored by simultaneous use of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The loss of mass of the investigated samples at 900 °C was in the range of 8–16%. Thermal treatment of geopolymers at 900 °C did not have much effect on the change in compressive strength of investigated samples. The results of thermal treatment of geopolymers at 900 °C showed that this is approximately the temperature at which the structure of the geopolymer turns into a ceramic-like structure. All investigated properties of the geopolymers are closely connected to the precursors and the constituents of the geopolymers. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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14 pages, 5619 KiB  
Article
Investigating the Mechanical Property and Enhanced Mechanism of Modified Pisha Sandstone Geopolymer via Ion Exchange Solidification
by Changming Li, Lisha Song, Yali Cao, Shunbo Zhao, Hui Liu, Chen Yang, Haifeng Cheng and Dongyang Jia
Gels 2022, 8(5), 300; https://doi.org/10.3390/gels8050300 - 13 May 2022
Cited by 6 | Viewed by 1650
Abstract
The Yellow River has the highest sediment concentration in the world, and the Yellow River coarse sediment mainly comes from a particular kind of argillaceous sandstone, Pisha sandstone. This paper reports an investigation of the possibility of development of low-cost engineering materials using [...] Read more.
The Yellow River has the highest sediment concentration in the world, and the Yellow River coarse sediment mainly comes from a particular kind of argillaceous sandstone, Pisha sandstone. This paper reports an investigation of the possibility of development of low-cost engineering materials using Pisha sandstone via ion exchange modification. The effect of modifiers with different concentration on the inhibition of volume expansion and the strength enhancement of modified Pisha sandstone were studied via ion exchange solidification. The effects of the concentration of ten types of modifier solutions and curing age were considered. The hydration of the mineral components, particle surface potential and reaction products were studied, respectively, by XRD, zeta potential, TG/DTG and SEM. Expansion volume and shear strength tests were conducted to assess the volume stability and mechanical property of modified Pisha sandstone. It showed that the expansion of Pisha sandstone was controlled and that the volume stability and shear strength were improved via ion exchange modification. The results of XRD, TG/DTG and SEM showed that the spacing of the crystal layers of the Pisha sandstone clay mineral and the mass lost had decreased significantly. When the concentration of the modifier was 0.05 mol/L, the volume reduced by 54.55% maximum and the shear strength reached the peak of 138 kPa. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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23 pages, 4555 KiB  
Article
Evaluation of Artificial Intelligence Methods to Estimate the Compressive Strength of Geopolymers
by Yong Zou, Chao Zheng, Abdullah Mossa Alzahrani, Waqas Ahmad, Ayaz Ahmad, Abdeliazim Mustafa Mohamed, Rana Khallaf and Samia Elattar
Gels 2022, 8(5), 271; https://doi.org/10.3390/gels8050271 - 26 Apr 2022
Cited by 45 | Viewed by 3226
Abstract
The depletion of natural resources and greenhouse gas emissions related to the manufacture and use of ordinary Portland cement (OPC) pose serious concerns to the environment and human life. The present research focuses on using alternative binders to replace OPC. Geopolymer might be [...] Read more.
The depletion of natural resources and greenhouse gas emissions related to the manufacture and use of ordinary Portland cement (OPC) pose serious concerns to the environment and human life. The present research focuses on using alternative binders to replace OPC. Geopolymer might be the best option because it requires waste materials enriched in aluminosilicate for its production. The research on geopolymer concrete (GPC) is growing rapidly. However, substantial effort and expenses are required to cast specimens, cures, and tests. Applying novel techniques for the said purpose is the key requirement for rapid and cost-effective research. In this research, supervised machine learning (SML) techniques, including two individual (decision tree (DT) and gene expression programming (GEP)) and two ensembled (bagging regressor (BR) and random forest (RF)) algorithms were employed to estimate the compressive strength (CS) of GPC. The validity and comparison of all the models were made using the coefficient of determination (R2), k-fold, and statistical assessments. It was noticed that the ensembled SML techniques performed better than the individual SML techniques in forecasting the CS of GPC. However, individual SML model results were also in the reasonable range. The R2 value for BR, RF, GEP, and DT models was 0.96, 0.95, 0.93, and 0.88, respectively. The models’ lower error values such as mean absolute error (MAE) and root mean square errors (RMSE) also verified the higher precision of ensemble SML methods. The RF (MAE = 2.585 MPa, RMSE = 3.702 MPa) and BR (MAE = 2.044 MPa, RMSE = 3.180) results are better than the DT (MAE = 4.136 MPa, RMSE = 6.256 MPa) and GEP (MAE = 3.102 MPa, RMSE = 4.049 MPa). The application of SML techniques will benefit the construction sector with fast and cost-effective methods for estimating the properties of materials. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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14 pages, 3431 KiB  
Article
Circular Economy of Coal Fly Ash and Silica Geothermal for Green Geopolymer: Characteristic and Kinetic Study
by Himawan Tri Bayu Murti Petrus, Muhammad Olvianas, Muhammad Faiz Shafiyurrahman, I Gusti Agung Arvin Nanda Pratama, Siti Nurul Aisyiyah Jenie, Widi Astuti, Muhammad Istiawan Nurpratama, Januarti Jaya Ekaputri and Ferian Anggara
Gels 2022, 8(4), 233; https://doi.org/10.3390/gels8040233 - 11 Apr 2022
Cited by 8 | Viewed by 2926
Abstract
The study of geopolymers has become an interesting concern for many scientists, especially in the infrastructure sector, due to having inherently environmentally friendly properties and fewer energy requirements in production processes. Geopolymer attracts many scientists to develop practical synthesis methods, useful in industrial-scale [...] Read more.
The study of geopolymers has become an interesting concern for many scientists, especially in the infrastructure sector, due to having inherently environmentally friendly properties and fewer energy requirements in production processes. Geopolymer attracts many scientists to develop practical synthesis methods, useful in industrial-scale applications as supplementary material for concrete. This study investigates the geopolymerization of fly ash and geothermal silica-based dry activator. The dry activator was synthesized between NaOH and silica geothermal sludge through the calcination process. Then, the geopolymer mortar was produced by mixing the fly ash and dry activator with a 4:1 (wt./wt.) ratio. After mixing homogeneously and forming a paste, the casted paste moved on to the drying process, with temperature variations of 30, 60, and 90 °C and curing times of 1, 3, 5, 7, 14, 21, 28 days. The compressive strength test was carried out at each curing time to determine the geopolymer’s strength evolution and simulate the reaction’s kinetics. In addition, ATR-FTIR spectroscopy was also used to observe aluminosilicate bonds’ formation. The higher the temperature, the higher the compressive strength value, reaching 22.7 MPa at 90 °C. A Third-order model was found to have the highest R2 value of 0.92, with the collision frequency and activation energy values of 1.1171 day−1 and 3.8336 kJ/mol, respectively. The utilization of coal fly ash and silica geothermal sludge as a dry activator is, indeed, an approach to realize the circular economy in electrical power generations. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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9 pages, 1720 KiB  
Article
An Alternative Radiation Shielding Material Based on Barium-Sulphate (BaSO4)-Modified Fly Ash Geopolymers
by Ammar A. Oglat and Sabri M. Shalbi
Gels 2022, 8(4), 227; https://doi.org/10.3390/gels8040227 - 07 Apr 2022
Cited by 9 | Viewed by 2473
Abstract
Geopolymers are a new environmentally friendly cementitious material, and the application of geopolymers can reduce the carbon dioxide emissions caused by the development of the cement industry. Purpose: This study investigates the radiation shielding capacity of fly ash geopolymers (FAGP) as a viable [...] Read more.
Geopolymers are a new environmentally friendly cementitious material, and the application of geopolymers can reduce the carbon dioxide emissions caused by the development of the cement industry. Purpose: This study investigates the radiation shielding capacity of fly ash geopolymers (FAGP) as a viable alternative to conventionally used ordinary Portland cement (OPC) due to the high demand for an environmentally friendly, cost-effective and non-toxic shield material. Methods: The FAGP material was fabricated and combined with Barium sulphate (BaSO4) at different ratios (0, 5, 10 and 15%). Different thicknesses (3, 6 and 9 cm) of the samples were also prepared. An energy-dispersive X-ray (EDX) was used to determine the elemental percentages of the materials, which were then used to calculate their effective atomic number (Zeff). An ion chamber was used to detect the dose of radiation transmitted through the samples. Results: The lowest radiation dosage (34.68 µGy) and highest Zeff were achieved with FAGP combined with 15% BaSO4 at 9 cm thickness. The decrease in radiation dosage can be attributed to the increase in Zeff with the addition of BaSO4 to FAGP, which in turn increases the density of FAGP. Conclusions: Thus, the radiation dose can be significantly reduced with a higher ratio of BaSO4 to FAGP. This study shows that FAGP combined with BaSO4 is a promising radiation shielding material, as well as a viable alternative to OPC. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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20 pages, 6496 KiB  
Article
Microstructure Analysis and Effects of Single and Mixed Activators on Setting Time and Strength of Coal Gangue-Based Geopolymers
by Xiaoyun Yang, Yan Zhang and Cheng Lin
Gels 2022, 8(3), 195; https://doi.org/10.3390/gels8030195 - 21 Mar 2022
Cited by 12 | Viewed by 2197
Abstract
Geopolymer is a green non-metallic material with high strength and favorable properties in resistance to corrosion, fire, and high temperature, which makes it a potential substitute for Portland cement. The existing studies have primarily focused on the preparation of geopolymers using silico-alumina materials [...] Read more.
Geopolymer is a green non-metallic material with high strength and favorable properties in resistance to corrosion, fire, and high temperature, which makes it a potential substitute for Portland cement. The existing studies have primarily focused on the preparation of geopolymers using silico-alumina materials such as fly ash, red mud, metakaolin, volcanic ash, and blast furnace slag to develop geopolymers. This study explores the potential of using ultrafine calcined coal gangue and ground granulated blast furnace slag to develop a new geopolymer with the activation of a single activator (sodium hydroxide) or mixed activator (sodium hydroxide, liquid sodium silicate, and desulfurization gypsum). The setting time and strength of the geopolymers were investigated, followed by the mineral, functional groups, microstructure, and elements analyses using X-ray diffraction, Fourier transform infrared diffraction, scanning electron microscope, and energy dispersive spectrometer to elucidate the effect of different activators on geopolymers. The results showed that the optimum molarity of NaOH single activator was 2 mol/L, the initial setting time and final setting time were 37 min and 47 min, respectively, and the compressive and flexural strengths at 28 days were 23.2 MPa and 7.5 MPa. The optimal mixing ratio of the mixed activator was 6% desulfurization gypsum, 0.6 Na2SiO3 modulus, and 16% SS activator; the initial setting time and final setting time were 100 min and 325 min, respectively, and the compressive and flexural strengths at 28 days were 40.1 MPa and 7.8 MPa. The coal gangue geopolymers were mainly C–A–S–H, N–A-S-H, and C–N–A–S–H gels. The mixed activator tended to yield higher strengths than the single activator, the reason is that the hydration reaction was violent and produced more gels. Meanwhile, the relation between setting time and activator and the relation between strength and activator were also obtained, which provide theoretical support for predicting the setting time of coal gangue base polymer and the ratio of alkali activator for geopolymers with a certain strength. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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14 pages, 18509 KiB  
Article
The Ratio Optimization and Strength Mechanism of Composite Cementitious Material with Low-Quality Fly Ash
by Xiaobing Yang, Zepeng Yan, Shenghua Yin, Qian Gao and Weiguang Li
Gels 2022, 8(3), 151; https://doi.org/10.3390/gels8030151 - 01 Mar 2022
Cited by 5 | Viewed by 1938
Abstract
To resolve the limited large-scale methods of disposal of low calcium fly ash with poor activity, based on the double excitation principle, clinker and desulfurized gypsum are used as alkali/salt activators to activate fly ash and slag, avoiding the inconvenience of strong alkali [...] Read more.
To resolve the limited large-scale methods of disposal of low calcium fly ash with poor activity, based on the double excitation principle, clinker and desulfurized gypsum are used as alkali/salt activators to activate fly ash and slag, avoiding the inconvenience of strong alkali activating fly ash in industry. Firstly, the strength test of a filling body with multiple ratio composite cementing material is carried out, and the weight coefficient of each material to strength is analyzed by grey correlation degree. The composition of the hydration products, microstructure, and pore structure of the filling body was analyzed by X-ray diffractometer, scanning electron microscope, thermogravimetric test, and mercury compression test. The strength mechanism of the cemented body was confirmed. The results show that cemented backfill prepared by composite cementitious material, which contained high content and low-quality fly ash, can meet the strength requirements of subsequent backfill in a mine. The degree of composite cementitious material influence on 7 d strength is slag > desulfurized gypsum > fly ash > clinker; the degree of influence on 28 d strength is: fly ash > slag > desulfurized gypsum > clinker. The main hydration products of the composite cementable material with high content low-quality fly ash are C–S–H gel and ettringite, and the unreacted fly ash particles can still be seen at 28 d. As the curing age grows, the difference in the number of hydration products under different proportioning conditions has a weaker effect on the strength, while the influence of raw materials and product morphology on the pore structure determines the development trend of the strength. Therefore, the threshold pore size can be used to characterize the strength advantages and disadvantages reasonably. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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24 pages, 11560 KiB  
Article
Compressive and Flexural Properties of Ultra-Fine Coal Gangue-Based Geopolymer Gels and Microscopic Mechanism Analysis
by Xiaoyun Yang, Yan Zhang and Cheng Lin
Gels 2022, 8(3), 145; https://doi.org/10.3390/gels8030145 - 25 Feb 2022
Cited by 10 | Viewed by 2435
Abstract
Geopolymer gel that possesses advantageous features of fast setting, high strength, and good durability is increasingly used in civil engineering, including rapid retrofit projects, roadway, and other construction projects. Furthermore, geopolymer gel is also a green and economical material as it derives from [...] Read more.
Geopolymer gel that possesses advantageous features of fast setting, high strength, and good durability is increasingly used in civil engineering, including rapid retrofit projects, roadway, and other construction projects. Furthermore, geopolymer gel is also a green and economical material as it derives from solid wastes. In this study, activators with different sodium silicate modulus and alkali content were used to activate ultrafine coal gangue and slag powder to prepare coal-gangue-based geopolymers with high strength. To study the influence of slag powder content, sodium silicate modulus, and alkali activator content on strength, a two-stage design was adopted. In the first stage, the orthogonal test with three factors and four levels (10–40% slag, 0.4–1.0 modulus, 16–22%) was used to obtain the influence of each factor on the strength and select the design range of the specimen mix ratio with higher strength. In the second stage, based on the orthogonal experiment, the scope was narrowed to continue to find the optimal excitation scheme and the relationship between the influencing factors and strength. Further, mineral compositional, microstructural, functional group and elemental analyses were performed using X-ray diffraction technique, IR infrared diffraction, electron microscope observation and energy spectrum analysis to elucidate the mechanisms of the strength development. The results show that the factors affecting the geopolymer’s strength were in the order of slag content > alkali content > modulus. The optimum dosage of alkali activator was 18–20%, and the sodium silicate modulus was 0.6–0.8, and the compressive and flexural strength could reach above 40 MPa and 5.9 MPa, respectively. The compressive strength and modulus were in a parabolic relationship. Three types of cementing gels (N-A-S-H, C-A-S-H, and C-N-A-S-H) that were characterized with dense structure and high strength were identified from coal gangue and slag powder after alkali excitation. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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11 pages, 2950 KiB  
Article
Structure and Properties of Phosphate-Based Geopolymer Synthesized with the Spent Fluid Catalytic-Cracking (SFCC) Catalyst
by Qian Wan, Ruobing Zhang and Yimin Zhang
Gels 2022, 8(2), 130; https://doi.org/10.3390/gels8020130 - 18 Feb 2022
Cited by 9 | Viewed by 1833
Abstract
As a common industrial by-product, the spend fluid catalytic-cracking (SFCC) catalyst was used to prepare phosphate-based geopolymer for the first time. The structure and property of geopolymer with phosphoric acid concentration ranging from 6 to 14 mol/L was characterized by compressive strength measurements, [...] Read more.
As a common industrial by-product, the spend fluid catalytic-cracking (SFCC) catalyst was used to prepare phosphate-based geopolymer for the first time. The structure and property of geopolymer with phosphoric acid concentration ranging from 6 to 14 mol/L was characterized by compressive strength measurements, X-ray powder diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and 27Al and 29Si nuclear magnetic resonance (NMR). A stable binder was formed with the compressive strength in the range of 9.8 to 30.2 MPa when the acid concentration was between 6 and 12 mol/L. The higher concentration of acid can promote the dissolution of raw materials and formation of geopolymer gels. The coordination of silicon and aluminum in geopolymer gel synthesized with the SFCC catalyst and metakaolin is similar. Compared with the geopolymer with metakaolin, which forms more Si-O-Al bonds, in the networks of geopolymer with the SFCC catalyst, more Si(Al)-O-P bonds were formed. These results indicate that the SFCC catalyst can be an excellent raw material for the synthesis of phosphate-based geopolymer. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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11 pages, 3489 KiB  
Article
Study of the Interfacial Transition Zone Characteristics of Geopolymer and Conventional Concretes
by Hani Alanazi
Gels 2022, 8(2), 105; https://doi.org/10.3390/gels8020105 - 09 Feb 2022
Cited by 17 | Viewed by 2487
Abstract
The properties and performance of geopolymer at different length scales have been intensively studied, but only limited studies on geopolymer have investigated the zone located between paste and aggregates, which is called the interfacial transition zone (ITZ). The microstructure of ITZ and its [...] Read more.
The properties and performance of geopolymer at different length scales have been intensively studied, but only limited studies on geopolymer have investigated the zone located between paste and aggregates, which is called the interfacial transition zone (ITZ). The microstructure of ITZ and its nanomechanical properties in geopolymer concrete are examined in this study. Fly ash-based geopolymer has great potential to be an alternative to traditional concrete. To this end, scanning electron microscopy (SEM) and nanoindentation tests were performed to investigate the microstructural characteristics and nanomechanical properties of the ITZ, and the results were compared with the ITZ of traditional concrete. Results show that traditional concrete demonstrated a weak ITZ with pores and microcracks, while the geopolymer concrete microstructure did not present weak ITZs in the vicinity of aggregates. More pores and crack were observed in the ITZ in traditional concrete. Further, a considerable amount of fly ash particles, that appear to be unreacted or partially reacted in the matrix phase, was observed. Based on the nanoindentation results, 58% of the microstructure is composed of unreacted or partially reacted fly ash particles. The results of nano- and microscale tests will enhance the understanding of how concrete behaves and performs at large scales. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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24 pages, 8129 KiB  
Article
Effects of Sulfate and Sulfuric Acid on Efficiency of Geopolymers as Concrete Repair Materials
by Rayed Alyousef, Ahmed Abdel Khalek Ebid, Ghasan Fahim Huseien, Hossein Mohammadhosseini, Hisham Alabduljabbar, Shek Poi Ngian and Abdeliazim Mustafa Mohamed
Gels 2022, 8(1), 53; https://doi.org/10.3390/gels8010053 - 12 Jan 2022
Cited by 10 | Viewed by 2966
Abstract
Various geopolymer mortars (GPMs) as concrete repairing materials have become effective owing to their eco-friendly properties. Geopolymer binders designed from agricultural and industrial wastes display interesting and useful mechanical performance. Based on this fact, this research (experimental) focuses on the feasibility of achieving [...] Read more.
Various geopolymer mortars (GPMs) as concrete repairing materials have become effective owing to their eco-friendly properties. Geopolymer binders designed from agricultural and industrial wastes display interesting and useful mechanical performance. Based on this fact, this research (experimental) focuses on the feasibility of achieving a new GPM with improved mechanical properties and enhanced durability performance against the aggressive sulfuric acid and sulfate attacks. This new ternary blend of GPMs can be achieved by combining waste ceramic tiles (WCT), fly ash (FA) and ground blast furnace slag (GBFS) with appropriate proportions. These GPMs were designed from a high volume of WCT, FA, and GBFS to repair the damaged concretes existing in the construction sectors. Flexural strength, slant shear bond strength, and compatibility of the obtained GPMs were compared with the base or normal concrete (NC) before and after exposure to the aggressive environments. Tests including flexural four-point loading and thermal expansion coefficient were performed. These GPMs were prepared using a low concentration of alkaline activator solution with increasing levels of GBFS and FA replaced by WCT. The results showed that substitution of GBFS and FA by WCT in the GPMs could enhance their bond strength, mechanical characteristics, and durability performance when exposed to aggressive environments. In addition, with the increase in WCT contents from 50 to 70%, the bond strength performance of the GPMs was considerably enhanced under sulfuric acid and sulfate attack. The achieved GPMs were shown to be highly compatible with the concrete substrate and excellent binders for various civil engineering construction applications. It is affirmed that the proposed GPMs can efficiently be used as high-performance materials to repair damaged concrete surfaces. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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14 pages, 3836 KiB  
Article
The Effect of Gel-Type Contributions in Lime-Sand Bricks, Alkali-Activated Slags and CEMI/CEMIII Pastes: Implications for Next Generation Concretes
by Claus Henning Rüscher, Ludger Lohaus, Fongjan Jirasit and Hervé Kouamo Tchakouté
Gels 2022, 8(1), 9; https://doi.org/10.3390/gels8010009 - 23 Dec 2021
Cited by 3 | Viewed by 2126
Abstract
Lime-sand bricks of different ages were investigated using IR-spectroscopy, thermogravimetry, and X-ray diffraction/scattering. After subtraction of the dominant quartz contribution (80%), the IR spectra show the absorption peaks of the hydrothermally formed binder phases. The spectra also show the alteration of the binder [...] Read more.
Lime-sand bricks of different ages were investigated using IR-spectroscopy, thermogravimetry, and X-ray diffraction/scattering. After subtraction of the dominant quartz contribution (80%), the IR spectra show the absorption peaks of the hydrothermally formed binder phases. The spectra also show the alteration of the binder during ageing under atmospheric conditions by the influence of CO2 forming carbonate and a condensed SiO2-gel (secondary gel). The alteration could also be proven in X-ray pattern, obtaining a separation between crystalline CSH and amorphous contributions in the freshly produced lime-sand brick, too. Here, the formation of CSHamorph could be understood as a precursor state (primary gel) to the crystallization of CSH phases. X-ray patterns of aged bodies of alkali-silicate solution activated slags (AAS), CEM-I/CEM-III pastes, and CEM-I concrete indicate that in all cases a similar amorphous CSH-type phase (CSHamorph) was formed, which is responsible for the hardening properties as the glue. The main X-ray peak of CSHamorph obtained using CuKα-radiation with a usual diffractometer is observed between 24° and 35° 2 Theta with maximum at about 29° 2 Theta, whereas it appears much more broadly distributed between 15° and 35° 2 Theta with maximum between 26° and 28° 2 Theta for a geopolymer body prepared using the reaction of alkali-silicate solution and metakaolin (AAMK). This is due to the network formed by siloxo and sialate units in the case of AAMK, given that any crystallization can be ruled out. The origin of increasing mechanical strength during the ageing of AAS mortars must be due to further crosslinking of the preformed siloxo chains. Thermal treatment up to 800 °C leads to a complete loss of any mechanical strength of the CEM pastes due to the destruction of crystalline CSH-phases, whereas geopolymer bodies maintain their strength. Implications for next generation concrete include that cement clinker could be completely replaced by using a using alkali silcate solution technology for gel formation. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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Review

Jump to: Research

12 pages, 234 KiB  
Review
Research Progress and Development Direction of Filling Cementing Materials for Filling Mining in Iron Mines of China
by Hui Cao, Qian Gao, Xizhi Zhang and Bin Guo
Gels 2022, 8(3), 192; https://doi.org/10.3390/gels8030192 - 20 Mar 2022
Cited by 18 | Viewed by 2531
Abstract
Backfill mining is the only way to realize no-waste mining and create green mines, but complicated backfill mining technology, high mining costs, and low-production capacity greatly restrict its application in low-quality iron mines. To reduce the cost of iron ore backfill mining, a [...] Read more.
Backfill mining is the only way to realize no-waste mining and create green mines, but complicated backfill mining technology, high mining costs, and low-production capacity greatly restrict its application in low-quality iron mines. To reduce the cost of iron ore backfill mining, a large number of low-cost green backfill cementing materials have been developed in China over the past 10 years. This paper first introduces the research and development of green cementitious materials using solid waste. Then, it points out the key technologies in the development of green filling cementing materials, reveals the hydration mechanism of green cementing materials through microscopic analysis and research, and optimizes the ratio of green cementing materials based on an orthogonal test. Finally, the development direction of green filling cementing materials is put forward: combining technology development with the filling mining method and filling process; taking the development route from technology to products and from products to commodities. To reduce the cost of filling mining and pursue the economic benefits of filling mining, a demonstration mine of tailings and green cementing materials is taken as the breakthrough point to comprehensively promote the development of iron ore full solid-waste filling mining technology and achieve its large-scale promotion and application. Full article
(This article belongs to the Special Issue Geopolymer Gels for Next-Generation Construction)
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