Geopolymers: Synthesis, Characterization and Applications

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Minerals minerals	2.2	4.1	2011	18 Days	CHF 2400
Materials materials	3.1	5.8	2008	13.9 Days	CHF 2600
Ceramics ceramics	2.7	3.0	2018	20.7 Days	CHF 1600
Geotechnics geotechnics	-	-	2021	14.3 Days	CHF 1000
Construction Materials constrmater	-	-	2021	20.8 Days	CHF 1000

16 pages, 27248 KiB

Open AccessArticle

Synthesis, Characterization, and Application of Geopolymer/TiO₂ Nanoparticles Composite for Efficient Removal of Cu(II) and Cd(II) Ions from Aqueous Media

by Khalid Khatib, Loubna Lahmyed and Mohamed El Azhari

Minerals 2022, 12(11), 1445; https://doi.org/10.3390/min12111445 - 15 Nov 2022

Cited by 16 | Viewed by 2479

Abstract

The use of fly ash wastes as inexpensive sorbents, mostly for heavy metal cations, is one method of recycling the millions of tons of fly ash waste produced each year. In this paper, a fly ash-based geopolymer was used as an adsorbent for [...] Read more.

The use of fly ash wastes as inexpensive sorbents, mostly for heavy metal cations, is one method of recycling the millions of tons of fly ash waste produced each year. In this paper, a fly ash-based geopolymer was used as an adsorbent for Cu²⁺ and Cd²⁺ from an aqueous solution. To improve geopolymer sorption efficiency, fly ash was modified by incorporating titanium oxide (TiO₂) nanoparticles that were synthesized hydrothermally and annealed at a temperature of 500 °C. The adsorbents were characterized before and after adsorption by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM-EDX). Regarding the developed materials, Cu²⁺ and Cd²⁺ adsorption equilibria (Langmuir model and Freundlich model) and kinetics (pseudo-first-order and pseudo-second-order model) were investigated. The results show that geopolymer-NanoTiO₂ adsorbs heavy metal cations better, which is superior to geopolymer. The maximum experimental adsorption capacity of geopolymer-NanoTiO₂ composite for Cu²⁺ and Cd²⁺ was 1708.2 mg/g and 706.9 mg/g, respectively. Therefore, geopolymer-NanoTiO₂ composite has shown great application prospects in the prevention and control of heavy metal pollution. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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14 pages, 3076 KiB

Open AccessArticle

Synthesis of Geopolymer from a Novel Aluminosilicate-Based Natural Soil Precursor Using Electric Oven Curing for Improved Mechanical Strength

by Muhammad Zain-ul-abdein, Furqan Ahmed, Iftikhar Ahmed Channa, Muhammad Atif Makhdoom, Raza Ali, Muhammad Ehsan, Abdullah Aamir, Ehsan Ul Haq, Muhammad Nadeem, Hafiz Zahid Shafi, Muhammad Ali Shar and Abdulaziz Alhazaa

Materials 2022, 15(21), 7757; https://doi.org/10.3390/ma15217757 - 3 Nov 2022

Cited by 2 | Viewed by 3039

Abstract

Natural soil (NS)-based geopolymers (GPs) have shown promise as environmentally friendly construction materials. The production of ordinary Portland cement is known to release significant amounts of greenhouse gas (CO₂) into the atmosphere. The main objective of this work is to synthesize [...] Read more.

Natural soil (NS)-based geopolymers (GPs) have shown promise as environmentally friendly construction materials. The production of ordinary Portland cement is known to release significant amounts of greenhouse gas (CO₂) into the atmosphere. The main objective of this work is to synthesize a geopolymer (GP) from an uncommon aluminosilicate-based NS and a sodium silicate (SS) activating solution that would not only minimize the emission of harmful gases, but also offer improved mechanical strength. Samples of different compositions were produced by varying the wt.% of NS from 50% to 80% and adding a balancing amount of SS solution. The drying and curing of the samples were carried out in an electric oven at specific temperatures. The degree of geopolymerization in the samples was measured by Fourier transform infrared spectroscopy, and microstructural analysis was performed using a scanning electron microscope. Mechanical tests were conducted to evaluate the range of compressive strength values of the prepared GP samples. A minimum compressive strength of 10.93 MPa at a maximum porosity of 37.56% was observed in a sample with an NS to SS ratio of 1:1; while a ratio of 3:1 led to the maximum compressive strength of 26.39 MPa and the minimum porosity of 24.60%. The maximum strength (26.39 MPa) was found to be more than the reported strength values for similar systems. Moreover, an improvement in strength by a factor of three has been observed relative to previously developed NS-based GPs. It may be inferred from the findings that for the given NS, with almost 90% aluminosilicate content, the extent of geopolymerization increases significantly with its increasing proportions, yielding better mechanical strength. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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16 pages, 4267 KiB

Open AccessArticle

Properties and Durability Performance of Lightweight Fly Ash Based Geopolymer Composites Incorporating Expanded Polystyrene and Expanded Perlite

by Dimitrios Kioupis, Aggeliki Skaropoulou, Sotirios Tsivilis and Glikeria Kakali

Ceramics 2022, 5(4), 821-836; https://doi.org/10.3390/ceramics5040060 - 21 Oct 2022

Cited by 15 | Viewed by 3002

Abstract

In this study, the use of expanded polystyrene and expanded perlite as lightweight aggregates for the preparation of lightweight geopolymers is tested. The geopolymers’ performance was evaluated through physical, mechanical and thermal testing. Polypropylene fibers were used as reinforcement agents, while the long-term [...] Read more.

In this study, the use of expanded polystyrene and expanded perlite as lightweight aggregates for the preparation of lightweight geopolymers is tested. The geopolymers’ performance was evaluated through physical, mechanical and thermal testing. Polypropylene fibers were used as reinforcement agents, while the long-term durability was assessed though repeated wet–dry and freeze–thaw cycles and sorptivity tests. The results showed that the introduction of lightweight aggregates in the geopolymer mixes decreased the compressive and flexural strength of the specimens by 77% and 35%, respectively. However, the density and thermal conductivity were substantially improved because of the addition of low-density aggregates. The fiber reinforcement of lightweight samples led to a drastic increase in flexural strength by 65%, leaving unaffected the compressive strength and density of the specimens. The freeze–thaw and sorptivity tests were also improved after the introduction of both aggregates and fibers. Lightweight geopolymer composites exhibiting density in the range of 1.0–1.6 g/cm³, compressive strength of 10–33 MPa, flexural strength of 1.8–6.3 MPa, thermal conductivity of 0.29–0.42 W/mK, and sorptivity of 0.031–0.056 mm/min^0.5 were prepared. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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18 pages, 5346 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Fly Ash-Based Geopolymer Cementitious Composites

by Guanglong Yu and Yanmin Jia

Minerals 2022, 12(7), 853; https://doi.org/10.3390/min12070853 - 4 Jul 2022

Cited by 14 | Viewed by 3259

Abstract

In this paper, the microstructure, mechanical properties, and preparation of geopolymer were investigated. The effects of the proportion of slag and fly ash, the modulus of water glass, and the water–binder ratio on the microstructure, mechanical properties, and preparation of geopolymer were analyzed. [...] Read more.

In this paper, the microstructure, mechanical properties, and preparation of geopolymer were investigated. The effects of the proportion of slag and fly ash, the modulus of water glass, and the water–binder ratio on the microstructure, mechanical properties, and preparation of geopolymer were analyzed. The research content of this paper is as follows: Taking the 7-day and 28-day compressive strength and flexural strength of the geopolymer specimens as the evaluation criteria, considering the proportion of slag and fly ash, the modulus of water glass, and the water–binder ratio, the three factors and five levels are respectively considered for a total of 25 sets of orthogonal experiments. Through the range analysis and variance analysis, the influence of each factor on the mechanical properties was analyzed, and the best mix ratio was obtained. Using scanning electron microscope and X-ray diffraction analysis and other testing methods, the mechanical properties, microstructure, and phase composition of geopolymers under the influence of various factors were studied and analyzed. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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24 pages, 4651 KiB

Open AccessArticle

Green Protective Geopolymer Coatings: Interface Characterization, Modification and Life-Cycle Analysis

by Aoxuan Wang, Yuan Fang, Yingwu Zhou, Chenman Wang, Biqin Dong and Cheng Chen

Materials 2022, 15(11), 3767; https://doi.org/10.3390/ma15113767 - 25 May 2022

Cited by 12 | Viewed by 3548

Abstract

In the interest of solving the resource and environmental problems of the construction industry, low-carbon geopolymer coating ensures great durability and extends the service life of existing infrastructure. This paper presents a multidisciplinary assessment of the protective performance and environmental impacts of geopolymer [...] Read more.

In the interest of solving the resource and environmental problems of the construction industry, low-carbon geopolymer coating ensures great durability and extends the service life of existing infrastructure. This paper presents a multidisciplinary assessment of the protective performance and environmental impacts of geopolymer coating. Various parameters, such as main substance, water-solid (W/S) ratio, activator type and curing time, were investigated for their effects on interface characterization in terms of contact angle, surface energy, mechanical properties and microstructure. These parameters had negligible effects on the amounts and types of hydrophilic functional groups of geopolymer surfaces. A combination of organic surface modifiers and geopolymer coatings was shown to ensure hydrophobic surface conditions and great durability. Silicon-based modifiers exhibited better wetting performance than capillary crystalline surfactants by eliminating hydroxyl groups and maintaining structural backbone Si-O-T (Si, Al) on geopolymers’ surfaces. Finally, life-cycle analysis was conducted to investigate the environmental performance. Geopolymer coating yielded substantially lower environmental impacts (50–80% lower in most impact categories) than ordinary Portland cement (OPC) coating. Silicon-based modifiers had negligible influence due to their minimal usage. Increasing the W/S ratio diluted the geopolymer coating and decreased the environmental impacts, and slag-based geopolymer coating achieved lower environmental impacts than FA-based and MK-based varietie. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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25 pages, 12824 KiB

Open AccessArticle

Characterization and Performance Evaluation of Metakaolin-Based Geopolymer Foams Obtained by Adding Palm Olein as the Foam Stabilizer

by Qinglin Yu, Xueying Li, Zheng Wang and Jing Xue

Materials 2022, 15(10), 3570; https://doi.org/10.3390/ma15103570 - 17 May 2022

Cited by 9 | Viewed by 2669

Abstract

Geopolymer foams with different pore structures can be used in construction, water treatment, and heavy metal adsorption. The preparation of high porosity geopolymer foams using vegetable oil as a foam stabilizer is a feasible and cost-effective route. In this study, metakaolin-based geopolymer foams [...] Read more.

Geopolymer foams with different pore structures can be used in construction, water treatment, and heavy metal adsorption. The preparation of high porosity geopolymer foams using vegetable oil as a foam stabilizer is a feasible and cost-effective route. In this study, metakaolin-based geopolymer foams with hierarchical pore structures were fabricated by adding H₂O₂ as the foaming agent with palm olein as the foam stabilizer. The effects of H₂O₂ and palm olein content on the chemical features and pore structure of geopolymer foams were evaluated. Water absorption, thermal conductivity, and mechanical behaviors of geopolymer foams were also investigated. The results indicate that fatty acid salt surfactants were generated in situ in the geopolymer matrix due to the addition of palm olein. Geopolymer foams with H₂O₂ and palm olein addition possess a homogeneously concentrated macropore distribution. Palm olein exhibits a refining effect on intrinsic pores formed by geopolymerization. In addition, using appropriate amounts of palm olein and H₂O₂, geopolymer foams can achieve higher open porosity and better pore connectivity, resulting in the improvement of water absorption and thermal insulation capacity. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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15 pages, 3551 KiB

Open AccessArticle

Hydration and Mechanical Properties of Blended Cement with Copper Slag Pretreated by Thermochemical Modification

by Daolin Wang, Qinli Zhang, Yan Feng, Qiusong Chen, Chongchun Xiao, Hongpeng Li, Yujing Xiang and Chongchong Qi

Materials 2022, 15(10), 3477; https://doi.org/10.3390/ma15103477 - 12 May 2022

Cited by 9 | Viewed by 2386

Abstract

The application of granulated copper slag (GCS) to partially replace cement is limited due to its low pozzolanic activity. In this paper, reconstituted granulated copper slag (RGCS) was obtained by adding alumina oxide (Al₂O₃) to liquid copper slag. Blended [...] Read more.

The application of granulated copper slag (GCS) to partially replace cement is limited due to its low pozzolanic activity. In this paper, reconstituted granulated copper slag (RGCS) was obtained by adding alumina oxide (Al₂O₃) to liquid copper slag. Blended cement pastes were formulated by a partial substitute for ordinary Portland cement (OPC) with the RGCS (30 wt%). The pozzolanic activity, mechanical development, and the microstructure were characterized. The results show that 5–10 wt% Al₂O₃ contributes to the increase in magnetite precipitation in RGCS. The addition of Al₂O₃ alleviates the inhibition of C₃S by RGCS and accelerates the dissociation of RGCS active molecules, thus increasing the exothermic rate and cumulative heat release of the blended cement pastes, which are the highest in the CSA10 paste with the highest Al₂O₃ content (10 wt%) in RGCS. The unconfined compressive strength (UCS) values of blended cement mortar with 10 wt% Al₂O₃ added to RGCS reach 27.3, 47.4, and 51.3 MPa after curing for 7, 28 and 90 d, respectively, which are the highest than other blended cement mortars, and even exceed that of OPC mortar at 90 d of curing. The pozzolanic activity of RGCS is enhanced with the increase in Al₂O₃ addition, as evidenced by more portlandite being consumed in the CSA10 paste, forming more C-S-H (II) gel with a higher Ca/Si ratio, and a more compact microstructure with fewer pores than other pastes. This work provided a novel, feasible, and clean way to enhance the pozzolanic activity of GCS when it was used as a supplementary cementitious material. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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17 pages, 4888 KiB

Open AccessArticle

Mechanical Properties and Microstructural Characterization of Metakaolin Geopolymers Based on Orthogonal Tests

by Shoushuai Dai, Hongguang Wang, Shuai An and Long Yuan

Materials 2022, 15(8), 2957; https://doi.org/10.3390/ma15082957 - 18 Apr 2022

Cited by 27 | Viewed by 3354

Abstract

Metakaolin was used as a raw material for the preparation of geopolymers, where two types of alkali activators (Na₂SiO₃ + NaOH and Na₂SiO₃ + NaOH) were used to prepare metakaolin geopolymers at room temperature. The mechanical properties [...] Read more.

Metakaolin was used as a raw material for the preparation of geopolymers, where two types of alkali activators (Na₂SiO₃ + NaOH and Na₂SiO₃ + NaOH) were used to prepare metakaolin geopolymers at room temperature. The mechanical properties and microstructures of the metakaolin geopolymers were analyzed. A three-factor, four-level orthogonal test was designed to investigate the mechanical properties of the metakaolin geopolymer with different ratios. The compressive and flexural strength of different specimens were tested for 7 and 28 days. Both the Na-based and K-based geopolymers exhibited excellent mechanical properties, but the K-based geopolymer had better mechanical properties. The optimal compressive strength and flexural strength of the K-based geopolymer were 73.93 MPa and 9.37 MPa, respectively. The 28-day optimal compressive strength of the Na-based polymer was 65.79 MPa, and the flexural strength was 8.71 MPa. SEM, XRD, and FTIR analyses showed that the mechanical properties of the geopolymers could be greatly improved by using a higher alkaline solution concentration, proper Na₂SiO₃/MOH mass ratio, and proper mass ratio of alkali exciter to metakaolin. Amorphous silicoaluminate was more favorable for the dissolution of silicon–alumina raw materials, promoted the formation of an amorphous silicoaluminate gel, and caused the internal structure of the geopolymer to be more compact. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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26 pages, 5972 KiB

Open AccessArticle

The Effect of the Type of Activator Anion on the Hydration of Ground Granulated Blast Furnace Slag

by Łukasz P. Gołek, Wojciech Szudek and Michał Malik

Materials 2022, 15(8), 2835; https://doi.org/10.3390/ma15082835 - 12 Apr 2022

Cited by 3 | Viewed by 1994

Abstract

In this study, ground granulated blast furnace slag was activated with a wide variety of sodium salts to compare the effects of their pH and anion size on the hydration progress and compressive strength development of GGBFS pastes. Research was carried out on [...] Read more.

In this study, ground granulated blast furnace slag was activated with a wide variety of sodium salts to compare the effects of their pH and anion size on the hydration progress and compressive strength development of GGBFS pastes. Research was carried out on samples activated with twelve different sodium salts and cured for one year. Changes in their phase composition (XRD), loss on ignition at different temperatures, expansion and microstructure (SEM + EDS) were examined over the entire curing period. The results showed that the presence of sodium ions is more important than the pH of the system, as activation took place even in the case of compounds whose solutions are characterized by a low pH, such as sodium tartrate or phosphate. The compressive strength of the pastes ranged from approximately 8 to 65 MPa after one year of curing. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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15 pages, 3598 KiB

Open AccessArticle

Thermal Properties of Geopolymer Based on Fayalite Waste from Copper Production and Metakaolin

by Aleksandar Nikolov and Alexandar Karamanov

Materials 2022, 15(7), 2666; https://doi.org/10.3390/ma15072666 - 5 Apr 2022

Cited by 10 | Viewed by 3162

Abstract

In the present study, thermal properties of geopolymer paste, based on fayalite waste from copper producing plants and metakaolin, were analyzed. The used activator solution was a mixture of sodium water glass, potassium hydroxide and water with the following molar ratio: SiO₂ [...] Read more.

In the present study, thermal properties of geopolymer paste, based on fayalite waste from copper producing plants and metakaolin, were analyzed. The used activator solution was a mixture of sodium water glass, potassium hydroxide and water with the following molar ratio: SiO₂/M₂O = 1.08, H₂O/M₂O = 15.0 and K₂O/Na₂O = 1.75. High strength geopolymers pastes were evaluated after exposure to 400, 800 and 1150 °C. The physical properties (absolute and apparent density, water absorption) and compressive strength were determined on the initial and the heat treated samples. The phase composition, microstructure and spectroscopic characteristics were examined by XRD, SEM-EDS, FTIR and Mössbauer spectroscopy, respectively. The structure of the heat-treated geopolymers differs in the outer and inner layers of the specimens due to variation in the phase composition. The outer layer was characterized by a reddish color and more rigidity, while the inner core was black and less viscous at elevated temperatures. The results showed that geopolymer pastes based on fayalite are fire-resistant up to 1150 °C. Moreover, after heat treatment at this temperature, the compressive strength increased by 75% to 139 MPa, while water absorption reduced by about 9 times to 1.2%. These improvements are explained with the crystallization of the geopolymer gel to leucite and K,Na-sanidine, and substitutions of Al/Fe in the geopolymer gel and iron phases. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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11 pages, 3845 KiB

Open AccessArticle

Study on Solidification and Stabilization of Antimony-Containing Tailings with Metallurgical Slag-Based Binders

by Yunyun Li, Wen Ni, Wei Gao, Siqi Zhang, Pingfeng Fu and Yue Li

Materials 2022, 15(5), 1780; https://doi.org/10.3390/ma15051780 - 26 Feb 2022

Cited by 11 | Viewed by 2797

Abstract

Blast furnace slag (BFS), steel slag (SS), and flue gas desulfurized gypsum (FGDG) were used to prepare metallurgical slag-based binder (MSB), which was afterwards mixed with high-antimony-containing mine tailings to form green mining fill samples (MBTs) for Sb solidification/stabilization (S/S). Results showed that [...] Read more.

Blast furnace slag (BFS), steel slag (SS), and flue gas desulfurized gypsum (FGDG) were used to prepare metallurgical slag-based binder (MSB), which was afterwards mixed with high-antimony-containing mine tailings to form green mining fill samples (MBTs) for Sb solidification/stabilization (S/S). Results showed that all MBT samples met the requirement for mining backfills. In particular, the unconfined compressive strength of MBTs increased with the curing time, exceeding that of ordinary Portland cement (OPC). Moreover, MBTs exhibited the better antimony solidifying properties, and their immobilization efficiency could reach 99%, as compared to that of OPC. KSb(OH)₆ was used to prepare pure MSB paste for solidifying mechanism analysis. Characteristics of metallurgical slag-based binder (MSB) solidified/stabilized antimony (Sb) were investigated via X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). According to the results, the main hydration products of MSB were C-S-H gel and ettringite. Among them, C-S-H gel had an obvious adsorption and physical sealing effect on Sb, and the incorporation of Sb would reduce the degree of C-S-H gel polymerization. Besides, ettringite was found to exert little impact on the solidification and stabilization of Sb. However, due to the complex composition of MSB, it was hard to conclude whether Sb entered the ettringite lattice. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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22 pages, 15998 KiB

Open AccessArticle

Methodologies for the Possible Integral Generation of Geopolymers Based on Copper Tailings

by Hengels Castillo, Humberto Collado, Thomas Droguett, Sebastián Sánchez, Mario Vesely, Pamela Garrido and Sergio Palma

Minerals 2021, 11(12), 1367; https://doi.org/10.3390/min11121367 - 3 Dec 2021

Cited by 3 | Viewed by 3244

Abstract

It is of interest to study the use of copper tailings as a raw material to generate geopolymers due to the exorbitant amounts of existing tailings deposits, which also produce different risks to nearby communities. Therefore, using this industrial waste as construction material [...] Read more.

It is of interest to study the use of copper tailings as a raw material to generate geopolymers due to the exorbitant amounts of existing tailings deposits, which also produce different risks to nearby communities. Therefore, using this industrial waste as construction material would result in several environmental and economic benefits. Due to the above, it is necessary to perform laboratory tests that account for the relevant variables to obtain fresh geopolymer pastes with good consistency, and to obtain hardened geopolymers with good mechanical strength. This report gives an account of the experimental work carried out in the laboratory of the CIMS Sustainable Mining Research Center of the Engineering Consulting Company JRI, exposing the preliminary results observed in the generation of geopolymers by means of seven different methods using copper tailings and NaOH. Of the seven methods evaluated in the laboratory, it was observed that two of them deliver better results from a qualitative point of view, where the influence of the curing stage stands out, reflecting that temperature is one of the critical variables for the formation of geopolymers based on copper tailings and NaOH. The best means to work the mixtures should be studied to optimize the solubility of the NaOH and, therefore, the dissolution of the aluminosilicates in the tailings. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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13 pages, 1298 KiB

Open AccessArticle

Life Cycle Assessment and Impact Correlation Analysis of Fly Ash Geopolymer Concrete

by Xiaoshuang Shi, Cong Zhang, Yongchen Liang, Jinqian Luo, Xiaoqi Wang, Ying Feng, Yanlin Li, Qingyuan Wang and Abd El-Fatah Abomohra

Materials 2021, 14(23), 7375; https://doi.org/10.3390/ma14237375 - 1 Dec 2021

Cited by 46 | Viewed by 3986

Abstract

Geopolymer concrete (GPC) has drawn widespread attention as a universally accepted ideal green material to improve environmental conditions in recent years. The present study systematically quantifies and compares the environmental impact of fly ash GPC and ordinary Portland cement (OPC) concrete under different [...] Read more.

Geopolymer concrete (GPC) has drawn widespread attention as a universally accepted ideal green material to improve environmental conditions in recent years. The present study systematically quantifies and compares the environmental impact of fly ash GPC and ordinary Portland cement (OPC) concrete under different strength grades by conducting life cycle assessment (LCA). The alkali activator solution to fly ash ratio (S/F), sodium hydroxide concentration (C_NaOH), and sodium silicate to sodium hydroxide ratio (SS/SH) were further used as three key parameters to consider their sensitivity to strength and CO₂ emissions. The correlation and influence rules were analyzed by Multivariate Analysis of Variance (MANOVA) and Gray Relational Analysis (GRA). The results indicated that the CO₂ emission of GPC can be reduced by 62.73%, and the correlation between CO₂ emission and compressive strength is not significant for GPC. The degree of influence of the three factors on the compressive strength is C_NaOH (66.5%) > SS/SH (20.7%) > S/F (9%) and on CO₂ emissions is S/F (87.2%) > SS/SH (10.3%) > C_NaOH (2.4%). Fly ash GPC effectively controls the environmental deterioration without compromising its compressive strength; in fact, it even in favor. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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21 pages, 5781 KiB

Open AccessFeature PaperArticle

Preparation and Characterization of the Functional Properties of Synthetic Aggregates from Silico-Manganese Slag

by Zhibing Xing, Fenglan Han, Jiuliang Tian, Zhichao Xu, Jiaqi Wang, Tengteng Liu, Bin Zheng and Jiahe Huang

Materials 2021, 14(23), 7303; https://doi.org/10.3390/ma14237303 - 29 Nov 2021

Cited by 9 | Viewed by 2815

Abstract

A large number of natural aggregates are used in the field of construction materials, resulting in the exhaustion of natural aggregates. Therefore, looking for an alternative will slow down the consumption of natural aggregates. The sintering method not only consumes a lot of [...] Read more.

A large number of natural aggregates are used in the field of construction materials, resulting in the exhaustion of natural aggregates. Therefore, looking for an alternative will slow down the consumption of natural aggregates. The sintering method not only consumes a lot of energy to prepare aggregates but also produces a lot of pollutants. In this study, silico-manganese (SM) slag was dried, ground into powder, and used as raw material. Solid and liquid alkaline activator methods were used to prepare SM slag non-burning aggregate (SMNA) by the cold bonding method. The effects of grinding time, amounts of solid and liquid alkaline activators, curing temperature, and the amount of added fly ash on aggregate properties were investigated. The aggregate microstructure was characterized by XRD, SEM, and FTIR methods, and the toxic leaching analysis of aggregate was performed. The results showed that with a fixed amount of liquid activator (16.2% wt.) and solid activator (15% wt.) and fly ash (20% wt.), respectively, and curing was performed at room temperature, the aggregate properties were optimal: the bulk density of 1236.6–1476.9 kg/m³ and the water absorption lower than 4.9–5.5%. The apparent density was 1973.1–2281.6 kg/m³, and the bulk crushing strength was 24.7–27.9 MPa. The XRD, SEM, and FTIR results indicated that amorphous gel could be formed from SM under an alkaline activator, improving the aggregate strength. The results of toxic leaching showed that the aggregate prepared from SM exhibited environmentally friendly characteristics. The SMNA was obtained via the simple and low-energy consumption production process, paving the new way toward large-scale utilization of SM. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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28 pages, 3115 KiB

Open AccessReview

Factors Affecting the Compressive Strength of Geopolymers: A Review

by Hengels Castillo, Humberto Collado, Thomas Droguett, Sebastián Sánchez, Mario Vesely, Pamela Garrido and Sergio Palma

Minerals 2021, 11(12), 1317; https://doi.org/10.3390/min11121317 - 25 Nov 2021

Cited by 101 | Viewed by 10822

Abstract

Geopolymers are created by mixing a source of aluminosilicates, which can be natural or by-products from other industries, with an alkaline solution. These materials based on by-products from other industries have proven to be a less polluting alternative for concrete production than ordinary [...] Read more.

Geopolymers are created by mixing a source of aluminosilicates, which can be natural or by-products from other industries, with an alkaline solution. These materials based on by-products from other industries have proven to be a less polluting alternative for concrete production than ordinary Portland cement (OPC). Geopolymers offer many advantages over OPC, such as excellent mechanical strength, increased durability, thermal resistance, and excellent stability in acidic and alkaline environments. Within these properties, mechanical strength, more specifically compressive strength, is the most important property for analyzing geopolymers as a construction material. For this reason, this study compiled information on the different variables that affect the compressive strength of geopolymers, such as Si/Al ratio, curing temperature and time, type and concentration of alkaline activator, water content, and the effect of impurities. From the information collected, it can be mentioned that geopolymers with Si/Al ratios between 1.5 and 2.0 obtained the highest compressive strengths for the different cases. On the other hand, high moderate temperatures (between 80 and 90 °C) induced higher compressive strengths in geopolymers, because the temperature favors the geopolymerization process. Moreover, longer curing times helped to obtain higher compressive strengths for all the cases analyzed. Furthermore, it was found that the most common practice is the use of sodium hydroxide combined with sodium silicate to obtain geopolymers with good mechanical strength, where the optimum SS/NaOH ratio depends on the source of aluminosilicates to be used. Generally speaking, it was observed that higher water contents lead to a decrease in compressive strength. The presence of calcium was found to be favorable in controlled proportions as it increases the compressive strength of geopolymers, on the other hand, impurities such as heavy metals have a negative effect on the compressive strength of geopolymers. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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19 pages, 6189 KiB

Open AccessArticle

Long-Term Physical and Mechanical Properties and Microstructures of Fly-Ash-Based Geopolymer Composite Incorporating Carbide Slag

by Xianhui Zhao, Haoyu Wang, Linlin Jiang, Lingchao Meng, Boyu Zhou and Jiashuo Zhang

Materials 2021, 14(21), 6692; https://doi.org/10.3390/ma14216692 - 6 Nov 2021

Cited by 12 | Viewed by 2706

Abstract

The long-term property development of fly ash (FA)-based geopolymer (FA–GEO) incorporating industrial solid waste carbide slag (CS) for up to 360 d is still unclear. The objective of this study was to investigate the fresh, physical, and mechanical properties and microstructures of FA–GEO [...] Read more.

The long-term property development of fly ash (FA)-based geopolymer (FA–GEO) incorporating industrial solid waste carbide slag (CS) for up to 360 d is still unclear. The objective of this study was to investigate the fresh, physical, and mechanical properties and microstructures of FA–GEO composites with CS and to evaluate the effects of CS when the composites were cured for 360 d. FA–GEO composites with CS were manufactured using FA (as an aluminosilicate precursor), CS (as a calcium additive), NaOH solution (as an alkali activator), and standard sand (as a fine aggregate). The fresh property and long-term physical properties were measured, including fluidity, bulk density, porosity, and drying shrinkage. The flexural and compressive strengths at 60 d and 360 d were tested. Furthermore, the microstructures and gel products were characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results show that the additional 20.0% CS reduces the fluidity and increases the conductivity of FA–GEO composites. Bulk densities were decreased, porosities were increased, and drying shrinkages were decreased as the CS content was increased from 0.0% to 20.0% at 360 d. Room temperature is a better curing condition to obtain a higher long-term mechanical strength. The addition of 20.0% CS is more beneficial to the improvement of long-term flexural strength and toughness at room temperature. The gel products in CS–FA–GEO with 20.0% CS are mainly determined as the mixtures of sodium aluminosilicate (N–A–S–H) gel and calcium silicate hydration (C–S–H) gel, besides the surficial pan-alkali. The research results provide an experimental basis for the reuse of CS in various scenarios. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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19 pages, 6688 KiB

Open AccessArticle

Recycling of Mechanically Ground Wind Turbine Blades as Filler in Geopolymer Composite

by Kinga Pławecka, Jakub Przybyła, Kinga Korniejenko, Wei-Ting Lin, An Cheng and Michał Łach

Materials 2021, 14(21), 6539; https://doi.org/10.3390/ma14216539 - 30 Oct 2021

Cited by 37 | Viewed by 3448

Abstract

This paper concerns the recycling of waste material from wind turbine blades. The aim of the research was to determine the possibility of using ground waste material derived from the exploited structures of wind turbines as a filler in geopolymer composites. In order [...] Read more.

This paper concerns the recycling of waste material from wind turbine blades. The aim of the research was to determine the possibility of using ground waste material derived from the exploited structures of wind turbines as a filler in geopolymer composites. In order to determine the potential of such a solution, tests were carried out on three different fractions originating from the ground blades of wind turbines, including an analysis of the morphology and chemical composition of particles using SEM and an EDS detector, the analysis of organic and inorganic matter content and tests for multivariate geopolymer composites with the addition of waste material. The compression and flexural strength, density and absorbability tests, among others, were carried out. The composite material made of the geopolymer matrix contained the filler at the level of 5%, 15% and 30% of dry mass. The addition of the filler showed a tendency to decrease the properties of the obtained geopolymer composite. However, it was possible to obtain materials that did not significantly differ in properties from the re-reference sample for the filler content of 5% and 15% of dry mass. As a result of the research, it was found that waste materials from the utilization of used wind power plants can become fillers in geopolymer composites. It was also found that it is possible to increase the strength of the obtained material by lowering the porosity. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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13 pages, 3426 KiB

Open AccessArticle

KCl Extracted from Chlorine Bypass Dust as Activator for Plain Concrete

by Hong-Beom Choi, Jin-Man Kim, Sun-Mi Choi and Sung-Su Kim

Materials 2021, 14(20), 6091; https://doi.org/10.3390/ma14206091 - 15 Oct 2021

Cited by 1 | Viewed by 2342

Abstract

This study demonstrated the use of KCl separated from chlorine bypass dust (CBD) as an activator for plain concrete. The separated KCl was mixed with either ground granulated blast-furnace slag (BFS) alone, or a mixture of BFS and cement. The mixed paste of [...] Read more.

This study demonstrated the use of KCl separated from chlorine bypass dust (CBD) as an activator for plain concrete. The separated KCl was mixed with either ground granulated blast-furnace slag (BFS) alone, or a mixture of BFS and cement. The mixed paste of separated KCl and BFS set within 24 h, and exhibited a compressive strength of 22.6 MPa after 28 d. The separated KCl, cement, and BFS mixture exhibited a more rapid setting and a higher initial activity. Further, the compressive strength at 28 d was 57.7 MPa, which was 26.2% higher than that of the mixture without the activator. Water curing of samples with added separated KCl led to the generation of hydrocalumite, or Friedel’s salt. However, this hydrocalumite was decomposed while being cured under autoclave conditions at 180 °C. Overall, KCl was an effective activator for composite materials containing cement, and resulted in superior properties compared to mineral admixtures without an activator. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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15 pages, 4851 KiB

Open AccessArticle

Determination of the Influence of Hydraulic Additives on the Foaming Process and Stability of the Produced Geopolymer Foams

by Michał Łach, Kinga Pławecka, Agnieszka Bąk, Katarzyna Lichocka, Kinga Korniejenko, An Cheng and Wei-Ting Lin

Materials 2021, 14(17), 5090; https://doi.org/10.3390/ma14175090 - 6 Sep 2021

Cited by 26 | Viewed by 3193

Abstract

The research described in this article was aimed at determining the influence of hydraulic additives on the foaming process and the stability of the produced geopolymer foams. These foams can be used as insulation materials to replace the currently commonly used insulations such [...] Read more.

The research described in this article was aimed at determining the influence of hydraulic additives on the foaming process and the stability of the produced geopolymer foams. These foams can be used as insulation materials to replace the currently commonly used insulations such as expanded polystyrene or polyurethane foams. Geopolymers have low thermal conductivity, excellent fire- and heat-resistant properties, and have fairly good mechanical properties. Research on foamed materials shows that they have the highest class of fire resistance; therefore, they are most often used as insulation products in construction. Geopolymer foams were made of aluminosilicate materials (fly ash) and foaming agents (H₂O₂ and Al powder), and the stabilizers were gypsum and portland cement. Additionally, surfactants were also used. It was found that better foaming effects were obtained for H₂O₂—it is a better foaming agent for geopolymers than Al powder. When using a hydraulic additive—a stabilizer in the form of cement—lower densities and better insulation parameters were obtained than when using gypsum. Portland cement is a better stabilizer than gypsum (calcium sulfates), although the effect may change due to the addition of surfactants, for example. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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14 pages, 10602 KiB

Open AccessArticle

Foamed Geopolymer Composites with the Addition of Glass Wool Waste

by Barbara Kozub, Patrycja Bazan, Rihards Gailitis, Kinga Korniejenko and Dariusz Mierzwiński

Materials 2021, 14(17), 4978; https://doi.org/10.3390/ma14174978 - 31 Aug 2021

Cited by 25 | Viewed by 3618

Abstract

This study examines foamed geopolymer composites based on fly ash from the Skawina coal-fired power plant in Poland. The paper presents the effect of adding 3% and 5% by weight of glass wool waste on selected properties of foamed geopolymers. The scope of [...] Read more.

This study examines foamed geopolymer composites based on fly ash from the Skawina coal-fired power plant in Poland. The paper presents the effect of adding 3% and 5% by weight of glass wool waste on selected properties of foamed geopolymers. The scope of the tests carried out included density measurements, compressive and bending strength tests, measurements of the heat conduction coefficient, and the results of measurements of changes in thermal radiation in samples subjected to a temperature of 800 °C. The obtained results indicate that glass wool waste can be successfully used to lower the density and heat conduction coefficient of foamed geopolymer composites with a fly ash matrix. In addition, the results of changes in thermal radiation in the samples subjected to the temperature of 800 °C showed a positive effect of the addition of glass wool waste. Moreover, the introduction of the addition of glass wool waste made it possible to increase the compressive strength of the examined foamed geopolymers. For the material modified with 3% by weight of mineral wool, the increase in compressive strength was about 10%, and the increase in fibers in the amount of 5% by weight resulted in an increase of 20% concerning the base material. The obtained results seem promising for future applications. Such materials can be used in technical constructions as thermal insulation materials. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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20 pages, 39966 KiB

Open AccessArticle

Printing Parameter Requirements for 3D Printable Geopolymer Materials Prepared from Industrial Side Streams

by Qaisar Munir, Riku Peltonen and Timo Kärki

Materials 2021, 14(16), 4758; https://doi.org/10.3390/ma14164758 - 23 Aug 2021

Cited by 17 | Viewed by 3162

Abstract

The objective of this investigation is to study the printing parameter requirements for sustainable 3D printable geopolymer materials. Side streams of the paper, mining, and construction industries were applied as geopolymer raw materials. The effect of printing parameters in terms of buildability, mixability, [...] Read more.

The objective of this investigation is to study the printing parameter requirements for sustainable 3D printable geopolymer materials. Side streams of the paper, mining, and construction industries were applied as geopolymer raw materials. The effect of printing parameters in terms of buildability, mixability, extrudability, curing, Al-to-Si ratio, and waste materials utilisation on the fresh and hardened state of the materials was studied. The material performance of a fresh geopolymer was measured using setting time and shape stability tests. Standardised test techniques were applied in the testing of the hardened material properties of compressive and flexural strength. The majority of developed suitable 3D printable geopolymers comprised 56–58% recycled material. Heating was used to improve the buildability and setting of the material significantly. A reactive recyclable material content of greater than 20% caused the strength and material workability to decrease. A curing time of 7–28 days increased the compressive strength but decreased the flexural strength. The layers in the test samples exhibited decreased and increased strength, respectively, in compressive and flexural strength tests. Geopolymer development was found to be a compromise between different strength values and recyclable material contents. By focusing on specialised and complex-shape products, 3D printing of geopolymers can compete with traditional manufacturing in limited markets. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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21 pages, 22743 KiB

Open AccessArticle

Effect of Fine Aggregate Particle Characteristics on Mechanical Properties of Fly Ash-Based Geopolymer Mortar

by Heng Li, Pengpeng Gao, Fang Xu, Tao Sun, Yu Zhou, Jing Zhu, Chao Peng and Juntao Lin

Minerals 2021, 11(8), 897; https://doi.org/10.3390/min11080897 - 19 Aug 2021

Cited by 25 | Viewed by 3900

Abstract

This research aimed to investigate the effect of fine aggregate particles on mechanical properties of fly ash-based geopolymer mortar. In this work, seven kinds of river sand particles were designed based on different fine aggregate characteristics. The fineness modulus was adopted to quantitatively [...] Read more.

This research aimed to investigate the effect of fine aggregate particles on mechanical properties of fly ash-based geopolymer mortar. In this work, seven kinds of river sand particles were designed based on different fine aggregate characteristics. The fineness modulus was adopted to quantitatively describe the gradation of sands. The fluidity, compressive, flexural, and tensile strengths of geopolymer mortar with different sand gradations were analyzed by laboratory tests. Furthermore, the composition and morphology of fly ash-based geopolymer mortar was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reasonable gradation range and filling effect of sand were obtained. The results show that fluidity and compressive and flexural strengths of geopolymer mortar both improve with the increase of the fineness modulus, while specific surface area and voidage are opposite. The tensile strength of mortar largely lies on the interface properties between the geopolymer binder and fine aggregates. When the pass rate of the key sieving size 1.18 mm is 75–95%, the pass rate of the key sieving size 0.15 mm is 15–25%, the fineness modulus is 2.2–2.6 and the appropriate filling coefficient of geopolymer paste is around 1.0–1.15, the comprehensive performance of geopolymer mortar is the best. This research paper could provide a basis for the design of geopolymer mortar based on fly ash, and it is of great significance for its popularization and application. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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15 pages, 3901 KiB

Open AccessArticle

The Influence of Short Coir, Glass and Carbon Fibers on the Properties of Composites with Geopolymer Matrix

by Kinga Korniejenko, Michał Łach and Janusz Mikuła

Materials 2021, 14(16), 4599; https://doi.org/10.3390/ma14164599 - 16 Aug 2021

Cited by 29 | Viewed by 2753

Abstract

The aim of the article is to analyze the influence of short coir, glass and carbon fiber admixture on the mechanical properties of fly ash-based geopolymer, such as: flexural and compressive strength. Glass fiber and carbon fibers have been chosen due to their [...] Read more.

The aim of the article is to analyze the influence of short coir, glass and carbon fiber admixture on the mechanical properties of fly ash-based geopolymer, such as: flexural and compressive strength. Glass fiber and carbon fibers have been chosen due to their high mechanical properties. Natural fibers have been chosen because of their mechanical properties as well as for the sake of comparison between their properties and the properties of the artificial ones. Fourth series of fly ash-based geopolymers for each fiber was cast: 1, 2, and 5% by weight of fly ash and one control series without any fibers. Each series of samples were tested on flexural and compressive strength after 7, 14, and 28 days. Additionally, microstructural analysis was carried out after 28 days. The results have shown an increase in compressive strength for composites with fibers—an improvement in properties between 25.0% and 56.5% depending on the type and amount of fiber added. For bending strength, a clear increase in the strength value is visible for composites with 1 and 2% carbon fibers (62.4% and 115.6%). A slight increase in flexural strength also occurred for 1% addition of glass fiber (4.5%) and 2% addition of coconut fibers (5.4%). For the 2% addition of glass fibers, the flexural strength value did not change compared to the value obtained for the matrix material. For the remaining fiber additions, i.e., 5% glass fiber as well as 1 and 5% coconut fibers, the flexural strength values deteriorated. The results of the research are discussed in a comparative context and the properties of the obtained composites are juxtaposed with the properties of the standard materials used in the construction industry. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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13 pages, 5192 KiB

Open AccessArticle

Workability and Flexural Properties of Fibre-Reinforced Geopolymer Using Different Mono and Hybrid Fibres

by Jacob Junior, Ashish Kumer Saha, Prabir Kumar Sarker and Alokesh Pramanik

Materials 2021, 14(16), 4447; https://doi.org/10.3390/ma14164447 - 8 Aug 2021

Cited by 18 | Viewed by 2624

Abstract

The effects of mono (single type) and hybrid (mixed types) fibres on the workability, compressive strength, flexural strength, and toughness parameters of fly ash geopolymer mortar were studied. The ratio of sand to geopolymer paste of the mortar was 2.75. It was found [...] Read more.

The effects of mono (single type) and hybrid (mixed types) fibres on the workability, compressive strength, flexural strength, and toughness parameters of fly ash geopolymer mortar were studied. The ratio of sand to geopolymer paste of the mortar was 2.75. It was found that workability of mortar decreased more with the use of PP fibres due to its higher dispersion into individual filaments in geopolymer mortar compared to the bundled ARG and PVA fibres. Compressive strength increased by 14% for using 1% steel with 0.5% PP fibres compared to that of the control mixture, which was 48 MPa. However, 25 to 30% decrease of compressive strength was observed in the mortars using the low-modulus fibres. Generally, flexural strength followed the trend of compressive strength. Deflection hardening behaviours in terms of the ASTM C1609 toughness indices, namely I5, I10 and I20 were exhibited by the mortars using 1% steel mono fibres, 0.5% ARG with 0.5% steel and 1% PVA with 0.5% steel hybrid fibres. The toughness indices and residual strength factors of the mortars using the other mono or hybrid fibres at 1 or 1.5% dosage were relatively low. Therefore, multiple cracking and deflection hardening behaviours could be achieved in fly ash geopolymer mortars of high sand to binder ratio by using steel fibres in mono or hybrid forms with ARG and PVA fibres. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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14 pages, 4189 KiB

Open AccessArticle

Long-Term Strength Development of Fly Ash-Based One-Part Alkali-Activated Binders

by Sani Haruna, Bashar S. Mohammed, Mohamed Mubarak A. Wahab, Mubarak Usman Kankia, Mugahed Amran and Abdurra’uf Mukhtar Gora

Materials 2021, 14(15), 4160; https://doi.org/10.3390/ma14154160 - 27 Jul 2021

Cited by 46 | Viewed by 3180

Abstract

This research aims to study the effect of the dosage of anhydrous sodium metasilicate activator on the long-term properties of fly ash-based one-part alkali-activated binders (OPAAB) cured at ambient conditions. Powdered sodium metasilicate activator was utilized in the range of 8–16% by weight [...] Read more.

This research aims to study the effect of the dosage of anhydrous sodium metasilicate activator on the long-term properties of fly ash-based one-part alkali-activated binders (OPAAB) cured at ambient conditions. Powdered sodium metasilicate activator was utilized in the range of 8–16% by weight of the fly ash in producing the OPAAB. The properties examined are hardened density, compressive strength, flexural strength, water absorption, efflorescence formation, and microstructural analysis. The experimental result revealed that the binders exhibited excellent long-term strength properties. The compressive strength of the OPAAP is well correlated with its hardened density. The pastes were found to exhibit good soundness characteristics over the long-term. The absorption of water decreases with an increase in the activator dosage from 8–12%, and beyond that, the water absorption relatively remains the same. Field emission scanning electron microscope (FESEM) micrograph revealed uniformly formed solid matrices with the micro-crack present were observed in the samples. The larger pore size promotes the crystallization of the resulting hydrate substances (N, C)-A-S-H gel. The initial dissolution of the OPAAP occurred within the first 30 min. At longer age of curing, mixtures with a higher dosage of powdered activator tend to absorb less water. Strength properties beyond 28 days are considered as the long-term strength. Full article

(This article belongs to the Topic Geopolymers: Synthesis, Characterization and Applications)

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