Research

18 pages, 55046 KiB

Open AccessArticle

Evaluation of As-Received Green Liquor Dregs and Biomass Ash Residues from a Pulp and Paper Industry as Raw Materials for Geopolymers

by Rafael Vidal Eleutério, Lisandro Simão, Priscila Lemes and Dachamir Hotza

Minerals 2023, 13(9), 1158; https://doi.org/10.3390/min13091158 - 31 Aug 2023

Cited by 1 | Viewed by 906

Abstract

This study aimed to investigate the impact of as-received biomass fly ashes (BFA) and green liquor dregs obtained from a pulp and paper plant in Brazil as substitutes for metakaolin in geopolymeric formulations. The properties of this type of waste material vary widely [...] Read more.

This study aimed to investigate the impact of as-received biomass fly ashes (BFA) and green liquor dregs obtained from a pulp and paper plant in Brazil as substitutes for metakaolin in geopolymeric formulations. The properties of this type of waste material vary widely between different industrial plants. This study refrains from subjecting the waste materials to any form of pretreatment, taking into account their organic matter and particle size heterogeneity, requiring extensive characterization to evaluate their influence on the compressive strength, apparent open porosity, and water absorption of the geopolymeric samples. The objective was to assess their potential for upcycling purposes as an alternative to energy-intensive materials, such as ordinary Portland cement (OPC) and advanced ceramics. This potential arises from the ability of alkali-activated materials (AAM) to undergo curing at ambient temperatures, coupled with the possibility of compositions primarily derived from waste materials. To improve the sustainability of the products, the amorphous content of the raw material, which is more reactive than crystalline phases, was quantified and used as the base for mixture ratios. This approach aimed to reduce the requirement for alkaline activators, which have significant environmental impacts, while also increasing the waste content in the formulation. The incorporation of waste materials into the geopolymer matrix generally led to a reduction in the compressive strength compared to the benchmark metakaolin sample (19.4 MPa) but did not present a trend. The dregs led to values of 4.1 MPa at 25 wt% and 7.1 MPa at 50 wt%, a behavior that is somewhat counterintuitive, and BFA at 10 wt% presented 5.7 MPa. Nevertheless, the apparent open porosity remained at high levels for all the samples, close to 50%, and the compressive strength of most of them was over the values obtained for the metakaolin-only samples with mixture ratios calculated from the total composition instead of the amorphous composition. The decrease in strength and the increase in porosity were attributed to the specific characteristics of the waste materials, such as their high crystallinity, presence of organic matter, heterogeneous particle composition, and size. Overall, this study provides insight into the variations in geopolymerization based on the bulk and amorphous content of the aluminosilicate sources and how the characteristics of the waste materials influence the geopolymer matrix. It also highlights how calculating mixture ratios based on the amorphous composition improves the possibility of waste valorization through alkali activation. Additionally, it suggests that BFA and dregs might be effectively utilized in applications other than OPC substitution, such as adsorption, filtration, and catalysis. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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17 pages, 4122 KiB

Open AccessArticle

Rheology, Setting, Heat of Reaction, and Compressive Strength of a Geopolymer Radioactive Waste Form

by Sepideh Akhbarifar, Weiliang Gong, Werner Lutze and Ian L. Pegg

Minerals 2023, 13(8), 999; https://doi.org/10.3390/min13080999 - 28 Jul 2023

Viewed by 841

Abstract

This work contributes to our understanding of the properties of geopolymers as waste forms made of three pozzolans, to be used, e.g., to immobilize liquid low-activity radioactive waste. A binary blast furnace slag and metakaolin geopolymer composition was tailored to achieve flexible rheological [...] Read more.

This work contributes to our understanding of the properties of geopolymers as waste forms made of three pozzolans, to be used, e.g., to immobilize liquid low-activity radioactive waste. A binary blast furnace slag and metakaolin geopolymer composition was tailored to achieve flexible rheological properties and workability for in-can mixing or mixing/pumping applications by adding fly ash, a third pozzolan. We investigated quantitatively the early stages of geopolymerization (before and after setting) of alkali-activated slag–metakaolin–fly ash pozzolans. The effect of fly ash glass particle size on material properties was studied as well. Measurements include heat of reaction, compressive strength, yield stress, plastic viscosity, rheological setting, as well as initial and final setting following the Vicat method. A rheological time of initial setting is suggested for geopolymers, in analogy to Portland cement. The results of Vicat needle and rheological measurements are compared and quantitatively related to heat and set time data. Maximum heat flow and compressive strength are linearly correlated. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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Graphical abstract

18 pages, 4906 KiB

Open AccessArticle

Strength Development and Durability of Metakaolin Geopolymer Mortars Containing Pozzolans under Different Curing Conditions

by Burak Işıkdağ and Mohammad Rahim Yalghuz

Minerals 2023, 13(7), 857; https://doi.org/10.3390/min13070857 - 24 Jun 2023

Cited by 2 | Viewed by 1443

Abstract

This study presents the strength development and durability of heat and non-heat-cured geopolymer mortars (GMs) produced using metakaolin (MK), ground granulated blast-furnace slag (GGBFS), silica fume (SF), ground calcined perlite (GCP), raw perlite (RP), potassium hydroxide (KOH), sodium metasilicate (Na₂SiO₃ [...] Read more.

This study presents the strength development and durability of heat and non-heat-cured geopolymer mortars (GMs) produced using metakaolin (MK), ground granulated blast-furnace slag (GGBFS), silica fume (SF), ground calcined perlite (GCP), raw perlite (RP), potassium hydroxide (KOH), sodium metasilicate (Na₂SiO₃), standard sand, and tap water. An optimal combination of MK with various pozzolans and constant solid/liquid and alkaline activator ratios were determined. It was found that the GMs, including MK and GGBFS with a 1.45 solid/liquid ratio and 2.0 alkaline activator ratio, resulted in compressive strength at 88 MPa. Analysis of GMs was performed using scanning electron microscopy (SEM), EDX (Energy Scattered X-ray Spectrophotometer), and X-ray diffraction (XRD). According to the results obtained, mainly alumino-silicate-based formation, potassium from KOH solution, and calcium from GGBFS were determined. The SEM images showed that the grains with high silica content, approximately 6–7 µm in size, are quartz crystals and embedded in the gel structure. The heat-cured GMs were exposed to MgSO₄, Na₂SO₄, and HCl solutions for the durability tests. The strength of the heat-cured GMs was higher than the non-heat-cured GMs, and the durability of the heat-cured GMs was found as sufficient. The use of pozzolans in GMs resulted in improvements in terms of strength and durability. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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11 pages, 2919 KiB

Open AccessArticle

Effect of Hydrogen Peroxide on the Thermal and Mechanical Properties of Lightweight Geopolymer Mortar Panels

by Cleidson Alves, Fernando Pelisser, João Labrincha and Rui Novais

Minerals 2023, 13(4), 542; https://doi.org/10.3390/min13040542 - 12 Apr 2023

Viewed by 1122

Abstract

Lightweight geopolymers have been researched and used in specific applications due to their differentiated properties and, particularly, due to the lower environmental impacts in their manufacture, mainly associated with the use of raw materials with a low environmental impact and the reduction in [...] Read more.

Lightweight geopolymers have been researched and used in specific applications due to their differentiated properties and, particularly, due to the lower environmental impacts in their manufacture, mainly associated with the use of raw materials with a low environmental impact and the reduction in greenhouse gas emissions. In this study, light geopolymers, using metakaolin, sodium silicate, sodium hydroxide, and hydrogen peroxide (H₂O₂), were evaluated. The effects of H₂O₂ concentration were evaluated up to a concentration of 1% in pastes and mortars. The properties of thermal conductivity, density, compressive strength, and modulus of elasticity were determined. The simulation of the thermal transmittance of cladding panels applied to a facade was also performed. Mortars with a H₂O₂ concentration of 0.2% obtained a compressive strength of 18 MPa and thermal conductivity of 0.55 W/mK, which was 60% less than the thermal conductivity obtained for the reference composition. The simulation of a panel for use on a facade showed that the thermal resistance increased from 0.27 (m².K/W) to 0.42 (m².K/W), indicating the efficiency of the geopolymer for use as a thermal control material. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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17 pages, 6981 KiB

Open AccessArticle

Research on Reducing Shrinkage Behavior of Ground Granulated Blast Furnace Slag Geopolymers Using Polymer Materials

by Wen-Ten Kuo, Chuen-Ul Juang and Yu-Wei Shiu

Minerals 2023, 13(4), 475; https://doi.org/10.3390/min13040475 - 28 Mar 2023

Viewed by 964

Abstract

Geopolymers are a new type of environmentally friendly cement-based material with serious drying shrinkage problems. In order to overcome this problem and improve the engineering performance and durability of geopolymers, in this study we added 0%, 0.3%, 0.5%, 0.7%, and 0.9% polymer materials, [...] Read more.

Geopolymers are a new type of environmentally friendly cement-based material with serious drying shrinkage problems. In order to overcome this problem and improve the engineering performance and durability of geopolymers, in this study we added 0%, 0.3%, 0.5%, 0.7%, and 0.9% polymer materials, namely, polyacrylamide, sodium polyacrylate, and sodium tetraborate, respectively, to geopolymers to reduce their degree of shrinkage. We also assessed changes in their length and durability to determine how the addition of polymer materials could reduce their degree of shrinkage. The results indicate that 0.7% sodium tetraborate yielded the most favored shrinkage, and, through imaging technology, the crack change at the age of 0–3 days was measured, during which polyacrylamide (PAM) effectively slowed down the dimensions of crack propagation by 0.47% compared with the control group. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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21 pages, 12594 KiB

Open AccessFeature PaperArticle

Study of Carbonated Clay-Based Phosphate Geopolymer: Effect of Calcite and Calcination Temperature

by Rania Derouiche, Marwa Zribi and Samir Baklouti

Minerals 2023, 13(2), 284; https://doi.org/10.3390/min13020284 - 17 Feb 2023

Cited by 4 | Viewed by 1418

Abstract

This study aims to use natural carbonated Tunisian clay as an aluminosilicate precursor for the elaboration of phosphate-based geopolymers, which yields to the valorization of this common material in Tunisia. In addition, the presence of calcium carbonate in this clay allows the investigation [...] Read more.

This study aims to use natural carbonated Tunisian clay as an aluminosilicate precursor for the elaboration of phosphate-based geopolymers, which yields to the valorization of this common material in Tunisia. In addition, the presence of calcium carbonate in this clay allows the investigation of this associated mineral’s effect on the properties of geopolymeric materials. To achieve these purposes, several experimental techniques were used, namely fluorescence (FX), particle size analysis, thermogravimetric analysis (TGA), differential thermal analysis (DTA), dilatometric analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The mechanical strength and the open porosity of the obtained geopolymeric samples were tested by the compression test and the standard test method for water absorption, respectively. The findings of this work show that the used Tunisian clay can present an attractive aluminosilicate precursor for the synthesis of phosphate-based geopolymers. It also shows that the chosen calcination temperature of the raw clay considerably modifies the reactivity of minerals during geopolymerization and, consequently, strongly affects the properties and structure of the geopolymeric samples. These effects were attributed essentially to the formation of new calcium crystalline phases in the obtained geopolymeric samples. In fact, the anorthite (CaAl₂Si₂O₈) phase appears in all the samples but in greater abundance in those obtained from the clay calcined at 550 °C, and the brushite phase (CaHPO₄·2H₂O) appears only in the samples obtained from the clay calcined at 950 °C. All these new crystalline phases are strongly dependent on the state of the calcite present in the calcined clay. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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17 pages, 1643 KiB

Open AccessArticle

Use of Seashell and Limestone Fillers in Metakaolin-Based Geopolymers for Masonry Mortars

by Joseph Jean Assaad and Marianne Saba

Minerals 2023, 13(2), 186; https://doi.org/10.3390/min13020186 - 27 Jan 2023

Cited by 1 | Viewed by 1493

Abstract

Mortars intended for plastering and masonry works normally comply to EN 413-1 and/or ASTM C91 specifications. This paper seeks to assess the suitability of geopolymers (GPs) composed of metakaolin and seashell wastes for masonry applications. The sodium hydroxide and sodium silicate activators contained [...] Read more.

Mortars intended for plastering and masonry works normally comply to EN 413-1 and/or ASTM C91 specifications. This paper seeks to assess the suitability of geopolymers (GPs) composed of metakaolin and seashell wastes for masonry applications. The sodium hydroxide and sodium silicate activators contained air-entraining molecules to secure about 10% ± 2% air content. Just like the cement-based mortars, test results showed that the mechanical properties of GPs including the compressive strength, flexural strength, pull-off adhesion, and water sorptivity decreased when the seashell concentration increased in the mixture. This was mainly related to a dilution effect that reduces the aluminosilicate precursor content and formation of rigid bonds. The replacement of limestone filler by seashell powder slightly increased the mechanical properties, which was attributed to higher seashell hardness that densifies the microstructure and provides additional resistance to support the external stresses. Yet, the grinding of seashells into fine powder required higher energy than what is needed for the comminution of clinker or limestone. The use of GPs is particularly advantageous for masonry applications, as it speeds up the construction operations while eliminating the hassle of moist curing normally required with cement-based plasters. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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16 pages, 3243 KiB

Open AccessArticle

Improving the Behaviour of Green Concrete Geopolymers Using Different HEMP Preservation Conditions (Fresh and Wet)

by Mª Paz Sáez-Pérez, Jorge Alberto Durán-Suárez and Joao Castro-Gomes

Minerals 2022, 12(12), 1530; https://doi.org/10.3390/min12121530 - 29 Nov 2022

Cited by 5 | Viewed by 2017

Abstract

This paper evaluates a type of geopolymer concrete that uses hemp fibres as a natural aggregate due to the various advantages offered by these woody materials. These advantages include ease of cultivation and processing and their use in the essential structure of concretes [...] Read more.

This paper evaluates a type of geopolymer concrete that uses hemp fibres as a natural aggregate due to the various advantages offered by these woody materials. These advantages include ease of cultivation and processing and their use in the essential structure of concretes used for green construction purposes. The sampling study was prepared using an environmentally friendly inorganic binder, based on geopolymerization reactions (Si-Na). The improvement in the hemp aggregate using two different preservation methods (fresh and wet) was assessed. The type of conservation enables anaerobic reactions to take place in the structure of the hemp, in such a way as to modify the proportions of the organic compounds contained in the hemp and the morphology of the fibres. It also encourages the proliferation of cellulose nanofibrils (CNC), which enhance the mechanical results, improving plasticity and thixotropy. The hempcrete studied in this paper could be a good alternative material for sustainable, environmentally friendly construction, as much less CO₂ is emitted during the production process in comparison with conventional concrete. Using wet-preserved hemp means that less water must be added to the mix during preparation of the concrete. This also helps reduce production costs, and by extension, the cost of the final product. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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18 pages, 3742 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Alkali-Activated Metakaolins: Mineral Chemistry and Quantitative Mineral Composition

by Marta Valášková, Zdeněk Klika, Jozef Vlček, Lenka Matějová, Michaela Topinková, Helena Pálková and Jana Madejová

Minerals 2022, 12(11), 1342; https://doi.org/10.3390/min12111342 - 23 Oct 2022

Cited by 3 | Viewed by 1605

Abstract

The reaction products resulting from the alkali-activation of metakaolin are impacted by the composition of the initial kaolin, and amount of alkali-activated kaolinite and water. The present study focused on analyzing these parameters on the metakaolins calcined at 800 °C from three kaolins, [...] Read more.

The reaction products resulting from the alkali-activation of metakaolin are impacted by the composition of the initial kaolin, and amount of alkali-activated kaolinite and water. The present study focused on analyzing these parameters on the metakaolins calcined at 800 °C from three kaolins, and the metakaolins’ alkali activation for 2, 3 and 28 days. The first objective was to evaluate the mineral chemistry and quantitative mineral phase composition from the bulk chemical analysis using the chemical quantitative mineral analysis (CQMA) procedure and conduct a comparison of the chemistry of the metakaolins after alkali activation for 28 days according to the elements Al, Si, Na and K, using the leaching test in distilled water. The second task was to search for possible relationships between the quantitative number of phases in alkali-activated metakaolins and compressive strength. The main methods used for the characterization of material were X-ray fluorescence, X-ray diffraction, thermal TG/DTA and infrared spectroscopy. Metakaolins alkali activated for 28 days contained crystalline quartz, muscovite, orthoclase, and unreacted metakaolinite contained zeolite A (Z-A), hydrosodalite (HS) and thermonatrite (TN) in the amorphous/weakly crystalline phase. The compressive strengths (CS) from 6.42 ± 0.33 to 9.97 ± 0.50 MPa are related positively to H₂O+ and H₂O bound in HS and TN. Full article

(This article belongs to the Special Issue Development in Geopolymer Materials and Applications)

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