Geopolymers: Synthesis, Characterization and Applications II

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closed (29 February 2024)

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30 April 2024

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Topic Information

Dear Colleagues,

This proposed Interdisciplinary Topic is a continuation of the successful Special Issue “Geopolymers” in Minerals in 2018 and Interdisciplinary Topic “Geopolymers: Synthesis, Characterization and Applications” in 2021. Since its closure in September 2022, the 25 publications in the aforementioned Interdisciplinary Topic have had over 35000 views. Encouraged by the interest shown by readers, MDPI has decided to propose a second edition.

The term “geopolymer” was introduced in the early 1970s by Joseph Davidovits for inorganic polymeric materials, synthesized (by him) from natural (geo-) silicon and aluminum-containing sources, reacted with alkaline media (solvent). Geopolymers consist of repeating siloxonate (Na, K, Ca) (-Si-O-Si-O-) or sialate (Na, K, Ca) (-Si-O-Al-O-) units (oligomers), polycondensed into typically ceramic, covalently bounded, non-crystalline (amorphous) 3D networks. Further research widened their definition by adding ferro-sialate and alumino-phosphate oligomers, as well as acidic (using phosphoric or humic acids as solvent) geopolymerization routes.

The scientific interest in this innovative class of materials is driven by three main factors:

1. A series of features, making geopolymers applicable and even preferred for many industrial applications, including but not limited to:

• Geopolymer resins and binders;
• Geopolymer cements and concretes:
  • Low-tech building materials (geopolymer bricks, blocks and other cast elements);
  • Low-CO₂ cements and concretes.
• Fixing of potentially hazardous chemicals in water resistant (insoluble) geopolymers.

2. The possibility of employing in their synthesis a number of inorganic industrial waste products, such as blast furnace slags, thermal power plant fly-ash, mine tailings, etc., some of which are abundantly available all over the world.

3. Environmentally friendly industrial production. The use of industrial waste can enormously enhance the resource efficiency of industrial branches generating such waste, such as mining or metallurgy. On the other hand, the use of already-existing waste material can significantly diminish large waste dumps, directly improving the environmental status of affected areas.

4. The possible replacement (even partial) of ordinary cements and concretes by geopolymers (produced by carbon-free sources) is also a route to low-carbon production, diminishing the industrial tension on climate change.

In order to cover a wider area of geo-waste utilization, in this second edition, we aim to enhance the strict geopolymerization with studies on alkali activation and vitrification.

Considering the interdisciplinary character of the topic, we are launching it across a wider range of MDPI journals, in the hope of attracting papers that cover this subject from different points of view.

Prof. Dr. Thomas N. Kerestedjian
Prof. Dr. Alexander Karamanov
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Ceramics ceramics	2.8	3.0	2018	19.7 Days	CHF 1600	Submit
Construction Materials constrmater	-	-	2021	25.9 Days	CHF 1000	Submit
Geotechnics geotechnics	-	-	2021	15.6 Days	CHF 1000	Submit
Materials materials	3.4	5.2	2008	13.9 Days	CHF 2600	Submit
Minerals minerals	2.5	3.9	2011	18.7 Days	CHF 2400	Submit

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Published Papers (3 papers)

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17 pages, 5358 KiB  

Open AccessArticle

Experimental Study on Geopolymerization of Lunar Soil Simulant under Dry Curing and Sealed Curing

by Jinhui Gu and Qinyong Ma

Materials 2024, 17(6), 1413; https://doi.org/10.3390/ma17061413 - 20 Mar 2024

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Abstract

The construction of lunar surface roads is conducive to improving the efficiency of lunar space transportation. The use of lunar in situ resources is the key to the construction of lunar bases. In order to explore the strength development of a simulated lunar [...] Read more.

The construction of lunar surface roads is conducive to improving the efficiency of lunar space transportation. The use of lunar in situ resources is the key to the construction of lunar bases. In order to explore the strength development of a simulated lunar soil geopolymer at lunar temperature, geopolymers with different sodium hydroxide (NaOH) contents were prepared by using simulated lunar regolith materials. The temperature of the high-temperature section of the moon was simulated as the curing condition, and the difference in compressive strength between dry curing and sealed curing was studied. The results show that the high-temperature range of lunar temperature from 52.7 °C to 76.3 °C was the suitable curing period for the geopolymers, and the maximum strength of 72 h was 6.31 MPa when the NaOH content was 8% in the sealed-curing mode. The 72 h strength had a maximum value of 6.87 MPa when the NaOH content was 12% under dry curing. Choosing a suitable solution can reduce the consumption of activators required for geopolymers to obtain unit strength, effectively reduce the quality of materials transported from the Earth for lunar infrastructure construction, and save transportation costs. The microscopic results show that the simulated lunar soil generated gel substances and needle-like crystals under the alkali excitation of NaOH, forming a cluster and network structure to improve the compressive strength of the geopolymer. Full article

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

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23 pages, 4063 KiB  

Open AccessArticle

Effect of Microwaves on the Rapid Curing of Metakaolin- and Aluminum Orthophosphate-Based Geopolymers

by Jasmine Aschoff, Stephan Partschefeld, Jens Schneider and Andrea Osburg

Materials 2024, 17(2), 463; https://doi.org/10.3390/ma17020463 - 18 Jan 2024

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Abstract

This paper deals with the influence of microwaves on the hardening and curing of geopolymer binders synthesized from metakaolin or aluminum orthophosphate with sodium silicate solution as the activator. Pure geopolymer pastes as well as geopolymer mortars were considered. The variable parameters were [...] Read more.

This paper deals with the influence of microwaves on the hardening and curing of geopolymer binders synthesized from metakaolin or aluminum orthophosphate with sodium silicate solution as the activator. Pure geopolymer pastes as well as geopolymer mortars were considered. The variable parameters were the modulus of the sodium silicate solutions (molar ratio of SiO₂ to Na₂O: 1.5, 2.0 and 2.5) and the Si/Al ratio (3/1 and 2/1). Selected samples were cured in a microwave oven until hardening, so the curing time depended on the mixture. For comparison some samples were cured at ambient temperature. To investigate the influence of microwave radiation on the reaction kinetics, isothermal heat flow calorimetry, ultrasonic velocity measurements and rheological investigations into the variation of curing temperature were used. In addition, the mechanical properties of the cured samples were characterized. The results show that microwave curing only takes a few minutes, so it is the most time-saving method. Key factors influencing the geopolymer reaction under microwave radiation are the raw materials as well as the Si/Al ratio. Metakaolin-based geopolymer binders are more stable than those based on aluminum orthophosphate, especially regarding their salt efflorescence. Microwave radiation is an efficient method to accelerate the geopolymer reaction. Full article

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

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14 pages, 7642 KiB  

Open AccessArticle

Effective Stabilization of Cadmium and Copper in Iron-Rich Laterite-Based Geopolymers and Influence on Physical Properties

by Rachel Yanou Nkwaju, Joëlle Nadia Fekoua Nouping, Soumayah Bachirou, Tatiane Marina Abo, Juvenal Giogetti Nemaleu Deutou and Jean Noël Yankwa Djobo

Materials 2023, 16(24), 7605; https://doi.org/10.3390/ma16247605 - 12 Dec 2023

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Abstract

This study aimed to investigate the efficiency of a geopolymer binder of the type of Na-poly(ferro–silico–aluminate) as a matrix for the stabilization of heavy metals along with their effect on the development of structural performances. The artificial contamination of soil with ions was [...] Read more.

This study aimed to investigate the efficiency of a geopolymer binder of the type of Na-poly(ferro–silico–aluminate) as a matrix for the stabilization of heavy metals along with their effect on the development of structural performances. The artificial contamination of soil with ions was carried out and used to prepare an alkali-activated iron-rich lateritic soil binder. Further, various microstructural analyses were carried out to explain the stabilization mechanism. The stabilization efficiency was assessed by leaching tests in de-ionized water and hydrochloric acid (0.1 M, HCl). Then, the physical properties were determined to evaluate the impact of heavy metals on the structural performance of the binder. Results demonstrated that the prepared geopolymer binder has the lowest stabilization capacity in an acidic medium (low pH) than in water with high pH. However, the stabilization of Cu ions was effective at 99%, while the Cd ion is barely retained in the matrix. Firstly, the mechanism consists of chemical bonds through ion exchange with sodium of the Na-poly(ferro–silico–aluminate) network. Secondly, through physical interaction with the pore network of the matrix, the heavy metals induced structural deterioration in the geopolymer matrix with a decrease in the compressive strength and bulk density and an increase of both apparent porosity and water absorption. Full article

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

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