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Minerals
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Alkali Activation of Clay-Based Materials
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Alkali Activation of Clay-Based Materials

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Clays and Engineered Mineral Materials".

Deadline for manuscript submissions: 30 September 2025 | Viewed by 4051

Special Issue Editors

Dr. Barbara Horvat

E-Mail Website
Guest Editor
Milan Vidmar Electric Power Research Institute, Hajdrihova 2, SI-1000 Ljubljana, Slovenia
Interests: hazardous and radioactive waste materials; radioactive materials/fuel; electromagnetic irradiation; radiation
Special Issues, Collections and Topics in MDPI journals
Dr. Lea Žibret

E-Mail Website
Guest Editor
Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana, Slovenia
Interests: alkali-activated material; clay-based materials; clay bricks; secondary raw materials; geology; X-ray diffraction
Special Issues, Collections and Topics in MDPI journals
Dr. Sara Tominc

E-Mail Website
Guest Editor
Slovenian National Building and Civil Engineering Institute, Dimičeva 12, SI-1000 Ljubljana, Slovenia
Interests: clay-based materials; nanomaterials; waste materials; circular economy; TG-DTA; sintering; electron microscopy; microstructure

Special Issue Information

Dear Colleagues,

Alkali-activated materials (AAMs) can be made from any material containing enough silica and alumina in amorphous content, i.e., from natural resources or secondary raw materials. For the construction industry, AAMs represent a sustainable and resource-efficient alternative to conventional cement-based materials, offering potential environmental benefits.

Just like AAMs, clay can be used to safely store different hazardous substances and is an abundant material that represents waste for different types of mining industries. AAMs can, therefore, be synthesized using various types of clay, but they need to be optimized in terms of strength, durability, sustainability, and their impact on the environment.

Alkali activation is also a useful approach for improving the geomechanical properties of clay-rich materials in geotechnical embankments (e.g., flood embankments). Moreover, alkali activators can improve the mechanical properties of rammed earth construction.

In the scope of these considerations, authors are invited to contribute original research articles as well as review articles focused on the synthesis and characterization of alkali-activated clays (used as sole precursors or additives, calcined or raw), aiming for sustainability in the building industry. Papers dealing with investigating the environmental impact of such AAMs, particularly on soil contamination (i.e., the immobilization of pollutants), are particularly welcome.

Dr. Barbara Horvat
Dr. Lea Žibret
Dr. Sara Tominc
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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. Minerals 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 2400 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

  • alkali activation
  • clay
  • metakaolin
  • waste and raw materials
  • building industry sector
  • rammed earth construction
  • geotechnical embankments
  • sustainability
  • impact on environment life-cycle assessment

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Published Papers (3 papers)

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Research

30 pages, 11351 KiB  
Article
Rapid Immobilisation of Chemical Reactions in Alkali-Activated Materials Using Solely Microwave Irradiation
by Anže Tesovnik and Barbara Horvat
Minerals 2024, 14(12), 1219; https://doi.org/10.3390/min14121219 - 29 Nov 2024
Cited by 1 | Viewed by 1542
Abstract
Efflorescence, a time-dependent and water-driven phenomenon, is a major concern in alkali-activated materials (AAMs), impacting their practical use and preservation in a time-frozen state for post-characterisation. Although a method for stopping chemical reactions in conventional cements exists, it is time-consuming and not chemical-free. [...] Read more.
Efflorescence, a time-dependent and water-driven phenomenon, is a major concern in alkali-activated materials (AAMs), impacting their practical use and preservation in a time-frozen state for post-characterisation. Although a method for stopping chemical reactions in conventional cements exists, it is time-consuming and not chemical-free. Therefore, this study explored the effects of low-power microwave-induced dehydration on efflorescence, mechanical performance, and structural integrity in AAMs, to create an alternative and more “user-friendly” dehydration method. For this purpose, several mixtures based on secondary raw (slag, fly ash, glass wool, and rock wool) and non-waste (metakaolin) materials were activated with a commercial Na-silicate solution in ratios that promoted or prevented efflorescence. Characterisation techniques, including Fourier-transform infrared spectroscopy and X-ray diffraction, showed that microwave dehydration effectively removed water without altering crystallinity, while mercury intrusion porosimetry and compressive strength tests confirmed increased porosity. In addition to being an efficient, time-saving, and solvent-free manner of stopping the reactions in AAMs, microwave irradiation emerged as an innovative, chemical-free method for evaluating curing finalisation and engineering foams in a stage when all other existing methods fail. However, the artificially provoked efflorescence in aged dehydrated AAMs connected the slipperiness of AAM with the instant extraction of Na, which raised the need for further research into alternative alkali replacements to evaluate the practical use of AAM. Full article
(This article belongs to the Special Issue Alkali Activation of Clay-Based Materials)
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19 pages, 6058 KiB  
Article
Influence of Precursor Particle Size and Calcium Hydroxide Content on the Development of Clay Brick Waste-Based Geopolymers
by Ronaldo A. Medeiros-Junior, Marisa Thiesen, Andrea Murillo Betioli, Juliana Machado Casali, Luiz Fernando Zambiasi Trentin, Andreza Frare and Allan Guimarães Borçato
Minerals 2024, 14(11), 1169; https://doi.org/10.3390/min14111169 - 18 Nov 2024
Cited by 1 | Viewed by 987
Abstract
This study evaluated the effect of precursor particle size and calcium hydroxide (CH) incorporation on the microstructure, compressive strength, and rheological properties of clay brick waste (BW)-based geopolymers. Rheological analyses were used to evaluate the fresh state of the geopolymers. XRD, SEM, and [...] Read more.
This study evaluated the effect of precursor particle size and calcium hydroxide (CH) incorporation on the microstructure, compressive strength, and rheological properties of clay brick waste (BW)-based geopolymers. Rheological analyses were used to evaluate the fresh state of the geopolymers. XRD, SEM, and EDS analyses were performed to analyze the microstructure. The results showed that the particle size reduction in BW and the incorporation of CH significantly contributed to obtaining better compressive strength in the geopolymers. Furthermore, the particle size reduction decreased the yield stress, plastic viscosity, and hysteresis area of the geopolymers, while the incorporation of CH promoted the opposite effect. Increasing the CH incorporation content accelerated the geopolymerization reactions and reduced the workability of the geopolymers over time. However, since the milling process is costly, milling BW for 2 h was more efficient from a technical–economic point of view. In addition, the incorporation of CH not only promoted the early hardening of the geopolymers when necessary, but also contributed to the improvement of the compressive strength through matrix densification. Therefore, the results of this study show the definition of more efficient material proportions for geopolymers using waste as an aluminosilicate source. Full article
(This article belongs to the Special Issue Alkali Activation of Clay-Based Materials)
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25 pages, 19369 KiB  
Article
Applying Alkali Activator and Hydrophobic Agents in Clay-Based Mortars for Enhanced Properties
by Aspasia Karozou, Fotini Kesikidou, Eleni Pavlidou and Maria Stefanidou
Minerals 2024, 14(10), 1035; https://doi.org/10.3390/min14101035 - 15 Oct 2024
Viewed by 930
Abstract
Clay-based mortars are susceptible to water intake and exhibit low mechanical strength, presenting challenges in their application within the construction sector. This research addresses these vulnerabilities by investigating the combination of alkali activators with waterproofing agents, specifically a nano-clay and an acrylic emulsion, [...] Read more.
Clay-based mortars are susceptible to water intake and exhibit low mechanical strength, presenting challenges in their application within the construction sector. This research addresses these vulnerabilities by investigating the combination of alkali activators with waterproofing agents, specifically a nano-clay and an acrylic emulsion, to enhance the properties of clay mortars. Alkali-activated materials are known for their superior mechanical properties and sustainable potential, especially when derived from low-cost by-products. Recent studies have focused on alkali activation using clays and soils as precursors to improve their physical and mechanical properties while increasing durability. However, the high absorbency of these mortars remains a concern, as it can lead to matrix degradation. Therefore, to address these problems, this research studied the combination of a highly alkaline activator (potassium metasilicate) with hydrophobic agents, such as a nano-clay and an acrylic emulsion, using two different clayey soils. The results indicated that potassium metasilicate (PO) enhanced the mechanical properties and stability for both aluminosilicate systems, while nano-clay (PONC) significantly reduced the capillary absorption through time, especially in A2 systems. The addition of acrylic emulsion (POD) proved highly effective in both systems, significantly improving durability. By integrating these agents, the mortar systems were protected against water intake, while durable construction materials were formed. Full article
(This article belongs to the Special Issue Alkali Activation of Clay-Based Materials)
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