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Geopolymers and Alkali-Activated Materials: Preparation and Properties

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: 20 September 2025 | Viewed by 2186

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Special Issue Editors

Dr. Antonio D’Angelo

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Guest Editor

Department of Engineering, University of Campania “Luigi Vanvitelli”, Aversa, CE, Italy
Interests: geopolymers; alkali-activated materials; sol–gel chemistry; hybrid materials; composites; antimicrobial assessment; FT-IR spectroscopy

Prof. Dr. Michelina Catauro

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Guest Editor

Department of Engineering, University of Campania “Luigi Vanvitelli”, Aversa, CE, Italy
Interests: Geopolymers; sol–gel technology; biomaterials; bioglass; organic/inorganic hybrid materials; drug delivery; thin films
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Special Issue Information

Dear Colleagues,

As Guest Editors of this Special Issue, titled “Geopolymers and Alkali-Activated Materials: Preparation and Properties”, we cordially invite you to contribute research articles, review articles, short communications, technical notes and/or perspectives. This Special Issue will comprise a collection of articles from top researchers that cover new insights and perspectives on the development and characterization of geopolymers (GPs) and alkali-activated materials (AAMs). Nowadays, because of the strong need to reduce pollution from Portland cement production and setting, waste disposal, and resource consumption, several GPs and AAMs have been synthesized using various wastes. However, there are many properties that need to be understood when adjusting precursors and synthesis conditions.

This Special Issue aims to shed light on a deeper understanding of the mechanisms and processes controlling the development and performance of GPs and alkali-activated materials from synthesis to application, material chemistry and engineering, inorganic chemistry, GP and AAM composites, mineralogy, waste management, sustainability, etc.

We look forward to receiving your contributions.

Dr. Antonio D’Angelo
Prof. Dr. Michelina Catauro
Guest Editors

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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. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

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

Keywords

geopolymers
alkali-activated materials
geopolymer composites
sustainability
physico-chemical properties
compressive strength
alternative precursors
waste recycling

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Published Papers (4 papers)

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Research

31 pages, 30962 KiB

Open AccessArticle

Study on the Effects and Mechanisms of Fly Ash, Silica Fume, and Metakaolin on the Properties of Slag–Yellow River Sediment-Based Geopolymers

by Ge Zhang, Kunpeng Li, Huawei Shi, Chen Chen and Chengfang Yuan

Materials 2025, 18(8), 1845; https://doi.org/10.3390/ma18081845 - 17 Apr 2025

Viewed by 229

Abstract

The incorporation of mineral admixtures plays a crucial role in enhancing the performance and sustainability of geopolymer systems. This study evaluates the influence of fly ash (FA), silica fume (SF), and metakaolin (MK) as typical mineral admixtures on slag–Yellow River sediment geopolymer eco-cementitious materials. The impact of varying replacement ratios of these admixtures for slag on setting time, workability, reaction kinetics, and strength development were thoroughly investigated. To understand the underlying mechanisms, microstructural analysis was conducted using thermogravimetric–differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS), and mercury intrusion porosimetry (MIP). The results indicate that the incorporation of FA, SF, and metakaolin delayed the initial reaction, prolonged the induction period, and reduced the acceleration rate. These effects hindered early strength development. At 30% FA content, the matrix exhibited excellent flowability and sustained heat release. The 28-day splitting tensile strength increased by 42.40%, while compressive strength decreased by 2.85%. In contrast, 20% SF significantly improved compressive strength, increasing the 28-day compressive and splitting tensile strengths by 11.19% and 6.16%, respectively. At 15% metakaolin, the strength improvement was intermediate, with 28-day compressive and splitting tensile strengths increasing by 3.55% and 10.59%, respectively. However, dosages exceeding 20% for SF and metakaolin significantly reduced workability. The incorporation of FA, SF, and metakaolin did not interfere with the slag’s alkali-activation reaction. The newly formed N-A-S-H and C-S-H gels integrated with the original C-A-S-H gels, optimizing the pore structure and reducing pores larger than 1 µm, enhancing the matrix compactness and microstructural reinforcement. This study provides practical guidance for optimizing the use of sustainable mineral admixtures in geopolymer systems. Full article

(This article belongs to the Special Issue Geopolymers and Alkali-Activated Materials: Preparation and Properties)

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28 pages, 10963 KiB

Open AccessArticle

Optimization of Synergy Among Granulated Blast Furnace Slag, Magnesium Oxide, and Basalt Fiber for the Solidification of Soft Clay

by Henggang Ji, Xiang Fan and Fan Ding

Materials 2025, 18(7), 1577; https://doi.org/10.3390/ma18071577 - 31 Mar 2025

Viewed by 198

Abstract

In order to reuse granulated blast furnace slag (GBFS) and low-strength soft clay (SC), this study developed a curing material using magnesium oxide (MgO) as an alkali activator to excite the GBFS and basalt fiber (BF) as reinforcing material to prepare the SC. The mixing ranges of GBFS, MgO, and BF were established as 9.48%~14.52%, 0.48%~5.52%, and 0%~1.00454% of the dry clay mass, respectively, and the mixing ratios of the three were optimized using the central composite design (CCD) test. Through the analysis of variance, factor interaction analysis, and parameter optimization of the CCD test, the optimal mass ratio of GBFS, MgO, and BF was determined to be 13.35:4.47:0.26. The curing material of this ratio was named GMBF and mixed with SC to prepare GMBF solidified clay. An equal amount of ordinary Portland cement (OPC) was taken and formed with SC to form OPC solidified clay. The mechanical properties, durability, and hydration products of GMBF solidified clay were clarified by the unconfined compressive strength (UCS) test, freeze–thaw cycle test, X-ray diffraction (XRD) test, and scanning electron microscopy (SEM) test. The UCS of the GMBF solidified clay was 1.08 MPa and 2.85 MPa at 7 and 91 days, respectively, which was 45.9% and 33.8% higher than that of the OPC solidified clay (0.74 MPa and 2.13 MPa) at the same curing time. After ten freeze–thaw cycles, the UCS of GMBF and OPC solidified clay decreased from the initial 2.85 MPa and 2.13 MPa to 1.59 MPa and 0.7 MPa, respectively, with decreases of 44.2% and 67.1%, respectively. By XRD and SEM, the hydration products of GMBF solidified clay were mainly calcium silicate hydrate gel and hydrotalcite. The interface bonding and bridging effect formed between BF and SC or hydration products, indicating that these interactions contributed to the solidified clay enhanced structural integrity. This study demonstrates that the CCD approach provides solution for recycling SC and GBFS. Laboratory tests confirm the potential of the optimized GMBF formulation for practical engineering applications. Full article

(This article belongs to the Special Issue Geopolymers and Alkali-Activated Materials: Preparation and Properties)

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28 pages, 25047 KiB

Open AccessArticle

Effects of Steel Slag, Desulfurization Gypsum, and Ground Granulated Blast-Furnace Slag on the Characterization of Recycled Cement-Stabilized Macadam

by Haoyu Tan, Henggang Ji, Peilong Yuan and Xiang Fan

Materials 2025, 18(4), 874; https://doi.org/10.3390/ma18040874 - 17 Feb 2025

Viewed by 452

Abstract

Steel slag powder (SS), ground granulated blast-furnace slag (GGBS), and flue gas desulfurization gypsum (FDG) are environmentally friendly and cost-effective substitute materials for ordinary Portland cement (OPC). This study investigated the use of industrial solid wastes, including SS, GGBS, and FDG, as auxiliary materials in OPC to stabilize pretreated recycled concrete aggregate (pretreated RCA). The use of pretreated RCA, mixed cementitious materials, and water at the optimum content created a mixture designated recycled cement-stabilized macadam (RCSM). A series of mechanical tests were conducted to clarify the performance of the RCSM, and microscopic tests were performed to elucidate the microcharacteristics of the mixed cementitious materials. With a curing time from 3 days to 28 days, the unconfined compression strength (UCS) of the mixed cementitious materials (A4) composed of SS, GGBS, FDG, and OPC increased by 5.94–10.79% compared with that of the cementitious material of OPC (A0). The UCS of the mixture composed (C4) of SS, GGBS, FDG, OPC, and pretreated RCA was greater than that of the mixture composed (C0) of OPC and RCA from 7 days to 90 days, increasing by 4.26–8.35%. The total drying shrinkage coefficient of C4 was lower than that of C0, whereas the temperature shrinkage coefficient of C4 was higher than that of C0, indicating that the use of A4 can effectively reduce drying shrinkage cracking in C4. The hydration products of A4 primarily consisted of flocculent calcium silicate hydrate (C-S-H) gel, fibrous calcium aluminate hydrate gel, and needle-like ettringite crystals. The interlocked growth of C-S-H gel and ettringite crystals continued and promoted an increase in the UCS of the cementitious system. The test results provide a reference for the application of similar materials. Full article

(This article belongs to the Special Issue Geopolymers and Alkali-Activated Materials: Preparation and Properties)

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12 pages, 3264 KiB

Open AccessArticle

Effect of Waste Concrete Powder Content and Microwave Heating Parameters on the Properties of Porous Alkali-Activated Materials from Coal Gangue

by Vasilii Mischinenko, Andrey Vasilchenko and Georgy Lazorenko

Materials 2024, 17(22), 5670; https://doi.org/10.3390/ma17225670 - 20 Nov 2024

Cited by 1 | Viewed by 848

Abstract

The objective of this research is to fabricate waste-based alkali-activated foams with better properties in a quick time by using energy-efficient techniques such as microwave irradiation. The present study reports the effect of microwave heating parameters, including heating time and output power, on the properties of porous alkali-activated materials (AAMs) that use coal gangue (CG) as a precursor. The effects of concrete waste (CW) content (0–20 wt %) on the performance and microstructure of CG-based AAMs were investigated. Mechanical, thermal, and microstructural investigations were conducted to characterize the obtained materials. The experimental results indicate that the best characteristics of CG-based alkali-activated foams were achieved when microwave power and microwave heating time were 800 W and 10 min, respectively. The foams prepared by adding the waste concrete powder increased stability and showed lower bulk density and thermal conductivity. When the waste concrete powder content was 10 wt %, the CG-based alkali-activated foams showed the best overall performance. At the same time, the mechanical properties of the alkali-activated foams declined only slightly (~9%). The findings of this work provide a basis for further studies on improving the characteristics of CG-based alkali-activated foams due to the physical effect of a microwave field on fresh mortar without the use of a chemical foaming agent while reducing energy consumption in the production process. Full article

(This article belongs to the Special Issue Geopolymers and Alkali-Activated Materials: Preparation and Properties)

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