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2nd Edition: Advances in Alkali-Activated Materials

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (31 October 2022) | Viewed by 10545

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Special Issue Editors

Dr. Ruby Mejía de Gutiérrez

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Guest Editor

Universidad del Valle, Cali, Composites Materials Group (CENM), Cali, Colombia
Interests: alkali-activated materials; geopolymers; building materials; waste valorization; corrosion and durability

Prof. Dr. Francisca Puertas

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Guest Editor

CSIC - Instituto de Ciencias de la Construcción Eduardo Torroja (IETCC), 28033 Madrid, Spain
Interests: cement; concrete; durability and sustainability of cementitious materials; admixtures and additives for concrete; alternative binders; alkali-activated materials

Special Issue Information

Dear Colleagues,

Alkali-activated materials (AAM) represent a line of research of great interest around the world in terms of considering a real alternative to replace Portland cement (OPC). Despite this global interest, however, it is believed that current and future research should focus on overcoming the challenges that this technology faces with regard to its application at an industrial level. One of the main barriers to scale at the industrial level is the scarcity of studies on truly available and sustainable raw materials (precursors and activators). In general, AAMs have a global warming potential (GWP) lower than that of ordinary Portland cement (OPC)—that is to say, the manufacturing processes can be less energy intensive according to the precursor and activator used. It is noted that “alkali-activated cements and concretes” (AACs), including so-called "geopolymers" (GPs), which allow the use of supplementary cementitious materials (wastes and industrial by-products) (SCMs) (100%) as the base material, giving rise to OPC-free cements, and other groups are “hybrid cements” (HYCs), also known as “alkali-activated Portland blended cement”, which combine two technologies, i.e., the positive effects of OPC with AACs. AAMs can be utilized in many high added value applications such as soil stabilization, ceramics, and composite production, structural elements, repair and protective coatings, immobilization of toxic metal and nuclear wastes, thermal insulation, biomedical materials, and others.

The scope of this Special Issue, which is the second edition of “Advances in Alkali-Activated Materials”, is to promote broad potential raw materials (precursors and activator), new applications, and a better understanding of the chemical, mechanical, and durability behaviors of AAMs in different applications. Potential topics for submissions include (but are not limited to):

Precursors of alkali-activated materials (natural pozzolan, construction and demolition wastes, fly ashes, slags, and others);
Conventional and alternative activators;
Alkali-activated concretes (design methodology, properties, durability);
One-part mix designs (“just add water” dry mixtures);
Hybrid cements;
Life cycle assessment (LCA).

Dr. Ruby Mejía de Gutiérrez
Prof. Dr. Francisca Puertas
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. Molecules 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 2700 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-activated materials
Geopolymers
Hybrid cements
Low-carbon binders
New precursors and alternative activators
Circular economy

Published Papers (5 papers)

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Research

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14 pages, 6644 KiB

Open AccessArticle

Valorization of Fly Ashes and Sands Wastes from Biomass Boilers in One-Part Geopolymers

by Inês Silveirinha Vilarinho, Marinélia Neto Capela, Ana Sofia Pinto, João António Labrincha and Maria Paula Seabra

Molecules 2022, 27(20), 6881; https://doi.org/10.3390/molecules27206881 - 14 Oct 2022

Cited by 4 | Viewed by 1160

Abstract

Fly ash (FA) and exhausted bed sands (sands wastes) that are generated in biomass burners for energy production are two of the wastes generated in the pulp and paper industry. The worldwide production of FA biomass is estimated at 10 million tons/year and is expected to increase. In this context, the present work aims to develop one-part alkali-activated materials with biomass FA (0–100 wt.% of the binder) and sands wastes (100 wt.% of the aggregate). FA from two different boilers, CA and CT, was characterized and the mortar’s properties, in the fresh and hardened conditions, were evaluated. Overall, the incorporation of FA decreases the compressive strength of the specimens. However, values higher than 30 MPa are reached with 50 wt.% of FA incorporation. For CA and CT, the compressive strength of mortars with 28 days of curing was 59.2 MPa (0 wt.%), 56.9 and 57.0 MPa (25 wt.%), 34.9 and 46.8 MPa (50 wt.%), 20.5 and 13.5 MPa (75 wt.%), and 9.2 and 0.2 MPa (100 wt.%), respectively. The other evaluated characteristics (density, water absorption, leached components and freeze–thaw resistance) showed no significant differences, except for the specimen with 100 wt.% of CA. Therefore, this work proved that one-part geopolymeric materials with up to 90 wt.% of pulp and paper industrial residues (FA and sand) can be produced, thus reducing the carbon footprint associated with the construction sector. Full article

(This article belongs to the Special Issue 2nd Edition: Advances in Alkali-Activated Materials)

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18 pages, 8138 KiB

Open AccessArticle

Effect of Non-Calcined Sugarcane Bagasse Ash as an Alternative Precursor on the Properties of Alkali-Activated Pastes

by Leila Nóbrega Sousa, Pâmella Fernandes Figueiredo, Sâmara França, Marcos Vinicio de Moura Solar Silva, Paulo Henrique Ribeiro Borges and Augusto Cesar da Silva Bezerra

Molecules 2022, 27(4), 1185; https://doi.org/10.3390/molecules27041185 - 10 Feb 2022

Cited by 14 | Viewed by 2194

Abstract

BFS-MK-based alkali-activated materials are well established as an alternative for sustainable and green construction. This work aims to collaborate and encourage the use of biomass ashes, such as sugarcane bagasse ash (SCBA), as a precursor in alkali-activated materials (AAM). This ash is a rich source of aluminosilicate, which is a primary requirement for this application. In addition, this waste is still an environmental liability, especially in developing countries, and with a large volume of annual production. Thus, in this research, alkali-activated pastes (AA) were produced using sugarcane bagasse ash (SCBA), granulated blast furnace slag (BFS) and metakaolin (MK) as precursors. In addition, environmental gains were encouraged with energy savings, with no extra reburn or calcination steps in the SCBA. Thus, the precursors were characterized by laser granulometry, X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The pastes were produced by mixing the precursors with the activator, composed of a mixture of sodium hydroxide 8 mol/L and sodium silicate. Aiming to study the incorporation of SCBA, all samples have a precursor/activator ratio and a BFS/(BFS + MK) ratio constant of 0.6. The compressive strength analysis, FTIR, XRD, TGA, SEM and isothermal calorimetry analyses pointed out the occurrence of alkaline activation in all proposed samples for curing times of 7, 28 and 91 days. The sample GM0.6-BA0 (15% SCBA) achieved the highest compressive strength among the samples proposed (117.7 MPa, at 91 days), along with a good development of strength throughout the curing days. Thus, this work presents the properties of alkaline-activated pastes using SCBA as a sustainable and alternative precursor, seeking to encourage the use of raw materials and alternative waste in civil construction. Full article

(This article belongs to the Special Issue 2nd Edition: Advances in Alkali-Activated Materials)

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21 pages, 2086 KiB

Open AccessArticle

Hybrid Cements: Mechanical Properties, Microstructure and Radiological Behavior

by Ana María Moreno de los Reyes, José Antonio Suárez-Navarro, María del Mar Alonso, Catalina Gascó, Isabel Sobrados and Francisca Puertas

Molecules 2022, 27(2), 498; https://doi.org/10.3390/molecules27020498 - 13 Jan 2022

Cited by 8 | Viewed by 1833

Abstract

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic specimens in alkaline pastes was found to be valid. The variables involved in hybrid cement activation were shown to have no impact on specimen radioactive content. The powder samples, however, emanated ²²²Rn (a descendent of ²²⁶Ra), possibly due to the deformation taking place in fly ash structure during alkaline activation. Further research would be required to explain that finding. Full article

(This article belongs to the Special Issue 2nd Edition: Advances in Alkali-Activated Materials)

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14 pages, 7863 KiB

Open AccessArticle

Alkali-Activated Hybrid Cements Based on Fly Ash and Construction and Demolition Wastes Using Sodium Sulfate and Sodium Carbonate

by William Valencia-Saavedra, Rafael Robayo-Salazar and Ruby Mejía de Gutiérrez

Molecules 2021, 26(24), 7572; https://doi.org/10.3390/molecules26247572 - 14 Dec 2021

Cited by 9 | Viewed by 2254

Abstract

This article demonstrates the possibility of producing alkali-activated hybrid cements based on fly ash (FA), and construction and demolition wastes (concrete waste, COW; ceramic waste, CEW; and masonry waste, MAW) using sodium sulfate (Na₂SO₄) (2–6%) and sodium carbonate (Na₂CO₃) (5–10%) as activators. From a mixture of COW, CEW, and MAW in equal proportions (33.33%), a new precursor called CDW was generated. The precursors were mixed with ordinary Portland cement (OPC) (10–30%). Curing of the materials was performed at room temperature (25 °C). The hybrid cements activated with Na₂SO₄ reached compressive strengths of up to 31 MPa at 28 days of curing, and the hybrid cements activated with Na₂CO₃ yielded compressive strengths of up to 22 MPa. Based on their mechanical performance, the optimal mixtures were selected: FA/30OPC-4%Na₂SO₄, CDW/30OPC-4%Na₂SO₄, FA/30OPC-10%Na₂CO₃, and CDW/30OPC-10%Na₂CO₃. At prolonged ages (180 days), these mixtures reached compressive strength values similar to those reported for pastes based on 100% OPC. A notable advantage is the reduction of the heat of the reaction, which can be reduced by up to 10 times relative to that reported for the hydration of Portland cement. These results show the feasibility of manufacturing alkaline-activated hybrid cements using alternative activators with a lower environmental impact. Full article

(This article belongs to the Special Issue 2nd Edition: Advances in Alkali-Activated Materials)

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Review

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18 pages, 3782 KiB

Open AccessReview

Self-Compacting Alkali-Activated Materials: Progress and Perspectives

by Zengqing Sun, Qingyu Tang, Xiaohui Fan, Min Gan, Xuling Chen, Zhiyun Ji and Xiaoxian Huang

Molecules 2022, 27(1), 81; https://doi.org/10.3390/molecules27010081 - 23 Dec 2021

Cited by 2 | Viewed by 2406

Abstract

Alkali-activated materials (AAMs) are considered to be alternative cementitious materials for civil infrastructures. Nowadays, efforts have been made in developing AAMs with self-compacting ability. The obtained self-compacting AAMs (SCAAMs) accomplish superior passing and filling properties as well as excellent mechanical and environmental advantages. This work critically revisits recent progresses in SCAAMs including mixture proportions, fresh properties, mechanical strength, microstructure, acid and sulfate resistance, high temperature behaviors, impact resistance and interface shear strength. To facilitate direct comparison and interpretation of data from different publications, mixture proportions were normalized in terms of the content of key reactive components from precursors and activators, and correlation with mechanical behaviors was made. Moreover, special attention was paid to current research challenges and perspectives to promote further investigation and field application of SCAAMs as advanced construction material. Full article

(This article belongs to the Special Issue 2nd Edition: Advances in Alkali-Activated Materials)

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