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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 (30 September 2020) | Viewed by 31920

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Special Issue Editors

Prof. Dr. Angel Palomo

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Guest Editor

Cement and Recycling Materials Department, Eduardo Torroja Institute (IETcc-CSIC), 28033 Madrid, Spain

Prof. Dr. Ana Fernandez-Jimenez

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Guest Editor

Cement and Recycling Materials Department, Eduardo Torroja Institute (IETcc-CSIC), 28033 Madrid, Spain
Interests: Cement; Materials Chemistry; Material Characteristics Materials Engineering; Material Characterization; Building Materials Concrete; Concrete Durability; Construction; Construction Materials

Special Issue Information

Dear Colleagues,

Alkali-activated materials (AAMs) have emerged as alternative low-CO₂ binders that can replace Portland cement-based binders in construction. In addition, AAMs can be utilized in many high added value applications such as ceramic-like products, advanced composites, solidification/stabilization of hazardous wastes, and environmental applications, to name just a few examples. Furthermore, several large-volume mineral wastes and industrial byproducts can be utilized as raw material for AAMs. Therefore, AAMs have an important role in mitigating climate change and promoting a circular economy.

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

Cost and environmental impact optimization of mix designs (especially in terms of alkali activators);
Admixture development;
Micro and nanostructural characterization of AAMs;
One-part mix designs (“just add water” dry mixtures);
Durability of AAMs;
Life cycle assessment (LCA);

Prof. Angel Palomo
Prof. Ana Fernandez-Jimenez
Guest Editors

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Keywords

alkali-activated materials
geopolymers
low-carbon binders
circular economy

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Published Papers (11 papers)

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19 pages, 12206 KiB

Open AccessArticle

Effect of Alkaline Salts on Calcium Sulfoaluminate Cement Hydration

by Luís Urbano D. Tambara Júnior, Janaíde C. Rocha, Malik Cheriaf, Pilar Padilla-Encinas, Ana Fernández-Jiménez and Angel Palomo

Molecules 2021, 26(7), 1938; https://doi.org/10.3390/molecules26071938 - 30 Mar 2021

Cited by 14 | Viewed by 2865

Abstract

This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (Na₂SO₄, Na₂CO₃, and Na₂SiO₃) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH₃, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. Na₂SO₄ induces cracking in the ≥28-d pastes due to post-hardening gypsum and ettringite formation from the excess SO₄^2– present. Anhydrite dissolves more rapidly in the presence of Na₂CO₃, prompting carbonation. Na₂SiO₃ raises compressive strength and exhibits strätlingite as one of its reaction products. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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13 pages, 3536 KiB

Open AccessArticle

Effect of the Introduction of Reactive Fillers and Metakaolin in Waste Clay-Based Materials for Geopolymerization Processes

by Caterina Sgarlata, Alessandra Formia, Francesco Ferrari and Cristina Leonelli

Molecules 2021, 26(5), 1325; https://doi.org/10.3390/molecules26051325 - 2 Mar 2021

Cited by 10 | Viewed by 1820

Abstract

In this study, the role of two reactive fillers, specifically a sand from a clay washing process as an alternative to waste glass powder and a commercial metakaolin (MK), into the geopolymerization process of waste clay-based materials was assessed. Three kinds of clayey wastes from mining operations—halloysitic, kaolinitic and smectitic clays—were tested as potential precursor of geopolymeric materials in view of a potential valorisation of these by-products. A mix-design based on the addition of low percentages (20%) of these fillers or MK to improve the mechanical and chemico-physical properties of geopolymeric formulations was evaluated. All the clays were thermally treated at a temperature of 650 °C, while the geopolymeric pastes were cured at room temperature. In particular, the chemical stability in water (pH and ionic conductivity of leachate water, weight loss), the variations in the microstructure (XRD, SEM), and in the mechanical performance (compressive strength) were analysed. The most reactive additive was MK, followed by sand and waste glass at very similar levels—1:1 or 2:1—depending upon the type of the clay but not strictly related to the clay type. The increase of geopolymeric gel densification due to the presence of MK and sand was replaced by a crack deflection mechanism in the case of the WG grains. The worst performance (chemical stability and mechanical properties) was found for the halloysitic clay, while kaolinitic and smectitic clays developed strengths slightly below 30 MPa. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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14 pages, 4079 KiB

Open AccessFeature PaperArticle

ZnO Nanoparticles for Photocatalytic Application in Alkali-Activated Materials

by Hector R. Guzmán-Carrillo, Alejandro Manzano-Ramírez, Ines Garcia Lodeiro and Ana Fernández-Jiménez

Molecules 2020, 25(23), 5519; https://doi.org/10.3390/molecules25235519 - 25 Nov 2020

Cited by 9 | Viewed by 2463

Abstract

This paper reports an Alkali-Activated Materials (AAM) using two different precursors, metakaolin and a metallurgical slag with photocatalytic zinc oxide nanoparticles, as novel photocatalytic composites. The photodegradation performance of the composites using methylene blue (MB) dye as a wastewater model was investigated by ultraviolet radiations (UV-vis) spectroscopy. Adsorption in dark conditions and photodegradation under UV irradiation are the mechanisms for removing MB dye. The pseudo-first-order kinetic and pseudo-second-order kinetic models were employed, and the experimental data agreed with the pseudo-second-order model in both cases with UV and without UV irradiations. As new photocatalytic materials, these composites offer an alternative for environmental applications. Full article

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17 pages, 8255 KiB

Open AccessArticle

Hydration and Microstructure of Steel Slag as Cementitious Material and Fine Aggregate in Mortar

by Wu Jing, Jinping Jiang, Sha Ding and Ping Duan

Molecules 2020, 25(19), 4456; https://doi.org/10.3390/molecules25194456 - 28 Sep 2020

Cited by 29 | Viewed by 3571

Abstract

Due to the low hydration activity and poor volume stability, extensive steel slag utilization is restricted. In this paper, the hydration process and microstructure of alkali-activated materials with steel slag as a cementitious material and fine aggregate were studied. The phase composition and micro-morphology of hydration products were measured using XRD, NMR and SEM. The response relationship between microstructure and mechanical properties during hydration was revealed. The results show that the main hydration products of the alkali-activated steel slag powder-granulated blast furnace slag powder cementitious system are Ca(OH)₂ and calcium aluminosilicate hydrate (C-A-S-H) gel. With the progress of hydration, the amount of calcium silicate hydrate (C-S-H) gel and the average molecular chain length increase, Al[4]/Si decreases, while C/S increases first and then decreases, and the structure of cement paste becomes much more compact. The interface between steel slag sand and cement paste is denser than that of river sand, since the hydration occurs on the surface of steel slag sand, which leads to the formation of C-A-S-H gel and Ca(OH)₂. As a result, the compressive strength of concrete prepared by steel slag sand is higher than that of river sand with the same mix proportion. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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16 pages, 12125 KiB

Open AccessArticle

Geopolymer Carbon-Based for Ultra-Wideband Absorbent Applications

by Ioana Nicoleta Vlasceanu, Ameni Gharzouni, Olivier Tantot, Edson Martinod and Sylvie Rossignol

Molecules 2020, 25(18), 4218; https://doi.org/10.3390/molecules25184218 - 14 Sep 2020

Cited by 4 | Viewed by 2307

Abstract

Dimension reduction, cost efficiency, and environmental sustainability are important factors in absorbent designs. Geopolymers represent an eco-friendly and cost-efficient solution for such applications, and the objective of this study is to develop new geopolymer-based composites with tailored dielectric properties. To develop such composites, different formulations based on three types of carbon and various surfactants are tested. The nonionic surfactant is preferred over the anionic surfactant. Dielectric investigations between 2 and 3.3 GHz are performed. The results reveal that the carbon content and its type (origin) have significant effects on the dielectric characteristics and less on the magnetic characteristics. Indeed, an increase in permittivity from 2 to 24 and an increase from 0.09 to 0.6 for loss tangent are shown with changes in the carbon content and type. A permittivity (ε) of 2.27 and loss (tan δ) of 0.19 are obtained for a pore size of 1.6 mm, for the carbon type with the lowest purity, and with a nonionic surfactant. Finally, it is shown that the addition of magnetite has little impact on the overall magnetic properties of the geopolymer. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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18 pages, 6414 KiB

Open AccessArticle

Resistance to Chemical Attack of Hybrid Fly Ash-Based Alkali-Activated Concretes

by William G. Valencia-Saavedra and Ruby Mejía de Gutiérrez

Molecules 2020, 25(15), 3389; https://doi.org/10.3390/molecules25153389 - 27 Jul 2020

Cited by 16 | Viewed by 2659

Abstract

The environmental impacts related to Portland cement production in terms of energy consumption, the massive use of natural resources and CO₂ emissions have led to the search for alternative cementitious materials. Among these materials, alkali-activated cements based on fly ash (FA) have been considered for concrete production with greater sustainability. In the present article, the chemical durability properties (resistance to sulphates, chloride permeability, and resistance to carbonation) of a hybrid alkali-activated concrete based on fly ash–ordinary Portland cement (FA/OPC) with proportions of 80%/20% were evaluated. It is noted that the FA was a low-quality pozzolan with a high unburned carbon content (20.67%). The results indicated that FA/OPC concrete had good durability with respect to the OPC concrete, with 95% less expansion in the presence of sodium sulphate and a 2% strength loss at 1100 days, compared with the 56% strength loss of the OPC concrete. In addition, FA/OPC showed lower chloride permeability. On the contrary, the FA/OPC was more susceptible to carbonation. However, the residual compressive strength was 23 MPa at 360 days of CO₂ exposure. Based on the results, FA/OPC, using this type of FA, can be used as a replacement for OPC in the presence of these aggressive agents in the service environment. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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12 pages, 3599 KiB

Open AccessArticle

Utilization of ZeoliticWaste in Alkali-Activated Biomass Bottom Ash Blends

by Danutė Vaičiukynienė, Dalia Nizevičienė, Agnė Mikelionienė and Algirdas Radzevičius

Molecules 2020, 25(13), 3053; https://doi.org/10.3390/molecules25133053 - 3 Jul 2020

Cited by 5 | Viewed by 2172

Abstract

This study aims to investigate the effects of ammonium-bearing zeolitic waste (FCC) on alkali-activated biomass bottom ash (BBA). FCC was obtained from the oil-cracking process in petroleum plants. In this study, two types of production waste were used: biomass bottom ash and ammonium-bearing zeolitic waste. These binary alkali-activated FCC/BBA blends were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) methods. The compressive strength of the hardened samples was evaluated. The results show that the samples made from alkali-activated BBA biomass bottom ash had low (8.5 MPa) compressive strength, which could be explained with low reactive BBA and insufficient quantities of silicon and aluminum compounds. The reactivity of BBA was improved with incorporating zeolitic waste as an aluminosilicate material. This zeolitic waste was first used for ammonium sorption; then, it was incorporated in alkali-activated samples. Additional amounts of hydrated products formed, such as calcium silicate hydrate, calcium aluminum silicate hydrate and calcium sodium aluminum silicate hydrate. The silicon and aluminum compound, which varied in zeolitic waste, changed the mineral composition and microstructure of alkali-activated binder systems. NH₄Cl, which was incorporated in the zeolitic waste, did not negatively affect the compressive strength of the alkali-activated BBA samples. This investigation proved that waste materials can be reused by producing alkali-activated binders. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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14 pages, 2545 KiB

Open AccessArticle

Biodiesel Processing Using Sodium and Potassium Geopolymer Powders as Heterogeneous Catalysts

by Renata F. Botti, Murilo D.M. Innocentini, Thais A. Faleiros, Murilo F. Mello, Danilo L. Flumignan, Leticia K. Santos, Giorgia Franchin and Paolo Colombo

Molecules 2020, 25(12), 2839; https://doi.org/10.3390/molecules25122839 - 19 Jun 2020

Cited by 23 | Viewed by 4177

Abstract

This work investigates the catalytic activity of geopolymers produced using two different alkali components (sodium or potassium) and four treatment temperatures (110 to 700 °C) for the methyl transesterification of soybean oil. The geopolymers were prepared with metakaolin as an aluminosilicate source and alkaline activating solutions containing either sodium or potassium in the same molar oxide proportions. The potassium-based formulation displayed a higher specific surface area and lower average pore size (28.64–62.54 m²/g; 9 nm) than the sodium formulation (6.34–32.62 m²/g; 17 nm). The reduction in specific surface area (SSA) after the heat treatment was more severe for the sodium formulation due to the higher thermal shrinkage. The catalytic activity of the geopolymer powders was compared under the same reactional conditions (70–75 °C, 150% methanol excess, 4 h reaction) and same weight amounts (3% to oil). The differences in performance were attributed to the influences of sodium and potassium on the geopolymerization process and to the accessibility of the reactants to the catalytic sites. The Na-based geopolymers performed better, with FAME contents in the biodiesel phase of 85.1% and 89.9% for samples treated at 500 and 300 °C, respectively. These results are competitive in comparison with most heterogeneous base catalysts reported in the literature, considering the very mild conditions of temperature, excess methanol and catalyst amount and the short time spent in reactions. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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15 pages, 3271 KiB

Open AccessArticle

Unsaturated Response of Clayey Soils Stabilised with Alkaline Cements

by Nuno Araújo, Manuela Corrêa-Silva, Tiago Miranda, António Topa Gomes, Fernando Castro, Tiago Teixeira and Nuno Cristelo

Molecules 2020, 25(11), 2533; https://doi.org/10.3390/molecules25112533 - 29 May 2020

Cited by 4 | Viewed by 2349

Abstract

The influence of suction on the mechanical behaviour of unsaturated chemically stabilised soils is still mostly unknown and unquantified. This is also motivated by the difficulties associated with the experimental procedure required to fully characterise the unsaturated response of the soil, including its direct influence on traditional strength tests. The present paper presents the soil water retention curves obtained for a Portuguese soil before and after being stabilised with Portland cement (OPC) and an alkali-activated cement (AAC). Saturated undrained triaxial tests were also performed for the same curing conditions (0, 28, and 90 days). Previous attempts to characterise the retention curve of soils stabilised with AAC are unknown, and the results showed that the pore volume structure is already formed after 28 days, prior to the full development of the gel matrix responsible for the strength increase between 28 and 90 days. The curve changed after stabilisation, and with each binder, as the OPC presented a higher air-entry value and a narrower suction range compared to the AAC solution. The significant differences between the curves obtained from each binder suggest the future development of a methodology to assess the quality of the AAC stabilisation. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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25 pages, 8422 KiB

Open AccessArticle

Alkalinity and Its Consequences for the Performance of Steel-Reinforced Geopolymer Materials

by Andreas Koenig, Hitham Mahmoud, Oliver Baehre and Frank Dehn

Molecules 2020, 25(10), 2359; https://doi.org/10.3390/molecules25102359 - 19 May 2020

Cited by 6 | Viewed by 3255

Abstract

This paper investigates the development of the alkalinity and its impact on carbon steel reinforcement embedded in alkali-activated fly ashes (AAFA) and alkali-activated fly ashes with ten percentage mass (wt%) of blast furnace slag (AAFAS)-based materials (geopolymer–GP). The pH analysis of eluates indicates a remarkable decrease of alkalinity in AAFA and AAFAS in the first hours of the geopolymerization process. Phenolphthalein solution and pore solution tests on concretes also show a sharp decrease of alkalinity with increased Ca content in the binder due to carbonation. Micro X-ray computer tomography (µXCT) and electrochemical techniques indicate that the changed pH in the GP systems was accompanied by a decrease in the corrosion rates of steel reinforcement when compared to ordinary Portland cement (OPC) systems. In contrast to calcite and vaterite, which were detected in OPC and AAFAS after a carbonation process, only sodium carbonate natron was determined at lower levels in AAFA by X-ray diffraction (XRD). Full article

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28 pages, 1113 KiB

Open AccessReview

Carbonation and Chloride Ions’ Penetration of Alkali-Activated Materials: A Review

by Xuanhan Zhang, Kaidi Long, Wei Liu, Lixiao Li and Wu-Jian Long

Molecules 2020, 25(21), 5074; https://doi.org/10.3390/molecules25215074 - 1 Nov 2020

Cited by 24 | Viewed by 3316

Abstract

Alkali-activated materials (AAMs) are widely recognized as potential alternatives to ordinary Portland cement (OPC) due to their lower carbon footprint. However, like OPC, AAMs can also generate some durable problems when exposed to aggressive environments and the mechanisms and possible improvements are still not fully clear in existing investigations. Furthermore, the corrosion mechanisms of AAMs are different from OPC due to the discrepant reaction products and pore structures. Thus, this study’s aim is to review the chemical reaction mechanisms, factors, and mitigation methods when AAMs are attacked by carbonation and chloride ions, along with a summative discussion regarding instructive insights to durable problems of AAMs. Full article

(This article belongs to the Special Issue Advances in Alkali-Activated Materials)

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