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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Applications".

Deadline for manuscript submissions: closed (28 February 2022) | Viewed by 24871

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Prof. Dr. Ildiko Merta

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TU Wien Faculty of Civil Engineering, Institute of Material Technology, Building Physics and Building Ecology, Karlsplatz 13/E207-1, 1040 Vienna, Austria
Interests: cement-based composites; geopolymers; polymer fibre-reinforced composites; fibre-reinforced concretes; building material science; sustainable bio-based composites; using waste materials in composites; supplementary cementitious materials; durability and long-term performance of composites; high-performance composites
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Dear Colleagues,

We are writing to invite you to submit your research work to a Special Issue of the Polymers. The topic will be Geopolymer Composite.

Geopolymers (or alkali-activated binders) have been the most commonly researched sustainable alternative to the traditional cement-based binders in concretes (and mortars) throughout the past decade. In geopolymers, different solid prime materials (natural and waste materials such as fly ash obtained from thermal power plant coal combustion procedure, ground granulated blast furnace slag, micro silica, etc.) are activated using various alkaline solutions.

Available research results show that geopolymers can provide adequate mechanical properties for a potential replacement of structural concrete if properly designed and cured. Based on the alkali-activated product formed after the activation of the solid prime materials, two different categories can be defined: i) calcium silicate hydrate gel and ii) alkaline alumino-silicate hydrate gel (also known as inorganic or geopolymer gel).

The aim of this Special Issue is to provide an update on new advances and research results in the field of geopolymer composites (or alkali-activated materials) and their applications in the area of alternative sustainable building materials. The specific areas of interest of the Special Issue include (but are not limited to) the composition and matrix mix design of geopolymer cements, mortars and concretes along with reinforced matrices (longitudinal-, fibre-, or textile reinforcement). The issue will address the composites’ properties in fresh- and hardened states including their physical, mechanical and fracture mechanical characteristics. Topics may include creep, shrinkage, carbonation as well as durability- and long-term behavior aspects of the composite. Applications of geopolymer composites in building constructions, retrofit and maintenance are also welcomed.

Ideally, contributions focus on fundamental results, mechanisms, and applications that will help to compile the current state-of-the-art and to highlight their range of the application. Both original contributions and reviews are welcome.

Dr. Ildiko Merta
Guest Editor

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. Polymers 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

Geopolymer mix design
Geopolymer mortar
Geopolymer concrete
Fiber-reinforced geopolymer
Physical properties
Mechanical properties
Fracture properties
Durability properties
Geopolymer applications

Published Papers (10 papers)

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Research

11 pages, 3351 KiB

Open AccessArticle

Effect of the Class C Fly Ash on Low-Reactive Gold Mine Tailing Geopolymers

by Yibran Perera-Mercado, Ahmadreza Hedayat, Lori Tunstall, Cara Clements, Julia Hylton, Linda Figueroa, Nan Zhang, Héctor Gelber Bolaños Sosa, Néstor Tupa, Isaac Yanqui Morales and Reynaldo Sabino Canahua Loza

Polymers 2022, 14(14), 2809; https://doi.org/10.3390/polym14142809 - 9 Jul 2022

Cited by 2 | Viewed by 1743

Abstract

Beneficiation of industrial wastes, such as mine tailings (MTs), through development of alternative eco-friendly geopolymer binders for construction composites offers a twofold environmental benefit, as it reduces the demand for cement and it increases the sustainability of industrial processes by creating a value-added product from an industrial byproduct. While MTs have the requisite composition for use as a geopolymer precursor, they are often low-reactive. This study explored the effect of Class C Fly Ash (FAc) on the geopolymerization of low-reactive gold MTs. A 10 M sodium hydroxide (NaOH) solution was used as the alkaline activator with four different concentrations of FAc (5, 10, 15 and 20 wt.%). The results indicated that the combination of FAc with the low-reactive gold MTs improved the physicochemical stability of the final geopolymerized samples, with a 95–120% increase in compressive strength, compared to the geopolymer samples of only low-reactive gold MTs. Although some of the strength improvement could be attributed to geopolymerization of the FAc itself, the presence of the FAc also improved the reactivity of the MTs, increasing the geopolymer production of the MTs. This study documents the positive effects of the FAc on gold MTs with low-calcium content and their conversion into sustainable inorganic composite geopolymers for the construction field. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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16 pages, 3816 KiB

Open AccessArticle

The Influence of Accelerated Carbonation on Physical and Mechanical Properties of Hemp-Fibre-Reinforced Alkali-Activated Fly Ash and Fly Ash/Slag Mortars

by Ildiko Merta, Bojan Poletanovic, Jelena Dragas, Vedran Carevic, Ivan Ignjatovic and Miroslav Komljenovic

Polymers 2022, 14(9), 1799; https://doi.org/10.3390/polym14091799 - 28 Apr 2022

Cited by 7 | Viewed by 1689

Abstract

The physical and mechanical properties of hemp-fibre-reinforced alkali-activated (AA) mortars under accelerated carbonation were evaluated. Two matrices of different physical and chemical properties, i.e., a low Ca-containing and less dense one with fly ash (FA) and a high Ca-containing and denser one with FA and granulated blast furnace slag (GBFS), were reinforced with fibres (10 mm, 0.5 vol% and 1.0 vol%). Under accelerated carbonation, due to the pore refinement resulting from alkali and alkaline earth salt precipitation, AA hemp fibre mortars markedly (20%) decreased their water absorption. FA-based hemp mortars increased significantly their compressive and flexural strength (40% and 34%, respectively), whereas in the denser FA/GBFS matrix (due to the hindered CO₂ penetration, i.e., lower chemical reaction between CO₂ and pore solution and gel products), only a slight variation (±10%) occurred. Under accelerated carbonation, embrittlement of the fibre/matrix interface and of the whole composite occurred, accompanied by increased stiffness, decreased deformation capacity and loss of the energy absorption capacity under flexure. FA-based matrices exhibited more pronounced embrittlement than the denser FA/GBFS matrices. A combination of FA/GBFS-based mortar reinforced with 0.5 vol% fibre dosage ensured an optimal fibre/matrix interface and stress transfer, mitigating the embrittlement of the material under accelerated carbonation. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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14 pages, 4584 KiB

Open AccessArticle

Microstructural Characterization of Alkali-Activated Composites of Lightweight Aggregates (LWAs) Embedded in Alkali-Activated Foam (AAF) Matrices

by Katja Traven, Wolfgang Wisniewski, Mark Češnovar and Vilma Ducman

Polymers 2022, 14(9), 1729; https://doi.org/10.3390/polym14091729 - 23 Apr 2022

Cited by 5 | Viewed by 1785

Abstract

Alkali-activated composites of lightweight aggregates (LWAs, with beneficial insulating properties) and alkali-activated foams (AAFs, higher added value products due to their production from waste materials at well below 100 °C) allow for the expectation of superior properties if a chemical bonding reaction or mechanical interlocking occurs during production. However, the interfaces between LWAs and an AAF have not been studied in detail so far. Chemical reactions are possible if the LWA contains an amorphous phase which can react with the alkaline activators of the AAF, increase the bonding, and thus, also their mechanical strengths. These, in turn, allow for an improvement of the thermal insulation properties as they enable a further density reduction by incorporating low density aggregates. This work features a first-detailed analyses of the interfaces between the LWAs’ expanded polystyrene, perlite, expanded clay and expanded glass, and the alkali-activated foam matrices produced using industrial slags and fly ash. Some are additionally reinforced by fibers. The goal of these materials is to replace cement by alkali-activated waste as it significantly lowers the environmental impact of the produced building components. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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20 pages, 1919 KiB

Open AccessArticle

Prediction of the Compressive Strength of Fly Ash Geopolymer Concrete by an Optimised Neural Network Model

by Ali Abdulhasan Khalaf, Katalin Kopecskó and Ildiko Merta

Polymers 2022, 14(7), 1423; https://doi.org/10.3390/polym14071423 - 31 Mar 2022

Cited by 9 | Viewed by 2420

Abstract

This article presents a regression tool for predicting the compressive strength of fly ash (FA) geopolymer concrete based on a process of optimising the Matlab code of a feedforward layered neural network (FLNN). From the literature, 189 samples of different FA geopolymer concrete mix-designs were collected and analysed according to ten input variables (all relevant mix-design parameters) and the output variable (cylindrical compressive strength). The developed optimal FLNN model proved to be a powerful tool for predicting the compressive strength of FA geopolymer concrete with a small range of mean squared error (MSE = 10.4 and 15.0), a high correlation coefficient with the actual values (R = 96.0 and 97.5) and a relatively small root mean squared error (RMSE = 3.22 and 3.87 MPa) for the training and testing data, respectively. Based on the optimised model, a powerful design chart for determining the mix-design parameters of FA geopolymer concretes was generated. It is applicable for both one- and two-part geopolymer concretes, as it takes a wide range of mix-design parameters into account. The design chart (with its relatively small error) will ensure cost- and time-efficient geopolymer production in future applications. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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14 pages, 7827 KiB

Open AccessArticle

Strength, Elastic Properties and Fiber–Matrix Interaction Mechanism in Geopolymer Composites

by Susana P. Arredondo, Ramón Corral, A. Valenciano, Carlos A. Rosas, Jose M. Gómez, Teresita J. Medina, Magnolia Soto and Jesús M. Bernal

Polymers 2022, 14(6), 1248; https://doi.org/10.3390/polym14061248 - 20 Mar 2022

Cited by 3 | Viewed by 2295

Abstract

The current geopolymers have limited mechanical strength against the effect of tension, which makes them susceptible to brittle failure. However, owing to their potential as a sustainable construction material, there is growing interest in improving the poor mechanical properties of geopolymers. This study experimentally investigated crucial properties of polypropylene-fiber-reinforced fly ash-based geopolymer composites. The effects of polypropylene fibers (PPF) addition (0.5%, 1.0% and 1.5% by volume) on the mechanical properties of the geopolymer composites were investigated with respect to compressive and flexural strength, deformation behavior of Young’s and shear moduli, and resilience capacity. In addition, scanning electron microscopy was performed to establish the morphology of the geopolymeric matrix and the fiber–matrix interfacial interaction. The addition of PPF significantly increased the flexural strength: compared with the control, at 7 days it was 27% greater for the 0.5% PPF composite and 65% greater for the 1.0% PPF composite. By 14 days it was 31% and 61% greater, respectively. By contrast, the 1.5% PPF composite had lower strength parameters compared with the control because the fiber dispersion increased the porosity. Similar trends were seen for resilience. The SEM observations showed the dispersion of the fibers and helped elucidate the fiber–matrix interaction mechanism. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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19 pages, 10030 KiB

Open AccessArticle

Influence of the Integration of Geopolymer Wastes on the Characteristics of Binding Matrices Subjected to the Action of Temperature and Acid Environments

by Rabii Hattaf, Abdelilah Aboulayt, Nouha Lahlou, Mohamed Ouazzani Touhami, Moussa Gomina, Azzeddine Samdi and Redouane Moussa

Polymers 2022, 14(5), 917; https://doi.org/10.3390/polym14050917 - 25 Feb 2022

Cited by 6 | Viewed by 1792

Abstract

Recycling geopolymer waste, by reusing it as a raw material for manufacturing new geopolymer binding matrices, is an interesting asset that can add to the many technical, technological and environmental advantages of this family of materials in the construction field. This can promote them as promising alternatives to traditional materials, such as Portland cements, which are not so environmentally friendly. Recent studies have shown that the partial replacement of reactive aluminosilicates (metakaolin and fly ash) up to a mass rate of 50% by geopolymer waste does not significantly affect the compressive strength of the new product. In line with these findings, this paper investigates the effects of aggressive environments, i.e., high temperatures (up to 1000 °C) and acid attacks (pH = 2), on the characteristics of these new matrices. Different techniques were used to understand these evolutions: mineralogical analysis by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TGA-DTA), mechanical characterization and scanning electron Microscopy (SEM) observations. The results are very satisfactory: in the exposure temperature range explored, the new matrices containing geopolymer waste suffered losses in compressive strength similar to those of the matrices without waste (considered as materials reference). On the other hand, the new matrices exhibited good chemical stability in acid media. These results confirm that the reuse of geopolymer waste is a promising recycling solution in the construction sector. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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23 pages, 2897 KiB

Open AccessArticle

Properties of Lime-Cement Concrete Containing Various Amounts of Waste Tire Powder under Different Ground Moisture Conditions

by Leili Mohammadifar, Hania Miraki, Aida Rahmani, Soheil Jahandari, Bahareh Mehdizadeh, Haleh Rasekh, Parisa Samadi and Bijan Samali

Polymers 2022, 14(3), 482; https://doi.org/10.3390/polym14030482 - 25 Jan 2022

Cited by 13 | Viewed by 4293

Abstract

Lime-cement concrete (LCC) is a non-structural concrete in which lime and cement are used as the main binders. However, although LCC has many applications in reducing the settlement of foundations and providing a support layer for shallow foundations, little research has been conducted to evaluate its behaviour in various moisture conditions. Previous researchers have studied the feasibility of using waste tires in conventional concrete to alleviate their negative environmental impacts. However, in field projects, rubber has not been widely used because its application leads to the strength reduction of concrete. In the case of LCC, attaining high strengths is not required and thus application of waste tire particles sounds reasonable. This research evaluated the impact of various rubber powder contents on the fresh, geotechnical and durability properties of LCC at different saturation degrees induced by the capillary action and groundwater level increment, which has not been studied before. The results of more than 320 tests showed that the application of tire powder increases workability and decreases the water absorption of LCC. Moreover, all 60-day cured specimens exposed to 100% saturation degree experienced a strength reduction of less than 10% by using rubber powder contents varying from 0 to 20%. Moreover, increasing the saturation degree from 0 to 100% decreased the average compressive strength by 13.5 and 22% for 60-day cured samples of two different mix designs. The results of this research confirm that LCC containing up to 10% rubber powder could be promisingly used underneath or close to the groundwater table without its strength and geotechnical properties being jeopardized due to rubber employment and/or exposure to ground moisture. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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18 pages, 27482 KiB

Open AccessArticle

Effect of Waste Ceramic Powder on the Properties of Alkali–Activated Slag and Fly Ash Pastes Exposed to High Temperature

by Gui-Yu Zhang, Sung-Chul Bae, Run-Sheng Lin and Xiao-Yong Wang

Polymers 2021, 13(21), 3797; https://doi.org/10.3390/polym13213797 - 2 Nov 2021

Cited by 15 | Viewed by 1994

Abstract

This paper presents the effects of alkali-activated blast furnace slag and fly ash (AASF) paste added with waste ceramic powder (WCP) on mechanical properties, weight loss, mesoscopic cracks, reaction products, and microstructure when exposed to 300, 600, and 900 °C. Using waste ceramic powder to replace blast furnace slag and fly ash, the replacement rate was 0–20%. The samples cured at 45 °C for 28 days were heated to 300, 600, and 900 °C to determine the residual compressive strength and weight loss at the relevant temperature. We evaluated the deterioration of the paste at each temperature through mesoscopic images, ultrasonic pulse velocity (UPV), thermogravimetric analysis (TG), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and with a scanning electron microscope (SEM). Relevant experimental results show that: (1) with the increase in waste ceramic powder content, the compressive strength of samples at various temperatures increased, and at 300 °C, the compressive strength of all the samples reached the highest value; (2) the residual weight increased with the increase in the content of the waste ceramic powder; (3) with a further increase in temperature, all the samples produced more mesoscopic cracks; (4) at each temperature, with the rise in waste ceramic powder content, the value of the ultrasonic pulse velocity increased; (5) the TG results showed that, as the content of waste ceramic powder increased, the formation of C-A-S-H gel and hydrotalcite decreased; (6) XRD and FTIR spectra showed that, at 900 °C, the use of waste ceramic powder reduced the formation of harmful crystalline phases; (7) the SEM image showed that, at 900 °C, as the content of waste ceramic powder increased, the compactness of the sample was improved. In summary, the addition of waste ceramic powder can improve the mechanical properties of the alkali-activated paste at high temperatures, reduce the occurrence of cracks, and make the microstructure denser. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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14 pages, 3307 KiB

Open AccessArticle

Influence of the Composition and Curing Time on Mechanical Properties of Fluidized Bed Combustion Fly Ash-Based Geopolymer

by Natalia Wielgus, Jan Kubica and Marcin Górski

Polymers 2021, 13(15), 2527; https://doi.org/10.3390/polym13152527 - 30 Jul 2021

Cited by 6 | Viewed by 1611

Abstract

This paper presents novel research on a fluidized bed combustion (FBC) fly ash-based geopolymer as a contribution to the problem of FBC fly ash disposal, and a proposal for a new geopolymer composition—an environmentally friendly material that is possible to use in construction. Geopolymer samples of various composition (containing FBC fly ash as the main raw material, metakaolin and CRT glass as additional components, and sodium silicate and sodium hydroxide as activators) were subjected to flexural and compressive strength tests. An investigation on the effect of the demolding time was carried out on one selected mixture. The test showed that both the composition and the demolding time have a decisive influence on the basic mechanical properties. A mixture containing FBC fly ash to metakaolin in a mass ratio of 3:1, removed from the mold after 14 days, was found to be the best in terms of the mechanical parameters expected from a material that could be used in construction, e.g., for the production of precast elements. According to the results obtained, FBC fly ash is a promising and environmentally friendly raw material for the production of geopolymer, with good mechanical properties and low density. Moreover, a high compressive strength can be obtained by curing the geopolymer at ambient temperature. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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17 pages, 4215 KiB

Open AccessArticle

The Effects of Nanosilica on Mechanical Properties and Fracture Toughness of Geopolymer Cement

by Cut Rahmawati, Sri Aprilia, Taufiq Saidi, Teuku Budi Aulia and Agung Efriyo Hadi

Polymers 2021, 13(13), 2178; https://doi.org/10.3390/polym13132178 - 30 Jun 2021

Cited by 35 | Viewed by 2907

Abstract

Nanosilica produced from physically-processed white rice husk ash agricultural waste can be incorporated into geopolymer cement-based materials to improve the mechanical and micro performance. This study aimed to investigate the effect of natural nanosilica on the mechanical properties and microstructure of geopolymer cement. It examined the mechanical behavior of geopolymer paste reinforced with 2, 3, and 4 wt% nanosilica. The tests of compressive strength, direct tensile strength, three bending tests, Scanning Electron Microscope-Energy Dispersive X-ray (SEM/EDX), X-ray Diffraction (XRD), and Fourier-transform Infrared Spectroscopy (FTIR) were undertaken to evaluate the effect of nanosilica addition to the geopolymer paste. The addition of 2 wt% nanosilica in the geopolymer paste increased the compressive strength by 22%, flexural strength by 82%, and fracture toughness by 82% but decreased the direct tensile strength by 31%. The microstructure analysis using SEM, XRD, and FTIR showed the formation of calcium alumina-silicate hydrate (C–A–S–H) gel. The SEM images also revealed a compact and cohesive geopolymer matrix, indicating that the mechanical properties of geopolymers with 2 wt% nanosilica were improved. Thus, it is feasible for nanosilica to be used as a binder. Full article

(This article belongs to the Special Issue Geopolymer Composite)

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