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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Macromolecular Crystals".

Deadline for manuscript submissions: closed (28 January 2022) | Viewed by 21019

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Dr. Shima Pilehvar

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Guest Editor

Faculty of Engineering, Ostfold University College, NO-1757 Halden, Norway
Interests: building materials; geopolymer composites; Portland cement composites; mechanical properties of building materials; energy saving; phase change materials; thermal properties of building materials

Dr. Luís G. Baltazar

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Guest Editor

NOVA School of Science and Technology | FCT NOVA, Campus Caparica, 2829-516 Caparica, Portugal
Interests: rheology of colloidal suspensions; old stone masonry consolidation; sustainable construction materials
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Special Issue Information

Dear Colleagues,

Geopolymers consist of silico-aluminates in a semi-crystalline three-dimensional structure. The geopolymer binder is synthesized by mixing materials rich in silica and amorphous alumina with a strong alkaline solution. Geopolymer composites are a very interesting concrete alternative, with an improved performance compared to traditional concretes, while utilizing a high proportion of industrial waste and by-products such as fly ash (FA), coal ash, and blast furnace slag. Geopolymers are therefore more environmentally friendly and cheaper than Portland cement and can significantly reduce the amount of CO₂ emission from the cement industry—the primary driver of global warming.

Geopolymers exhibit excellent performance characteristics such as quick controllable setting and hardening, high compressive strength, freeze–thaw resistance, excellent durability in sulfate environment, superior resistance to acid and salt attacks, high fire resistance, low thermal conductivity, low shrinkage, and adequate radiation shielding.

The aim of this Special Issue is to invite researchers to publish their new and novel findings about physical, mechanical, thermal, and microstructural properties of geopolymer composites and inorganic building materials, the life cycle assessment of geopolymers, geopolymers for 3D printing, the durability and sustainability of geopolymer composites, and any other topics relevant to geopolymers.

Dr. Shima Pilehvar
Prof. Dr. Luis G. Baltazar
Guest Editors

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Keywords

geopolymers
geopolymer composites
inorganic building materials
3D printing
geopolymer mixture design
physical properties of geopolymers
mechanical properties of geopolymers
thermal properties of geopolymers
microstructural study of geopolymers
durability
life cycle assessment of geopolymers

Published Papers (10 papers)

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Research

19 pages, 7156 KiB

Open AccessArticle

Experimental Studies on Mechanical Properties and Microscopic Mechanism of Marble Waste Powder Cement Cementitious Materials

by Tongkuai Wang, Wenwei Yang and Jintuan Zhang

Crystals 2022, 12(6), 868; https://doi.org/10.3390/cryst12060868 - 19 Jun 2022

Cited by 6 | Viewed by 1618

Abstract

The resource utilization of waste stone powder is a meaningful way to realize sustainable development. This paper aims to study the influence of marble waste powder particle size and replacement cement dosage on the mechanical properties of cementitious materials and evaluate its microstructure and mineral characterization by SEM and XRD. The results show that the early strength of cementitious materials is obviously improved when the dosage of marble waste powder is in the range of 0–15%, and the lifting effect of marble waste powder with a particle size of 600 mesh instead of cement on the strength and microstructure of cementitious materials is the most obvious. The replacement of cement with different particle sizes of marble waste powder found that it had low chemical activity and participated in the hydration reaction of cement, but the reaction degree was low. The smaller the particle size of marble waste powder instead of cement, the denser the early microstructure, the more obvious the nucleation phenomenon, and the more serious the agglomeration between particles. In addition, the mechanism model of marble waste powder replacing cement cementitious materials was proposed. The strength prediction function model between the material dosage and compressive strength was constructed, and the accuracy of the model was verified. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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9 pages, 3746 KiB

Open AccessCommunication

Performance of Silica Fume-Based Geopolymer Grouts for Heritage Masonry Consolidation

by Luis G. Baltazar

Crystals 2022, 12(2), 288; https://doi.org/10.3390/cryst12020288 - 18 Feb 2022

Cited by 2 | Viewed by 2079

Abstract

Despite the increasing number of studies on geopolymer-based materials, a lack of information still prevails concerning the use of geopolymer materials for the consolidation and conservation of the built heritage. Since the introduction of the term “geopolymer” by Davidovits, several studies have pointed out geopolymers as a potential replacement for traditional binders, mainly due to their advantages associated with mechanical properties and low carbon dioxide emissions. The geopolymers (also known as alkali-activated materials or inorganic polymers) are obtained by a chemical process through which precursors rich in silica and alumina interact with an alkaline medium to result in a material with binding properties. The aim of this study is to exploit the potential of geopolymer-based grouts in the consolidation of stone masonry buildings. Grouting or grout injection is a technique used for the consolidation of heritage masonry buildings; it consists of the introduction of a binding agent to fill the internal voids and cracks. An experimental program was carried out to improve knowledge of geopolymer grouts suitable for consolidation purposes. The experimental findings revealed that the silica-fume-based geopolymer grout has a worse performance from a rheological point of view, whereas it showed promising results in terms of mechanical strength when compared to traditional hydraulic-lime-based grout. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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21 pages, 59071 KiB

Open AccessArticle

Assessment of the Durability Dynamics of High-Performance Concrete Blended with a Fibrous Rice Husk Ash

by David O. Nduka, Babatunde J. Olawuyi, Olabosipo I. Fagbenle and Belén G. Fonteboa

Crystals 2022, 12(1), 75; https://doi.org/10.3390/cryst12010075 - 06 Jan 2022

Cited by 6 | Viewed by 1902

Abstract

The present study examines the durability properties of Class 1 (50–75 MPa) high-performance concrete (HPC) blended with rice husk ash (RHA) as a partial replacement of CEM II B-L, 42.5 N. Six HPC mixes were prepared with RHA and used as 5%, 10%, 15%, 20%, 25%, and 30% of CEM II alone and properties are compared with control mix having only CEM II. The binders (CEM II and RHA) were investigated for particle size distribution (PSD), specific surface area (SSA), oxide compositions, mineralogical phases, morphology, and functional groups using advanced techniques of laser PSD, Brunauer–Emmett–Teller (BET), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared/attenuated total reflection (FTIR/ATR), respectively, to understand their import on HPC. Durability properties, including water absorption, sorptivity, and chemical attack of the HPC samples, were investigated to realise the effect of RHA on the HPC matrix. The findings revealed that the durability properties of RHA-based HPCs exhibited an acceptable range of values consistent with relevant standards. The findings established that self-produced RHA would be beneficial as a cement replacement in HPC. As the RHA is a cost-effective agro-waste, a scalable product of RHA would be a resource for sustainable technology. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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18 pages, 3365 KiB

Open AccessArticle

TiO₂ Modified Geopolymers for the Photocatalytic Dye Decomposition

by Martina Novotná, Petr Knotek, Tomáš Hanzlíček, Petr Kutálek, Ivana Perná, Klára Melánová, Eva Černošková and Kateřina Kopecká

Crystals 2021, 11(12), 1511; https://doi.org/10.3390/cryst11121511 - 03 Dec 2021

Cited by 3 | Viewed by 2334

Abstract

This article studies the photocatalytic activity of three types of industrially produced TiO₂ powder (P25, CG100 and CG300) incorporated into a parent geopolymer matrix, and their pure counterparts, based on the decomposition of Rhodamine B dye. Rhodamine B dye is applied as a model substance because it is frequently used in the textile industry and thus may be present in the wastewater. The average particle size, specific surface area and mineralogical composition of TiO₂ powders have been determined. The geopolymer matrix works well as a supporting material for the CG100 and P25 pure types of TiO₂ powder as these input materials have better properties such as a higher average particle size, lower specific surface area, mineralogicalcomposition, etc., than the CG300 TiO₂ powder. These properties (or their combination) affect the photocatalytic activity of the resulting materials, which may thus become advanced composites with an additional purifying ability, e.g., materials that can be used for wastewater treatment or air purification. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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15 pages, 2322 KiB

Open AccessArticle

Axial Behavior of Concrete-Filled Double-Skin Tubular Stub Columns Incorporating PVC Pipes

by Muhammmad Faisal Javed, Haris Rafiq, Mohsin Ali Khan, Fahid Aslam, Muhammad Ali Musarat and Nikolai Ivanovich Vatin

Crystals 2021, 11(12), 1434; https://doi.org/10.3390/cryst11121434 - 23 Nov 2021

Cited by 2 | Viewed by 2160

Abstract

This experimental study presents concrete-filled double-skin tubular columns and demonstrates their expected advantages. These columns consist of an outer steel tube, an inner steel tube, and concrete sandwiched between two tubes. The influence of the outer-to-inner tube dimension ratio, outer tube to thickness ratio, and type of inner tube material (steel, PVC pipe) on the ultimate axial capacity of concrete-filled double-skin tubular columns is studied. It is found that the yield strength of the inner tube does not significantly affect the ultimate axial capacity of concrete-filled double-skin tubular composites. With the replacement of the inner tube of steel with a PVC pipe, on average, less than 10% strength is reduced, irrespective of size and dimensions of the steel tube. Hence, the cost of a project can be reduced by replacing inner steel tubes with a PVC pipes. Finally, the experimental results are compared with the existing design methods presented in AISC 360-16 (2016), GB51367 (2019), and EC4 (2004). It is found from the comparison that GB51367 (2019) gives better results, followed by AISC (2016) and EC4 (2004). Full article

(This article belongs to the Special Issue Geopolymer Composites)

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30 pages, 6761 KiB

Open AccessArticle

Strength, Fracture and Durability Characteristics of Ambient Cured Alkali—Activated Mortars Incorporating High Calcium Industrial Wastes and Powdered Reagents

by Dhruv Sood and Khandaker M. A. Hossain

Crystals 2021, 11(10), 1167; https://doi.org/10.3390/cryst11101167 - 25 Sep 2021

Cited by 6 | Viewed by 1574

Abstract

Alkali-activated mortars (AAMs) are developed incorporating binary/ternary combinations of industrial wastes comprising of fly ash class C (FA-C), fly ash class F (FA-F) and ground granulated blast furnace slag (GGBFS) with alkaline reagents and silica sand. The use of high calcium precursors, calcium-based powder form reagents, dry mixing method, and ambient curing with performance characterization based on chemical ratios and fracture properties are some novel aspects of the study. The mechanical (dry density, compressive strength, ultrasonic pulse velocity, elastic modulus, fracture/crack tip toughness and fracture energy), durability (shrinkage/expansion and mass change in water and ambient curing conditions, water absorption and freeze-thaw resistance) and microstructural (SEM/EDS and XRD analyses) characteristics of eight AAMs are investigated. The binary (FA-C + GGBFS) mortars obtained higher compressive strengths (between 35 MPa and 42.6 MPa), dry densities (between 2032 kg/m³ and 2088 kg/m³) and ultrasonic pulse velocities (between 3240 m/s and 4049 m/s) than their ternary (FA-C + FA-F + GGBFS) counterparts. The elastic modulus and fracture toughness for mortars incorporating reagent 2 (calcium hydroxide: sodium sulphate = 2.5:1) were up to 1.7 and five times higher than those with reagent 1 (calcium hydroxide: sodium metasilicate = 1:2.5). This can be attributed to the additional formation of C-S-H with C-A-S-H/N-C-A-S-H binding phases in mortars with reagent 2. Ternary mortars exhibited comparatively lower shrinkage/expansion and initial sorptivity indices than their binary counterparts due to the lower geopolymerisation potential of fly ash class F that facilitated the reduction of matrix porosity. All mortar specimens demonstrated 100% or more relative dynamic modulus of elasticity after 60 freeze-thaw cycles, indicating the damage recovery and satisfactory durability due to probable micro-level re-arrangement of the binding phases. This study confirmed the viability of producing cement-free AAMs with satisfactory mechanical and durability characteristics. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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10 pages, 4894 KiB

Open AccessArticle

Effect of Aggregate Types on the Mechanical Properties of Traditional Concrete and Geopolymer Concrete

by Hani Alanazi

Crystals 2021, 11(9), 1110; https://doi.org/10.3390/cryst11091110 - 12 Sep 2021

Cited by 4 | Viewed by 2374

Abstract

For the same concrete quality, different types of coarse aggregates may result in different mechanical properties. This paper presents a study on the effect of aggregate types on the mechanical properties of two concretes, namely, geopolymer concrete (GP) and traditional Portland cement (TC) concrete. The mechanical properties were investigated through several large-scale tests. Moreover, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and laser scanning microscope (LSM) images were obtained to study the microstructure of tested mixes. The results revealed that the aggregate type has different effects on the mechanical properties of TC and GP, as they were behaving opposite to quartz and limestone aggregates. Microstructure analysis further confirmed the growth of well-bonded regions between the paste and aggregate in the GP with limestone aggregates, and the formation of several weak interfacial zones in concrete mixtures made with quartz aggregates. It was concluded that the mechanical properties of GP are very sensitive to the stiffness of aggregate, concentrations of stress, and the physical and chemical reactions occurring in the interfacial transition zone which may lead to improved or weakened bond strength between paste and aggregates. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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17 pages, 5853 KiB

Open AccessArticle

The Influence of the Environment on the Properties of Hybrid Cement-Based Concrete with Steel and Air-Cooled Slags

by Pavel Martauz, Vojtěch Václavík and Branislav Cvopa

Crystals 2021, 11(9), 1087; https://doi.org/10.3390/cryst11091087 - 07 Sep 2021

Cited by 2 | Viewed by 1525

Abstract

This article presents the results of research that dealt with the development of non-traditional concrete using a hybrid alkali-activated cement. It is concrete based on by-products from a metallurgical plant that replaced 100% of the natural aggregates. Steel slag (CSS, fraction: 0/8 mm) was used as a filler in combination with air-cooled slag (ACBFS, fraction: 8/16 mm and 16/32 mm). Portland blended cement (CEM II/B-S 42.5N) and H-CEMENT were used as binding components in the development of the concrete mixture designs. Both of these cements were produced by Považská cementáreň, a.s., Ladce. Attention was focused on testing the physical and mechanical properties of the developed concretes in various environments. An aqueous environment was selected as the first environment for the placement of test specimens (cubes with 150 mm edges and prisms with dimensions of 100 × 100 × 400 mm³) according to the ČSN EN 206-1 standard and the outdoor environment (August to October). The determination of the cube strength was made after 7, 28, and 90 days, the determination of the flexural and compressive strength was made at the end of the prisms, and the determination of the dynamic modulus of elasticity was made after 28 days on the prisms. The test results of the test specimens, which were placed in two environments, were compared and it was found that, after 90 days, the outdoor environment caused a decrease in the concrete’s strength characteristics when using Portland blended cement (CEM II/ B-S 42.5N) of about 8%; in contrast, when using H-CEMENT, the concrete’s strength increased by about 14%. The use of H-CEMENT and the addition of PUZZOLANIT in the amount of 30% in combination with CEM II/B-S 42.5N in the amount of 70% reduced the decrease in the strength of the concrete after 90 days by about 3%. The research results confirm the suitability of using H-CEMENT and the addition of PUZZOLANIT for the production of concrete based on steel slag (CSS) and air-cooled slag (ACBFS). Full article

(This article belongs to the Special Issue Geopolymer Composites)

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10 pages, 6295 KiB

Open AccessArticle

Microstructure Evolution Mechanism of Geopolymers with Exposure to High-Temperature Environment

by Yuanen Lu, Na Cui, Yougong Xian, Jiaqing Liu, Chao Xing, Ning Xie and Dawei Wang

Crystals 2021, 11(9), 1062; https://doi.org/10.3390/cryst11091062 - 02 Sep 2021

Cited by 2 | Viewed by 1942

Abstract

The investigation on geopolymers has intrigued broad interests in the past decades, due to the requirements for the recycling of aluminosilicate solid wastes, such as red mud, slags, sludges and demolished concrete. Previous studies have demonstrated the feasibility of reusing this Aluminosilicate as a resource to prepare cementitious materials and indicated their promising properties at ambient temperature. However, when this material was exposed to high temperatures, especially above 1000 °C, the microstructure evolution mechanisms were not systematically investigated. In this study, the microstructural evolution process of metakaolin-based K geopolymer (molar ratio of K:Al:Si was 1:1:4) is investigated. The crystalized leucite originated from the geopolymer precursor was detected above 1000 °C. The SEM results indicate that the microstructure of the geopolymer before heating was composed of non-reacted metakaolin with a typical layered structure and reacted amorphous binder phase. As the geopolymer heated to 1000 °C, the microstructure of the geopolymer changed to a porous structure with an average pore size from 10 to 30 μm. When the heating temperature reached 1100 °C, the pores started to close along with the leucite crystallization process. As the heating temperature reached 1200 °C, most of the pores were closed. The TEM results show that the microstructure of the geopolymer, after being heated to 1400 °C, was composed of an amorphous glassy phase and crystallized leucite phase. The crystallized leucite grains originated from the nano-sized crystal nuclei, with an average size of 2–3 nm. The TEM-EDS results indicate that the chemical composition of the glassy phase was complicated. It varied from area to area because of the movement and uneven distribution of K. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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11 pages, 1580 KiB

Open AccessArticle

New Metakaolin-Based Geopolymers with the Addition of Different Types of Waste Stone Powder

by Ivana Perná, Martina Novotná, Daniela Řimnáčová and Monika Šupová

Crystals 2021, 11(8), 983; https://doi.org/10.3390/cryst11080983 - 19 Aug 2021

Cited by 11 | Viewed by 1919

Abstract

The search for new alternative raw materials and their subsequent use supports the sustainability of natural resources. This article describes the use of waste stone powder (WSP) in geopolymer synthesis. Five different types of WSP (feldspar, limestone, marlstone, dolomite, marble) were comprehensively characterized and their influence on the resulting properties (especially mechanical and textural properties, setting time and structure) of metakaolin-based geopolymer composites was investigated. Their comparison with a geopolymer composite containing only quartz sand has revealed that WSP additions have a small but positive effect on the mechanical or textural properties of geopolymers. Moreover, setting time measurements have shown that waste stone powders can be used as an accelerator of geopolymer reaction solidification. The results demonstrated that the mentioned types of WSP, previously landfilled, can be used for the preparation of geopolymers. This can help reduce the environmental burden. Full article

(This article belongs to the Special Issue Geopolymer Composites)

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