A Comprehensive Review on Fly Ash-Based Geopolymer

Solidification and utilization of municipal solid waste incineration ashes: Advancements in alkali-activated materials and stabilization techniques, a review

Researchers are actively investigating methodologies for the detoxification and utilization of Municipal Solid Waste Incineration Bottom Ash (MSWIBA) and Fly Ash (MSWIFA), given their potential as alkali-activated materials (AAMs) with low energy consumption. Recent studies highlight that AAMs from MSWIFA and MSWIBA demonstrate significant durability in both acidic and alkaline environments. This article provides a comprehensive overview of the processes for producing MSWIFA and MSWIBA, evaluating innovative engineering stabilization techniques such as graphene nano-platelets and lightweight artificial cold-bonded aggregates, along with their respective advantages and limitations. Additionally, this review meticulously incorporates relevant reactions. Recommendations are also presented to guide future research endeavors aimed at refining these methodologies.

Critical methods of geopolymer feedstocks activation for suitable industrial applications

As health and safety issues emanating from human activities on terrestrial environment is becoming ever challenging, the production of Ordinary Portland Cement is identified as a key contributor. This technology threatens environmental quality by emitting significant quantity of carbon dioxide (CO2) that threatens Net Zero delivery. Consequently, the development of cement alternatives with substantial CO2 reduction/sequestration during production has become imperative. Geopolymers obtained from industrial residues are poised as promising alternatives in managing environmental systems but selection of appropriate method of activation has limited their wider industrial applications. This article discusses four key activation methods and their combinations used in four main feedstocks to advise on their energy requirements, product compressive strength and environmental/industrial applications. Reviewing and characterising 302 published literatures with focus on most relevant and recent advances in the field, this review found that hybrid techniques combining mechanical activation method produces geopolymers with the highest compressive strength and thus the best method. Geopolymer made by mechano-chemical activation method of slag achieved the highest compressive strength while geopolymer produced by microwave assisted activation of clay and ultrasonic activation of fly ash cum slag are most economical in curing energy demand. Hybrid activation is the current development in the field and integration of this method with mechanical activation is poised as the future geopolymer activation technology as it demonstrates greatest efficiency potential.

Potential use of fly ash in structural fill application: a review

Globally, over the years, fly ash (FA) has been successfully used in structural fills as a substitute for conventional infill material. As per the global industry trends and forecast report, the utilization rate of FA in 2021 was 74% in China, 65% in India, and 70% in the United States (US). Despite substantial research being done on the usage of FA as a substitute all over the world, only up to 15% by mass of total produce has been utilized as a replacement for infill soils. This indicates that there is a lot of potential for increased usage. From the view point of increasing the utilization rate, the present study focuses on summarizing the geotechnical properties of FA by taking strength characteristics into account as compared to conventional infill material. Moreover, this review underlines the chemical composition, index, and engineering properties. Firstly, it reviews the current state of the application of FA in structural fills by considering 141 articles that have been published since 2004 to till date. Secondly, it emphasizes the limited literature available on structural fill applications of FA. It also recommends the classification of FA besides the existing ASTM codes. Moreover, considering future research, this review also highlights the gaps in the previous studies, such as the need for amendments in existing standard codes for FA utilization as structural fill.

Influence of Waste Glass Addition on the Fire Resistance, Microstructure and Mechanical Properties of Geopolymer Composites

Nowadays, humanity has to face the problem of constantly increasing amounts of waste, which cause not only environmental pollution but also poses a critical danger to human health. Moreover, the growth of landfill sites involves high costs of establishment, development, and maintenance. Glass is one of the materials whose recycling ratio is still insufficient. Therefore, in the presented work, the influence of the particle size and share of waste glass on the consistency, morphology, specific surface area, water absorption, setting time, and mechanical properties of geopolymers was determined. Furthermore, for the first time, the fire resistance and final setting time of such geopolymer composites were presented in a wide range. Based on the obtained results, it was found that the geopolymer containing 20% unsorted waste glass obtained a final setting time that was 44% less than the sample not containing waste glass, 51.5 MPa of compressive strength (135.2% higher than the reference sample), and 13.5 MPa of residual compressive strength after the fire resistance test (164.7% more than the reference sample). Furthermore, it was found that the final setting time and the total pore volume closely depended on the additive's share and particle size. In addition, the use of waste glass characterized by larger particle sizes led to higher strength and lower mass loss after exposure to high temperatures compared to the composite containing smaller ones. The results presented in this work allow not only for reducing the costs and negative impact on the environment associated with landfilling but also for developing a simple, low-cost method of producing a modern geopolymer composite with beneficial properties for the construction industry.

Analytical Review of Geopolymer Concrete: Retrospective and Current Issues

The concept of sustainable development provides for the search for environmentally friendly alternatives to traditional materials and technologies that would reduce the amount of CO₂ emissions into the atmosphere, do not pollute the environment, and reduce energy costs and the cost of production processes. These technologies include the production of geopolymer concretes. The purpose of the study was a detailed in-depth analytical review of studies of the processes of structure formation and properties of geopolymer concretes in retrospect and the current state of the issue. Geopolymer concrete is a suitable, environmentally friendly and sustainable alternative to concrete based on ordinary Portland cement (OPC) with higher strength and deformation properties due to its more stable and denser aluminosilicate spatial microstructure. The properties and durability of geopolymer concretes depend on the composition of the mixture and the proportions of its components. A review of the mechanisms of structure formation, the main directions for the selection of compositions and processes of polymerization of geopolymer concretes has been made. The technologies of combined selection of the composition of geopolymer concrete, production of nanomodified geopolymer concrete, 3D printing of building structures from geopolymer concrete, and monitoring the state of structures using self-sensitive geopolymer concrete are considered. Geopolymer concrete with the optimal ratio of activator and binder has the best properties. Geopolymer concretes with partial replacement of OPC with aluminosilicate binder have a denser and more compact microstructure due to the formation of a large amount of calcium silicate hydrate, which provides improved strength, durability, less shrinkage, porosity and water absorption. An assessment of the potential reduction in greenhouse gas emissions from the production of geopolymer concrete compared to the production of OPC has been made. The potential of using geopolymer concretes in construction practice is assessed in detail.

Solid-to-Liquid Ratio Influenced on Adhesion Strength of Metakaolin Geopolymer Coating Paste Added Photocatalyst Materials

Coating materials are used on surfaces such as steel and ceramic to offer protection, corrosion resistance, wear and erosion resistance, a thermal barrier, or aesthetics. Although organic coating materials such as epoxy resins, silane, and acrylic are widely used, there are restrictions and drawbacks associated with their use, including the ease with which cracking, hazardous and harmful human health and environment, peeling, and deterioration occur. Organic matrices also have the capacity to release vapor pressure, which can lead to the delamination of coatings. Geopolymer coating materials offer an environmentally friendly solution to this concern to encourage sustainable growth. The simplicity with which geopolymers can be synthesized and their low emission of greenhouse gases such as CO2, SO2, and NOx are advantages of geopolymers. The advent of geopolymer coatings with photocatalytic properties is advantageous for the decomposition of pollution and self-cleaning properties. The aim of this paper is to study the optimum solid-to-liquid ratio of metakaolin geopolymer paste added TiO2 and ZnO by adhesion strength. Through iterative mixture optimization, we investigated the effects of different design parameters on the performance of a metakaolin-based geopolymer as a coating material. The assessed material was a metakaolin which was activated by an alkali activator (a mixture of sodium hydroxide and sodium silicate), with the addition of titanium dioxide and zinc oxide as photocatalyst substances. Varying proportions of solid-to-liquid ratio were tested to optimize the best mix proportion related to the coating application. Adhesion analyses of geopolymer coating paste were evaluated after 7 days. According to the findings, the optimal parameters for metakaolin geopolymer coating material are 0.6 solid-to-liquid ratios with the highest adhesion strength (19 MPa) that is suitable as coating material and enhanced the properties of geopolymer.

A Review on the Incorporation of Diatomaceous Earth as a Geopolymer-Based Concrete Building Resource

The development of geopolymer building composites at a lower cost with a smaller carbon footprint may lessen the growing concerns about global warming brought on by emissions of a critical greenhouse gas (CO₂) paired with the high production costs in the cement sector. Diatomaceous earth, commonly used as an admixture or partial replacement of cement owing to its most effective pozzolanic properties, has been investigated as a precursor in geopolymer concrete development. Several studies have been examined to develop a greater understanding of its characterization, inclusion status, and impacts on the performance aspects of concrete. The literature review showed that using diatomaceous earth is one of the effective ways to create sustainable, insulating, lightweight building materials while minimizing the harmful economic and environmental effects of industrial solid wastes. However, since most studies have focused on its integration as a partial cement substitute or a replacement for fine aggregate, further research on diatomaceous earth-based clinker-free concrete is required. A lack of research on geopolymer concrete's reinforcement with either natural or synthetic fibers, or a combination of the two, was also discovered. This review also showed that there has been remarkably little effort made towards theoretical property correlation modeling for predicting concrete performance. It is anticipated that the detailed overview presented herein will guide potential researchers in defining their future paths in the study area.

Fly Ash-Based Geopolymer Composites: A Review of the Compressive Strength and Microstructure Analysis

Geopolymer (GP) concrete is a novel construction material that can be used in place of traditional Portland cement (PC) concrete to reduce greenhouse gas emissions and effectively manage industrial waste. Fly ash (FA) has long been utilized as a key constituent in GPs, and GP technology provides an environmentally benign alternative to FA utilization. As a result, a thorough examination of GP concrete manufactured using FA as a precursor (FA-GP concrete) and employed as a replacement for conventional concrete has become crucial. According to the findings of current investigations, FA-GP concrete has equal or superior mechanical and physical characteristics compared to PC concrete. This article reviews the clean production, mix design, compressive strength (CS), and microstructure (Ms) analyses of the FA-GP concrete to collect and publish the most recent information and data on FA-GP concrete. In addition, this paper shall attempt to develop a comprehensive database based on the previous research study that expounds on the impact of substantial aspects such as physio-chemical characteristics of precursors, mixes, curing, additives, and chemical activation on the CS of FA-GP concrete. The purpose of this work is to give viewers a greater knowledge of the consequences and uses of using FA as a precursor to making effective GP concrete.

The Mechanical Properties of Plant Fiber-Reinforced Geopolymers: A Review

Both geopolymer and plant fiber (PF) meet the requirements of sustainable development. Geopolymers have the advantages of simple preparation process, conservation and environmental protection, high early strength, wide source of raw materials, and low cost. They have broad application prospects and are considered as the most potential cementitious materials to replace cement. However, due to the ceramic-like shape and brittleness of geopolymers, their flexural strength and tensile strength are poor, and they are sensitive to microcracks. In order to solve the brittleness problem of geopolymers, the toughness of composites can be improved by adding fibers. Adding fibers to geopolymers can limit the growth of cracks and enhance the ductility, toughness and tensile strength of geopolymers. PF is a good natural polymer material, with the advantages of low density, high aspect ratio. It is not only cheap, easy to obtain, abundant sources, but also can be repeatedly processed and biodegradable. PF has high strength and low hardness, which can improve the toughness of composites. Nowadays, the research and engineering application of plant fiber-reinforced geopolymers (PFRGs) are more and more extensive. In this paper, the recent studies on mechanical properties of PFRGs were reviewed. The characteristics of plant fibers and the composition, structure and properties of geopolymers were reviewed. The compatibility of geopolymer material and plant fiber and the degradation of fiber in the substrate were analyzed. From the perspective of the effect of plant fibers on the compression, tensile and bending properties of geopolymer, the reinforcing mechanism of plant fibers on geopolymer was analyzed. Meanwhile, the effect of PF pretreatment on the mechanical properties of the PFRGs was analyzed. Through the comprehensive analysis of PFFRGs, the limitations and recommendations of PFFRG are put forward.

Properties of Fiber-Reinforced One-Part Geopolymers: A Review

Geopolymers have the advantages of low carbon, being environmentally friendly and low price, which matches the development direction of building materials. Common geopolymer materials are also known as two-part geopolymers (TPGs). TPGs are usually prepared from two main substances, which are formed by polymerization of a silicoaluminate precursor and an alkaline activator solution. The TPG has many limitations in engineering application because of its preparation on the construction site, and the use of solid alkaline activator in one-part geopolymers (OPGs) overcomes this shortcoming. However, the brittleness of OPGs such as ceramics also hinders its popularization and application. The properties of the new OPG can be improved effectively by toughening and strengthening it with fibers. This review discusses the current studies of fiber-reinforced one-part geopolymers (FOPGs) in terms of raw precursors, activators, fibers, physical properties and curing mechanisms. In this paper, the effects of the commonly used reinforcement fibers, including polyvinyl alcohol (PVA) fiber, polypropylene (PP) fiber, polyethylene (PE) fiber, basalt fiber and other composite fibers, on the fresh-mixing properties and mechanical properties of the OPGs are summarized. The performance and toughening mechanism of FOPGs are summarized, and the workability, macroscopic mechanical properties and durability of FOPGs are investigated. Finally, the development and engineering application prospect of FOPGs are prospected.