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Performance of Self-Compacting Geopolymer Concrete Using Spent Garnet as Sand Replacement |
Introduction
Rapid industrial growth has witnessed the ever-increasing utilization of sand from rivers for various construction purposes, which has led to the over-exploitation of riverbeds and disturbed the ecosystem. Numerous problems have emerged, including increases in riverbed depth, the lowering of water tables, increases in salinity, and the destruction of river embankments (Gourley, 2003). Recently, intensive research has proven that obtaining modified concrete by incorporating waste materials can lead to sustainable product development. Such concrete structures not only allow for greener and more environmentally sound construction but also protect against the excessive consumption of natural non-renewable fine aggregates (Temuujin, 2010).
Thus, the proper use of fine aggregates as alternative materials in concrete has become an absolute necessity for the replacement of river sand. In this regard, the utilization of spent garnets has emerged as a promising alternative in its own right. Garnet is a generic word that refers to an assemblage of multifaceted minerals of silicate compounds containing calcium (Ca), magnesium (Mg), ferrous iron (Fe) or manganese (Mn), aluminum (Al), chromium (Cr), ferric iron (Fe), or even titanium (Ti), each having analogous crystal lattice structures and varied chemical formulas (Castel, 2010). Interestingly, the angular fractures and hardness properties of garnets together with their ability to be recycled make them advantageous for numerous abrasive applications. The common chemical composition of garnet is A3B2(SiO4)3, wherein the element A may be Ca, Mg, ferrous iron or Mn, Al, Cr, ferric iron, or Ti (Rodina, 2013). Garnets have major industrial uses such as water jet cutting, abrasive blasting, water filtration, and others (Lindtner, 2014).
A comprehensive assessment of a major shipyard industry in the southern province of Malaysia revealed that the country imported approximately 2000 MT of garnets in 2013 alone, and a large quantity was dumped as waste. Generally, abrasive blasting is used to prepare the surfaces for coating and painting (Roskill Information Services, 2000). This technique is used for the construction of vessels, ship maintenance, and repair activities. Thus, the blasting process creates large quantities of exhausted garnet waste mixed with surface elements such as paint chips and oil. Such waste causes many environmental and health hazards such as water contamination when it enters the waterways during floods or through runoffs. Therefore, spent garnets pose a threat to the ecological balance and biodiversity. Garnets can be reused about three to five times while keeping their overall properties intact. Moreover, these recycled garnets degrade at a level beyond which they are non-reusable for abrasive blast purposes. Afterward, these inoperative garnets are removed from the shipyard and designated as spent garnets (Garnett, 2013). Recently, it has been recognized that the utilization of these spent garnets as a replacement for fine aggregates in self-compacting geopolymer concrete (SCGPC) may provide greener alternative construction materials to ordinary Portland cement (OPC)-based concrete.
Universally, OPCās excellent mechanical properties and moderately cheap and easy accessibility make it the most commonly used binder for the production of construction materials. Thus, OPC-based concrete is preferred for diverse purposes (Davidovits, 1991). Nonetheless, OPC manufacturing leads to the depletion of natural habitats, the manufacturing of fossil fuels, and substantially higher CO2 emissions, which our planet can no longer afford. To overcome those threats, many dedicated efforts have been made to search for efficient alternative substances such as alkali-activated materials interpreted as geopolymers (GPs). The cost production of GP concrete is 1.7% higher than OPC for the same grade (Tahri et al., 2017).
These alternative substances are proven to be advantageous for sustainable development when industrial by-products are partially applied as precursor matter as a substitute for the main raw mineral binder, including OPC. Moreover, the final product exhibits improved characteristics over OPC-based concrete, depending on the implemented raw minerals and alkali activations. Factors such as the low heat of hydration, the rapid development of early strength, the formation of a stronger aggregate-to-matrix interface, poorer thermal conduction (TC), and elevated resistance to acid and fire (Provis, 2010) also considerably influence the overall properties of the ultimate products. Generally, alkali-activated materials are classified into two categories: (1) a high calcium system with granulated blast furnace slag as the usual precursor, where gel of calcium alumina silicate hydrate is the major product of reaction, (2) a low calcium product having class-F fly ash (FA) and metakaolin as the constituent raw materials, where gel of sodium alumina silicate hydrate in the form of a three-dimensional network is produced as the main product of reaction.
Categorically, the ability of self-compacting concretes (SCCs) to flow under their own weight without requiring any exterior compaction vibration has modernized the placement of concretes. A group of researchers from Japan first introduced the concept of SCC in the late 1980s (Domone, 2006). It was established that greatly workable concrete such as SCCs display a flow under their own weight via constrained segments in the absence of any segregation or bleeding. Such concretes must possess a comparatively small yield to guarantee enhanced flow capacity and reasonable viscosity to oppose separation and bleeding. Furthermore, they must retain homogeneity during transport, placement, and curing to guarantee sufficient structure performance and long-standing endurance.
Despite the many studies toward sand replacements for concrete infrastructures, the exploitation of spent garnet waste as construction material is seldom addressed. Considering the notable engineering properties of spent garnet waste, this book explores the feasibility of incorporating different levels of spent garnet as a replacement for river sand to achieve an enhanced SCGPC. SCGPC specimens were thoroughly characterized to determine their compressive, flexural, workable durability and microstructures as a function of varying percentages of spent garnet inclusion.
There are three main research questions in this book:
1. What are the effects of spent garnet on the fresh and hardened characteristics of the SCGPC concrete in terms of workability and mechanical strength?
2. What are the effects of spent garnet SCGPC durability such us carbonation, sulfate attack, acid attack?
3. What are the effects of spent garnet on the morphology of SCGPC concrete such us bonding and thermal analysis?
Several experiments (for synthesis, characterization, and performance evaluation) were conducted for this work, the main focus of which was to develop a Āsustainable spent garnet-based SCGPC with varying levels (25%, 50%, 75%, and 100%) of replacement of river sand. The properties of the constituent concrete materials, including leaching behavior, carbonation, and thermal and mechanical Ācharacteristics, and the microstructures of the garnet were examined. The workability, mechanical strengths, deformation (modulus of elasticity), and durability characteristics of the developed SCGPC were evaluated for comparison with that of traditional concretes. Tests such as slump flow, L-box, V-funnel, T50, compressive strength, flexural strength, indirect tensile strength, drying shrinkage, modulus of elasticity, carbonation, and acid and sulfate resistance were carried out to determine the performance of formulated SCGPC. Hardened SCGPC of optimum composition was selected to examine its crystallinity, microstructure, and bonding and thermal properties using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis/differential thermal analysis (TGA/DTA).
Significance of the Book
Certainly, the use of spent garnet in SCGPC as an alternative to river sand is beneficial in terms of avoiding environmental pollution and the over-exploitation of natural resources. Most of the recycling problems that limit waste disposal can be overcome by properly using spent garnet in making SCGPC (Lottermoser, 2011). The use of spent garnet directly contributes to sustainable development and is a cost-effective way of manufacturing SCGPC and preserving natural sand from further degradation. Currently, enormous amounts of spent garnet are regularly disposed of and used for landfill, which has high transportation costs and is labor intensive. This not only pollutes the environment but precludes monetary gain. The present work will solve these existing problems by systematically incorporating spent garnet in place of sand to prepare new compositions of sustainable SCGPC. This kind of SCGPC will be economically viable because of its high abundance, its non-toxic nature, and the cost-effectiveness of using spent garnet as the main constituent. It will be demonstrated that spent garnet is a potential substitute material for river sand in building and structural engineering. Thus, the use of spent garnet in place of fine aggregates to make concrete will avoid the over-use of natural sand. This research is expected to modernize the Malaysian construction industries and encourage builders and engineers to use eco-friendly spent garnet-based SCGPC rather than that based on conventional natural river sand.
Book Organization
The present book is composed of seven chapters, as follows:
Chapter 1 provides a brief background and overview of the research to identify the research gap and clarifies the problem statement and the rationale of the research. Based on the problem to be solved, it sets a goal and relevant objectives. Furthermore, it discusses the research scope and significance.
Chapter 2 presents a comprehensive literature review to justify the problem statement. It emphasizes past developments in SCGPC, ongoing activities in the field of spent garnet-based concrete production, and future trends in SCGPC based on spent garnets as a replacement for river sand.
Chapter 3 presents the experimental results in terms of analyses, discussions, evaluations, and comparisons with other works on similar SCGPCs. The physico-chemical properties of spent garnets and their effects on the properties of fresh as well as hardened SCGPC are highlighted. Results are obtained on workability using tests such as slump flow, L-box, V-funnel, and T50, and hardened properties are discussed in terms of compressive, flexural, and tensile strengths, drying shrinkage, and modulus of elasticity.
Chapter 4 explains and discusses the results obtained from different tests on durability performed on control specimens as well as spent garnet-based GP concrete. Results from durability tests on SCGPC, such as drying shrinkage, water absorption, accelerated carbonation, and resistance to acid and sulfate attacks, are investigated.
Chapter 5 presents the thermal properties, bonding vibrations, crystalline structures, surface morphology, and microstructures of spent garnets obtained via XRD, FESEM, FTIR, and TGA/DTA analysis. Furthermore, results from microstructural studies of SCGPC are presented at 6 months of strength development and above.
Chapter 6 concludes on the overall performance of spent garnet as a replacement for sand in SCGPC, its major contributions, and the novelties of the present subject.
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Introduction
In recent times, the steady escalation in the amount of waste generated from mining and diversified industries has created environmental concern related to the depletion of natural resources and landfill-mediated pollution (Siddique, 2011). For the remediation of such hazards, the effective management of solid waste has become inevitable worldwide. Due to insufficient space for landfill and the increasing costs of land disposal, it has become imperative to recycle and reutilize industrial waste materials. Mine waste materials and industrial by-products are categorized into various groups. The use of these waste materials in concrete not only reduces disposal concerns and eases environmental concerns but also makes these concretes economical as well as sustainable (Singh, 2013). Natural sand is declining due to its enormous consumption in the construction industries. Therefore, it is vital to replace natural river sand with other fine aggregates that are suitable for making sustainable self-compacting geopolymer concrete (SCGPC), such as spent garnet. This is the recurring theme of this book.
In recent times, the use of spent garnet as an alternative fine aggregate to natural sand in SCGPC has become a new trend for large-scale recyclable waste. Limited literature exists on waste garnet as appropriate construction material. Diverse by-products and wastes from different industries have previously been used in concrete as fine aggregate replacements (Aggarwal, 2014). These include waste foundry sand, coal bottom ash, stone dust, recycled fine aggregate, glass cullet, and copper tailings. Many studies have been conducted to achieve optimum mix compositions with good mechanical properties. Despite many research efforts, an optimum composition of sustainable SCGPC with the desired properties based on waste materials as a suitable replacement for river sand is far from being achieved (Chan, 2013).
This chapter describes the detailed literature on waste garnet-based SCGPC production, the basic need for the development of SCGPC using spent garnet as an alternative fine aggregate to sand, and the past research activities related to waste garnets. Through a comprehensive literature survey, it is demonstrated that there are several open avenues and unsolved problems in spent garnet-based SCGPC production and optimization, the thorough characterization o...
