Fly Ash Based Geopolymer Composites Research Articles

Characterization of fly ash–based geopolymer composites reinforced with biomass-derived Phoenix sp. fibers

Characterization of fly ash–based geopolymer composites reinforced with biomass-derived Phoenix sp. fibers

Investigation into the strength and toughness of polyvinyl alcohol fiber-reinforced fly ash-based geopolymer composites

This study investigates the influence of polyvinyl alcohol (PVA) fiber dosage and length on the porosity, mechanical strength, and toughness of fly ash-based geopolymer composites. The experimental data are analyzed to examine the deflection-load relationship in the flexural toughness tests of fiber-reinforced geopolymer composites (FRGPC) with different PVA fiber parameters. The results indicate that the addition of a certain amount of PVA fibers effectively enhances the flexural resistance of FRGPC. Particularly, the optimal performance is achieved with the addition of 2.0 vol% of 9 mm PVA fibers, where the 28-day flexural strength reaches 13.16 MPa, representing a 150.95 % increase compared to the control group, and the deflection at peak load increases by 308.00 %. However, the compressive strength of FRGPC with PVA fiber dosage at 1.6 vol%, 2.0 vol%, and 2.4 vol% decreases by 0.89 %, 6.39 %, and 10.13 %, respectively. Microscopic observations of FRGPC indicate that an increase in fiber dosage and length results in larger pores and uneven distribution of fibers. Notably, 12 mm PVA fibers exhibit significant aggregation, confirming the findings from mechanical property tests. This study, through an in-depth exploration of the mechanical properties of PVA fiber-reinforced fly ash-based geopolymer composites, provides crucial experimental data and a theoretical foundation for the development of sustainable construction materials.

Effect of Waste Tire Aggregate on Thermal and Strength Characteristics of Fly Ash–Based Geopolymer Composites Produced at Various Binder Contents

Effect of Waste Tire Aggregate on Thermal and Strength Characteristics of Fly Ash–Based Geopolymer Composites Produced at Various Binder Contents

Geopolymer fly ash composites modified with cotton fibre

The work’s primary goal is to assess the influence of the cotton fibres addition and their proportion on the strength properties and thermal conductivity of foamed geopolymer composites based on fly ash.Fly ash from a thermal power plant was used as the foundation material to create the geopolymer composites in this study. Volcanic silica was used as an additional source of silicon. As an additive, the recycled cotton flock was used in amounts of 0.5%, 1% and 2% by weight of dry ingredients. The density, compressive, and three-point bending strength of the created geopolymers were measured. Moreover, the thermal conductivity measurements for three temperature ranges: 0–20C, 20–40C, and 30–50C for all investigated geopolymers were conducted. The structure of tested materials was observed using a scanning electron microscope (SEM).It was demonstrated within the context of the study that the addition of cotton fibres to foamed fly ash-based geopolymers aids in slightly reducing their density. Cotton fibres can be used to boost the strength of the examined geopolymers; for samples with 1% cotton fibres added, compressive strength rose by around 22% and flexural strength by about 67%. Additionally, it is feasible to lower their thermal conductivity coefficient by incorporating cotton fibres into foamed fly ash-based geopolymers.The results obtained highlight the potential of fly ash-based geopolymer composites with the addition of cotton flocks for application as insulating materials in the building industry.The novelty of this work is the demonstration of the possibility of producing foamed geopolymers based on fly ash with the addition of recycled cotton fibres, with properties that make them suitable for use as building insulation materials.

Influence of wood pretreatment, hardwood and softwood extractives on the compressive strength of fly ash-based geopolymer composite

This paper investigated the specific compressive strength (specific strength) of fly ash-based geopolymer composites with four hardwood extractives and two softwood extractives, as well as specific wood extractives. Additionally, the effect of the portion of pine wood (i.e., sapwood and heartwood) and wood pretreatment with NaOH were considered. Geopolymer paste (with extractives) and geopolymer wood composites (GWCs) were cured at 60 °C for 24 h. The samples were stored in a climate chamber (20 °C, 65% RH) for 7 days before finally testing under compression. From the results, the specific strengths of geopolymers with hardwood extractives were not significantly affected. However, geopolymers containing pine extractives showed the most significant reduction in specific strength. There were no significant differences in the specific strengths of geopolymers containing polyphenols and resin acid. Generally, geopolymers containing fatty acids recorded the lowest specific strengths. There was no difference between the GWCs with untreated sapwood and heartwood. However, the wood pretreatment led to a 21% and 10% increase in the specific strengths of GWCs with sapwood and heartwood, respectively. The findings of this study form the basis for improved GWCs production and a wide range of applications for green composite materials.

Effect of Admixtures on Selected Properties of Fly Ash-Based Geopolymer Composites

This research was carried out to expand our knowledge of the effects of different admixtures on the properties of fly ash-based geopolymer composites. Three admixtures were used: a liquifying admixture based on stabilized polycarboxylates, a plasticizing admixture, and a liquifying admixture based on modified polynaphthalenes. The effect of variable activator content relative to the binder was also tested. The most favorable flexural and compressive strengths as well as water absorption were obtained in the series with a liquifying admixture based on stabilized polycarboxylates and an activator to fly ash ratio of 0.5 or 0.6. An increase in flexural and compressive strengths of 11% and 32%, respectively, was obtained compared to the series without admixtures. No positive effect was found for plasticizing admixtures or those based on modified polynaphthalenes.

Properties and Durability Performance of Lightweight Fly Ash Based Geopolymer Composites Incorporating Expanded Polystyrene and Expanded Perlite

In this study, the use of expanded polystyrene and expanded perlite as lightweight aggregates for the preparation of lightweight geopolymers is tested. The geopolymers’ performance was evaluated through physical, mechanical and thermal testing. Polypropylene fibers were used as reinforcement agents, while the long-term durability was assessed though repeated wet–dry and freeze–thaw cycles and sorptivity tests. The results showed that the introduction of lightweight aggregates in the geopolymer mixes decreased the compressive and flexural strength of the specimens by 77% and 35%, respectively. However, the density and thermal conductivity were substantially improved because of the addition of low-density aggregates. The fiber reinforcement of lightweight samples led to a drastic increase in flexural strength by 65%, leaving unaffected the compressive strength and density of the specimens. The freeze–thaw and sorptivity tests were also improved after the introduction of both aggregates and fibers. Lightweight geopolymer composites exhibiting density in the range of 1.0–1.6 g/cm3, compressive strength of 10–33 MPa, flexural strength of 1.8–6.3 MPa, thermal conductivity of 0.29–0.42 W/mK, and sorptivity of 0.031–0.056 mm/min0.5 were prepared.

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.

A Comprehensive Review on Fly Ash-Based Geopolymer

The discovery of an innovative category of inorganic geopolymer composites has generated extensive scientific attention and the kaleidoscopic development of their applications. The escalating concerns over global warming owing to emissions of carbon dioxide (CO2), a primary greenhouse gas, from the ordinary Portland cement industry, may hopefully be mitigated by the development of geopolymer construction composites with a lower carbon footprint. The current manuscript comprehensively reviews the rheological, strength and durability properties of geopolymer composites, along with shedding light on their recent key advancements viz., micro-structures, state-of-the-art applications such as the immobilization of toxic or radioactive wastes, digital geopolymer concrete, 3D-printed fly ash-based geopolymers, hot-pressed and foam geopolymers, etc. They have a crystal-clear role to play in offering a sustainable prospect to the construction industry, as part of the accessible toolkit of building materials—binders, cements, mortars, concretes, etc. Consequently, the present scientometric review manuscript is grist for the mill and aims to contribute as a single key note document assessing exhaustive research findings for establishing the viability of fly ash-based geopolymer composites as the most promising, durable, sustainable, affordable, user and eco-benevolent building materials for the future.

An Investigation of the Ground Walnut Shells’ Addition Effect on the Properties of the Fly Ash-Based Geopolymer

The development of geopolymers is in line with the requirements of sustainable development. Creating a new type of material from various industrial and bio-based wastes and by-products can lead to reduced energy consumption, reduced waste generation, reduced global CO2 emissions, as well as reduced resource extraction of natural resources. In this study, geopolymer composites based on class F fly ash with the addition of fine quartz sand and ground walnut shells used as a substitute for sand were examined. The study focused on investigating the effects of different weight percentages of ground walnut shells and quartz sand on the density and strength properties, including compressive and flexural strength, thermal conductivity, efflorescence formation, and water absorption of the fly ash-based geopolymer composites. The microstructure of the studied geopolymers was also analyzed using a scanning electron microscope (SEM). It was observed that the addition of ground walnut shells contributes to the decrease in density and mechanical properties, increase in absorption properties, and decrease in porosity of fly ash-based geopolymers. Furthermore, the addition of ground walnut shells allows for a significant reduction in efflorescence on the surface of the tested geopolymer composites. Moreover, partial or complete replacement of sand by ground walnut shells in geopolymer composites based on fly ash allows for a significant reduction in their thermal conductivity, which makes it possible to use these composites as insulation materials.

Elevated Temperature Effects on Fly Ash-Based Geopolymer Composites Produced with Waste Granite Dust

Elevated Temperature Effects on Fly Ash-Based Geopolymer Composites Produced with Waste Granite Dust

Macro and micro characteristics of eco-friendly fly ash-based geopolymer composites made of different types of recycled sand

The main objective of the present study is to explore alternative recycled sand materials to river sand. Within this context, six different types of recycled sand materials obtained from the recycling of construction materials were considered to be alternatives to the river sand. In producing fly ash-based geopolymer composites, the river sand was substituted with recycled sands. Then, the properties of geopolymer composites in the fresh and hardened states were studied comparatively. In this regard, flow table test, rheology, and fresh unit weight were determined as fresh state properties whereas dry unit weights, flexural and compressive strengths, and ultrasonic pulse velocity performance were determined as hardened state characteristics. In addition, the interfacial transition zone occurring between these sands and geopolymer paste was displayed using the scanning electron microscope technique. In a general perspective, all the investigated characteristics of the geopolymer composites were influenced by substituting the river sand with recycled sands. The flowability of the geopolymer mixtures decreased whereas they performed more viscous behavior when the river sand was replaced with recycled sands. Among the recycled sands, only the sand recycled from basalt tile increased the fresh and dry unit weights of geopolymer composite while the others resulted in decreases. Replacing the river sand with the sands recycled from tiles did not significantly influence the flexural strength, however, the sands recycled from basalt, granite, and marble tiles led to increasing the compressive strength. Regarding the results achieved in the current study, it could be stated that these recycled sands could be utilized in the production of the geopolymer composites in a controlled manner.

Improving the Mechanical Properties of Fly Ash-Based Geopolymer Composites with PVA Fiber and Powder

In this work, polyvinyl alcohol (PVA) fiber and powder were added to geopolymer composites to toughen fly ash-based geopolymer, and their different toughening mechanisms were revealed. Firstly, different contents of active granulated blast furnace slag (GBFS) were added to the geopolymer to improve the reactivity of the GBFS/fly ash-based geopolymer, and the best ratio of GBFS and fly ash was determined through experiments testing the mechanical properties. Different contents of PVA powders and fibers were utilized to toughen the geopolymer composites. The effect of the addition forms and contents of PVA on the mechanical properties, freeze–thaw cycle resistance, and thermal decomposition properties of geopolymer composites were systematically studied. The results showed that the toughening effect of PVA fiber was better than that of PVA powder. The best compressive strength and flexural strength of geopolymer composites toughened by PVA fiber were 41.11 MPa and 8.43 MPa, respectively. In addition, the composition of geopolymer composites was explored through microstructure analysis, and the toughening mechanisms of different forms of PVA were explained. This study provided a new strategy for the toughening of geopolymer composites, which can promote the low-cost and efficient application of geopolymer composites in the field of building materials.

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

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.

Enhanced mechanical and thermal properties of fly ash-based geopolymer composites by wollastonite reinforcement

The present study investigated the mechanical and thermal properties of geopolymer composite. The geopolymer composite was prepared by mixing fly ash and wollastonite with the alkaline activator, which was 6 M KOH:K2SiO3 in a mass ratio of 1:1 and a solid:liquid mass ratio of 3:2. The compressive strength at 28 days of geopolymer was 33.3 MPa and possessed the highest strength of 38.3 MPa when 30 wt% wollastonite was added. The flexural strength presented differently whereby it increased from 2.1 MPa to 6.8 MPa. It increased remarkably up to 200% with the addition of 50 wt% wollastonite. The geopolymer composites were exposed to high temperatures at 800℃ to 1100°C for 2 h. Cracks were reduced since 20 wt% wollastonite was added. A high percentage of wollastonite presented excellent thermal stability. The total weight loss of the geopolymer composite at temperatures of 30℃ to 1400°C was minimized. It decreased from 25% to 12% when 50 wt% wollastonite was added, and the dilatometric data resulted in a dimensional change of almost zero. The phase development of the geopolymer composites at high temperatures showed the crystallization of leucite, kalsilite, calcium silicate, calcium aluminium silicate, and calcium aluminium oxide, which were the high temperature stable phases. The results indicated that wollastonite reinforced fly ash-based geopolymer composites are promising for use in high temperature applications.

Sustainable utilization of waste carbon black in alkali-activated mortar production

This article investigates the potential utilization of waste carbon black (WCB) resulting from the aluminum industry as a by-product material in the fly ash-based geopolymer composites production. Experimental study was conducted to evaluate the effect of WCB on the performance of the geopolymer. Different contents of WCB including 5%, 10%, 15%, 20%, 30%, and 40%,by weight of the fly ash, have been incorporated in the geopolymer mix as either additives or fly ash replacement. Life cycle assessment (LCA) has also been conducted to evaluate the landfills utilization and the environmental impact of the WCB incorporation. The experimental results reflected that the WCB could be used as additives in small quantities (5% of fly ash weight) to the geopolymer mix without negatively affecting its performance. Adding 5% of WCB insignificantly enhanced the compressive strength of the geopolymer by 5%, increased its workability and density by 3% and 4%, respectively, and did not affect its excellent thermal stability. Scanning electron microscopic (SEM) imaging showed more unreacted fly ash particles combined with more voids and cracks within the microstructure of the geopolymer with high WCB content. Finally, incorporating WCB in the geopolymer production improved the utilization of landfills use and reduced the global warming potential, acidification potential, eutrophication potential and abiotic depletion potential.

Effect of nano SiO2 on mechanical properties of micro-steel fibers reinforced geopolymer composites

This paper presents the mechanical properties of micro steel fiber reinforced fly ash geopolymer composites containing different amounts of nano-silica. Four different fly ash-based geopolymer composites (GPC) are prepared by using a fixed amount of micro-steel fibers (0.5% by weight) and four different amounts of nano silicon dioxide (SiO2) consisting of 0%, 1%, 2%, and 3% amounts by weight. The GPC with 0% nano SiO2 having 0.5% micro-steel fibers is taken as the control mix. Different mechanical and microstructural properties of fabricated GPC are examined by assessing their stress-strain behavior, compressive strength, flexural strength, bending load-deflection behavior, impact strength, fracture toughness, toughness modulus, elastic modulus, toughness indices, hardness, and scanning electron microscopy (SEM). The outcomes of tests depicted that the addition of nano SiO2 significantly enhanced the mechanical properties and microstructure of micro-steel fiber-reinforced GPC by producing a denser matrix and refining the interfacial zones. According to the results of this study, the recommended amount of nano SiO2 to be utilized in GPC for the optimal behavior is 2%.

Long-Term Properties of Different Fiber Reinforcement Effect on Fly Ash-Based Geopolymer Composite

Geopolymer composites have been around only for 40 years. Nowadays, they are used in buildings and infrastructures of various kinds. A geopolymer’s main benefit is that it is a green material that is partially made by utilizing waste products. The carbon footprint from geopolymer matrix manufacturing is at least two times less than Portland cement manufacturing. Due to the nature of the geopolymer manufacturing process, there is a high risk of shrinkage that could develop unwanted micro-cracks that could reduce strength and create higher creep strains. Because of this concern, a common strategy to reduce long-term strains of the material, such as shrinkage and creep, is to add fiber reinforcement that would constrain crack development in the material. This article aims to determine how various kinds and amounts of different fiber reinforcement affect fly ash-based geopolymer composites’ creep strains in compression. Specimen mixes were produced with 1% steel fibers, 1% polypropylene fibers, 5% polypropylene fibers, and without fibers (plain geopolymer). For creep and shrinkage testing, cylindrical specimens Ø46 × 190 mm were used. The highest creep resistance was observed in 5% polypropylene fiber specimens, followed by 1% polypropylene fiber, plain, and 1% steel fiber specimens. The highest compressive strength was observed in 1% polypropylene fiber specimens, followed by plain specimens, 1% steel fiber specimens, and 5% polypropylene fiber-reinforced specimens. The only fiber-reinforced geopolymer mix with improved long-term properties was observed with 1% polypropylene fiber inclusion, whereas other fiber-introduced mixes showed significant decreases in long-term properties. The geopolymer composite mix with 1% polypropylene fiber reinforcement showed a reduction in creep strains of 31% compared to the plain geopolymer composite.

Process Development of Fly Ash-Based Geopolymer Mortars in View of the Mechanical Characteristics.

This study aimed to determine the effects of design parameters, including the liquid/solid ratio (L/S), Na2SiO3/NaOH weight ratio, and curing temperature, on class F fly ash-based geopolymer composites. For this purpose, two disparate sources of fly ash were supplied from Çatalağzı (FA) and İsken Sugözü (FB) Thermal Power Plants in Turkey. Two different L/S ratios of 0.2 and 0.4 were used. The Na2SiO3/NaOH ratios in the alkaline solutions were 1, 1.5, 2, 2.5, and 3 by weight for each type of geopolymer mixture. Then, 40 different mixes were cured at two specific temperatures (70 °C and 100 °C) for 24 h and then preserved at room temperature until testing. Thereafter, the physical water absorption properties, apparent porosity, and bulk density were examined at 28 days on the hardened mortars. Additionally, compressive and flexural tests were applied to the geopolymers at 7, 28, and 90 days. It was found that the highest compressive strength was 60.1 MPa for the geopolymer manufactured with an L/S of 0.2 and Na2SiO3/NaOH ratio of 2. Moreover, the best thermal curing temperature for obtaining optimal strength characteristics was 100 °C for the FB.

Effect of various NaOH molarities and various filling materials on the behavior of fly ash based geopolymer composites

Among the recent research interests in the construction section, Geopolymers, represent a rising trend due to their significant performance in terms of strength and long term properties. In this research, an attempt was conducted to examine the effect of using different filling materials and the effect of different NaOH concentrations on the properties of the resulted composites. Strength properties, physical properties, abrasion resistance, and freezing-thawing behavior were tested along with a microstructural characterization that included scanning electron microscopy (SEM) and X-ray diffraction (XRD). In general, the effect of including crushed limestone and waste foundry sand was beneficial in terms of the general properties of the fabricated specimens. Also, the microstructural analyses showed a compact matrix that could be considered in line with the obtained results from the other tests.