Application Of Geopolymer Research Articles

A low-cost and eco-friendly powder catalyst: Iron and copper nanoparticles supported on biochar/geopolymer for activating potassium peroxymonosulfate to degrade naphthalene in water and soil.

A low-cost and environment-friendly biochar/geopolymer composite loaded with Fe and Cu nanoparticles (Fe-Cu@BC-GM) was prepared by impregnation-calcination using lignin and kaolin as precursors. SEM, FTIR and XRD analysis suggested that the Fe-Cu@BC-GM had a certain pore structure, rich functional groups and stable crystal structure. The obtained Fe-Cu@BC-GM was used as the catalyst of potassium peroxymonosulfate (PMS) for remediation of wastewater and soil polluted by naphthalene (NAP). Experimental results indicated that Fe-Cu@BC-GM exhibited outstanding catalytic performance, and the maximum degradation rate of NAP in water and soil reached 98.35% and 67.98% within 120min, respectively. The XPS measurement confirmed the presence of successive Fe (Ⅲ)/Fe (Ⅱ) and Cu(Ⅱ)/Cu(Ⅰ) redox pairs cycles on the surface of Fe-Cu@BC-GM, which made Fe (Ⅲ) and Cu(Ⅰ) continuously generated Fe (Ⅱ) activating PMS to produce SO4·- and ·OH for the degradation of NAP. The effects of Fe-Cu@BC-GM/PMS system on plant toxicity were evaluated by analyzing the degradation intermediates and bioassay of mung bean. It was proved that the Fe-Cu@BC-GM/PMS system could degrade NAP into less toxic intermediates, and the seed germination rate, root and stem length of mung bean after soil remediation were not notably different from those of the uncontaminated soil. This work opened new prospect for the application of geopolymer in degradation of persistent organic pollutants (POPs) and provided a cost-effective option for the remediation of the persistent organic pollutants contaminated water and soil.

The Effects of Soil Porosity and Mix Design of Volcanic Ash-Based Geopolymer on the Surface Strength of Highly Wind Erodible Soils

Surface stabilization of loose, non-cohesive, and fine soils has always been a challenging task for geotechnical engineers. These soils show meager mechanical behavior and are very vulnerable to wind erosion. Many attempts have been made to combat wind erosion of soils. These attempts, including a variety of soil surface amendment methods, have faced complications in terms of financial efficacy, reduced long-term behavior at elevated temperatures, and limitations in stabilization of a wide range of soil types. The application of geopolymers for surface stabilization is a novel approach, which has its own challenges in terms of selecting an appropriate precursor type, mix design, and preparation method. This study evaluated the challenges of using volcanic ash (VA)-based geopolymer, through the 1 Phase (1P) method for stabilization of two silty and sandy soils. A series of uniaxial compressive strength (UCS) and penetrometer tests were performed on cylindrical specimens and soil surface-treated samples, respectively, to evaluate the resistance of treated samples with different porosities. Moreover, the rheological behavior of geopolymer paste having various binder-to-activator ratios is discussed. The available rheological characteristics of geopolymer in this study fit well with the Bingham model. It was found that, despite the minimal crust thickness formed on the topsoil, significant surface resistance is acquired. The results show notable performance of the 1P method for surface amendment of both the silty and sandy soil samples.

Experimental Study on the Mechanical Properties and Microstructure of Metakaolin-Based Geopolymer Modified Clay.

Clay is found in some countries all over the world. It usually has low compressive strength and cannot be used as a bearing material for subgrade soil. In this paper, the influence of basicity on a metakaolin-based polymer binder to improve clay was studied. The effects of the molar concentration of the alkali activator, different concentration of the metakaolin-based geopolymer and curing time on unconfined compressive strength were studied. The alkali activator-to-ash ratio was maintained at 0.7. The percentage of metakaolin added to the soil relative to metakaolin and soil mixture was 6%, 8%, 10% and 12%. The sodium hydroxide concentrations are 2M, 4M, 6M and 8M. Unconfined compressive strength (UCS) was tested on days 3, 7, 14 and 28, respectively. Compared with original clay, the results show that the unconfined compressive strength increases with the increase in metakaolin content and molar concentration of NaOH. The maximum compressive strength of the sample with NaOH concentration of 8M and percentage of 12% was 4109 kN on the 28th day, which is about 112% higher than that of the original clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the cementing compound covered the clay particles due to the reaction of the geopolymer with the clay, resulting in the formation of adhesive particles. The main purpose of this study is to verify the effectiveness and stability of metakaolin-based geopolymer binder polymerization under normal temperature and a strong alkali environment. The results can provide parameters for the application and promotion of metakaolin-based geopolymers in soil improvement engineering.

Application of Geopolymer in Stabilization/Solidification of Hazardous Pollutants: A Review.

Geopolymers, as a kind of inorganic polymer, possess excellent properties and have been broadly studied for the stabilization/solidification (S/S) of hazardous pollutants. Even though many reviews about geopolymers have been published, the summary of geopolymer-based S/S for various contaminants has not been well conducted. Therefore, the S/S of hazardous pollutants using geopolymers are comprehensively summarized in this review. Geopolymer-based S/S of typical cations, including Pb, Zn, Cd, Cs, Cu, Sr, Ni, etc., were involved and elucidated. The S/S mechanisms for cationic heavy metals were concluded, mainly including physical encapsulation, sorption, precipitation, and bonding with a silicate structure. In addition, compared to cationic ions, geopolymers have a poor immobilization ability on anions due to the repulsive effect between them, presenting a high leaching percentage. However, some anions, such as Se or As oxyanions, have been proved to exist in geopolymers through electrostatic interaction, which provides a direction to enhance the geopolymer-based S/S for anions. Besides, few reports about geopolymer-based S/S of organic pollutants have been published. Furthermore, the adsorbents of geopolymer-based composites designed and studied for the removal of hazardous pollutants from aqueous conditions are also briefly discussed. On the whole, this review will offer insights into geopolymer-based S/S technology. Furthermore, the challenges to geopolymer-based S/S technology outlined in this work are expected to be of direct relevance to the focus of future research.

Recycling of unseparated construction and demolition waste (UCDW) through geopolymer technology

Geopolymer technology has been recognized as an ideal option for recycling construction and demolition waste (CDW) streams as new value-added products. However, most research efforts have been devoted to the geopolymer derived from the individual fraction separated from CDW. Given the technological complexity presented in separating CDW fractions on a commercial scale, using unseparated CDW (UCDW) in geopolymer application can achieve higher environmental and economic benefits. This paper investigated the feasibility of using UCDW consisting of various constituents, i.e., unbound aggregates (UA), red clay bricks (RCB), waste concrete (WC), waste glass (WG), and waste tiles (WT), in geopolymer production. The effects of these constituents on the reactivity of UCDW and the performance of the resulting geopolymer paste were studied. Results showed that all UCDW constituents can provide reactive phases and highly reactive bonds. RCB, WG, and WT can serve as the aluminosilicate source, while UA and WC mainly offer silica and calcium. The changes in constituents affected the mechanical performance of the UCDW-based geopolymer by conditioning the content of reactive Si, Al, and Ca in the precursor. A Si/Al molar ratio of 5–8 and a Ca/Si of 1.5 were found to achieve the higher compressive strength (up to 29.7 MPa) of geopolymer. In addition, a fitting formula was proposed to predict the compressive strength of UCDW-based geopolymer paste. This work contributes to understanding the alkali-activated performance of UCDW and promotes its utilization as a mineral precursor in geopolymer production.

An Alternative Radiation Shielding Material Based on Barium-Sulphate (BaSO4)-Modified Fly Ash Geopolymers.

Geopolymers are a new environmentally friendly cementitious material, and the application of geopolymers can reduce the carbon dioxide emissions caused by the development of the cement industry. Purpose: This study investigates the radiation shielding capacity of fly ash geopolymers (FAGP) as a viable alternative to conventionally used ordinary Portland cement (OPC) due to the high demand for an environmentally friendly, cost-effective and non-toxic shield material. Methods: The FAGP material was fabricated and combined with Barium sulphate (BaSO4) at different ratios (0, 5, 10 and 15%). Different thicknesses (3, 6 and 9 cm) of the samples were also prepared. An energy-dispersive X-ray (EDX) was used to determine the elemental percentages of the materials, which were then used to calculate their effective atomic number (Zeff). An ion chamber was used to detect the dose of radiation transmitted through the samples. Results: The lowest radiation dosage (34.68 µGy) and highest Zeff were achieved with FAGP combined with 15% BaSO4 at 9 cm thickness. The decrease in radiation dosage can be attributed to the increase in Zeff with the addition of BaSO4 to FAGP, which in turn increases the density of FAGP. Conclusions: Thus, the radiation dose can be significantly reduced with a higher ratio of BaSO4 to FAGP. This study shows that FAGP combined with BaSO4 is a promising radiation shielding material, as well as a viable alternative to OPC.

Process and mechanisms of multi-stage water sorptivity in hydrophobic geopolymers incorporating polydimethylsiloxane

Geopolymers as emerging green cementitious materials have attracted much attention, while they can be infiltrated by water involving harmful ions due to their hydrophilic matrix and porous structure. In this work, metakaolin-based geopolymers that hydrophobically modified by polydimethylsiloxane (PDMS) were comprehensively investigated in terms of integral wettability, pore structure, and water sorptivity kinetics. Results demonstrate that an ultra low sorptivity stage occurs at the beginning of the water absorption process for hydrophobic geopolymers, which is derived from the change in pressure drop caused by the PDMS layer on pore walls. Although the low sorptivity stage is temporary due to continuous moisture diffusion, it is of great significance for the application of geopolymers in waterproof engineering. The hydrophobic matrix (contact angles: ∼130°) and the improved pore structure jointly contribute to low water sorptivity and transport of modified geopolymers. Moreover, a multi-stage water sorptivity model was established to further explain the sorptivity process and its mechanisms.

Evaluation of corrosion protective properties of fly ash-red mud based geopolymer coating material for mild steel

Geopolymeric materials are fabricated via alkali activation of aluminosilicate materials by utilizing waste materials containing amorphous silica and alumina. Fly ash, red mud, metakaolin and blast furnace slag are the most common choices for the preparation of geopolymer. Among various well known applications of geopolymer, protective coating application has received increasing attention in recent years. The present work aimed to develop corrosion protective geopolymer coating for mild steel utilizing fly ash, red mud, alkali activators and additives. Coating material was prepared by addition of water and organic additives to nano sized geopolymer precursor which was prepared through solid state chemistry route. Developed coating was coated on cleaned and treated mild steel using spray coating technique. Coated plates were evaluated for adhesion strength, scratch test, impact test, water absorption and corrosion resistance by accelerated salt fog test as per ASTM/IS standards. Based on the results it is found that the developed coating material provides excellent corrosion protection and helps to enhance the service life of mild steel based structures.

Geopolymer as the future oil-well cement: A review

The petroleum and cement manufacturing industries have been accused of contributing substantial quantities of carbon dioxide (CO 2 ) into the atmosphere. Additionally, Portland cement systems suffer carbonation and degradation in high saline and acidic environments. Geopolymer, a much cleaner cementitious binder, synthesized through the reaction of aluminosilicate materials and alkaline solution has been a leading alternative to ordinary Portland cement (OPC). The feasibility of using geopolymer in oil-well cementing is still being explored. The objective of this review study is to provide a single document that summarizes the findings from these studies. In general, researchers have explored geopolymer application in aggressive environments and well plug and abandonment operations, the effect of temperature, and its compatibility with drilling fluid. Compared to OPC systems, geopolymer is more resistant to acidic environments, performs better in high saline conditions, and is highly compatible with drilling mud. The geopolymer being a green technology coupled with its optimized properties implies that it is the future of oil-well cement. For further studies, we suggest in-depth characterization of lightweight geopolymers. • The state of research on the application of geopolymer for oil well cementing has been explored. • Geopolymer overcomes many of the issues faced with ordinary Portland cement (OPC). • Geopolymer would be an excellent alternative to OPC-based systems.

Study of the rheology of lunar regolith simulant and water slurries for geopolymer applications on the Moon

To reduce transportation costs for building a lunar base station, it is important to utilise in-situ resources like lunar regolith. Lunar regolith can be used to create a concrete-like material by means of geopolymerization. For application of geopolymerizing mixtures, the rheology of the slurry must be known in advance. This article investigates the rheology of mixtures of lunar dust simulants with water, NaOH (as alkaline agent) and urea (as superplasticizer). The rheology of all the mixtures can be approximated with the Bingham Model. Aging has a dramatic effect on the rheology of the water + simulant mixture and, after 2 days, the yield stress decreases by six times. The presence of NaOH, on the contrary, increases both the apparent viscosity and the yield stress as it promotes geopolymerization. The addition of urea reduces the viscosity by 25%, but it has a limited effect on the yield stress. These findings can enable the design of construction 3D printers on the moon.

Hybrid Effect of PVA Fibre and Carbon Nanotube on the Mechanical Properties and Microstructure of Geopolymers

The concept of geopolymers has been widely studied since it was proposed. However, the wide range of applications of geopolymers is affected by brittleness and poor crack resistance. In this study, the mechanical properties of geopolymers with single-doped PVA fibres, single-doped carbon nanotubes, and mixed PVA fibers and carbon nanotubes were studied respectively first. It was found that PVA fibres and carbon nanotubes had a positive effect on improving the mechanical properties of geopolymers, especially bending strength and flexural strength. Moreover, the incorporation of PVA fibre could improve the damage morphology of geopolymers. Additionally, the phase analysis, structural group analysis, and strengthening mechanism were studied via scanning electron microscopy, mercury intrusion porosimetry analysis, X-ray diffraction pattern characterisation, Fourier transform infrared spectroscopy analysis, and magic angle spinning nuclear magnetic resonance analysis. It was found that the strengthening effect of PVA fiber to the geopolymer was primarily a physical strengthening effect, whereas the strengthening effect of carbon nanotubes to the geopolymers was both chemical and physical. Finally, based on the previous study, a multi-scale dual-fibre strengthening mechanism was proposed. Micro-nano fibre composites were used to improve microstructure via physical and chemical effects. This is helpful to improve the performance and application of geopolymers. Furthermore, it lays a preliminary theoretical foundation for engineering applications and technical improvement of geopolymers in the future.

Geopolymers as Sustainable Material for Strengthening and Restoring Unreinforced Masonry Structures: A Review

Unreinforced masonry (URM) structures are vulnerable to earthquakes; thus, materials and techniques for their strengthening and restoration should be developed. However, the materials used in some of the existing retrofitting technologies for URM and the waste produced at its end-of-life are unsustainable. The production of ordinary Portland cement (OPC) worldwide has enormously contributed to the global carbon footprint, resulting in persistent environmental problems. Replacing OPC with geopolymers, which are more sustainable and environmentally friendly, presents a potential solution to these problems. Geopolymers can replace the OPC component in engineering cementitious composites (ECC), recommended to strengthen and restore URM structures. In the present paper, the state-of-the-art knowledge development on applying geopolymers in URM structures is discussed. The discussion is focused on geopolymers and their components, material characterization, geopolymers as a strengthening and restoration material, and fiber-reinforced geopolymers and their application to URM structures. Based on this review, it was found that the mechanical properties of geopolymers are on par with that of OPC; however, there are few studies on the mentioned applications of geopolymers. The characterization of geopolymers’ mechanical and physical properties as a restoration material for URM structures is still limited. Therefore, other properties such as chemical interaction with the substrate, workability, thixotropic behavior, and aesthetic features of geopolymers need to be investigated for its wide application. The application method of geopolymer-based ECC as a strengthening material for a URM structure is by grouting injection. It is also worth recommending that other application techniques such as deep repointing, jacketing, and cement-plastering be explored.

Characterization, reactivity and rheological behaviour of metakaolin and Meta-halloysite based geopolymer binders

The type of aluminosilicate precursor used in the synthesis of geopolymer binders plays a huge role in the resulting performance. Thus, it is critical to understand the properties of precursors and how they influence the corresponding performance of geopolymer binders. In this study, metakaolin and meta halloysite are used as the aluminosilicate precursor in the synthesis of geopolymer binders. These precursors are obtained locally in order to propel the sustainable development and application of geopolymers. The precursors were characterized and the corresponding influence on the reactivity, rheology and setting times of geopolymers was investigated. In addition to the influence of precursor type on the properties of the geopolymers, the effect of two silica moduli (i.e. 1.3 and 1.5) was also evaluated. The results from this study indicated that increasing the activator silica modulus from 1.3 to 1.5 extended the setting times and increased the stress strain of the geopolymer binders. Characterization of the precursors indicated that metakaolin has a higher amorphous content compared to that of meta halloysite. However, the finer particles of meta halloysite embodied it with the ability to participate in a faster geopolymerization and result in more formation of activation products.

Mechanical and microstructural properties of phosphate-based geopolymers with varying Si/Al molar ratios based on the sol-gel method

Phosphate-based geopolymers with different Si/Al molar ratios were synthesized using Al2O3-nSiO2 powder obtained by the sol–gel method. The influence of different Si/Al molar ratios on the synthesis process and geopolymer properties was studied. The physical and mechanical properties of the geopolymer were evaluated using the three-point bending resistance test. With increasing Si/Al molar ratios, the flexural strength increased and reached a maximum value at an Si/Al ratio of 2.5 and then decreased. However, the reaction speed and curing speed slowed with increasing the Si/Al molar ratios. When the Si/Al ratio equalled 1.5, the geopolymer exhibited high expansibility, and the speed of reaction increased. Additionally, its compressive strength reached 2 MPa after 5 min. This study is of great significance for the application of geopolymers in practical emergency rescue projects, such as water gushing in tunnel engineering and pipeline gushing in hydraulic engineering.

Tailoring rheological–strength–ductility properties of self-cleaning geopolymer composites with asphalt emulsion

Metakaolin based-geopolymer is a promising construction material because of its sustainability and high strength. The frailty in road engineering application of geopolymer lies in its low ductility. Fortunately, a novel ductile fiber-reinforced geopolymer, known as engineered geopolymer composite (EGC)is developed. Nevertheless, its fluidity decreased obviously because of the bridging effect offibers. Asphalt emulsion (AE), as anself-cleaning building material, plays a significant role in improving rheological behavior,which remains understudied in EGC system. Thus, this study investigated the effects of adding PE fibers and AE on the rheological–strength–ductility properties of self-cleaning geopolymer composites as well as the geopolymerization reaction mechanisms. The mechanical test results, indicated that PE fibers dramatically improve ductility, while the strength first increases and then decreases with increasing AE content. The fluidity and rheological test results indicated the ability of AE to balance the ductility–rheological properties. Fourier-transform infrared spectroscopy revealedthat AE had an inhibiting effect on geopolymerization reaction but without a new functional group, and scanning electron microscopy/energy dispersive X-ray spectroscopy results indicatedthat the variation in AE contentchanged the particle size and shape of geopolymer gels and their geopolymerization degree. The nanoparticle size and zeta potential of geopolymers at 28 days quantitatively demonstrated the combined effect of PE fibers and AE on tailoring the rheological–strength–ductility properties. From above micro-scale analysis, a microscopic model illustrating the tailoring mechanism of self-cleaning geopolymer composites through AE addition was proposed, which offers the possibility to not only deeply discusses the role of AE in geopolymers but also unambiguously exhibits a prospective application in road engineering, such as 3D printing, and prefabricated cement concrete pavement.

Alkali leaching and mechanical performance of epoxy resin-reinforced geopolymer composite

Geopolymer material has emerged as a new binder in concrete production, mainly because of the low energy consumption and low greenhouse gas emission compared to Portland cement manufacture. However, low flexural strength and a high tendency to leach alkalis limit the application of this material in the construction field. In this study, a series of fly ash/ground granulated blast furnace slag based geopolymer composites reinforced with different amounts of bisphenol F epoxy resin were produced with an aim to investigate the effect of epoxy resin on alkali leaching and mechanical performance on geopolymer. The results show that the inclusion of a small amount of epoxy resin can significantly enhance the mechanical properties and reduce the total amount of alkali leaching of ambient-cured geopolymer, thus promising the extensive application of geopolymer in the construction industry.

Fibre-Reinforced Geopolymer Composites Micro-Nanochemistry by SEM-EDS Simulations

The focus of the present study is on fibre-reinforced geopolymer composites, whose optimization and application necessarily need a detailed chemical characterization at the micro-nanoscale. In this regard, many geopolymer composites presenting micro and nanometric architectures pose a challenge for scanning electron microscopy with energy dispersive X-ray microanalysis (SEM-EDS) quantification, because of several potential sources of errors. For this reason, the present work reports a SEM-EDS Monte Carlo approach to carefully investigate the complex physical phenomena related to the cited quantification errors. The model used for this theoretical analysis is a simplified fibre-reinforced geopolymer with basalt-derived glass fibres immersed in a potassium-poly(sialate-siloxo) matrix. The simulated SEM-EDS spectra showed a strong influence on the measured X-ray intensity of (i) the sample nano-to-micro architecture, (ii) the electron beam probing energy and (iii) the electron probe-sample-EDS detector relative position. The results showed that, compared to a bulk material, the X-ray intensity for a nano-micrometric sized specimen may give rise to potential underestimation and/or overestimation of the elemental composition of the sample. The proposed Monte Carlo approach indicated the optimal instrumental setup depending on the sample and on the specific SEM-EDS equipment here considered.

Effects of mixing duration on engineering properties of geopolymer concrete

Despite being investigated for over 50 years, the adaptation and application of geopolymers in construction are still very limited. One major reason behind this slow and often underappreciated acceptance of geopolymer concrete in industries is the lack of reports outlining observations and knowledge gained in field applications. Although geopolymers are well-accepted in the research community owing to their comparable or even better performance as a substitution of cement as a concrete binder, major initiatives still need to be undertaken in studying and reporting field observations of this product. The flash set phenomenon of a proven geopolymer concrete mix on a field trial motivated this investigation to identify the effects of mixing duration on geopolymer concrete performance. As such, this paper describes laboratory investigations undertaken to study the fresh, hardened, and durability properties of geopolymer concrete incorporating 65% fly ash and 35% slag, mixed for durations of 1 min and 10 min. The longer mixing duration significantly improved the workable time, at least five times longer workable time was achieved. It also resulted in relatively better mechanical strength and durability. The importance of proper mixing of geopolymer concrete constituents has been emphasized based on knowledge acquired from a combination of field trials and subsequent laboratory experiments.

High-flexural-strength of geopolymer composites with self-assembled nanofiber networks

Natural-fiber-reinforced geopolymer composites are environmentally friendly materials that have garnered considerable attention. In practice, the drying shrinkage and uneven dispersion of fibers in geopolymers result in low flexural strength, which limits the use of large-scale composites. In this study, high-flexural strength geopolymer composites with self-assembled nanofiber networks were hybridized using in situ polymerization. Composites with different fiber contents were evaluated via morphology and mechanical strength assessments. A mixed nanofiber and geopolymer solution was created to achieve uniform dispersion, and then the geopolymers were optimized at the nanoscale level using a bottom-up approach to achieve self-assembled nanofiber networks with good interfacial bonding. Due to the water retention properties of the nanofibers and subsequent gel material, the networks facilitated internal curing of the geopolymers, thus preventing drying shrinkage. This ultimately reduced the weight loss and increased the density of the composites. In addition, high flexural strength properties were observed in composites with a fiber content of 0.5%, due to the combination of fiber reinforcement and porosity. Thus, this work introduces new considerations for geopolymer applications.

Effect of ultrafine red mud on the workability and microstructure of blast furnace slag-red mud based geopolymeric grouts

Aims at improving the utilization rate of red mud and preparing a low-cost grouting material for underground engineering, the ultrafine red mud was adopted to prepare a slag-red mud based grout, and its fresh and hardened state properties were investigated comparing with the coarse red mud. The results showed that the incorporation of red mud could prolong the setting time and decrease the viscosity and thixotropy of slag-based geopolymeric grout, and ultrafine red mud has a better decrement effect. Ultrafine red mud has an enhancement effect on the slurry stability. The mechanical strength decreased with the adoption of red mud, while the ultrafine red mud has a higher mechanical strength than coarse red mud. The microstructure analysis showed that red mud plays a filling role in the geopolymerization process, and mechanical activation could increase the reactivity of red mud, furthermore, the iron component in ultrafine red mud could take part in the geopolymerization process. The results shed light on the utilization of red mud and the application of geopolymer in grouting engineering.