Characteristics Of Geopolymers Research Articles

Strength, durability, and toxicity characteristics of water treatment sludge based geopolymers for subgrade application

This study examined the strength, durability and toxicity characteristics of geopolymer made from water treatment sludge (WTS) using fly ash (FA) and ground granulated blast furnace slag (GGBS) as binding materials for the subgrade application. The mechanical properties of WTS-FA-GGBS geopolymers were assessed considering various parameters such as binder proportions, curing period, curing condition, Sodium silicate (SS) to Sodium hydroxide (SH) ratio (i.e. SS/SH), and Sodium hydroxide (NaOH) concentration. The results showed that increasing binder proportions, NaOH concentration, and curing period positively impacted the strength of the WTS-FA-GGBS geopolymer. The unconfined compressive strength (UCS) of the geopolymer samples with an SS/SH ratio of 2.5 showed higher compressive strength than those at an SS/SH ratio of 1. WTS-FA-GGBS geopolymers cured at 100°C showed increased UCS values after 1 to 3 days, but strength decreased after 7 days due to a faster geopolymerisation reaction, resulting in excessive moisture loss and microcracks in the geopolymerized samples. The study also found that all the geopolymer samples met the minimum strength criteria for cement-stabilized mix with a maximum mass loss of 8.17 % are well within the specified limits (<14 %) as per IRC:37–2018. The California Bearing Ratio (CBR) values of WTS-FA-GGBS geopolymers, which range from 41.11 % to 260.32 %, surpass the minimum criteria for cement stabilized subgrade or subbase material, as specified by IRC: SP:89–2010. Additionally, the changes during geopolymerization were confirmed by FESEM, EDS, and XRD analysis. The toxicity characteristic leaching procedure (TCLP) test results showed that the amounts of heavy metals in the geopolymer leachate were within the USEPA-mandated limits.

Research on improving the flexural performance of alkali-activated geopolymer cemented coal gangue through layered addition of fibers

The brittle characteristics of geopolymers during failure seriously hinder their practical engineering applications. To improve the toughness of low-energy alkali-activated geopolymer cementing coal gangue (AGCCG), the flexural performance of alkali-activated geopolymer cementing coal gangue (AGCCG) was enhanced by layering polypropylene fibers. Based on DIC digital speckle technology, the four-point flexure test of AGCCG was carried out, and the strength formation mechanism of the material was analyzed in depth by combining SEM-EDS and XRD. 3D visualization and analysis of the inside of the specimen with the help of CT scanning technology. The internal crack evolution law of the sample was illustrated by PFC numerical simulation. The results showed that the crack formation threshold, peak flexural strength and residual flexural strength of the specimens reached a local maximum at 3 % NaOH doping. With the increase of NaOH dosage, the cementitious product becomes more and more dense and homogeneous, and the area of void defects in the hydration product within the field of view becomes smaller and smaller. The peak bending strength of specimen B4-#4 is 79.43 % of that of specimen B5-#1–4, in which the cost of specimen B5-#1–4 is four times of that of specimen B4-#4, and the way of fiber assignment in specimen B4-#4 is more reasonable when considered together. The layered addition of fibers has a directional strengthening effect on the mechanical properties of geopolymer, and the overall addition of fibers can improve the overall strength and toughness of geopolymer. The numerical simulation results basically coincide with the macroscopic test results, and are consistent with the progressive damage law of the specimens obtained from the numerical scattering test. The results of the study can provide a theoretical basis for improving the bearing capacity of geopolymer and optimizing its structural performance. As well as reducing the impact of solid waste on the environment and improving the efficiency of resource use.

Mechanics and microstructure analysis of geopolymer utilizing ilmenite tailing and metakaolin powder as alkali-activated materials

Geopolymers derived from bulk solid waste are considered ideal substitutes for cement-based materials in developing environmentally friendly construction materials. The utilization of solid waste tailings powder as a precursor for alkali activation of geopolymer can enhance the mechanical characteristics of geopolymer. This study conducted extensive experimental studies on the compressive strength, flexural strength, SEM microstructure, thermogravimetric curve, and variable influence of alkali-activated ilmenite tailings (IT) geopolymer mortar, using the liquid-solid ratio and the number of tailings as variables. An analysis was conducted on the mortar's mechanical characteristics, microstructure, and machine-learning properties. Furthermore, the impact of different atomic ratios on the structure and characteristics of geopolymer mortars was also examined. The test results revealed that the metakaolin-iron titanium tailings geopolymer, when doped with 10% ilmenite tailings, exhibited a compressive strength of 72.30MPa at 14 days. Similarly, the flexural strength of the geopolymer reached 4.76MPa at 14 days when doped with 30% ilmenite tailings. XRD analysis showed that Magnesiohornblende particles Mg-F-A-S-H and C-A-S-H gel had positive and negative correlations, respectively, with the tailings doping level. TG results indicated that the specimens exhibit enhanced thermal stability following treatment with tailings. SEM analysis revealed that combining ilmenite tailings with metakaolin formed Me-(F)-A-S-H gels. The examination of surface porosity, pore shape, and unreacted material determined that adding ilmenite tailings increased the Si/Al and Fe/Si ratios, enhancing the transformation of the lamellar structure to the three-dimensional disordered gel mesh structure. Additionally, the tailings contributed a significant amount of Ca, elevating the Ca/Na ratio (0.1−0.6) and triggering calcium precipitation within a Ca/Si range of 0.03−0.2. This increase in calcium led to a decrease in the sample's strength as the curing time was extended. Based on prior research and the application of the Gray Wolf optimization algorithm in extreme learning, a clear negative correlation was identified between the liquid-solid ratio and strength. Furthermore, increasing the Si/Al ratio enhanced the geopolymer's strength, while an extended curing time negatively correlated with strength. The impact of tailings mixing was deemed insignificant when the tailings amount did not exceed 20%. Geopolymers may derive significant environmental and industrial benefits from the improvement of their mechanical properties, thermal stability, and optimization using machine learning.

Strength and durability characteristics of geopolymer treated pond ash as pavement material

This study evaluated the strength and durability characteristics of pond ash (PA) treated with geopolymer (3%, 6%, 9%, 12%, and 15%, by dry weight of PA) and compared them with Portland cement and hydrated lime stabilizations at same additive contents. Unconfined compressive strength of specimens was evaluated at curing durations of 1, 3, 7, 28, and 90 days. The durability of 28-day cured stabilised specimens against wet-dry cycles, freeze-thaw cycles, water slaking cycles, water immersion, capillary action, and dispersion was assessed. Geopolymer-stabilized PA achieved higher strength and durability than cement and lime-stabilised PA. It is due to the formation of a dense microstructure with significant reaction products. PA stabilised with 3% geopolymer and 15% cement satisfies the strength properties of the cementitious subbase in flexible pavements. Whereas, 6% geopolymer content fulfils the requirements of the cementitious base in flexible pavements and the cementitious subbase in rigid pavements as per IRC: 37-2018 and IRC: 59-2015, respectively.

Impact of NH4OH treatment on the ion exchange and pore characteristics of a metakaolin-based geopolymer.

We investigated the viability and influence of NH4OH post-synthetic treatment on the pore characteristics of geopolymers. Geopolymers are a class of materials with amorphous aluminosilicate three-dimensional frameworks, regarded as amorphous analogues of zeolites. Similar to zeolites, when geopolymers are used in catalysis or adsorption applications, post-synthetic treatments such as ion exchange with NH4 + salts (e.g., NH4Cl and NH4NO3) and desilication (using strong bases such as NaOH) are necessary to introduce active sites and modify their pore structure, respectively. Recently, it has been shown that treatment with NH4OH combines these two steps, in which acidic sites are introduced and the pore structures of zeolites are modified simultaneously. Considering the increasing interest in geopolymers in catalysis and adsorption applications, understanding the impact of such treatment on the structure of geopolymers is needed. Our diffuse reflectance infrared Fourier-transform spectra show that NH4 + exchanges Na+ in the geopolymer, and laser diffraction with scanning electron microscopy images show that the particle size of the powdered geopolymer decreases after NH4OH treatment. N2 sorption isotherms and 129Xe and 1H NMR measurements revealed information about the changes in pore structures: micropores were larger than mesopores and inborn mesopores increased in diameter, thereby reducing the surface area to volume ratio. However, pore accessibility and pore connectivity were not altered by NH4OH treatment. Since solid-state NMR and X-ray fluorescence revealed desilication, these changes in particle size and pore characteristics are considered to be due to desilication caused by NH4OH treatment.

Microstructure and transport properties of metakaolin-based geopolymers subjected to accelerated leaching

Towards the development of net-zero carbon concrete and the wider application of geopolymers, understanding the durability of geopolymers has become essential. However, knowledge on the evolution of microstructure and transport properties of the materials under aggressive conditions due to their interaction with external chemicals is limited. Therefore, this study investigated the leaching behaviors of metakaolin-based geopolymers with high water-to-binder (w/b) ratios under a 6 M NH4NO3 attack, focusing on their microstructure and transport properties. Microstructural insights were assessed through N2-adsorption, Mercury intrusion porosimetry, and water porosity analyses. After 28 days of leaching, total porosity slightly decreased, but pore size distribution (PSD) shifted towards larger pore sizes. The materials close to the exposed surface exhibited a relatively higher porosity and larger PSD than the deeper parts. The potential formation of Al(OH)3 and silica layers as a result of dealumination, confirmed by mass gain and SEM/EDS, contributed to the pore structural evolution. These alterations led to slight reductions in water permeability and CH4 diffusion coefficients but mostly increased the He diffusion coefficients of the geopolymers after 28-day leaching. These findings underscored the inherent microstructural characteristics of geopolymers (e.g., porosity, pore size distribution, and tortuosity) and the size of diffusing species as key factors shaping the transport properties. Notably, the permeability and diffusivity of both leached and intact geopolymers exhibited exponential correlations with the accessible porosity.

Influence of activator ratios and concentration on the physio-mechanical and microstructural characteristics of the geopolymers derived from sandstone processing waste.

Natural stones have been utilized to meet various needs of human civilization since ancient times. The exploitation of any resource is associated with the production of redundant materials called wastes. Sandstone waste (SW) is one such waste obtained during the industrial processing of sandstones. Due to its siliceous composition, extensive yield, and disorganized dumping, noxious conditions related to land and human health are promoted. However, the lack of comprehensive engineering studies, mineralogical analysis, and design methodologies associated with the utilization of sandstone processing wastes restricted their applicability only to fillers or partial substitutes with pozzolans and traditional cement in meager volumes. In the past, limited efforts have been made to utilize SW as a construction entity, particularly for binding purposes. Thus, to enhance the scope of its utilization, a comprehensive investigation has been performed in this research to transform sandstone waste into a novel construction material by geopolymerization. Mix design tailoring and laboratory tests were implemented to understand the effects of sodium hydroxide concentration and sodium silicate to sodium hydroxide ratio on the dissolution and physio-mechanical characteristics of SW-based geopolymers. The activator-to-binder ratio was restricted to 0.4 to obtain pastes with sufficient workability without hindering the properties of the matrix. Besides, a high temperature-curing regime was selected based on SW's crystallographic and reactivity analysis. Subsequently, a total of 48 samples were prepared and tested at the curing age of 28 days. Detailed characterization of SW and SW-based geopolymer samples was performed using optical, X-ray, and infrared spectroscopies aided by electron imaging and thermogravimetric techniques. SW-based geopolymer samples showed compressive strengths in the range of 6-12 MPa, ~2 to 3 times higher than those obtained in previous experimentations. Phase analysis and microstructural examinations confirmed SW's participation in geopolymerization. Overall, it could be advocated that geopolymerization is an innovative approach for solving issues related to the disposal and re-utilization of SW, extending its possible application to the fields of cement mixes, wall tiles, mortars, and masonry as per the commendations of ASTM and ACI committee.

ГЕОПОЛИМЕРЫ, ПОЛУЧЕННЫЕ МЕХАНОАКТИВАЦИЕЙ ИСХОДНЫХ КОМПОНЕНТОВ: ОБЗОР ТЕКУЩИХ ТЕНДЕНЦИЙ

The reaction potential of a substance can be significantly increased by thermal, mechanical, and chemical methods. A combined method is also possible, as in the case of developing geopolymers, the technology of which involves treating precursors with chemical reagents. On the other hand, with the increase in the number of publications devoted to the development of geopolymers, research to reduce the amount of CO2 emissions and the cost of geopolymers production becomes relevant. This review examines three generations of geopolymers: 1 – metakaolin based geopolymers, 2 – geopolymers based on rocks, and 3 – fly ash based geopolymers. A comparative analysis of ways to improve the physical and mechanical properties of fly ash based geopolymers by mechanical activation is presented. It has been established that mechanical activation of fly ash, in addition to improving the strength characteristics of geopolymers, makes it possible to synthesize a geopolymer without thermal curing. After this, the focus is on the method of mechanical activation of fly ash and clay minerals, especially kaolinite. The particular interest in metakaolin based geopolymers is due to the high potential for widespread application, since these geopolymer technologies have greater potential to reduce CO2 emissions and, therefore, production costs. Also, the development of protection against heavy metals or radioactive substances requires the implementation of technology exclusively using geopolymers based on metakaolin.

Effect of Kaolin and Basalt Composition on Geopolymer Characteristics

Effect of Kaolin and Basalt Composition on Geopolymer Characteristics

Characteristics of metakaolin-based geopolymers using bemban fiber additives

&lt;p&gt;The aim of this study was to investigate the chemical composition and thermal properties of kaolin, the physical properties of metakaolin, and the mechanical properties of metakaolin-based geopolymers using bemban fiber. Kaolin was calcinated to become metakaolin at 600 ℃ for 2 h for optimum conditions. The chemical composition of kaolin mostly consisted of 59.30% SiO&lt;sub&gt;2&lt;/sub&gt;, 34.30% Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;, and 3.06% Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;. The transformation of kaolin into metakaolin with temperature was determined through thermal stability tests and analyzed using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Regarding the thermal properties of kaolin, predehydroxylation occurred at 31.07–92.69 ℃, dihydroxylation occurred at 400–600 ℃, and the endothermic peak in the DTA curve was recorded at 505.63 ℃. This research also analyzed the physical and mechanical characteristics of metakaolin-based geopolymers, with the additional variation percentages of bemban fiber alloys resulting from a 3% NaOH alkalization treatment for 2 h. The test results indicate that the bemban fiber improves the physical and mechanical characteristics of geopolymers. This improvement is related to the enhanced geopolymer characteristics, including a water absorption capacity of 1.10%, porosity of 2.32%, compressive strength of 35.33 MPa, and splitting tensile strength of 11.29 MPa with the addition of 1.5% bemban fiber. Although the split tensile strength increases as the fiber content increases, adding 1.5% of bemban fiber is optimum because a higher content decreases the workability of mixtures.&lt;/p&gt;

Masonry structures retrofitting by geopolymer plaster reinforced with natural fibers

Geopolymers describe a class of aluminosilicate materials obtained by alkaline activation of an aluminosilicate precursor at low temperatures and, nowadays, represents a very strong competitor to Portland cement-based materials in the field of constructions. To improve the mechanical characteristics of geopolymers, the adoption of fibers (natural or not) has been proposed and this is the topic of a very large literature. From the other hand, nowadays the problem of environmental sustainability is very important and the geopolymers possess many features making them as the cutting-edge material of the future. Further, the adoption of natural fibers makes geopolymers even more interesting from the environmental sustainability point of view. In many cases of practical application strengthening of existing masonry structures represents a very important topic involving the field of structural engineering as well as that of restoration. In both fields it is important to adopt sustainable materials showing the required mechanical characteristics. Aim of the paper is to verify the use of geopolymer plaster reinforced by natural fibers as strengthening tool for masonry structures. The aim will be firstly reached by suitably modelling the mechanical behaviour of samples of geopolymer plaster realized in laboratory starting from experimental results and secondly modelling the behaviour of a masonry panel reinforced with such plaster by means of a suitable FEM model in Abaqus.

Synergistic utilization of industrial waste red mud and rice husk ash for eco-friendly geopolymer preparation: enhancing strength and mitigating hazardous leaching.

The prolonged stacking of substantial volumes of industrial waste red mud (RM) can have significantly hazardous effects on the environment. In order to address this critical problem, this study proposes the synergistic preparation of geopolymers utilizing RM in conjunction with another industrial waste, rice husk ash (RHA). Geopolymers with varying incorporation of RHA were prepared using sodium hydroxide and sodium silicate composite alkaline activator. The mechanical properties, microstructure, and environmental characteristics of geopolymers were investigated. The incorporation of RHA significantly enhanced the strength of RM-based geopolymers, with the highest strength of 25.40MPa achieved at 40% incorporation. According to XRD patterns and FTIR spectra, C-(A)-S-H and N-(A)-S-H were generated during the geopolymerization, thereby enhancing the strength of geopolymers. From SEM micrographs of geopolymers, it was evident that the geopolymer matrix was constituted by the encapsulation of unreacted inert particles of RM and residual fragments of RHA with C-(A)-S-H and N-(A)-S-H. The leaching levels of trace elements and heavy metals in geopolymers are both below the regulatory thresholds, thereby effectively mitigating the presence of hazardous substances in raw materials. These findings proved that the reuse of RM and RHA for the synergistic preparation of environmentally friendly geopolymers is a promising approach to address the issue of substantial RM stacking.

Comprehensive Analysis of Geopolymer Materials: Properties, Environmental Impacts, and Applications

The advancement of eco-friendly technology in the construction sector has been improving rapidly in the last few years. As a result, multiple building materials were developed, enhanced, and proposed as replacements for some traditional materials. One notable example presents geopolymer as a substitute for ordinary Portland concrete (OPC). The manufacturing process of (OPC) generates CO2 emissions and a high energy demand, both of which contribute to ozone depletion and global warming. The implementation of geopolymer concrete (GPC) technology in the construction sector provides a path to more sustainable growth and a cleaner environment. This is due to geopolymer concrete’s ability to reduce environmental pollutants and reduce the construction industry’s carbon footprint. This is achieved through its unique composition, which typically involves industrial byproducts like fly ash or slag. These materials, rich in silicon and aluminum, react with alkaline solutions to form a binding gel, bypassing the need for the high-energy clinker production required in OPC. The use of such byproducts not only reduces CO2 emissions but also contributes to waste minimization. Additionally, geopolymer offers extra advantages compared to OPC, including improved mechanical strength, enhanced durability, and good stability in acidic and alkaline settings. Such properties make GPC particularly suitable for a range of construction environments, from industrial applications to infrastructure projects exposed to harsh conditions. This paper comprehensively reviews the different characteristics of geopolymers, which include their composition, compressive strength, durability, and curing methods. Furthermore, the environmental impacts related to the manufacturing of geopolymer materials were evaluated through the life-cycle assessment method. The result demonstrated that geopolymer concrete maintains positive environmental impacts due to the fact that it produces fewer carbon dioxide CO2 emissions compared to OPC concrete during its manufacturing; however, geopolymer concrete had some minor negative environmental impacts, including abiotic depletion, human toxicity, freshwater ecotoxicity, terrestrial ecotoxicity, and acidification. These are important considerations for ongoing research aimed at further improving the sustainability of geopolymer concrete. Moreover, it was determined that silicate content, curing temperature, and the proportion of alkaline solution to binder are the major factors significantly influencing the compressive strength of geopolymer concrete. The advancement of geopolymer technology represents not just a stride toward more sustainable construction practices but also paves the way for innovative approaches in the field of building materials.

Thermal insulation of phenolic resin modified fly ash geopolymer

Phenolic resin has been widely used owing to its excellent thermal insulation performance. However, the application of phenolic resin in the field of geopolymer remains unexplored. Here, the foamed fly ash geopolymer samples with high porosity were prepared using phenolic resin for the purpose of foaming materials. The thermal insulation properties of these samples were evaluated by Transient Plane Source Method, and the effect of phenolic resin on pore characteristics was investigated by Mercury Intrusion Porosimetry (MIP), aim to explore how phenolic resin affects the thermal conductivity by changing the pore characteristics of geopolymer. In addition, considering that the internal gas thermal conductivity of pores with different pore sizes is also different (Knudsen effect), in order to predict the thermal conductivity more accurately, this research proposes an iterative calculation method to establish a thermal conductivity model. The results show that phenolic resin can improve the thermal insulation effect of geopolymer, and the minimum thermal conductivity of the sample is 0.17 W/m·K. In addition, according to the test results of MIP, it can be found that phenolic resin mainly promotes the porosity of micron pores (>1 μm) whereas there is slight inhibition on nano pores (<1 μm), but the beneficial effect of the increase of micron-sized pores (>1 μm) on the thermal insulation performance of geopolymer is greater than the negative influence effect of the disappearance of nano pores. Moreover, according to the results of MIP, phenolic resin can narrow the throat in the pore of the ink bottle, limit the thermal convection of the gas between the pores, and reduce the thermal conductivity. Finally, the newly modified Russell model considering the Knudsen effect can effectively predict the thermal conductivity by using the experimental data. This study provides a new method to improve thermal insulation performance of geopolymers and offers a new building insulation product.

Mesoscopic damage characteristics of hydrophobicity-modified geopolymer composites under freezing-thawing cycles based on CT scanning

The mesoscopic damage characteristics of geopolymer under freezing-thawing (F-T) cycles affect its macroscopic physical and mechanical properties, which further influence the safety of geopolymer buildings. This paper presents a study on the mesoscopic damage characteristics of hydrophobicity-modified geopolymer composites (HM-GC) based on the CT scanning technique. The damage degree and damage distribution characteristics of geopolymer composites (GC) before and after hydrophobic modification were compared. The gradient distribution characteristics of damage caused by F-T cycles in HM-GC were further analyzed. The results show that the volumetric porosity of the GC is always larger than that of HM-GC under the same F-T cycle number, indicating the hydrophobic treatment can reduce the F-T cycle damage rate and damage degree. The results also show that the damage induced by F-T cycles in GC and HM-GC shows obvious spatial gradient characteristics. As the F-T cycle number increases, the average gradient coefficient of GC increases first and then decreases, while the average gradient coefficient of HM-GC increases first and then stabilizes. The hydrophobic treatment can reduce the gradient characteristics of the F-T cycle damage and improve the F-T durability of geopolymer composites.

Comparative study of metakaolin-based geopolymer characteristics utilizing different dosages of water glass in the activator solution

Geopolymers gained attention from researchers due to their durability and potential to replace materials based on Portland cement. They offer a promising and eco-friendly alternative as binders in the construction industry. This study goal is to investigate the effects of varying dosages of sodium silicate (water glass) and sodium hydroxide in activator solutions, as well as the impact of different curing temperatures, on metakaolin-based geopolymer binder. Kaolin was heated to 750 °C for 3hr to produce metakaolin, and activator solutions were prepared with various amounts of water glass (0, 25, 50, 75, and 100) wt%. The fresh geopolymer binder was cured at two temperatures: 60 °C and 75 °C for one day. After a curing period of 28 days, various properties such as microstructural characteristics (examined through SEM), chemical bonding (analyzed using FTIR), chemical compositions (analyzed XRD), thermal conductivity and bulk density, volumetric shrinkage, and efflorescence were determined. Compressive measurements were conducted at early stages (7, 14, and 28 days) to assess mechanical properties, revealing a significant increase in mechanical strength. The geopolymer sample with 50 wt% of water glass cured at 60 °C exhibited optimal characteristics, including a higher compressive strength of 16.3 MPa and minimal efflorescence. This composition achieved an appropriate Si/Al ratio of 1.85, resulting from the formation of gel products through the reaction of compact structures. When the water glass content exceeded 50 wt%, the higher Si/Al ratio led to the deposition of the Al–Si phase, slowing down the interaction between the metakaolin powder and the alkaline activator. Regarding the influence of curing temperature, the average compressive strength of the geopolymer binder cured at 60 °C was greater as compared to the binder cured at 75 °C. Moisture loss and porosity increased with higher curing temperatures. The geopolymer binders exhibit a thermal conductivity value range (0.09–0.39)W/m.k.

Extensive rheological evaluation of geopolymer mortars incorporating maximum amounts of recycled concrete as precursors and aggregates

Due to accelerated geopolymerization kinetics, the control and prediction of rheological behavior of geopolymers (GPs) is quite complicated compared to their Portland cement-based counterparts. A comprehensive understanding of the crucial design factors influencing the rheological characteristics of GPs can provide important insights into their adoption in large scale applications. This study aims to comprehensively investigate the rheological behavior of geopolymer mortars (GPM) incorporating maximum amounts of construction and demolitions wastes (CDW) as precursors and aggregates. The binder composition was designed based on recycled concrete (RC) as the main precursor, while investigating its combined use with recycled clay brick (RB) and recycled ceramic tile (RT) at mono, binary and ternary mixtures. However, metakaolin (MK) was also incorporated in all compositions at a 30% replacement rates with CDWs to provide the required targeted ratio of SiO2/Al2O3. The effect of including 100% recycled concrete aggregate (RA) as compared to silica sand (SS) and natural sand (NS) was assessed for all CDW-based mortars prepared with the same water to binder (W/B) and aggregates to binder (A/B) ratios. All synthesized GPMs exhibited pseudoplastic or shear-thinning behavior, where the maximum shear and yield stresses, apparent and plastic viscosities and thixotropy were obtained with the increased amount of RT compared to RB into RC-based binary and ternary binder compositions. Although the addition of 100% RA in GPMs caused enhanced yield stresses, plastic viscosity and rigidity compared to SS and NS-based geopolymer mortars, it also attained higher thixotropy, which could play an important role in enhanced buildability at the early stages of geopolymerization.

Expandable Geopolymers Improve Zonal Isolation and Plugging

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212493, “Expandable Geopolymers for Improved Zonal Isolation and Plugging,” by Foster D. Gomado, SPE, Mahmoud Khalifeh, SPE, and Jan A. Aasen, SPE, University of Stavanger. The paper has not been peer reviewed. _ The sealability performance of an expanding geopolymer (E-GP) is compared with that of an expansive commercial cement (EC) with regard to shear bond strength (SBS) and hydraulic bond strength (HBS) at curing conditions of 25°C and 34.5 bar. A neat Class G (NG) cement and a neat geopolymer (N-GP) were characterized alongside corresponding expansive versions. The effect of these expansive agents on cement and geopolymers was evaluated in terms of linear expansion using the annular ring test. The complete paper reveals that geopolymers can be deployed as an alternative to Portland cement upon optimization. Geopolymer Characteristics and Use In recent years, geopolymers have been receiving attention as a viable and environmentally friendly alternative for zonal isolation and plugging and abandonment (P&amp;A) operations because of their robust features such as higher strength, lower permeability, and durability in high-pressure/high-temperature conditions. Geopolymers can be described as binders formed by a chemical reaction between aluminosilicate materials and alkali hydroxide or soluble silicates. In this study, cement/casing bonding properties are the primary focus. Greener options for cementing, zonal isolation, and P&amp;A must meet acceptable criteria before mass adoption. Geopolymers, like Portland cement, experience shrinkage to some extent. To improve cement bonding, expansive agents are regarded as relevant additives, correlating volume changes to bonding properties, mostly SBS. In the case of geopolymers, few studies have been directed toward the study of volumetric changes with and without expansive additives. The current literature for geopolymers lacks correlation between the performance of expansive agents on geopolymers in terms of HBS, SBS, and load-to-displacement profile. Thus, the authors explored the effect of expansive agents on SBS and accompanying interfacial friction and hydraulic sealability for both NG and EC, as well as neat geopolymers and expansive versions at equal conditions. Experimental Procedures NG cement was used as a reference because it is the most widely used cement in the Norwegian North Sea. The EC was made by the addition of a commercially available expansive agent [made of a blend of calcium oxide (CaO) and quartz] to NG at a concentration of 5% by weight of cement (BWOC). The geopolymer deployed in this study was synthesized in house. The E-GP was synthesized by the addition of a calcium salt in a concentration of 1.1% of the solid precursors. The complete paper details slurry preparation and the methodology for linear-expansion (shrinkage) tests, SBS/bond slip tests, and HBS tests.

Mechanical characteristics and solidification mechanism of slag/fly ash-based geopolymer and cement solidified organic clay: A comparative study

Geopolymers have recently received intensive research interests in the solidification of various soft soils due to their low-carbon footprint and environmentally friendly. However, understanding of the solidification characteristics of geopolymers in organic clay is still limited. In this study, a range of unconfined axial compression, pH value, moisture content, phase analysis, micromorphology, element composition and pore structure tests was conducted to comparatively investigate the physical properties and micromechanism of slag/fly ash-based geopolymer solidified organic clay (GSO) and cement solidified organic clay (CSO). Furthermore, the reinforcement effect of different parameters (geopolymer content and alkali-activator content) on the mechanical characteristics of GSO in the presence of humic acid was also investigated. The results show that the moisture content of CSO and GSO gradually increases with the content of humic acid, but the pH value and strength gradually decrease. Sustainable geopolymer is proven to be superior to cement in improving the physical-mechanical properties of organic clay. The unconfined compressive strength (UCS) of 28-day cured GSO2 containing 6% humic acid can reach 1.31 MPa, about 1.96 times of CSO1 containing 3% humic acid. The UCS of GSO can be significantly increased by the reasonable content of geopolymer and alkali-activator. Specifically, the 28-day UCS of GSO6 containing 20% geopolymer is 1.92 times and 2.68 times that of GSO2 (15%) and GSO5 (10%), respectively. The analysis of microscopic characteristics confirms that the strength formation of CSO and GSO is mainly affected by the number of cementitious products and the cementation degree of clay particles, which is attributed to the compactness of the matrix structure. The research results provide insights for a more comprehensive understanding of the application potential of geopolymers in organic clay solidification.

Effect of nano-alumina and graphene oxide on the behavior of geopolymer composites: A state of the art of review

Geopolymer composite has been widely recognized as an environment-friendly alternative to cement composite. Despite its popularity, Geopolymer (GP) has a limited number of real-world applications due to various factors affecting its performance. As a result, various novel techniques are adopted to enhance the performance of geopolymers; one such promising method is the use of nanomaterials. In order to improve material performance, nanomaterials focus on altering the properties of materials at the nanoscale. Nanomaterials influence the characteristics of GPs in their hardened and fresh state by microstructure modifications. The present review study concentrates on the impact of graphene oxide (GO) and nano-alumina (NA) on the behavioral assessment of GP composites, where the microstructural alterations brought on by their use are carefully assessed. Further, the influence of microstructural modifications on the hardened properties, such as mechanical and durability characteristics, as well as the fresh properties, such as workability and setting time, is explored. The review of research studies so far has revealed that GPs included with NA and GO have the potential to enhance the hardened state properties while adversely affecting the properties of the fresh state. Further, NA and GO’s distinct properties enable their use in high-temperature resistant composites, as coatings, and in a variety of uses associated with the environment, including wastewater treatment. However, the cost and energy associated with producing nanomaterials and their detrimental effect on human health and the ecosystem while they are in use prevent their widespread application, necessitating the need for research that balances all aspects.