Geopolymer Research Articles

Regional metakaolin particle size reduction for higher strength geopolymer

AbstractThe objective of this project was to further develop new composites and a testing program for the performance‐based specification for natural Amazonian geopolymer (GP) for use in ceramics and construction. While fly ash‐based alkali activated materials are now an established technology, metakaolin‐based GPs still need to be developed and optimized regarding the knowledge of the specific characteristics and properties of local resources. Amazonian kaolin was calcined into metakaolin (AMK). AMK particle size reduction for better reactive material was evaluated by means of dry and wet ball milling and sieving. Three types of metakaolin were analyzed for particle size distribution, and their size d50 ranged from 7.9 to 2.8 µm. Further GP characterization followed physical and mechanical properties in flexural strength tests. In addition, scanning electron microscopy and energy dispersive spectroscopy were used to investigate the microstructure of the materials. Energy dispersive X‐ray fluorescence was used to measure the GP material composition. Analysis of the results revealed that the strength and stiffness of sodium–metakaolin‐based GP were inversely proportional to particle size. All distinct particle size GPs showed, in general, some increase in strength and stiffness within curing times ranging from 3 to 28 days.

Predictive modelling of compressive strength of fly ash and ground granulated blast furnace slag based geopolymer concrete using machine learning techniques

Ordinary Portland cement (OPC) is proving to be hazardous to the environment. To replace the OPC, geopolymers (GPs) are introduced. However, to fully replace the OPC by GPs extensive laboratory tests are required to assess the long-term and short-term properties of GPs in different scenarios. Given the shortage of time for performing such extensive testing, artificial intelligence (AI) is used to analyze the properties of GPs. In this study, different AI techniques such as artificial neuro network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and gene expression programming (GEP) are used to obtain the predictive models for estimating the compressive strength of fly ash and ground granulated blast furnace slag-based GP concrete. Different statistical parameters are used to evaluate the performance of predictive models. Similarly, sensitivity and parametric analysis are also conducted on the input parameters. Additionally, multiple linear regression was also performed on the whole database. After comparing all the results, it was concluded that GEP is the best AI technique to predict the compressive strength of GP-based concrete.

Compositions and Microstructures of Carbonated Geopolymers with Different Precursors.

It is thought that geopolymers are easy to carbonate, especially when they are cured in ambient temperatures. Matrix gel's composition and microstructure, and new products of geopolymers (GPs) after carbonation were investigated in this study on the basis of XRD and SEM-EDS measurements and ternary diagram analysis, which were prepared from low-lime fly ash (FA) and ground granulated blast-furnace slag (GGBS) alone or a blend, as a precursor. The specimens were hardened in a 20 °C environment with alkali activator solution (S/N = 1.1 in mole), followed by storage under sealing or accelerated carbonation. XRD patterns show that carbonation products were nahcolite for the sole FA-based GP and calcite for the GPs using GGBS alone or as a blend. The SEM images of carbonated samples show that there were cube-shaped calcite and small calcite particles in the GGBS-based GP, but hail-like particles in the FA/GGBS blend-based GP. The hail-like particles were complexes of calcite and C-A-S-H gels determined by ternary diagram analysis, and were found to plug the top of the pores of the spongy C-A-S-H gels. We also confirmed that combined ternary diagram analysis of S-(C + M + N)-A and A-(C + M)-N are very effective in determining the gel type of a geopolymer, as well as the products and compositional changes after carbonation, in which oxide components of gels are determined by SEM-EDS. In the former diagram, C-A-S-H gels were plotted linearly along the (C + M + N)-albite (Ab) join, while N-A-S-H gels showed a scattered distribution. In the latter diagram, the plots for N-A-S-H and C-A-S-H gels are distributed in different zones. N = Na2O, C = CaO, M = MgO, A = Al2O3, S = SiO2, H = H2O.

Influence of curing temperature and pressure on the mechanical and microstructural development of metakaolin-based geopolymers

This research investigates the mechanical and microstructural evolution of a metakaolin-based geopolymer (GP) subjected to combined temperature and pressure curing conditions. The study's methodology encompassed measuring compressive strengths through both ultrasonic cement analysis (UCA) and destructive uniaxial testing. To evaluate thermal stability, pore size distribution, and morphology, the study employed thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), and environmental scanning electron microscopy (ESEM), respectively. The findings indicate that a curing temperature of 90 °C encourages the development of regular nanoporosity, while higher temperatures contribute to increased porosity. Conversely, curing pressure was found to either promote or inhibit the material's reorganization, with pressures of 20 MPa facilitating and those above 40 MPa preventing this process. An enhancement in the refinement of macropores to micropores was observed across all pressure levels. The optimal curing conditions, in terms of both mechanical and morphological characteristics, were identified as 50 °C and 20 MPa for a minimum duration of one day, which yielded a 177 % improvement in compressive strength compared to curing at 21°C under atmospheric pressure. This study significantly advances the understanding of pressurized thermal curing processes for the rapid setting of geopolymers, presenting new avenues for diverse applications.

Synergistic effects of hybrid microfibers on mechanical, thermal, and microstructural characterization of nanocomposites.

The use of geopolymers (GP) in cementitious composites provides a solution to reduce the significant carbon emissions associated with conventional cement production, thereby advancing environmentally friendly concrete construction practices. The promise of hybrid fiber-reinforced fly ash (FA)-based GP (HFGP) composites that combine microfibers and nanoparticles has not yet been fully comprehended. This research aims to enhance the mechanical and microstructural properties of HFGP blends by varying the proportion of nano calcium carbonate ( ). The production of HFGP involved the use of two types of fibers: 1% carbon fibers and 0.5% basalt fibers. To achieve HFGP blends with a consistent fiber ratio, we incorporated four different levels of , comprising 1%, 2%, 3%, and 4% of the mixture. The analysis of fractured samples encompassed microstructural and mineralogical characterization, which was conducted using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analysis. The results unveiled that the HFGP blend containing 3% exhibited the highest levels of hardness, compressive strength, toughness modulus, and flexural strength while the use of 2% produced the highest results for fracture toughness and impact strength. SEM analysis illustrated that had a significant positive impact on the microstructure of GP. A considerable rise in hump intensity between 20 and 40°C ( ) was also seen in the XRD examination, indicating that calcium silicate hydrate (CSH) had formed after the primary binder, such as sodium aluminosilicate hydrate (NASH), had been present. The stretching of O-H bonds in water molecules was also seen in the HFGP spectra at 3399, 3436, 3436, and 3438cm-1. Due to the higher water content in the HFGP network, which may influence the material's strength, these bands were more apparent and larger in specimens with additions of nanoparticles and hybrid fibers.

Stability analysis of a granite-based geopolymer sealant for CO2 geosequestration: In-situ permeability and mechanical behavior while exposed to brine

When considering the use of geopolymers (GPs), as potential alternatives for Portland cement, high durability during exposure to brine at encountered downhole is a key requirement. This study delves into the response of a granite-based GP system designed especially for CO2-geosequestration upon exposure to brines with different concentrations of NaCl. Exposure was carried out by imposed flow in a triaxial apparatus, at 90 °C and 13.8 MPa confining pressure. Mechanical properties were tested in the same apparatus once exposure was completed. A suite of micro-scale analytical techniques was then used to assess the GP's microstructure, mineralogical composition, and chemical bonding. The obtained results revealed increasing compressive strength with increasing brine salinity, suggesting greater resistance to deformation and potential cracking. Concurrently, decreasing Poisson's ratios and increasing Young's moduli could lead to an elevated risk of mechanical failure under strain. In addition, following a 3-week injection period, permeability of NaCl-flooded samples decreased by 20%–35% from initial values. Analysis of the effluents showed fluctuations in the pH and ion content with time, mainly attributed to complex chemical interactions including cation exchange, silicate dissolution and hydrolysis, precipitation of alkali-enriched gels, and mineral alterations. Micro-scale analyses revealed that the improved durability is linked with the formation of new minerals, especially zeolites in the presence of NaCl or portlandite when deionized water was introduced. In conclusion, this study presents new data on the durability of a rock-based GP system when exposed to brine and elevated pressure and temperature, offering insights for optimization to downhole environments.

Ammonium Removal in Wastewater Treatments by Adsorbent Geopolymer Material with Granite Wastes: Full-Scale Validation

Elevated ammonium (NH4+) concentrations in untreated waterways contribute to eutrophication and dissolved oxygen depletion. Geopolymer (GP) materials are introduced as sustainable, straightforward operation and low-cost option for pollutant adsorption through ion exchange mechanism. In the present study, a porous metakaolin-based geopolymer with granite waste additions was synthetized, characterised and validated as adsorbent material for NH4+ pollution in water. At this point, treatments to reduce GP alkalis leaching were also considered to comply with the water discharge regulations. The adsorption mechanism was analysed by Redlich-Peterson isotherm model concluding that NH4+ was disposed on the GP surface as a monolayer with strong physical-chemical attraction between molecules. Kinetics of the process followed the Weber-Morris rate equation being the intraparticle diffusion the limiting process. Continuous experiments at lab-scale suggested a maximum removal of 97% during the first hours and an adsorption capacity (q) of 25.24 mg/g. Additionally, as a main novelty of the work, the GP was validated in a full-scale pilot plant monitoring pH, electrical conductivity and NH4+ concentration. The obtained data revealed that the GP is high selective in a real wastewater stream and removed 81% of NH4+, higher adsorption values than those reported for natural and some synthetic zeolites.

A Study on the Shrinkage and Compressive Strength of GGBFS and Metakaolin Base Geopolymer under Different NaOH Concentrations.

Geopolymers (GPs) are gaining prominence due to their low carbon emissions and sustainable attributes. However, one challenge with GPs, particularly those made with ground granulated blast furnace slag (GGBFS), is their significant shrinkage during the geopolymerization process, limiting its practical applicability. This study focuses on how the substitution ratio of metakaolin (MK) and the concentration of sodium hydroxide (NaOH) in the activator can influence the shrinkage and strength of a GGBFS-based GP. The experimental approach employed a 3 × 3 parameter matrix, which varied MK substitution ratios (0%, 50%, and 100%) and adjusted the NaOH concentration (6 M, 10 M, and 14 M). The results revealed that increasing MK substitution, particularly with 6 M NaOH activation, reduced the GP shrinkage but also diminished compressive strength, requiring higher NaOH concentrations for strength improvement. Statistical tools, including analysis of variance (ANOVA) and second-order response surface methodology (RSM), were employed for analysis. ANOVA results indicated the significant impacts of both the MK content and NaOH concentration on compressive strength, with no observable interaction. However, the shrinkage exhibited a clear interaction between MK content and NaOH concentration. The RSM model accurately predicted compressive strength and shrinkage, demonstrating a high predictive accuracy, for which the coefficients of determination (R2) were 0.99 and 0.98, respectively. The model provides a reliable method for determining the necessary compressive strength and shrinkage for GGBFS-based GP based on MK substitution and NaOH concentration. Within the optimization range, the RSM model compared with experimental results showed a 6.04% error in compressive strength and 0.77% error in shrinkage for one interpolated parameter set. This study establishes an optimized parameter range ensuring a GP performance that is comparable to or surpassing OPC, with a parameter set achieving a compressive strength of 34.9 MPa and shrinkage of 0.287% at 28 days.

Microstructure and mechanical properties of geopolymers utilizing excavated soils, metakaolin and slags

This paper presents a study on the potential of geopolymer (GP) as a substitute for ordinary Portland cement (OPC) in construction applications. OPC is widely used in construction due to its high strength and durability. However, manufacturing is extremely energy-intensive and produces large amounts of carbon dioxide (CO2) emissions. Also, In France, 130 million tons of excavated soils are generated each year [1] and classified as waste material without proper disposal methods. Therefore, the use of excavated clays coming from construction projects in GP formulations will have a positive impact on decreasing waste materials. Moreover, flash calcination used as heat thermal technique eliminate the organic matter and enhance the geopolymerization reaction with the alkaline reagent used in GP. On the other hand, GP are a type of alternative material made from industrial by-products such slags. This study used various methods to optimize GP mix design by evaluating the fresh and hardened properties. The results has shown that GP has a higher compressive strength than OPC in short term (between +5% and 76% at 1 day) and present a comparable strength in long term. The analysis of the microstructure throughout nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) has shown the GP designed has a stable reticulated polymeric structure. Mercury porosity has shown a finer nonometric porosity that corresponds to a compacted and fitted micelle structure. This study provides a solid contribution to the sustainability of the construction industry by developing a GP binder composed of flash-calcined excavated clay (FCC), metakaolin (MK), and slag (GBFS) that can achieve better results than OPC binder.

Evaluation of Properties of Concrete Without Cement Produced Using Fly Ash‐Based Geopolymer

AbstractThe use of ordinary Portland cement (OPC) in the construction industry is inevitable. The huge production of OPC and its use in infrastructural development pose an environmental impact. Greenhouse gas emitted increases the global temperature and it is an alarming sign to everybody on the planet. Concrete is the most consuming material which is produced by using OPC and it is proven that OPC contributes a lot to CO2 emission. Hence in this study attempt is made to produce concrete by using environment‐friendly material like fly ash along with alkaline activators, which is termed Geo polymer concrete. The by‐product fly ash is widely available worldwide. It is a by‐product of thermal power plants. The use of fly ash in concrete produces less expensive and more cost‐effective concrete than concrete made up using OPC. Due to its high silicate and alumina content, fly ash reacts with an alkaline solution to create an aluminosilicate gel that binds the aggregate and results in high‐quality concrete. Fly ash is finer than cement, it occupies the pores of cement after hydration. This would result in denser concrete which gives higher strength. In comparison to ordinary concrete, fly ash‐based geopolymer concrete offers better resistance to aggressive environments and high temperatures. In the present study, an alkaline activator of molarity 8 is used to prepare geopolymer concrete. The test specimens are cast and cured for 28 days. Test results indicate that an alkaline liquid fly‐ash ratio (0.4) produces higher mechanical properties. Hence, geopolymer concrete produced in this study is found to be cost‐effective and environment friendly.

Study of the preparation and properties of hydrophobic and high strength geopolymers

An excellent hydrophobic geopolymer (GP) composite modified by fatty acid and polydimethylsiloxane (PDMS) with high mechanical strength was prepared successfully. The results of this research show that, when the mass fraction of fatty acid and PDMS were 50 % and 5 % respectively, the maximum water contact angle, 24 h minimum water absorption and maximum softening coefficient of GP obtained by composite modification method could reach 143°, 0.36 % and 0.88, respectively. Meanwhile, the maximum compressive strength exceeds 47.25 MPa.

Oil and Organic Liquids Incorporation into Fresh Geopolymer Pastes Using Suitable Quaternary Ammonium Surfactants.

The direct incorporation of low viscosity organic liquids (OL) such as dodecane and tributylphosphate (TBP) into fresh geopolymers (GP) is difficult and generally leads to variable amounts of un-incorporated OL remaining outside the hardened geopolymer. Experimentally, it is observed that a regular torque increase during OL incorporation corresponds to a suitable dispersion of the OL in the form of fine micrometric droplets. This can be obtained for TBP and dodecane by adding a small quantity of quaternary ammoniums salts (QAs) such as cetyltrimethylammonium bromide (CTAB). Shorter alkyl chains QAs, such as hexamethyltrimethylammonium (HMTA) can also be used but with a reduced efficiency. The positive impact of CTAB is then confirmed by the Washburn capillary rise method, showing that the interactions between TBP and CTAB-modified metakaolin are weaker compared to untreated powder. Finally, it is observed that the incorporation of TBP into geopolymer slurries is much easier than the incorporation of dodecane. The low interfacial tension measured between TBP and the activating solution (around 8 mN·m -1 ), contrasting with dodecane (29 mN·m -1 ), explains that the dispersion of TBP droplets in fresh metakaolin suspensions is more efficient.

Optimization of formulation ratios of geopolymer mortar based on metakaolin and biomass fly ash

This study investigated the factors affecting the properties of geopolymer (GP) mortars through a two-stage experimental program created through central composite design of experiments. Stage I focused on the effects of SiO₂/Al₂O₃, H₂O/Na₂O, and total water-to-total solids (W/S) ratios on mortars formulated using metakaolin (MK) as the only geopolymerization precursor, while Stage II evaluated the impact of introducing biomass fly ash (BFA) as a second precursor. Most importantly, the SiO₂/Al₂O₃ ratio was defined based on raw materials’ dissolution tests rather than on their starting chemical composition, setting this study apart from most published literature. The mortars’ properties of interest, taken as response variables, were the flow test spreading diameter, and the efflorescence level and compressive strength after 7 days of curing under ambient conditions. The results of Stage I, regarding GP mortars based on MK only, show that SiO₂/Al₂O₃, H₂O/Na₂O, and W/S all had a statistically significant effect on compressive strength. Regarding the efflorescence level, SiO₂/Al₂O₃ had the most significant effect, H₂O/Na₂O showed a small contribution, and W/S effect was not statistically significant. In stage II, the incorporation of BFA led to (MK + BFA)-based mortars with lower spreading diameter and compressive strength, and higher efflorescence levels, with % BFA being the most important factor affecting these three response variables. Based on the developed models, appropriate combinations of factor values that simultaneously maximize the compressive strength while maintaining the spreading diameter and efflorescence levels within suitable limits were found: GP mortars based only on MK with SiO₂/Al₂O₃ = 4.5, H₂O/Na₂O = 19.0, and W/S = 0.17 are expected to achieve 53MPa of compressive strength at 7 days; (MK + BFA)-based GP mortars with % BFA = 39.0, H₂O/Na₂O = 15.5, SiO₂/Al₂O₃ = 4.5 and W/S = 0.17 are expected to achieve 30MPa. These results provide valuable insights into the factors affecting the properties of GP mortars and can be useful for optimizing formulations for different applications.

How acid attack and high temperature affect the microstructure of adsorbent geopolymers

Geopolymers (GPs) are versatile materials that have low intrinsic porosity. This characteristic can be used as a motivator for the development of porous GPs, since separation processes require adsorbents with a high specific area. Thus, this work aimed to elucidate how acid attack and calcination affect the microstructure of GPs. For this purpose, a GP was exposed to H2SO4 and 200 °C, being later characterized in terms of morphology, mineralogy, functional groups, and textural properties. Acid etching and calcination proved to be effective strategies for surface area improvement, making the modified GP a strong candidate for use as an adsorbent.

Physical and mechanical properties of fly ash‐based geopolymer with disposable medical mask reinforcement

AbstractA tremendous amount of the nonbiodegradable microplastic waste has been generated after the outbreak of COVID‐19 by the widespread use of single‐use personal protective equipment, especially disposable medical masks (DMMs). This has caused harm to the health and safety of human beings and various organisms. Finding a way to properly deal with these single‐use medical wastes has become an urgent problem. In this paper, an innovative way was explored to use DMMs in geopolymer (GP). The physical properties, mechanical strength, and resistance to high temperatures (200–800°C) of the composites were investigated. The findings of the study revealed that DMMs had negligible influence on resistance to high temperatures, but showed a positive influence on enhancing the compressive and flexural strengths of GPs at ambient temperature. The optimum DMMs content was 0.4 wt%, at which the compressive and flexural strengths of the GP composites were enhanced by 5.8% and 22.68% compared with the pure GP, respectively. The same polypropylene (PP) fiber amount increased compressive and flexural strengths by 7.49% and 9.76%, respectively. This thus confirmed that DMMs can be sustainably utilized in green building materials, playing a role as PP fibers toughening and contributing to the effective management of waste plastics.

Geopolymer Materials for Extrusion-Based 3D-Printing: A Review.

This paper examines how extrusion-based 3D-printing technology is evolving, utilising geopolymers (GPs) as sustainable inorganic aluminosilicate materials. Particularly, the current state of 3D-printing geopolymers is critically examined in this study from the perspectives of the production process, printability need, mix design, early-age material features, and sustainability, with an emphasis on the effects of various elements including the examination of the fresh and hardened properties of 3D-printed geopolymers, depending on the matrix composition, reinforcement type, curing process, and printing configuration. The differences and potential of two-part and one-part geopolymers are also analysed. The applications of advanced printable geopolymer materials and products are highlighted, along with some specific examples. The primary issues, outlooks, and paths for future efforts necessary to advance this technology are identified.

Preparation and performance study of a novel conductive geopolymer

A novel conductive geopolymer (GP) based on fly ash (FA) and modified by carbon fiber (CF) was successfully developed in this study. Detailed investigations were conducted on various factors influencing resistivity, such as the type and content of CF, liquid-solid ratio, modulus of alkali activator, and the material’s sensitivity to temperature, pressure, moisture. The research findings highlight that short-cut CF enhances both the electrical conductivity and mechanical properties of GP, along with its sensitivity. Specifically, at an FA and short-cut CF mass fraction of 80% and 1.0% respectively, the resistivity and compressive strength of GP reached 5.58 Ω·m and 51.20 MPa, representing a 99.95% reduction in resistivity and a 40.66% increase in strength compared to pure GP. Additionally, the introduction of CF1 into the modified GP exhibited significant negative temperature coefficient and piezoresistive effects. Furthermore, FA not only enhanced the conductivity but also improved its water resistance of GP. This study provides a creative opportunity for design and fabrication of novel conductive intelligent GP materials.

Fast‐setting mineral‐impregnated carbon‐fiber (MCF) reinforcements based on geopolymers

AbstractMineral‐impregnated carbon‐fiber (MCF) reinforcements are an innovative type of fiber‐reinforced composites, which combine the valuable properties of high‐performance fibers with durable inorganic matrix materials. The application of mineral‐based matrices to produce MCFs offers a wide range of advantages, such as high resistance to elevated temperatures, low cost, adequate physical and chemical bond with concrete substrates and high technological flexibility in automated processing. In particular, specific‐designed geopolymer (GP) impregnation suspensions allow stable rheological properties with a sufficient long‐lasting processing window as well as moderate curing temperatures to accelerate a fast setting on demand ‐ similar to organic based thermosets. The paper at hand studies the effect of various thermal curing regimes of a GP impregnation matrix and for the forming process of the resulting MCF composite. The fabrication of MCFs were performed by using commercially available raw materials and a continuous pultrusion line with subsequent oven heating at 50 °C and 75 °C. A wide range of experimental investigations at multiple scales have been performed to understand the GP matrix development, fiber‐matrix interface and final MCF properties.

Effect of Addition of Cement in Binary Blended Geopolymer Concrete

The construction industry contributes significant greenhouse gases to the climate by consuming vast amounts of cement. Researchers are looking at alternative cement methods to decrease the adverse effects, one of which is Geopolymer Concrete (GPC). The GPC is made from industrial waste materials high in silica and activated with sodium hydroxides (NaOH) to form sodium silicate (Na2SiO3) because Geo polymer is a material that is just two decades old and is an area of extensive research. To study the effect of the addition of cement to GPC’s mechanical properties by replacing up to 50% of the ground granulated blast furnace slag (GGBFS) and fly ash with ten per cent increments. The outcomes are contrasted with the Geo Polymer Concrete control mix. For this study, an analysis of activators to fly ash at 0.35, NaOH to Na2SiO3 at 2.5, and the molarity of sodium hydroxide was set at 8M. At different ages, the compressive strength of cubes was calculated, as well as their split and flexural strengths following a 28-day curing period. The findings revealed that adding cement to the mix improves the mechanical properties. The best results are obtained at 40% cement, fly ash, and GGBFS at 60%.

Durability Performance of Ferro Geo Polymer Concrete

The expansion of the building sector is ultimately driving up the manufacturing of Portland cement, which rises pollution. Consequence of this is global warming. Sustainable alternatives are being used in concrete on a large scale to minimise the impact of greenhouse gases. Concrete made of geo-polymers is one of such alternative. Since Geo Polymer Concrete (GPC) is inherently known for its resistance to aggressive environment, to add to its characteristics, steel wire mesh was incorporated into geo polymer concrete which can largely be termed as “Ferro Geo Polymer Concrete” (FGPC). In the current study, durability properties of FGPC such as resistance to acid attack, Half-Cell Potential (HCP) and resistance to abrasion have been studied. Welded square wire mesh has been used in the specimens with different number of layers. FGPC specimens were compared to GPC specimens of same grade without mesh. Double layered FGPC specimens have shown better resilience to acid attack having weight loss and strength loss of 0.44% and 17.24% when immersed in H2SO4 and 0.45% and 8.4% when immersed in HCL correspondingly. Double layered FGPC has better resistance towards abrasion of concrete with PWL of 2.43% and ADA of 1.07 mm.