Geopolymer Foams Research Articles

Rapid performance optimization strategy of MK-FA-GBFS based geopolymer foam heavy-metal adsorbent

Geopolymer foams (GPFs) are promising materials for heavy-metal-containing wastewater treatment. However, because of the diversity of precursors and the complex application environments, it is challenging to balance the processing and application performances. Herein, a “simplex-centroid” mixture design method was explored to optimize the performances and establish relationships between the precursors, microstructure, and molecular structure. Further, according to the design performance and rheological limitations of the foaming system, an optimal component was selected to fabricate a GPF using chemical foaming. The fabricated GPF exhibited a high compressive strength (0.86 MPa) and high open porosity (∼86%) with uniform pores with diameters of 0.1–1.2 mm. Pb2+, Cu2+, and Ni2+ static adsorption capacities of 112.8, 64.9, and 40.2 mg/g, respectively, were achieved. The combination of simplex-centroid method and chemical foaming is effective for optimizing the processing and application performances of GPF, and could be beneficial for future large-scale manufacturing of GPFs for water-treatment applications.

Investigation on pore properties, thermal conductivity, and compressive behavior of fly ash/slag‐based geopolymer foam

AbstractGeopolymer foam has emerged as a promising inorganic porous material in the last decade. Despite of the numerous advantages, there are some pending issues to be addressed, on top of that is the low compressive strength. To overcome this, this study synthesizes a high‐strength geopolymer foam by the partial substitution of fly ash (FA) with ground granulated blast furnace slag and carries out an intensive investigation into its microstructure, pore properties, thermal conductivity as well as compressive behavior. The microstructure is firstly analyzed by X‐ray diffraction and Fourier transform infrared spectroscopy techniques. The pore characteristics are also scrutinized, including pore size distribution, total porosity and water absorption. Then, the thermal conductivity is investigated and the applicability of basic effective thermal conductivity models to characterize the relationship with total porosity is evaluated. Afterward, the compressive strength together with the softening coefficient is examined, and the relationship with total porosity is also studied. Finally, comparisons between the proposed geopolymer foam and other FA‐based geopolymer foams in the literature are performed. The results show that the proposed geopolymer foam possesses not only a comparable thermal conductivity but also a far superior compressive strength, which sheds light on the widespread applications in thermal insulation.

STUDY OF REGULARITY OF CHANGES IN VOLUMETRIC MASS OF FOAMED GEOPOLYMER MATERIALS ON BASIS OF LIMESTONE WAST

The creation of composite construction materials, which have a less harmful impact on the environment both at the stage of their production and in the process of their use, is of great interest in the global construction industry. Recent innovations have led to the creation of foamed geopolymer concrete or geopolymer foam, which includes the operational advantages of thermal and acoustic insulation materials, saves energy by reducing heat loss, and contributes to the reduction of CO2 emissions into the environment. For a better understanding of the properties and benefits related to the use of foamed geopolymer materials, this paper presents studies of the volumetric mass of these materials obtained from limestone waste and silicate activator. Samples with a ratio of components (limestone waste: activator) of 70:30, 75:25, and 80:20 were obtained. Studies of the volumetric mass depending on changes in the concentration of alkali in the solution of the gas generation activator showed that the minimum values of the volumetric mass are achieved at 1 mol/L concentration of alkali. In addition, it was found that the best foaming geopolymer material is achieved at a ratio of components of 80:20 and at a content of the gas generation activator solution in the mixture of 18% mass. Keywords: foamed geopolymer, volumetric mass, porosity, thermal insulation material.

STUDY OF REGULARITY OF CHANGES IN VOLUMETRIC MASS OF FOAMED GEOPOLYMER MATERIALS ON BASIS OF LIMESTONE WASTE

The creation of composite construction materials, which have a less harmful impact on the environment both at the stage of their production and in the process of their use, is of great interest in the global construction industry. Recent innovations have led to the creation of foamed geopolymer concrete or geopolymer foam, which includes the operational advantages of thermal and acoustic insulation materials, saves energy by reducing heat loss, and contributes to the reduction of CO2 emissions into the environment. For a better understanding of the properties and benefits related to the use of foamed geopolymer materials, this paper presents studies of the volumetric mass of these materials obtained from limestone waste and silicate activator. Samples with a ratio of components (limestone waste: activator) of 70:30, 75:25, and 80:20 were obtained. Studies of the volumetric mass depending on changes in the concentration of alkali in the solution of the gas generation activator showed that the minimum values of the volumetric mass are achieved at 1 mol/L concentration of alkali. In addition, it was found that the best foaming geopolymer material is achieved at a ratio of components of 80:20 and at a content of the gas generation activator solution in the mixture of 18% mass. Keywords: foamed geopolymer, volumetric mass, porosity, thermal insulation material.

Geopolymer fly ash composites modified with cotton fibre

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

Use of sodium metasilicate as silica source and stabilizing agent in two-part metakaolin–H2O2 geopolymer foams

The synergistic effects of the SiO2/Al2O3 ratio (2.0, 2.5, and 3.0) and H2O2 content (1.5%, 3.0%, and 6.0%) were evaluated in metakaolin-based geopolymer foams using sodium metasilicate pentahydrate as a complementary silica source. Sodium metasilicate helped to stabilize the pores in foams with SiO2/Al2O3 molar ratios of up to 2.5 cured at 50 °C without stabilizing additives. The optimum porous system for insulation cores was obtained using a SiO2/Al2O3 ratio of 2.5 and H2O2 content of 6%. Furthermore, a SiO2/Al2O3 molar ratio of 3.0 reduced pore formation as the increased geopolymerization and viscosity served as a barrier to bubble diffusion.

Development of Foam Fly Ash Geopolymer with Recycled High-Density Polyethylene (HDPE) Plastics.

Adapting sustainable construction, which involves responsible consumption of natural resources and reducing carbon emissions, could be a unified action to address the intensifying effects of global warming and the increasing rate of waste pollution worldwide. Aiming to lessen the emission from the construction and waste sector and eliminate plastics in the open environment, a foam fly ash geopolymer with recycled High-Density Polyethylene (HDPE) plastics was developed in this study. The effects of the increasing percentages of HDPE on the thermo-physicomechanical properties of foam geopolymer were investigated. The samples' measured density, compressive strength, and thermal conductivity at 0.25% and 0.50% HDPE content was 1593.96 kg/m3 and 1479.06 kg/m3, 12.67 MPa and 7.89 MPa, and 0.352 W/mK and 0.373 W/mK, respectively. Obtained results are comparable to structural and insulating lightweight concretes with a density of less than 1600 kg/m3, compressive strength of greater than 3.5 MPa, and thermal conductivity of less than 0.75 W/mK. Thus, this research concluded that the developed foam geopolymers from recycled HDPE plastics could be a sustainable alternative material and be optimized in the building and construction industry.

Foaming processes and properties of geopolymer foam concrete: Effect of the activator

In this paper, an ambient-cured geopolymer foam concrete (GFC) was produced based on the chemical foaming method, in which the mixed fly ash (FA) and ground granulated blast furnace slag (GGBS) were used as the precursor, water glass was used as the alkaline activator and aluminum powder was used as the foaming agent. The different properties of the alkali solution, including Na2O contents (i.e., from 4% to 7%) and modulus ratios (i.e., from 1.1 to 1.5), were adopted in the mixture design and the resultant properties were compared for investigating their effects. The density, compressive strength, and thermal conductivity of the GFC ranged within 280.8 ∼ 865.8 kg/m3, 1.10 ∼ 8.13 MPa, and 0.088 ∼ 0.20 W/(m × K), respectively. In addition, more attention was paid to the properties of GFC during the foaming process, including the gas generation rates and rheological properties of the geopolymer slurry, which were determinants of the pore characteristics (e.g., porosity, pore size distribution and roundness) and the macroscopic properties of the GFC (e.g., density, compressive strength, and thermal conductivity). The test results indicated that the higher gas generation rate and lower viscosity of the slurry, which were obtained at higher Na2O content and lower modulus ratio, resulted in higher porosity, lower compressive strength, and lower thermal conductivity.

Mechanical and Thermal Insulation Properties of rGFRP Fiber-Reinforced Lightweight Fly-Ash-Slag-Based Geopolymer Mortar

As a lightweight cementitious material for thermal insulation, the mechanical performance of foamed geopolymer is always compromised by its density reduction. In this study, recycled-glass-fiber-reinforced plastic (rGFRP) fiber was used to reinforce the fly ash-slag based foamed geopolymer, and vitrified micro bubbles (VMB) were applied to further decrease the thermal conductivity and modify the resistance of the lightweight mortar against drying shrinkage. The results revealed that the density, compressive strength, and thermal conductivity of the foamed geopolymer with/without VMB decreased with the increase in foaming agent content. By adding 2~6% of rGFRP fiber, the compressive strength was increased by 25~165%, and the drying shrinkage was reduced the most, by 55%. After the addition of 10% of VMB, the density, thermal conductivity, and drying shrinkage of foamed geopolymer mortar were further decreased, with the highest reductions of 8%, 26%, and 64%, respectively, due to the reduced pore volume and increase proportion of closed pores. With 6% of rGFRP fiber and 25% of foaming agent, the lightweight geopolymer mortar had the optimum performance, with compressive strength of 1.343 MPa, thermal conductivity of 0.134 W/(m·K), and drying shrinkage of 0.095%. This study developed a sustainable lightweight mortar with multiple types of industrial by-products, which benefit both the development of thermal insulation materials and reuse of solid wastes.

Influence of the addition of phase change materials on thermal insulation properties of foamed geopolymer structures based on fly ash

The purpose of this study was to analyze the addition of phase-change materials to foamed geopolymer materials. Phase-change materials are compounds, or groups of compounds, that are capable of accumulating, absorbing, and losing energy at the phase transformation temperature. By weight, 5–15% of MikroCaps (MikroCaps, Slovenia), GR42, and PX25 (Rubitherm, Germany) were introduced as phase change materials. Geopolymer materials were produced based on fly ash with the addition of ash microspheres. The geopolymer composites were prepared using hydrogen peroxide, H2O2, Portland cement stabilizer, and a surfactant. The curing process of the geopolymer foams was carried out at 60 °C. The materials produced were tested for physical, mechanical, and thermal properties. The study included an analysis of the base material oxide composition, a particle size analysis of the phase change additives, and a determined the density of the composites and their structure. Thermal properties were studied in the temperature ranges of 0–20 °C, 20–40 °C, and 30–50 °C, while the specific heat was studied between 27.5 and 32.5 °C. The addition of phase-change materials to the geopolymer material increases the specific heat and the compactness of the phase-change material, but these values vary depending on the form of phase-change material used. With the introduction of PCM, it is possible to increase the heat capacity by up to 54% compared to samples without the addition of PCM. The effect phase-change materials have on strength properties also varies, with a reduction observed at low modifier densities. However, adding 10–15% increases strength by up to 30%. The obtained results show the strong potential of using geopolymers containing phase-change material additives within the construction industry. They could be used as insulating materials as they have strong insulating properties and accumulate heat very well.

Slurry rheological behaviors and effects on the pore evolution of fly ash/metakaolin-based geopolymer foams in chemical foaming system with high foam content

Interstitial slurry rheology significantly influences the pore structure of chemically foamed geopolymer foams (GPFs). However, the relationship between these two factors has not been elucidated completely. To achieve a range of slurry rheological properties, different metakaolin/fly ash ratios were used, and a high-foam-content system was realized using a H2O2 solution. The slurry rheological properties, foaming properties, and pore structures of the GPFs were tested to establish the influence mechanism of rheology on bubble behavior and pore structures from the perspective of foaming systems. Moreover, equations describing the relationship between the internal and external bubble pressure, extrusion pressure, and slurry yield stress are discussed from the perspective of a single bubble. Four sequential phases of bubble deformation were identified during the foaming process, namely, bubble nucleation, extrusion, expansion, and solidification. The intrinsic relationship between the interstitial slurry rheology and final pore structure of the GPF established herein will provide essential guidance for designing and synthesizing porous cementitious materials.

Influence of elevated temperatures on the mechanical properties of foamed geopolymer materials

AbstractCurrent research focuses heavily on geopolymer concrete as possible applications for insulation materials. The aim of the research is to test the strength properties of lightweight geopolymer concrete after exposure to high temperatures. Waste material from the Wieczorek mine (Poland) was used to produce the foamed geopolymers. Alkaline activation took place by mixing the mine powder with an aqueous solution of sodium hydroxide combined with an aqueous sodium silicate with a concentration of 10 M. Prepared geopolymer samples after temperature curing at 75 °C for 24 hours in a laboratory dryer, they were seasoned for 28 days, after which the strength properties were determined. Mechanical tests: compressive strength and bending strength were carried out at temperatures: 20 °C, 200 °C, 600 °C, 800 °C, 1100 °C. Research has shown the precursor activation with the presence of hydrogen peroxide enabled the manufacturing of foamed geopolymers. Heating in the temperature range up to 1100 °C influenced, to some extent, the total porosity of the tested foams. The geopolymer foams based on coal gangue present stable mechanical properties in the range up to 800 °C. No sharp mechanical performances decrease or material chipping was observed. Only colour change of heated samples occurred.

Environmental Friendly Manufacturing the Geopolymer Foam from Aluminosilicate Wastes Completely Excluding the Cement

Environmental Friendly Manufacturing the Geopolymer Foam from Aluminosilicate Wastes Completely Excluding the Cement

Thermomechanical properties of environmentally friendly slag-based geopolymer foam composites in different curing conditions

This study investigates the effect of curing temperature and foam/slag ratio on Na2SiO3- and NaOH-activated slag-based geopolymer foam composites (GFC) having thermal insulation properties. In this regard, samples used in the study were produced by adding foam at three different ratios (12.5, 15, and 17.5% by weight of slag) to the slag-based GFC having solutions with two different activator concentrations (7M NaOH and 3M Na2SiO3). Then, these samples were exposed to three different curing temperatures (40, 60, and 22°C). The compressive strength, dry density, unit weight, water absorption, capillarity, apparent porosity, ultrasonic pulse velocity, and thermal conductivity tests were performed on the GFC samples for 1, 3, 7, and 28days. Scanning electron microscopy (SEM) analyses were also conducted to characterize the pore structure and crack development of the GFCs. In addition, XRD analyses were performed on selected series to determine the formed reaction products of GFCs. As a result, it was observed that high curing temperature both improved mechanical strength and physical properties in GFC samples. The highest mechanical strength was obtained in the GFC with a 12.5% foam ratio and curing at 60°C, while the lowest thermal conductivity coefficient was achieved in GFC with a 17.5% foam ratio and cured at 60°C. In general, with the increase of foam ratio in slag-based GFC samples, unit weight, compressive strength, and ultrasonic pulse velocity results decreased, while capillarity, water absorption, and apparent porosity results increased. According to the results, it was seen that slag-based GFCs could be used in the construction of load-bearing and non-load-bearing walls.

Physico-mechanical, thermal insulation and resistance characteristics of diatomite and attapulgite based geopolymer foam concrete: Effect of different curing regimes

This study investigated the physicomechanical, durability and microstructure characteristics of geopolymer foam concrete (GFC) with a unit weight of less than 1500 kg/m3produced using attapulgite and diatomite. In the blends, as the main binder was used 10, 20 and 40% attapulgite instead of ground blast furnace slag (GBFS). In addition, 30, 40 and 50 kg/m3foam were used in the blends. Three alternative curing methods were used on GFC: steam (80 °C), water (∼22 °C), and an oven (80 °C). Thermal curing regimens last 24 h at a temperature of 80 °C. The blends’ porosity ranges from 36.8 to 53.3%, while their levels of water absorption range from 32.5 to 49.4%. Unit weights of hardened GFC samples range from 475 to 1226 kg/m3. On the 28th day, after applying the steam curing to blends with a 30 kg/m3foam dosage, the compressive strength is greater than 5 MPa. After 900 °C heat treatment (elevated temperature effect), a blend with a foam dosage of 30 kg/m3and 40% attapulgite produced compressive strengths of greater than 4 MPa. The blends’ depths of water penetration range from 22.1 to 27.8 mm. The drying shrinkage of the blends was increased by adding more foam and attapulgite. GFC’s thermal conductivity coefficient varies from 0.134 to 0.354 W/m.K. Increasing the attapulgite and foam decreased the thermal conductivity coefficient. Reaction products such as CASH and NASH gels were observed in SEM examinations. As a result, it has been determined that the most suitable results (In terms of physico-mechanical, thermal insulation and strength Properties) can be obtained if steam curing is applied in blends with 20% attapulgite and 30 kg/m3foam dosage.

A novel foam of geopolymer based on ZSM‐5 zeolite fabricated using templating emulsion/chemical foaming method and its application in batch and continuous dye removal systems

AbstractGeopolymers as sustainable and environmentally friendly “green materials,” can be synthesized by utilizing waste material and by‐products. A porous geopolymer foam adsorbent based on ZSM‐5 zeolite was prepared using templating emulsion/chemical foaming method in different conditions and used for removal of low‐concentration dye in batch and continuous systems. The parameters affecting the dye adsorption including temperature, concentration, pH, kinetics, isotherm, and thermodynamics of the process were investigated. The results of the geopolymer foam synthesis showed that thermal pretreatment of the zeolite has a positive effect on the strength and adsorption capacity. Moreover, the increase in sodium silicate more than the stoichiometric reduces the strength and adsorption capacity. The findings obtained from the batch adsorption process showed that the adsorption kinetics of the pseudo‐second‐order model and the adsorption isotherm of the Temkin model is adjusted with the experimental data. Thermodynamic results indicated that the process of dye adsorption with geopolymer foam is exothermic. The results from continuous experiments indicated more compatibility of the adsorption process with the models of Thomas and Bohart–Adams. The maximum adsorption capacity of methylene blue in batch and continuous processes was 9.82 and 8.17 mg/g. The adsorbent reduction was performed successfully by chemical and thermal processes.

Preparation of metakaolin-fly ash cenosphere based geopolymer matrices for passive fire protection

In this paper, fly ash cenosphere (FAC) with spherical and hollow structure has been adopted as a pore-forming agent to prepare low density and high strength geopolymer foams. Serial analyses of physical properties, mineral characterization, and thermostability have been employed to investigate the feasibility of metakaolin (MK)-FAC based geopolymer for passive fire protection. FAC addition not only significantly decreases the dry bulk density and thermal conductivity of geopolymer blocks, but also helps to achieve acceptable compressive strength. Meanwhile, FAC addition into geopolymer matrices has brought obviously negative effects on heat transfer and led to the reaction enthalpy rise under high temperature. Owing to the conversion of the amorphous geopolymer gel at the surface to ceramics and excellent thermal insulation performance, the reverse-side temperatures of the geopolymer specimens with FAC addition from 30 to 90 wt% always maintain at about 260 °C until the end of the fire resistance tests. Although weak reactions between alkali activator and FAC have happened and enhanced the bonding between FAC and geopolymer gels, the improvement in physical properties of the MK-FAC based geopolymers would mainly be attributed to the physical characteristics of the FAC. This study could open opportunities to employ MK-FAC geopolymers as alternatives in the application of thermal insulation and fire protection.

Study of thermomechanical properties of foamed and unfoamed fly ash-based geopolymer using FT Raman spectroscopy and 29Si MAS NMR

• Raman spectroscopy was used to study microstructural changes in foamed and unfarmed fly ash-based geopolymer. • The strength of GP decreases 68 % at 300 °C and 89 % at 600 °C and for GPF 35 % at 300 °C and 95 % at 600 °C. • Qn coordination type of “SiO 4 ” changed when exposed to high temperature. • GPF samples show a higher degree of depolymerisation than the GP samples. The aim of this work is to investigate the influence of exposure to high temperature on the mechanical and microstructural properties of geopolymers (GP) and geopolymer foams (GPF). The GPs were elaborated using fly ash sourced from the Jorf Lasfar power plant in Morocco with the alkaline solution. The samples prepared and cured for 28 days were exposed to high temperatures (300 °C and 600 °C). Compressive strength tests on the prepared samples were carried out before and after heat treatment. X-ray fluorescence (XRF), X-ray diffraction (XRD), FT Raman spectroscopy, Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy ( 29 Si MAS NMR) and scanning electron microscope (SEM) analysis were performed for the characterization of the raw materials and the elaborated GP. The structures of GP and GPF, as well as the microstructural changes observed after heat treatment, were studied using FT Raman spectroscopy and 29 Si MAS NMR. Raman spectroscopy results showed for GP and GPF samples that the bond assigned to Si-O-Si, Si-O-Al or O-Si-O shifted to a lower wavenumber after exposure to high temperatures.

Comparison of thermal conductivity of foamed geopolymers containing phase change materials

The aim of this work was to investigate the effect of Phase Change Materials on the insulation properties - thermal conductivity coefficient [λ], of fabricated foamed geopolymer panels. Phase Change Materials have been widely reported in the public literature, making them increasingly popular in recent times. PCMs have the ability to accumulate heat, which they can absorb or release due to thermal transformation, which contributes to energy efficiency. This paper presents the results of research on geopolymers based on fly ash with the addition of microencapsulated and macroencapsulated phase change materials (PCMs). Geopolymer composites were prepared by adding 0%, 5%, 10% and 15% PCM and the curing process was carried out at 60°C. Three different phase change materials with melting points of 28°C (MicroCapsPCM28 (Slovenia)) and 25°C and 42°C (PX25 and GR42 (Germany), respectively) were used. All the phase change materials used belong to the paraffin group. The obtained composite sheets were subjected to thermal conductivity tests in 3 temperature ranges (0-20°C; 20-40°C; 30-50°C). The paper also presents the density results of the foamed composites investigated, as well as the visual evaluation and the morphology of the porous structure using scanning electron microscopy. As a result of the study, it was found that foamed geopolymer composites without PCM addition have lambda coefficient values of 0.06 - 0.07 [W/m*K], while with the addition of phase change materials 0.07 - 0.085 [W/m*K]. The obtained test results give the potential to use these materials in construction as insulating materials. The use of these substances in building partitions results in the decrease of daily temperature amplitudes inside the building, as well as in the phase shift of the time of release of stored heat.

Synthesis and characterization of geopolymer foams from mineral wastes: application as adsorbent for Cu(II) and Pb(II) ions from aqueous solutions

Synthesis and characterization of geopolymer foams from mineral wastes: application as adsorbent for Cu(II) and Pb(II) ions from aqueous solutions