Geopolymer Foams Research Articles

In-situ formation of geopolymer foams through addition of silica fume: Preparation and sinterability

Recently, the production of clean binding materials without energy consumption and CO2 emission has paid a great attention. In-situ formation of geopolymer foams through addition of silica-fume waste is the main goal of the present study. Moreover, an attempt to study the effect sintering temperature on the prepared geopolymer foams was also conducted. Through geopolymer formation, the silicon impurity in silica fume reacted with the alkali activator and produced hydrogen gas which entrapped inside the structures generating highly porous foams. Geopolymer foams were prepared by alkali activation of metakaolin with partially replacement by 2.5, 5 and 7.5 mass-% silica fume. To study the effect of temperature or sinterability, the prepared geopolymer foams were sintered at 800, 1000 and 1200 °C. Both dried and sintered geopolymers were subjected for assessment by various tools. The physical, microstructural and mechanical properties were investigated. The results revealed that porosity percentage of dried and sintered geopolymers increased with increasing the amount of added silica fume and decreased with increasing sintering temperature. On the other hand, the compressive strength was opposite to the porosity trend. Generally, the best results were for the geopolymer that contains 5% silica fume. The optimum sintering temperature to produce sintered ceramics having good properties was 1000 °C.

Porous Metakaolin Geopolymers with Tailored Thermal Conductivity

In this work, a novel lightweight metakaolin geopolymers were produced by using hydrogen peroxide as foaming agent. The influence of the hydrogen peroxide incorporation content (0.25 – 1.25%) on density, compressive strength and thermal conductivity was evaluated. The experimental results show that the density and compressive strength were decrease with increasing content of hydrogen peroxide. However, the thermal insulating properties of the geopolymer foams were improved with increasing content of foaming agent. Geopolymers exhibiting thermal conductivity as low as 0.172 W/mK and a density of 0.5 g/cm3 were produced, showing the potential of these materials in applications requiring lightweight and low thermal conductivity materials.

Mechanical Properties and Thermal Conductivity of Lightweight Foamed Geopolymer Concretes

Foamed geopolymer concretes have a better performance in the thermal insulation properties compared to normal geopolymer concretes. In this research, lightweight aggregate geopolymer concretes was incorporated with different percentage of foaming agents (hydrogen peroxide). Compressive strength and thermal conductivity were measured. From results obtained, increased H2O2 contents will decrease the strength of lightweight foamed geopolymer concretes. Lightweight aggregate foamed geopolymer concretes (LWAFGC) with foaming agent content of 0.2wt.% obtained the highest strength of 19.601 MPa. Furthermore, Increased of H2O2 contents also will decrease the thermal conductivity of lightweight foamed geopolymer concretes. Lightweight foamed geopolymer concretes with 2wt.% H2O2 gave the good thermal insulating behavior when the thermal conductivity value recorded the lowest value compare to other wt.% of H2O2 content. The thermal conductivity value of lightweight foamed geopolymer concretes with 2wt.% of H2O2 was 0.072 W/m. K while, the thermal conductivity of other mixtures ranged between 0.077 W/m. K to 0.087 W/m. K., respectively.

Crystallization behavior and mechanical properties of high open porosity dolomite hollow microspheres filled hybrid geopolymer foams

A novel kind of hybrid geopolymer cellular composite foam (DM/KGP) with multi-scale pores was produced by adding dolomite hollow microspheres into geopolymeric matrix via hydrogen peroxide. Effects of the dolomite type, foaming agent (H2O2) and microsphere content, high-temperature treatment on the microstructure, pore structure and mechanical properties of final foams were investigated. The DM/KGPs were composed of amorphous phase. The total and open porosity of samples reached ~88.8 vol% and 82.1 vol%, respectively. Compression strength of the foams decreased with increasing the content of H2O2, while it had the diametric increase when the DMs content increased. After high-temperature treatment, DM/KGPs were converted to DMs/leucite ceramic foams, which also showed good strength (4.49 MPa) and high open porosity (77.0 vol%). This fresh geopolymer foams could have great potential in membrane supports, catalysis and filtration applications.

A physical approach towards controlling the microstructure of metakaolin-based geopolymer foams

Geopolymer foams are promising sustainable lightweight materials combining insulation efficiency with interesting mechanical and fire resistance properties. Controlling their pore size remains challenging because intrinsic foam aging processes act before hardening. We highlight a physical approach to counteracting aging processes in fresh geopolymer foams and to maintaining the pore morphology that has been set initially by mixing metakaolin suspension with precursor aqueous foam. More precisely, it is shown that arrest of foam aging can be achieved if solid particle concentration in the suspension is larger than a critical value which is proved to depend on both bubble size and gas volume fraction. This behavior is understood through the jamming transition occurring for the metakaolin suspension when confined in the foam network, providing significant solid elasticity against bubble motions. The general significance of the reported result makes it useful, as a complement to chemical formulation, for designing morphology-controlled geopolymer foams.

Green synthesis of high porosity waste gangue microsphere/geopolymer composite foams via hydrogen peroxide modification

A novel coal gangue microsphere/geopolymer composite foam (CGM/KGP) was firstly synthesized by adding coal gangue microspheres (CGM) into geopolymer foams. Effects of coal gangue microspheres, foaming agent (H2O2) and stabling agent (SDS) on the microstructure, pore structure and mechanical properties of CGM/KGPs were investigated. The CGM/KGPs were composed of amorphous phase with some peaks of microshpheres. CGMs were dispersed and bonded well with the geopolymer matrix. Total and open porosity of M4H5S3 samples reached maximum value of 88.3 vol% and 80.5 vol%, respectively. Compression strength of CGM/KGPs reached the maximum value of 5.70 ± 0.88 MPa for the M4H1S3 sample. The increasing addition of H2O2 led to the decrease strength of pure foams and CGM/KGPs. Moderate surfactant (SDS, 3 wt%) contributed to the formation of homogeneous cell size and porosity in the composite foams. The novel geopolymer composite foams have potential applications in membrane supports, catalysis and filtration fields.

A micromechanical investigation for the effects of pore size and its distribution on geopolymer foam concrete under uniaxial compression

This study investigates the influences of pore-structure and mortar properties on the fracture behaviour of geopolymer foamed concrete. The discrete element method (DEM) is utilised to explicitly describe the internal pore-structure, while the mortar phase is modelled at the micro/meso-scale using a cohesive-frictional model. Numerical tests are conducted on numerous DEM foam concrete specimens with various porosities and pore-size distributions. The numerical results show that the pore-size can have a profound effect on the material’s fracture resistance. A decrease in pore size results in higher compressive strength and this influence is more significant for foam concrete with lower porosity. However, the elastic modulus seems to be less sensitive to the pore size variation. Further looking at the fracture process of the foam concrete at the micro-scale shows a gradual transition contact bonds from compressive to tensile modes, which is triggered by the breakage of contact bonds persisting as the loading continues. The study also demonstrates that the pore size distribution mainly affects the empirical power exponent of Balshin’s equation of compressive strength-porosity relationship, while the mortar properties have a profound influence on the strength of the material at zero porosity.

Development of lightweight insulating building materials from perlite wastes

This paper investigates the development of geopolymer foam boards, using perlite wastes as raw material. This type of lightweight materials combines the geopolymerization technology with the foaming process. The mechanism of foaming is based on the generation of a gas that is retained by the geopolymer matrix in the form of individual or interconnected voids. In this study, the inorganic foaming agent is hydrogen peroxide (H2O2), which is added into the initial paste in different quantities by mechanical stirring. The produced porous materials have effective densities between 408–476.5 kg/m3, thermal conductivities between 0.076–0.095 W/m.K and different type of microstructure, depending on the concentration of the activator and the foaming agent content. To assess the porosity and the size distribution of the voids, image processing techniques were applied on digital images of the samples. According to these results, the synthesized lightweight materials exhibit similar or even better thermal properties than the current concrete porous materials.

Effects of Water on Pore Structure and Thermal Conductivity of Fly Ash-Based Foam Geopolymers

The influence of the water-to-solid ratio (W/S) on the viscosity, pore characteristics, bulk density, compressive strength, and thermal conductivity of foamed fly ash-based geopolymers with thermal conductivity less than 0.065 W/(m·K) was investigated, and their properties and cost analysis were also compared with that of foamed ordinary Portland cement (OPC). When the W/S varied from 0.38 to 0.5, the apparent viscosity of geopolymer paste 15 min after the preparation decreased significantly from 168 Pa·s to 6 Pa·s. The increasing W/S ratio contributed to the rise of the number of microcapillaries (φ < 50 nm) and macrocapillaries (50 nm < φ < 50 μm) but contributed to the decline of artificial air pores (φ > 50 μm). The refinement of pore characteristics lowered the 28 d thermal conductivity of foamed geopolymers from 0.06 W/(m·K) to 0.048 W/(m·K). Although the slight increase of total porosity of foamed geopolymers from 89% to 92% with the increase of the W/S ratio weakened their 28 d compressive strength from 0.75 MPa to 0.45 MPa, this strength still meets the Ordinary Portland Cement (OPC) based Foam Insulation Board standard of JC/T2200-2013 (>0.4 MPa for 0.25 g/cm3). The production cost of foamed geopolymers was slightly higher by 1.1–1.5 times than that of foamed OPC. However, considering the more beneficial effect of environmental load reductions and better mechanical and thermal properties of foamed geopolymers than those of foamed OPC, slightly higher cost would be acceptable for practical application.

Preparation of geopolymer inorganic membrane and purification of pulp-papermaking green liquor

This paper describes a low-cost and highly efficient metakaolin-based geopolymer composite membrane (support + dense layer) at normal pressure and <70 °C. The support was fabricated using geopolymer foam materials and shows a large water flux and good mechanical properties. The dense layer was prepared using a dip-coating process with geopolymer paste on the porous geopolymer support surface. This study explored the influence of the foam agent content on the support membrane microstructure, water flux and compressive strength, and determined that the optimal foam agent content is 1.0 mass%. By adjusting the viscosity of the geopolymer paste in accordance with the water flux and removal rate, the thickness of the dense layer was determined as 500 μm. The composite membrane shows a distribution of pore sizes (approximately 0.09 μm of dense layer), amorphous structure, high permeable water flux (245 kg·m−2·h−1), good interface combination and can be reused. The preliminary ultra-filtration test (0.2 MPa operation pressure) demonstrates that the geopolymer-based composite membrane can effectively treat suspended particles in wastewater and is expected to be applied in the field of wastewater treatment. We then used the composite membrane in the pulp-papermaking green liquor at different temperatures, and it was found that the SS (suspended solids) of the filtrate can be decreased to 3.45 mg/L at 80 °C or to 0.79 mg/L at 30 °C, far below the industrial requirements of green liquor recycling (SS < 20 mg·L−1).

Design of lightweight metakaolin based geopolymer foamed with hydrogen peroxide

Monolithic metakaolin based geopolymer foams were synthetized by direct foaming using hydrogen peroxide (H2O2) as a blowing agent and surfactants to stabilize the resulting gas bubbles. The influence of the H2O2 content and the nature of the surfactant (cationic vs air entraining) have been investigated in the liquid and the solid state. The reaction rate constants for the oxygen produced by the catalytic decomposition of hydrogen peroxide (k = 5.5 × 10−4 and 2.1 × 10−4 s−1 for the air entraining and cationic based geopolymer foams, respectively) are reported for the first time, as calculated from volume expansion data in the liquid state. These constants were found to be independent of the initial H2O2 content. In the solid state, although the physical, mechanical, and microstructural properties of the resulting foams are known to be influenced by the amount of H2O2 in the geopolymer paste, the chemical composition of the surfactant had a startling effect on the morphology and topology of the macroporous network. Indeed, while faceted closed pores form in the cationic based geopolymer, a 3D network of connected pores forms in the air entraining one. As expected therefore, the cationic samples were found to have a much higher compressive strength than the air entrained ones (0.57–5.9 MPa compared with 0.26–4.3 MPa, respectively) for equivalent apparent densities (varying from 0.23 to 1.1 g cm−3).

Fabrication and characterization of thermally-insulating coconut ash-based geopolymer foam

This study aims at synthesizing porous coconut ash (CA)-based geopolymer foam with high thermal insulation property. Sodium hydroxide (NaOH), alumina slag (AS) and water contents as the main parameters, which affect the performance hardened CA, have been studied. The porosity was developed by hydrogen gas resulted from the interaction of Al metal, in AS, with NaOH. The compressive strength, bulk density, porosity and thermal conductivity were evaluated. The results proved that the AS has a potential impact on the reduction of thermal conductivity of CA-based geopolymer foam by creation of high porous system. Open celled hardened CA-based geopolymer with high porosity (∼87%), low thermal conductivity (∼0.045 W/m·K), compressive strength (1.3 MPa) and bulk density (∼0.60 g/cm3) was obtained when 7% AS (by weight of CA powder) and water to CA powder ratio of 0.4 were used.

Quasi-Static Mechanical Characterization of Lightweight Fly Ash-Based Geopolymer Foams

This paper investigates the compressive and flexural behavior of a closed-cell fly ash-based geopolymer foam with a density of 240 kg/m3. The influence of loading speed (0.1, 10, 100, 250 and 500 mm/min) and anisotropy (in-plane and out-of-plane directions) on the compressive mechanical properties at room temperature were investigated. Under compressive loads, the stress-strain curves shows a cellular material typical behavior with three different regions: linear-elastic, plateau and densification region. On the other hand, the three-point bending tests were carried out on both un-notched and notched specimens (for fracture toughness determination). In compression, the foam progressively collapsed with a complete destruction of the successive rows of cells, while in the case of bending it exhibited a brittle behavior without plastic deformation, the fracture occurring by the propagation of a single crack.

The Mechanical Properties and Thermal Resistance of Fly Ash Geopolymer Foams

In the present work, a comparative study of the thermal performance of unfoamed and foamed geopolymers was investigated. The geopolymers were prepared by mixing fly ash with alkali activator (a mixture of sodium hydroxide and sodium silicate). The geopolymer foams were prepared by adding hydrogen peroxide (H2O2, 2wt.% and 4wt.%). The geopolymers were cured at room temperature (29°C) for 24 hours and at 60°C for another 24 hours. The bulk density and compressive strength decreased with increasing H2O2 up to 2wt.% and increased when 4wt.% of H2O2 was added. In order to test the thermal resistance, the geopolymers were heated at elevated temperature (200- 1000°C). Unheated geopolymers showed bulk density and compressive strength in the range of 1.6– 1.7g/cm3 and 15–17MPa, respectively. When heated up to 1000°C, the geopolymers could withstand high temperature without any disintegration and spalling. Both unfoamed and foamed geopolymers showed highest compressive strength at 200°C (17–22MPa). Further decreased in compressive strength was observed upon heating up to 800°C (10–17MPa). The compressive strength regained (14–21MPa) when heated up to 1000°C. The compressive strength was even higher than that recorded at room temperature. In the present work, unfoamed geopolymers showed overall higher thermal resistance than foamed geopolymers.

Pore structure analysis and properties evaluations of fly ash-based geopolymer foams by chemical foaming method

In this paper, a new kind of fly ash-based geopolymer foams was prepared by chemical foaming method. The effects of foaming agent, foam stabilizer and foaming temperature on the dry density, fluidity, compressive strength, thermal conductivity and capillary water absorption of the geopolymer foams were studied. The pore structure parameters of geopolymer foams specimens including porosity, pore size distribution, Feret diameter and average roundness, were obtained by ImagePro plus image analysis software. Moreover, the influence of pore structure parameters on the properties of geopolymer foams was analyzed. The morphology and characteristics of pore structure of the geopolymer foams were also observed by shape measurement laser microscope and scanning electron microscope. The dry densities of geopolymer foams could range from 142 kg/m3 to 1021 kg/m3 and the compressive strength could range from 3.2 MPa to 44.81 MPa. The specimens of geopolymer foams possess good pore structure at 3.5% content of H2O2 and 2.85% content of sodium dodecyl sulfate. The dry density, compressive strength and thermal conductivity have a good correlation with the pore structure parameters of geopolymer foams. From the observation of the microscopic tests, the microstructure of geopolymer foams is loose and porous. Besides, the morphology and size of typical pores could be obtained. The microstructure and morphology characteristics could be well explained the macroscopic properties of the geopolymer foams.

Fabrication of hollow microspheres filled fly ash based foam geopolymers with ultra-low thermal conductivity and relative high strength

Fabrication of lightweight inorganic thermal insulation materials with high strength and ultra-low thermal conductivity is a great challenge and is receiving growing attention worldwide. Herein, a kind of geopolymer based materials with excellent performance were successfully fabricated by simultaneous incorporation of air foams and hollow microspheres in geopolymer matrix. Mechanical strength, bulk density, and thermal conductivity, were conducted as the key performance indexes for the evaluation of prepared samples in this study. On the other hand, materials foam structures, in terms of porosity, pore diameter, and through-hole rate, were analyzed by means of “image-fitting” method in this work. Compared to pure foamed geopolymer specimen (P-series), hollow microspheres filled foam geopolymers (H-series) behaved much better performance in strength and thermal insulation properties in same density levels. The optimal performances in terms of density versus compressive strength and thermal conductivity are as follows: (300 kg/m3 vs. 2.84 MPa vs. 0.0711 W/(m·K)), (250 kg/m3 vs. 1.57 MPa vs. 0.05509 W/(m·K)), and (200 kg/m3 vs. 1.06 MPa vs. 0.05223 W/(m·K)). The incorporation of hollow microspheres lead to the much thicker foam walls of H-series sample than P-series, which is regarded as the key reason of its highly improved performance.

Effect of calcium stearate based foam stabilizer on pore characteristics and thermal conductivity of geopolymer foam material

Foam stabilizer plays a crucial role in the synthesis of geopolymer foam materials (GFMs). To better clarify the effects of calcium stearate based foam stabilizer (CSFS) on pore characteristics and thermal conductivity of materials, GFMs prepared with 0–2% CSFS were investigated for foam characterization, compressive strength, bulk density, geopolymerization products, pore distribution, and thermal conductivity. Results shows that (1) the foam time and initial setting time match optimally with 1.0% CSFS content. And at this point, the foam time and foam volume of GFMs were increased obviously by 42.8% and 28.6% respectively. (2) 28 d compressive strength of GFMs with a bulk density of 0.31 g/cm3 at 1.0% CSFS content were the lowest, 1.45 MPa, but still better than the standard of 1.0 MPa for 0.325 g/cm3 according to the Chinese National Standards GB11968-2006. (3) CSFS displayed limited effect on the quantity or type of geopolymerized products. (4) With CSFS/FA increasing from 0.5% to 2.0%, The quantity of macroscopic scale pores sized 10–100 µm rose considerably and then drop obviously, but still more than that of sample with free CSFS. The quantity of microscopic scale pores sized 10–100 nm grew stably. (5) Overall, 1.0% CSFS optimized pore characterization well with a largest porosity, 82%, where the thermal conductivity of GFMs reached a bottom point at 0.095 W/(m K). (6) The relationship between thermal conductivity and total porosity conforms to a Maxwell-Euchen or modified Cheng-Vachon model and the value of parameter t is determined as 1.1.

Research of Geopolymer Foam Concrete on the Base of the Wastes Produced By Kemerovo Heat and Power Enterprises

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Sustainable one-part geopolymer foams with glass fines versus sand as aggregates

The ever increasing demand for high-quality river sand in construction, which poses economic and environmental concerns, highlights the necessity for finding suitable alternatives. Waste glass has a very low impact tolerance, which makes it very easy to grind and use as a fine aggregate in the construction of lightweight building elements. In this study, glass fines are used as a replacement for fine sand in manufacturing geopolymer foams. The thermal and mechanical properties of the two systems with different densities are investigated and compared with a control sample of geopolymer foam with no aggregates. The geopolymer paste with sand aggregates has a density that was approximately 100 kg/m3 higher than the paste with glass aggregates. The heavier samples with sand aggregates required a higher degree of foaming to drop the density to a similar range, which negatively affects their strength. For a density of 1000 kg/m3, the geopolymer foams with glass aggregates are 25% stronger than the foams with sand aggregates. The strength improves further by 31% and 77% as the density drops down to 800 kg/m3 and 600 kg/m3, respectively. The shape of the bubbles in geopolymer foams with glass aggregates is more regular with less interconnectivity between pores, especially at lower densities. This pore characteristic enhances the insulation capacity of lightweight foams with glass aggregates where thermal conductivity of 0.15 W/mK was achieved in the sample with 600 kg/m3 density.

Preparation, characterization, and determination of mechanical and thermal stability of natural zeolite-based foamed geopolymers

This study is the first attempt to evaluate the effect of two foaming agents, aluminum powder and hydrogen peroxide (30 wt% water solution) on zeolite-based geopolymers and their possible use as building material according to Ecuadorian technical standards. These foamed geopolymers were prepared by alkali activation of an Ecuadorian natural zeolitic tuff and by alkali activation using NaOH (10 M), Ca(OH)2 and Na4Si5O12, with the use of two different foaming agents mentioned. In the case of aluminum powder, the experimental range was between 0.05 and 0.25 wt%; on the other hand, the percentages of hydrogen peroxide ranged from 0.5 to 4.0%. For characterization of the foamed geopolymer samples, quantitative X-ray diffraction (QXRD), thermogravimetric (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) techniques were used. The results of both foaming agents in zeolite-based geopolymers met Ecuadorian technical standards NTE INEN 643 and NTE INEN 638; nevertheless, the use of aluminum powder as foaming agent exhibited a better pore size distribution, suggesting a better performance. On the basis of these results, foamed geopolymers are suitable construction materials for the application of manufactured for masonry wall in houses.