Geopolymer Samples Research Articles

The Effects of Solid to Liquid Ratio on Fly Ash Based Lightweight Geopolymer

Geopolymer material was used as the raw material because it promotes the green technology. In this study, lightweight geopolymer was produced using fly ash as raw material with the addition of alkali activation which is mixture of sodium silicate and sodium hydroxide, foaming agent that gives lightweight properties and finally, underwent curing process. The molarity of sodium hydroxide (NaOH) used was fixed at 12 M while the ratio of fly ash to alkali activator (solid to liquid) used were varied in the range of 2.0, 2.5, 3.0 and 3.5, by mass. Besides that, foaming agent (Polyoxyethylene alkyether Sulfate) was added to the geopolymer sample to give the lightweight properties. The samples were cured at 80 °C for 24 hours in the oven for curing process and left at room temperature prior for testing for 14 days. The testing of sample was conducted in this study which includes density test, compression strength test, water absorption test and scanning electron microstructure (SEM) test. The results obtained for optimum solid to liquid ratio is 2.5, by mass with the optimum value of compressive strength density value. The mechanical and physical properties of lightweight geopolymer were based on the ASTM International Standard.

Effect of water on the thermal properties of argillite – based geopolymers.

This study focuses on the effect of consolidation time and water immersion on the thermal behavior of geopolymers based on mixture of kaolin and argillite calcined at 750 °C. In order to assess the fire resistance water and thermal treatment at 1000 °C were performed. Compressive strength and structural changes of the samples before and after treatment were investigated. It was demonstrated that the age of geopolymer (7, 14 and 28 days of consolidation) does not have a significant effect on strength neither before (22 MPa) nor after (30 MPa) thermal treatment. The results also show that all samples present higher compressive strength ratio (σafter/σbefore ~ 1.4). The geopolymer samples do not exhibit structural variation over the time in agreement with the compressive strength values. The good performance of compressive strength after 1000 °C was due to the formation of the same crystalline phases after heat treatment such as zeolite (4%) and leucite type phases (62%) and wollastonite (18%) which were also evidenced by SEM observations. The decrease of compressive strength after water immersion (16 MPa) and after thermal treatment (19 MPa) was explained by the decrease of arcanite by 70% as well as the amorphous phase content. Nevertheless, leucite (46%) and wollastonite (24%) were formed. In conclusion, the use of mixture of kaolin and argillite calcined at 750 °C leads to water and thermal resistant geopolymers.

The Effect of Seawater on The Strength, Microstructure and Elemental Distribution of Fly Ash/ Kaolin Based Underwater Geopolymer

Concrete in seawater is subjected to various aggressive constituents in seawater commonly sulphate, chloride and carbonate. This paper investigates the potential effects towards mechanical and physical properties of geopolymer when used as underwater concreting material. Besides identifying the microstructure using Scanning Electron Microscopy (SEM), the sample is also characterized using Synchrotron based micro X-Ray Fluorescence (µ-XRF) to identify the elemental distribution that had occurred in the underwater geopolymer. Other essential properties for concrete such as compressive strength, water absorption and density were also determined. The compressive strength result indicates a slightly lower strength for underwater geopolymer (31.40 MPa) compared to normal geopolymer (35.91 MPa). Relevant to the strength, the water absorption and density also shows a slight difference between the geopolymer samples. The µ-XRF analysis shows the presence of chlorine (Cl) element only for underwater geopolymer which indicates that the are chloride penetration for underwater geopolymer. Additionally, other element distribution such as Silica (Si), Aluminum (Al) and Calcium (Ca) shows a different value when comparing normal geopolymer and underwater geopolymer. Despite the difference in elemental distribution between sample, geopolymer is proven to have the potential to be used as underwater material since it is able to retain at least 70% strength of the control sample.

Physical properties and microstructure of nickel slag/metakaolin-based geopolymer with different contents of nickel slag

Geopolymer pastes based on nickel slag/metakaolin (NS/MK) were prepared and their physical properties and microstructure as a function of NS content were studied. The results showed that the addition of NS in an appropriate proportion not only enhanced the compressive strength but also led to volume-expansive behaviour of the hardened pastes. Analysis of the pore size distribution indicated that increasing the NS content reduced the total pore volume and increased the average pore size. The silicate species dissolved from the NS participated in the geopolymerisation and influenced the mineralogical composition and microstructure of the gel phase. The addition of NS had no detrimental effect on the concentrations of alkali metals and pH of the leaching solution obtained from the geopolymer samples. In addition, the addition of NS had no detrimental effect on the dissolution behaviour of MK. This work presents a further step in the development of alternative ‘low-carbon’ binders for the construction industry.

Atomic-structure, microstructure and mechanical properties of glass powder modified metakaolin-based geopolymer

This objective of this study is to utilize recycled glass powder as a partial replacement precursor of the metakaolin-based geopolymer to develop a sustainable geopolymer material. Four glass powder replacement ratios were selected for the metakaolin-based geopolymer preparation (0%, 5%, 10%, and 20% by the total precursor weight). The pair distribution function (PDF) analysis indicated that a higher amount of the four-membered ring structures in the formed gel with the added glass powder. Both PDF and EDX analysis showed that the Si/Al ratio of the binder phase increased with glass powder content in the mixtures. The added glass powder can improve the workability of the geopolymer binder and prolong the setting time of the synthesized geopolymer samples. The nanoindentation test results showed that the elastic modulus of the formed gel increased with replaced 10% and 20% glass powder. In addition, the samples with 5% of glass powder achieved the highest compressive strength among tested samples. The test results indicated that the appropriate glass powder replacement can affect the geopolymerization process and modify the formed gels in the metakaolin-based geopolymer to improve the mechanical properties of the mixture. The information obtained in this study can promote the utilization of waste glass powder as a partial replacement of the precursor for the production of sustainable alkali-activated materials.

Influence of the Kaolinite Calcination Conditions on the Compressive Strength of Geopolymer

Among the cementitious materials, geopolymers not only attract interest due to the low emission of CO2 in their manufacturing process, but also because of their good mechanical and chemical properties, together with their resistance to fire. They can be made from different raw materials including various wastes from industrial activities and mineral extraction. In this study, metakaolin was obtained from kaolinite calcined under different conditions. In this case kaolinite is a by-product of sand extraction. It was observed that the calcination conditions (kiln heating rate, calcination time and temperature) had a strong influence on the compressive strength of geopolymer after 28 days of cure. They also affected the composition of the geopolymer, which was prepared by mixing metakaolin, alkaline sodium silicate and sodium hydroxide solution.Compressivestrengthsintherangefrom10MPato50MPamaybeobserved, depending on the combination of these factors. A factorial design of experiments allowed the isolation of the effect of each factor and its interactions, offering new insights into the complexity of the geopolymeric reactions and highlighting the need for a rigid control of the calcination conditions of kaolinite and the composition of the geopolymer samples to obtain the desired compressive strength.
 Keywords: kaolinite, calcination, metakaolin, geopolymer, compressive strength.

Evaluation of the 12–24 mm basalt fibers and boron waste on reinforced metakaolin-based geopolymer

Concerning sustainability and recycling considerations, geopolymers have recently raised as one of the most active alternatives to the current cement-based composites, in addition to that, the existence of fibers in any binding matrix yields a significant improvement in the behavior of the matrix. On the other hand, using waste materials in the binding matrices fulfills one of the main aims of sustainability, namely reusing wastes. In this concern, the previous research attempts focused on the effect of using fibers and wastes separately and hence using them together in one matrix is not clearly highlighted. The main objective of this study was to examine the engineering properties of metakaolin-based geopolymer mortars in the case of colemanite substitution up to 30% and basalt fiber of different lengths. In the 10 series produced, firstly 7th day and 28th day compressive and flexural strengths, UPV, abrasion resistance test, porosity, unit weight, and water absorption results were examined. As the durability tests, 90 cycles of freezing-thawing between −20 and +20 °C, high-temperature tests of 250, 500 and 750 °C were applied. Also, geopolymer samples were exposed to 10% Hydrosulfuric Acid (H2SO4) for 3 months. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Thermogravimetric/Differential Thermal Analysis (TGA-DTA) analyses were performed at the end of the durability tests. The results showed that in the case of 10% colemanite substitution, it increased the compressive strength results and lowered it at higher rates. With a colemanite substitution of 10%, the compressive strength results of 28 days increased by 1.71%, and in the case of 20% and 30% colemanite substitution, there was a decrease in the compressive strength of 13.64% and 26.99%, respectively. The compressive strength results showed that 24 mm long basalt fiber reinforced samples had better results than 12 mm long basalt fiber reinforced samples. It was seen that geopolymer specimens maintain stability in freezing-thawing, elevated temperatures, and sulfuric acid effects.

Production of lightweight geopolymer concrete

Lightweight concrete has been known all around the world for decades. As a masonry material, there is an advantage: it has sufficient mechanical strength despite of its light weight. This research focuses on the production of recycled concrete based lightweight geopolymer concrete samples using glass foam aggregates. During the research geopolymer and concrete samples were made and finally their properties were investigated and compared. In the research work an alkaline silicate reaction (ASR) was also studied on the glass foam lightweight aggregates, which is very important for concrete failure. Material structural and morphological tests were obtained by scanning electron microscopy (SEM) to characterize the geopolymer concrete samples. Compressive strength of lightweight concrete and lightweight geopolymer was determined at the age of 7 days. Glass foam is suitable for use as a lightweight aggregates for workability. Based on the 7 days compressive strength results no crust typical of the ASR reaction was detected on the surface of the mixtures.

The study of ecological impact of fly ash-based geopolymer binders on soil and aquatic biota

Coal power plants represent the large source of environmental pollution in soils, ground and surface water by leaching out toxic compounds from open landfilled and impounded coal combustion residuals (CCR) such as fly ash. The use of fly ash as a main component in geopolymer binder (GB) systems is one of the effective methods of CCR beneficial utilization. The toxicity assessment as well as leachability of harden geopolymers were tested in aqueous media where oat seeds were used as affected test objects. Bio-resistance of the developed geopolymers was evaluated by the resistance to mold fungi growth. The developed geopolymers demonstrated a very low toxicity and leachability to the biota based on the low effect to germinating ability and growth retardation of the exposed oat seeds. Therefore, the studied fly ash products were proved to be environmentally safe when used in GB systems. The absence of fungi growth observed on the surface of geopolymer samples demonstrates high bio-resistance.

Geopolymer Synthesis with Low Sodium Hydroxide Concentration

In this study, fly ash was utilized to synthesize geopolymer by activating with 4 M sodium hydroxide. Samples were cured at 120 °C for 6, 15 and 24 h, and they were aged for 7, 28 and 90 days. The degree of reaction was determined, and leaching tests were performed on all geopolymer samples according to US EPA TCLP method. The microstructural properties of samples were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscope (SEM) techniques. Increase in both curing and aging durations resulted in higher compressive strength values. The results of leaching tests indicated that the metals were successfully immobilized. The major bonds of geopolymers were observed in FTIR spectrum. The intensity of the Al–O and Si–O asymmetric bonds increased with increase in curing duration. In XRD diffractograms, it was observed that all of the geopolymer samples had amorphous structure containing mainly two crystal phases. FTIR, XRD and SEM results revealed that geopolymerization was achieved in these synthesis conditions despite low molarity.

Evaluation of the Antibacterial Activity of a Geopolymer Mortar Based on Metakaolin Supplemented with TiO2 and CuO Particles Using Glass Waste as Fine Aggregate

Metakaolin-based geopolymer cements were produced by alkaline activation with a potassium hydroxide and potassium silicate solution. To produce the geopolymer composites, 10 wt.% titanium oxide (TiO2) and 5 wt.% copper oxide (CuO) nanoparticles were used. The geopolymer mortar was prepared using glass waste as fine aggregate. The raw materials and materials produced were characterized by X-ray diffraction, electron microscopy, and Fourier-transform infrared spectroscopy techniques. Likewise, the geopolymer samples were characterized to determine their physical properties, including their density, porosity, and absorption. The photocatalytic activity of the materials was evaluated by activating the nanoparticles in a chamber with UV–Vis light during 24 h; then, different tests were performed to determine the growth inhibition of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa bacteria in nutrient agar for times of up to 24 h. The study results showed that a geopolymer mortar containing glass waste as fine aggregate (GP-G) exhibited a water absorption 56.73% lower than that of the reference geopolymer paste without glass (GP). Likewise, glass particles allowed the material to have a smoother and more homogeneous surface. The pore volume and density of the GP-G were 37.97% lower and 40.36% higher, respectively, than those of the GP. The study with bacteria showed that, after 24 h in the culture media, the GP-G mortars exhibited a high inhibition capacity for the growth of P. aeruginosa from solutions of 10−4 mL and in solutions of 10−6 mL for E. coli and S. aureus. These results indicate the possibility of generating antibacterial surfaces by applying geopolymer composite.

Development of precast geopolymer concrete via oven and microwave radiation curing with an environmental assessment

Geopolymer is identified as a type of promising alternative binder to Portland cement due to its sustainability and excellent properties. This paper investigated the influence of two types of curing regimes (i.e. oven and microwave radiation curing) on the compressive strengths of geopolymer samples, facilitated by scanning electron microscope analysis, which was adopted in the interpretation of strength results. Besides, a comparative life cycle assessment based on Europe was conducted between geopolymer and Portland cement samples with details. Results indicate that it took less time to prepare precast geopolymer concrete with desired strengths using microwave radiation than oven curing. Meanwhile, the source of PFA would greatly influence the strength development of geopolymer samples. Finally, the preparations of geopolymer samples presents lower environmental burdens and CO2 emissions than Portland cement samples, however, the quality and availability of PFA and GGBS in UK led to a re-evaluation of the environmental impacts and strengths of the precast geopolymer concrete in the near future.

Alkali Activation of Waste Clay Bricks: Influence of The Silica Modulus, SiO2/Na2O, H2O/Na2O Molar Ratio, and Liquid/Solid Ratio.

This study was conducted to investigate the influence of various reaction conditions, namely the silica modulus SiO2/Na2O, H2O/Na2O molar ratio, and liquid/solid ratio on the geopolymerization reaction of the waste fired clay bricks (Grog). The starting raw material and the generated geopolymer specimens produced by different geopolymerization reaction conditions have been characterized using different techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal analysis. Furthermore, physico–mechanical characterization has been carried out through the determination of bulk density, porosity, water absorption, and compressive strength for each sample at interval curing times of up to 28 days. The results indicated that the geopolymerization system of the waste fired clay bricks is influenced by the investigated reaction conditions at room temperature. The compressive strength of the geopolymer sample produced at optimum conditions increased significantly by up to 37.5 MPa, in comparison with 4.5 MPa for other conditions. Finally, an optimum recommendation and useful conclusions concerning the recycling and utilization of this waste material through the geopolymerization process are made for compatibility with construction applications.

Effect of red mud proportion on the strength and microstructure of ferrosialate based geopolymer mortar

This paper studies the effect of various red mud proportions on the strength and microstructural changes in theferrosialate geopolymer mortar. The optimum percentage of red mud (RM) has to be found with respect to the molarity ofSodium hydroxide (NaOH) to maintain the suitable alkalinity of the mixture for maximum strength gain. This percentagehas been found to be between 20 and 30% RM proportions. From XRD micrographs, it has been found that the crystallinitypercentage increased with the increase in red mud content. For oven-cured samples, SEM images showed that, till the redmud replacement reaches 20%, any increase in the red mud leads to denser microstructure and a decrease in intensity ofunreactive particles. Beyond that, samples displayed a higher number of undissolved phases. Whereas, for ambientcuringspecimens, this limit is found to be 30%. Synergy has to be found among the red mud content, curing type and curingtemperature for optimum results. Ferrosialate geopolymer samples has shown 53.34% higher maximum compressivestrength than sialate geopolymer samples. The oxide ratios of SiO2/Al2O3 = 4.0 to 4.3, Na2O/SiO2 = 0.15 to 0.17 andFe2O3/Al2O3 = 0.27 to 0.37 have found to be limits for favouring maximum strength gain.

Comparative Study on Geopolymer Binders Based on Two Alkaline Solutions (NaOH and KOH)

This study specifically investigated the influence of the composition of aluminosilicate material i.e. the substitution of metakaolin by rice husk ash and the nature of alkaline activators (Na+/K+) on mineralogical, structural, physical and mechanical properties of geopolymer binders. This influence was evaluated based on X-ray diffraction (XRD), Fourier Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscope (SEM analyses, apparent density, water accessible porosity, compressive strength and thermal properties. Two types of geopolymer binder were synthesized according to the type of alkali activator used, the NaOH-based geopolymer and the KOH-based geopolymer. The results of characterization performed after 14 days of curing of geopolymer samples showed that the activation of the aluminosilicate powder using alkaline solution led to change in their microstructure. The highest compressive strength was obtained with the NaOH-based geopolymer.

Structural and electrical properties of geopolymer materials based on different precursors (kaolin, bentonite and diatomite)

Geopolymers (GP) were successfully synthesized from metabentonite (MB), metadiatomite (MD) and metakaolinite (MK). Characterization of their phase structure and microstructure was performed by XRD, FTIR, SEM/EDX methods. A SEM micrograph of GPMD shows a homogeneous surface with some longitudinal cavities in the gel, and it is significantly different from the micrographs of the other two geopolymer samples, GPMB and GPMK. A considerable amount of unreacted particles, as well as the presence of pores in the geopolymer matrix of GPMK and GPMD, indicate an incomplete reaction in the system. Aluminosilicate inorganic polymers, geopolymers, are quasi solid electrolytes which possess a high electrical conductivity at room temperature in relation to materials of similar chemical composition. The highest conductivity was found for the sample obtained from GPMK, amounting to 2.14 × 10–2 Ω–1cm–1at 700 ºC. The corresponding activation energies of conductivity for this sample amounted to 0.33 eV in the temperature range of 500–700 ºC. The geopolymer synthesized from metakaolin has good ionic conductivity values, which recommends it for use as an alternative material for an SOFC (Solid Oxide Fuel Cell).

Elevated temperature, freezing-thawing and wetting-drying effects on polypropylene fiber reinforced metakaolin based geopolymer composites

In this study, metakaolin-based geopolymer samples produced by substitution of silica fume and colemanite waste up to 20% were subjected to high-temperature effects at 300, 600, 900 °C, the wetting-drying effect of 5, 15 and 25 cycles and freezing-thawing effect of 56 and 300 cycles. At the end of the tests, compressive and flexural strengths, ultrasonic pulse velocity and weight changes’ results were examined. In addition to these, micro-computed tomography (CT), XRD and SEM analyses were performed to examine the microstructure properties as well as visual inspection. 5 series produced for high temperature and wetting-drying effects were also produced with polypropylene fiber. It has been observed that samples exposed to 900 °C maintained their stability. Polypropylene fiber has been shown to increase the samples’ flexural strength results compared to the non-fiber samples after exposing to high temperatures. For the freezing-thawing effect, air-entraining admixture was added to 5 series. An increase for compressive strength was seen after 56 cycles but a decrease was seen after 300 cycles. The geopolymer samples thus began to suffer the real distortion effect in subsequent cycles after the freezing-thawing effect, which contributed to geopolimerization in a sense occurring in the first 56 cycles. During the wetting-drying cycles, fluctuations were observed in the results and an increase in the compressive strength, UPV and weight changes’ results after 5 cycles, a decrease in the results after 15 cycles and an increase again in the results after 25 cycles were seen.

Effects of Microwave Energy on Fast Compressive Strength Development of Coal Bottom Ash-Based Geopolymers

Microwave energy has been shown to be effective for geopolymer synthesis due to its fast and penetrative heating characteristics; however, the changes in the physicochemical properties of the geopolymer, resulting from the microwave irradiation, have not been fully elucidated. Therefore, this study is aimed at investigating the effect of the microwaving on the properties of coal bottom ash(CBA) geopolymers. We prepared geopolymer samples by casting a mixture of ground CBA and 14 M NaOH solution against cubic molds with a hand press machine, followed by pre-curing in a dry oven at 75 °C for 24 h and microwaving under various powers and durations. The compressive strength strongly depended on the moisture content, i.e., the strength increased from 21 to 65 MPa or higher as the moisture content decreased to critical values, after which the strength began to decrease. The results showed that microwave energy stimulated an additional geopolymerization by evaporating the redundant free water. This led to the strength gain, although the over-irradiation generated a high internal stress and poor structural integrity, which resulted in the strength loss. Therefore, the appropriate application of microwave energy is a promising option for synthesizing high-strength geopolymers in a cost- and time-effective manner.

Mechanical, microstructural and structural investigation of phosphate-based geopolymers with respect to P/Al molar ratio

The purpose of this work is to study the effect of P/Al molar ratio on the mechanical properties, microstructure and structure of phosphate-based geopolymers. Brazilian tests were made in order to identify the optimal P/Al molar ratio. The mechanical behavior of different samples showed a ductile behavior for P/Al molar ratio equal to 2 and a fragile one for other samples. A dense structure was observed for geopolymers that presented a fragile behavior and a bubble structure was observed for geopolymers that displayed a ductile behavior. For the structural study, different techniques were used: atomic absorption measurements, X-ray Powder Diffraction (XRD), 29Si, 27Al and 31P Magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier Transform Infrared spectroscopy (FTIR). These techniques revealed that the geopolymer sample obtained with deficiency of acid presents an amorphous composite material composed of a geopolymeric network based on Al–O–P units and another one based on Si–O–Al–O–P units. The geopolymer sample obtained with the optimum quantity of acid also revealed an amorphous composite material. However, it does not present only these two geopolymeric networks, but also some Si–O–P units in the terminal chains of Si layer. The geopolymer sample obtained with excess of acid revealed a gel based almost on a crystalline phase of Aluminum Phosphate Silicate Hydrate compound and some amorphous geopolymeric networks.

Mechanical property, nanopore structure and drying shrinkage of metakaolin-based geopolymer with waste glass powder

This paper investigates the mechanical properties, nanopore structure and drying shrinkage behavior of the metakaolin-based geopolymer mixtures containing 0%–20% waste glass powder. The prepared samples were cured under ambient temperature and high temperature (60 °C), respectively. The mechanical properties of the samples can be improved by introducing the low content of glass powder (5%–10%). Microstructure and nanopore structure analysis indicated that a denser gel phase was formed in the glass powder modified geopolymer samples. The added glass powder reduced the water loss rate of the samples under drying condition, leading to a reduction of drying shrinkage at early ages. The capillary stress in the prepared geopolymer samples was analyzed based on the pore size distribution of the mixtures. The magnitude of capillary stress generated in glass powder containing samples was similar to that of geopolymers without glass powder. The improved creep modulus with added glass powder facilitated the reduction of the shrinkage of the samples at later ages. This study can facilitate the recycling of waste glass into geopolymer for sustainable construction applications.