Geopolymer Preparation Research Articles

Statistical Methods for Modeling the Compressive Strength of Geopolymer Mortar.

In recent years, geopolymer has been developed as an alternative to Portland cement (PC) because of the significant carbon dioxide emissions produced by the cement manufacturing industry. A wide range of source binder materials has been used to prepare geopolymers; however, fly ash (FA) is the most used binder material for creating geopolymer concrete due to its low cost, wide availability, and increased potential for geopolymer preparation. In this paper, 247 experimental datasets were obtained from the literature to develop multiscale models to predict fly-ash-based geopolymer mortar compressive strength (CS). In the modeling process, thirteen different input model parameters were considered to estimate the CS of fly-ash-based geopolymer mortar. The collected data contained various mix proportions and different curing ages (1 to 28 days), as well as different curing temperatures. The CS of all types of cementitious composites, including geopolymer mortars, is one of the most important properties; thus, developing a credible model for forecasting CS has become a priority. Therefore, in this study, three different models, namely, linear regression (LR), multinominal logistic regression (MLR), and nonlinear regression (NLR) were developed to predict the CS of geopolymer mortar. The proposed models were then evaluated using different statistical assessments, including the coefficient of determination (R2), root mean squared error (RMSE), scatter index (SI), objective function value (OBJ), and mean absolute error (MAE). It was found that the NLR model performed better than the LR and MLR models. For the NLR model, R2, RMSE, SI, and OBJ were 0.933, 4.294 MPa, 0.138, 4.209, respectively. The SI value of NLR was 44 and 41% lower than the LR and MLR models’ SI values, respectively. From the sensitivity analysis result, the most effective parameters for predicting CS of geopolymer mortar were the SiO2 percentage of the FA and the alkaline liquid-to-binder ratio of the mixture.

A review on the porous geopolymer preparation for structural and functional materials applications

AbstractGeopolymer (also called inorganic polymers) is a kind of amorphous gel material with a 3D structure consisting of SiO4 and AlO4 tetrahedra. It has drawn international attention due to its environmental friendliness and excellent performance. This review covers raw materials, preparation methods, and applications of porous geopolymer materials with micropore, mesopore, or macropore. The preparation methods can be divided into five categories: (i) self‐forming method, (ii) direct foaming method, (iii) adding filler method, (iv) particles stacking method, and (v) other methods. In this paper, different raw materials and applications were combined with the preparation methods, and some general conclusions of porous geopolymer were summarized. The applications of porous geopolymer materials in building materials, adsorbents, porous ceramics, membrane separation, catalyst, pH regulator, and other fields were introduced as well.

The use of limestone sludge for the geopolymer preparation

The study investigates the effect of sludge waste from mining and washing of limestone on the properties of geopolymer binders based on metakaolin and blast furnace slag. The effect of adding two types of limestone sludge on workability, setting time, compressive strengths, durability and pore distribution was investigated. Limestone sludge was dosed in an amount of 0–30 %. Sodium water glass was used as an alkaline activator in the ratio of 5:4. A linear correlation between the flowability and limestone sludge content was observed, and very satisfactory results of compressive strength after 90 days were obtained for samples with sodium water glass (about 55 MPa). The positive effect of CaCO3 on strength was confirmed. The increased content of clay components resulted in a reduction of compressive strength.

A review on developments of environmentally friendly geopolymer technology

This study aims to present an overview of the progress of geopolymer composites with regards to the latest developments on its constituents (binders, activators, and aggregates) and manufacturing techniques. Some ecological, economic, and industrial limitations of the traditional aluminosilicate binders yield to the pursuit of alternative ones over the period. Some of these latest binders e.g. ferrochrome ash, mine tailings, rice husk ash, red mud, have been highlighted in this paper. Current advances on replacement of natural fine and coarse aggregates such as mine tailings (iron ore tailings), recycled/lightweight aggregates for geopolymer preparation have been reviewed from the past literature. The paper also focuses on developments regarding the new class of green alkaline and acidic activators, which is traditionally considered to be the binding agent in the preparation of geopolymer composites. Different geopolymer production methods have been briefly discussed to study their effectiveness in achieving a strong and durable composite. This paper may serve to encourage further experimental research works for achieving more sustainable, cost-effective geopolymer composites with enhanced mechanical properties.

Predictive modeling of the compressive strength of bacteria-incorporated geopolymer concrete using a gene expression programming approach

The performance of gene expression programming (GEP) in predicting the compressive strength of bacteriaincorporated geopolymer concrete (GPC) was examined in this study. Ground-granulated blast-furnace slag (GGBS), new bacterial strains, fly ash (FA), silica fume (SF), metakaolin (MK), and manufactured sand were used as ingredients in the concrete mixture. For the geopolymer preparation, an 8 M sodium hydroxide (NaOH) solution was used, and the ambient curing temperature (28oC) was maintained for all mixtures. The ratio of sodium silicate (Na2SiO3) to NaOH was 2.33, and the ratio of alkaline liquid to binder was 0.35. Based on experimental data collected from the literature, an evolutionary-based algorithm (GEP) was proposed to develop new predictive models for estimating the compressive strength of GPC containing bacteria. Data were classified into training and testing sets to obtain a closed-form solution using GEP. Independent variables for the model were the constituent materials of GPC, such as FA, MK, SF, and Bacillus bacteria. A total of six GEP formulations were developed for predicting the compressive strength of bacteria-incorporated GPC obtained at 1, 3, 7, 28, 56, and 90 days of curing. 80% and 20% of the data were used for training and testing the models, respectively. R2 values in the range of 0.9747 and 0.9950 (including train and test dataset) were obtained for the concrete samples, which showed that GEP can be used to predict the compressive strength of GPC containing bacteria with minimal error. Moreover, the GEP models were in good agreement with the experimental datasets and were robust and reliable. The models developed could serve as a tool for concrete constructors using geopolymers within the framework of this research.

Porous metakaolin-based geopolymer granules for removal of ammonium in aqueous solution and anaerobically pretreated piggery wastewater

This research investigates the applicability of porous metakaolin-based geopolymer granules as an adsorbent to removal ammonium in aqueous solution and anaerobically pretreated piggery wastewater. The air foam content in porous geopolymer preparation was varied at 0, 5, 10, and 15 wt%. The porosity, water adsorption, average pore width, and total pore volume were found positively correlated with air foam content. The ammonium removal efficiency and air foam content were also positively related. The 15 wt% foamed geopolymer (GF15) provided highest ammonium removal efficiencies and adopted as the granular adsorbent. The maximum ammonium adsorption capacity of GF15 geopolymer granules was 47 mg g−1. It was obtained at pH 6.4, 30 °C, 24 h contact time and initial ammonium concentration of 2000 mg L−1. The adsorption kinetic data followed the pseudo-second-order model, with adsorption equilibrium condition reached within 120 min. The GF15 geopolymer granules could be reused multiple times after desorption with 0.2 M NaCl and 0.3 M NaOH. The GF15 geopolymer granules achieved 84% ammonium removal efficiency for anaerobically pretreated piggery wastewater having 75 mg L−1 ammonium initial concentration. The results demonstrated high selectivity toward ammonium ion of the porous geopolymer granules even with the presence of organic compounds and competing ions. This research demonstrates the application of porous geopolymer granules with tailored macropore structure for effective removal of ammonium ion from piggery wastewater.

Bulk Utilization of Red Mud in Geopolymer Based Products

Red Mud is the solid residue generated from Alumina refinery during the process of bauxite ore processing through Bayer’s process. Typical generation of red mud is 1.5 tons of red mud per ton of alumina produced. The disposal and storage of red mud has been a concern for the alumina industry since its inception, more than a hundred years ago. With the increase in alumina production, the magnitude of the problem is getting multiplied. Its alkaline nature (Na2O ~ 3-7%) and fine size make red mud unsuitable for many applications; a limited utilization is reported in cement industries as one of the raw mix components for cement. The present work deals with the utilization of red mud in geopolymer based paving blocks. Alumina, silica and alkali are the essential items required for geopolymer preparation. Having all these in red mud, the current study attempted to use the same in geopolymer based products. The focus has been on bulk utilization of red mud; target strength of 20 MPa after 28 days of curing (M20 grade) has been the goal as this strength is sufficient for many applications. The study focused on optimizing the red mud content, alkali concentration, fly ash content, etc. The samples are tested for its compressive strength and leachability. The study reveals that significant amount of red mud incorporation is possible with products conforming to USEPA 1311 norms.

Undehydrated kaolinite as materials for the preparation of geopolymer through phosphoric acid-activation

This work focuses on the geopolymerization of undehydrated kaolinite in place of the more commonly used dehydrated kaolinite via phosphoric acid-activation. The results showed that the compressive strength, microstructure, and chemical composition of acid-activated undehydrated kaolinite were greatly affected by the concentration of phosphoric acid. When kaolinite was acid-activated by 10 mol/L and 12 mol/L phosphoric acid, metavariscite and geopolymer with P–O–Al network were obtained; but the products possessed porous and inhomogeneous microstructure, which exhibited low compressive strength. When kaolinite was acid-activated by 14 mol/L phosphoric acid, geopolymer dominant with Si–O–P–O–Al networks was synthesized, which had compact and dense microstructure. The compressive strength of the geopolymer product was greatly improved. These results demonstrate the feasibility of using undehydrated kaolinite as the starting material for the preparation of phosphoric acid-based geopolymer. The findings of this study have meaning not only for extending the application field of kaolinite but for reducing the energy input in geopolymer preparation.

Experimental study on metakolin and baggashe ash based geopolymer concrete

In this experimental study, the bagasse ash and metakaolin is used to develop the geopolymer concrete. The fly ash based geopolymer concrete was prepared with bagasse ash and metakaolin which were used to replace fly ash at different percentages i.e., 10%, 20%, 30%, and 40% to study the microstructure, mechanical and durability properties. Geopolymer Concrete was prepared with the use of alkaline solutions NaOH and Na2Sio3. Geopolymer concrete samples for bagasse ash and metakaolin based were cured at oven for 24 h at 90˚C and then kept under room temperature for curing. Metakaolin contained geopolymer concrete has shown better mechanical and durability properties as compared with bagasse ash contained geopolymer concrete. Geopolymer concrete is raw material based concrete that leads to the usage of materials which are produced as a raw material from industries and when these raw materials were induced in the geopolymer preparation it leads to the reduction of carbon emissions and acts as a greener concrete towards environment. Microstructure studies concluded that the metakaolin contained geopolymer concrete has denser intermolecular bonding of materials as compared to the bagasse ash contained geopolymer due to which metakaolin shows better results in mechanical and durability properties when compared with bagasseash.

The Impact of the Amount of Water Used in Activation Solution and the Initial Temperature of Paste on the Rheological Behaviour and Structural Evolution of Metakaolin-Based Geopolymer Pastes

This study aimed to determine the impact of the initial temperature of the paste (from 5 °C to 35 °C) and the addition of water, which reflects a decrease in the molarity of activation solutions (AS) by diluting 10 M NaOH with distillate water, on the rheological properties of geopolymer pastes. Additionally, this resulted in changes to the physical–mechanical properties of geopolymers after curing. A higher amount of water in the AS composition and higher initial paste temperature led to an increase in the spread values up to 28% and decreases viscosity. A smaller amount of water in the AS composition and a higher initial paste temperature accelerated the speed of the geopolymer structure formation up to 1.5 times during the curing period, increased compressive strength and reduced apparent porosity and pore size. X-ray diffraction confirmed the compressive strength test results and revealed that the lower amount of water in the AS and the higher initial paste temperature for the geopolymer preparation significantly affected the mineral formation and physical and mechanical properties of the samples.

Setting and Hardening Behaviour of Alkali-Activated Landfilled Fly Ash-Slag Binder at Room Temperature.

A geopolymer is normally considered an environmentally friendly binder due to the utilisation of industrial wastes. This study focusses on the potential of geopolymer preparation at room temperature from landfilled fly ash (LFA) which has been discharged to the land for more than three years. To accelerate the reaction process, 20–30 wt.% LFA was replaced by ground-granulated blast-furnace slag (GGBS). The effect of water glass modulus, Na2O content, water-to-solid ratio, and GGBS content on the setting time and strength development of the binder was discussed. Results showed that to activate LFA, the optimal value of the sodium silicate modulus for alkaline solution was 1.4–1.6 with a Na2O content of 10%, and the water-to-solid ratio was 0.4. In addition, the setting time of the binder reduced with increasing content of GGBS replacement, and the compressive strength increased due to the coexistence of C–(A)–S–H and zeolite-like phases. The maximum compressive strength of the binder was 29.2 MPa after 56 days of curing. The relatively low strength was likely due to the absence of the Q4 unit with a three-dimensional structure.

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.

Feasibility study of red mud for geopolymer preparation: effect of particle size fraction

The storage of red mud has seriously damaged the ecological environment, and its utilization is urgent. The roles of particle size fraction of red mud on the geopolymer properties was investigated, to provide guidance for the preparation of red mud-based geopolymer. The composition variation, workability, mechanical strength, and microstructure of each red mud fraction were analyzed, and the results show that the chemical composition changed with the classification. The fluidity decreased first and then increased with the decrement of particle fraction, and all the specimens showed the rheological characteristics of Herschel–Buckley model. The specimens with coarser and finer particles both had excellent mechanical strength and lower porosity. The microstructure of red mud-based geopolymer with different red mud particle fractions was analyzed by FTIR, XRD and SEM–EDS. The results showed that the main hydration products were geopolymer gel (N-A-C-S-H). And the particle fraction has a little effect on the kinds of hydration products. Finally, the particle fraction of red mud was classified according to the properties of red mud-based geopolymer.

Geopolymer Preparation from Bamboo Ash Containing Kaolin as Ash Fusion Control Agent

Bamboo is a prospective biomass fuel due to its high heating value and growth rate. The addition of kaolin is necessary in the thermal conversion of biomass to increase its ash fusion temperature (AFT), thus reducing fouling and corrosion of the combustion system. This study evaluates the feasibility of utilizing bamboo-kaolin co-processing residue for geopolymer synthesis. Thermochemical calculations suggest that bamboo culm ash liquidus increases by 15% by adding kaolin during combustion at a biomass to kaolin mass ratio of 95:5%. A 23 full factorial experiment measures the effect of activator Na2SiO3:KOH ratio, KOH concentration, and heat-curing period at 60 °C on the early strength of geopolymer mortars. Co-processing residue of bamboo-kaolin at a mass ratio of 95:5% produces geopolymer mortars with compressive strengths in the 10.7-40.3 MPa range. ANOVA treatment of the data indicate strong positive effect of KOH concentration. Crystalline phase characterizations indicate that the co-processing is able to convert kaolin to the amorphous, more reactive metakaolin. A shift in the IR absorption band from 1034 to 1008 cm-1 is attributed to the conversion of Si-O-Si bonds of the co-processing residue into Si-O-Al and Si-O-K bonds of the geopolymer gel phase. These results suggest the feasibility of geopolymerization as a waste valorization pathway to ensure the sustainability of the biomass-based energy production.

Synthesis and toxic metals (Cd, Pb, and Zn) immobilization properties of drinking water treatment residuals and metakaolin-based geopolymers

Using aluminum/iron-based drinking water treatment residuals (DWTR) to replace metakaolin (MK) in geopolymerization can improve resource utilization from solid waste and reduce the cost of geopolymer preparation. This study researched the preparation feasibility of geopolymer with DWTR and MK and investigated its immobilization performance on toxic heavy metals. Results indicated that a composite geopolymer with higher mechanical strength was successfully prepared with DWTR and MK. The characterization results showed that the microstructure of the geopolymer was more stable with curing time, and the geopolymeric process with suitable proportion can be completed in a shorter time. According to the leaching properties results, the immobilization efficiency of heavy metals was between 97.79 and 99.72%. The immobilization efficiency of Cd was significantly higher than Pb and Zn, and the immobilization mechanism of Cd was different from those of Pb and Zn. This study indicated that the DWTR could be used as a substitute material for MK in geopolymer preparation, which provides a cost-effective method for strength enhancement of geopolymers.

Flexural Behaviour of Geopolymer Concrete Beams using Recycled Waste Glass as Fine Aggregate

Cement substitutes and concrete alternatives are currently on the market to help in creating concrete a very ecofriendly material. In cement concrete production, heating and compounding method need large amounts of energy and emits minacious amounts of CO2 into the atmosphere. There has been an increasing significant interest in the development of cement less concrete called geopolymer concrete. In this study, cement is replaced entirely by ash and GGBS for making of geopolymer concrete. Now a days, the scarcity of river sand can have an effect on the development trade and hence there's a requirement of finding a replacement different material to switch the river sand. Non-reactive recycled waste glass is chosen as alternative to the river sand. Various grades of concrete including M 20, M 40 and M 60 grades are developed in GP concrete and also same proportion is used for making GP concrete with glass aggregate. In geopolymer preparation, NaOH of 8 molarity concentration is used. Flexural behaviour of beams is studied by casting of nine beams of size 125 mm × 200 mm × 1100 mm. The beams are designed as under reinforced sections. Out of nine beams, three beams of M 20, M 40 and M 60 grade conventional cement concrete beams, three beams of GP beams and the remaining three beams are made with RWGFA in GP. Beams are tested under two point loading for flexure. The ultimate load carrying capability of all beams is obtained. The crack and deflections of the beams are studied. The experimental results are compared with finite element modeling using ANSYS software

Use of Water Glass from Rice Husk and Bagasse Ashes in the Preparation of Fly Ash Based Geopolymer

The aim of this work is to study the feasibility of preparation of fly ash based geopolymer using sodium water glass from agricultural waste as alternative activators. Rice husk ash and bagasse ash were used as raw materials for producing sodium water glass solution. The sodium water glass were produced by mixing rice husk ash and bagasse ash with NaOH in ball mill and boiling. The prepared sodium water glass were analyzed and used in geopolymer preparation process. The geopolymer paste were prepared by adding the obtained water glass and NaOH with fly ash. After cured at ambient temperature for 7 days, mechanical properties were investigated. Bonding and phases of the geopolymer were also characterized. The geopolymer from rice husk ash presented highest compressive strength about 23 MPa while the greatest for bagasse ash was about 16 MPa.

Synergistic utilization of red mud for flue-gas desulfurization and fly ash-based geopolymer preparation.

As an industrial waste characterized by huge volume and high alkalinity, red mud has become a serious environmental problem. The reuse of red mud has been explored in previous studies, including as building materials and for soil and waste water treatment. In this study, an innovation was made for the reuse of red mud to create a synergistic effect. Red mud was first used in flue gas desulfurization (FGD), and then the desulfurized red mud was again reused to make a geopolymer material. By using one type of original red mud and three types of fly ash, this study revealed that with high alkalinity and desulfurization capacity, the red mud could serve as an excellent FGD sorbent. After FGD, the sodium sulfate in the desulfurized red mud acted as a chemical activator for geopolymer made with class C fly ash. A 25% increase in strength was observed between the geopolymers with the red mud after FGD and with the original one. There are no significant benefits of FGD on the class F fly ash-based geopolymers and further study is required.

Penerapan Metode Taguchi pada Perancangan Eksperimen Beton Geopolimer Berbasis Abu Layang

PT Petrokima Gresik produces fly ash from coal burning about 8048,89 tons in 2015. In general, one ton of coal burning can produce around 0.15 to 0.17 tons of fly ash waste. Fly ash waste can be utilized as a mixture where the main elements of fly ash are aluminum and silica, fulfilling criteria as the material having cement and geopolymer properties. Geopolymer preparation can be done by the sol-gel method at low temperature, where the emission of CO2 gas produced is a minimum amount. The problem faced is finding the right composition of geopolymer so that it produces the maximum compressive strength. One way is by designing a Taguchi experiment. The choice of the Taguchi method is based on the advantages of this method that can combine experimental results through controlled factors and optimal levels so it can achieve the maximum compressive strength of geopolymer. This research used 3 levels (-1,0,1) and 4 factors of fly ash, the solid/liquid ratio (SL), the molarity of NaOH (A), Sand/pasta geopolymer ratio (P/PG). Anova test showed significant effect on compressive strength of fly ash, S / L and A with value of 12,27> 2,90; 61,12> 2,90; 19,477> 2,90. While the value for P / PG is 1.92 <2.90 where the value of F-statistic is less than F table which means P / PG does not significantly affect the compressive strength of Geopolymer. With S/N higher is better to know the optimum composition of fly ash, S / L, A and P / PG equal to: 370 gram; 2.33 (70:30); 9 Molar, and 1.5. The prediction of Geopolymer maximum compressive strength with Taguchi method was obtained 18,71 Mpa. Keywords: Fly ash, Optimation, Taguchi, Geopolymer

Optimization of the metakaolin geopolymer preparation for maximized ammonium adsorption capacity

Geopolymers are functional materials that can be used in various environmental applications such as adsorbents in pollutant removal from wastewaters. Metakaolin geopolymer (MK-GP) has been proven to be especially suitable for ammonium (NH4 +) removal. In this research, the optimal reagent and raw material ratios in the preparation of MK-GP in terms of NH4 + adsorption capacity were investigated. The response surface methodology based on the face-centered central composite design was used to optimize the levels of three factors: the amounts of hydroxide, silicate, and metakaolin. In addition, the effect of Na or K as the charge-balancing cation was studied. Empirical models were fitted to the experimental data using multiple linear regression. The significance of the models was confirmed by means of analysis of variance. Optimal NH4 + removal efficiency was achieved when the amounts of hydroxide and silicate were maximized, the amount of metakaolin was minimized, and Na-based reagents were used. These trends are most likely a result of optimized conversion of metakaolin into MK-GP.