Compressive Strength Of Geopolymers Research Articles

Machine Learning to Predict Workability and Compressive Strength of Low- and High-Calcium Fly Ash–Based Geopolymers

The potential substitution of Portland cement–based concrete with low- and high-calcium fly ash–based geopolymers was investigated. However, predicting the workability and compressive strength of geopolymers with the desired physical and mechanical properties is a complicated process because of the variety of chemical compositions found in aluminosilicate sources. Therefore, machine-learning techniques were used to predict the physical and mechanical properties of the geopolymers and eliminate the usual trial-and-error laboratory procedures. The experimental and predicted results of geopolymer properties using the multilayer perceptron regressor, voting regressor, and XGBoost techniques were compared. The XGBoost model outperformed the other models in terms of accuracy for predicting workability and compressive strength, producing the R2 of 0.96 and 0.89, respectively. Sensitivity analysis determined that the percentage of CaO had the largest effect on geopolymer workability of 27.13%. Fly ash content had the largest effect on compressive strength of 34.44%. Our approach offers a straightforward and dependable strategy for designing and optimizing fly ash–based geopolymers.

Innovative assessment of reactivity in fly ash: The role of particle size distribution characteristics

The relationship between the intrinsic properties of seven different types of fly ash and the compressive strength of the resulting geopolymers was investigated. A comprehensive examination of the effect of chemical and mineralogical compositions, particle size distribution, on the compressive strength of the fly ash-based geopolymers were performed. Results revealed that particle size distribution had a more significant impact on reaction activity than amorphous phase content or average particle size alone. Therefore, a novel concept of 'reaction volume' based on the geopolymerization reaction mechanism was proposed, which reveals a high correlation between the reactivity of fly ash and the compressive strength of geopolymers, thereby enhancing the predictability of the process. The degree of reactivity, formulated through the integration of reaction volume and amorphous silica-aluminum content, was identified as a robust predictor of compressive strength, which can serve as a crucial tool for evaluating fly ash for the production of alkali-activated materials.

Effect of synthesis conditions on mechanical properties and microstructure of coal gasification slag-based geopolymer

Coal gasification slag (CGS) is an industrial solid waste produced during coal gasification, and it is mostly deposited on the land at present, resulting in serious environmental pollution. In order to promote its resource utilization, geopolymer was synthesized from CGS in this study. The influence of important factors containing the water-solid ratio, alkali activator dosage, activator modulus and curing temperature on the mechanical properties and microstructure of geopolymers were investigated. Micromorphology, chemical composition, mineralogy and chemical bonding of the geopolymer were assessed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. Results indicate that the compressive strength of geopolymer can be improved by reducing the amount of initial water. The optimal mechanical properties of geopolymer are obtained when the alkali activator dosage is 25 % and the activator modulus is 1. The moderate temperature (e.g. 60 °C) is the most favorable to the compressive strength development of geopolymer. Under these optimal conditions, the 90 days compressive strength of the CGS-based geopolymer (CGSG) can reach 58.3 MPa. The Si/Al molar ratio of the geopolymer gels is between 2.0 and 3.1, and the Al/Na molar ratio is around 1.0. These results can provide a reference for recycling of the CGS and production of eco-friendly building materials.

Preparation of geopolymer for in-situ pavement construction on the moon utilizing minimal additives and human urine in lunar regolith simulant

Constructing lunar pavements is of great significance for improving the transportation efficiency of materials and personnel transfer at lunar bases. Utilizing lunar regolith for the in-situ preparation of geopolymer is an effective means of supplying raw materials for lunar pavement construction. This present study prepared geopolymers for pavement material with lunar regolith simulant. The influence of NaOH on the compressive strength of geopolymers was understood by using different percentages of NaOH as alkaline activator. The effect of urine on the compressive strength of geopolymers by using artificial urine of different pH values as liquid phases. The results indicated that the addition of artificial urine slightly reduces the compressive strength of geopolymers, and the effects of pH and NaOH percentage are different. Microstructural analysis performed by Mercury Intrusion Porosimetry and Scanning Electron Microscope, indicated that choosing fine-particle lunar regolith simulant as precursor is more conducive to the preparation of high-strength geopolymers using human urine.

Effect of Data Augmentation Using Deep Learning on Predictive Models for Geopolymer Compressive Strength

In recent years, machine learning models have become a potential approach in accurately predicting the concrete compressive strength, which is essential for the real-world application of geopolymer concrete. However, the precursor system of geopolymer concrete is known to be more heterogeneous compared to Ordinary Portland Cement (OPC) concrete, adversely affecting the data generated and the performance of the models. To its advantage, data enrichment through deep learning can effectively enhance the performance of prediction models. Therefore, this study investigates the capability of tabular generative adversarial networks (TGANs) to generate data on mixtures and compressive strength of geopolymer concrete. It assesses the impact of using synthetic data with various models, including tree-based, support vector machines, and neural networks. For this purpose, 930 instances with 11 variables were collected from the open literature. In particular, 10 variables including content of fly ash, slag, sodium silicate, sodium hydroxide, superplasticizer, fine aggregate, coarse aggregate, added water, curing temperature, and specimen age are considered as inputs, while compressive strength is the output of the models. A TGAN was employed to generate an additional 1000 data points based on the original dataset for training new predictive models. These models were evaluated on real data test sets and compared with models trained on the original data. The results indicate that the developed models significantly improve performance, particularly neural networks, followed by tree-based models and support vector machines. Moreover, data characteristics greatly influence model performance, both before and after data augmentation.

Preparation of one-part geopolymers using coal gasification slag: Effect of alkali fusion product additive and liquid/solid ratio

In this work, one-part geopolymers were synthesized through the alkali fusion and component additive method (AFCAM), utilizing coal gasification slag as the primary raw material. The investigation delved into the influence of varying fusion product contents and liquid/solid (L/S) ratios on the geopolymer properties. The experimental results demonstrated a non-linear correlation between the increase in fusion product content and the compressive strength of geopolymers, revealing an initial ascent followed by a subsequent decline. Additionally, a lower L/S ratio of 0.3 was observed to enhance compressive strength compared to the L/S ratio of 0.4. Notably, the optimal combination of an L/S ratio of 0.3 and a fusion product percentage of 30 % resulted in a remarkable compressive strength of 25.2 MPa. The comprehensive strength analysis suggested that an adequate amount of fusion product enhances the geopolymerization reaction, evidenced by the transformation of aluminum coordination states. Specifically, the conversion of five-coordinated and six-coordinated aluminum in slag to four-coordinated aluminum in geopolymers was observed. Concurrently, increased silicon and aluminum reactivity led to the formation of a robust Q4(4Al) network in the geopolymer gel. The impact of L/S ratios was attributed to the accelerated dissolution and hydrolysis of aluminosilicates at an elevated L/S ratio of 0.4, hindering polycondensation. These outcomes underscore the pivotal role of fusion product content and L/S ratio in governing the strength development of one-part geopolymers.

Production, characterization and performance of green geopolymer modified with industrial by-products

Industrial by-products; have received a lot of attention as a possible precursor for cement and/or concrete production for a more environmentally and economically sound use of raw materials and energy sources. Geopolymer is a potentially useful porous material for OPC binder applications. The use of industrial wastes to produce a greener geopolymer is one area of fascinating research. In this work, geopolymer pastes were developed using alkali liquid as an activator and metakaolin (MK), alumina powder (AP), silica fume (SF), and cement kin dust (CKD) as industrial by-products. Several geopolymer samples have been developed. Research has been carried out on its processing and related physical and mechanical properties through deep microstructure investigation. The samples were cured in water by immersion with relative humidity (95 ± 5%), and at room temperature (~ 19–23 °C) prior to being tested for its workability and durability. The effect of the different composition of precursors on water absorption, density, porosity, and the compressive strength of the prepared geopolymers have been investigated. The results showed that the compressive strength of geopolymers at 28 days of curing is directly proportional to the ratio of the alkali liquid. Ultimately, the best geopolymer paste mixture (GPD1 and GPD2), was confirmed to contain (15% of CKD + 85% MK and Alumina solution (55 wt%)) and (25% of CKD + 75% MK + Alumina solution (55 wt%)) respectively, with 73% desirability for maximum water absorption (~ 44%) and compressive strength (4.9 MPa).

Influence of liquid-to-solid ratios on properties and microstructure of coal gasification slag-based one-part geopolymer

Limited studies have been conducted on the synthesis of one-part geopolymer involving coal gasification slag by alkali fusion and component additive method (AFCAM). The ratio of liquid-to-solid (L/S) is the key aspect that has a major impact on the one-part geopolymer's compressive strength (UCS). Our research aims to determine how different L/S ratios affect the microstructure and characteristics of one-part geopolymers. MIP analysis and hydration heat test were conducted to analyze the influence caused by different L/S ratios. The results showed that as the L/S ratio increased, the UCS of geopolymers decreased, and the setting time of fresh slurry increased steadily. Additionally, geopolymer with 0.25 as an L/S ratio (G-L/S-0.25) achieved a higher UCS at 48.31 MPa, whereas the total setting time was more than 23 h. The low L/S ratio produced more gel pores and less total porosity in the geopolymer matrix, which improved the UCS. Moreover, lower porosity suggested that the geopolymer sample had higher compactness and a better internal structure. It is found that the dissolution of the fusion product released heat in the first hour, and no coal gasification slag dissolution heat was detected after one hour. This suggested coal gasification slag showed low reactivity as the additive and was embedded in the geopolymer matrix after 28-day curing. The tested results showed that G-L/S-0.25 had a greater reaction degree. This study illustrated the effects of the L/S ratio on one-part geopolymer and provided a new thought to enhance the UCS of coal gasification slag-based geopolymer.

Investigation of the Properties of Metakaolin-Based Geopolymer Materials Using Ferrisilicates as Additives Synthesised in Sodium Hydroxide Solution or Distilled Water

The main objective of this work is to investigate the behaviour of ferrisilicates prepared from hematite and two silica sources (rice husk ash and silica fume) on the compressive strength of geopolymer materials. Some ferrisilicates were synthesised in 2M sodium hydroxide solution. Others were prepared using distilled water as a solvent. The Fe2O3/SiO2 molar ratio contained in the ferrisilicates is set to 0.2. Metakaolin and sodium silicate solution with a molar ratio of SiO2/Na2O of 1.6 were used as the aluminosilicate and hardener in this work. The control geopolymer compressive strength is 53.34 MPa. For ferrisilicates prepared in alkaline solution using rice husk ash and silica fume, their compressive strength values are 71.91 and 77.72 MPa, respectively. The compressive strengths of the geopolymer materials made from ferrisilicates prepared in distilled water using rice husk ash and silica fume are 74.13 and 44.73 MPa, respectively. In the presence of ferrisilicate obtained by dissolving silica fume and hematite in sodium hydroxide solution, the maximum compressive strength of 77.72 MPa was obtained. When ferrisilicates from the mixture of silica fume, hematite, and distilled water are used as an additive, the minimum compressive strength of 43.73 MPa is achieved. It can be concluded that additives synthesised in an alkaline medium and those obtained in distilled water with rice husk ash improve compressive strength. On the other hand, the compressive strength of the geopolymer material that uses the additive produced with silica fume in distilled water is lower (44.73 MPa).

Artificial Intelligence Prediction of One-Part Geopolymer Compressive Strength for Sustainable Concrete

Artificial Intelligence Prediction of One-Part Geopolymer Compressive Strength for Sustainable Concrete

Retracted: Empirical Investigation on Compressive Strength of Geopolymer and Conventional Concretes by Nondestructive Method

Retracted: Empirical Investigation on Compressive Strength of Geopolymer and Conventional Concretes by Nondestructive Method

Preparation and properties of metakaolin-fumed-silica geopolymer modified with sodium silicate and potassium silicate activators

Geopolymers, which are environmentally friendly materials with aluminosilicates as raw materials, are expected to replace cement in construction materials. Here, the effect of fumed silica (FS) on the properties of metakaolin (MK)-based geopolymer materials was investigated with MK, sodium silicate, and potassium silicate as the main raw materials; their microstructures were characterized, and their performance was tested. The geopolymer's compressive strength, particle size, and curing characteristics were measured with X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy for microstructural analysis. The total dissolved solids (TDS) method was employed to study the geopolymer and evaluate the effect of the resulting gel products on TDS. The results revealed that the strength of 4% FS could reach 56.3MPa after 7 days of incorporation, and the strength increased by 20% and 12% compared with the 0% and 2% groups, respectively. Meanwhile, studying the microstructure of kaolin revealed that the best mechanical and physical properties were obtained when kaolin was calcined at 700°C. In addition, the mixture of alkaline activators increased the reactivity of MK, and the mixed alkaline-excited geopolymer from sodium silicate and potassium silicate exhibited enhanced matrix strength properties compared to the single alkaline activators. Overall, the inclusion of the FS material resulted in the optimization of the mechanical properties, confirming the improvement in the mechanical properties.

Composite Geopolymers Based on Mechanically Activated Fly Ash Blended with SrCO3 (Strontianite) and BaCO3 (Witherite)

In this study, geopolymers based on mechanically activated mixtures of fly ash (FA) with SrCO3 (strontianite) and BaCO3 (witherite) were synthesized. NaOH solution was used as an alkaline agent and curing was carried out under ambient conditions. XRD, FTIR spectroscopy, thermogravimetry, and SEM were used to study the geopolymerization process and microstructure. The product of geopolymerization of the milled (FA + SrCO3) and (FA + BaCO3) blends was X-ray amorphous N-A-S-H gel. The beneficial impact of mechanical activation on the compressive strength of geopolymers was most evident during the initial stages of the curing process. The strength of geopolymers based on the (FA + carbonate) blends after 7 d was either less than the corresponding strength of geopolymers based on the 100% FA or, within the measurement accuracy, equal to it. With increasing curing time, the strength development of geopolymers synthesized from (70% FA + 30% carbonate) blends exceeded the strength growth of geopolymers containing less carbonates; after curing for 180 d, these geopolymers showed the highest compressive strength (20–27 MPa). This trend was more pronounced for the geopolymers based on the (FA + SrCO3) blends. The influence of SrCO3 and BaCO3 addition to the FA on the strength of composite geopolymers was explained by dilution and microfiller effects. The geopolymers based on the FA blended with SrCO3 and BaCO3 exhibit potential applications in immobilizing radioactive strontium and producing radiation shielding materials.

Assessing the viability of a high performance one-part geopolymer made from fly ash and GGBS at ambient temperature

This study aims to investigate the feasibility of preparing a one-part geopolymer using fly ash (FA) and ground granulated blast furnace slag (GGBS) as the main raw materials and solid sodium hydroxide and sodium silicate as activation conditions under ambient conditions. Orthogonal tests were conducted to study effects of FA on the GGBS mass ratio (F:G), solid alkali content, sodium hydroxide–to–sodium silicate mass ratio (SH:SS), and water-to-solid ratio on the unconfined compressive strength (UCS), setting time, and fluidity of the one-part geopolymers. The microstructure, composition, and pore distribution characteristics of the geopolymers were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and mercury intrusion porosimetry (MIP). The findings revealed that (1) the mechanical characteristics of the geopolymer were most severely influenced by F:G, and the compressive strength of the geopolymer considerably decreased with an increase in F:G. (2) The influences of the alkali content and water-to-solid ratio on the setting time of the geopolymer were essentially the same and significantly larger than those of the F:G and SH:SS variables. (3) The most important element affecting the fluidity of the geopolymer was the water-to-solid ratio. Microscopic analysis verified the results of the macroscopic experiments. The XRD and SEM-EDS tests indicated that the reaction system produced a mixed gel by activating some of the Ca in the GGBS was activated with FA, which filled the pores of the geopolymer and increased its strength. The MIP test also revealed that specimen S7 exhibited the smallest pore space among the selected specimens. The microscopic experiments revealed that the reaction system produced a mixture of calcium silicate hydrate (C-S-H) gels and hydrated sodium silicate N(C)-A-S-H gels.

Optimization of Geopolymer Compressive Strength Using Response Surface Methodology

Geopolymers have issues related to cracking resistance and pore filling, decreasing their mechanical strength. However, the addition of nanosilica and Cellulose Nanocrystals (CNCs) has been found to enhance their mechanical properties. This study focused on optimizing the utilization of nanosilica and CNCs to enhance the compressive strength of geopolymers. This research employed Response Surface Methodology (RSM) with Central Composite Design (CCD). The concentrations of nanosilica and CNCs used in the experiments ranged from 2% to 4% and 1% to 3%, respectively. The experimental results consist of 13 runs, including 5 center point runs. The model suggested concentrations of nanosilica and CNCs of 3.98% and 1%, respectively, for an optimal compressive strength of 22.20 MPa. The proposed quadratic model exhibited high accuracy, as evidenced by an R2 of 0.9865, Adj- R2 of 0.9769, and predicted R2 of 0.9168. The closeness of R2 to 1 indicates a strong correlation between the actual and predicted values, thus highlighting the model's significant relevance. Ultimately, the model developed in this study holds the potential for predicting the compressive strength of geopolymers incorporating nanosilica and CNCs.

ГЕОПОЛИМЕРНЫЕ МАТЕРИАЛЫ НА ОСНОВЕ МЕХАНОАКТИВИРОВАННЫХ КОМПОЗИЦИЙ НИЗКОКАЛЬЦИЕВОЙ ЗОЛЫ ТЭЦ И НЕФЕЛИНА

The processes of hardening of geopolymers containing low-calcium Apatitskaya Thermal Power Plant fly ash and nepheline concentrate with the use of preliminary mechanical activation using sodium hydroxide solutions as an alkaline agent have been studied. The influence of various factors (duration and conditions of mechanical activation, composition of the mixture, concentration of NaOH solution, hardening conditions) on the compressive strength of geopolymers is considered.

Accelerated carbonation pretreatment of municipal solid waste incineration fly ash and its conversion to geopolymer with coal fly ash

Recycling municipal solid waste incineration fly ash (FA) to prepared geopolymer has received wide attentions due to its excellent physical–chemical properties. However, the rich chloride salts and heavy metals in FA limit its FA additive amount during geopolymerization. To address large-scale FA conversion to geopolymer, this work conducted the carbonation pretreatment of FA with H2CO3, (NH4)2CO3 and Na2CO3 (made as H-FA, N-FA and Na-FA, respectively) and further converted it into geopolymers with coal fly ash (CFA). The effect of carbonated FA (50–70 wt.%) on the compressive strength characteristics, efflorescence properties and leaching properties of geopolymer was investigated. The results showed that three types of carbonate solutions changed the mineral phases of FA and consequently affected the properties of geopolymers. The main mineral phases of H-FA and Na-FA were calcite, while calcite and vaterite were the coexisting main mineral phases of N-FA. The prepared geopolymers with Na-FA exhibited the best performance (denser microstructure, better compressive strength, etc.), owing to the formation of more C-S-H and calcite. In particular, the compressive strength of geopolymer with 60 wt.% Na-FA reached the maximum value of 149.89 MPa at curing time for 28 d. Furthermore, the highest leaching concentration of Na in the geopolymers was only 4.52 mg/L, which was at a low level. The leaching concentrations of Pb, Cd, Cr, Cu, Ni and Zn in the geopolymers were far lower than the thresholds of GB 18598–2019. The results confirmed that carbonation pretreatment was a promising approach to improve the recycling of hazardous FA, and converting it to geopolymers with CFA, and FA-based geopolymers had the potential to be applied as building materials.

29Si and 27Al NMR study of the structural transformation of calcined kaolin residue-based geopolymer using low alkali activator content for sustainable construction materials

Geopolymer commercialization efforts in parallel with unconventional research are the only pathway to achieve the large-scale deployment of geopolymer technology. Geopolymers with a low quantity of alkali activator produced by the compression process are one way to bring this technology to industry because of the higher strength and lower efflorescence of the product. In this work, calcined kaolin residue-based geopolymers with a low alkali activator content were synthesized by various Si/Al mole ratios with soluble silicate from Na2SiO3 to adjust the Si ratio. The effects of Si/Al mole ratios on the structural transformation, microstructure, and compressive strength of geopolymers containing low alkali activator content were studied. The structural transformation and microstructure of geopolymers were characterized by NMR, SEM, and BET, and the compressive strength was assessed using a mechanical testing machine. The results present that geopolymer synthesized with various Si/Al mole ratios of precursor materials impacted the change in polymerization degree of silicate species (Qn(mAl)) and aluminate species. The Q4(4Al) and Q4(3Al) structures were transformed into the Q4(2Al) structure, and the content of the AlIV structure decreased when the Si/Al mole ratio of geopolymer was increased to 1.58. However, the contents of Q4(4Al) and AlIV structures increased again when the geopolymer had a Si/Al mole ratio of 1.62. SEM/EDX and BET results of geopolymers presented denser matrices, more amorphous aluminosilicate gels, and higher Si/Al ratios in aluminosilicate gels, while the pore size and pore volume were quite small when the Si/Al mole ratio of precursor materials was increased. In contrast, the highest Si/Al mole ratio of 1.62 showed different properties. The compressive strength of geopolymer was maximized at a Si/Al mole ratio of 1.58, and the decline in compressive strength of geopolymer with higher Si/Al mole ratio was related to the contents of Si–O–Si, Si–O–Al, and Al–O–Al bonds, content of aluminosilicate gels, and properties of the microstructure. The geopolymer synthesis using calcined kaolin residue and low alkali activator content is considered an eco–friendly process, which uses waste materials and less chemicals, and obtains high-strength products.

Investigation on the Effect of Calcium on the Properties of Geopolymer Prepared from Uncalcined Coal Gangue

In this paper, the influence of calcium on coal gangue and fly ash geopolymer is explored, and the problem of low utilization of unburned coal gangue is analyzed and solved. The experiment took uncalcined coal gangue and fly ash as raw materials, and a regression model was developed with the response surface methodology. The independent variables were the CG content, alkali activator concentration, and Ca(OH)2 to NaOH ratio (CH/SH). The response target value was the coal gangue and fly-ash geopolymer compressive strength. The compressive strength tests and the regression model obtained by the response surface methodology showed that the coal gangue and fly ash geopolymer prepared with the content of uncalcined coal gangue is 30%, alkali activator content of 15%, and the value of CH/SH is 1.727 had a dense structure and better performance. The microscopic results demonstrated that the uncalcined coal gangue structure is destroyed under an alkali activator's action, and a dense microstructure is formed based on C(N)-A-S-H and C-S-H gel, which provides a reasonable basis for the preparation of geopolymers from the uncalcined coal gangue.

Potential Evaluation for Preparing Geopolymers from Quartz by Low-Alkali Activation

Alkali fusion of granite sawdust at a high alkali dosage can significantly improve geopolymerization activity, but also result in a high alkali consumption and a poor geopolymer performance. In this work, quartz, the most inert component in granite sawdust, was selected to explore the effect of low-alkali activation on its reactivity and the compressive strength of geopolymer. It was found that the amount of activated quartz is mainly determined by the amount of alkali used for activation. The surface of a quartz particle can be effectively activated by an alkali fusion process at a low alkali dosage of 5%. The metakaolin-based geopolymer synthesized with quartz activated by an alkali dosage of 5% shows a high compressive strength of 41 MPa, which can be attributed to the enhanced interfacial interaction between quartz and the geopolymer gel, suggesting that low-alkali activation is a potential way to improve the geopolymerization ability of granite sawdust.