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17 pages, 5138 KiB

Open AccessArticle

Effect of Different Types of Aluminosilicates on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites

by Jan Kohout, Petr Koutník, Pavlína Hájková, Eliška Kohoutová and Aleš Soukup

Polymers 2022, 14(22), 4838; https://doi.org/10.3390/polym14224838 - 10 Nov 2022

Cited by 5 | Viewed by 1678

Abstract

In this study, the effect of different types of aluminosilicates on the thermo-mechanical properties of metakaolinite-based geopolymer binders and composites was examined. The metakaolinite-based geopolymer binders and composites were produced from three different types of aluminosilicates (one metakaolin and two calcined claystones) and [...] Read more.

In this study, the effect of different types of aluminosilicates on the thermo-mechanical properties of metakaolinite-based geopolymer binders and composites was examined. The metakaolinite-based geopolymer binders and composites were produced from three different types of aluminosilicates (one metakaolin and two calcined claystones) and a potassium alkaline activator. Chamotte was added as a filler, amounting to 65% by volume, to create geopolymer composites. Geopolymer binders were characterized by X-ray diffraction, rotary rheometer and scanning electron microscopy. The mechanical properties, thermal dilatation and thermal conductivity were investigated on geopolymer composites with three different aluminosilicates before and after exposure to high temperatures (up to 1200 °C). The results showed that the geopolymer binders prepared from calcined claystones had a lower dynamic viscosity (787 and 588 mPa·s) compared to the geopolymer binders prepared from metakaolin (1090 mPa·s). Geopolymer composites based on metakaolin had lower shrinkage (0.6%) and higher refractoriness (1520 °C) than geopolymers from calcined claystones (0.9% and 1.5%, 1500 °C and 1470 °C). Geopolymers based on calcined kaolinitic claystones are a promising material with higher compressive (95.2 and 71.5 MPa) and flexural strength (12.4 and 10.7 MPa) compared to geopolymers based on metakaolin (compressive strength 57.7 MPa). Full article

(This article belongs to the Special Issue Development in Geopolymers)

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24 pages, 9869 KiB

Open AccessArticle

Effect of Organic Polymers on Mechanical Property and Toughening Mechanism of Slag Geopolymer Matrix

by Xiaotong Xing, Jiangxiong Wei, Weiting Xu, Beihan Wang, Shunjie Luo and Qijun Yu

Polymers 2022, 14(19), 4214; https://doi.org/10.3390/polym14194214 - 08 Oct 2022

Cited by 3 | Viewed by 1687

Abstract

In this work, two series of chemically reactive polymers, silane coupling agents (SCAs) and water-soluble polymers, were specifically designed as an additive to improve the ductility of slag geopolymer paste by vibration pressure technique. The influences of organic polymers on the fluidity, rheological [...] Read more.

In this work, two series of chemically reactive polymers, silane coupling agents (SCAs) and water-soluble polymers, were specifically designed as an additive to improve the ductility of slag geopolymer paste by vibration pressure technique. The influences of organic polymers on the fluidity, rheological behavior, mechanical property, porosity, and toughening mechanism of slag geopolymer were investigated. The polycondensation and bonding characteristics of organic–inorganic products were calculated by ¹H liquid nuclear magnetic resonance (NMR) technology and Fourier transform infrared (FT-IR). The polymerization degree of composite geopolymer was evaluated by ²⁹Si NMR and X-ray photoelectron spectroscopy (XPS). The microscopic morphology of the geopolymer matrix was analyzed using scanning electron microscopy (SEM). The results showed that the dosage of the KH570 and PAA-Na with 5 wt% behaved best in improving the flexural strength and the compressive strength of geopolymer in their corresponding organic series, respectively. The addition of polymers decreased the fluidity and the fluidity loss ratio of geopolymer slurry but reduced the harmful pores of hardened geopolymer. The organic polymers acting as bridge-fixed water molecules weakened the repulsion force, and formed a three-dimensional network through molecular interweaving in a geopolymer matrix. Methacryloxy in silane coupling agents and carboxyl group in water-soluble polymers may contribute to the improvement of hydration product structure through strong bonding with C-A-S-H. Microscopic measurements indicated that the addition of KH570 and PAA-Na in geopolymer could form 73.55% and 72.48% Si-O-Si with C-A-S-H gel, higher than the reference, and increase the polycondensation degree of C-A-S-H phase, reflected by the increased generation of Q² and Q²(1Al) and the longer chain length, leading to a higher densified geopolymer matrix with high ductility. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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15 pages, 2440 KiB

Open AccessArticle

Coagulation Mechanism and Compressive Strength Characteristics Analysis of High-Strength Alkali-Activated Slag Grouting Material

by Mingjing Li, Guodong Huang, Yi Cui, Bo Wang, Binbin Chang, Qiaoqiao Yin, Shuwei Zhang, Qi Wang, Jiacheng Feng and Ming Ge

Polymers 2022, 14(19), 3980; https://doi.org/10.3390/polym14193980 - 23 Sep 2022

Cited by 7 | Viewed by 1208

Abstract

In deep coal mining, grouting reinforcement and water blockage are the most effective means for reinforcing the rock mass of extremely broken coal. However, traditional cement grouting materials are not suitable for use in complex strata because of their insufficient early mechanical strength [...] Read more.

In deep coal mining, grouting reinforcement and water blockage are the most effective means for reinforcing the rock mass of extremely broken coal. However, traditional cement grouting materials are not suitable for use in complex strata because of their insufficient early mechanical strength and slow setting time. This study innovatively proposes using alkali-activated grouting material to compensate for the shortcomings of traditional grouting materials and strengthen the reinforcement of extremely unstable broken coal and rock mass. The alkali-activated grouting material was prepared using slag as raw material combined with sodium hydroxide and liquid sodium silicate activation. The compressive strength of specimens cured for 1 d, 3 d, and 28 d was regularly measured and the condensation behavior was analyzed. Using X-ray diffraction and scanning electron microscopy, formation behavior of mineral crystals and microstructure characteristics were further analyzed. The results showed that alkali-activated slag grouting material features prompt and high strength and offers the advantages of rapid setting and adjustable setting time. With an increase in sodium hydroxide content, the compressive strength first increased (maximum increase was 21.1%) and then decreased, while the setting time continued to shorten. With an increase in liquid sodium silicate level, the compressive strength increased significantly (and remained unchanged, maximum increase was 35.9%), while the setting time decreased significantly (and remained unchanged). X-ray diffraction analysis identified the formation of aluminosilicate minerals as the main reason for the excellent mechanical properties and accelerated coagulation rate. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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13 pages, 3537 KiB

Open AccessArticle

Effect of Carbon Fibres on Electromagnetic-Interference-Shielding Properties of Geopolymer Composites

by Dimuthu Wanasinghe, Farhad Aslani and Guowei Ma

Polymers 2022, 14(18), 3750; https://doi.org/10.3390/polym14183750 - 08 Sep 2022

Cited by 8 | Viewed by 1549

Abstract

Many of the construction materials available are known to cause a drastic level of damage to the environment during their manufacturing stages. Hence, many researchers have attempted to formulate construction materials that are more environmentally friendly. Additionally, the rise in wireless communications in [...] Read more.

Many of the construction materials available are known to cause a drastic level of damage to the environment during their manufacturing stages. Hence, many researchers have attempted to formulate construction materials that are more environmentally friendly. Additionally, the rise in wireless communications in recent decades has seen a rapid increase in electromagnetic pollution and interference, which affects the functionality of sensitive electronic devices. This research is focused on fabricating a more sustainable construction material that could prevent electromagnetic interference for electronic devices housed inside. Carbon fibres of three different lengths were added in four variations to a geopolymer control mix to study their effect on electromagnetic interference shielding. The results showed that the amount of shielding produced by these composites increases with carbon fibre length and quantity. Morphological analyses showed that the interconnectivity of the fibres plays a crucial role in having a high level of shielding. While the flexural strength showed an improvement with the addition of carbon fibre, the compressive strength showed a slight reduction with the increase in carbon fibre length. The optimal level of shielding was produced by the specimen containing 0.7% of 12 mm carbon fibre, which was the maximum amount of fibre of any length used in this study; the optimal level of shielding generated was 43.43 dB within the frequency range of 30 MHz to 1.5 GHz. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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13 pages, 2037 KiB

Open AccessArticle

Synthesis Metakaolin-Based Geopolymer Incorporated with SiC Sludge Using Design of Experiment Method

by Kang-Wei Lo, Wei-Ting Lin, Ya-Wen Lin, Ta-Wui Cheng and Kae-Long Lin

Polymers 2022, 14(16), 3395; https://doi.org/10.3390/polym14163395 - 19 Aug 2022

Cited by 6 | Viewed by 1518

Abstract

This study uses metakaolin, sodium hydroxide, sodium metasilicate, and water content as the reaction variables in the application of the design of experiment (DOE) method. At the same time, the various component factors and their interactions were analyzed to understand how these factors [...] Read more.

This study uses metakaolin, sodium hydroxide, sodium metasilicate, and water content as the reaction variables in the application of the design of experiment (DOE) method. At the same time, the various component factors and their interactions were analyzed to understand how these factors affect the mechanical properties of a metakaolin-based geopolymer incorporated with SiC sludge (SCSGPs). The results of the statistical analysis showed that the compressive strength of SCSGPs was affected by the Na/Si molar ratio (NSR) (p-level = 0.000 <0.05), the Na/Al molar ratio (NAR) (p-level= 0.000 <0.05), and the interaction between the dissolution rate of Si (DRA). Within the design scope of this study, the maximum compressive strength of SCSGPs and the coefficients of the NSR, the NAR, and the DRA of SCSGPs was evaluated. The multiple regression analysis and the tested coefficient of r² were also studied. The multiple regression analysis models provide an effective reference for the application of SCSGPs. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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16 pages, 6377 KiB

Open AccessArticle

The Length Change Ratio of Ground Granulated Blast Furnace Slag-Based Geopolymer Blended with Magnesium Oxide Cured in Various Environments

by Yen-Chun Chen, Wei-Hao Lee, Ta-Wui Cheng, Walter Chen and Yeou-Fong Li

Polymers 2022, 14(16), 3386; https://doi.org/10.3390/polym14163386 - 18 Aug 2022

Cited by 3 | Viewed by 1425

Abstract

Geopolymer (GP) has been considered a potential material to replace ordinary Portland cement (OPC) because of its excellent mechanical properties and environmentally friendly process. However, the promotion of GP is limited due to the large shrinkage and the different operating procedures compared to [...] Read more.

Geopolymer (GP) has been considered a potential material to replace ordinary Portland cement (OPC) because of its excellent mechanical properties and environmentally friendly process. However, the promotion of GP is limited due to the large shrinkage and the different operating procedures compared to cement. This study aims to reduce the shrinkage of ground granulated blast furnace slag (GGBFS) based GP by the hydration expansion properties of activated magnesium oxide (MgO). The slurry of GP was blended from GGBFS, MgO, and activator; and the compositions of the activator are sodium hydroxide (NaOH), sodium silicate (Na₂SiO₃), and alumina silicate(NaAlO₂). Herein, the GGFBS and MgO were a binder and a shrinkage compensation agent of GP, respectively. After unmolding, the GP specimens were cured under four types of environments and the lengths of the specimens were measured at different time intervals to understand the length change ratio of GP. In this study, two groups of GP specimens were made by fixing the activator to binder (A/B) ratio and the fluidity. The test results show that adding MgO will reduce the shrinkage of GP as A/B ratio was fixed. However, fixing the fluidity exhibited the opposite results. The X-ray diffraction (XRD) was used to check the Mg(OH)₂ that occurred due to the MgO hydration under four curing conditions. Three statistical and machine learning methods were used to analyze the length change of GP based on the test data. The testing and analysis results show that the influence of curing environments is more significant for improving the shrinkage of GP than additive MgO. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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21 pages, 4811 KiB

Open AccessArticle

Compressive Strength Estimation of Geopolymer Composites through Novel Computational Approaches

by Muhammad Nasir Amin, Kaffayatullah Khan, Waqas Ahmad, Muhammad Faisal Javed, Hisham Jahangir Qureshi, Muhammad Umair Saleem, Muhammad Ghulam Qadir and Muhammad Iftikhar Faraz

Polymers 2022, 14(10), 2128; https://doi.org/10.3390/polym14102128 - 23 May 2022

Cited by 21 | Viewed by 2158

Abstract

The application of artificial intelligence approaches like machine learning (ML) to forecast material properties is an effective strategy to reduce multiple trials during experimentation. This study performed ML modeling on 481 mixes of geopolymer concrete with nine input variables, including curing time, curing [...] Read more.

The application of artificial intelligence approaches like machine learning (ML) to forecast material properties is an effective strategy to reduce multiple trials during experimentation. This study performed ML modeling on 481 mixes of geopolymer concrete with nine input variables, including curing time, curing temperature, specimen age, alkali/fly ash ratio, Na₂SiO₃/NaOH ratio, NaOH molarity, aggregate volume, superplasticizer, and water, with CS as the output variable. Four types of ML models were employed to anticipate the compressive strength of geopolymer concrete, and their performance was compared to find out the most accurate ML model. Two individual ML techniques, support vector machine and multi-layer perceptron neural network, and two ensembled ML methods, AdaBoost regressor and random forest, were employed to achieve the study’s aims. The performance of all models was confirmed using statistical analysis, k-fold evaluation, and correlation coefficient (R²). Moreover, the divergence of the estimated outcomes from those of the experimental results was noted to check the accuracy of the models. It was discovered that ensembled ML models estimated the compressive strength of the geopolymer concrete with higher precision than individual ML models, with random forest having the highest accuracy. Using these computational strategies will accelerate the application of construction materials by decreasing the experimental efforts. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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16 pages, 5134 KiB

Open AccessArticle

Determination of the Thermal Parameters of Geopolymers Modified with Iron Powder

by Karol Prałat, Justyna Ciemnicka, Artur Koper, Michał Marek Szczypiński, Piotr Łoś, Van Vu Nguyen, Van Su Le, Cezary Rapiejko, Roberto Ercoli and Katarzyna Ewa Buczkowska

Polymers 2022, 14(10), 2009; https://doi.org/10.3390/polym14102009 - 13 May 2022

Cited by 5 | Viewed by 1687

Abstract

The paper presents the results of research concerning the influence of a metallic micromaterial on the thermal conductivity λ, specific heat Cp, and thermal diffusivity a of modified geopolymers. Iron oxide in the form of powder with an average granulation of 10 [...] Read more.

The paper presents the results of research concerning the influence of a metallic micromaterial on the thermal conductivity λ, specific heat Cp, and thermal diffusivity a of modified geopolymers. Iron oxide in the form of powder with an average granulation of 10 μm was used as the geopolymer-modifying material. The research concerned geopolymer composite samples with metakaolin (activated with potassium silicate) and the addition of iron in amounts ranging from 0.5% to 2.5% in relation to the weight of the metakaolin. Additionally, the samples were modified with sand and fireclay in two different amounts—1:1 and 1:1.2 in relation to the metakaolin. The addition of fireclay caused a decrease in the thermal conductivity of the composites by 30% when compared to the samples with the addition of sand. The lowest value of the thermal conductivity coefficient λ was obtained for the geopolymer with metakaolin and fireclay. When the ratio of these components in the composite was 1:1, the value of thermal conductivity was equal to 0.6413 W/(m·K), while in the case of their ratio being 1:1.2, it was equal to 0.6456 W/(m·K). In the samples containing fireclay, no significant influence of the added iron on the values of thermal conductivity was noticed. In the case of the geopolymer with sand, the effect was noticeable, and it was most visible in the samples containing metakaolin and sand in the ratio of 1:1.2. It was noticed that with an increase in the addition of Fe, the thermal conductivity of the composite increased. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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16 pages, 2876 KiB

Open AccessArticle

Development of Geopolymers Based on Fly Ashes from Different Combustion Processes

by Kinga Pławecka, Patrycja Bazan, Wei-Ting Lin, Kinga Korniejenko, Maciej Sitarz and Marek Nykiel

Polymers 2022, 14(10), 1954; https://doi.org/10.3390/polym14101954 - 11 May 2022

Cited by 12 | Viewed by 1830

Abstract

The main aim of this research is to assess different fly ashes as raw materials for the manufacturing of geopolymers. Three different fly ashes have been investigated. First, a conventional fly ash from the Skawina coal power plant (Poland), obtained at a temperature [...] Read more.

The main aim of this research is to assess different fly ashes as raw materials for the manufacturing of geopolymers. Three different fly ashes have been investigated. First, a conventional fly ash from the Skawina coal power plant (Poland), obtained at a temperature of 900–1100 °C. Second, ultra-fine fly ash from a power plant in China; the side product received at 1300 °C. The third fly ash was waste was obtained after combustion in incineration plants. To predict the properties and suitability of materials in the geopolymerization process, methods based on X-ray analysis were used. The applied precursors were tested for elemental and chemical compounds. The investigations of geopolymer materials based on these three fly ashes are also presented. The materials produced on the basis of applied precursors were subjected to strength evaluation. The following research methods were applied for this study: density, X-ray fluorescence (XRF), X-ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), flexural and compressive strength. The obtained results show that materials based on fly ashes had a similar compressive strength (about 60 MPa), while significant differences were observed during the bending test from 0.1 to 5.3 MPa. Ultra-fine fly ash had a lower flexural strength compared to conventional fly ash. This study revealed the need for process optimization for materials based on a precursor from a waste incineration plant. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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12 pages, 3246 KiB

Open AccessArticle

Fire Resistance of Geopolymer Foams Layered on Polystyrene Boards

by Van Su Le, Van Vu Nguyen, Artem Sharko, Roberto Ercoli, Thang Xiem Nguyen, Doan Hung Tran, Piotr Łoś, Katarzyna Ewa Buczkowska, Stanisław Mitura, Tomáš Špirek and Petr Louda

Polymers 2022, 14(10), 1945; https://doi.org/10.3390/polym14101945 - 11 May 2022

Cited by 12 | Viewed by 1884

Abstract

Geopolymer foams are excellent materials in terms of mechanical loads and fire resistance applications. This study investigated the foaming process of geopolymers and foam stability, with a focus on the fire resistance performance when using polystyrene as the base layer. The main purpose [...] Read more.

Geopolymer foams are excellent materials in terms of mechanical loads and fire resistance applications. This study investigated the foaming process of geopolymers and foam stability, with a focus on the fire resistance performance when using polystyrene as the base layer. The main purpose is to define the influence of porosity on the physical properties and consequently to find applications and effectiveness of geopolymers. In this study, lightweight materials are obtained through a process called geopolymerization. Foaming was done by adding aluminum powder at the end of the geopolymer mortar preparation. The interaction between the aluminum powder and the alkaline solution (used for the binder during the mixing process) at room temperature is reactive enough to develop hydrogen-rich bubbles that increase the viscosity and promote the consolidation of geopolymers. The basic principle of thermodynamic reactions responsible for the formation of foams is characterized by hydrogen-rich gas generation, which is then trapped in the molecular structure of geopolymers. The geopolymer foams in this study are highly porous and robust materials. Moreover, the porosity distribution is very homogeneous. Experimental assessments were performed on four specimens to determine the density, porosity, mechanical strength, and thermal conductivity. The results showed that our geopolymer foams layered on polystyrene boards (with optimal thickness) have the highest fire resistance performance among others. This combination could withstand temperatures of up to 800 °C for more than 15 min without the temperature rising on the insulated side. Results of the best-performing geopolymer foam underline the technical characteristics of the material, with an average apparent density of 1 g/cm³, a volume porosity of 55%, a thermal conductivity of 0.25 W/mK, and excellent fire resistance. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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13 pages, 13534 KiB

Open AccessArticle

Intumescent Silicate Coatings with the Addition of Alkali-Activated Materials

by Nicoleta Florentina Cirstea, Alina Badanoiu and Aurelian Cristian Boscornea

Polymers 2022, 14(10), 1937; https://doi.org/10.3390/polym14101937 - 10 May 2022

Cited by 7 | Viewed by 1973

Abstract

Fireproof inorganic coatings based on sodium silicate solution with intumescent additions were prepared and tested to assess their ability to limit the negative effect of a fire. The intumescent materials were obtained by the alkali activation of waste glass powder (obtained by the [...] Read more.

Fireproof inorganic coatings based on sodium silicate solution with intumescent additions were prepared and tested to assess their ability to limit the negative effect of a fire. The intumescent materials were obtained by the alkali activation of waste glass powder (obtained by the grinding of recycled soda-lime culet) and slag (waste resulting from the metallurgical industry). The replacement of talc (used as filler in paint formulation) with the intumescent materials obtained by the alkaline activation of waste glass powder (WGP), determined an increase in the intumescence coefficient (up to 65%) and decreased the activation temperature of this process. To evaluate these coatings’ abilities to prevent or delay the temperature increase in metal structures, the paints were applied on steel plates and tested in direct contact with the flame of a butane burner for 60 min. The coatings prevented the increase in the steel substrate temperature over one considered critical (500°C) for steel mechanical properties; the combination of two coatings, with different intumescence activation temperatures, correlated with the increase in the coating’s thickness, sensibly reduced the rate of temperature increase (up to 75%) in the steel substrate. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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21 pages, 4390 KiB

Open AccessArticle

Application of Soft Computing Techniques to Predict the Strength of Geopolymer Composites

by Qichen Wang, Waqas Ahmad, Ayaz Ahmad, Fahid Aslam, Abdullah Mohamed and Nikolai Ivanovich Vatin

Polymers 2022, 14(6), 1074; https://doi.org/10.3390/polym14061074 - 08 Mar 2022

Cited by 45 | Viewed by 3301

Abstract

Geopolymers may be the best alternative to ordinary Portland cement because they are manufactured using waste materials enriched in aluminosilicate. Research on geopolymer composites is accelerating. However, considerable work, expense, and time are needed to cast, cure, and test specimens. The application of [...] Read more.

Geopolymers may be the best alternative to ordinary Portland cement because they are manufactured using waste materials enriched in aluminosilicate. Research on geopolymer composites is accelerating. However, considerable work, expense, and time are needed to cast, cure, and test specimens. The application of computational methods to the stated objective is critical for speedy and cost-effective research. In this study, supervised machine learning approaches were employed to predict the compressive strength of geopolymer composites. One individual machine learning approach, decision tree, and two ensembled machine learning approaches, AdaBoost and random forest, were used. The coefficient correlation (R²), statistical tests, and k-fold analysis were used to determine the validity and comparison of all models. It was discovered that ensembled machine learning techniques outperformed individual machine learning techniques in forecasting the compressive strength of geopolymer composites. However, the outcomes of the individual machine learning model were also within the acceptable limit. R² values of 0.90, 0.90, and 0.83 were obtained for AdaBoost, random forest, and decision models, respectively. The models’ decreased error values, such as mean absolute error, mean absolute percentage error, and root-mean-square errors, further confirmed the ensembled machine learning techniques’ increased precision. Machine learning approaches will aid the building industry by providing quick and cost-effective methods for evaluating material properties. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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14 pages, 5666 KiB

Open AccessArticle

Highly Efficient Adsorption of Sr²⁺ and Co²⁺ Ions by Ambient Prepared Alkali Activated Metakaolin

by Yi-Hsuan Huang and Yu-Chun Wu

Polymers 2022, 14(5), 992; https://doi.org/10.3390/polym14050992 - 28 Feb 2022

Cited by 3 | Viewed by 1764

Abstract

This study aimed to explore a low cost and sustainable adsorbent to remove Sr²⁺ and Co²⁺ ions, which are major radioactive ions in nuclear wastewater. The material properties of the alkali-activated metakaoline as a function of soaking time at ambient temperature [...] Read more.

This study aimed to explore a low cost and sustainable adsorbent to remove Sr²⁺ and Co²⁺ ions, which are major radioactive ions in nuclear wastewater. The material properties of the alkali-activated metakaoline as a function of soaking time at ambient temperature from 1 day to 7 days were examined by XRD, XRF, SEM, and solid-state NMR. Adsorption isotherms were used to evaluate the appropriate soaking time for the optimal sorption performance for both Sr²⁺ and Co²⁺ ions. The alkali-activated metakaolin soaked for 3 days (BK3) presented the maximum adsorption capacities of 3.81 meq/g (167.5 mg/g) and 4.02 meq/g (118.5 mg/g) for Sr²⁺ and Co²⁺, respectively. The sorption mechanisms for Sr²⁺ and Co²⁺ in the BK3 sample were investigated, and the experimental results indicated that adsorption for Sr²⁺ was achieved via ion exchange. By contrast, surface complexation in combination with ion exchange contributed to the sorption mechanisms for the removal of Co²⁺. Competitive adsorption experiments revealed that the alkali-activated metakaolin favored the adsorption for divalent ions (i.e., Sr²⁺ and Co²⁺), and it was less effective for Cs⁺. Finally, the used adsorbent could be directly mineralized and vitrified by heat treatment to immobilize the Sr²⁺ and Co²⁺ ions. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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18 pages, 6527 KiB

Open AccessArticle

Fresh Properties and Sulfuric Acid Resistance of Sustainable Mortar Using Alkali-Activated GGBS/Fly Ash Binder

by Osama Ahmed Mohamed and Rania Al Khattab

Polymers 2022, 14(3), 591; https://doi.org/10.3390/polym14030591 - 01 Feb 2022

Cited by 23 | Viewed by 2864

Abstract

In this study, sorptivity, setting time, resistance to sulfuric acid, and compressive strength of mortars that use alkali-activated GGBS and fly ash as binders, were evaluated experimentally. The activation of binders, was achieved at room temperature of 22 ± 2 °C using combinations [...] Read more.

In this study, sorptivity, setting time, resistance to sulfuric acid, and compressive strength of mortars that use alkali-activated GGBS and fly ash as binders, were evaluated experimentally. The activation of binders, was achieved at room temperature of 22 ± 2 °C using combinations of sodium silicates (Na₂SiO₃) and sodium hydroxide (NaOH) solutions in ratios of 1.5, 2.0, and 2.5. The parameters considered in terms of their effects on fresh and hardened properties include: NaOH molarity, activator ratio Na₂SiO₃/NaOH, mortar sample age, and relative amount of GGBS/fly ash in binder combination. Sorptivity, change in mass, and compressive strength were determined for mortar samples that were submerged in 10% sulfuric acid solution for 7 days, 28 days, and 90 days. The binder for mortar samples tested at each of the specified ages consisted of 100% GGBS (G100), 75%GGBS+25% fly ash (G75F25), or 50% GGBS + 50% fly ash (G50F50). The binder was activated using Na₂SiO₃ solution, combined with 10 M, 12 M, 14 M, or 16 M NaOH solution. It was found that sorptivity decreases with increase in curing age, for all activator ratios, concentrations, and relative amounts of GGBS/fly ash. Binder consisting of 75%GGBS + 25% fly ash with NaOH concentration of 12 M had the lowest sorptivity. Exposure of alkali-activated GGBS/fly ash mortar samples to sulfate attack did not cause loss in mass nor visible signs of damage/deterioration. All binder combinations experienced increase in compressive strength after curing in 10%sufluric acid solution, with the optimum G75F25 mix achieving a 28-day strength of 80.53 MPa when NaOH molarity is 10 M, which increased to 91.06 MPa after 90 days. Variation in concentration of NaOH didn’t cause significant change in the magnitudes of 28-day or 90-day compressive strengths of G50F50. However, despite slow dissolution of fly ash and immersion in 10% sulfuric acid solution, G50F50 developed 28-day compressive strength of 56.23 MPa and 90-day compressive of 86.73 MPa, which qualifies G50F50 as high strength mortar for practical purposes. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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15 pages, 9097 KiB

Open AccessArticle

Effects of Composition Type and Activator on Fly Ash-Based Alkali Activated Materials

by Chan-Yi Lin and Tai-An Chen

Polymers 2022, 14(1), 63; https://doi.org/10.3390/polym14010063 - 24 Dec 2021

Cited by 5 | Viewed by 2306

Abstract

The compressive strengths of fly ash-based alkali-activated materials (AAM), produced using various activators of only sodium hydroxide, were measured. Fly ash-based AAM specimens, produced by mixing different kinds of fly ash and ground granulated blast-furnace slag (GGBFs) with an activator containing only sodium [...] Read more.

The compressive strengths of fly ash-based alkali-activated materials (AAM), produced using various activators of only sodium hydroxide, were measured. Fly ash-based AAM specimens, produced by mixing different kinds of fly ash and ground granulated blast-furnace slag (GGBFs) with an activator containing only sodium hydroxide, were cured at ambient temperature, and then placed in air for different numbers of days. The short- and long-term compressive strengths and shrinkage of fly ash-based AAM were measured and compared to one another. The effects of type of fly ash, alkali-equivalent content, GGBFs replace percentage, and ages on the compressive strengths and shrinkage of fly ash-based AAM were investigated. Even when different fly ash was used as the raw material for AAM, a similar compressive strength can be achieved by alkali-equivalent content, GGBFs replaces percentage. However, the performance of shrinkage due to different types of fly ash differed significantly. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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Review

Jump to: Research

10 pages, 647 KiB

Open AccessReview

Minimizing the Global Warming Potential with Geopolymer-Based Insulation Material with Miscanthus Fiber

by Steffen Witzleben

Polymers 2022, 14(15), 3191; https://doi.org/10.3390/polym14153191 - 05 Aug 2022

Cited by 10 | Viewed by 2665

Abstract

Approximately 45% of global greenhouse gas emissions are caused by the construction and use of buildings. Thermal insulation of buildings in the current context of climate change is a well-known strategy to improve the energy efficiency of buildings. The development of renewable insulation [...] Read more.

Approximately 45% of global greenhouse gas emissions are caused by the construction and use of buildings. Thermal insulation of buildings in the current context of climate change is a well-known strategy to improve the energy efficiency of buildings. The development of renewable insulation material can overcome the drawbacks of widely used insulation systems based on polystyrene or mineral wool. This study analyzes the sustainability and thermal conductivity of new insulation materials made of Miscanthus x giganteus fibers, foaming agents, and alkali-activated fly ash binder. Life cycle assessments (LCA) are necessary to perform benchmarking of environmental impacts of new formulations of geopolymer-based insulation materials. The global warming potential (GWP) of the product is primarily determined by the main binder component sodium silicate. Sodium silicate’s CO₂ emissions depend on local production, transportation, and energy consumption. The results, which have been published during recent years, vary in a wide range from 0.3 kg to 3.3 kg CO₂-eq. kg⁻¹. The overall GWP of the insulation system based on Miscanthus fibers, with properties according to current thermal insulation regulations, reaches up to 95% savings of CO₂ emissions compared to conventional systems. Carbon neutrality can be achieved through formulations containing raw materials with carbon dioxide emissions and renewable materials with negative GWP, thus balancing CO₂ emissions. Full article

(This article belongs to the Special Issue Development in Geopolymers)

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