Hydroxide Ratio Research Articles

An Experimental and Predictive Models for Compressive Strength of Geopolymer Concrete Made with GGBFS and Fly ash

This work investigated the potential synergy between Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) as binder solids in the manufacturing of Geopolymer Concrete (GPC), a concrete that does not contain Ordinary Portland Cement (OPC). At a ratio of 1:1, the ideal mixture of binder solids was attained. Based on absolute volume, the mix design was created using techniques akin to those found in ACI 211.1. In order to investigate the impact on the evolution of strengths, the alkaline activator content (AAC) to binder solid ratio—which is comparable to the water/binder ratio in OPC concrete—was varied in the ratios of 0.25, 0.3, 0.35, 0.4, and 0.5. For every mixture, the ratio of sodium hydroxide to sodium silicate was maintained at 1.5. To evaluate the functional relationships between the response variable (strength) and the independent variables (GPC constituents), a nonlinear regression analysis was conducted. Experimental results on workability for all mixes are in agreement with ACI 211.1 criteria. In all mixes, GPC specimens exhibited higher compressive strengths than OPC specimens; with a maximum value of 73.67 Mpa and 72.67 Mpa respectively. Nonlinear regression results provide equations that predict the strengths with excellent correlation. In addition to F-statistics that are statistically significant within acceptable probabilities.

Biogas upgrading using aqueous bamboo-derived activated carbons.

CO2/CH4 separation is crucial for biogas upgrading. In this study, the bamboo-derived activated carbons (BACs) were prepared with different ratios of potassium hydroxide (KOH)/bamboo charcoal (BC), and the hybrid sorbents of aqueous BACs were developed for CO2/CH4 separation. Both the gas solubility and sorption rate were measured, and Henry's constant and liquid-side mass-transfer coefficient as well as the CO2/CH4 selectivity were calculated. Meanwhile, the comprehensive performances of aqueous BACs were evaluated using a novel index, and the cost of biogas upgrading using the aqueous BACs was estimated and compared to the commercialized technology. The results proved the effectiveness of aqueous BACs, and the comprehensive performance of 7.0 wt% aqueous BAC with the KOH/BC mass ratio of 2:1 was 4.2 times than that of H2O, having the potential to decrease the average CO2/CH4 separation cost by 65.0% compared to the commercialized technology.

Accelerated microwave curing of hybrid geopolymers with nano-silica for enhanced physico-mechanical properties

This paper presents the microwave curing method as an alternative to conventional thermal curing of hybrid (fly ash-slag) geopolymer mortars (GMs) to achieve comparable performance with significantly reduced curing times. This study aimed to ascertain the impact of varying nano-silica contents (0.5%, 0.75%, and 1%) on the geopolymer matrix to identify the optimal dosage for enhancing densification and bond improvement phases. Mixture proportions were designed to achieve high mechanical and durability performances. The activator/binder (A/B) ratio was set at 0.71, the sodium silicate to sodium hydroxide ratio at 1.5, and the sand/binder (S/B) ratio at 2.5. This study considered two curing methods: thermal curing at 80 °C for 24 hours and microwave curing at 119 W for 3 minutes. The latter method produces equivalent thermal effects in a significantly shorter time. Physical properties tested after seven days included water absorption, porosity, and mechanical properties related to compressive and flexural strength. The results demonstrated that incorporating NS markedly enhanced the physical and mechanical characteristics. Moreover, microwave curing has been identified as a promising approach for producing hybrid geopolymers, offering a low-energy and high-performance alternative.

Alkaleri Metakaolin Powder Performance Evaluation by Response Surface Method.

Alkaleri metakaolin (AMK) based geopolymer binder has been identified as one of the alternatives to the Ordinary Portland Cement (OPC), which qualifies the criteria for green construction material. In this work, 20No of experimental mix proportions (RUNs) were designed by Central Composite Design (CDD) of Response Surface Method (RSM). Mixture of AMK and Alkaline Solution was heated for 45mins at 60oc with stirring interval of 15mins, after which aggregates were added to the hot mix. 60No of 100X100X100mm cubes were cast. Samples were tested at the 28th day of ambient curing. The reported Compressive Strengths are the average of the 60 sample tested with 38.6N/mm2 as the maximum, hence established the experimental optimum mix proportion (EOMP). The ANOVA model developed statistically validated by having F-value of 15.54 and P-value of less than 0.0001 indicating that the model is statistically significant. Also, the adequate precision of 10.7850 which is greater than 4.00 indicates adequate signal and desirable. Furthermore, the difference between predicted R2 and adjusted R2 is less than 0.2 testifying that they are rationally in good agreement. Effects of three principal variables namely: molarity of sodium hydroxide, sodium silicate to sodium hydroxide ratio, and fineness (particle size) on the properties of the fresh and hardened AMK geopolymer concrete (normal consistency, soundness, setting times, slump, dry density, water absorption, compressive strength, flexural strength, split tensile strength, sorptivity and acid attack) were investigated. All the results for the properties investigated were found to have fallen within the ranges of the international standard codes such as ASTM and British Standard, hence AMK is qualify to be used as Metakaolin based geopolymer binder.

Multi-objective optimization and prediction of strength along with durability in acid-resistant self-compacting alkali-activated concrete

Sustainability in concrete production reduces the environmental impact and conserves resources, yielding durable concrete. This study focuses on developing and analyzing an acid-resistant Self-Compacting alkali-activated concrete (SCAC). Optimization of mix proportions of SCAC containing GGBFS as a binder was performed through experimental methods and multi-objective optimization. The fresh and mechanical characteristics of SCAC were evaluated, examining the impact of sodium hydroxide (NaOH) molarity and sodium silicate to sodium hydroxide (SS/SH) ratio on strength loss under acid exposure. Optimal mix proportions were identified experimentally for both M25 and M45 SCAC grades. A comprehensive database of 120 observations from experimental findings was used to develop a machine learning (ML) model to predict compressive strength and loss of strength due to acid attack. The gradient boost regression with R2 of 0.96 and the long short-term memory (LSTM) model with R2 of 0.93 were established to be best performing in predicting strength and strength loss respectively. These models were then used as objective functions in a multi-objective optimization to maximize strength and minimize acid-induced strength loss. A cost-based comparison of experimentally and analytically optimized mix proportions was provided. The established optimal NaOH molarity and SS/SH ratio for both M25 and M45 grade SCGC were 12 M and 2.3 along with 12 M and 2.5 respectively. This research offers valuable insights for further experimental work on sustainable and resilient SCAC.

SYNTHESIS OF 1-VINYL-3(5)-METHYL-4-NITROPYRAZOLE AND STUDY OF THE EFFECT OF METHYL SUBSTITUTES IN THE PYRAZOLE RING DURING RADICAL POLYMERIZATION

The aim of this work was to develop a convenient preparative method for the direct N-alkylation of 3(5)-methyl-4-nitropyrazole under conditions of phase-transfer catalysis (PTC). The need for development was also dictated by the fact that the reaction products are simultaneously intermediates in the synthesis of an important class of compounds - vinylpyrazoles. Alkylation of 3(5)-methyl-4-nitropyrazole under standard conditions of PTC (benzene-water-KOH-TEBACH (triethylbexylammonium chloride)) did not lead to the desired result. Apparently, benzene interrupts the transfer of the nitropyrazole anion from the aqueous organic medium, as a result of which the yield of the control alkyl compound is only 50%. During alkylation in the absence of benzene, under the influence of potassium hydroxide in water, deprotonation easily proceeds and the corresponding potassium salt of 3(5)-methyl-4-nitropyrazole is formed, which blocks the dehydrochlorination of 1,2-dichloroethane and leads to the selective course of the process of alkylation of the taken nitropyrazole. At an equimolar ratio of nitropyrazole and potassium hydroxide, the yield of a mixture of the resulting 1-(2-chloroethyl)-3- and 1-(2-chloroethyl)-5-methyl-4-nitropyrazoles reaches 80%. The dehydrochlorination of the obtained substituted chloroethylpyrazoles in a methanol solution, under conditions of PTC, and in an aqueous solution of N-methylmorpholine-N-oxide (NMO/H2O), in the presence of potassium hydroxide was also studied. Although the homogeneous method of dehydrochlorination is technologically imperfect, however, it makes it possible to obtain a mixture of 1-vinyl-3- and 1-vinyl-5-methyl-4-nitropyrazole isomers with a yield of 45%. Dehydrochlorination under PTC conditions is an alternative to a homogeneous process; however, it is not able to provide a high yield of the expected compounds - 20%. It has been established that the dehydrochlorination of the studied 1-(2̕'-chloroethyl)-3(5)-methyl-4-nitropyrazoles proceeds significantly successfully in the presence of KOH in the NMO/H2O system, leading to the total yield of 1-vinyl-3- and 1-vinyl -5-methyl-4-nitropyrazoles up to 60%. The effects of methyl substituents of the pyrazole ring during radical polymerization have been studied. The identified monomers exhibit different activities under the same conditions. Thus, in the process of radical polymerization, the isomer in which the methyl group is in the fifth position of the pyrazole ring polymerizes at a higher rate than the isomer in which the methyl group is in the third position. For citation: Bichakhchyan L.A., Markosyan A.J., Shakhatuni A.G., Badalyan K.S., Attaryan O.S., Khachatryan A.N. Synthesis of 1-vinyl-3(5)-methyl-4-nitropyrazole and study of the effect of methyl substitutes in the pyrazole ring during radical polymerization. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 12. P. 39-46. DOI: 10.6060/ivkkt.20246712.7065.

Artificial intelligence prediction of the mechanical properties of banana peel-ash and bagasse blended geopolymer concrete

This research explores the application of Artificial Intelligence (AI) techniques to assess the mechanical properties of geopolymer concrete made from a blend of Banana Peel-Ash (BPA) and Sugarcane Bagasse Ash (SCBA), using a sodium silicate (Na2SiO3) to sodium hydroxide (NaOH) ratio ranging from 1.5 to 3. Utilizing three AI methodologies—Artificial Neural Networks (ANN), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Gene Expression Programming (GEP)—the study aims to enhance prediction accuracy for the mechanical properties of geopolymer concrete based on 104 datasets. By optimizing mix designs through varying proportions of BPA and SCBA, alkaline activator molarity, and aggregate-to-binder ratios, the research identified combinations that significantly enhance mechanical properties, demonstrating notable international relevance as it contributes to global efforts in sustainable construction by effectively utilizing industrial by-products. The experimental results demonstrated that increasing the molarity of the alkaline activator from 4 to 10 M significantly enhanced both the compressive and flexural strengths of the geopolymer concrete. Specifically, a mixture containing 52.5% SCBA and 47.5% BPA at a 10 M molarity achieved a maximum compressive strength of 33.17 MPa after 20 h of curing. In contrast, a mixture composed of 95% SCBA and 5% BPA at a 4 M molarity exhibited a substantially lower compressive strength of only 21.27 MPa. Additionally, the highest recorded flexural strength of 9.95 MPa (77.25% SCBA and 22.5 BPA) was observed at the 10 M molarity, while the flexural strength at 4 M was lowest, at 4.12 MPa (95% SCBA and 5% BPA). Microstructural analysis through Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (ED-SEM) revealed insights into the pore structure and elemental composition of the concrete, while Thermogravimetric Analysis (TGA) provided data on the material’s thermal stability and decomposition characteristics. Performance analysis of the AI models showed that the ANN model had an average MSE of 1.338, RMSE of 1.157, MAE of 3.104, and R2 of 0.989, while the ANFIS model outperformed with an MSE of 0.345, RMSE of 0.587, MAE of 1.409, and R2 of 0.998. The GEP model demonstrated an MSE of 1.233, RMSE of 1.110, MAE of 1.828, and R2 of 0.992, confirming that ANFIS is the most accurate model for predicting the mechanical and rheological properties of geopolymer concrete. This study highlights the potential of integrating AI with experimental data to optimize the formulation and performance of geopolymer concrete, advancing sustainable construction practices by effectively utilizing industrial by-products.

Investigating the influence of various metakaolin combinations with different proportions of pond ash and Alccofine 1203 on ternary blended geopolymer concrete at ambient curing.

This paper explores the use of a ternary blended geopolymer concrete (TBGPC) incorporating metakaolin (MK), pond ash (PA), and Alccofine 1203 (AF). Three combinations of MK (25%, 50%, and 75%) with varying proportions of PA and AF were prepared, validating against M30 grade cement concrete (CC). TBGPC was prepared with an 8 molarity sodium hydroxide, sodium silicate to sodium hydroxide ratio of 2.0, liquid to binder ratio of 0.5, and an ambient curing mode. For CC, a water to cement ratio of 0.42 and water curing mode were adopted. The mechanical properties and durability behavior of TBGPC and CC specimens were evaluated through compressive strength, rapid chloride penetration test, permeability test, sorptivity test, and water absorption test. The M50P35A15 mix demonstrated remarkable compressive strength improvements, showing a 203% increase over the CC mix at 1day and 250% by 3days. This trend continued with a 155% increase at 7days, 68% at 28days, and 52% at 90days, consistently outperforming the CC mix. Additionally, microstructure characteristics of the M50P35A15 mix were analyzed through SEM studies, providing validation for the observed strength development. Notably, M50P35A15 mix demonstrated substantially higher early and later strength gain. This enhancement in strength was attributed to the gradual densification of the microstructure over time and the formation of additional NASH and CASH gel in M50P35A15 mix. At 28days, the M50P35A15 mix exhibited excellent durability characteristics, with a Coulomb value of 1008, permeability of 10mm, sorptivity of 0.45mm/√min × 10-4, and water absorption of 1.07%. This study demonstrates the potential of MK, PA, and AF as viable materials for sustainable geopolymer concrete, offering a low-carbon alternative to traditional cement concrete with superior strength and durability aspects.

Study of silicon dioxide nanoparticles on the rheological and mechanical behaviors of self-compacting geopolymer concrete

AbstractGeopolymer concrete (GPC) is a rising eco-conscious substitute for traditional cement-based concrete, bringing the construction industry closer to sustainability. Self-compacting geopolymer concrete (SCGC) enhances the concrete flowability and fills the congested reinforced areas without vibrators in concrete structures such as bridges, tunnels and canals. This study aims to analyze the impact of silicon dioxide nanoparticles (NS) on the rheological and mechanical properties of SCGC to optimize the dosage of NS in SCGC. For this purpose, NS (0–6%) blended in partially distributed binders of fly ash and ground granulated blast furnace slag (50:50) with 0.5 alkaline binder ratio, 2% superplasticizers (9 kg m−3) (MasterGlenium SKY 8233) and 12% extra water (54 kg m−3). Sodium silicate solution and sodium hydroxide ratio of 2.5 was used for this study. It is observed that SCGC with 3% NS replacement complied with the guidelines of EFNARC. According to the T50cm slump flow test, V-funnel test, and L-box test results meet the guidelines of up to 4% NS replacement, and 3% NS addition offers excellent mechanical properties in SCGC. This study concluded that the replacement of 3% of NS improved the fresh and hardened properties of SCGC, which can apply to construction.

Effect of sodium gluconate addition on setting, hardening, and microstructure behaviour of hybrid alkaline mortar

In this investigation, the influence of adding 2 %, 4 %, 7 %, and 10 % sodium gluconate (SG) on the setting time of hybrid alkaline paste, and hardened and microstructure properties of hybrid alkaline mortar mixes were examined, and the results were compared with a control mix that made without addition of sodium gluconate. The hybrid alkaline paste and mortar mixes were prepared using a fixed proportion of OPC/fly ash (25 %/75 %), NaOH solution molarity of 9 M, and sodium silicate to hydroxide ratio of 1.5. The results of this investigation found that the quick setting and abrupt loss of flowability of the control mix were improved by adding sodium gluconate, however, more promising results were observed at 7 % and 10 % sodium gluconate. The delay in polymerization due to lower availability of calcium ions, and adsorption of carboxyl and hydroxyl groups associated with sodium gluconate on the unreacted particles of binding materials and earlier formed products assisted in prolonging the time required for hardening. Further, the compressive strength declined at a higher dosage of sodium gluconate, however, the mortar mixes made with 2 % and 4 % sodium gluconate exhibited higher compressive strength than the control mix. The peak intensity of albite, nepheline, and C–S–H gel decreased at higher dosages of sodium gluconate, which was supported by a weaker microstructure characterized by more pores, micro-cracks, and partially reacted fly ash particles. Furthermore, the lower bridging oxygen content and greater Si–O–Na/ Si–O–T ratio at higher dosage of sodium gluconate confirms the delayed polymerization process.

Tensile strength and durability performances-based evaluation of 3D-printed and mold-cast fibrous geopolymer composites produced at various alkaline activator combinations

This study aimed to investigate the effects of the sodium silicate-to-sodium hydroxide ratio, SH molarity, and carbon fiber volume fraction on the tensile strength and durability properties of mold-cast and 3D-printed geopolymer composites, including flexural and splitting tensile strengths, ultrasonic pulse velocity, water absorption, sorptivity index, and chloride penetration properties. For that purpose, the ground-granulated blast furnace slag and fly ash were employed as alumino-silicate-rich raw material. In order to activate the alumino-silicate-rich raw material, two sodium silicate/sodium hydroxide ratios of 1 and 2 and three sodium hydroxide molarities of 8M, 10M, and 12M were designated. Furthermore, carbon fiber was incorporated into the geopolymer composites at three volume fractions: 0 %, 0.3 %, and 0.6 %. In total, 18 nonfibrous and fibrous geopolymer composites were manufactured in two different ways: mold-cast and 3D-printed. The findings demonstrated that the strength and durability characteristics of 3D-printed specimens were inferior to those of mold-cast specimens, attributed to the presence of weak interfacial bonds between layers. It has been observed that the incorporation of carbon fiber has the effect of improving tensile strength performance. Nevertheless, the addition of carbon fiber led to a slight decrease in UPV values, and an increase in water absorption and sorptivity index values. Also, it adversely influenced the chloride penetration of geopolymer composites. The findings of the study also indicated that increasing the sodium hydroxide molarity had a positive impact on the strength and durability properties of the composites. Nevertheless, it was observed that increasing the sodium silicate-to-sodium hydroxide ratio led to a decrease in both tensile strength and durability performances. Additionally, the microstructure of the geopolymer composites was analyzed using scanning electron microscope (SEM) images.

Mechanical property and microstructure of fly ash-based geopolymer by calcium activators

Geopolymer is a green and environmentally friendly new type of gel material generated from the reaction of activators with silica-alumina raw materials, possessing extensive research and application value. Fly ash can be used as reaction material, enabling the industrial solid waste to be recycled and reused. In this paper, unconfined compressive strength test, X-ray diffraction analysis, Fourier transform infrared light, 29Si nuclear magnetic resonance, scanning electron microscope and energy disperse spectroscopy, and physisorption experiment were carried out to study the effects of the type and dosage on the mechanical property and microstructure of fly ash-based geopolymer activated by calcium hydroxide, calcium sulfate and their compound. The results indicated that calcium hydroxide and calcium sulfate can promote the dissolution of fly ash crystals, providing adequate Ca2+ for the formation of gel products. The products of calcium hydroxide and calcium sulfate activation are hydrated calcium aluminate, hydrated calcium sulfate, and ettringite, respectively. The effect of the compound activator is superior to that of single activators. With the increase of the proportion of calcium hydroxide, the reorganization and polymerization of gel products were accelerated so that the integrity and continuity of the microstructure of geopolymer were improved, and then the strength increased. When the ratio of calcium hydroxide to calcium sulfate was 3:1 and the total dosage was 20 %, the unconfined compressive strength reached the maximum value. According to this study, it was investigated that type and dosage of calcium activators had evident influence on the geopolymerization of fly ash. And the reutilization and resource utilization of fly ash waste can be achieved, which can provide an engineering theoretical basis for using fly ash-based geopolymer to alter the physical and chemical properties of special soils and achieve solidification effect.

Preparation of solid alkali activator for geopolymer synthesis using vanadium-bearing shale tailing

The vanadium-bearing shale tailing (VST) with large reserves pollutes the environment and urgently needs to be utilized as a resource. Due to its main component being silica, VST has great potential as a raw material for geopolymer. Therefore, this study uses VST to prepare the solid alkali activator (SAA) by thermochemical methods. Analysis show that the temperature and NaOH dosage of thermochemical reaction significantly affect the alkaline activation effect of SAA. Temperature affects the silicate content and the amount of NaOH affects the soluble silicate content in SAA. When the reaction temperature is high (such as above 900 ℃) and the amount of sodium hydroxide is low (such as the mass ratio of sodium hydroxide to VST is 0.6), quartz almost transforms into silicates, but the silicates have a stable cyclic chemical structure and are difficult to dissolve during the geopolymerization reaction. When the reaction temperature is low (such as less than 700 ℃) and the amount of sodium hydroxide is high (such as the mass ratio of sodium hydroxide to VST is 0.9), quartz in VST is difficult to fully convert into silicates, there are unreacted quartz and sodium hydroxide in SAA, and SAA has poor alkaline activation performance. The optimal synthesis process conditions for SAA are as follows: synthesis temperature is 900 °C and the mass ratio of sodium hydroxide to VST is 0.95. The main silicate components of SAA are Na2SiO3 and Na15.6Ca3.8Si12O36. During the synthesis of one-part geopolymer (OPG), Na2SiO3 dissolution generates a strong alkaline reaction environment and provides active silicon-oxygen tetrahedron monomers or oligomers, Na15.6Ca3.8Si12O36 is bonded with geopolymer gel structure by stable cyclic silicate structure, which makes OPG have a compact integrated structure. When the mass ratio of SAA to MK is 1:1.3, the 7-day compressive strength of the prepared OPG is about 49 MPa, SAA has the potential as a substitute for commercial sodium silicate to prepare geopolymers.

Strength, durability, and toxicity characteristics of water treatment sludge based geopolymers for subgrade application

This study examined the strength, durability and toxicity characteristics of geopolymer made from water treatment sludge (WTS) using fly ash (FA) and ground granulated blast furnace slag (GGBS) as binding materials for the subgrade application. The mechanical properties of WTS-FA-GGBS geopolymers were assessed considering various parameters such as binder proportions, curing period, curing condition, Sodium silicate (SS) to Sodium hydroxide (SH) ratio (i.e. SS/SH), and Sodium hydroxide (NaOH) concentration. The results showed that increasing binder proportions, NaOH concentration, and curing period positively impacted the strength of the WTS-FA-GGBS geopolymer. The unconfined compressive strength (UCS) of the geopolymer samples with an SS/SH ratio of 2.5 showed higher compressive strength than those at an SS/SH ratio of 1. WTS-FA-GGBS geopolymers cured at 100°C showed increased UCS values after 1 to 3 days, but strength decreased after 7 days due to a faster geopolymerisation reaction, resulting in excessive moisture loss and microcracks in the geopolymerized samples. The study also found that all the geopolymer samples met the minimum strength criteria for cement-stabilized mix with a maximum mass loss of 8.17 % are well within the specified limits (<14 %) as per IRC:37–2018. The California Bearing Ratio (CBR) values of WTS-FA-GGBS geopolymers, which range from 41.11 % to 260.32 %, surpass the minimum criteria for cement stabilized subgrade or subbase material, as specified by IRC: SP:89–2010. Additionally, the changes during geopolymerization were confirmed by FESEM, EDS, and XRD analysis. The toxicity characteristic leaching procedure (TCLP) test results showed that the amounts of heavy metals in the geopolymer leachate were within the USEPA-mandated limits.

Analytical Solution for Predicting the Elastic Modulus of a Cement Slurry System with the Effect of Calcium Dissolution.

The dissolution of calcium ions in concrete in a low-alkalinity environment is an important factor causing a significant increase in the porosity of internal concrete, leading to a deterioration in its mechanical properties and affecting the durability of the concrete structure. In order to improve the reliability of concrete durability design and significantly increase the service life of concrete structures located in soft water environments, it is crucial to establish an analytical method to predict the elastic modulus (Edc) of cement slurry systems suffering from calcium dissolution. Firstly, the hydrated cement particles are regarded as a three-phase composite sphere composed of unhydrated cement particles (UC), a high-density hydrated layer (H-HL), and a low-density hydrated layer (L-HL). By introducing the equivalent inclusion phase (EQ) composed of UC and H-HL, the three-phase composite sphere model can be simplified into an equivalent hydrated cement particle model composed of EQ and L-HL. Finally, the Edc of the two-phase composite sphere composed of the equivalent hydrated cement particles and the porosity of the dissolved cement slurry system are solved by using elasticity theory. The effectiveness of the developed analytical method is verified by comparing it with third-party numerical results. Based on this method, the effects of hydration degree, volume ratio of calcium hydroxide (CH) to hydrated calcium silicate (C-S-H), and volume ratio of inner C-S-H to outer C-S-H on the Edc of the dissolved cement slurry system are analyzed. The parameter analysis indicates that among the three influencing parameters, the hydration degree has the greatest effect on the Edc of the dissolved cement slurry system. This study provides an analytical method for predicting Edc, which can provide some references for the durability design of concrete after calcium dissolution.

Closing the loop: Biochar-supported nickel catalyst for efficient hydrogen-rich syngas production

Thermochemical conversion of agricultural by-products into hydrogen-rich syngas is a technology that offers both economic and environmental benefits. In this work, we investigated a biochar-supported nickel-based catalyst for the catalytic pyrolysis of straw biomass to produce hydrogen-rich syngas. The by-product, straw biochar, was used as a material for synthesizing fresh catalysts, achieving a closed-loop process. We explored gas yields under various conditions. The highest yields of CO and H2, reaching 0.52 L/g and 0.48 L/g, respectively, were obtained under the conditions of a pyrolysis temperature of 900 °C, a residence time of 20 min, a calcination temperature of 400 °C, a nickel loading of 15 wt%, and a citric acid to potassium hydroxide ratio of 1:4. The catalysts were characterized using XRD, H2-TPR, SEM, and TEM. The results demonstrated that biochar provides excellent support and synergy, enabling the catalyst to function at high temperatures and offering antioxidative protection to the active metals during the thermal process. Overall, this catalytic pyrolysis process, aiming for green and efficient conversion, achieved high yields of syngas and hydrogen.

Preparation of biomass-derived porous biochar for efficient removal of iodized X-ray contrast media in water: Adsorption performance and underlying mechanism

Hydrophilic Iodized X-ray contrast medias (ICM) are difficult to separate from water. Here, a novel porous biochar (MBC) with a high specific surface area (1435.1 m2 g−1) was prepared by one-step pyrolysis, which showed excellent adsorption capacity for Iodized X-ray contrast media, including diatrizoic acid (95.1 mg g-1), iohexol (297.8 mg g-1), and iopamidol (298.9 mg g-1). The optimal pyrolysis temperature for MBC was 700 ℃, and the ratio of sodium hydroxide to sodium carbonate was 1:3. Adsorption kinetic was well fitted by the pseudo-second-order model. Adsorption isotherm was best fitted to the Freundlich model. Adsorption thermodynamics suggested that ICM adsorption was spontaneous and endothermic. Material characterizations demonstrated that good adsorption performance of MBC for ICM mainly depended on pore filling, π-π interaction. The density functional theory (DFT) showed that H-bonding between oxygen-containing functional groups on MBC and ICM further promoted adsorption. Recycling experiments showed that MBC had good reusability. The study indicated that one-step pyrolysis synthesis of alkaline substance pretreatment biochar could be a promising adsorbent for water purification.

An innovative approach to fly ash-based geopolymer concrete mix design: Utilizing 100 % recycled aggregates

Concrete is a widely used construction material globally, known for its ability to incorporate substantial quantities of industrial by-products such as fly ash (FA) and construction and demolition (C&D) debris. These by-products, originating from thermal power plants and construction activities, often pose environmental challenges when disposed of improperly. To address this issue, recycled aggregate geopolymer concrete (RAGPC) has emerged as a promising solution. However, the lack of a suitable mix design method has hindered the structural application of RAGPC. This study aims to introduce a novel mix design method utilizing 100 % recycled aggregate (RA) combined with FA through geopolymer technology, offering a simpler and more rational approach than previous methodologies. The proposed approach was validated through various concrete tests, utilizing a sodium silicate to sodium hydroxide ratio of 1.5 and a concentration of sodium hydroxide of 16 M as alkaline activation content (AAC), with an AAC to binder (B) ratio ranging from 0.3 to 0.8. Results indicate that incorporating FA and RA into concrete, coupled with elevated curing at 60 °C for 24 h for RAGPC hardening, yields compressive strengths (CS) ranging from approximately 14 to 35 MPa after a 28-day curing period. SEM and XRD tests were also conducted to analyse the polymerization processes, revealing the significant positive influence of FA on RAGPC performance. The findings suggest that fly ash has a superior synergistic influence on recycled aggregate geopolymer concrete performance. Moreover, due to its excellent resistance to chloride ingress and seawater corrosion, geopolymer concrete is well-suited for marine applications, including the construction of ports, harbours, offshore platforms, and coastal protection structures.

Introducing a novel optimised binder activator with redcar mudstone feedstock in the UK for geopolymer cement formation

This paper evaluates Redcar Mudstone (RM), a type of shale rock, as a potential geopolymeric binder for cement production, highlighting its preparation through milling and calcination, followed by blending with an alkali activator. The study utilises an L8 orthogonal array matrix to determine the optimal mix design based on maximum compressive strength. Mechanical tests reveal that sodium-activated RM serves as a viable feedstock, producing cement comparable to or better than other mineral-based feedstocks, achieving a maximum mean compressive strength of 71.98 MPa. The mix optimisation process indicates the RM to alkali ratio and the sodium silicate to sodium hydroxide ratio as critical factors in developing this geopolymer cement. Results show a significant presence of aluminosilicates in their oxidised state, essential for the geopolymerisation process, aligning with all mineralogical analyses. The competitive results of this cement experimentation with Ordinary Portland Cement (OPC) and other geopolymers underscore its potential. This research underscores the environmental and strength performance advantages of RM derived geopolymers, suggesting their potential as an effective waste valorisation method and a green alternative in cement production, driven by the global push to reduce CO2 emissions and the extensive research on geopolymers and innovative binders.

Synthesis and multi-objective optimization of fly ash-slag geopolymer sorbents for heavy metal removal using a hybrid Taguchi-TOPSIS approach

This study develops and evaluates a highly effective geopolymer sorbent specifically designed for the removal of heavy metals from wastewater. Single and binary blends of fly ash and slag were utilized as the binding material. The geopolymer composite was activated using either sodium hy solely or in combination with sodium silicate. The Taguchi method was employed to design the geopolymer mixes, having four factors, each with four levels of variation. These factors included the fly ash-to-slag ratio (FA), binder content (BC), the molarity of the sodium hydroxide solution (M), and the sodium silicate-to-sodium hydroxide ratio (SS/SH). The performance of the geopolymer sorbent was rigorously assessed against a comprehensive set of criteria, including metal sorption capacity, setting time, flowability, density, compressive strength, abrasion resistance, water absorption, permeable voids, sorptivity, carbon footprint, and cost. The TOPSIS methodology was applied to aggregate the response criteria and determine the optimal mix for superior performance. The results showed that the optimum mix consisted of an FA of 33 %, BC of 1050 kg/m3, M of 10, and SS/SH of 3. A sensitivity analysis confirmed that changes in the weighting of the performance criteria did not significantly impact the proportioning of the optimum mix. Furthermore, the analysis of variance (ANOVA) revealed that the FA contributed the most to the sorbent’s performance, followed by the SS/SH, BC, and M. The development of this geopolymer sorbent not only addresses a critical environmental concern but also offers great potential for practical applications in industries and municipalities worldwide.