Increasing Solution Concentration Research Articles

Effect of sodium occupancy and solute concentration on the swelling pressure and hydraulic conductivity of Boom Clay

The poorly indurated Boom Clay (BC) has been studied as a potential host formation for the geological disposal of radioactive waste including the intermediate-level long-lived bituminized radioactive waste called Eurobitum. In case of leaching of Eurobitum, fluids with altered chemical compositions would be expected to infiltrate locally into the BC. To evaluate the effect of salinity on the Boom Clay hydromechanical behaviour, a series of one-dimensional constant-volume swelling tests were conducted on intact BC samples that were first percolated with mixed sodium-calcium-nitrate solutions ((Na,Ca)NO3) with varying sodium concentrations, resulting in varying Na+ occupancies in the clay. Results showed that the swelling pressure of BC decreased with an increase in the solute concentration and sodium occupancy. Additionally, higher Na+ concentrations led to a faster stabilization of the swelling pressure. The hydraulic conductivity of BC increased with increasing solute concentration and sodium occupancy. Moreover, the sodium occupancy and concentration affected the swelling pressure and hydraulic conductivity in a similar way. This phenomenon could be elucidated by two primary mechanisms: i) the influence of solute concentration on the Diffuse Double Layer (DDL), and ii) the effect of cation type and hydrated radius within the interbasal space of montmorillonite sheets, especially concerning sodium occupancy.

Advanced Modeling and Comparative Analysis of Nanofiltration Membrane Parameters: NF90 vs. NP010

Purpose: This study aimed to characterize commercial nanofiltration membranes (NF90 and NP010) by determining their membrane parameters and estimating osmotic pressure using the virial equation. Method: A comparison has been conducted using the Van't Hoff equation for both dilute and concentrated mixtures. Membrane parameters (σ, Ps, and ks) have been experimentally obtained, and osmotic pressure has been calculated using the virial equation, with results compared to the Van't Hoff equation. Various solutes, including lactose, Al3+, Mg2+, Na+, and Cl-, have been tested at different concentrations to investigate the membrane behavior. Result: Result: The virial equation has shown better agreement with experimentally measured fluxes than the Van't Hoff equation. With an increase in solute concentration, σ has decreased, while Ps and ks have increased. Higher cation valency has increased rejection rates, with lactose exhibiting the highest rejection. The rejection rates have followed the order of RLactose > RAl3+ > RMg2+ > RNa > RCl. The order of σ values has been as follows: σLactose > σAl3+ > σMg2+ > σNa+ > RσCl. While the order of Ps and ks values has been Cl->Na+>Mg2+>Al3+>lactose. Conclusion: The virial equation has proven to be more effective in estimating osmotic pressure. The findings have provided valuable insights into membrane behavior under varying conditions, optimizing the application of NF membranes across various industries.

Effects of Na2SiO3/NaOH ratio in alkali activator on the microstructure, strength and chloride ingress in fly ash and GGBS based alkali activated concrete

In this study, the impact of alkaline solutions composed of various Na2SiO3/NaOH ratio and NaOH molarity on the strength, chloride ingress and chloride binding capacity of fly ash (FA) and ground granulated blast furnace slag (GGBS) based alkali activated concrete (AAC) was investigated. The microstructural properties of alkali activated binders (AAB) composites was also studied to understand its influence on the chloride permeability of AAC. Chloride permeability of concrete was tested by using the rapid chloride penetration test (RCPT) and by immersing concrete in NaCl solution (ASTM C1556). The compressive strength, chloride ingress and chloride binding capacity of AAC was compared with Portland cement-based concrete (OPC). Results showed that higher Na2O/SiO2 ratio in alkaline solutions resulted in a weak microstructure with, low strength and high chloride ingress. Concrete activated by alkaline solutions with Na2O/SiO2 molar ratio =1 (+3), exhibited greater compressive strength and resistance to chloride ion penetration. The increase of SiO2 concentration in alkaline solution greatly reduces the binding capacity of AAC while the bound chlorides increased with the NaOH molarity. No chemical chloride binding was observed in AAC but for OPC concrete, calcium salts formed in the microstructure after immersion in NaCl solution. Compared to OPC concrete, AAC showed superior performance in terms of strength and chloride diffusion making it a potential candidate for application in marine structures.

Flow regimes in a melting system composed of binary fluid: transition from penetrative convection to diffusion

In a horizontally heated melting system, where a solid substance is subject to melting by a warmer liquid beneath, the presence of solute in the liquid introduces a complex interplay between temperature and concentration dynamics. Employing a recently developed sharp interface method (Xue et al., J. Comput. Phys., vol. 491, 2023), we conduct direct numerical simulations to investigate the transient behaviour of the system across a broad range of Rayleigh numbers and solute concentrations. Our observations reveal distinct flow regimes: at low concentrations, the system resembles a temperature-driven melting problem, characterized by vortex rolls beneath the melting interface. As the solute concentration increases, a stably stratified layer emerges beneath the interface, leading to the transition from thermal convection to penetrative convection, which resembles those flow characteristics observed in the double-diffusive convection. This shift results from the competition between the stabilizing effect induced by solute concentration gradient and the destabilizing effect caused by temperature gradient. Otherwise in the diffusion regime, characterized by very high solute concentrations, the flow becomes static due to the complete suppression of convection by the stably stratified layer. This regime further exhibits two distinct patterns: ‘melting’ and ‘dissolution’. Beyond characterizing diverse flow patterns, our study conducts a quantitative analysis, examining heat/mass transfer, melting rates, and the evolution of temperature and concentration at the interface. These insights contribute to a better understanding of the intricate interplay between temperature and solute concentration during phase change, with implications for accurately estimating melting rates in binary fluid systems.

A quantitative study of the solute diffusion zone during solidification of Al-Cu alloys via in-situ synchrotron X-radiography and numerical simulation

The solute diffusion zone plays a critical role in determining nucleation efficiency during heterogeneous nucleation. In this study, in-situ synchrotron X-radiography and numerical modeling were employed to investigate the Solute Suppressed Nucleation Zone (SSNZ) surrounding growing equiaxed grains in Al-13Cu alloys. Quantitative analysis of SSNZ and constitutional undercooling was conducted using image processing techniques. Solute concentration and SSNZ length in the <110> direction exceed those in the <100> direction, suggesting higher solute enrichment in dendrite centers. This causes greater undercooling in the dendrite growth direction (<100>) with faster dendrite growth rates. As equiaxed dendrites grow, SSNZ length in the <100> direction decreases while increasing significantly in the <110> direction. Utilizing data obtained from numerical simulations, we refined the analytical equation governing solute distribution preceding the solid–liquid interface under three-dimensional conditions, and the computational equation determining the SSNZ length. The SSNZ lengths derived from the optimized equation along the <100> and <110> directions demonstrate more agreement with both experimental observations and numerical simulation outcomes. Higher growth rates rapidly increase undercooling, limiting the development of nucleation-free zone. Additionally, SSNZ area growth slows at higher cooling rate, correlating with increased solute concentration and reduced area in SSNZ.

Bioactive electrospun zein fibers integrated with ZnO nanoparticles: In vitro investigations

The objective of the current study was the fabrication and characterization of electrospun zein-ZnO fibers containing various concentrations of cumin essential oil (CEO) (0, 1, 2, and 3% (v/v)). The electrospinning solution's apparent viscosity, conductivity, and surface tension were measured. Also, the electrospun's morphological, color, encapsulation efficiency, antioxidant and antimicrobial properties, thermal stability, and release kinetic were investigated. The results represented that following the increase in CEO concentration, the conductivity and surface tension of the electrospinning solution changed from 182.92 μS/cm to 145.22 μS/cm and 19.52 mN/m to 22.35 mN/m, respectively. The scanning electron microscope (SEM) revealed the homogenous and free-bead structure of electrospun fibers. Besides, the diameter of fibers enhanced with a rise in CEO concentration from 217.13 nm to 321.67 nm. The finding estimated the maximum encapsulation efficiency and loading capacity at about 95.09% and 25.65%, respectively in electrospun containing the highest concentration of CEO (3%). CEO inclusion in electrospinning fibers augmented the value of contact angle, color difference, TPC, antioxidant, and antimicrobial properties. The favorable interaction between the CEO ingredients and electrospinning fibers was confirmed through FTIR and XRD analysis. Furthermore, the incorption of CEO enhanced the thermal stability of fibers. Release kinetic in different simulant (aqueous, acidic, alkaline, and fatty) revealed that Fick's diffusion was the main release mechanism. The highest diffusion coefficient was observed in electrospun fibers containing 3% CEO in the fatty media simulant. These findings could present a new horizon into electrospinning fiber's application in various fields of medicine, tissue engineering, food, and pharmaceutical industry.

Thermodynamic behavior and microstructure evolution of Inconel 718 alloy by laser metal deposition

The temperature evolution, stress evolution, and dendrite growth during the laser metal deposition (LMD) process of Inconel 718 alloy were simulated using a multi-scale model that combines the finite element method and the Cellular Automata (CA) method. This model established the relationship between the thermal behavior of the molten pool and the solidification characteristics, and predicted the morphological size of the solidified structure. Research indicates that under conditions of higher cooling rate and lower shape control factor, equiaxed grains are prone to form, with a lower degree of elemental segregation in this region, which is conducive to the precipitation of granular Laves phase. Conversely, under conditions of lower cooling rate and higher shape control factor, columnar grains are more likely to form, with a higher degree of elemental segregation in this region, leading to the precipitation of chain-like Laves phase. The results of thermo-mechanical coupled simulation suggest that the maximum transient thermal stress is located at the overlap position, and when the component cools down to room temperature, the maximum normal stress along the scanning direction is observed. Dendritic growth results demonstrate that during the equiaxed grain growth process in the top region of the melt pool, the released solute is constrained by time and space, leading to the accumulation of solute and the formation of interdendritic segregation. In areas with a higher grain density, the solute accumulation zones overlap, resulting in an increase in solute concentration, which inhibits dendrite growth. In the middle region of the melt pool, during the columnar grain growth process, the solute concentration in the gaps between adjacent grains continuously increases, resulting in micro-segregation phenomena. Experimental measurements have shown that the temperature field's melt pool morphology, stress values along the scanning path, and dendritic morphology are in good agreement with the experimental outcomes.

Ion Association and Hydration of Some Heavy-Metal Nitrate Salts in Aqueous Solution.

Aqueous solutions of four heavy-metal nitrate salts (AgNO3, TlNO3, Cd(NO3)2 and Pb(NO3)2) have been studied at 25 °C using broadband dielectric relaxation spectroscopy (DRS) at frequencies 0.27 ≤ ν/GHz ≤ 115 over the approximate concentration range 0.2 ≲ c/mol L-1 ≲ 2.0 (0.08 ≲ c/mol L-1 ≲ 0.4 for the less-soluble TlNO3). The spectra for AgNO3, TlNO3, and Pb(NO3)2 were best described by assuming the presence of three relaxation processes. These consisted of one solute-related Debye mode centered at ∼2 GHz and two higher-frequency solvent-related modes: one an intense Cole-Cole mode centered at ∼18 GHz and the other a small-amplitude Debye mode at ∼500 GHz. These modes can be assigned, respectively, to the rotational diffusion of contact ion pairs (CIPs), the cooperative relaxation of solvent water molecules, and its preceding fast H-bond flip. For Cd(NO3)2 solutions an additional solute-related Debye mode of small-amplitude, centered at ∼0.5 GHz, was required to adequately fit the spectra. This mode was consistent with the presence of small amounts of solvent-shared ion pairs. Detailed analysis of the solvent modes indicated that all the cations are strongly solvated with, at infinite dilution, effective total hydration numbers (Zt0 values) of irrotationally bound water molecules of ∼5 for both Ag+ and Tl+, ∼10 for Pb2+, and ∼20 for Cd2+. These results clearly indicate the presence of a partial second hydration shell for Pb2+(aq) and an almost complete second shell for Cd2+(aq). However, the hydration numbers decline considerably with increasing solute concentration due to ion-ion interactions. Association constants for the formation of contact ion pairs indicated weak complexation that varies in the order: Tl+ < Ag+ < Pb2+ < Cd2+, consistent with the charge/radius ratios of the cations and their Gibbs energies of hydration. Where comparisons were possible the present constants mostly agreed well with the rather uncertain literature values.

Addition of Fe‐humic acids to overcome analytical issues in measurements of isotopically exchangeable P in soil

AbstractIsotopic dilution has been widely used to measure isotopically exchangeable phosphorus (P) in soil (E value), as a measure of potentially plant‐available P. However, in soils with low E values and/or strong P sorption, measurement of E values can be challenging due to very low solution concentrations and the interference of colloidal non‐exchangeable species, thus confounding the measurements in the soils of most interest. The addition of a complexing compound could increase solution concentrations and reduce these analytical issues, as has been found in the case of metals. Therefore, we investigated the addition of Fe‐humic acid (Fe‐HA) as a P‐complexing compound to the soil suspension prior to isotopic exchange. This results in the formation of P‐Fe‐HA complexes, thus increasing P solution concentrations by solubilizing P from the labile pool and reducing errors caused by suspended colloids. We used this method to measure E values in five soils with low P status, without or with the addition of carrier P. The addition of Fe‐HA (at 50 or 200 mg Fe‐HA/L to the equilibration solution) substantially decreased the measured E value without carrier P addition in four of the five soils, while there was no or little effect when carrier P was added. The higher Fe‐HA rate increased solution concentrations of stable and radioactive P more than the lower rate, but there was no significant difference in measured E values between the two Fe‐HA rates. The method was also applied to 15 subsoils with low P status. Overall, our results indicated that the addition of Fe‐HA provides an easy and robust way to avoid analytical issues in the determination of E values in soils with low concentrations of P in solution.

Formation mechanism of high biofilm phosphorus storage capacity and its effect on phosphorus uptake-release and carbon source consumption

Phosphorus recovery from wastewater is an effective method to alleviate the shortage of phosphorus resources. The biofilm phosphorus recovery process can realize simultaneous removal and enrichment of phosphorus in wastewater. In this study, a sequencing batch biofilm reactor was constructed to study the rapid phosphorus release and slow phosphorus release stages in the phosphorus recovery cycle. The relationship between high biofilm phosphorus storage capacity (Pbiofilm), phosphorus recovery solution concentration, phosphorus uptake-release behavior and carbon source consumption were explored. The increase in phosphorus recovery solution concentration promotes the elevation of Pbiofilm, which, conversely promotes phosphorus release in the next recovery cycle. In addition, the distinct phosphorus uptake-release characteristics of extracellular polymeric substances and cells were illustrated. This study provides a theoretical foundation to elevate the phosphorus recovery efficiency and reduce carbon source consumption in biofilm phosphorus recovery process.

Acute toxicity of deoxynivalenol and bioremediation of a highly effective deoxynivalenol degrading Achromobacter spanius P-9 on zebrafish embryos and adults

Deoxynivalenol (DON) is one of the mostly concerned mycotoxins and several microbes showed bioremediation effects on DON toxic effects. In this study, the acute toxicity of a new DON degrading strain Achromobacter spanius P-9 with DON on zebrafish embryos and adults were firstly performed. For zebrafish embryos, bacterial concentrations of 2.5 × 107 CFU/mL and 5.0 × 107 CFU/mL had no significant effects on growth and development. However, at 7.5 × 107 CFU/mL, some effects were observed, and at 10.0 × 107 CFU/mL, the embryo survival rate decreased to 70%, with 3.3% teratogenicity. Higher bacterial concentrations correlated with faster heart rates. DON (100 μg/mL) significantly reduced embryo survival to 36.7% in 96 h. Bacterial solutions at 7.5 × 107 CFU/mL and 10.0 × 107 CFU/mL expanded the zebrafish intestinal tissue wall, while DON at 100 μg/mL negatively impacted intestinal morphology. Liver tissue in zebrafish exposed to Achromobacter spanius P-9 showed no significant differences from the control group. However, exposure to DON solution increased liver fluorescence intensity and caused liver cell changes, including edema, vacuolization, and blurred boundaries. For adult zebrafish, the ROS and 8-OHdG contents in the exposure group increased with the increase of bacterial solution concentration, the SOD enzyme activity, CAT enzyme activity, GST enzyme activity and MDA was not significantly different with the control group. Compared with the control group, the content of ROS, GST enzyme activity, MDA and 8-OHdG after DON treatment showed an upward trend, SOD and CAT enzyme activities showed a decreasing trend. Achromobacter spanius P-9 has no obvious inhibitory effect on the growth and development of zebrafish embryos and has no obvious death and toxicity during the growth of adult fish, providing data support for the future application of this strain in the biodegradation of DON.

Determination of Critical Micelle Concentration (CMC) of Sodium Stearate Solution in Distilled Water

Surfactant is an organic compound having polar and nonpolar parts. The specific conductivity of sodium stearate surfactant in double distilled water has been studied by conductometric method at three temperatures (298.15, 308.15, and 318.15) K. conductivity of the surfactant increases with increase in temperature and concentration of solution. Critical Micelle Concentration (CMC) of sodium stearate was determined attemperature 298.15 K is 0.00095Mol/lit using the easy plot software. FESEM image shows themorphological structure of the sodium stearate surfactant.

Correlation of dopant solution on doping mechanism and performance of F4TCNQ‐doped P3HT

AbstractUnderstanding the doping mechanism between the dopants and the conjugated polymers (CPs) is crucial for efficiently utilizing the doping process in a controllable manner. In this work, we doped the poly(3‐hexylthiophene) (P3HT) films with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) from a chlorobenzene/acetonitrile (CB/AN) solvent blend and pure AN solvent by using the common sequential doping method. We found that the dissolution ability of the dopant solvent to P3HT and the concentration of the dopant solution were two critical factors to determine the doping process (solution doping or sequential doping) and the doping region (the amorphous or the crystalline phase). When the concentration of the dopant solution was low, solution doping was dominant in the P3HT film doped with F4TCNQ CB/AN solution, and the amorphous regions were doped in the P3HT film doped with F4TCNQ AN solution. With the increase of the dopant solution concentration, the ratio of ordered integer charge transfer (ICT) species, which formed from sequentially doped crystalline domains in the P3HT precast film, increased. Based on the above doping mechanism, a P3HT film with good electrical and tensile performance could be constructed by doping from F4TCNQ CB/AN solution with a relatively low concentration. Our work indicates that the dissolution or swelling ability of the dopant solvent to CP is an important factor in determining not only the doping mechanism but also the electrical and mechanical performances of doped CP films.

Electrochemical Amalgamation Optimization as Part of the Development of the OREATE Process

Oxide reduction by electrochemical amalgamation and thermal extraction (OREATE) is an electrochemical process in which metal oxides are converted to highly pure metals. This process that is currently being developed at LANL involves the dissolution and chlorination of the metal oxide into an acidic medium. This metal cation is then electrochemically amalgamated via reduction using a mercury pool cathode. Finally, mercury's high vapor pressure allows an easy thermal extraction process to obtain the metal. In addition to its ability to electrochemically form amalgams, mercury is used because it has a high hydrogen evolution overpotential, allowing for a higher current efficiency for reduction of the metals in acidic solution. As a critical step of the OREATE process, the electrochemical amalgamation reaction must be optimized in order to advance the overall performance.In this work, we studied the electrochemical amalgamation of cerium through anodic stripping voltammetry (ASV) experiments using a silver-based mercury film electrode (SBMFE). The SBMFE allows for the electrochemical amalgamation to be optimized at a smaller scale than the mercury pool, which not only minimizes the amount of mercury needed, but also drastically reduces the experiment time. This study included several different experimental parameters such as the pH of the buffered solution, concentration of cerium, reduction potential, and temperature. For each parameter, the reaction rate and current efficiency were evaluated to determine the optimal conditions for the electrochemical amalgamation reaction.The results showed that the pH of the buffered solution must be 3.5 or lower to avoid the formation of cerium hydroxides, which can passivate the surface of the mercury electrode. However, an increasingly acidic solution promotes the hydrogen evolution reaction, which directly competes with the electrochemical reduction of cerium, decreasing the overall current efficiency. Likewise, it has been demonstrated that an increase of the cerium concentration in solution drops the current efficiency of the electrochemical amalgamation reaction. This effect can be explained by the fact that cerium is a small cation with a +3 charge that leads to a high degree of solvation. Therefore, as the cerium concentration in solution increases, more water molecules are brought to the electrode surface during electrochemical amalgamation. This favors the water reduction reaction that increases hydrogen evolution and lowers current efficiency. However, increasing the concentration of cerium enhances the reaction rate of the electrochemical amalgamation, resulting in more cerium entering the mercury film. Furthermore, as the reduction potential is moved towards more negative potentials, the reaction rate increases. However, a more negative reduction potential promotes a faster hydrogen evolution reaction, which diminishes the current efficiency. Finally, it has been demonstrated that temperature increases the reaction rate, though it does not have a significant effect on the current efficiency.In conclusion, a variety of system parameters were explored for their effect on current efficiency and reaction rate of the electrochemical amalgamation reaction. This allowed for the determination of the optimal parameters to be used during the electrochemical amalgamation in the large-scale OREATE process.

Structural and dynamic behaviour of concentrated aqueous solutions of (poly)ethylene glycols: Insight into the impact of hydrophobicity, hydrogen bonding and chain length

Understanding the delicate interplay between hydrophobicity/hydrophilicity, hydrogen bonding ability and solute size in modulating the chemico-physical properties of aqueous solutions with increasing solute concentration is a challenging task. Here, we focus on how bulk properties, such as diffusion and aggregation behaviour, are affected by the different hydration patterns observed for differently concentrated aqueous solutions of (poly)ethylene glycols, and their corresponding methoxyethers, of various lengths. Using a combined experimental and computational approach, we analyse solutions of ethylene glycol (EG), dimethoxyethane (DME), polyethylene glycol with 4 repeating units capped with either hydroxyl (PEG200) or methoxyl (PEG250DME) tails, and polyethylene glycol with 9 repeating units (PEG400). By disentangling the contributions of hydrophobicity, hydrogen bonding ability, and chain length, we observe that for the smaller solutes electristriction and hydrophobic hydration are the main phenomena occurring. Instead, as the solute becomes larger, these effects give way to the non-trivial conformational flexibility that can either favour or disfavour intermolecular interactions which lead to the formation of water-rich regions excluded from the solute.

Enhancing growth rate in homoepitaxial growth of β-Ga2O3 with flat surface via hydrochloric acid addition in mist CVD

Gallium oxide (Ga2O3) is a wide-bandgap oxide semiconductor, with a bandgap of ∼4.9 eV, making it a promising material for power device applications. This study focuses on the effect of hydrochloric acid addition on the growth rate in homoepitaxial growth of β-Ga2O3 using a mist chemical vapor deposition method. For homoepitaxial growth on a (001) β-Ga2O3 substrate, we introduced different concentrations of HCl into the source solution to assess its impact on the growth rate, crystal structures, and surface morphologies of the films. At a growth temperature of 900 °C, HCl addition linearly increased film thickness, enhancing the growth rate by 4.8 times with 9.09 vol. % HCl. No peaks associated with other phases were exhibited by each sample, indicating pure homoepitaxial growth. When comparing samples with similar film thicknesses, the root-mean-square (rms) roughness was enhanced by 1/7 with an increase in the HCl concentration. However, at 800 °C, an increasing solution concentration caused pronounced step bunching and elevated rms roughness, in contrast with the minimal effect observed at 900 °C. In experiments with hydrochloric acid addition at 900 °C, we observed a striped morphology, which maintained consistent rms roughness despite higher temperature.

A sensitive benzothiazole fluorescent probe for the detection of γ-glutamyl transpeptidase activity and its application.

A sensitive benzothiazole fluorescent probe (PBZO) for the detection of γ-glutamyl transpeptidase (GGT) activity was developed. Based on the enzymatic hydrolysis of peptide bonds by glutamyl transpeptidase, it can be specifically recognized by PBZO. The PBZO has a good linear relationship with different gradients of GGT activity at the emission wavelength of 560 nm, the Stokes shift reached 215 nm, and the detection limit of GGT activity is 0.1644 U/ml. With the increase of GGT concentration in the probe solution, the color of the solution gradually changed from orange to dark yellow under the 365 nm UV lamp. The same color change was also observed on the probe test paper. In addition, there is a linear relationship between the GGT activity and the R-value of the probe solution. More importantly, the probe has a good recovery rate in serum. Therefore, this probe can be used as a convenient tool for detecting GGT activity.

Performance of geopolymer paste under different concentrations of sodium hydroxide solution

Compared with traditional cement pastes, geopolymer pastes can effectively alleviate environmental and economic problems caused by the construction industry as they are characterised as low carbon dioxide materials, with energy reduced energy consumption and emissions. However, the mechanical properties of geopolymer pastes are greatly affected by the composition of the alkaline activators used in their preparation, and existing research results on this influence is not consistent. In this study, the effects of alkaline activators composed of varying concentrations of sodium hydroxide (NaOH) solution under standard curing conditions on the mechanical properties and material characteristics of geopolymer pastes made with fly ash and slag were investigated. Under standard curing conditions, the mechanical properties of the geopolymer pastes increased with an increase of sodium hydroxide solution (SHS) concentration in the alkaline activator. The use of alkaline activator with 16 M SHS led to the greatest flexural and compressive strengths of the geopolymer pastes at 28 days, reaching values of 5.43 MPa and 39.13 MPa, respectively. Increasing the SHS concentration in the alkaline activator promoted the production of gel products such as N-A-S-H, which formed a dense microstructure and led to higher mechanical properties.

Sulfate resistance of UHPC during dry-wet cycling and energy dissipation under compression

To study the sulfate resistance of ultra-high performance concrete (UHPC) in saline soil area of western China, four kinds of sulfate solution concentrations (0 %, 5 %, 10 %, 15 %) and 18 dry-wet cycle tests for 540 days were carried out on UHPC specimens. The effects of sulfate dry-wet cycles on the evolution of UHPC strength and energy were studied, the characteristic stress points during uniaxial compression of UHPC under sulfate dry-wet cycle were determined, based on the evolution law of each energy (total energy U, dissipated energy Ud , elastic stress Ue) at the characteristic stress points, the energy storage index was established to measure the damage degree of UHPC. The results show that the energy evolution process and damage mechanism of UHPC samples under sulfate-wet and dry cycle erosion are closely related to macro and micro changes. With the development of sulfate dry-wet cycle, the dissipative energy Ud and elastic strain energy Ue of UHPC at the characteristic stress points increased first and then decreased. The development trend of elastic strain energy Ue and dissipative energy Ud is more severe with the increase of sulfate solution concentration. The ratio of elastic strain energy at damage stress to elastic strain energy at peak stress (Ueib/Uei) is taken as the energy storage index Kib to measure the damage degree of UHPC, under 10%Na2SO4 erosion, Kib can be increased by 21.41 % at the highest and decreased by 29.67 % at the lowest compared with the initial value. It shows that the damage process of UHPC is difficult and then easy, and this index can accurately reflect the external force required for the damage of UHPC under sulfate dry-wet cyclic erosion, and provide a reference for the safe and stable operation of UHPC in saline soil area.

Coupled model for electro‐osmosis consolidation and ion transport considering chemical osmosis in saturated clay soils

AbstractThe electro‐osmosis approach efficiently facilitates the rapid dewatering of soil with high water content and contributes to reducing contaminant levels within the clay soil. However, the changes of chemical field caused by ion transport in the clay soil during electro‐osmosis process will also influence the clay soil consolidation effect. Existing theories predominantly tend to disregard this crucial physical process and its resultant effects, thereby restraining a comprehensive analysis of electro‐osmosis consolidation (EOC) behavior under intricate chemical conditions. This study introduces a concise model of EOC and ion transport considering chemical osmosis. The model considers the nonlinear variation of clay soil parameters such as compressibility, permeability, and effective diffusion coefficients, along with the interaction between EOC and ion transport. Meanwhile, the correctness of the model is verified from different aspects such as theoretical derivation and model comparison. Based on the proposed model, the impacts of the variation in electrical field intensity and chemical concentration on the coupled behaviors between EOC and ion transport are systematically investigated, with and without incorporating nonlinear consolidation characteristics. The results show that diffusion and electro‐migration exhibit a more pronounced effect on ion transport during EOC. Simultaneously, with the increase of ion concentration in clay soil pore solution, the effects of chemical osmosis become increasingly apparent, thereby enhancing clay soil settlement.