Water Saturation Level Research Articles

Peculiarities of Clarias gariepinus Physiological State under Conditions of Food Deprivation and Water Environment Quality

The paper is dealt with the study of <i>Clarias gariepinus</i> physiological state under conditions of food deprivation, and also of the influence of the products of its metabolism on the formation of water environment quality in turnover systems. The performed experimental studies suggest that fish cultivation under conditions of deprivation accompanied by the deterioration in water quality results in the decrease in its fatness indices, including primarily liver and abdominal fat mass, and also in the use of energy reserves of the organism -glycogen, proteins, and lipids. The influx of fish metabolites into the water results in the deterioration in its quality, including primarily the increase in the concentration of inorganic nitrogen and phosphorus phosphates, and worsens <i>Clarias gariepinus</i> living conditions. Ammonium and nitrite transformation into less dangerous nitrate is registered at a sufficient level of water saturation with oxygen.

Effect of Water Saturation on Gas-Accessible Effective Pore Space in Gas Shales

Abstract The existence and content of water will certainly affect the effective pore space of shales and therefore is a key point for the evaluation of in-situ gas content and gas flow capacity of shale reservoirs. In order to reasonably evaluate the gas storage and flow capacities of water-bearing shale reservoirs, the effect of water on the effective pore space of shales needs to be understood. In this study, the Upper Permian Longtan shale in the southeastern Sichuan Basin, China, was selected as an example to conduct nuclear magnetic resonance cryoporometry (NMRC) measurements under different water saturation levels. The gas-accessible effective pore spaces in shales under different water saturation levels were quantified, and the effect of water saturation on gas-accessible effective pore space in shales was investigated. The results show that water plays an important role in the gas-accessible effective pore space of shales. When the Longtan shale increases from a dry state to a water saturation of 65%, 75%, and 90%, the gas-accessible effective pore volume decreases by 35%-60% (average 46.3%), 50%-70% (average 58.8%), and 65%-82% (average 75.8%), respectively. Water has an effect on the gas-accessible effective pore space regardless of pore size, and the effect is the strongest in the 4-100 nm range, which may be mainly due to the high content of clay minerals in the Longtan shale. Our studies are of important theoretical significance and application prospects for accurately evaluating the gas-accessible effective pore space of gas shales under actual geological conditions.

Constructed wetlands for the treatment of household organic micropollutants with contrasting degradation behaviour: Partially-saturated systems as a performance all-rounder

The degradability of specific organic micropollutants in constructed wetlands (CWs) may differ depending on the prevalence of oxic or anoxic conditions. These conditions are governed, among other factors, by the water saturation level in the system. This study investigated the removal of three environmentally-relevant organic micropollutants: bisphenol-group plasticizer bisphenol S (BPS), household-use insecticide fipronil (FPN) and non-steroidal anti-inflammatory drug ketoprofen (KTP) in the model CWs set up in an outdoor column system. BPS and KTP, in contrast to FPN, exhibit higher biodegradability potential under oxic conditions. The experimental CWs were operated under various saturation conditions: unsaturated, partially saturated and saturated, and mimicked the conditions occurring in unsaturated, partially-saturated intermittent vertical-flow CWs and in horizontal-flow CWs, respectively. The CWs were fed with synthetic household wastewater with the concentration of the micropollutants at the level of 30–45 μg/L. BPS and KTP exhibited contrasting behaviour against FPN in the CWs in the present experiment. Namely, BPS and KTP were almost completely removed in the unsaturated CWs without a considerable effect of plants, but their removal in saturated CWs was only moderate (approx. 50%). The plants had only a pronounced effect on the removal of BPS in saturated systems, in which they enhanced the removal by 46%. The removal of FPN (approx. 90%) was the highest in the saturated and partially-saturated CWs, with moderate removal (66.7%) in unsaturated systems. Noteworthy, partially-saturated CWs provided high or very high removal of all three studied substances despite their contrasting degradability under saturated and unsaturated conditions. Namely, their removal efficiencies in planted CWs were 95.9%, 94.5% and 81.6%, for BPS, KTP and FPN, respectively. The removal of the micropollutants in partially-saturated CWs was comparable or only slightly lower than in the best treatment option making it the performance all-rounder for the compounds with contrasting biodegradability properties.

Effects of biochar particle size, biochar application rate, and moisture content on thermal properties of an unsaturated sandy loam soil

Although biochar is considered as a potential soil amendment, the effect of its rates and particle sizes on soil properties such as soil thermal properties, especially in a light-textured soil has not been widely discussed. Due to the importance of soil thermal properties in many engineering, climatological and agricultural applications, this study aims to investigate and model the effects of biochar particle size, biochar rate, and soil moisture content on the thermal properties of a sandy loam soil through column experiments. The experiments were conducted using three biochar application rates (0 (as control), 1%, and 5% w/w), three biochar particle diameters (<0.15, 0.15–1, and 1–2 mm), and three water saturation (Sw) levels (0.07, 0.2, and 0.78) in three replicates. Given the experimental data, soil thermal properties were modeled using the Campbell, Zhao et al., and de Vries models. According to the results, a higher biochar application rate (i.e. 5%) significantly (P < 0.05) altered soil physical and chemical properties, i.e. bulk density, porosity, EC and pH, and soil thermal properties. Biochar particle sizes had a remarkable effect on soil thermal properties. Adding 5% biochar with particle sizes of < 0.15, 0.15–1 and 1–2 mm decreased soil thermal conductivity to 21%, 26%, and 32% at Sw= 0.07, respectively indicating a lower reduction of thermal conductivity when biochar with a smaller particle size (<0.15 mm) is applied. Applying 5% biochar of the smallest size decreased soil thermal conductivity and diffusivity, and heat capacity by 21%, 17%, and 9%, respectively, and increased thermal resistivity by 27% at Sw= 0.07. The effect of soil moisture on thermal properties (especially thermal conductivity and resistivity) was more robust than biochar amendment. Experimental modeling showed a linear relationship between soil moisture and thermal conductivity, diffusivity and heat capacity, and a power law relationship between soil moisture and thermal resistivity. Mathematical modeling showed the Campbell, de Vries, and Campbell/de Vries models perform the best in estimating thermal conductivity, heat capacity, and thermal diffusivity, respectively. The findings of this research could be used for controlling and predicting soil temperature, improving irrigating scheduling, and optimizing the quantity of biochar amendment required in agricultural fields.

CO2-Containing Reservoir Evaluation Based on the Joint Inversion of Nuclear Logs and Resistivity Logs: A Case Study of Ultrahigh-Temperature and High-Pressure Gas Reservoirs in the Yinggehai Basin, China.

Due to the unique characteristics of reservoirs in the Yinggehai Basin in the South China Sea, such as high temperature and high pressure (HPHT), low porosity, low permeability, complex pore structure, and high lime content, the log responses of these reservoirs have very complex characteristics, which makes it difficult to evaluate reservoir parameters accurately. In addition, most reservoirs in Ledong Block of the Yinggehai Basin in the South China Sea contain CO2, posing great difficulties for subsequent exploration and development. Accurate evaluation of CO2 layers is of paramount importance for the development of oil and gas fields. In this study, we used a method for the joint inversion of multiple well logs to evaluate the reservoirs and determine CO2 saturation level and other formation parameters. We optimized the joint inversion model based on the characteristics of the reservoirs in the Yinggehai Basin and adjusted the forward simulation model to consider the effects of high temperature and high pressure on gas density. In view of high lime content in the formations in this area, we adjusted the resistivity forward simulation model to consider the effect of lime content. The inversion results show that the values of porosity, permeability, and water saturation level obtained through inversion are largely consistent with the core data. The CO2 saturation level determined through joint inversion is 22%, which represents a deviation of less than 10% from the drilling system testing (DST) result, indicating that the joint inversion method is accurate. The error in the water saturation level determined through the joint inversion method is smaller than that in the calculated results from conventional multimineral inversion models. We performed forward simulation of the results calculated with the joint inversion method and compared the results of forward simulation with actual log curves. For the sandstone interval, the results of forward simulation are largely consistent with the actual log curves, indicating that the joint inversion method is accurate. In summary, the method presented in this paper can accurately determine reservoir parameters and provide strong support for the exploration and development of oil and gas fields in the Yinggehai Basin in the South China Sea.

Multiphase, multidimensional modeling of proton exchange membrane water electrolyzer

The water in a proton exchange membrane water electrolyzer (PEMWE) used for hydrogen production undergoes a multiphase flow, which makes it difficult to analyze the mass transfer phenomenon and predict the performance of the PEMWE. Therefore, the multiphase flow in the PEMWE requires a comprehensive study. This work theoretically investigates multiphase mass transfer along with the electrochemical reaction in a PEMWE using a three-dimensional computational modeling approach. First, the model was validated based on an in-house experiment, and a good agreement was achieved. Subsequently, the spatial distribution of species and the electrochemical process were investigated, and the liquid water saturation level was monitored. It was observed that the high current density results in low liquid saturation in the cathode. Oxygen is accumulated under the land owing to its longer diffusion path. Higher temperatures increase and decrease liquid saturation in the cathode and anode, respectively, because they weaken the capillary transport of water inside the porous layer. The concentration overpotential is significantly lower than the activation overpotential. Furthermore, it was found that the high porosity and low contact angle of the porous material aid the capillary transport of water inside the diffusion layer.

Degradation Effect of Gas Diffusion Layer on Water Transport in Polymer Electrolyte Membrane Fuel Cell

Hydrogen is converted to electric power by proton exchange membrane fuel cells (PEMFCs), which have received significant attention for transportation applications because of their high energy efficiency. In order to ensure the long-term stability, understanding about their long-term durability is essential because the operating performance deteriorates over time. Gas diffusion layers (GDLs) manage the transport of water generated from the CL during chemical reactions, and the degradation of the GDL significantly deteriorate the fuel cell performance. Compared to the fresh GDL, the water transport characteristics of GDL aged by inserting hydrogen peroxide solutions are investigated. The dynamic movement of the water meniscus inside the GDL is visualized using synchrotron X-ray imaging. Unlike the pristine GDL having snap-off patterns, water continuously transports through the degraded GDL representing the piston-like movement, and pressure fluctuations are not observed. This difference shows the change of the dominant local transport mechanisms due to GDL degradation. The temporal pressure variations are simultaneously measured, and the pressure and time at breakthrough (BT) are compared. The aged GDL exhibits a larger BT pressure and requires a longer time to achieve the first BT. Longer BT time in the degraded GDL can reflect a higher water saturation level. GDL degradation leads to the loss of polytetrafluoroethylene (PTFE) which is commonly treated to ensure efficient mass transport by restraining water clogging in the GDL pores due to the increase of hydrophobicity. Despite the reduction in hydrophobicity, The PTFE loss can increase BT pressure by reducing the pore size and the actual path length of the water flow. The increase in the BT time and BT pressure, as well as continuous transport, can disrupt fuel supply to chemical reaction sites, thereby deteriorating the PEMFC performance. This study provides a comprehensive understanding of the effect of GDL degradation on mass transport in PEMFCs. Figure 1

Optimization of gas diffusion layer thickness for proton exchange membrane fuel cells under steady-state and load-varying conditions

This work proposes a design principle of the optimal thickness for cathode gas diffusion layers (GDLs) of proton exchange membrane fuel cells (PEMFCs) based on a balance of cell performances under both steady-state and load-varying conditions. Using a three-dimensional and two-phase model, the effects of cathode GDL thickness (50, 100, 200, and 400 μm) on steady-state performances and transient response characteristics are studied. The results show that under steady-state conditions, an extremely thin cathode GDL would lead to non-uniform oxygen and liquid water distributions, whereas an especially thick cathode GDL would increase oxygen transport resistance. Thus, there is an optimal cathode GDL thickness, yielding the best steady-state performance. A current overshoot phenomenon, arising from high local oxygen concentrations at cathode catalyst layers (CLs), is observed when the load voltage decreases abruptly. Thinner cathode GDLs would weaken the overshoot and shorten the recovery time of current density. Conversely, low local oxygen concentrations at cathode CLs caused by high liquid water saturation levels lead to a current undershoot phenomenon when the load voltage increases abruptly. Thinner cathode GDLs would strengthen the undershoot but shorten the recovery time of current density. The optimal choice of cathode GDL thickness should weigh up the steady-state and the transient performance. Based on this principle, the optimal cathode GDL thickness is selected as 100 µm.

The Effect of Drilling Fluid on Coal’s Gas-Water Two-Phase Seepage

In the process of coal bed methane (CBM) production, the output of CBM is mainly related to the relative permeability of gas and water in coal seams. However, during the drilling process, the invasion of drilling fluid into CBM reservoirs changes the wettability, which may cause the gas and water’s redistribution through the pores and cracks, further changing their two-phase seepage characteristics and influencing CBM production. Therefore, studying the effect of drilling fluid on coal’s gas-water two-phase seepage has practical implications. Using a steady-state method, the influence of changing wettability and reducing the solution’s interfacial tension on relative permeability is investigated by adding different surfactants. The increase in coal’s hydrophilicity exhibits an impact on its relative gas-water permeability. At the same water saturation level, the relative gas permeability decreases and the relative water permeability increases. The hydrophilicity of coal was enhanced after adding anionic surfactants, which reduced gas permeability. Cationic surfactants are difficult to adsorb to the surface of coal due to the fact that the interfacial tension of the water and coal surface is reduced when the coal seam water is added to the cationic surfactants. After adding cationic surfactants, the gas permeability increased in favor of CBM production. The findings of this study could help to better understand the influence of drilling fluid intrusion on coal’s gas-water two-phase seepage and provide technical guidance for selecting better surfactants during the preparation of drilling fluids and help to increase CBM production.

Thermodynamic Characterization of Chemical Damage in Variably Saturated Water-Active Shales

A constitutive framework is developed for variably saturated water-active swelling rocks undergoing chemical damage using modified mixture theory and continuum damage mechanics. The Helmholtzian thermodynamic potential for the skeletal system is derived as a function of the state variables including deformation, damage, two-phase fluid pressures, and chemical potential. Using this, in addition to chemo-poroelastic constitutive equations, a thermodynamically consistent first-order estimation of the damage variable is developed. The working of the theory is shown through the numerical example of water uptake in clay-rich shale rocks solved by the finite element method. The numerical results portray the significance of including variably saturated conditions in constitutive equations as a unique damage-dependent poroelastic behavior was observed for wet and dry regions. The theoretical-based damage estimation corroborated by previous experimental observations illustrates that the rock strength is dominantly controlled by the time of exposure to water rather than the level of water saturation. Contrary to what was perceived, the results show that poroelastic and chemo-poroelastic responses do not coincide even in less reactive shales due to the time-dependent water-induced microstructural deterioration of the rock. The microstructural deterioration increases the storage and flow capacity in the water-saturated region giving rise to substantive spatio-temporal changes in matrix stresses. The research findings provide valuable insights to understand how poromechanics plays a role in causing water uptake in water-sensitive rocks and how such behavior is coupled with associated microstructural chemical damage.

Displacement characteristics of CO2 flooding in extra-high water-cut reservoirs

Carbon dioxide (CO2) flooding is a widely applied recovery method during the tertiary recovery of oil and gas. A high water saturation condition in reservoirs could induce a ‘water shielding’ phenomenon after the injection of CO2. This would prevent contact between the injected gas and the residual oil, restricting the development of the miscible zone. A micro-visual experiment of dead-end models, used to observe the effect of a film of water on the miscibility process, indicates that CO2 can penetrate the water film and come into contact with the residual oil, although the mixing is significantly delayed. However, the dissolution loss of CO2 at high water-cut conditions is not negligible. The oil-water partition coefficient, defined as the ratio of CO2 solubility in an oil-brine/two-phase system, keeps constant for specific reservoir conditions and changes little with an injection gas. The NMR device shows that when CO2 flooding follows water flooding, the residual oil decreases—not only in medium and large pores but also in small and micro pores. At levels of higher water saturation, CO2 displacement is characterized initially by a low oil production rate and high water-cut. After the CO2 breakthrough, the water-cut decreases sharply and the oil production rate increases gradually. The response time of CO2 flooding at high water-cut reservoirs is typically delayed and prolonged. These results were confirmed in a pilot test for CO2 flooding at the P1-1 well group of the Pucheng Oilfield. Observations from this pilot study also suggest that a larger injection gas pore volume available for CO2 injection is required to offset the dissolution loss in high water saturation conditions.

A laboratory study on the dielectric spectroscopy of sandstone and the improvement of dispersion model

Dielectric spectroscopy can be used to identify the fluid properties of complex reservoirs, but no existing model can accurately describe the dielectric dispersion behavior of rocks in a wide frequency band. In this study, dielectric spectroscopy measurements were performed on 20 natural sandstone samples with different water saturation levels and salinity in the frequency band of 20–1000 MHz. A model named textural-EP was established based on the textural model by changing the dielectric constant of water in the pores, which further improved the accuracy of the rock's dielectric spectroscopy. Experimental results show that the effect of interfacial polarization cannot be ignored in rock dielectric spectroscopy at low frequencies when the salinity of the pore water is high, resulting in poor correlation at low frequencies when using the textural model to fit the rock dielectric spectroscopy. Another model named textural-EPMW with correction terms was obtained by adding the Maxwell–Wagner formula to the textural model, which improved the shortcoming of the textural model's poor correlation with the rock dielectric spectroscopy in low-frequency bands. The results obtained using the textural-EPMW model have a high consistency with rock's dielectric spectroscopy in a wide frequency band; thus, the textural-EPMW model is more suitable for describing the dielectric dispersion behavior of rocks.

Microscopic modelling of gas diffusivity in unsaturated cementitious materials considering multiple diffusion regimes

Common degradations of concrete including reinforcement corrosion and carbonation are highly associated with the transport of aggressive gases. However, it is still challenging to accurately understand the gas diffusion behaviour and determine the gas diffusivity in unsaturated cementitious materials. This study proposes a pore-scale model for simulating gas diffusivity in unsaturated cement paste covering multiple gas diffusion mechanisms. The representative volume elements of colloidal calcium silicate hydrate and heterogeneous cement paste with various water saturation degrees are established, capturing the structural attributes of hierarchical cement paste and water-gas distribution with minimum surface energy. A finite difference model for diffusion considering Knudsen effect and molecular diffusion is developed to simulate the diffusion process of various gases through partially saturated cement pastes with different pore structures. Results indicate that gas diffusivity decreases with the increasing water saturation level, the evolution of which can be divided into stable, decreasing and non-diffusive stages. The gas diffusion in partially saturated cement paste is highly dependent on the pore structure and diffusive gas type. The results obtained from this study are expected to provide a deeper insight into the solution of diffusion-related durability problems and the prediction of service life of concrete.

An Intelligent Approach For Obtaining True Resistivity (𝑅𝑇) From Rock Acoustic Data : A Laboratory Verification

Rock true resistivity (Rt) is known as more sensitive than compressional-wave velocity (Vp), the principal output of a seismic survey, to variation in water saturation. Therefore, it would be of a great value if there were a way to predict resistivity distribution from seismic signals. This study is essentially an effort to see the possibility of predicting Rt from Vp through a pattern recognition approach. For the purpose, a series of laboratory tests were performed on some Central Sumatran clay-free sandstone samples of various porosity values and at various water saturation levels. For studying the pattern of relationship, artificial neural networks (ANNs) were applied. From the ‘training’ (i.e.pattern recognition) activity performed using the ANNs, it has been show between Vp and Rt in the following ‘blind test’, it has also been shown that the trained relationship can be used to estimate Rt reliably using other data as input. Comparisons between estimated and observed Rt data have indicated good agreement implying the success of the approach taken in the study. This has laid the foundation and justification for further application of the approach on seismic and well-log data.

Influence of water to cement ratio on mechanical performance of concrete canvas reinforced with warp-knitted spacer fabric

Concrete canvas (CC) has been studied and applied for more than a decade; it has yet to be substantially studied in the field of water dosage. The unreasonable choice of water to cement ratio (w/c) might affect the quality and performance of CC. Thus, in this study, the experimental tests on the setting time, mechanical properties, X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) of CC were carried out. The flexural and bursting behaviors in the early curing stage were also illustrated. The selected w/c was based on the water saturation level of CC during spraying. The obtained results indicated that mechanical properties of CC improved with the increase of w/c, while too much water somewhat delayed the hydration process in the first 3 days of curing. On the other hand, the low w/c would lead to insufficient hydration products and large size of loose defective structure in the interlayer of CC. An appropriate overdosage of water is considered suitable for CC solidification by spraying.

Multiscale modelling of ionic diffusivity in unsaturated concrete accounting for its hierarchical microstructure

This study presents an integrated multiscale framework for modelling ionic diffusivity in unsaturated concrete accounting for its microstructural features and 3D moisture distribution. The hierarchical microstructure of concrete at multiscale from nano- to meso-scale is mimicked, based on which the fluid-solid interaction and moisture distribution in pore network of concrete with various saturation levels are simulated using a lattice Boltzmann multiphase model. A lattice Boltzmann-finite difference model for diffusion is developed to mimic the ionic diffusion and predict the ionic diffusivity in unsaturated concrete. Results indicate that ionic diffusivity in unsaturated concrete highly depends on moisture content and distribution, pore structure, and aggregate content. As the water saturation level drops to around 90%, interfacial transition zone starts to retard ionic diffusion. Voids have a great contribution to water saturation level but less effect on ionic diffusivity. The simulation results of ionic diffusivity at each scale agree well with experimental data.

Impact of water saturation on diffusion coefficients determined by constant volume diffusion method

In recent decades, carbon dioxide (CO2) injection has become a promising technique for enhanced oil recovery (EOR). To design and model the CO2-EOR process in a petroleum reservoir, knowledge of the molecular diffusion of CO2 in oil is required. In this research, the constant volume diffusion (CVD) method is utilized to determine the diffusion coefficient of CO2 in a core saturated with synthetic oil. In addition, the effect of the water saturation level in the core on the resulted diffusion coefficients is examined. This method includes an oil-saturated core, which is in direct contact with a CO2 chamber. CVD tests were conducted at initial pressure and temperature of 410 psi and 64°C for water saturation of 0, 39, and 53%. CO2 is injected from the top of the core and oil is produced from the bottom. Once the CVD initial condition is established, the injector and producer valves are shut-in and the CVD test starts. In the CVD test, the pressure drop data are collected and used to tune the diffusion coefficients using a compositional reservoir simulation model equipped with a developed equation of state. History matching of the pressure decay data is conducted to determine the tuned diffusion coefficients. Experimental results show that the existence of water in the core causes a smaller pressure drop in the system. We find that diffusion coefficients decrease linearly with increasing water saturation in the core operating at the same initial pressure and the system temperature. The presence of water in the core reduces the rate of CO2 diffusion into the synthetic oil. Finally, we present an empirical relationship of the diffusion coefficient and the irreducible water saturation at the proposed lab conditions.

Influence of equilibration time, soil texture, and saturation on the accuracy of porewater water isotope assays using the direct H2O(liquid)–H2O(vapor) equilibration method

The hydrogen and oxygen stable isotopes of water (δ2H and δ18O) are powerful tracers for studying subsurface water flow processes, but the extraction of porewater from unsaturated soil is complex and laborious. The direct liquid–vapor equilibration method (DLVE) for isotope analysis overcomes this challenge by analyzing headspace vapor in isotopic equilibrium with the porewater under closed system conditions. However, the effect of the equilibration time, soil texture, and porewater saturation on isotopic results is not fully understood yet. We tested three differently textured, disaggregated soils (sandy, silty loam and clay) to assess how the equilibration time is impacted by (i) porewater saturation (100%, 80%, 60%, and 40%), and (ii) soil surface area. For all tests, the water loss through diffusion was negligible (<0.3%). The experiments showed that for disaggregated sandy soil, 24 h was a sufficient isotopic equilibration time regardless of water saturation level. Similarly, 24 h was sufficient for kaolinite samples with 100% saturation exhibiting little isotopic variance even after 168 h of equilibration. For saturated silty loam with 2% organic carbon content, 96 h was the optimal equilibration time, whereas saturated silty loam with 4% organic carbon content did not reach isotopic equilibrium by 168 h. The optimal equilibration time increased depending on whether soil samples were disaggregated or kept in a core cutter. Inconclusive results for silty soils with organic carbon revealed the need to further investigate the possible influence of organic carbon on the DLVE method.

Lattice Boltzmann modelling of ionic diffusivity in non-saturated limestone blended cement paste

The accurate prediction of ionic diffusivity in non-saturated limestone blended cement paste is essential for the durability design of blended cementitious materials. This paper presents an integrated framework for simulating the ionic diffusivity in limestone blended cement paste considering its 3D microstructure, water saturation level, and distribution of water and gas phases in the pore network. The 3D microstructure of hydrating blended cement paste with various limestone powder (LP) contents and water-to-binder (w/b) ratios was simulated using the voxel-based CEMHYD3D model, based on which a lattice Boltzmann model with in-house codes was employed to simulate the solid–fluid interaction and ionic diffusivity in cement paste. Results indicate that the relative ionic diffusivity in blended cement paste is strongly dependent on the water saturation level, the evolution of which consists of the sharp drop, slow decrease, slight decrease and depercolation periods. For blended cement paste with 10% LP and w/b ratio of 0.5 at 28 d, the change in decrease rate occurs at the critical water saturation levels of 69%, 34% and 7%, respectively. With the increase of w/b ratio and LP content, the relative ionic diffusivity decreases due to the increasing volume fraction and connectivity of capillary pores. However, the relative ionic diffusivity at degrees of saturation above 70% only undergoes a slight decrease from 0.24 to 0.17 with the increasing LP content from 0% to 20%, which can be ascribed to the low reactivity of LP that cannot much modify the pore structure.

Interaction of resorcinol-formaldehyde carbon aerogels with water: A comprehensive NMR study

Carbon aerogels prepared from resorcinol-formaldehyde aerogels are promising platforms for electrodes, catalysts, adsorbents in environmental chemistry and as electric conductors. For these applications the knowledge of their structure and behavior in aqueous medium is essential. In this work two resorcinol-formaldehyde (RF) carbon aerogels prepared in different ways were characterized with various NMR methods while their pore structure was stepwise saturated with water. The wetting properties were studied by vapor adsorption and low-field NMR relaxometry, while the morphology was followed by NMR cryoporometry during the hydration process. At several water saturation levels the self-diffusion of water was measured. The comprehensive evaluation of the results led to a detailed description of the wetting process of these carbon aerogels beyond the pore size distributions. At low hydration level water clusters formed on and around the hydrophilic functional groups of the surface being able to adsorb water, but no continuous water layer developed on the surface. With increasing water content, spherical water drops formed inside the pore system, and vapor phase diffusion was observed in the partially filled pores. Subsequently the interconnected pore structure was saturated. The determined wet structure was compared to low temperature nitrogen gas adsorption results and scanning electron microscopy images.