Water Absorption Process Research Articles

Study on the influence of water injection pressure on water absorption process and water injection effect of coal

AbstractRock burst disasters can be reduced and prevented with the help of coal dust water injection. In this study, the high‐pressure water injection device is used to examine how the water absorption rate changes over time under various water injection pressures. The results reveal that the water absorption rate of coal samples increases quickly initially before slowing down with water absorption time. Its change can be described using the Langmuir equation. In addition, the Langmuir equation is utilized to demonstrate how water injection pressure affects the maximum water absorption of coal samples. The effects of experimental findings and numerical analysis are investigated on water injection pressure. The breadth and extent of coal bodies with increased moisture are continuously expanding at the same water injection pressure and water injection time. The water absorption of coal close to the borehole remains relatively unchanged with an increase in water injection pressure, but the water absorption range of coal in the vicinity increases. Therefore, raising the water injection pressure and duration will improve the effective range of water injection. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

A cross-scale hygro-mechanical coupling model for hollow glass bead/resin composite materials

Hollow glass bead/resin composite materials are now mainly used in the deep sea submersibles. They are also targeted for application in aviation, aerospace and military applications in the future because of their good material properties, such as low density and high compressive strength. However, there is a coupling relationship between the stress and hygroscopicity in their water absorption process. This reduce the safety of structures produced by hollow glass bead/resin composite materials, especially the underwater and deep-sea structures. In this paper, a hygro-mechanical coupling model and its simplified model for hollow glass bead/resin composites are proposed based on Fick’s second law. A number of experiments are conducted to validate these two models. Comparisons of the predictions of these two models with experimental data show good agreement. The distribution and variation of the stress, water absorption and diffusion coefficient of the composite during the water absorption process were studied. The relationship between the deviation and the water absorption in the simplified model has been given. These results can guide the engineering application of hollow glass bead/resin composite materials, especially in deep sea environments.

EXPERIMENTAL STUDY ON THE EVOLUTION OF MICROPORE STRUCTURE SOFTENED BY NONPRESSURE WATER ABSORPTION STRENGTH OF SANDSTONE

With the increase of mining depth of a coal mine, the strength of the surrounding rock in deep roadways decreases due to the influence of groundwater, which seriously affects the safety of on-site personnel in production. To study the influence of water-rock interaction on the properties of surrounding rock, taking the sandstone in the deep roadway of Wanfu Coal Mine as the research object. The nonpressure water absorption experiment was carried out. According to the compression tests of key water content (0%, 0.8%, 1.6%, 2.4%, 3.3%), the mechanical evolution law of sandstone during water absorption was studied. At the same time, mercury porosimetry (MIP), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) experiments are used to study the evolution of experimental microscopic pores. The strength-softening mechanism of sandstone in Wanfu Coal Mine is discussed. The results show the following: (1) The NMR T<sub>2</sub> spectrum curve of sandstone presented a single peak characteristic. With the increase of water content, the total spectrum area increases continuously, and the corresponding relaxation time of peak shifts to the right. According to the ratio of spectral area in the experimental process, the traditional process of water absorption is further divided into four stages: rapid water absorption, uniform water absorption, pore transformation, and stable water absorption, in which the pore transformation mainly occurs in stage III (31-113 h). (2) The strength of sandstone decreases nonlinearly with the increase of water content, and the degree of attenuation is affected by confining pressure. The softening degree of strength decreases with the growth of confining pressure. With the rise in water content, both cohesion and internal friction angle show a negative exponential decreasing trend. (3) Expansion of clay minerals and the restraint of a quartz skeleton during the experiment are reasons for the closure of pores; misalignment of quartz particles, the flow of pore water, and dissolution of soluble minerals will lead to pore enlargement during water absorption. (4) In addition to the lubrication of water film and the decrease of the cementation ability of clay minerals, the expansion and connectivity of the pore are also important aspects of the softening of sandstone and influence the final destructive form of sandstone.

Identifying parameters for wood protection against water absorption

An issue related to using wood and timber for building structures is to ensure the stability and durability during operation within wide limits. Therefore, the object of research was the inhibition of the process of water absorption of pine and hornbeam wood during a thermal change in its structure. It is proved that in the process of thermal modification of wood, its structure changes, and, accordingly, water absorption. Namely, the maximum increase in mass under the action of water on an untreated sample of wood was more than 40 %, after thermal modification – less than 35 %. The increase in the mass of wood samples thermally modified and treated with a hydrophobic agent was less than 25 %. On the basis of the obtained results of physicochemical studies, discrepancies were found in the IR spectra of wood, both during thermal modification and with additional treatment with a hydrophobic agent, indicating structural changes in the components. In particular, the decrease or absence of the intensities of the absorption bands of some functional groups and the appearance or intensification of others. On the original hornbeam and pine thermogram, thermally modified, and thermally modified with the addition of a hydrophobic coating, thermogravimetric curves are similar to each other and are characterized by a loss of sample mass. This is possible with increasing temperature due to the processes of dehydration, destruction of hemicellulose, lignin, and cellulose with the formation of a non-combustible residue. During heat treatment of cellulose in the region of temperatures of 150÷450 °C, two processes take place in parallel. This is dehydration, accompanied by the destruction of the pyranose cycle and carbonization to form a carbon residue. Also, the process of destruction of glycosidic bonds while maintaining hydroxyl groups, accompanied by regrouping of pyranose cycles.

3D printing lightweight aggregate concrete prepared with shell-packing-aggregate method - Printability, mechanical properties and pore structure

It is a challenge to use porous lightweight aggregates to prepare 3D printing concrete as the water absorption process of porous lightweight aggregates has significant effect on its printability, especially when the content of lightweight aggregate is relatively high. In this paper, the effects of preparation methods on the rheological properties and printability of 3D printing lightweight aggregate (3DPLWC) are studied, aiming to prepare 3DPLWC with high lightweight aggregate content. 3DPLWC with 50, 75 and 100 vol.-% substitution of fine river sand with clay ceramsite sand (CCS) are successfully prepared with shell-packing-aggregate method. The mechanical properties and pore structure of 3DPLWC with different CCS contents are then studied. It is found that the printing process has caused the anisotropy of 3DPLWC, and the specific strength of 3DPLWC is lower than cast counterparts. For 3DPLWC, the increase of pre-wetted CCS content contributes to the decrease of matrix porosity and the increase of circularities of matrix pores in the printed specimens. The results of this study can provide guidance for the preparation of 3DPLWC with different density levels.

Numerical Implementation of the Barcelona Basic Model Based on Return-Mapping Integration

This paper implemented the Barcelona basic model (BBM) into the OpenGeoSys (OGS) platform for numerical modeling of the coupled hydro-mechanical (HM) behavior of unsaturated soil. Within the implicit integration approach in the OGS, the integration rule of the BBM was developed first and the integration form of the BBM under a return mapping algorithm was built. The closest point projection method was used for calculating the return mapping directions with the associative flow rule. The numerical simulation results show that the BBM is feasible in fitting the experimental results. The numerical integration algorithm can reflect the elastic–plastic mechanical behavior of materials, and improve the calculation accuracy. The material exhibits obvious elastic–plastic characteristics during numerical simulation and experiment, and the water absorption process can lessen the mixture’s compression stiffness while enhancing its recovery stiffness.

Real-Time Experimental Monitoring for Water Absorption Evolution Behaviors of Sandstone in Mogao Grottoes, China

Rock mass has typical pore structure, and the induced coupling effects of fluid and solid matrix appear in the disaster evolution process of deep energy exploitation and overground rock hydration. As a representative case, influenced by the water absorption environment, the surrounding rock and murals of Mogao Grottoes produce hydration diseases, which may be related to unclear interaction mechanisms between the surrounding rock and water. In this study, the self-developed physical experimental system for real-time experimental monitoring was applied to test the water absorption evolution behaviors of sandstone. The experimental results showed that the water evaporation of the rock sample during the process of water absorption could be measured through this well-designed physical experimental system, and the actual water absorption of the rock sample is the difference between the decrease of water in the water storage bucket, measured by the balance and the water evaporation in the process of experiment; by drawing the actual water absorption curve of the rock sample, the time when the water absorption of the rock sample reaches saturation could be determined accurately; and the curve of water absorption with time could be expressed as an exponential function. The experimental techniques and methods in this study provide a feasible research idea for studying the water absorption evolution behaviors and mechanisms of the surrounding rock weathering when it meets water, and have significance for revealing the disease mechanisms of the surrounding sandstone in Mogao Grottoes, China.

Experimental study on the moisture migration and triaxial mechanical damage mechanisms of water-bearing coal samples

To investigate the internal moisture migration patterns and mechanical damage characteristics of water-bearing coal, X-ray diffraction (XRD), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, acoustic emission (AE) tests, and conventional triaxial tests were carried out on coal samples saturated at different water pressures. The results showed that the saturated water content of the samples increased exponentially with the water pressure and reached a threshold value, from which the limiting water pressure and limiting water height were approximated. Under non-destructive immersion, the water absorption process of the coal samples was a combination of layer-by-layer saturation and downward water transport. As the water pressure increased, the number of pores indicated by the NMR analysis increased, and the degree of internal damage defined by the integrated area of the T2 curve also increased. These results were used to quantitatively characterize the damage degree of the samples. The triaxial test results showed that the peak strength, residual strength, modulus of elasticity, and Poisson's ratio of the saturated coal samples all decreased linearly or exponentially upon increasing the water pressure. The breaking angle and number of shear cracks increased, and localized deformation damage eventually developed in the form of narrow shear zones. A modified Mohr-Coulomb criterion based on water pressure and water level was proposed after the experimental results were verified by theoretical derivation. This work provides a scientific basis for studying rock weakening mechanisms in water environments.

Microstructure, Deformation Characteristics and Energy Analysis of Mudstone under Water Absorption Process

In geological engineering, a series of safety problems caused by expansive mudstone are common, such as slope instability and roadbed up-arch. In this paper, the mineral composition of mudstones in the Xining area was analyzed by X-ray diffraction (XRD), and the microstructural and morphological changes of mudstones after water absorption were observed by scanning electron microscopy (SEM) test to analyze the internal factors and microstructural evolution patterns of water absorption and swelling of mudstones. Based on the microstructural units, the mudstones were defined into two categories, one is N-type mudstone with flat sheet-like stromatolite units, and the other is SN-type mudstone with more clastic particle units. Water absorption experiments were conducted on the rock samples to study the microstructure of these two types of mudstones under different water absorption conditions. The pore characteristics of the mudstones were analyzed by using Image-Pro Plus to reveal the water absorption mechanism. The results show that the pore area of N-type mudstone is smaller, as well as the distribution of pore diameter. The pore area of N-type mudstone develops rapidly, in the early stage of water absorption, lots of pores are produced, and the pore area of SN-type mudstone shows an overall decreasing trend. The pore area and the number of SN-type mudstones are at a low level after full water absorption. Under the condition of full immersion, water enters the pores rapidly and soluble salts are dissolved in large quantities. The change of water absorption rate of mudstone with time can be divided into the stage of sudden increase, decrease and stability of water absorption rate. Then, based on the stress theory, the relationship between the macroscopic expansion process and the microstructure of mudstone was analyzed. Finally, the energy basis of mudstone water absorption is discussed. In the swelling of mudstone, the energy gradually turns into swelling strain energy.

Effect of humid and thermal environments on the performance of an epoxy resin pavement filling joint material

Modified epoxy resins have shown good results for the repair of pavement cracks. However, as the grouting material is directly exposed to the atmosphere, its performance is affected by humid and heat, resulting in a certain deterioration in its performance and service life. To explore the influence of humid and heat on an epoxy resin joint filling material (EPFM), EPFM was treated in humid and thermal environments for varying periods of time in this study, and the water absorption characteristics, mechanical properties, and road performance of the EPFM were tested. The stress relaxation index was used to evaluate the stress relaxation performance of the EPFM after humid and heat treatments. The results show that in a humid environment, EPFM undergoes a three-stage water absorption process, and the increase in water content reduces its glass transition temperature. In low-temperature environments, the tensile and shear strengths of the EPFM are reduced, but the deformation properties are enhanced under different stress patterns. In a high-temperature environment, the internal macromolecular structure of the EPFM is damaged, causing a significant reduction in its toughness. Under the −10 °C test conditions, the tensile strength reaches a maximum of 31 MPa, and the elongation at breaking decreases to less than 60 %. Through stress relaxation tests, it is found that compared with the thermal environment, water further weakens the stress relaxation performance of the EPFM.

Study on Energy Density Distribution and Mass Fractal of Deep Saturated Coal Samples under Uniaxial Stepwise High Stressed Loading and Unloading Path

The geostress in deep coal roadway is high and affected by mining frequently; under the influence of water-rock interaction, the bearing capacity of coal continues to deteriorate. Based on the characteristics of short water absorption process and low moisture content of deep coal samples in this experiment, the threshold range of quantitative division of water absorption stage of coal samples is given, and the structural characteristics of deep coal samples that are more susceptible to cracks are analyzed. The actual loading process is simulated through uniaxial stepwise high stressed loading and unloading experiments, the gradual development of cracks was the root cause of instability of coal, and saturated water mainly aggravates the instability process through these cracks; the stepwise high stressed loading and unloading path makes cracks more likely to occur in the sample. After each level of loading and unloading, the average stiffness is approximately linear trend degradation. By calculating the energy density of deep coal samples in each stage before the peak, the change of energy density indexes between saturated and dried samples is different from relative shallow samples, and the energy density indexes do not decrease but increases instead. However, the proportion of each energy is generally positive and inverted “U”-type distribution. The change trend of plastic energy in proportion to dissipation energy can be used as the judgment feature of coal sample instability. The instability of deep coal samples is mainly caused by the gradual dissipation of plastic energy to generate cracks and divided into fragments with large and long edge, resulting in low mass fractal dimension. In engineering practice, the loading times should be reduced and the suitable pressure grouting should be conducted timely to delay the deterioration process of crack development in deep water-bearing coal under high stress disturbance.

Influence of different curing conditions on water absorption of cement-based materials under dry and wet cycles

As the main structural material of a subway, the precast concrete segment is produced under the steam-curing condition, and frequently experienced dry–wet cycles environment. In this study, steam-curing and dry–wet cycling methods were used to simulate the water absorption process of cement-based materials under special circumstances. The results showed that the water absorption in cement-based materials decreased with an increase in the number of dry–wet cycles. Based on a micro-analysis, the proportion of large capillary pores (dimension >0.1 μm) in the steam-cured mortar increased during the water absorption process with the increase in the number of dry–wet cycles compared with the standard cured mortar. Through thermodynamic and kinetics analysis, the mechanism and model were calculated to explain the component transformation mechanism of cement-based materials under dry and wet cycles.

Investigation on the effect of fiber wettability on water absorption kinetics of geopolymer composites

Fiber-reinforced geopolymer composites receive widespread attention due to their desirable mechanical properties but the effect of fiber wettability on the water transport properties is rarely investigated. This work aims to reveal the effect and mechanism of hydrophilic and hydrophobic fibers, represented by polyvinyl alcohol fiber (PVAF) and polypropylene fiber (PPF), on the water absorption kinetics of geopolymer composites. Results indicate that both fibers can slightly weaken the water absorption capacity due to increased micron-scale voids and capillary length. Moreover, waterproof composite with a water contact angle of ∼120° can be fabricated by adding PPF and polydimethylsiloxane. PPF weakens the vaporization-condensation process of moisture, thereby extending the duration of the induction stage by 16.7 h, within which a low water absorption rate is maintained. In contrast, hydrophilic PVAF promotes the water absorption process. Therefore, hydrophobic fibers are more beneficial to improve the waterproof performance of geopolymer composites. The development of waterproof fiber-reinforced geopolymer composites is of great potential to improve the corrosion resistance and durability of buildings serving in high-humidity environments.

Foliar Water Uptake Capacity in Six Mangrove Species

Foliar water uptake (FWU) is a mechanism that enables plants to acquire water from the atmosphere through their leaves. As mangroves live in a saline sediment water environment, the mechanism of FWU might be of vital importance to acquire freshwater and grow. The goal of this study was to assess the FWU capacity of six different mangrove species belonging to four genera using a series of submersion experiments in which the leaf mass increase was measured and expressed per unit leaf area. The foliar water uptake capacity differed between species with the highest and lowest average water uptake in Avicennia marina (Forssk.) Vierh. (1.52 ± 0.48 mg H2O cm−2) and Bruguiera gymnorhiza (L.) Lam. (0.13 ± 0.06 mg H2O cm−2), respectively. Salt-excreting species showed a higher FWU capacity than non-excreting species. Moreover, A. marina, a salt-excreting species, showed a distinct leaf anatomical trait, i.e., trichomes, which were not observed in the other species and might be involved in the water absorption process. The storage of leaves in moist Ziplock bags prior to measurement caused leaf water uptake to already occur during transport to the field station, which proportionately increased the leaf water potential (A. marina: −0.31 ± 0.13 MPa and B. gymnorhiza: −2.70 ± 0.27 MPa). This increase should be considered when performing best practice leaf water potential measurements but did not affect the quantification of FWU capacity because of the water potential gradient between a leaf and the surrounding water during submersion. Our results highlight the differences that exist in FWU capacity between species residing in the same area and growing under the same environmental conditions. This comparative study therefore enhances our understanding of mangrove species’ functioning.

Relationships between leaf water potential and soil water potential in grasses subjected to water stress

For grasses and other crops in general, soil water potential has been widely studied to determine if there is a deficit or excess of water content in the soil. However, the plant water absorption process is not only modulated by soil water potential but also by the combination of meteorological, soil depth, and crop canopy factors, which could be elucidated through water relations responses. The objective of this work was to compare the water relations of grass species established in different soil depths and subjected to water stress. Santo Agostinho (Stenotaphrum secundatum), Esmeralda (Zoysia japonica), Tanzania (Panicum maximum) and Tifton 85 (Cynodon spp.) were used in this trial. The four species of grasses were tested in four different soil rooting depths: 10, 20, 30 and 40 cm. The grasses were irrigated at soil moisture field capacity level, until the time of imposing the water stress period. Soil depth had a direct influence on leaf water potential and soil water potential. Moreover, correlation coefficients are higher in deeper soil profiles. The strongest correlations between leaf water potential and soil water potential were found in the deeper soil depth treatments. Therefore, for the soil depth treatment of 40 cm, the average R² for the four species was 0.55, the highest being 0.70 in Tanzania grass. It is possible to relate leaf water potential and soil water potential independently of the grass species used or the depth of soil available to the roots, which would allow the creation of new irrigation management strategies.

Prediction Method of Water Absorption of Soft Rock Considering the Influence of Composition, Porosity, and Solute Quantitatively

The study of water absorption of soft rock is of great significance to the prevention engineering disasters. However, the research on the prediction method of water absorption of soft rock considering the influence of composition, porosity, and solute is insufficient. Aiming to solve the above problem, water absorption tests are carried out by synthesizing soft rocks and water solutions. Then, the prediction model of water absorption of soft rock is established through quantitative analysis of water absorption data and compared with the water absorption characteristics of natural rock to verify the reliability of the model. The results show that the changes in water content and water absorption velocity of soft rock with time obey the second-order exponential attenuation function and the linear function (double logarithmic coordinates axis), respectively. The types of cations and anions and the type and content of clay minerals have the greatest influence on the process of rock water absorption. In addition, the water absorption prediction model could better predict the water absorption process of natural rock. The research results solve the problem of insufficient research on the soft rock water absorption prediction method considering the influence of composition, porosity and solute.

Visualization and quantification of water penetration in cement pastes with different crack sizes

Cracks promote the rapid ingress of water into concrete and shorten the service life of concrete structures. As different deterioration factors form cracks of different sizes, it is necessary to study the water penetration mechanism in cracks. In this study, the capillary absorption process of cement pastes with different crack sizes was monitored by X-ray radiography. With the image processing method of X-ray radiography, a two-dimensional distribution of water during the absorption process was precisely quantified. It was found that cracks provided a direct path for water diffusion and made the water distribution uniform. As the crack width decreased, capillary rises in cracks became higher, which increased the water content along the crack direction. Although water absorption started in two dimensions due to cracks, with the progress of the water absorption process, the influence of cracks decreased, and the absorption of the whole sample could be regarded as one-dimensional.

Experimental study of water-sorption and desorption of several varieties of oil palm mesocarp fibers

The availability and mechanical performance of palm nut mesocarp fibers make them a serious alternative to synthetic fibers for certain textile and composite applications. However, their use can be limited by the lack of knowledge of the process of water absorption and moisture recovery of these fibers as well as the mechanisms of desorption. This work highlights the porous character of palm nut mesocarp fibers (OPMF) by SEM analysis; this character is amplified by NaOH treatment. X-ray diffraction, Thermogravimetric Analysis and Infrared spectrometry of OPMF are also performed. The study of the drying kinetics of OPMF shows that the desorption model of Verna et al. best describes their drying process at three desorption isotherms (60, 70 and 80 °C). The diffusion coefficient is lower for the interior fibers than the exterior ones at all isotherms. The activation energy of the outer Tenera fibers (21.3 kJ/mol) is twice that of the Dura variety (10.2 kJ/mol). Moisture uptake is about 10% for Dura and inner Tenera varieties and 7% for outer Tenera fibers while water uptake is about 160% for Dura and Tenera varieties and 114% for outer Tenera fibers. The models of Sikame et al. and Mohsenin best describe the water and moisture uptake kinetics of OPMF. The moisture diffusion coefficient varies from 2.31 × 10−12 m2/s to 5.26 × 10−12 m2/s while the water diffusion coefficient varies from 3.32 × 10−10 m2/s for external Tenera fibers to 4.85 × 10−10 m2/s for internal Tenera fibers. There is great versatility between the water and moisture diffusion parameters from one variety of OPMF to another as well as within the same variety between external and internal fibers.

Waterproof geopolymer composites modified by hydrophobic particles and polydimethylsiloxane

Geopolymer is a green porous aluminosilicate material that can be tailored with fillers and additives to achieve various functions. In this work, waterproof geopolymer composites fabricated by blending hydrophobic metakaolin and quartz particles, as well as PDMS agents, were innovatively developed. The contrast-enhancing X-ray computed tomography and gravimetry were used to rate their waterproof efficacy. The results show that water absorption is greatly inhibited in PDMS-hydrophobic particle composites due to the capillary surface modification and long tortuous water transport channels caused by micron-sized particles and macropores. A new low-sorptivity stage lasting ∼150 h occurs at the beginning of the water absorption process, and the final absorbed-water volume significantly reduces. This work reveals the waterproof mechanisms and water absorption kinetics of geopolymer composites with hydrophobic materials and points the way to waterproof engineered geopolymer materials.

Influence of Hydrothermal Aging under Two Typical Adhesives on the Failure of BFRP Single Lap Joint

Facing increasingly serious resource crises, energy conservation is becoming the development trend of various delivery vehicles, and lightweight is an important way to achieve energy conservation. In this paper, the basalt fiber-reinforced resin composite material (BFRP) was selected to study the effect of its bonding structure, and it was used to make BFRP-BFRP joints. Two adhesives, Araldite®2012 and Araldite®2015, were used to make single-lap joints and dumbbell-shaped specimens. Aging environments of 80 °C/95% RH and 80 °C/pure water were used for the 0-day (unageing), 10-day, 20-day, and 30-day aging tests, respectively. According to Fick’s second law, the moisture absorption change model of two adhesives was established, and it was found that the water absorption process could be divided into two stages, which explains the precipitation of water molecules and the reaction of water molecules with functional groups. The maximum average failure load and load-displacement curves under different environments and different joints were obtained by using the electronic universal tensile machine, and the exposure time was more important than the effect of humidity. At the same time, the change law of failure strength and ductility were analyzed. The change of Tg (Glass transition temperature) was analyzed by differential scanning calorimetry (DSC) equipment, and the results showed that molecular chain rupture was the reason for the decrease of Tg. It could be seen from the joint failure mode distribution that Araldite®2012 adhesive was easily affected by the environment, and the joint of Araldite®2015 adhesive was affected by the combined effect of the adhesive and BFRP.