Water Permeability Characteristics Research Articles

Experimental investigation of the mechanical properties of mold-bag concrete (MBC) for primary support in tunnels

Considering the shortcomings of traditional tunnel support methods like shotcrete, including large rebound, poor water retention, and dust pollution, this paper proposes an innovative method to use mold-bag concrete (MBC) for initial tunnel support. Through macroscopic mechanical tests and microscopic structural characterization, a high-fluidity mix ratio of MBC suitable for actual construction conditions has been developed. To clarify the mechanical properties of MBC, compressive tests were conducted, leading to important conclusions: 1) Mold-bags can significantly enhance the compressive strength and ductility of MBC. The specimens of mold-bag concrete of PP (MBC-PP) fail first but have good ductility, while specimens of mold-bag concrete of SNG-PET (MBC-SPET) have the best compressive performance but poor ductility; 2) Without pressurized drainage, mold-bags can increase the compressive strength of MBC due to the water permeability characteristics, with MBC-SPET having the largest increase in compressive strength, 69.1 %; 3) MBC-SPET tests show that increasing pressure has a better effect than increasing drainage time, with 90 s and 20 kg pressurized drainage being the best increase effect. These findings highlight the potential of MBC in addressing the limitations of traditional methods, providing strength enhancement, environmental benefits, and practical feasibility for tunnel support.

Effect of Electric Field on Water Absorption and Permeability Characteristics of Silicone Rubber

Effect of Electric Field on Water Absorption and Permeability Characteristics of Silicone Rubber

Effect of internal curing by superabsorbent polymers on the densification and microstructural development of cementitious materials exposed to different environmental conditions

Superabsorbent polymers (SAPs) are among the internal curing agents used in cementitious materials. This study aims to evaluate the influence of wider SAP dosages under different exposure environments on the microstructural densification of cementitious materials and the development of strength and durability based on this. With SAP incorporation, hydrate crystallization most easily occurs in the wet/dry condition through hydration with externally supplied water and by internal SAP curing, which leads to the formation of the densest microstructures. Microstructure densification further progresses as the SAP dosages increase. Despite the internal curing effect of SAPs, the ultrasonic pulse velocity and the compressive strength of S0.5 specimens compared with those of the REF specimens decrease due to SAP void presence. However, these mechanical properties of the S1.0 specimens are all recovered at later ages when exposed to the wet/dry condition, forming densest microstructures. As the SAP dosages increase, the sealing effect of SAPs improves the water permeability characteristics at early ages. The lowest water permeability coefficient is observed in the S1.0 specimen exposed to the wet/dry condition as the further hydration effect of SAPs is exerted with increasing ages. In conclusion, utilizing the appropriate amount of SAPs and environmental conditions can effectively densify the internal pore structures, thereby securing the mechanical and durable properties of concrete structures.

Temperature-dependent voids and their impact on SMA surface course permeability

This study investigates the water permeability characteristics of newly constructed Stone Mastic Asphalt (SMA) surface course, with a specific focus on the influence of connected voids arising from the compaction temperature during pavement construction. On-site evaluation of the permeability coefficient was performed, followed by core sample extraction from the same locations to investigate the correlation between the permeability coefficient and porosity. Industrial CT scanning was used to identify and separate void regions in the core samples. Three-dimensional digital reconstruction techniques were employed to analyze the morphology and spatial distribution of voids within the core. The connectivity of voids was assessed, providing insights into water infiltration pathways within the SMA course. Additionally, finite element simulation of the pavement temperature field was conducted to investigate the spatially differentiated distribution of voids within the SMA course.The findings reveal that approximately 38.3% of the voids are concentrated within a 1 cm depth below the top surface of the 4 cm-thick SMA course. The aggregation of voids enhances the likelihood of interconnection, facilitating water seepage. Water infiltrates through the open voids on the top surface and flows vertically and horizontally along the interconnected pathways. Notably, at a depth of approximately 2.5 cm, the flow transitions to horizontal spreading, aligning with the primary distribution interval of interconnected voids. The non-uniform distribution of voids is primarily influenced by the compaction temperature. The top and bottom portions exhibit higher void percentages, while the middle portion shows relatively fewer voids, consistent with the observed compaction temperature pattern.

In Situ Biomaterial Printing Technology Based on Transfer Molding

Skin is one of the largest and most important organs in the human body. When faced with a large, full-thickness skin burn, there is not enough healthy skin to graft. In this case, we can replace our skin with biomaterials. Due to its characteristics of water permeability, antibacterial properties, biocompatibility, self-debridement, and so on, the hydrogel is undoubtedly a better alternative material. Among the methods of hydrogel preparation, in situ material molding has attracted a lot of attention for its unique advantages. Here, we proposed an in situ forming process based on transfer printing and verified the feasibility of the transfer printing process using a three-axis platform. The in situ molding equipment was designed to realize the in situ material transfer process, which prepared the conditions for the subsequent process optimization, cell experiment verification, and animal experiment.

Experimental investigation on water/gas resistance and strength properties of clinoptilolite/Na-PAA amended compacted clay cover

Compacted clay is an effective and economical engineering barrier for seepage prevention and gas blocking in landfills (including tailings pond, landfill, etc.). In addition to the lack of durability such as desiccation cracks of compacted clay modified by clinoptilolite and sodium polyacrylate, it is also necessary to consider the changes of engineering properties such as water holding capacity, water and gas resistance, and strength of compacted clay. Therefore, through oven evaporation test, flexible wall permeability test and unconfined compressive strength test, this paper studies the water retention, permeability and strength characteristics of compacted clay with different amounts of clinoptilolite and sodium polyacrylate. Orthogonal experiment L16(45) was used to optimize the amount of clinoptilolite and sodium polyacrylate and the compaction conditions, and further combined with the analytic hierarchy process (AHP), the factors affecting the water retention, permeability and strength of the compacted clay before and after the modification of clinoptilolite and sodium polyacrylate were discussed simply and quickly, and the applicability of the orthogonal experiment traditional analysis method and the analytic hierarchy process in the modified compacted clay of clinoptilolite and sodium polyacrylate was studied.

Development of Superpermeable Wood-Based Forward Osmosis Membranes

Novel lignin-based membranes with excellent water permeability and salt rejection characteristics were developed for forward osmosis (FO) processes. The fabricated membranes are composed of three layers: (i) a bottom layer of nanofibrous electrospun sulfonated kraft lignin (SKL) (70 wt %) and poly(vinyl alcohol) (PVA) (30 wt %), (ii) an intermediate layer of PVA-glutaraldehyde (GA) hydrogel, and (iii) a top thin film of a selective polyamide (PA) layer. We coated the SKL-PVA support surface with four different PVA hydrogel concentrations (0.25, 0.5, 1, and 2 wt %). Increasing the concentration of the PVA hydrogel, the thickness of the deposited layer was increased accordingly. After forming the PA layer on top of the PVA hydrogel layer by the interfacial polymerization reaction, lignin-based thin film composite (LTFC-X) membranes were obtained, in which X denotes the PVA hydrogel concentration. According to the cross-sectional TEM images, the thickness of the deposited PA layer dropped from 450 nm on the LTFC-0.25 membrane to less than 60 nm in the LTFC-1 membrane. However, a further increase in the PVA hydrogel concentration enhanced the PA layer thickness to over 250 nm. Among all synthesized membranes, the LTFC-0.5 membrane demonstrated the lowest structural parameter (S) of 191.67 ± 5.88 μm, resulting in a minimal internal concentration polarization in this membrane. The FO performances of membranes were evaluated in two different configurations: the active PA layer facing the feed solution (ALFS) and the PA layer facing the draw solution (ALDS). The LTFC-0.5 membrane provided maximum water flux (Jw) in both ALDS (61.33 ± 2.85 LMH) and ALFS (56.60 ± 2.99 LMH) modes. The LTFC-0.5 membrane also showed the lowest specific salt flux (Js/Jw) of 0.087 ± 0.004 g/L among all fabricated membranes in the ALDS mode. However, the LTFC-1 membrane provided the best performance in the ALFS mode with a minimum Js/Jw value of 0.090 ± 0.011 g/L.

Investigation of the Physical Mechanical Properties and Durability of Sustainable Ultra-High Performance Concrete with Recycled Waste Glass

Construction material sustainability and waste reuse have emerged as significant environmental issues. Concrete is widely used in the building and engineering fields. Ultra-high performance concrete (UHPC), which has remarkably high mechanical properties, has become one of the most common concrete varieties in recent years. As a result, substantial amounts of Portland cement (PC) are frequently used, raising the initial cost of UHPC and restricting its broad use in structural applications. A significant amount of CO2 is produced and a large amount of natural resources are consumed in its production. To make UHPC production more eco-friendly and economically viable, it is advised that the PC in concrete preparations be replaced with different additives and that the recycled aggregates from various sources be substituted for natural aggregates. This research aims to develop an environmentally friendly and cost-effective UHPC by using glass waste (GW) of various sizes as an alternative to PC with replacement ratios of 0%, 10%, 20%, 30%, 40%, and 50% utilizing glass powder (GP). Fine aggregate “sand (S)” is also replaced by glass particles (G) with replacement ratios of 0%, 50%, and 100%. To accomplish this, 18 mixes, separated into three groups, are made and examined experimentally. Slump flow, mechanical properties, water permeability, and microstructural characteristics are all studied. According to the results, increasing the S replacement ratio with G improved workability. Furthermore, the ideal replacement ratios for replacing PC with GP and S with G to achieve high mechanical properties were 20% and 0%, respectively. Increasing the replacement rate of GP in place of PC at a fixed ratio of G to S resulted in a significant decrease in water permeability values. Finally, a microstructural analysis confirms the experimental findings. In addition, PC100-S100 was the best mix compared to PC100-S50 G50 and PC100-G100.

Effects of pure carbonation on pore structure and water permeability of white cement mortars

The effects of carbonation on cement-based materials have drawn much attention because of its profound influences on durability performance of concrete structures. Most accelerated carbonation in lab is conducted at RH 50%–70%, which also dries out cement-based materials. The introduced drying action changes pore structure significantly, making the effects of carbonation obscure. To clarify the effects of pure carbonation, water permeability and related micro-structural characteristics are measured on mature mortars, which have been carbonated at water-saturated state. It is found that after carbonation, the porosity of mortars decreases slightly, with finer overall pore structure and lower characteristic pore size. The water permeability also decreases by roughly 40% on average. Based on the pore size distribution curves obtained through the low-field proton nuclear magnetic resonance technique, water permeability is predicted by the Katz-Thompson and Kozeny-Carman theories with satisfactory accuracy. The decrease of water permeability after carbonation agrees well with the reduced characteristic pore length, which quantitatively verifies the observed refinement of nanoscale pore structure due to pure carbonation.

Performance evaluation of a coating protection system for concrete structures affected by internal expansive reactions

In the last decades, a significant number of large concrete structures with deterioration problems, related to internal expansive chemical reactions, have been detected in Portugal. This type of degradation is associated with the formation of expansive products in concrete causing its disruption, leading to the decrease of the structure’s service life and, ultimately, to the decommissioning or demolition of the structure. In Portugal, structures affected by this pathology are very important in economic and strategic terms, since these reactions are usually encountered in large dams, bridges and viaducts. Two separate material-based mechanisms have been identified to cause the concrete swelling: Alkali-Silica Reaction (ASR) and Delayed Ettringite Formation (DEF). Both reactions result in the formation of expansive products and a common requirement for their occurrence is the presence of a sufficient moisture content inside concrete. By controlling the humidity level in concrete, coatings applied onto the concrete surface should contribute to mitigate ASR or DEF by acting as a barrier against ingress of water and allowing the concrete to dry, as long as they have adequate water permeability characteristics. This paper presents the general criteria that may be followed to select a surface protection system, based on coating materials (hereinafter designated by coating system), for the rehabilitation of concrete structures affected by expansive reactions, in order to mitigate them and, thus, contribute to improve durability and service life of affected structures. In addition, a laboratory study is presented concerning the performance evaluation of a surface protection system, composed of two coating materials, in terms of its capacity to bridge cracks, its permeability to liquid and to water vapour, and on its effectiveness on controlling humidity inside concrete.

Assessment of Water Permeability Test on Polypropylene based Self-Compacted Fibre Reinforced Concrete (PSCFRC)

An investigation conducted to study the effect of water permeability and strength characteristics such as compressive strength of Polypropylene self-compacted fibre reinforced concrete (PSCFRC) is presented. Polypropylene fibres of lengths, 35 mm with a diameter of 0.44 mm, were systematically combined in different mix proportions to combinations of 0.2%, 0.4%, and 0.6% Polypropylene fibre volume fraction. For comparison, a concrete mix with no fibres was also mixed. A total of 72 cube specimens of 150 mm were tested, 36 each for compressive strength and water permeability at 28 and 56 days of curing. According to the findings of this study, a fibre combination of SCFRC 0.6 percent is the most acceptable fibre composition to use in Polypropylene self-compacted fibre reinforced concrete (PSCFRC) for maximum performance in terms of compressive strength and water permeability requirements together.

STRUCTURE FORMATION OF C-S-H FROM THE POSITION OF MICROMECHANICS OF COMPOSITE MEDIA

the creation of an environmentally friendly building material to protect the human environment can only be carried out from the position of a transdisciplinarity approach, taking into account modern achievements in geomimetics and micromechanics of composite media. A wide range of basalt-fiber-reinforced concrete based on composite binders has been developed, which have increased characteristics of impermeability and durability under extreme operating conditions. The nature of the influence of the composition and manufacturing technology of cement composites on the pore structure of the composite has been established, which has a positive effect on the charac-teristics of gas, water and vapor permeability. High early strength was obtained, which allows the use of materials for operational repair and construction in emergency situations. The positive influence of the composition of the developed composite on the performances has been proved. The water resistance of the modified composite provides a water pressure of 2 MPa for 148 hours, which corresponds to the W18 grade (for the control sample – W8), the frost resistance grade – F300. It was found that the water absorption of the modified concrete samples was lower than that of the control sample, which is explained by the decrease in the pore structure index λ by 28.4 times, and the average pore diameter by 3.05 times. The total pore volume of the modified concrete was lower and decreased with increasing dose of nanosilica.

Femtosecond laser structuring of permeable and resorbable biomaterial

Abstract Bioresorbable nanofiber nonwovens with their fascinating properties provide a wide range of potential biomedical applications. Modification of the material enables the adjustment of mechanical and biological characteristics depending on the desired application. Due to the nanosized fiber network, post-production structuring is very challenging. Within this study, we use femtosecond laser technology for structuring permeable and resorbable electrospun poly-L-lactide (PLLA) membranes. We show that this post-production process can be used without disturbing the fiber network near the structured areas. Furthermore, the modification of the water permeability and mechanical characteristics due to the laser structuring was investigated. The results prove femtosecond laser technology to be a promising method for the adjustment of the membrane properties and which in consequence can help to optimize cell adhesion, enable revascularization and open up applications of nanofiber membranes in personalized medicine.

Evaluation of pore size distribution and permeability reduction behavior in pervious concrete

Pervious concrete is an environmentally friendly material that improves water permeability, skid resistance, and sound absorption characteristics. However, due to a large number of pores and the absorption capacity, pervious concrete faces the problem of clogging caused by dust particles and solid contaminants entering the internal pores. In this study, both pore size distributions (PSD) of the pervious concrete and permeability reduction behavior are studied by laboratory tests. The extent of permeability reduction is addressed by designing the penetration test for 21 groups of pervious concrete mixes with varying aggregate gradations and specimen thickness. The PSD is determined by the two-dimensional (2D) sliced image scanned by the Computed Tomography (CT). An approach to represent the characteristic pore size of pervious concrete is proposed and verified. Results showed that: the effect of thickness on permeability is negligible while on clogging behavior is significant. The ratio between the clogging sand sizes and the characteristic pore size is an important parameter that affects the clogging behavior and can be used to predict the anti-clogging performance.

Relationship between water permeability and physical characteristics of polyolefins, vinyl polymers, and polycarbonates

Diagrams of compatibility of water permeability with glass transition temperature, density, and cohesion energy are constructed. The computer program “Cascade”, INEOS RAS was used. Polyolefins, vinyl polymers, and polycarbonates were analyzed. Compatibility diagrams are constructed for the areas of lowest and highest water permeability for different classes of polymers. For polyolefins and vinyl polymers, the lowest water permeability is selected in the range from 0 to 100 barrer, and the highest water permeability is from 1000 to 2000 barrer. For polycarbonates, the intervals from 0 to 70 barrer and from 3000 to 7000 barrer are selected. These diagrams allow you to select polymers that meet the specified values of density, cohesion energy, glass transition temperature, and the onset of temperature of intense thermal degradation.

Physical characterization of high methoxyl pectin and sunflower oil wax emulsions: A low-field 1 H NMR relaxometry study.

Pectin-wax-based emulsion systems could be used to form edible films and coatings with desired water permeability characteristics. Pectin is often used in food industry due to its gelling and viscosity increasing properties. Physical properties of pectin are highly dependent on its esterification degree. Waxes are commonly used as edible coatings to enhance the water barrier properties of food products. This study focuses on preparing emulsions with sunflower oil wax (SFW) and high methoxyl pectin (HMP) at different concentrations for any possible edible film or coating formulations. Sunflower oil (SFO) was added as the dispersed oil phase to these emulsions. Characterization of the emulsions was performed by using particle size, rheology, and time domain nuclear magnetic resonance (NMR) relaxometry measurements. Effects of HMP concentration and the presence of SFO in the emulsion formulations were explored. Mean particle size values were recorded between 1 and 3µm. Rheology measurements showed that increasing HMP concentrations and presence of SFO in emulsions resulted in more pseudoplastic behavior. NMR transverse relaxation times (T2 ) were measured to detect the differences between the emulsions. Relaxation spectrum analysis was also conducted for a detailed understanding of the transverse relaxations. Addition of SFO and higher HMP concentrations decreased the T 2 values of the emulsion systems (P<0.05). However, T2 decreasing effect of SFO was compensated at 10% (w/w) HMP concentration showing that SFO was well dispersed in this particular emulsion formulation. Changes in the rheological behavior and relaxation times provided insight on the formation and stability of the emulsions. PRACTICAL APPLICATION: Findings of this study can be utilized and integrated to produce edible films and coatings with different water permeability characteristics. This study showed that NMR relaxometry parameters were also effective in monitoring and determining the physical characteristics of the pectin-wax-based emulsion systems as other conventional techniques including rheology and particle size measurements. Our NMR relaxometry findings were in correlation with the flow behavior and particle size results of the investigated emulsion systems.

Selective Proton Transport for Hydrogen Production Using Graphene Oxide Membranes.

Graphene oxide has shown exceptional properties in terms of water permeability and filtration characteristics. Here the suitability of graphene oxide membranes for the spatial separation of hydronium and hydroxide ions after photocatalytic water splitting is demonstrated. Instead of relying on classical size exclusion by adjusting the membrane laminates' interlayer spacings, nonmodified graphene oxide is used to exploit the presence of its natural functional groups and surface charges for filtration. Despite a significantly larger interlayer spacing inside the membrane compared with the size of the hydrated radii of the ions, highly asymmetric transport behavior and a 6 times higher mobility for hydronium than for hydroxide are observed. DFT simulations reveal that hydroxide ions are more prone to interact and stick to the functional groups of graphene oxide, while diffusion of hydronium ions through the membrane is less impeded and aligns well with the concept of the Grotthuss mechanism.

Multiphase calcium alginate membrane composited with cellulose nanofibers for selective mass transfer

A multiphase calcium alginate membrane composited with cellulose nanofibers (CNF) was successfully prepared by using the method. The maximum stress and strain, water content, water permeability, and mass transfer characteristics were examined according to the addition ratio of CNF. Increasing of the amount of CNF enhanced the maximum stress and reduced the maximum strain, thereby suggesting that CNF impart flexibility and stiffness to the composite membrane. The CNF in the calcium alginate noticeably increased the water flux at the same pressure. The permeability of the composite of the CNF membrane was higher. The effective diffusion coefficient dramatically decreased 2.5 × 103 times when the molecular weight increased ten-fold (from 60 to 604 Da). Moreover, stronger dependency was observed in the CNF composite membrane. The morphology of the cross-section of the membrane was observed using scanning electron microscopy. The appearance of the CNF composite membrane became rougher when the amount of CNF increased.

A Systematic Framework for Optimizing a Sweeping Gas Membrane Distillation (SGMD).

The present work has undertaken a meticulous glance on optimizing the performance of an SGMD configuration utilized a porous poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) membrane. This was carried out by conducting a systematic framework for investigating and optimizing the pertinent parameters such as sweeping gas flow rate, feed temperature, feed concentration and feed flow rate on the permeate flux. For this purpose, the Taguchi method and design of experiment techniques were harnessed to statistically determine optimum operational conditions. Besides that, a comprehensive surface and permeation characterization was conducted against the hand-made membranes. Results showcased that the membrane performance was ultimately controlled by the feed temperature and was nearly (~680) % higher when the temperature raised from 45 to 65 °C. Also, to a lesser extent, the system was dominated by the feed flow rate. As the adopted feed flow rate increases (from 0.2 to 0.6 L/min), around 47.5% increment was bestowed on water permeability characteristics. In contra, 34.5% flux decline was witnessed when higher saline feed concentration (100 g/L) was utilized. In the meantime, with raising the sweeping gas flow rate (from 120 to 300 L/h), the distillate was nearly 129% higher. Based on Taguchi design, the maximum permeate flux (17.3 and 17 kg/m2·h) was secured at 35 g/L, 0.4 L/min, 65 °C and 300 L/h, for both commercial and prepared membranes, respectively.

The effect of chemical aging on water permeability of white cement mortars in the context of sol–gel science

In the sol–gel science, the influence of chemical aging on the fundamental water permeability remains open regarding to the durability performance of cement-based material. To reveal the pure effect of chemical aging, the water permeability and related micro-structural characteristics are measured on water-saturated mature mortars, whose aging is accelerated through heat treatment under water. It is found that, the chemical aging increases the volumetric porosity and coarsens the pore structure to a notable extent, which enlarge water permeability by 2.6–4.9 times. Based on the pore structure obtained through the low-field proton NMR technique, the water permeability is predicted by the Katz–Thompson theory with satisfactory accuracy, quantitatively confirming the direct effects of chemical aging on water permeability. Physically, because of the polymerization and rearrangement of C–S–H gel, cement mortars undergo substantial changes with enlarging radii for both interlayer and gel pores, slightly decreasing interlayer space but remarkably enlarging gel pore space.