Search Results (68)

Prestressed concrete railroad ties are the global standard for railway infrastructure due to their structural stability, durability, and cost-effective maintenance. However, their long-term performance is often compromised by premature deterioration. This study investigates the degradation of prestressed concrete railways ties from a Brazilian rail line after ten years of natural exposure, emphasizing critical implications for infrastructure maintenance. Two groups of ties, separated by 30 km, were analyzed through physical property assessments, petrography, X-ray diffraction (XRD), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The results reveal that deterioration was driven by the combined effects of alkali–silica reaction (ASR) and sulfate attack, confirmed by the presence of (N, C)ASH gels, ettringite crystallization, and cryptocrystalline materials within cracks and voids. Prestressing-induced stresses and environmental moisture further accelerated degradation, leading to a 66% reduction in mechanical strength in the T1 group. These findings demonstrate that internal swelling reactions and moisture exposure synergistically accelerate deterioration in prestressed concrete ties, particularly in low-prestress, poorly drained zones. Full article

Anion exchange membrane fuel cells (AEMFCs) have garnered significant attention for their potential to advance fuel cell technology. In this study, we developed and characterized anion exchange membranes (AEMs) composed of quaternized poly(vinyl alcohol) (QPVA) electrospun nanofiber mats with poly(acrylamide-co-diallyldimethylammonium chloride) (PAADDA) as a matrix filler for interfiber voids. The objective was to investigate the effect of varying PAADDA concentrations as a matrix filler for interfiber voids on the structural, mechanical, and electrochemical properties of QPVA-based electrospun AEMs. Membranes with various concentrations of PAADDA were fabricated and extensively characterized using FTIR, SEM, tensile strength, water uptake, swelling degree, ion exchange capacity (IEC), and hydroxide ion conductivity (σ). FTIR confirmed the successful incorporation of PAADDA into the membrane structure, while SEM images showed that PAADDA effectively filled the voids between the QPVA fibers, resulting in denser membranes. The results indicated that the eQPAD5.0 membrane, with the highest PAADDA content, exhibited the best overall performance. The incorporation of PAADDA into QPVA-based electrospun AEMs significantly enhanced their mechanical strength, achieving a tensile strength of 23.9 MPa, an IEC of 1.25 mmol g⁻¹, and hydroxide conductivity of 19.49 mS cm⁻¹ at 30 °C and 29.29 mS cm⁻¹ at 80 °C, making them promising candidates for fuel cell applications. Full article

Bentonite is widely used as an engineering barrier in radioactive waste disposal. This study examined the hydromechanical behavior and microstructural evolution of a bentonite mixture under controlled hydration, utilizing real-time X-ray micro-CT imaging to capture transitions from granular to dense homogeneous states. The results demonstrated that, during the early stages of hydration, bentonite pellets experienced substantial swelling, filling inter-pellet voids and transforming from a loosely packed granular structure to a compact, homogeneous matrix. This transformation significantly reduced the porosity from an initial value of 20% to below 0.1% after 60 days, thereby substantially lowering the material’s permeability. Particle displacement analysis, employing digital image correlation techniques, revealed axial displacements of up to 2.6 mm and radial displacements of up to 0.9 mm, highlighting pronounced void closure and structural reorganization. The study also examined the influence of initial dry density heterogeneities on swelling pressure and permeability, providing insights for optimizing barrier design. The findings affirm that hydrated bentonite serves as a highly effective low-permeability barrier for sealing deep geological repositories. Its capacity for environmental adaptation, demonstrated through self-healing and densification, further reinforces its suitability for critical and long-term engineering applications. Full article

Expansive soil poses significant challenges for engineering due to its susceptibility to swelling and shrinkage. This study aims to explore effective methods for improving its mechanical properties using single alkaline activators, single slag, and their combination. Laboratory experiments were conducted to evaluate the unconfined compressive strength (UCS) and analyze curing mechanisms through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that all three treatments enhance soil strength, with the combination of alkali-activated slag being the most effective, followed by the single alkaline activator and single slag. Optimal dosages were determined as 15% for the activator and slag individually and 15% activator combined with 20% slag, yielding the densest structure and highest UCS. The activator’s modulus of 1.5 was found to be optimal, and strength improved further with extended curing time. A microscopic analysis revealed that alkaline activation formed gel-like substances and dense needle-like structures, while slag generated CaCO₃ and Ca(OH)₂. The combination produces a synergistic effect, creating substantial amounts of C-S-H, C-A-S-H gel, and dense needle-like structures, which enhance soil compactness and strength by binding particles and filling voids. These findings provide insights into the curing mechanisms and offer practical solutions for improving expansive soil in engineering applications. Full article

Soils may not always be suitable to fulfill their intended function. Soil improvement can be achieved by mechanical or chemical methods, especially in transportation facilities. L and FA additives are frequently used as chemical improvement additives. In this study, two natural clay samples with extreme and very high plasticity were improved by using L and FA admixtures, and their properties under static and repeated loads were investigated by ML methods. Two soil samples from two different sites were analyzed. In this study, eight datasets were used. There are 14 inputs, including specific gravity (Gs), void ratio (eo), sieve analysis (+No.4, −No.200), clay size, LL, plastic limit (PL), plasticity index (PI), linear shrinkage (Ls), shrinkage limit (SL), cure day, agent, clay type, and agent percentage. The outputs are index and swelling properties (compressive, percent), compressive strengths, modulus of elasticity, and compressibility properties in soaked and non-soaked conditions. Prediction is attempted with different ML (ML) techniques. ML techniques used for regression (such as Decision Tree Regression (DTR) and K-nearest neighbors (KNN)). SHapley Additive Explanations (SHAP), the impact of inputs on outputs were observed, and it was generally found that PL and LL had the highest impact on outputs. Different performance metrics are used for evaluation. The results showed that these ML techniques can predict the static and cyclic properties of extremely high plasticity clays with high performance (R² > 0.99). These results highlight the general applicability of the used ML models on different datasets containing soil properties. Full article

The wetting of compacted clays and their subsequent swelling often result in damage to structures and infrastructures. Estimations of the swell that is expected to develop during wetting are usually based on standard laboratory tests. The standard procedure requires inundating the test specimens; this procedure represents an extreme wetting condition and provides an upper limit to the swell. However, wetting may result from less extreme conditions, for example by the absorption of water due to suction forces, which may result in a smaller swell. This paper describes a laboratory investigation of the swell difference in high-plasticity clay that may result from different wetting conditions. Swell tests were carried out on specimens prepared at different initial conditions and wetted under different wetting conditions of inundation or absorption. The results indicate that as the initial void ratio decreases and the degree of saturation increases, it is more likely that different wetting conditions will result in different swell magnitudes, where inundation may create a larger swell than absorption. The soil at a low initial void ratio and high degree of saturation seems to be characterized by mono-modal pore size distributions in the micropore range. This unique pore size distribution may be the explanation of the different swell magnitudes. Full article

CO₂ flooding plays a significant part in enhancing oil recovery and is essential to achieving CCUS (Carbon Capture, Utilization, and Storage). This study aims to understand the fundamental theory of CO₂ dissolving and diffusing into crude oil and how these processes vary under reasonable reservoir conditions. In this paper, we primarily use molecular dynamics simulation to construct a multi-component crude oil model with 17 hydrocarbons, which is on the basis of a component analysis of oil samples through laboratory experiments. Then, the CO₂ dissolving capacity of the multi-component crude was quantitatively characterized and the impacts of external conditions—including temperature and pressure—on the motion of the CO₂ dissolution and diffusion coefficients were systematically investigated. Finally, the swelling behavior of mixed CO₂–crude oil was analyzed and the diffusion coefficients were predicted; furthermore, the levels of CO₂ impacting the oil’s mobility were analyzed. Results showed that temperature stimulation intensified molecular thermal motion and increased the voids between the alkane molecules, promoting the rapid dissolution and diffusion of CO₂. This caused the crude oil to swell and reduced its viscosity, further improving the mobility of the crude oil. As the pressure increased, the voids between the internal and external potential energy of the crude oil models became wider, facilitating the dissolution of CO₂. However, when subjected to external compression, the CO₂ molecules’ diffusing progress within the oil samples was significantly limited, even diverging to zero, which inhabited the improvement in oil mobility. This study provides some meaningful insights into the effect of CO₂ on improving molecular-scale mobility, providing theoretical guidance for subsequent investigations into CO₂–crude oil mixtures’ complicated and detailed behavior. Full article

Thermomechanical processing (TMP) of ferritic–martensitic (FM) steels, such as HT9 (Fe–12Cr–1MoWV) steels, involves normalizing, quenching, and tempering to create a microstructure of fine ferritic/martensitic laths with carbide precipitates. HT9 steels are used in fast reactor core components due to their high-temperature strength and resistance to irradiation damage. However, traditional TMP methods for these steels often result in performance limitations under irradiation, including embrittlement at low temperatures (<~430 °C), insufficient strength and toughness at higher temperatures (>500 °C), and void swelling after high-dose irradiation (>200 dpa). This research aimed to enhance both fracture toughness and strength at high temperatures by creating a quenched and tempered martensitic structure with ultrafine laths and precipitates through rapid quenching and unconventional tempering. Mechanical testing revealed significant variations in strength and fracture toughness depending on the processing route, particularly the tempering conditions. Tailored TMP approaches, combining rapid quenching with limited tempering, elevated strength to levels comparable to nano-oxide strengthened ferritic alloys while preserving fracture toughness. For optimal properties in high-Cr steels for future reactor applications, this study recommends a modified tempering treatment, i.e., post-quench annealing at 500 °C or 600 °C for 1 h, possibly followed by a brief tempering at a slightly higher temperature. Full article

High-performance structural materials (HPSMs) are needed for the successful and safe design of fission and fusion reactors. Their operation is associated with unprecedented fluxes of high-energy neutrons and thermomechanical loadings. In fission reactors, HPSMs are used, e.g., for fuel claddings, core internal structural components and reactor pressure vessels. Even stronger requirements are expected for fourth-generation supercritical water fission reactors, with a particular focus on the HPSM’s corrosion resistance. The first wall and blanket structural materials in fusion reactors are subjected not only to high energy neutron irradiation, but also to strong mechanical, heat and electromagnetic loadings. This paper presents a historical and state-of-the-art summary focused on the properties and application potential of irradiation-resistant alloys predominantly strengthened by an oxide dispersion. These alloys are categorized according to their matrix as ferritic, ferritic–martensitic and austenitic. Low void swelling, high-temperature He embrittlement, thermal and irradiation hardening and creep are typical phenomena most usually studied in ferritic and ferritic martensitic oxide dispersion strengthened (ODS) alloys. In contrast, austenitic ODS alloys exhibit an increased corrosion and oxidation resistance and a higher creep resistance at elevated temperatures. This is why the advantages and drawbacks of each matrix-type ODS are discussed in this paper. Full article

The study reports the significance of carbon presence in affecting void nucleation in Fe. Without carbon, void nucleation rates decrease gradually at high temperatures but remain significantly high and almost saturated at low temperatures. With carbon present, even at 1 atomic parts per million, void nucleation rates show a low-temperature cutoff. With higher carbon levels, the nucleation temperature window becomes narrower, the maximum nucleation rate becomes lower, and the temperature of maximum void nucleation shifts to a higher temperature. Fundamentally, this is caused by the change in effective vacancy diffusivity due to the formation of carbon-vacancy complexes. The high sensitivity of void nucleation to carbon comes from the high sensitivity of void nucleation to the vacancy arrival rate in a void. The void nucleation is calculated by first obtaining the effective vacancy diffusivity considering the carbon effect, then calculating the defect concentration and defect flux change considering both carbon effects and pre-existing dislocations, and finally calculating the void nucleation rate based on the recently corrected homogeneous void nucleation theory. The study is important not only in the fundamental understanding of impurity effects in ion/neutron irradiation but also in alloy engineering for judiciously introducing impurities to increase swelling resistance, as well as in the development of simulation and modeling methodologies applicable to other metals. Full article

Natural biopolymers offer a sustainable alternative for improving soil behavior due to their inert nature, small dosage requirement, and applicability under ambient temperatures. This research evaluates the efficacy of natural biopolymers for ameliorating an expansive soil by using a 0.5% dosage of cationic chitosan, charge-neutral guar gum, and anionic xanthan gum during compaction. The results of laboratory investigations indicate that the flow through and volume change properties of the expansive soil were affected variably. The dual porosity, characterized by low air entry due to inter-aggregate pores (AEV₁ of 4 kPa) and high air entry due to the clay matrix (AEV₂ of 200 kPa) of the soil, was healed using chitosan and guar gum (AEV of 200 kPa) but was enhanced by the xanthan gum (AEV₁ of 100 kPa and AEV₂ of 200 kPa). The s-shaped swell–shrink path of the soil comprised structural (e from 1.23 to 1.11), normal (e from 1.11 to 0.6), and residual stages (e ranged from 0.6–0.43). This shape was converted into a j-shaped path through amendment using chitosan and guar gum, showing no structural volume change, with e from about 1.25 to 0.5, but was reverted to a more pronounced form by xanthan gum, with e from 1.5 to 1.32, 1.32 to 0.49, and 0.49 to 0.34 in the three stages, respectively. The consolidation behavior of the soil was largely unaffected by the addition of biopolymers such that the saturated hydraulic conductivity decreased from 10⁻⁹ m/s to 10⁻¹² m/s over a void ratio decrease from 1.1 to 0.6. At a seating stress of 5 kPa, the swelling potential (7.8%) of the soil slightly decreased to 6.9% due to the addition of chitosan but increased to 9.4% and 12.2% with guar gum and xanthan gum, respectively. The use of chitosan and guar gum will allow the compaction of the investigated expansive soil on the dry side of optimum. Full article

Polybenzoxazines (Pbzs) are advanced forms of phenolic resins that possess many attractive properties, including thermal-induced self-curing polymerization, void-free polymeric products and absence of by-product formation. They also possess high T_g (glass transition temperature) and thermal stability. But the produced materials are brittle in nature. In this paper, we present our attempt to decrease the brittleness of Pbz by blending it with polyvinylalcohol (PVA). Benzoxazine monomer (Eu-Ed-Bzo) was synthesized by following a simple Mannich condensation reaction. The formation of a benzoxazine ring was confirmed by FT-IR and NMR spectroscopic analyses. The synthesized benzoxazine monomer was blended with PVA in order to produce composite films, PVA/Pbz, by varying the amount of benzoxazine monomer (1, 3 and 5 wt. % of PVA). The property of the composite films was studied using various characterization techniques, including DSC, TGA, water contact angle analysis (WCA) and SEM. WCA analysis proved that the hydrophobic nature of Pbz (value) was transformed to hydrophilic (WCA of PVA/Pbz5 is 35.5°). These composite films could play the same role as flexible electrolytes in supercapacitor applications. For this purpose, the composite films were immersed in a 1 M KOH solution for 12 h in order to analyze their swelling properties. Moreover, by using this swelled gel, a symmetric supercapacitor, AC//PVA/Pbz5//AC, was constructed, exhibiting a specific capacitance of 170 F g⁻¹. Full article

New inorganic nanostructured matrices for fiber-reinforced composites with enhanced high-temperature stability were developed from alkali aluminosilicate polymers doped with different ultra-high-temperature ceramic (UHTC) particles. The alkali aluminosilicate matrices were synthesized at room temperature with a high SiO₂:Al₂O₃ ratio and then further functionalized by doping with 4–5 wt % of micrometric SiC, ZrB₂, ZrC, and HfC powders and finally thermally stabilized as glass–ceramics at 750 °C. The different UHTC-doped matrices were characterized according to their dimensional and microstructural changes after thermal cycling in air flux at 1000 °C. The first results showed that carbide-based UHTC powders improved the thermal stability of the matrices, preventing the excessive swelling of the material and the formation of detrimental voids that might result in the lack of adhesion with reinforcing fibers. Contrarily, the addition of ZrB₂ resulted in an excessive matrix swelling at high temperature, thus proving no efficacy compared to the undoped matrix. Impregnation tests carried out on C-fiber fabrics showed good processability, adhesion to the fibers, and fracture pull-out, especially for carbide-based matrices. Full article

A method to predict the swellability of clay-sand mixtures is proposed. This model is a modified form of the Studds (1997) prediction model for clay-sand mixtures. The new proposed model uses the laboratory fall cone penetration technique to produce a characterization chart. This chart presents slope levels that can be used to obtain an equation for the final clay void ratio versus the vertical effective stress for clays. The porosity of the clay-sand mixtures was worked out based on a correction factor obtained from compression and porosity measurements in the laboratory. The porosity of the mixture was merged into the clay profile equation to compute the final clay void ratio at a specified stress level, which made it possible to predict the swelling behavior for different and variable stress levels. The swellability slope was obtained using fall cone tests conducted on the fine portion. Mixtures of kaolinite and bentonite were introduced to represent soils with different swell potentials. The fall cone measurements of a few points can be used to establish the swellability relationships for natural clay. Merging fall cone points with the swellability slope chart can define the profile of the vertical effective stress versus the clay void ratio. Full article

Fluorinated polyimides incorporated with triptycene units have gained growing attention over the last decade since they present potentially interesting selectivities and a higher free volume with respect to their triptycene-free counterparts. This work examines the transport of single-gas and mixed-gas N₂ and CH₄ in the triptycene-based 6FDA-BAPT homopolyimide and in a block 15,000 g mol⁻¹/15,000 g mol⁻¹ 6FDA-mPDA/BAPT copolyimide by using molecular dynamics (MD) simulations. The void-space analyses reveal that, while the free volume consists of small-to-medium holes in the 6FDA-BAPT homopolyimide, there are more medium-to-large holes in the 6FDA-mPDA/BAPT copolyimide. The single-gas sorption isotherms for N₂ and CH₄ over the 0–70 bar range at 338.5 K show that both gases are more soluble in the block copolyimide, with a higher affinity for methane. CH₄ favours sites with the most favourable energetic interactions, while N₂ probes more sites in the matrices. The volume swellings remain limited since neither N₂ nor CH₄ plasticise penetrants. The transport of a binary-gas 2:1 CH₄/N₂ mixture is also examined in both polyimides under operating conditions similar to those used in current natural gas processing, i.e., at 65.5 bar and 338.5 K. In the mixed-gas simulations, the solubility selectivities in favour of CH₄ are enhanced similarly in both matrices. Although diffusion is higher in 6FDA-BAPT/6FDA-mPDA, the diffusion selectivities are also close. Both triptycene-based polyimides under study favour, to a similar extent, the transport of methane over that of nitrogen under the conditions studied. Full article