Search Results (162)

Freezing and thawing cycles significantly affect the mechanical and hydraulic behavior of soils, posing detrimental challenges for infrastructures in cold climates. This study develops and validates a coupled Thermal–Hydraulic–Mechanical (THM) model using COMSOL Multiphysics (Version 6.3) to demonstrate the complexities of vapor and water flux, heat transport, frost heave, and vertical stress build-up in unsaturated soils. The analysis focuses on fine sand, sandy clay, and silty clay by examining their varying susceptibilities to frost action. Silty clay generated the highest amount of frost heave and steepest vertical stress gradients due to its high-water retention and strong capillary forces. Fine sand, on the other hand, produced a minimal amount of frost heave and a polarized vertical stress distribution. The study also revealed that vapor flux is more noticeable in freezing fine sand, while silty clay produces the greatest water flux between the frozen and unfrozen zones. The study also assesses the impact of soil properties including the saturated hydraulic conductivity, the particle thermal conductivity, and particle heat capacity on the frost-induced phenomena. Findings show that reducing the saturated hydraulic conductivity has a greater impact on mitigating frost heave than other variations in thermal properties. Silty clay is most affected by these changes, particularly near the soil surface, while fine sand shows less noticeable responses. Full article

In actual service, asphalt pavement is subjected to freeze–thaw cycles and ultraviolet radiation (UV) over the long term, which can easily lead to mixture aging, enhanced brittleness, and structural damage, thereby reducing pavement durability. This study focuses on the influence of freeze–thaw cycles and ultraviolet aging on the performance of recycled asphalt mixtures. Systematic indoor road performance tests were carried out, and a fatigue prediction model was established to explore the comprehensive effects of recycled asphalt pavement (RAP) content, environmental action (ultraviolet radiation + freeze–thaw cycle), and other factors on the performance of recycled asphalt mixtures. The results show that the high-temperature stability of recycled asphalt mixtures decreases with the increase in environmental action days, while higher RAP content contributes to better high-temperature stability. The higher the proportion of old materials, the more significant the environmental impact on the mixture; both the flexural tensile strain and flexural tensile strength decrease with the increase in environmental action time. When the RAP content increased from 30% to 50%, the bending strain continued to decline. With the extension of environmental action days, the decrease in the immersion Marshall residual stability and the freeze–thaw splitting strength became more pronounced. Although the increase in RAP content can improve the forming stability, the residual stability decreases, and the freeze–thaw splitting strength is lower than that before the freeze–thaw. Based on the fatigue test results, a fatigue life prediction model with RAP content and freeze–thaw cycles as independent variables was constructed using the multiple nonlinear regression method. Verification shows that the established prediction model is basically consistent with the change trend of the test data. The research results provide a theoretical basis and optimization strategy for the performance improvement and engineering application of recycled asphalt materials. Full article

In high-elevation mining areas, the roadbeds of certain surface ore haul roads are predominantly composed of sandstone. These sandstones are exposed to cold climatic conditions for long periods and are highly susceptible to erosion by the effects of freeze–thaw, which can degrade their support properties. This paper investigates the mechanism of strength deterioration of sandstone containing prefabricated cracks under cyclic loading and unloading after experiencing freeze–thaw. Sandstone specimens containing prefabricated cracks were prepared and subjected to 0, 20, 40, 60, and 80 freeze–thaw cycle tests. The strength changes were tested, and the crack extension process was analyzed using numerical simulation techniques. The study results show the following: 1. The wave propagation speed within the sandstone is more sensitive to changes in the number of freeze–thaw cycles. In contrast, mass damage shows significant changes only when more freeze–thaw cycles are experienced. 2. As the number of freeze–thaw cycles increases, the frequency of energy release from the numerical model accelerates. 3. The trend of the Cumulative Strain Difference (${\epsilon }_c$) reflects that the plastic strain difference between numerical simulation and actual measurement gradually decreases with increasing stress cycle level. 4. With the increase in freeze–thaw cycles, the damage morphology of the specimen undergoes a noticeable change, which is gradually transformed from monoclinic shear damage to X-shaped conjugate surface shear damage. 5. The number of tensile cracks dominated throughout the cyclic loading and unloading process, but with the increase in freeze–thaw cycles, the percentage of shear cracks increased. As the freeze–thaw cycles increase, sandstones are more inclined to undergo shear damage. These findings are important guidelines for road design and maintenance in alpine mining areas. Full article

To comprehensively investigate the compressive behavior of basalt fiber-reinforced concrete (BFRC) subjected to multiple freeze–thaw cycles, a series of quasi-static and dynamic compression tests were conducted on BFRC at various fiber volume fractions and a wide strain rate range of 1 × 10⁻³–420 s⁻¹. The freeze–thaw deterioration characteristics of BFRC were analyzed from macro and micro perspectives. The influence of freeze–thaw degradation, strain rate effect, and fiber reinforcement effect on the mechanical performance of BFRC was investigated. It was found that when the fiber volume fraction was 0.2%, the fiber reinforcement performance of basalt fiber was optimal. By incorporating the damage factor of freeze–thaw cycles and the dynamic increase factor of strength into the Ottosen nonlinear elastic constitutive model, a dynamic constitutive model that considers the fiber content, strain rate enhancing effect, and freeze–thaw degradation influence was established. Full article

Considering the harsh marine environment characterized by dry–wet cycles, freeze–thaw action, chloride penetration, and sulfate attack, four optimized ultra-high-performance concrete (UHPC) mix designs were developed. Durability was assessed via electric flux, dry–wet cycles, and rapid freeze–thaw tests to evaluate the effects of curing methods, aggregate types, and mineral admixtures on key durability indicators, including chloride ion permeability, compressive strength loss, and mass loss. Scanning electron microscopy (SEM) examined microstructural changes under various conditions. Results showed that curing method significantly affected chloride ion permeability and sulfate resistance. High-temperature curing (70 ± 2 °C) reduced 28-day chloride ion electric flux by about 50%, and the compressive strength loss rate of specimens subjected to sulfate attack decreased by 2.7% to 45.7% compared to standard curing. Aggregate type had minimal impact on corrosion resistance, while mineral admixtures improved durability more effectively. Frost resistance was excellent, with mass loss below 0.87% after 500 freeze–thaw cycles. SEM analysis revealed that high-temperature curing decreased free cement particles, and mineral admixtures refined pore structure, enhancing matrix compactness. Among all mixtures, Mix Proportion 4 demonstrated the best overall durability. This study offers valuable insights for UHPC design in aggressive marine conditions. Full article

The bond interface is the weakest part of the repair system, and its performance is a key factor impacting the repair effectiveness of damaged concrete constructions. However, the research on the damage law and the mechanism of repair of the bonded interface in the cold region marine environment is not in-depth. In this study, the influence of polyvinyl alcohol (PVA) fibers and crystalline admixtures (CAs) on the mechanical properties and volumetric deformation performance of cementitious repair materials was researched. Furthermore, the deterioration patterns of the bond strength and chloride ion diffusion characteristics of the repair interface under the coupling of seawater-freeze-thaw cycles were investigated. Combined with the composition, micro-morphology, and micro-hardness of hydration products before and after erosion, the damage mechanism of the repaired bonding interface was revealed. The results indicate that the synergistic use of PVA fibers and CAs can significantly improve the compressive strength, bond strength and volume stability of the repair materials. The compressive strength and 40° shear strength of S0.6CA at 28 d were 101.7 MPa and 45.95 MPa, respectively. Under the seawater-freeze-thaw cycle action, the relationship between the contents of free and bound chloride ions in the bonded interface can be better fitted by the Langmuir equation. The deterioration process of the bonding interface and the penetration rate of chloride ions can be effectively delayed by PVA fiber and CAs. After 700 seawater-freeze-thaw cycles, the loss rates of bond strength and chloride diffusion coefficient of S0.6CA were reduced by 26.34% and 52.5%, respectively, compared with S0. Full article

The aim of the work is to analyze the survival strategy of Taxus baccata L., one of the promising plants for landscaping and the creation of woodlands, in the changing ecological conditions of the steppe zone of the Donetsk ridge. In order to achieve this goal, we used biomechanics methods, which help to understand the relationship between the physical and mechanical properties of living tissues and the overall stability of trees during interactions with environmental factors such as temperature, snow and ice storms, cyclic freeze–thaw processes, wind loads, and others. The work was based both on experimental studies on the estimation of the tissue elasticity modulus in response to temperature changes, the mechanical stability of plants, the field collection of materials, and studies on the modeling of forest stand conditions of English yew. As a result of the conducted experiments, it was established for the first time that at the absolute wood moisture content of 77 ± 5.1%, the density of wood tissues in the conditions of Donetsk is 907 ± 43 kg m⁻³. The modulus of elasticity of living tissues depending on the temperature factor varied in the following range: 8.8 ± 0.31 GN m⁻² (T = 288 K), 11.5 ± 0.55 GN m⁻² (T = 255 K) and 6.9 ± 0.47 GN m⁻² (t = 308 K). It was revealed that during the local thawing of skeletal branches and tables, the mechanical resistance of T. baccata is reduced by 20–22% and this critically affects the overall plant resistance. It was established for the first time that T. baccata in the conditions of the steppe zone has an adaptive strategy of preserving the integrity of the organism under the action of environmental factors with limited loads. The secret lies in the formation of the shape memory effect, under the influence of critical loads. The plant, thus, chooses not migration, not death, but adaptation to changes in environmental conditions, which can become a serious factor in the use of T. baccata in the landscaping of urban areas and the creation of artificial forests. Full article

In cold-region rock engineering, freeze–thaw cycle-induced crack propagation in fractured rock masses serves as a major cause of disasters such as slope instability. Existing studies primarily focus on the influence of individual fissure parameters, yet lack a systematic analysis of the crack propagation mechanisms under the coupled action of multiple parameters. To address this, we establish three groups of slope models with different rock bridge distances (d), rock bridge angles (α), and fissure angles (β) based on the PFC2D discrete element method. Frost heave loads are simulated by incorporating the volumetric expansion during water–ice phase change. The Parallel Bond Model (PBM) is used to capture the mechanical behavior between particles and the bond fracture process. This reveals the crack evolution laws under freeze–thaw cycles. The results show that, at a short rock bridge distance of d = 60 m, stress concentrates in the fracture zone. This easily leads to the rapid penetration of main cracks and triggers sudden instability. At a long rock bridge distance where d ≥ 100 m, the degree of stress concentration decreases. Meanwhile, the stress distribution range expands, promoting multiple crack initiation points and the development of branch cracks. The number of cracks increases as the rock bridge distance grows. In cases where the rock bridge angle is α ≤ 60°, stress is more likely to concentrate in the fracture zone. The crack propagation exhibits strong synergy, easily forming a penetration surface. When α = 75°, the stress concentration areas become dispersed and their distribution range expands. Cracks initiate earliest at this angle, with the largest number of cracks forming. Cumulative damage is significant under this condition. When the fissure angle is β = 60°, stress concentration areas gather around the fissures. Their distribution range expands, making cracks easier to propagate. Crack propagation becomes more dispersed in this case. When β = 30°, the main crack rapidly penetrates due to stress concentration, inhibiting the development of branch cracks, and the number of cracks is the smallest after freeze–thaw cycles. When β = 75°, the freeze–thaw stress dispersion leads to insufficient driving force, and the number of cracks is 623. The research findings provide a theoretical foundation for assessing freeze–thaw damage in fractured rock masses of cold regions and for guiding engineering stability control from a multi-parameter perspective. Full article

Hydraulic concrete structures in cold regions often suffer from the combined action of freeze-thaw (FT) cycles and external loads, indicating that these structures often depend on the combined effects of two or more factors. In recent years, researchers around the world have made considerable efforts and explorations to solve this challenge, achieving fruitful research results. This article provides a comprehensive literature review on performance degradation law and model construction of hydraulic concrete under FT cycles. Firstly, the theory and characterization method of FT damage for concrete are introduced. Given the inherent deficiencies of traditional detection methodologies and the constraints imposed by extant computed tomography (CT) technology, there is an urgent need to develop a high-precision segmentation technique for concrete. By capitalizing on the resultant microstructure, a more accurate predictive model can be established. Thereafter, an in-depth discussion is conducted on the damage mechanism of hydraulic structures when subjected to freeze-thaw (FT) cycles in conjunction with external loading scenarios, namely fracture, direct tension, triaxial stress, and hydraulic wear. As the combined effects of different factors cause more serious damage to hydraulic structures than a single factor, the evolution law is more complex. Although researchers have attempted to reveal the deterioration mechanism of multi-factor interaction by means of numerical methods, there are still many fundamental issues that require further exploration and more in-depth research due to the limitations of constitutive models. Finally, the existing research results are summarized, and novel insights are proposed for future research directions. This study promptly identifies the gaps that urgently need to be filled, especially the insufficient understanding of the complex stress state of hydraulic concrete structures and the inadequate research on the performance deterioration law under multi-factor combined action. This investigation aims to determine the future research focus in relation to hydraulic concrete in cold regions that could advance the revelation of the deterioration mechanism caused by multi-factor interaction. By providing a detailed overview of the current hydraulic concrete structures in terms of the combined action of FT cycles and external loads, highlighting the research limitations, and suggesting future research directions, this review seeks to contribute to the safe operation of hydraulic concrete structures in cold regions. Full article

As a primary construction material, concrete plays a vital role in the development of infrastructure, including bridges, highways, and large-scale buildings. In Northeast China, the structural integrity of concrete faces severe challenges due to freeze–thaw cycles and substantial diurnal temperature variations. This study involved a thorough examination of concrete’s performance under varying numbers of temperature differential cycling (60 to 300) and freeze–thaw cycles (75 to 300). The results showed that both freeze–thaw and temperature differential cycling led to increasing mass loss with the number of cycles. Peak mass losses reached 3.1% and 1.2% under freeze–thaw and temperature differential cycles, respectively, while the combined action resulted in a maximum mass loss of 4.1%. The variation trends in dynamic elastic modulus and compressive strength differed depending on the environmental conditions. Under identical freeze–thaw cycling, both properties exhibited an initial increase followed by a decrease with increasing temperature differential cycles. After 120 temperature differential cycles, the dynamic modulus and compressive strength increased by 4.7–6.2% and 7.5–10.9%, respectively. These values returned to near their initial levels after 180 cycles and further decreased to reductions of 17.0–22.6% and 15.3–29.4% by the 300th cycle. In contrast, under constant temperature differential cycles, dynamic modulus and compressive strength showed a continuous decline with increasing freeze–thaw cycles, reaching maximum reductions of 5.0–11.5% and 18.1–31.8%, respectively. Notably, the combined effect of temperature differential and freeze–thaw cycles was significantly greater than the sum of their individual effects. Compared to the superposition of separate effects, the combined action amplified the losses in dynamic modulus and compressive strength by factors of up to 3.7 and 1.8, respectively. Additionally, the fatigue life of concrete subjected to combined temperature differential and freeze–thaw cycles followed a two-parameter Weibull distribution. Analysis of the S-N_f curves revealed that the coupled environmental effects significantly accelerated the deterioration of fatigue performance. Full article

Background: Metritis, a common postpartum uterine infection in bovines, poses substantial challenges in livestock management, including compromised fertility and economic losses. Poor uterine drug penetration and systemic side effects, necessitating innovative localised delivery systems and limiting current systemic antibiotic treatments. Aim: This study aimed to develop and evaluate the potential effect of the ofloxacin-loaded hydrogel as a localised drug delivery system to treat metritis in bovine. The focus was on achieving sustained drug release, enhanced antibacterial efficacy and reduced inflammation in the endometrium. Materials and Methods: The CS/PVA hydrogel was synthesised using a freeze–thaw method and further optimised for drug encapsulation efficiency (96.7 ± 2.1%), stability and biocompatibility. Physicochemical characterisation included swelling behaviour, mechanical properties and rheological analysis. In vitro drug release profiles in the simulated uterine fluid were assessed over 72 h and antibacterial activity was tested against common uterine pathogens such as Escherichia coli and S. aureus. In vivo studies were conducted on bovines diagnosed with endometritis to evaluate clinical recovery. Results: The SEM image of the ofloxacin-loaded CS/PVA hydrogel resulted in a smooth and porous structure demonstrating larger pore size than the blank. The rheological study suggested higher stability and elastic behaviour. Antibacterial assays on E. coli and S. aureus revealed significant inhibition zones, respectively, indicating potent efficacy. In vivo, evaluated on treated bovine, reduced bacterial loads were exhibited (2.86 × 10^5A CFU/mL → 6.37 × 10^2B CFU/mL), clinical improvement was marked and uterine inflammation was resolved. Conclusions: Ofloxacin-loaded hydrogels represent a promising localised treatment for bovine metritis, offering sustained antibacterial action and improved clinical outcomes. This approach addresses the limitations of systemic antibiotic therapies and provides a practical solution for enhanced veterinary care. Further studies are recommended to validate these findings in more extensive field trials and explore commercialisation potential. Full article

Conventional concrete does not often meet engineering needs in high-impact scenarios, such as airport runways and bridges, due to its brittleness, low tensile strength and insufficient resistance to dynamic loading. Although existing rubberized concrete exhibits an enhanced toughness, granular rubber exhibits significantly poorer mechanical properties, limiting its wide application. For this reason, in this study, we propose incorporating rubber in the form of fiber and systematically investigate the effects of the rubber fiber type (NBR, silicone rubber, EPDM), admixture amount (5%, 10%, 15%) and length (6, 12, 18 mm) on the mechanical properties and impact resistance of concrete. Through cubic compression, split tensile and drop hammer impact tests, combined with SEM microanalysis and Weibull distribution modeling, the trends in properties and the mechanisms of action were revealed. The key findings included the following: (1) The equal-volume replacement of fine aggregates with fibrous rubber significantly reduced the static strength, with NBR exhibiting the lowest compressive strength loss (13.12%) compared to silicone rubber (30.86%) and EPDM (21.52%). The splitting tensile strength decreased by 10.11%, 23.67% and 13.56%, respectively. (2) The rubber dosage was negatively correlated with static strength, while an increased fiber length partially mitigated strength degradations. (3) Fibrous rubber markedly enhanced impact resistance: the final crack impact cycles of NBR, silicone rubber and EPDM were increased by 255%, 147.5% and 212.5%, respectively, compared to plain concrete. The optimal mix (15% dosage, 12mm NBR) improved the impact life by 330%. (4) Weibull distribution analysis confirmed that the impact resistance data conformed to a two-parameter model (R² ≥ 0.808), with a high consistency between the predicted and experimental results. The results of this research can be applied to transportation infrastructures (e.g., heavy-duty pavements, bridges) that require a high impact resistance, with environmental benefits. However, the study did not analyze the long-term durability (e.g., effects of freeze–thaw and chemical corrosion) or perform an economic analysis of rubber fiber processing costs; this needs to be further explored in the future to promote practical engineering applications. Full article

Fish scales, an abundant yet underutilized by-product of fish processing, are rich in proteins and thus hold significant potential for value-added applications. This study aimed to develop a sustainable method for converting grass carp (Ctenopharyngodon idella) scales into bioactive protein hydrolysates and evaluate their potential as natural antimicrobial agents. Fish scale protein hydrolysates (FSPHs) were prepared through citric acid extraction followed by pepsin enzymatic hydrolysis. Antimicrobial activity and stability were systematically assessed against Escherichia coli and Staphylococcus aureus, alongside mechanistic investigations. Results demonstrated the potent inhibitory effects of FSPHs against both pathogens, with minimum inhibitory concentrations (MICs) of 4.2 μg∙mL⁻¹ and minimum bactericidal concentrations (MBCs) of 67.5 μg∙mL⁻¹ for E. coli and 33.7 μg∙mL⁻¹ for S. aureus. FSPHs exhibited exceptional thermal stability (<100 °C) and retained functionality over 10 freeze–thaw cycles. Mechanistic studies have revealed enhanced bacterial membrane permeability upon FSPH treatment, with microscopic evidence of cell aggregation and lysis after 16 h of exposure. This work validates grass carp scales as a viable source of antimicrobial peptides through optimized extraction protocols, offering a circular economy solution for fishery waste. The findings provide actionable insights for policymakers to promote eco-friendly alternatives to synthetic antibiotics while advancing methodologies for bioactive peptide research. Full article

Under the action of freeze–thaw cycles, the internal temperature and water distribution of slope soils in cold regions change significantly, which directly affects the stability of slopes. In order to study the differences in hydrothermal reactions at different depths and their impacts on the stability of slopes. This study establishes both a freeze–thaw model and a hydrothermal coupling model, combining field measurements with numerical simulations to examine the dynamic changes in hydrothermal characteristics within the slope. The results indicate that the variation in slope temperature with depth can be divided into three stages: initial freezing, stable freezing, and thawing. In the freezing stage, the negative temperature gradient drives water to migrate towards the freezing front, forming segregated ice and inducing frost heave. In the thawing stage, the latent heat released by the phase change in segregated ice promotes water to move towards the slope toe, increasing the water content there and indirectly exacerbating the risk of slope instability. The heat and moisture transfer in frozen soil slopes shows non-linear and dynamic characteristics. The unique process of one-way freezing and two-way thawing makes the thawing rate 1.35 times that of the freezing rate, and this asymmetric characteristic is the key to understanding the mechanism of slope instability. Full article

Microbial-induced carbonate precipitation technology allows concrete to detect and diagnose cracks autonomously. However, the concrete’s compact structure and alkaline environment necessitate the adoption of a proper carrier material to safeguard microorganisms. In this study, various bacterial strains, including Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium, were immobilized in lightweight expanded clay aggregates (LECA) to investigate their effect on the self-healing performance, mechanical strength, and freeze–thaw durability. Self-healing concrete specimens were prepared using immobilized LECA, directly added bacterial spores, polyvinyl acetate (PVA) fibers, and air-entraining admixture (AEA). The pre-cracked prisms were monitored for 224 days to assess self-healing efficiency through ultrasonic pulse velocity (UPV) and surface crack analysis methods. A compressive strength restoration test was conducted by pre-loading the cube specimens with 60% of the failure load and re-testing them after 28 days for strength regain. Additionally, X-ray diffraction and scanning electron microscopy (SEM) were conducted to analyze the precipitate material. The findings revealed that self-healing efficiency improved with the biomineralization activity over the healing period demonstrated by the bacterial strains. Compression and flexural strengths decreased for the bacterial specimens attributed to porous LECA. However, restoration in compression strength and freeze–thaw durability significantly improved for the bacterial mixes compared to control and reference mixes. XRD and SEM analyses confirmed the formation of calcite as a self-healing precipitate. Overall, results indicated the superior performance of Bacillus megaterium followed by Bacillus sphaericus and Bacillus subtilis. The findings of the current study provide important insights for the construction industry, showcasing the potential of bacteria to mitigate the degradation of concrete structures and advocating for a sustainable solution that reduces reliance on manual repairs, especially in inaccessible areas of the structures. Full article