Freeze-thaw Conditions Research Articles

Effect of Fly Ash Content on the Microstructure and Strength of Concrete under Freeze–Thaw Condition

To understand the influence of fly ash (FA) content on the microstructure and strength of concrete under freeze–thaw cycles (FTCs), four groups of concrete with different FA contents (0–30%) were tested under FTC condition. Mass loss rate, relative dynamic modulus of elasticity (RDME), splitting tensile strength and other damage indicators were selected to describe the impact of macro properties. The micro physical changes, porosity and pore size distribution parameters were obtained through scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) experiments. The influence mechanism of FA content on the frost resistance durability of concrete under FTC was discussed from the macro and micro perspectives. The results show that under the action of FTC, the addition of FA fills the pores, reduces the pore spacing, improves the strength of concrete, and makes the RDEM and splitting tensile strength of concrete increase first and then decrease. Among them, 20% FA concrete has the best frost resistance. The pore structure parameters show that the content of pores smaller than 100 nm has a great impact on the frost resistance durability of FA concrete, and increasing the content of these pores can improve the frost resistance durability of concrete.

Reconstruct SMAP brightness temperature scanning gaps over Qinghai-Tibet Plateau

• SMAP brightness temperature ( TB ) scanning gaps were compensated. • Daily variation of TB was analyzed in function of influencing factors. • Seamless TB benefits the refinements of SMAP soil moisture products. Soil Moisture Active Passive (SMAP) satellite was used to monitor global soil moisture and freeze–thaw state using surface brightness temperature (TB). However, due to the limitation of scanning width and shifting track, the daily TB observation had stripe gaps in varying degrees, which imped scientific applications of SMAP official product. To solve this issue, we proposed a temporal fitting algorithm to produce daily seamless TB data over Qinghai-Tibet Plateau (QTP) from 2015 to 2021. This method was composed of two steps: (1) overall time trend fitting which used a spline function to fit the overall mean time trend for each pixel from 2015 to 2021; (2) daily variation correction which accounted for several influential factors including surface temperature, precipitation, and vegetation to establish an Ordinary Least Squares (OLS) model for predicting daily variation of TB in numerous time slices. Consequently, the missing TB observation was reconstructed by combining the overall temporal trend and daily variation. A 10-fold cross-validation and product comparison were carried out to validate the robustness of the proposed method. For cross-validation, we randomly removed available SMAP observations in certain periods as unavailable, and then compared the reconstructed values with the removed practical ones. The cross-validation results indicated the reconstructed TB agreed well with actual SMAP TB, with a high overall coefficient of determination (R 2 = 0.94) and low RMSE (RMSE = 3.7 K), implying the desirable performance of our proposed method. By comparison with Soil Moisture and Ocean Salinity (SMOS) TB, the reconstructed data had an approximate performance with actual SMAP TB. Furthermore, the effects of surface temperature and precipitation on TB in different periods (frozen and unfrozen) over QTP were also analyzed. Our method has the potential to generate seamless SMAP products.

Experimental study on the fissure structure and permeability evolution characteristics of coal under liquid nitrogen freezing and freeze–thaw

Liquid nitrogen (LN2) fracturing technology as a kind of waterless fracturing technology has received extensive attention in recent years. In order to investigate the evolution law of fissure structure and seepage characteristics of coal samples under LN2 freezing and freeze–thaw, the evolution of fissure of coal samples before and after LN2 freeze–thaw was monitored by micro-computed tomography, the change of permeability of coal samples under different LN2 freezing time and freeze–thaw cycles was measured, and the damage mechanism of LN2 freezing and freeze–thaw to coal was discussed. The experimental results show that (1) LN2 freeze–thaw can cause the shrinkage of the coal matrix, resulting in damage to the fissure structure of the coal sample, which promotes the initiation, expansion, and extension of fissure of coal sample to form new fissure and, finally, forms a fracture network. (2) The permeability and the increment of permeability of coal samples increase with increase of LN2 freezing time and the number of freeze–thaw cycles under different gas pressure and confining pressure condition. (3) Under the same freezing time, the permeability growth rate of coal samples under LN2 freeze–thaw condition is significantly greater than that of coal samples under LN2 freezing condition. (4) The frost-heave force and thermal stress are the main factors leading to the damage, promoting fissure formation and increasing permeability of coal samples LN2 freezing and freeze–thaw. This study provides a theoretical basis for the understanding of fracturing technology with LN2.

Active and dormant microorganisms on glacier surfaces.

Glacier and ice sheet surfaces host diverse communities of microorganisms whose activity (or inactivity) influences biogeochemical cycles and ice melting. Supraglacial microbes endure various environmental extremes including resource scarcity, frequent temperature fluctuations above and below the freezing point of water, and high UV irradiance during summer followed by months of total darkness during winter. One strategy that enables microbial life to persist through environmental extremes is dormancy, which despite being prevalent among microbial communities in natural settings, has not been directly measured and quantified in glacier surface ecosystems. Here, we use a combination of metabarcoding and metatranscriptomic analyses, as well as cell-specific activity (BONCAT) incubations to assess the diversity and activity of microbial communities from glacial surfaces in Iceland and Greenland. We also present a new ecological model for glacier microorganisms and simulate physiological state-changes in the glacial microbial community under idealized (i) freezing, (ii) thawing, and (iii) freeze-thaw conditions. We show that a high proportion (>50%) of bacterial cells are translationally active in-situ on snow and ice surfaces, with Actinomycetota, Pseudomonadota, and Planctomycetota dominating the total and active community compositions, and that glacier microorganisms, even when frozen, could resume translational activity within 24 h after thawing. Our data suggest that glacial microorganisms respond rapidly to dynamic and changing conditions typical of their natural environment. We deduce that the biology and biogeochemistry of glacier surfaces are shaped by processes occurring over short (i.e., daily) timescales, and thus are susceptible to change following the expected alterations to the melt-regime of glaciers driven by climate change. A better understanding of the activity of microorganisms on glacier surfaces is critical in addressing the growing concern of climate change in Polar regions, as well as for their use as analogues to life in potentially habitable icy worlds.

Mechanical Strength Decay Evaluation of Excavation Unloaded Rock Mass under Freeze-Thaw Conditions

The quality of excavated and unloaded rock masses on steep and high slopes in cold regions is prone to deterioration, which in turn affects the long-term stability and safety of excavated slopes. Based on a triaxial unloading-damage test of sandstone, the unloading quantity was used to analyze the evolution law of unloading damage; a freeze-thaw cycle test of the unloaded-damaged samples was carried out, and it was found that the average change in porosity and the reloading peak strength damage rate after freeze-thaw increased with the increase in the number of freeze-thaw cycles, and the porosity change characteristics were independent of the value of the confining pressure at the time of the unloading damage. An exponential decay model was used, and based on the average change in porosity after freeze-thaw, a freeze-thaw strength decay model that can take into account the effect of confining pressure was established, and its ability to predict the strength decay of unloaded-damaged rock samples after freeze-thaw was verified by experimental data. The research results provide a reference for the evaluation of freeze-thaw degradation of unloaded rock masses during slope excavation in cold regions.

Physicochemical and Sensory Properties Colored Whey Protein-Cellulose Nanocrystal Edible Films after Freeze-Thaw Treatment

Balancing physicochemical properties and sensory properties is one of the key points in expanding edible packaging applications. The work consisted of two parts, one was to investigate the effects of cellulose nanocrystals (CNC) on the packaging-related properties of whey protein isolate films with natural colorants (curcumin, phycocyanin, and lycopene) under freeze-thaw (FT) conditions; the other was to test oral tactility and visual sensory properties of the edible films and their overall acceptability in packed ice cream. FT treatment reduced the mechanical strength and moisture content and increased the water vapor permeability of the films, as water-phase transformation not only disrupted hydrogen bonds but also the film network structure through physical stress. The oral tactility produced by CNC and the visual effect produced by colorants could affect participants' preference for edible films. This study provides a good reference for the consumer-driven product development of packaged low-temperature products.

Responses of Soil Freeze–Thaw Processes to Climate on the Tibetan Plateau from 1980 to 2016

Soil freeze–thaw processes are remarkable features of the land surface across the Tibetan Plateau (TP). Soil moisture and temperature fluctuate during the freeze–thaw cycle, affecting the soil water and energy exchange between the land and atmosphere. This study investigates variations in the soil temperature, humidity, and freeze–thaw state and their responses to air temperature and precipitation on the TP from 1981 to 2016. Regional simulations of the TP using Community Land Model version 4.5 demonstrate that the climate of the TP has become warmer and wetter over the past 37 years, with increases in both regional average temperature and precipitation. Using empirical orthogonal function analysis and the Mann–Kendall trend test of air temperature, we show that 1980–1998 was relatively cold, and 1999–2016 was relatively warm. Soil temperature and moisture in most areas of the TP were affected by air temperature and precipitation, and both showed an upward trend during the past 37 years. Overall, from 1981 to 2016, the freezing date of the TP has become delayed, the thawing date has been hastened, and the duration of the freeze–thaw state has shortened. The surface soil freezes and thaws first, and these processes pervade deeper soil with the passage of time; freeze–thaw processes have an obvious hysteresis. Precipitation and air temperature had marked effects on the freeze–thaw processes. Higher air temperatures delay the freezing date, hasten the thawing date, and shorten the freeze–thaw period. Areas with the highest precipitation saw late soil freeze, early thaw, and the shortest freeze–thaw duration. Areas with less vegetation froze earlier and thawed later. The freeze–thaw duration increased in the northwest of the plateau and decreased on the rest of the plateau. This article informs research on frozen soil change in the context of global warming.

Hydrological and sediment connectivity under freeze–thaw meltwater compound erosion conditions on a loessal slope

Freeze-thaw processes can influence hydrology, soil erosion, and morphological development by altering the connectivity between active pathways of water and sediment transport. Concentrated flow experiments were conducted involving frozen, shallow thawed, and unfrozen soil slopes under 1, 2, and 4 L/min runoff rates at a temperature of approximately 5 °C. In this study, hydrological connectivity was analysed via the simplified hydrological curve and relative surface connection function. Sediment connectivity was analysed via the sediment structure connectivity and sediment functional connectivity. Results indicated that hydrological connectivity was greatest on frozen slopes (FS), followed by shallow thawed slopes (STS), and unfrozen slopes (UFS) given a constant flow rate. Hydrological connectivity increased with increasing runoff rate for each freeze-thaw condition. Freezing condition and runoff rate exhibited a positive response to the hydrological connectivity. Sediment structure connectivity increased with increasing runoff rate for each slope condition. The ordering of sediment structure connectivity across freeze-thaw condition was that FS was greater than STS while STS was greater than UFS independent of flow rate. Sediment functional connectivity included longitudinal, lateral, and vertical connectivity components. Sediment longitudinal and vertical connectivity indicated a trend of first increasing and then decreasing under the different runoff rates and freeze–thaw conditions. For a given runoff rate, the ordering of sediment longitudinal and vertical connectivity across freeze-thaw condition was that FS was greater than STS while STS was greater than UFS. Sediment lateral connectivity exhibited a trend of first decreasing and then stabilizing. The ordering of sediment lateral connectivity across freeze-thaw condition was that UFS was greater than STS while STS was greater than FS. FS could more easily reach longitudinal and vertical penetration. Sediment longitudinal and vertical connectivity rates demonstrated increasing trends with increasing runoff rate after runoff generation stabilization and gradually approached unity. This research further improves our understanding of the hydrological and erosional mechanisms of meltwater and the generation of flooding in frozen soil conditions.

Superhydrophobic coatings based on bionic mineralization for improving the durability of marine concrete

Designing a stable superhydrophobic surface has been a current research focus. A functional bionic mineralized layer is introduced into the coating system to enhance the applicability. In the process of bionic mineralization induced by dopamine, silver ions were in situ reduced to nanosilver by dopamine in the interstices of mineralization products, forming a micro-nano composite structure by the mineralized grains and nanosilver microspheres. Then the superhydrophobic (CA = 153°) antibacterial coating was obtained by silane modification. The characterization of the coating shows that it can significantly improve the antibacterial effect, the mineralization layer and the silane molecular network can delay nanosilver loss. Furthermore, the superhydrophobic coating has extreme stability and its wettability hardly changes under abrasion, biological environment and freeze–thaw conditions, obtaining higher superhydrophobic, antibacterial and anti-icing performance. Considering the above properties, this novel superhydrophobic coating is anticipated to be a promising protective material which solves the corrosion, biofouling and freeze–thaw problems confronting marine concrete.

Does the repeated freezing and thawing of the aerobic layer affect the anaerobic release of N2O from SWIS?

Subsurface wastewater infiltration systems (SWIS) is an efficient, economical, and less temperature affected sewage treatment technology. Pollutants are removed by physical, chemical, and biological reactions such as filtration, adsorption, oxidation, and degradation. Under the conditions of limited carbon source and inactivation of nitrous oxide reductase, N2O, an important greenhouse gas, is released from the anaerobic layers of SWIS. However, is N2O release affected by repeated freeze-thawing of the upper aerobic layer? How does microbial population structure and denitrogenate activity in different profiles respond to the freeze-thaw cycle (FTC)? These questions have not yet been revealed. In this study, a SWIS simulator with in-situ regulation of FTC was first constructed. The re-distribution of N2O, microbial composition and denitrogenate activity were analyzed in response to FTC. Furthermore, potential bio-markers were screened and identified. The results revealed that the release of N2O was correlated with FTC, with the anaerobic layer being the main contributor throughout, accounting for 73.32–75.8 % of the total release. The limiting factor for N2O emissions was the NO3−-N concentration in the anaerobic zone, and there were no simple linear communications between total nitrogen and N2O generations. High throughput sequencing results showed the main markers of SWIS were Proteobacteria, Gemmatimonadetes, Firmicutes, Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi and Nitrospirae, accounting for 97.4 %–98.1 % of the total relative abundance. A significant positive correlation between Firmicutes and anaerobic release of N2O was observed, where Firmicutes abundance increased from 5 % to 21 % during the experimental cycle, while N2O concentration increased from 2.65 mg·L−1 to 18.88 mg·L−1. The results indicated that Firmicutes was an important biomarker of N2O release under freeze-thaw conditions.

Freezing point of sodium sulfate loess in check dams after freeze-thaw

When evaluating the range of salt weathering of loess check dams during freeze-thaw, the freezing point and its relationship to suction should be considered. Field surveys on the salinity of loess slopes of check dams in Shenmu county of northern Shaanxi were conducted in spring from 2019 to 2021. Marked salt concentration was observed in the slope surface, approaching the threshold of saline soil of 0.3% and sodium sulfate was the main component. Freezing point, suction and microstructure of sodium sulfate loess after freeze-thaw were studied. Results show that soil freezing point decays with freeze-thaw cycles, which is linked to pore structure and particle morphology, as revealed from quantitative indexes of soil microstructure. The matric suction of sodium sulfate loess declines with freeze-thaw, while the osmotic suction that depends mainly on solute concentration is less correlated. The Mizoguchi model was found to be valid for estimating the freezing point of salt-free loess, but it deviates significantly for sodium sulfate loess. To address the above limitation, a modified model that considers the correlation between soil freezing point and suction under freeze-thaw conditions was suggested and verified by test data.

Compressive and Tensile Fracture Failure Analysis of Asphalt Mixture Subjected to Freeze–Thaw Conditions by Acoustic Emission and CT Scanning Technologies

The cracking of bitumen pavement in seasonal frozen areas has direct and significant influences on its properties. In order to study the compressive and tensile fracture failure features of basalt fiber-reinforced asphalt mix after freeze–thaw (F-T) treatment, the load–displacement curves under the compression and tensile modes of asphalt mixture after F-T conditions were tested. As a real-time detection means, acoustic emission (AE) was used for testing asphalt mix under compression and tensile load modes. X-ray computed tomography (CT) was employed to represent and evaluate the interior void in F-T conditions. The results showed that, as F-T conditions continue, the compressive and tensile strength of the specimens at different temperatures decreases. The amplitude and count of AE signals with the time history of load level show different characteristics of change in various intervals. AE signal indirect parameters reveal that under compressive and tensile load modes there is a gradual deterioration of performance for asphalt mix due to the coupling interactions between tensile and shear cracks. The asphalt mixtures have different behavior in F-T conditions, which are attributable to interior meso-void characteristics based on CT analysis. This study is limited to the type and loading mode of asphalt mixture in order to quantitatively predict the performance of asphalt mixture.

Freeze-thaw behaviour of basalt fibre reinforced recycled aggregate concrete filled CFRP tube specimens

This paper is focused on the behaviour of basalt fibre reinforced recycled aggregate concrete (BFRC) short specimens confined by carbon fibre reinforced polymer (CFRP) tubes under freeze–thaw conditions. The main parameters investigated are the replacement rate of recycled coarse aggregate (RCA), the number of freeze–thaw cycle (FTC), the related temperature range, and the shape of short specimen section. The failure mode, dynamic elastic modulus, ultimate bearing capacity and the load–strain response of the specimens are studied. The results show that the failure mode and the load–strain response of CFRP tube confined recycled aggregate concrete (RAC) specimen have insignificant change due to FTCs. However, with the increase of the FTCs, the bearing capacity of the specimen decreases, and the specimen with square cross-section is much more sensitive than that of the circular cross-section counterpart. The smaller the range of freeze–thaw temperature changed, the smaller loss of the dynamic modulus and the smaller decrease range of the ultimate bearing capacity after FTCs.

Durability and life prediction analysis of recycled aggregate concrete with ceramic waste powder under freeze-thaw conditions based on impact-echo method and Grey-Markov model

Utilizing recycled aggregate concrete (RAC) for cyclic usage in building materials is one of the most feasible methods for reducing the demand for natural aggregates in the construction sector and disposing of construction and demolition trash in landfills. Previous research has demonstrated that the weak freeze-thaw (F-T) resistance of RAC poses a significant threat to the safety of RAC structures in severe cold regions. Therefore, this paper explores the influence of ceramic waste powder (CWP) at various replacement rates on the freeze-thaw resilience of RAC. In this experiment, six groups of CWP doping ratios of 0%, 10%, 20%, 30%, 40, and 50% were designed. Before the F-T cycling test, each group of specimens’ basic mechanical and physical performance data was measured throughout the regular curing age. At the conclusion of each F-T cycle, the durability performance of RAC was tested using the impact-echo method and compressive strength test. To predict the lifetime of RAC mixtures, a Grey-Markov model was created. It was found that the impact-echo method is more appropriate for assessing the durability of RAC in a freeze-thaw condition. The RAC’s F-T resistance is greatest when the CWP content is 20%. The Grey-Markov model has a high degree of predictive accuracy, effectively reflecting the relationship between RAC durability and F-T cycles, and has wide practical applications.

Grey entropy analysis of strength and void structure of carbon nanotubes concrete under the coupling of sulfate attack and freeze-thaw cycles

This paper aims to investigate the primary and secondary effects of different void structure parameters (air content, specific surface area, spacing factor, and average chord length of voids) on the macroscopic damage of multi-walled carbon nanotube-fly ash concrete (MWCNTs-FAC) under the coupling action of sulfate attack and freeze-thaw cycles. Through coupling tests of sulfate attack and freeze-thaw cycles, as well as X-ray computed tomography (CT) scanning tests, analyzed how MWCNTs-FAC differ in their compressive strength and damage quantity as a function of the number of coupling cycles. The effect of different void structure parameters of MWCNTs-FAC on the compressive strength and the damage quantity was also discussed using the grey correlation entropy analysis. The results show that the addition of MWCNTs can effectively improve the salt freeze-thaw resistance of concrete. When the MWCNTs content is 0.05 wt%, MWCNTs-FAC has the best improvement effect of salt freeze-thaw resistance. When the content of MWCNTs remains constant, the compressive strength of MWCNTs-FAC decreases, and the damage quantity increases as the air content, spacing factor, and average chord length of voids increase. The effect of specific surface area on the macroscopic damage of MWCNTs-FAC is exactly the reverse. Under salt freeze-thaw conditions, air content and specific surface area are two major factors influencing compressive strength, whereas average chord length and spacing factor are the main elements influencing damage quantity.

Fibre-Reinforced Soil Mixed Lime/Cement Additives: A Review

Soil modification is a technique for improving poor soil properties to make them suitable for engineering projects. Regarding the previous studies, various types of stabilisations were used to improve mechanical properties in soil. Several methodologies and experimental tests were used to study the positive and negative effects of utilising fibre on lime/cement-modified soil. This paper reviews the strength behaviour and microstructural properties of Fibre-Reinforced Lime Stabilised (FRLS) soil and Fibre-Reinforced Cement Stabilised (FRCS) Soil. First, the impact of FRLS/FRCS soil on strength behaviour under freeze-thaw conditions, the California Bearing Ratio (CBR) value, and compression/tensile strength are all examined. Then synthetic and natural fibres are compared at the microstructure level. FRCS/FRLS soil has been studied for its influence on geotechnical characteristics such as peak strength, residual strength, ductility, bearing capacity, stiffness, and settlement values. In addition, the micro-level evidence demonstrates that lime/cement affects the interlocking between soil particles and fibre. Although lime/cement improves soil strength by making it solid and compact, it makes stabilised soil brittle. Fibre as reinforcement in lime/cement stabilised soil transforms the brittleness of the soil into ductility. Hence building various infrastructures on poor soils is possible if fibre with lime/cement is used as an improvement method. Here, these three most used soil additive materials are investigated in terms of strength, microstructural, mineralisation, and some open issues are suggested for further research.

The Freeze-Thaw Strength Evolution of Fiber-Reinforced Cement Mortar Based on NMR and Fractal Theory: Considering Porosity and Pore Distribution.

Predicting the strength evolution of fiber-reinforced cement mortar under freeze-thaw cycles plays an important role in engineering stability evaluation. In this study, the microscopic pore distribution characteristics of fiber-reinforced cement mortar were obtained by using nuclear magnetic resonance (NMR) technology. The change trend of T2 spectrum curve and porosity cumulative distribution curve showed that the freeze-thaw resistance of cement mortar increased first and then decreased with the fiber content. The optimal fiber content was approximately 0.5%. By conducting mechanical experiments, it is found that the uniaxial compressive strength (UCS) of the samples exhibited the ‘upward convex’ evolution trends with freeze-thaw cycles due to cement hydration, and based on fractal theory, the negative correlation between UCS and Dmin was established. Eventually, a freeze-thaw strength prediction model considering both porosity and pore distribution was proposed, which could accurately predict the strength deterioration law of cement-based materials under freeze-thaw conditions.

Guar Gum ile İyileştirilen Kil Zeminlerin Donma Çözülme Etkisinde Mukavemet ve Şişme Basınçlarının Araştırılması

Son yıllarda çevresel kaygılardan dolayı biyopolimerler gibi organik ve çevre dostu malzemelerin kullanım alanları hızla artmaktadır. Bu çalışmada bir biopolimer olan Guar Gum kullanılarak kohezyonlu bir zeminin iyileştirilmesi araştırılmıştır. Bu amaçla kohezyonlu bir zemine belli oranlarda (%1, %2 ve %3) guar gum karıştırılarak numuneler hazırlanmıştır. Numuneler farklı sürelerde kür edilmiş ve farklı sayılarda (1, 3, 5, 10) donma çözülmeye tabi tutulmuştur. Çalışmada Guar Gum’un karışım oranı ile kür süresi ve donma çözülmenin serbest basınç mukavemeti ve şişme basıncı üzerindeki etkileri araştırılmıştır. Sonuç olarak, biyopolimer katkı malzemesinin kohezyonlu bir zeminin serbest basınç mukavemeti ve şişme basıncı üzerinde olumlu etkileri olduğu belirlenmiştir. Ayrıca bu etkilerin kür süresi ve donma çözülme ile önemli ölçüde değiştiği elde edilmiştir.

Mechanical Properties and Constitutive Model of the Cement-Improved Loess under Freeze-Thaw Conditions.

Cement-improved loess (CIL) is used as a common filler for subgrade construction projects in loess areas. The freeze-thaw (F-T) conditions have a significant effect on the stability of cement-improved loess subgrades in seasonally frozen regions. In this paper, the CIL samples, experiencing different numbers of F-T cycles at varying freezing temperatures, were used in consolidated undrained triaxial compression tests to investigate the effect of F-T conditions on the mechanical properties of CIL. The results show the stress-strain curves of CIL are of a strain-softening type with strong elastic brittleness. The initial tangent modulus of CIL increases with the growing confining pressure and gradually decreases with the increase in the F-T cycle number and the decreasing freezing temperature. It loses 46.4% of its original value after the twelfth F-T cycle with the confining pressure of 150 kPa and at the freezing temperature of −15 °C. The strength of CIL decreases with the increasing F-T cycle number, but it gradually tends to keep stable after the sixth F-T cycle. The strength also decreases with the reduction in the freezing temperature. It loses 37.7% of its original value after the twelfth F-T cycle with the confining pressure of 150 kPa and the freezing temperature of −15 °C. To express the nonlinearity correlation between the strength and confining pressure under F-T conditions, the Weibull function was applied and a nonlinear Mohr-Coulomb strength criterion was proposed. Through introducing a breakage rate function and a local strain coefficient, a binary-medium constitutive model consisting of bonded elements (soil-particle cohesion) and frictional elements (soil particles or soil aggregations) was established to describe the stress-strain relationships of CIL under F-T conditions. The test results indicated that the model can well describe the strain-softening phenomenon of the stress-strain curve of CIL and reflect the breakage mechanism of CIL.

Enhancement of Release and Solubility of Curcumin from Electrospun PEO-EC-PVP Tripolymer-Based Nanofibers: A Study on the Effect of Hydrogenated Castor Oil.

This study reveals the state-of-the-art fabrication of a tripolymer-based electrospun nanofiber (NF) system to enhance the release, solubility, and transdermal penetration of curcumin (Cur) with the aid of in situ release of infused castor oil (Co). In this regard, Cur-loaded Co-infused polyethylene oxide (PEO), ethyl cellulose (EC), and polyvinyl pyrrolidone (PVP) tripolymer-based NF systems were developed to produce a hybridized transdermal skin patch. Weight percentages of 1–4% Cur and 3–10% of Co were blended with PEO–EC–PEO and PEO–EC–PVP polymer systems. The prepared NFs were characterized by SEM, TEM, FT-IR analysis, PXRD, differential scanning calorimetry (DSC), and XPS. Dialysis membranes and vertical Franz diffusion cells were used to study the in vitro drug release and transdermal penetration, respectively. The results indicated that maintaining a Cur concentration of 1–3 wt % with 3 wt % Co in both PEO–EC–Co–Cur@PEO and PEO–EC–Co–Cur@PVP gave rise to nanofibers with lowered diameters (144.83 ± 48.05–209.26 ± 41.80 nm and 190.20 ± 59.42–404.59 ± 45.31 nm). Lowered crystallinity observed from the PXRD patterns and the disappearance of exothermic peaks corresponding to the melting point of Cur suggested the formation of an amorphous NF structure. Furthermore, the XPS data revealed that the Cur loading will possibly take place at the inner interface of PEO–EC–Co–PEO and PEO–EC–Co–PVP NFs rather than on the surface. The beneficiary role of Co on the release and dermal penetration of Cur was further confirmed from the respective release data which indicated that PEO–EC–Co–Cur@PEO would lead to a rapid release (4–5 h), while PEO–EC–Co–Cur@PVP would lead to a sustained release over a period of 24 h in the presence of Co. Transdermal penetration of the released Cur was further evidenced with the development of color in the receiver compartment of the diffusion cell. DPPH results further corroborated that a sustained antioxidant activity is observed in the released Cur where the free-radical scavenging activity is intact even after subjecting to an electrospinning process and under extreme freeze–thaw conditions.