Mechanisms of structural deterioration in red tilapia fillets during freeze-thaw cycles: Ice crystal dynamics-driven muscle microstructural damage

High internal phase Pickering emulsions stabilized by natural deep eutectic solvents: The freeze-thaw stability and cryopreservation capability

The physical and mechanical properties, microstructure degradation characteristics, and damage mechanism of natural gypsum rock under 15, 30, and 45 freeze–thaw cycles were studied by using a self-developed program-controlled freeze–thaw experimental device. The results show that compared with natural gypsum, with the increase in freeze–thaw cycles, the mass of the sample increases first and then decreases, Poisson's ratio increases, the density decreases, and the longitudinal wave velocity, the uniaxial compressive strength, and the elastic modulus decrease. Indexes decrease greatly in the early stage of freeze–thaw and slowdown in the later stage. With the increase in freeze–thaw cycles, the slope of the pre-peak stage of the stress–strain curve decreases, the compaction stage is significantly prolonged, and the brittleness of the post-peak failure process decreases. Failure cracks of the specimens after freeze–thaw cycles are mainly inclined shear failure and axial tensile cracks. The analysis shows that the freeze–thaw damage of gypsum rock is caused by the superposition and mutual promotion of water-rock softening and pore frost heave. The specific performance is the damage of crystal particles and the loose pore structure at the mesoscale. On this basis, the cracks gradually develop and expand, which is consistent with the macroscopic test results of the sample. The research results have reference significance for the construction scheme design and frost damage prevention of gypsum surrounding rock tunnels in cold regions.

Performance degradation mechanism of adobe materials under freeze-thaw cycles based on moisture transportation characteristics and microstructural analysis

This paper presents an investigation into the coupled effects of chemical corrosion (by Nitric acid solution) and freeze-thaw cycles on the physical and mechanical properties and damage deterioration of tonalite specimens. The experiments included the uniaxial compression test, three-point bending test, the Young’s modulus test, the X-ray diffraction test and the scanning electron microscope test. The damage condition of tonalite specimens was analyzed using scanning electron microscope (SEM). The experimental results reveal that chemical erosion has a significant influence on the propagation of micro cracks and accelerates the development of damage in the tonalite samples under monotonic loading. Due to cementation, no noticeable difference in uniaxial compressive strength was observed between the specimens subjected to combined effects of chemical corrosion and freeze-thaw cycles and those subjected to freeze-thaw cycles only. The amount of cementing materials in the chemically treated samples was found using SEM, which shows that chemical reactions promoted mechanical properties to some extent.

Significant progress has been made in the low-temperature toughness and crack resistance of polypropylene fiber-reinforced composites. However, there is still a gap in the research on damage evolution under freeze–thaw cycles and complex stress ratios. To solve the problem of durability degradation of traditional rubble masonry in cold regions, this paper focuses on the study of polypropylene fiber-mortar-masonry blocks with different fiber contents. Using acoustic emission and digital image technology, the paper conducts a series of tests on the scaled-down polypropylene fiber-mortar-masonry structure, including uniaxial compressive tests, three-point bending tests, freeze–thaw cycle tests, and tests with different stress ratios. Based on the Kupfer criterion, a biaxial failure criterion for polypropylene fiber mortar-masonry stone (PPF-MMS) was established under different freeze–thaw cycles. A freeze–thaw damage evolution model was also developed under different stress ratios. The failure mechanism of PPF-MMS structures was analyzed using normalized average deviation (NAD), RA-AF, and other parameters. The results show that when the dosage of PPF is 0.9–1.1 kg/m3, it is the optimal content. The vertical stress shows a trend of increasing first and then decreasing with the increase in the stress ratio, and when α = 0.5, the degree of strength increase reaches the maximum. However, the freeze–thaw cycle has an adverse effect on the internal structure of the specimens. Under the same number of freeze–thaw cycles, the strength of the specimens without fiber addition decreases more rapidly than that with fiber addition. The NAD evolution rate exhibits significant fluctuations during the middle loading period and near the damage failure, which can be considered precursors to specimen cracking and failure. RA-AF results showed that the specimens mainly exhibited tensile failure, but the occurrence of tensile failure gradually decreased as the stress ratio increased.

Rapid freeze–thaw (FT) cycles were adopted to explore the damage deterioration mechanism and mechanical properties of sandstone specimens under the coupling effects of different chemical solutions and FT cycles. The variation regularities of the FT cycles and physical and mechanical properties of sandstone specimens immersed in different chemical solutions were analyzed by using sandstone sampled from a Chinese riverbank slope. The damage variable based on porosity variation was used in the quantitative analysis of the damage to the sandstone under the coupling effects of chemical corrosion and FT cycles. Experimental results showed that the sandstone specimens weakened substantially under those effects. Their fracture toughness KIC, splitting tensile strength, and compressive strength showed a similar deteriorating trend with various numbers of FT cycles. However, a difference exists in the deterioration degree of their mechanical parameters, i.e., the deterioration degree of their fracture toughness KIC is the greatest followed by that of splitting tensile strength, and that of compressive strength is relatively small. Strong acid solutions may aggravate the deterioration of FT damage in sandstones, but at the early stage of the experiment, strong alkaline solutions inhibited sandstone damage deterioration. However, the inhibiting effect disappeared when the number of FT cycles exceeded 25. The different chemical solutions had a different effect on the FT damage degree of the sandstone specimens; for example, SO42− ions had a greater effect on FT damage than did HCO3− ions. Water–chemical solutions and FT cycles promote each other in deteriorating rocks and simultaneously affect the damage deterioration degree of sandstones.

Seasonally frozen soils are exposed to freeze‒thaw cycles every year, leading to mechanical property deterioration. To reasonably describe the deterioration of soil under different conditions, machine learning (ML) technology is used to establish a prediction model for soil static strength. Six key influencing factors (moisture content, compaction degree, confining pressure, freezing temperature, number of freeze‒thaw cycles and thawing duration) are included in the modelling database. The accuracy of three typical ML algorithms (support vector machine (SVM), random forest (RF) and artificial neural network (ANN)) is compared. The results show that the ANN outperforms the SVM and RF. Principal component analysis (PCA) is combined with the ANN, and the PCA–ANN algorithm is proposed, which further improves the prediction accuracy. The deterioration of soil static strength is systematically researched using the PCA–ANN algorithm. The results show that the soil static strength decreased considerably after the first several freeze‒thaw cycles before the strength plateau occurred, and the strength reduction increased significantly with increasing moisture content and compaction degree. The PCA–ANN model can generate a reasonable prediction for the static strength or other soil properties of seasonally frozen soil, which will provide a scientific reference for practical engineering.

Research on interactions among parameters affecting dynamic mechanical properties of sandstone after freeze-thaw cycles

Study on strength deterioration mechanism of foamed concrete under freeze-thaw cycles: Experiment and numerical simulation

In the Loess Plateau, seasonal freeze and thaw cause great damage to the mechanical behavior and microstructure of soil, which leads to frequent geological disasters during winter and spring. To investigate the influence of freeze‐thaw (FT) cycling (FTC) on the shear strength and microstructure of intact loess, triaxial shear, nuclear magnetic resonance, and scanning electron microscope tests were carried out on soil samples after target FT cycles. The results indicate that the FTC has limited changes to the soil stress‐strain curve, but has a significant attenuation effect on the peak deviatoric stress. The peak deviatoric stress was attenuated by FTC but changed insignificantly after ten cycles. The cohesive force decays exponentially with the number of FT cycles, while the internal friction angle increases slightly. Moreover, under FTC, the T2 hydrogen spectra of soil samples showed a multimodal distribution, with the main peak appearing to have two obvious upward shifts that occurred at 6 and 10 FT cycles. Indeed, a depolarization phenomenon related to the directional frequency of soil particles was observed, and the mass fractal dimension of the pore network increased slightly. In an FT environment, the shear strength declines due to accumulated internal microstructural damage. These findings contribute to a better understanding of the response of loess to FTC and provide novel ideas for the prevention of frost damage in loess areas.

In cold regions, concrete channels are subjected to the combined effects of freeze–thaw cycles (FTC) and abrasion, leading to severe deterioration of the channel structures. However, the performance of desert sand concrete (DSC) under common environmental conditions such as freeze–thaw and abrasion remains unclear. In this study, desert sand (DS) was used to partially replace river sand (RS) to prepare. The performance variations of river sand concrete (RSC) and DSC under FTC, abrasion, and freeze–thaw–abrasion coupling action were investigated. Microstructural analysis of the concrete was conducted using scanning electron microscopy (SEM) to explore the damage mechanisms of DSC under the freeze–thaw–abrasion coupling action. The results indicate that incorporation of DS enhances the FTC resistance and abrasion resistance of the concrete. Under the sole action of abrasion, the abrasion resistance of DSC was 59.7% higher than that of RSC. Under the same number of FTC, the compressive strength of DSC consistently remained higher than that of RSC. Under the freeze–thaw–abrasion coupling action, the abrasion resistance of RSC and DSC decreased by 64.5% and 63.39%, respectively. Microstructural analysis revealed that the coupled damage from freeze–thaw and abrasion is far from a simple superposition of individual effects, exhibiting a significant synergistic interaction: FTC causes structural loosening of the concrete, exacerbating abrasion damage, while surface damage from abrasion accelerates water ingress, thereby intensifying freeze–thaw damage. This study provides theoretical insights for the practical application of DSC in engineering projects in desert and cold regions.

Frost Resistance of Thermoinsulating Recycled-Aggregate Concretes Containing Glazed Hollow Beads

A multistage coupling test was designed to investigate the deterioration behavior of basalt fiber concrete under the coupled interaction of load and freeze–thaw cycles. The damage laws of the strength and durability of basalt fiber concrete under coupling action were investigated, along with the evolution of the pore structure and microscopic morphology. The alleviating effects of basalt fibers on the properties and structural deterioration were evaluated. The compressive and bending strengths exhibited a three-phase variation pattern, and the reduction rate of the strength of the basalt fiber concrete was lower than that of ordinary concrete. The electric flux increased parabolically under the double-field coupling, and the trend and inflection point of the relative dynamic elastic modulus changed with the coupling stages. The pores of basalt fiber concrete mainly expand and coarsen, and basalt fibers suppress the increase in pore size and reduce the number of multiple detrimental pores. The toughening of basalt fibers can inhibit crack propagation in the width direction and improve the compactness of the microstructure.

With the increase of expressway construction in seasonal frozen soil region, the freeze-thaw problem of subgrade soil has attracted more and more attention. In addition, the comprehensive utilization of industrial solid waste has become an important measure to build a resource-saving and environment-friendly society. In order to improve the frost resistance of subgrade soil and realize the resource utilization of industrial solid waste, carbide slag (CS) and coal gangue powder (CG) were applied to the subgrade soil. The unconfined compressive strength (UCS) test, freeze-thaw cycle test, dry shrinkage test, temperature shrinkage test and scanning electron microscope (SEM) test were carried out on CS-CG stabilized soil with a ratio of CS:CG = 70:30 and dosages of 5%, 10% and 15%. The freeze-thaw cycle degradation model of CS-CG stabilized soil was constructed to show the freeze-thaw deterioration mechanism after the mechanical properties, pore structure, and durability characteristics of the stabilized soil were examined. The results showed that the CS-CG stabilized soil had good frost resistance. After 6 freeze-thaw cycles, the UCS at 7d and 28 d was 2.86 MPa and 3.79 MPa, respectively, which were 22.6% and 35.5% lower than in samples that underwent no freeze-thaw action. The CS-CG stabilized soil had good crack resistance, slightly better dry shrinkage strain than lime stabilized soil, and excellent temperature shrinkage performance. With the increase of CS-CG dosage, the hydration products increased continuously. After freeze-thaw cycles, however, large pores and cracks gradually appeared in the stabilized soil, which led to an increase of porosity and pore diameter, and a decrease of pore abundance. Due to the influence of hydration degree, the porosity change at 7 d was less than that at 28 d. There was a f(n)/f0=βexp−λΔh relationship between UCS residual ratio and porosity variation of the CS-CG stabilized soil, and it had a good correlation. The CS-CG stabilized soil had good frost resistance and shrinkage characteristics, and could replace traditional cementitious materials such as Portland cement (PC) and lime for subgrade soil improvement in regions with seasonal frozen soil. Future research needs to focus on the performance regulation of CS-CG stabilized soil, which can make it more widely used.

An essential criterion of Eucalyptus tree breeding programmes employed by the commercial forestry sector is the maintenance of potentially important species and genotypes for periods commensurate with field testing. Current methods for this purpose include conservation stands, clonal hedges and maintenance of cuttings in greenhouses and hydroponic systems. However, these methods, especially the maintenance of conservation stands and clonal hedges, require large tracts of land, which are now unavailable. The latter methods also have other disadvantages in that they are labour intensive and may be expensive to maintain. The conservation method of cryopreservation (the maintenance of plant cells, tissues and organs at subzero temperatures) may offer a cost-effective alternative with significant benefits, including the maintenance of plant material for theoretically unlimited periods. This field of science has experienced significant breakthroughs in the last two decades, especially in terms of the understanding of the physical, chemical and biological processes that occur during the freeze–thaw cycles. Consequently, several effective mechanisms of reducing the risk of ice crystal damage have been developed, resulting in the successful cryopreservation of numerous wild and domesticated plant species. Apart from germplasm conservation, cryopreservation may also be employed as a means of maintaining genetically engineered transformants while field testing is conducted. This is particularly advantageous considering the large numbers of transformants that can be generated during genetic engineering trials. Cryopreservation should, therefore, be considered a potentially important tool in commercial breeding strategies. This paper details the benefits and advantages of the technology, and also identifies and explains some of the key challenges that still exist, especially those associated with the cryopreservation of highly hydrated and/or desiccation-sensitive material such as Eucalyptus axillary buds.