Freeze-thaw Effect Research Articles

Deterioration laws of Hoek-Brown parameters in freeze–thaw multi-fractured rock mass

The Hoek-Brown criterion can better depict the nonlinear failure characteristics of rock mass, which has been widely used in the fields of large-scaled slopes, deep-buried tunnels, foundations in complex geological conditions, hydropower dams, and energy mining. In view of the previous studies mostly focused on the property reduction of freeze–thaw rock, the deterioration study of Hoek-Brown parameters for freeze–thaw multi-fractured rock mass was investigated in this study. Firstly, Monte-Carlo method was used to generate two-dimensional discrete fracture network, according to which the multi-fractured rock-like samples were prepared. Freeze-thaw cycle experiments were subsequently designed and executed to observe the apparent damage of freeze–thaw effect on the samples. Then, laboratory direct shear tests on freeze–thaw samples under multistage normal loading were carried out. The shear performances of freeze–thaw rock mass were analyzed based on the shear stress-shear displacement curves of samples with different freeze-thawed cycles. Besides, considering the deficiencies of the existing Hoek-Brown parameter estimation methods such as complicated sample preparation and strong subjectivity, a new estimation method based on shear test was proposed by deducing the shear expression of Hoek-Brown criterion, which was programmed in MATLAB and verified by direct shear test results. On this basis, the values of Hoek-Brown parameter of those samples under different freeze–thaw cycles were determined, and the variation law with freeze–thaw cycles was summarized. It turned out that the values of GSI and mi both decrease with the increase of freeze–thaw cycles, and the decreasing rate is also lowering, according with the negative exponential function model.

Effects of Biochar Application before and after Freeze-Thaw on Soil Hydrothermal and Cotton Growth under Drip Irrigation

Biochar as an organic soil conditioner has colossal application potential. Many recent studies revealed the influence of biochar on the soil during the crop growth period. However, few studies considered the effect of seasonal freeze-thaw on biochar’s improvement effect. Therefore, we conducted a field experiment to observe the impact of biochar on soil and cotton (Gossypium hirsutum L.). We used four biochar application rates (0.33%, 0.66%, 1.00%, and 1.33% of soil mass fraction) and applied biochar in the cotton field before and after seasonal freeze-thaw, respectively. The results showed that applying biochar after freeze-thaw was more effective on soil water storage and soil temperature preservation during the cotton growth period. Moreover, applying biochar with 0.66% soil mass fraction after freeze-thaw improved the cotton biomass by 5.31~36.13%, leaf area index by −10.82~32.52%, and seed cotton yield by 3.88~21.98%. Based on the principal component analysis of cotton fiber quality, we found that 0.66% biochar application after freeze-thaw improved cotton fiber most significantly. In total, applying biochar at 0.66% soil mass fraction after freeze-thaw was the most optimal application mode for improving soil hydrothermal conditions, cotton growth, and fiber quality. Our study can provide a scientific reference for applying biochar in northern Xinjiang, China.

Effect of fiber reinforcement on self-healing ability of asphalt mixture induced by microwave heating

Microwave heating is considered to be an effective method for accelerating the healing of the asphalt mixture with cracks that contain microwave-absorbing materials. Three fibers as microwave-absorbing materials (i.e., carbon fiber, steel fiber and steel wool) were used to fabricate self-healing asphalt mixtures, and their mechanical properties and self-healing ability were evaluated by semi-circular bending test. Effect of freeze–thaw cycles on the mechanical properties and healing effect of fiber modified asphalt mixtures were investigated, and the different fiber reinforcing effects were studied by the digital image correlation. Results show that although the addition of fibers can greatly improve the mechanical properties and healing ability of mixtures, freeze–thaw cycles have great adverse effects on these performances. Among the three fibers, steel fiber has the strongest reinforcement effect on the fracture behavior of asphalt mixture, and its reinforcement effect and healing ability are also less affected by moisture and freeze–thaw effect than that of steel wool and carbon fiber. Carbon fiber modified asphalt mixture has the lowest fracture and freeze–thaw resistance. Considering the harmful impacts of freeze–thaw cycles and the beneficial impacts of fiber reinforcing effect, steel fiber is recommended for fabricating self-healing asphalt mixture.

Evaluation of soil macro-aggregate characteristics in response to soil macropore characteristics investigated by X-ray computed tomography under freeze-thaw effects

As two complementary aspects of soil structure, the importance of macropore and macro-aggregate characteristics in maintaining soil functions and productivity is paramount. However, the changes in macropores and macro-aggregates and their interactions induced by the effects of freeze–thaw action have rarely been evaluated. This study aimed to evaluate the freeze-thaw effects on soil macropore and macro-aggregate characteristics and their relationships using X-ray computer tomography and dry sieving. Thirty-nine undisturbed soil columns were derived from a depth of 0–15 cm in the Mollisol area of Northeast China. Seven freeze-thaw treatments, including 0 (CK), 1 (FT.1), 3 (FT.3), 5 (FT.5), 7 (FT.7), 10 (FT.10), and 15 (FT.15) freeze-thaw cycles, and two initial soil mass water contents (30% and 40% the initial soil water content (ISWC)) were selected under controlled laboratory conditions. Our results showed that freeze-thaw effects significantly increased the total image porosity, mean pore diameter, porosity with branches, and connectivity density (p < 0.05). However, the total number of pores showed a “first increase – then decrease” trend with an increasing number of freeze-thaw cycles. During the freeze-thaw cycles, the macropore and macro-aggregate size distributions exhibited dynamic processes. Compared to the CK treatment, soils for 30% and 40% ISWC under the FT.15 treatment exhibited a lower > 7 mm macro-aggregates by 27.9% and 43.1%, but a higher < 3 mm macro-aggregates by 78.0% and 88.4%, respectively. The total image porosity, porosity with branches, and connectivity density were significantly positively and negatively correlated (p < 0.05) with the mean weight diameter and fractal dimension of macro-aggregates, respectively. The increase in macroporosity and pore branches easily induced the breakdown of the macro-aggregates. This study can help improve the understanding of the effects of changes in macropore characteristics and the processes of macro-aggregate breakdown and further enable the utilisation of soil structure as an indicator for assessing the sustainability and erodibility of soils.

Study on the geometry characteristics of soil primary mineral particles under cryogenic action

Repeated freeze–thaw causes the fragmentation and aggregation of soil particles, which affect particle shape (aspect ratio, roundness, etc.), and this process is a cryogenic weathering process. Changes in soil particle morphology record information about freeze–thaw processes and have the unique characteristics of freeze–thaw traces. To prove this conjecture, four soil specimens were selected in the experiment, and each specimen was studied after 0, 5, 10, 50 and 100 freeze–thaw cycles. The test results show that: Freeze–thaw will change the aspect ratio of particles, and the aspect ratio of particles is mainly distributed between 1 and 4. The particles with aspect ratio of 1.26 are stable and not easy to fragment, and the particles with aspect ratio more than 4 are easy to fragment. The freeze–thaw effect leads to changes in particle roundness, with different manners of change for the four specimens, but all undergo repeated freeze–thaw fragmenting and rounding process. Repeated freezing and thawing can not only lead to fragmentation particle edges and increased particle roundness, but also to fragmentation large-size particles and reduced particle roundness. Compared with the roundness before freeze–thaw and after 100 cycles of freeze–thaw, the coarse sand grains increased the most in roundness, indicating that the large grain size grains showed the most rounding. This study helps to understand the geometric characteristics of soil primary mineral particles under the action of cryogenic environments, and also helps to discern whether the particles have experienced the action of cryogenic environments, which is important for the study of cryogenic soil in cold environments.

Study on the acoustic emission and thermal infrared signal characteristics of granite with freeze-thaw damage in cycle loading process

Acoustic emission and thermal infrared signals are related to the process of rock breaking. In this paper, the acoustic emission and thermal infrared signals of rock are obtained during the loading process of indoor granite freeze-thaw cycle test and uni-axial compression test. Then the acoustic emission signals sent out during rock breaking are analyzed by short-time Fourier transform to get the peak frequency. infrared radiation thermographic sensor is applied to monitor and record the temperature change on the surface of rock so as to get the influence of thermal infrared radiation characteristics during rock materials deformation and breaking. Under the same axial stress, the samples passing through more freeze-thaw cycles have higher surface temperature. Both acoustic emission and thermal infrared temperature show that tensile failure is the main failure factor to granite samples. As freeze-thaw effect results in more micro fissures inside rock, the granite samples develop in the tendency of large breakage increases and small breakage decreases. This phenomenon shows that freeze-thaw cycle could restrict the heat release of granite sample.

Effect of Freeze-Thaw on Mechanical Properties of Loess with Different Moisture Content in Yili, Xinjiang

Various geological disasters such as collapses, landslides, and mudslides occur frequently in Yili, Xinjiang. The loess in this area provides a basis for the occurrence of landslides and other disasters. At the same time, Yili Valley is typically a seasonally frozen soil region. The freeze–thaw cycle is an essential disaster-inducing factor. However, scholars have lain a research emphasis on the material source of the Yili Loess, while lacking a systematic investigation of the degradation mechanism of the soil’s physical and mechanical properties under the freeze–thaw action. Therefore, it is prudent to investigate the changes in mechanical properties of loess in this region under the freeze–thaw cycle. In this study, focusing on a typical loess landslide in Yili, some in situ soil samples were collected to conduct related physical and mechanical tests. According to the maximum dry density and optimum moisture content of the loess in the region, four different groups of soil samples with varying moisture contents were prepared and subjected to different freeze–thaw cycles. The changes of apparent individual characteristics under freeze–thaw cycles were observed, and a consolidated undrained (CU) shear test was carried out to obtain the changes of shear strength indices of loess samples with varying moisture contents under freeze–thaw cycles. The results showed the obvious development of characteristics during freeze–thaw cycles, with the growth of many frost and ice crystals. At the freezing stage, the growth of ice crystals led to hexagonal peeling bodies on the surface layer. At the thawing stage, a rapidly melting network ice crystal pattern imposed a thermal thawing disturbance on the surface rock soil. After multiple freeze–thaw cycles, the soil’s peak strength dropped significantly and the internal friction angle changed slightly, but the cohesion was adversely affected, with frequent fluctuations. The present study enhances the research level of loess’s mechanical and strength properties under freeze–thaw cycles and provides a theoretical foundation for preventing loess landslides in this region.

Improving asphalt concrete resistance to rapid freeze–thaw effect using HIPS polymer

Two methods of high-impact polystyrene (HIPS) polymer addition to asphalt concrete (AC) mixtures were used to evaluate the effect of freeze–thaw (FT) cycles on the performance of unmodified AC and AC modified by using supplementary and additional HIPS polymer as asphalt aggregates. Various polymer contents were used to modify AC in both methods – namely, 0 (control), 5, 10, 15 and 20%. Marshall stability, flow, bulk density and indirect tensile strength (ITS) tests were performed on control and modified samples. A non-destructive test was performed by using the ultrasonic pulse velocity method. In the first method, replacing the mineral filler in AC with 10% HIPS polymer increased the density by 1%, the stability by 113%, the retained stability by 52% and the ITS by 56% compared with those of the control specimen. The results also show a 14% reduction in the damage caused by 8 weeks of FT cycles for modified AC compared with that of unmodified AC. However, modifying AC by using the second method did not provide promising results. The velocity within the specimen dropped by 20.9% at 10% HIPS addition before the FT effect compared with that of the control. The results of the first method revealed the feasibility of improving AC by using HIPS polymer to resist effective FT cycles.

Freeze-Thaw Effect on Riverbank Stability

The stability of riverbanks in cold regions is affected by the freeze-thaw action. The freeze-thaw process causes changes in the moisture content, friction angle, and cohesiveness of the bank material. Together with the freeze-thaw effect, seepage pressure influenced by the changing water levels, and the bank slope are the key factors affecting bank stability. A limit equilibrium bank stability model considering the infiltration water pressure effect is developed and applied to the Shisifenzi section of Inner Mongolia reach of the Yellow River. Laboratory tests of field samples with moisture contents of 15%, 18%, 21%, and saturated showed that the freeze-thaw action reduced the degree of saturation by 34.37 %, 30.71%, 32.48%, and 46.23%, respectively, accompanied by reductions in the internal friction angles by 1.78%, 2.74%, 6.33%, and 5.32%. These changes resulted in a 24.35% to 29.13% reduction in the safety factor of bank stability. Together with seasonal variations in the water levels the field data showed that the bank stability safety factor in the study site increases gradually through the melting period, dry period, wet period, flooding period, and low flow period. The slope stability safety factor increases with the stage of the river but decreases with the groundwater level.

Freeze-thaw effects on the performance of TRM-strengthened masonry

In recent years, textile-reinforced mortars (TRMs) have been introduced as a sustainable and effective mean of strengthening masonry and concrete structures. Although many recent studies have focused on understanding the mechanical performance of TRM composites and TRM-strengthened masonry panels, their long-term durability has remained unexplored. This article presents a multi-level experimental and analytical investigation on the effect of freeze-thaw conditions on the behavior of masonry components strengthened with TRMs. The adopted TRM strengthening system is composed of an AR-glass fabric reinforced embedded in a hydraulic lime-based mortar. The tests include characterization of the changes in material properties, TRM tensile behavior, the fabric-to-mortar and the TRM-to-substrate bond behavior, and finally, the in-plane and the out-of-plane response of TRM-strengthened masonry panels after exposure to freeze-thaw cycles. The results reveal that although deterioration of properties at the composite level is observed, the considered freeze-thaw cycles did not affect the in-plane and out-of-plane performance of the strengthened panels.

Effect of Biochar on Metal Distribution and Microbiome Dynamic of a Phytostabilized Metalloid-Contaminated Soil Following Freeze-Thaw Cycles.

In the present paper the effectiveness of biochar-aided phytostabilization of metal/metalloid-contaminated soil under freezing–thawing conditions and using the metal tolerating test plant Lolium perenne L. is comprehensively studied. The vegetative experiment consisted of plants cultivated for over 52 days with no exposure to freezing–thawing in a glass greenhouse, followed by 64 days under freezing–thawing in a temperature-controlled apparatus and was carried out in initial soil derived from a post-industrial urban area, characterized by the higher total content of Zn, Pb, Cu, Cr, As and Hg than the limit values included in the classification provided by the Regulation of the Polish Ministry of Environment. According to the substance priority list published by the Toxic Substances and Disease Registry Agency, As, Pb, and Hg are also indicated as being among the top three most hazardous substances. The initial soil was modified by biochar obtained from willow chips. The freeze–thaw effect on the total content of metals/metalloids (metal(-loid)s) in plant materials (roots and above-ground parts) and in phytostabilized soils (non- and biochar-amended) as well as on metal(-loid) concentration distribution/redistribution between four BCR (community bureau of reference) fractions extracted from phytostabilized soils was determined. Based on metal(-loid)s redistribution in phytostabilized soils, their stability was evaluated using the reduced partition index (Ir). Special attention was paid to investigating soil microbial composition. In both cases, before and after freezing–thawing, biochar increased plant biomass, soil pH value, and metal(-loid)s accumulation in roots, and decreased metal(-loid)s accumulation in stems and total content in the soil, respectively, as compared to the corresponding non-amended series (before and after freezing–thawing, respectively). In particular, in the phytostabilized biochar-amended series after freezing–thawing, the recorded total content of Zn, Cu, Pb, and As in roots substantially increased as well as the Hg, Cu, Cr, and Zn in the soil was significantly reduced as compared to the corresponding non-amended series after freezing–thawing. Moreover, exposure to freezing–thawing itself caused redistribution of examined metal(-loid)s from mobile and/or potentially mobile into the most stable fraction, but this transformation was favored by biochar presence, especially for Cu, Pb, Cr, and Hg. While freezing–thawing greatly affected soil microbiome composition, biochar reduced the freeze–thaw adverse effect on bacterial diversity and helped preserve bacterial groups important for efficient soil nutrient conversion. In biochar-amended soil exposed to freezing–thawing, psychrotolerant and trace element-resistant genera such as Rhodococcus sp. or Williamsia sp. were most abundant.

Deterioration mechanism of coal gangue concrete under the coupling action of bending load and freeze–thaw

Coal gangue, as a solid waste produced in the process of coal mining, has caused great harm to the environment and society. It is the most practical means to make concrete as coarse aggregate. In practical engineering, concrete materials are often subjected to the combined action of external load and environmental factors. Simply considering the freeze–thaw effect cannot reflect the deterioration characteristics of coal gangue concrete, so that the popularization and application of coal gangue cannot be realized. Based on this, through bending load and freeze–thaw coupling test (stress level 0, 0.2, 0.4, 0.6, 0.8), the mass loss rate, relative dynamic elastic modulus, damage layer thickness, and compressive strength of coal gangue concrete with a replacement rate of 40% were analyzed. The degradation characteristics of pore structure and interface transition zone of coal gangue concrete were studied by nuclear magnetic resonance test and microhardness test. The effects of different stress levels on pore size distribution, pore grade ratio, pore fluid characteristics, and interface zone characteristics were analyzed. The results show that the larger the bending stress ratio is, the faster the degradation of compressive strength and relative dynamic elastic modulus of coal gangue concrete is, the faster the thickness of damage layer increases, the larger the proportion of large pores in the specimen is, and the pore connectivity is enhanced. In addition, the interface area between coal gangue aggregate and mortar is the weak position of coal gangue concrete, and its thickness and microhardness are widened and decreased with the increase of stress level. The deterioration of the interface area makes the specimen close to failure.

Effects of low-temperature treatment on the coals mechanical properties microscale and airborne dust formation

The effect of freezing-thawing on the mechanical properties of coals at the microscale, the character of their destruction during cyclic nanoindentation, and the release of airborne dust have been studied. For these purposes, three hard coals from the Apsatsky deposit, two hard coals from the Pechora coal basin, and two lignites from the Kangalassky deposit were studied. It has been established that low-temperature impacts lead to a decrease in the content of airborne dust for all the coals. It was revealed that after freezingthawing of coals, their strength decreases, however, the character of destruction under mechanical impacts do not change. The exception is the coal of the middle stage of metamorphism of the Pechora basin, selected from a pack potentially prone to coal and gas outbursts. For this coal, low-temperature effects lead to a change in the character of its destruction during cyclic nanoindentation. Namely, there was a switch from the local (in the zone of contact with the indenter) character of destruction of the initial coal to the bulk one (outside the zone of contact with the indenter) for coal after low-temperature treatment. To assess the coals propensity to form fine dust particles, an index characterizing the degree of compaction of coal matter during cyclic nanoindentation with increasing load was introduced. It has been established that this index is proportionally connected with the content of airborne dust in coals (with sizes of less than 10 microns). It is shown that the coals proneness to form airborne dust under low-temperature impacts does not depend on the stage of coal metamorphism. For bituminous coals of the Apsatsky deposit with similar metamorphism degree the propensity to form dust is different. Variations in the propensity to form dust in coals of the Pechora basin, which also have a similar metamorphism degree, are apparently due to the peculiarities of the vitrinite structure of these coals.This work was carried out with the financial support of the Russian Science Foundation (Grant No. 18-77-10052).

Simulated Cropping Season Effects on N Mineralization from Accumulated No-Till Crop Residues

The adoption of no-till management practices has increased in the United States over the last decade. In the state of North Dakota, approximately 5.7 million hectares of cropland is managed under no-till or conservation tillage management practices. Even though conservation tillage is known for building soil health, increasing soil organic matter, capturing soil moisture, and reducing wind and water erosion, it also presents a unique best management practice since an increased mass of crop residue remains on the soil surface. Producers are concerned about whether plant needs are being met by nitrogen fertilizer that is currently being applied based on current North Dakota recommendations for long-term no-till systems. A Forman clay loam soil (fine-loamy, mixed, superactive, frigid Calcic Argiudolls) was used in this study, as it represented glacial till soils of the region. We examined whether N mineralization from surface-applied crop residue would result in similar or different results when compared to crop residue mixed into the soil. Soil freeze-thaw contribution to soil N mineralization was also evaluated. Six residue treatments with different C/N ratios including corn (Zea mays L.), soybean (Glycine max L.), forage radish (Raphanus sativus L.), winter pea (Pisum sativum L.), spring wheat (Triticum aestivum L.), and winter wheat (Triticum aestivum L.) were used. Five 10–14-week cycles with a three-week freeze period between each cycle at 0 ºC were evaluated for NO3-N production. Crop residues with a narrow C/N ratio contributed to greater instances of N mineralization during each incubation cycle, and the accumulation of crop residues with a wide C/N ratio over each incubation cycle following the first incubation did not offset the immobilization trends observed in the first incubation. A change in N mineralized in the untreated control soil during the last two incubation cycles may have been caused by freeze-thaw effects or a shift in microbial population due to a lack of fresh C inputs.

Effect of Freeze–Thaw Cycles on Mechanical and Microstructural Properties of Tailings Reinforced with Cement-Based Material

In China, more than 10,000 Tailings storage facilities (TSF) have been created on the ground surface through mineral mining processes, these TSF occupy a large amount of land. The strength of the tailings is too low to be able to stand on its own without strengthening. In order to save land resources and alleviate the damage to the environment caused by mineral mining, it is necessary to reinforce the TSF so that they can store more tailings. China is one of the countries with the largest area of permafrost and seasonal frozen regions, accounting for about 75% of the country’s total land area. The problem can be exacerbated in these regions where the freeze–thaw effect can further degrade the strength of tailings. A review of the literature suggests that there is little research on the mechanical and microstructural properties of tailings reinforced with cement-based materials under freeze–thaw conditions, especially when the tailings are to be discharged to land for sustainable development. This study investigates the effect of freeze–thaw cycles on the mechanical properties and microstructural changes of tailings reinforced with cement-based materials to mitigate environmental hazards. Unconfined compressive strength (UCS) tests, scanning electron microscopic images, X-Ray Diffraction tests, thermogravimetry tests and mercury intrusion porosimetry tests were conducted on samples of tailings. The results from this study show that freeze–thaw cycles reduce the UCS of all the tested samples eventually, but the frozen temperature does not significantly affect the UCS. The larger number of freeze–thaw cycles, the more damage is to the surface morphology and the matrix of the tailings. The results presented in the paper can help engineers and managers to effectively transport the TSF to other locations to minimize environmental hazards to achieve sustainable production of mineral mining processes.

Freeze—Thaw Behaviours of Half Grouted Sleeve Connections with High-Performance Grout

Grouted sleeve connections with high-performance grout have superior mechanical properties at room temperature, but there is inadequate evidence to prove that they have good resistance to freeze—thaw effects. This paper presents a freeze—thaw experimental study on the tensile behaviour and bond behaviour of grouted sleeve connections with antifoaming agents, early strength agents, and expanding agents. First, the damage appearance, mass loss, and compressive strength loss were studied to determine the freeze—thaw damage mechanisms of grout with different admixture contents, and three optimal composition ratios were chosen for further study. Then, grouted sleeve connections were subjected to tensile tests after different freeze—thaw cycles, and the damage modes and damage mechanisms were studied. The tensile strength of pure rebar was predicted to increase linearly with the number of cycles. For the rebar fracture specimens, the tensile strength of grouted sleeve connections was mainly derived from the tensile strength of the pure rebars and increased linearly with the number of cycles. The experimental results may provide a significant reference for grouted sleeve connections under freeze—thaw conditions.

Effects of cyclic freeze-thaw by liquid nitrogen on the coal breakage properties and fragment size distribution

Transforming intact coal seams into broken coals that are convenient to transport is one of the technical problems of fluidized coal mining. In this paper, cyclic freeze-thaw by liquid nitrogen (CFT-LN2) was adopted to improve the fragmentation degree of coal seams. The coal pore structure evolutions and coal breakage properties were explored using the acoustic emission (AE) parameter method (the kernel density estimation method), the fractal theory, and the nuclear magnetic resonance spectra. The main factors discussed include the number of freeze-thaw cycles, the LN2freezing time and the moisture content of the coal sample. Variations of these factors alter the mechanical and physical characteristics and pore structures of coal samples treated with CFT-LN2. The results reveal that the kernel density estimation method can distinguish the density region determined based on the rise angle (RA) and average frequency (AF) values and visualize the rupture modes of coal samples formed after CFT-LN2. As the number of freeze-thaw cycles grows, the tensile rupture mode gradually transits to shear rupture mode; the fractal dimension gradually increases; the equivalent average size gradually decreases; and the mass of different fragment sizes tend to be more uniform. Only freezing in LN2without CFT-LN2cannot notably change the rupture mode or fragmentation degree of a coal sample. During CFT-LN2, the coal matrix is subjected to repeated action of contraction in LN2and expansion at room temperature. As a result, new micro-pores are formed easily in the matrix, and micro-pores incline to connect into larger pores. Meanwhile, increasing the moisture content is conducive to coal fracturing through CFT-LN2.

The importance of freeze–thaw cycles for lateral tracer transport in ice-wedge polygons

Abstract. A significant portion of the Arctic coastal plain is classified as polygonal tundra and plays a vital role in soil carbon cycling. Recent research suggests that lateral transport of dissolved carbon could exceed vertical carbon releases to the atmosphere. However, the details of lateral subsurface flow in polygonal tundra have not been well studied. We incorporated a subsurface transport process into an existing state-of-the-art hydrothermal model. The model captures the physical effects of freeze–thaw cycles on lateral flow in polygonal tundra. The new modeling capability enables non-reactive tracer movement within subsurface. We utilized this new capability to investigate the impact of freeze–thaw cycles on lateral flow in the polygonal tundra. Our study indicates the important role of freeze–thaw cycles and the freeze-up effect in lateral tracer transport, suggesting that dissolved species could be transported from the middle of the polygon to the sides within a couple of thaw seasons. Introducing lateral carbon transport into the climate models could substantially reduce the uncertainty associated with the impact of thawing permafrost.

Mechanism Analysis of the Influence of Freeze-Thaw on the Damage and Debonding Evolution of Sandstone-Concrete Interface

During tunnel construction in cold regions, the good adhesion of surrounding rock-lining interface is one of the important preconditions to evaluate the durability of tunnel lining. However, the repeated fatigue damage between rock and concrete due to the freeze-thaw action leads to debonding at the interface, which significantly affects the protective effect of shotcrete. Accordingly, based on the combination of sandstone-concrete as the object, through the development of sandstone-concrete interface freeze-thaw cycling test, and combining the nuclear magnetic resonance (NMR) test and scanning electron microscopy (SEM) analysis, the mechanism of debonding by freeze-thaw damage at the sandstone-concrete interface was systematically revealed. The conclusions drawn are as follows: (1) With the increase of freeze-thaw times, the content of micropores and macropores at the interface gradually increases, while the content of mesoporous gradually decreases. At the same time, the decrease of freeze-thaw temperature also aggravates the growth of interface cracks, and the freeze-thaw damage of interface is closely related to the minimum freeze-thaw temperature. (2) The damage of the sandstone side becomes more serious under multiple freeze-thaw actions. Concrete as a water retaining plate inhibits the migration of water to its interior, and a pot cover effect exists at the interface to provide better storage space for water accumulation. (3) The C-S-H group is the main source of the bond force of sandstone-concrete interface, and the freeze-thaw effect aggravates the fracture of the C-S-H group, which leads to the interface debonding. This study could provide an experimental basis and theoretical support for systematically recognizing the evolution mechanism of freeze-thaw damage and debonding of shotcrete in tunnels in cold regions.

Experimental Study on Freeze-Thaw Effects on Creep Characteristics of Rubber Concrete

Crumb Rubber Concrete (CRC) can exhibit high freeze-thaw resistance, but its long-term creep behavior under various freeze-thaw conditions remains unclear, which is essential for the safety of pavement engineering in the severe cold zone. In this study, the freeze-thaw effects on the creep behavior of CRC under different stress levels were systematically analyzed by testing the compressive strength, the uniaxial creep under different stress levels, and the dynamic elastic modulus. To simulate real conditions of the road environment in the cold area, the lowest temperature of −20°C, six freeze-thaw cycles of 0, 30, 60, 90, 120, and 150, and seven different stress levels of 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 of the compressive strength were employed in this study. The test results showed that the mass loss rate was 6%–11.2% and the compressive strength decreased by 6.51%–47% after 30–150 freeze-thaw cycles. When the stress level reached its critical value, the relative dynamic elastic modulus decreased with the number of freeze-thaw cycles. After 150 freeze-thaw cycles, failure did not appear when the stress level was lower than 50%, above which the creep failure was determined by the stress level and the number of the freeze-thaw cycles. Meanwhile, it was found that the cracking and interfacial debonding between the matrix and the crumb rubber particle were the main reasons for the degradation of CRC creep performance. Finally, a Weibull distribution-based empirical creep damage model was established to predict the failure of CRC, which can enhance its application to related engineering.