Condition Of Freeze-thaw Cycles Research Articles

Experimental Study of Recycled Concrete under Freeze-Thaw Conditions.

Recycled concrete is a new and environmentally friendly material for future construction. When applying recycled concrete to cold and severe regions, it is necessary to consider the freeze-thaw resistance of recycled concrete. Using an indoor freeze-thaw cycle test system, the rapid freezing method was used to conduct rapid freeze-thaw tests on recycled concrete specimens under set freeze-thaw cycle conditions. Relevant parameters (such as compressive strength, quality loss rate, rebound value) were tested on recycled concrete specimens that completed the set number of freeze-thaw cycles. The influence of various factors (freeze-thaw cycle number, replacement rate of recycled aggregates) on the compressive strength, quality loss rate, and rebound value of recycled concrete was analyzed. The results indicate that with the increase of freeze-thaw cycles and recycled aggregate content, the workability, rebound value, and compressive strength of the specimens decrease, and the quality loss rate increases. The changes in workability of concrete are sharp, with a slump difference of 21 mm between concrete with 100% recycled coarse aggregate and concrete using natural coarse aggregate. The rebound value of the specimen shows a decreasing trend overall, but the rebound value varies for different measuring points on the same specimen. The attenuation of compressive strength is significant. When fully using recycled aggregates to prepare concrete, the compressive strength after 30 freeze-thaw cycles decreases by 49.42% compared to the compressive strength after 0 freeze-thaw cycles. The overall quality loss rate shows a decreasing trend, but the quality loss is not severe.

Study on the hydro-thermal-salt-mechanical coupling characteristics of sulfate saline soil under freeze-thaw cycles

The theoretical and experimental studies have been carried out on the water and salt migration and deformation characteristics of sulfate saline soil during freeze-thaw cycles. Based on the theory of unsaturated soil mechanics and the thermoelastic continuum and considering the influence of phase change within the pore on thermodynamic and hydrodynamic parameters, the multi-physical fields coupled model of hydro-thermal-salt-mechanical in unsaturated sulfate saline soil has been established. The variation processes of the temperature field, water field, salt field, and stress field of the soil during freeze-thaw cycles were analyzed, and the validity of the theoretical model was verified by indoor experiments. The results show that there are significant attenuation and hysteresis effects when heat is transferred in the soil during freeze-thaw cycles. The water content of migration in the soil increases with the height of the soil column, while the increment of migration water content decreases with the number of freeze-thaw cycles. The formation and dissolution of salt crystals from top to bottom and the sudden increase in the salt crystallization rate are mainly caused by variations in the solubility of the salt solutions due to temperature changes. The formation and dissolution of ice and salt crystals in the soil induce expansion and contraction, and the freeze-thaw cycle conditions have a significant effect on the expansion and residual deformation of the soil.

Experimental study on the engineering properties and failure mechanism of moraine in Southeast Tibet under freeze–thaw cycles conditions

The effect of freeze–thaw cycles (FTCs) is a prevalent hydrothermal phenomenon in seasonal permafrost regions, significantly affecting the micro and engineering properties of moraine. This study investigates the engineering properties and failure mechanisms of moraine induced by FTCs, using samples with varying dry densities subjected to 0–20 FTCs. The permeability characteristics, particle breakage characteristics, elastic modulus, stress–strain curve, excess pore water pressure, peak friction angle, and critical state line characteristics of the moraine were analyzed before and after the FTCs, and the microscopic failure mechanism of moraine induced by FTCs was revealed. The test results show a degradation in the engineering properties of moraine induced by FTCs, exhibiting the greater the dry density the more obvious the damage to the engineering properties of the moraine. In addition, the particle fragmentation and fine particle aggregation caused by the FTCs changed the distribution, shape, arrangement, and particle intercontact patterns, which revealed the failure mechanism of moraine induced by FTCs. The correlation analysis between the shear strength index and microstructural parameters demonstrated that the particle arrangement has the greatest effect on the peak friction angle and particle shape has the greatest effect on the critical state line of moraine under the FTCs conditions. The findings offer experimental evidence and theoretical support for preventing and resolving geological risks and engineering project problems resulting from the deterioration of moraine shear strength during FTCs in the alpine mountain region.

Research on the Variation law of Compressive Strength of Concrete under the Coupling Effect of Freeze-Thaw and Salt Corrosion

Due to its unique freeze-thaw and sulfate corrosion environment, the northwest region is an important factor causing the deterioration of concrete structures. Compressive strength is a key indicator of the macroscopic performance of concrete. Analyzing the changes in compressive strength of different water cement ratios under complex freeze-thaw environmental conditions is of great guiding significance for improving the service performance of concrete. Therefore, in order to obtain the variation law of compressive strength of concrete under freeze-thaw cycle conditions, this paper designs three water cement ratio concrete freeze-thaw cycle and sulfate solution freeze-corrosion coupling tests to analyze the compressive strength changes at different stages. The results show that in a water freezing and thawing environment, the compressive strength of concrete decreases continuously with the increase of experimental age, and the larger the water cement ratio, the greater the decrease in compressive strength. In sulfate solution freeze-thaw, in the early stage of the experiment, the decrease in compressive strength compared to water freeze-thaw decreased, and in the later stage of the experiment, the decrease increased. The larger the water cement ratio, the greater the impact of the above.

Computational Evaluation of the Fracture Behavior of Porous Asphalt Concrete Exposed to Moisture and Salt Erosion.

Salt erosion has an adverse impact on the durability of asphalt pavements. Porous asphalt concrete is particularly susceptible to the influence of salt. In this study, a finite element model was developed to investigate the fracture behavior of PAC exposed to salt erosion. The 2D heterogeneous structure of PAC was generated with an image-aided approach to computationally study the fracture behavior of PAC. Laboratory SCB tests were conducted to validate the finite element model. The simulation results of the SCB tests indicate that the peak load of the PAC decreased by 21.8% in dry-wet cycles and 26.1% in freeze-thaw cycles compared to the control group. The salt solution accelerated the degradation of the durability of PAC under both dry-wet cycles and freeze-thaw cycle conditions, which is consistent with laboratory tests. After flushing treatment before the drying phase, the peak load of the PAC in salt environments increased by 5.3% compared to that of the samples with no flushing. Salt erosion also results in a higher average value of scalar stiffness degradation (SDEG), and the damaged elements were primarily the cohesive elements in the fracture of the PAC. Additionally, the influence of crucial factors including the void content, adhesion and cohesion, and loading rate on the fracture behavior of the PAC was analyzed. As the void content increases, the average SDEG value of the cohesive elements increases and surpasses the average SDEG value of the adhesive elements at a void content of approximately 9%. The performance of the fine aggregate matrix (FAM) has a much greater impact than the FAM-aggregate interface on the durability of the PAC. And there were more damaged CZM elements with the increase in the loading rate. Salt erosion results in higher SDEG values and a larger number of cohesive damaged elements at each loading rate.

Analysis of asphalt microscopic and force curves under water-temperature coupling with AFM

Asphalt, as a crucial material in road construction, is affected by external environmental factors, among which water and temperature are the primary causes of water damage to asphalt pavements. Different hydro-thermal environments can cause varying types of damage to asphalt or the asphalt-aggregate interface. To analyze the micro-performance changes of different types of asphalt under various hydro-thermal environments, this study conducts tests onPG64–22 matrix asphalt, PG76–22 SBS-modified asphalt and PG82–34 high viscosity asphalt under different hydro-thermal coupling and freeze-thaw cycle conditions using Atomic Force Microscopy (AFM). The analysis is based on the obtained micro-morphology images and mechanical properties, exploring the impact mechanisms of different hydro-thermal environments on various asphalts. Results show that under different hydro-thermal conditions, the three asphalts exhibit different morphological changes: the asphalt surface's “bee-shaped structure” is gradually destroyed after hydro-thermal coupling, while a “disappearance-reappearance” phenomenon is observed under freeze-thaw cycles. Moreover, the roughness of the two modified asphalts shows a different trend from that of the matrix asphalt, indicating that the modifier alters the micro-structure of asphalt to some extent. Under hydro-thermal coupling, the adhesion force of the three asphalts decreases linearly, with matrix asphalt decreasing by 89.2% after 3 hours, SBS modified asphalt by 63.1%, and high-viscosity asphalt by 23.9%, showing that high-viscosity asphalt has better waterproof and heat-resistant performance. During freeze-thaw cycles, the adhesion force between the asphalt and the tip shows varying degrees of recovery. Additionally, there are differences in adhesion force across different areas of the asphalt surface, which tend to diminish with hydro-thermal coupling or freeze-thaw cycles. These results indicate that hydro-thermal coupling and freeze-thaw cycles have different mechanisms of damage to the internal structure of asphalt, providing important data for understanding the damage mechanisms in depth.

Damage and failure characteristics of single fractured cyan sandstone subjected to freeze–thaw cycles under uniaxial compression

In order to explore the freeze–thaw (FT) damage characteristics of fractured rock masses, FT cycle tests and uniaxial compression tests were conducted on intact and pre-cracked cyan sandstone samples, respectively. The degradation laws of physical and mechanical properties of samples under FT cycle conditions were analyzed, and the FT damage mechanism and failure mechanism were explored accordingly. The results indicate that as the number of FT cycles (N) increases, the saturation weight change rate and porosity of the sample continue to increase, while the P-wave velocity continues to decrease. The closure stress, initiation stress, damage stress, and peak stress decrease linearly with increasing FT cycles, and increase linearly with increasing crack inclination angle (β). Moreover, as FT cycles increase, the geological strength index GSI decreases linearly, while the damage factor (D) increases linearly. A Hoek Brown strength degradation model for fractured rocks subjected to FT damage under uniaxial compression was obtained, and its high reliability was verified using test results. The FT damage of cyan sandstone is mainly dominated by the frost heave force inside the rock, and the degree of FT damage of fractured samples is much higher than that of intact ones. The concentration of frost heave force at the crack tip leading to cracking is the key to exacerbating the FT damage in fractured rock masses. However, the crack initiation mechanism is still controlled by β. Whenβ = 90°, it exhibits tensile initiation mode, and whenβ = 45°, it mainly exhibits shear initiation mode. Moreover, the fracture of the single crack sample conforms to the compression-shear fracture criterion. Taking the sample with pre-crack inclination angle of 45° as an example, the variation of KI and KII, and the relationship between them are discussed accordingly. The results of this paper are beneficial to clarify the influence of FT cycles on the mechanical properties of cyan sandstone, and can provide reference for the study of related issues.

Frost-Heaving Behavior and Enhancement Approaches of Cement-Based Grout Materials under Freeze–Thaw Conditions

In the seasonally frozen regions, during the grouting of prestressed bridge ducts in low-temperature environments, incompletely cured grout materials undergo volumetric changes due to freeze–thaw cycling, resulting in structural cracks along the prestressing ducts of the bridge, thereby diminishing the bridge’s operational lifespan. In order to investigate the freeze–thaw characteristics of grouting materials under the influence of freeze–thaw cycles and propose improvement measures, the influence of various additives on the freeze–thaw stress characteristics of mortar under freeze–thaw cycle conditions was elucidated through freeze–thaw stress tests. The mechanisms for improving the freeze–thaw characteristics of grouting materials were explored through analyses of free water content, setting time, compressive strength, XRD, and SEM. In light of the requirements for comprehensive performance of grouting materials, composite additives are employed to enhance the freeze–thaw performance of the grout. The results indicate that reducing the water-cement ratio, incorporating calcium formate, sulfoaluminate cement, air-entraining agents, and carbamide all have a positive impact on mitigating frost-heaving stress in grout materials. However, the improvement mechanisms differ, and employing a single measure alone is insufficient to effectively reduce frost-heaving stress while meeting performance criteria such as compressive strength, setting time, and flowability. Free water content emerges as a crucial indicator determining the magnitude of frost-heaving stress in grout materials, with 11.5% of free water content representing the critical threshold for frost heaving in grout materials. Utilizing composite admixtures can simultaneously decrease free water content, lower the freezing point of free water, and alleviate frost-heaving deformation, resulting in a more efficient reduction of frost-heaving stress. When the admixture content reaches 9.9%, frost-heaving stress is eliminated, and the comprehensive performance parameters, including compressive strength, setting time, and flowability, meet the specified requirements. Overall, the conclusions of this research will offer a scientific foundation for the choice of cold-resistant grouting materials, the mitigation of grout material freeze–thaw risk, and the improvement of quality assurance levels in bridge construction within seasonally frozen areas.

Research on the Influencing Factors and Measurements of Freeze-thawing Resistance of Recycled Concrete

With the introduction of green building, solid waste utilization has become a key research focus in civil engineering. Recycled concrete technology plays a crucial role in the sustainable development of the concrete industry. However, its durability in cold regions remains a pressing challenge for engineers. This paper reviews domestic and international studies to summarize the performance and degradation mechanisms of recycled concrete under freeze-thaw cycles, focusing on four factors: recycled aggregate proportion, freeze-thaw cycle conditions, water-to-cement ratio, and admixtures. Evaluation systems for frost resistance of recycled concrete are also summarized. Finally, improvement measures for enhancing the frost resistance of recycled concrete are proposed, providing a theoretical basis for further research and engineering applications in this field.

Effects of nitrogen addition on greenhouse gas fluxes during continuous freeze-thaw cycles in a cold temperate forest.

Both nitrogen (N) deposition and soil freeze-thaw cycles (FTCs) induce pulses of greenhouse gas (GHG) emissions in cold temperate zones due to changes in soil carbon (C) and nitrogen (N) turnover. However, the combined effects of N addition and FTCs on GHG fluxes have received little research attention, particularly in boreal forests. We conducted a laboratory incubation experiment using intact soil cores from Rhododendron dauricum-Larix dahurica plots to investigate the GHG flux response to these combined effects. We separated the soil samples into seven groups (no, low, medium, and high sodium nitrate addition and low, medium, and high ammonium chloride addition) and exposed each group to continuous FTC conditions. The N2O and CO2 emissions were eventually stimulated by the FTCs, while CH4 uptake was inhibited by FTCs but responded differently under different N addition treatments. All the treatments had substantially increased N2O emissions compared to the control. However, the soil respiration rate significantly increased only with medium sodium nitrate addition, and high levels of N addition (regardless of form) inhibited CH4 uptake. These findings demonstrate that FTCs and N addition (in various forms and levels) have considerable effects on GHG emissions in temperate forest ecosystems. Moreover, dissolved organic carbon (DOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and inorganic nitrogen in soil are potential factors that drive GHG emissions and are necessary considerations in predicting future feedback effects of GHG emissions on climate change.

Experimental study on dynamic resilient modulus of subgrade with circulating fluidized bed combustion ash as filler

Using circulating fluidized bed combustion ash (CFBCA) as roadbed filler can solve the problem of secondary utilization, and dynamic resilient modulus (DRM) can match the dynamic performance of roadbed filler under driving load. In order to explore the dynamic performance of the subgrade with CFBCA as filler under driving load, based on the dynamic triaxial test and mercury intrusion porosimetry test, the DRM of the sample under different curing ages, compaction, moisture content, stress, dry-wet and freeze–thaw cycle conditions were studied, and the pore distribution characteristics of the sample were analyzed. The results show that the DRM of CFBCA samples increases significantly in the 0 ∼ 7d age curing period, and increases slowly in 7 ∼ 28d; with the increase of f-CaO and SO3 content, the DRM of CFBCA samples increased; after the dry-wet cycle and freeze–thaw cycle, the DRM of the CFBCA sample decreased, and the decrease was more obvious under the dry-wet cycle. With the increase of f-CaO and SO3 content, the total porosity and macropore of CFBCA samples decreased; with the decrease of moisture content, the total porosity and macropore of CFBCA samples increased, the DRM becomes smaller. Under different moisture content and compaction, the DRM fitting of the CFBCA sample shows that the prediction results of the three-parameter theoretical model with volume stress and octahedral shear stress as variables are compared with the test results with a high correlation (R2 > 0.96), it can effectively predict the DRM of the subgrade with CFBCA used as filler.

Effects of freeze-thaw intensities on N2O release from subsurface wastewater infiltration system

Subsurface wastewater infiltration system (SWIS) is a low-investment and cost-effective wastewater treatment technology. Nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, is a major by-product of biological denitrification processes within SWIS. Although SWIS has been widely applied in varying zones, until now, whether and how periodical freeze-thaw cycles (FTCs) occurring in aerobic layers affect N2O release still remain unclear? In this study, two runs were arranged, which covered two freeze-thaw (FT) intensities of − 5 °C/5 °C and − 15 °C/5 °C, respectively. An in-situ simulation system of SWIS was carried out to monitor N2O release and microbial community structure in different profiles. The result revealed that raising FT intensity decreased the rate of nitrogen removal of SWIS. Average removal rate of TN under strong FTCs was 88.65–88.97%, which was 1.32–2.47% lower than that under weak FTCs conditions. In addition, a positive correlation was found between FT numbers and N2O release. The contribution of anaerobic zone increased from 29.24% to 75.16% with extending the FT cycles from 1 to 9. High-throughput sequencing results showed that different FT intensities had distinct effects on microbial communities. Euryarchaeota abundance increased significantly under strong FT treatment, while Proteobacteria abundance sharply decreased from 49.5% to 7.6% at day 27 of stable operation. PCA analysis shows that bacterial community composition of samples treated with weak FT and CK is similar. While significant differences in sample composition were found between strong and weak FT treatments, which was the main reason resulting in different N2O release patterns.

Effect of Hydrophilic Polyurethane on Interfacial Shear Strength of Pisha Sandstone Consolidation under Freeze-Thaw Cycles.

The W-OH type polyurethane (W-OH) has been proven to be an economical and environmentally friendly slope protection solution for slope maintenance in Pisha sandstone areas. However, the Pisha area belongs to a typical temperate continental climate with large diurnal temperature changes in winter, spring, and autumn and freezing and thawing occurring alternately between days and nights. Under freeze-thaw cycle conditions, the effect of slope treatment largely depends on the interface shear strength between W-OH-treated Pisha sandstone and pristine sandstone. Therefore, this paper studies the interfacial shear strength and long-term durability of Bisha sandstone consolidation (W-OH-treated Pisha sandstone) and Pisha sandstone under freeze-thaw cycles. First, the effects of different W-OH concentrations and different water contents on the freeze-thaw cycle interface were studied using a direct shear test. Based on the experimental results, the W-OH material was further modified with ethylene vinyl acetate (EVA). Finally, the damaged surface of the sample was observed through an ultra-depth-of-field microscope, and the damage mechanism of the interface caused by the freeze-thaw cycles was further discussed. The experimental results show that the peak shear strength at the interface increases with the increase in W-OH concentration and decreases with the increase in freeze-thaw cycles. The cohesion at the interface generally increases with the increase in W-OH concentration and reaches a maximum value of 43.6 kPa when the W-OH concentration is 10%. At the same time, under the condition of high water content, the curing of the W-OH material has no significant effect on the bonding performance of the interface. Using EVA to modify the W-OH material can improve the freeze-thaw durability of the interface. After modification, the interfacial cohesion of the sample increases with the increase in the EVA concentration and can reach 162% of the original. Using an ultra-depth-of-field microscope, it was found that the repeated solidification-melting action of water between the interfaces makes the consolidated body on the damaged surface fall off, resulting in cracks. As the water content between the interfaces increases, the damage to the material is greater. However, the addition of EVA can fill the uncovered pores of W-OH cement, thereby improving the cohesion at the interface and effectively alleviating the freeze-thaw damage caused by the high water content at the interface. The results of this study can provide some theoretical references for slope treatment in the Pisha sandstone area using W-OH materials.

Effect of Mica Content on Mechanical Properties of Yili River Valley Loess under the Impact of Freezing and Thawing

Natural disasters, including collapse, landslides, and debris flows, commonly occur in the Yili River Valley as a result of its distinctive terrain and climate. A large proportion of these are loess landslides. Hence, studying the mechanism of their occurrence is crucial. The loess in the Yili River Valley has a high mica content. By using freeze-thaw (FT) cycling tests, unconsolidated and undrained triaxial shear tests, and FT cycling experiments, the study clarifies the impact of mica content on the mechanical properties of the loess in the Yili River Valley under FT cycling conditions. The findings demonstrated that the loess’s shear strength was negatively impacted by both the mica content and freeze-thaw cycles (FTCs). Under the same FT cycle conditions, the shear strength of the Yili Valley loess decreased with an increase in the mica content, particularly during the first ten cycles. Cohesion represented the impact of the mica content on the shear strength parameters. The cohesion decreases as the mica content increases. After ten cycles, the values of the cohesion tended to become stable, while the internal friction angle showed the opposite trend. For the same mica content, the shear strength of the Yili valley loess decreased with the increase in the number of FTCs, while the cohesion decreased, and the internal friction angle first increased and then decreased. The study’s findings might offer a theoretical foundation for preventing and reducing loess landslides in the Yili River Valley caused by FTCs and high mica content.

Analysis of Microscopic Pore Characteristics and Macroscopic Energy Evolution of Rock Materials under Freeze-Thaw Cycle Conditions

The repeated cyclic freeze-thaw effect in low-temperature environments causes irreversible damage and deterioration to the microscopic pore structure and macroscopic mechanical properties of a rock. To study the effects of the freeze-thaw cycle on the porosity and mechanical properties, the indoor freeze-thaw cycle test and mechanical tests of sandstone-like materials were conducted. Based on nuclear magnetic resonance, the influence of the freeze-thaw cycle on microscopic pores was analyzed, and the intrinsic relationship between porosity and mechanical strength was discussed. Meanwhile, the energy change in the uniaxial compression test was recorded using the discrete element software (PFC2D). The influence of freeze-thaw cycles on different types of energy was analyzed, and the internal relationship between different energies and freeze-thaw cycles was discussed. The results showed that the microscopic pore structure is dominated by micropores, followed by mesopores and the smallest macropores. With an increase in the freeze-thaw cycle, both micropores and mesopores showed an increasing trend. The porosity showed an exponentially increasing trend with the increase in freeze-thaw cycles. The peak strength and elastic modulus decreased exponentially with the increase in freeze-thaw times, while the peak strain showed an exponentially increasing trend. The strain energy and bond strain energy showed a trend of increasing and decreasing in the front and back stages of the peak strength, respectively. However, the frictional energy always showed an increasing trend. The total energy, strain energy, bond strain energy, and friction energy all showed exponential increases with the increase in the number of freeze-thaw cycles.

Effects of freeze-thaw cycles on nutrient removal from bioretention cells

There have been numerous summaries of the runoff purification characteristics of bioretention cells in warm climates. However, little has been done on the effects of freeze-thaw cycles (FTCs) that frequently occur in cold regions on bioretention cell performance. Three experimental columns were constructed to simulate the operation of the bioretention cell under the FTCs. The effects of FTCs on the nutrient removal efficiency of different filling bioretention cells were analyzed. The results showed that the ammonia nitrogen (NH4+-N) concentration in the effluent of the wood chip bioretention cell under the T3 conditions (WBCF) (2.35 mg/L) was significantly higher than that of the wood chip bioretention cell operating at room temperature (WBCR) (0.62 mg/L). The effluent NH4+-N concentration of aluminum sludge bioretention cell (ABCF) (0.096 mg/L) under the FTCs was lower than that of WBCF (0.91 mg/L). Under the T3 condition, the effluent nitrate nitrogen (NO3−-N) and total nitrogen (TN) concentrations of WBCF (5.33 mg/L and 8.86 mg/L) were higher than those of WBCR (5 mg/L and 6.11 mg/L) at room temperature. Under FTCs conditions, both WBCF and ABCF had high NO3−-N removal efficiency (up to 85.87% and 24.75%) at the initial stage of thawing of the filler, and the efficiency gradually decreased with the thawing of the filler. With the increase of FTCs, the NO3−-N removal efficiency of WBCF gradually decreased (always higher than 13.6%), while the removal efficiency of ABCF fluctuated wildly (the removal efficiency was primarily negative). The total phosphorus (TP) concentration in the effluent of WBCF (0.11 mg/L) under the T3 conditions was lower than that of WBCR (0.02 mg/L) at room temperature, and the TP concentration of ABCF (0.021 mg/L) in the effluent under the FTCs was slightly lower than that of WBCF (0.031 mg/L). The FTCs have a more significant impact on removing nitrogen pollutants in runoff, but have little effect on phosphorus. Compared with aluminum sludge, wood chips are more suitable for efficient removal of nitrogen pollutants in runoff under the FTCs. The experimental conclusions can provide a reference for the construction of bioretention cells in cold regions.

Thermoresponsive sol–gel containing probiotic’s cell free supernatant for dental caries prophylaxis

ABSTRACT Background Lactobacillus rhamnosus SD11 is a probiotic derived from the human oral cavity and has potential being used for dental prophylaxis. The cell free supernatant (CFS) of L. rhamnosus SD11 has good antimicrobial and antioxidant effects. Aim This study aimed to incorporate CFS of the probiotic into thermoresponsive copolymers to create a sol–gel formulation. Methods The sol–gel formulation was developed using Poloxamer 407 as the main polymer, which was mixed with natural polymers such as gellan gum, sodium alginate, and xyloglucan in different proportions. The sol–gel formulations were characterized based on their physicochemical parameters such as appearance, pH, viscosity, flow-ability in low temperature, antioxidant and antibacterial activity. An in vitro release study was performed using Franz’s diffusion cell and the stability was determined under freeze-thaw cycle conditions. Results The combination of 15% w/v of poloxamer 407 with 0.5% w/v of sodium alginate was the best sol–gel formulation to deliver the CFS of the probiotic. Conclusion This study was successful in creating a sol–gel formulation using a thermoresponsive copolymer, that could efficiently deliver CFS of the probiotic L. rhamnosus SD11.

Frost Resistance of Desert Sand Concrete

Demand for medium sand has increased greatly with increasing infrastructure construction items. The shortage of construction sand resources has become a serious problem in many districts. It not only increases the engineering cost, and the overexploitation of river sand and mountain as medium sand also brings a series of serious environment problems. There are abundant desert sand (DS) resources in western China. If DS resources can be used to substitute medium sand to produce desert sand concrete (DSC), which was suitable for engineering practice, the environment can be improved and engineering cost can be reduced. Although many researchers had focused on the mechanical performance of DSC, there were few documents on the frost resistance of DSC. Frost resistance experiments of DSC with 50% desert sand replacement ratio (DSRR) and ordinary concrete (OC) were performed in this paper. Influence of freeze-thaw cycles on the mechanical properties of OC and DSC was analyzed. Experimental results showed that, with increasing freeze-thaw cycles, the damage, peak strain, and porosity increased, while elastic modulus, Poisson's ratio, and peak stress declined, the stress-strain curves tended to be flat. Under the same condition of freeze-thaw cycles, the frost resistance of DSC with 50% DSRR was higher than that of OC. Constitutive model of DSC after different freeze-thaw cycles was formulated. The results predicted by constitutive model agreed well with experimental results, which can provide technical support for DSC engineering practice.

Microbial Succession under Freeze-Thaw Events and Its Potential for Hydrocarbon Degradation in Nutrient-Amended Antarctic Soil.

The polar regions have relatively low richness and diversity of plants and animals, and the basis of the entire ecological chain is supported by microbial diversity. In these regions, understanding the microbial response against environmental factors and anthropogenic disturbances is essential to understand patterns better, prevent isolated events, and apply biotechnology strategies. The Antarctic continent has been increasingly affected by anthropogenic contamination, and its constant temperature fluctuations limit the application of clean recovery strategies, such as bioremediation. We evaluated the bacterial response in oil-contaminated soil through a nutrient-amended microcosm experiment using two temperature regimes: (i) 4 °C and (ii) a freeze–thaw cycle (FTC) alternating between −20 and 4 °C. Bacterial taxa, such as Myxococcales, Chitinophagaceae, and Acidimicrobiales, were strongly related to the FTC. Rhodococcus was positively related to contaminated soils and further stimulated under FTC conditions. Additionally, the nutrient-amended treatment under the FTC regime enhanced bacterial groups with known biodegradation potential and was efficient in removing hydrocarbons of diesel oil. The experimental design, rates of bacterial succession, and level of hydrocarbon transformation can be considered as a baseline for further studies aimed at improving bioremediation strategies in environments affected by FTC regimes.

The Influence of Regional Freeze–Thaw Cycles on Loess Landslides: Analysis of Strength Deterioration of Loess with Changes in Pore Structure

The loess landslide in Gaoling District of Xi’an, Shaanxi in China is closely related to the seasonal freeze–thaw cycle, which is manifested by the destruction of pore structure and strength deterioration of the loess body under freeze–thaw conditions. In order to study the relationship between macro-strength damage and pore structure deterioration of saturated loess under freeze–thaw conditions and its influence on the stability of landslides, this paper explores the effect of freeze–thaw cycles on the strength of saturated undisturbed loess through triaxial compression test, and explores the micro-microstructure changes of saturated undisturbed loess through scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). This is to analyze the evolution of the pore structure and strength loss evolution of saturated loess during the freeze–thaw process, and to describe the freeze–thaw damage of saturated undisturbed loess through the change of porosity and strength deterioration. Then, the internal correlation expression between the porosity change and the strength degradation is established to realize the verification analysis of the test data based on the correlation model. The research results show that: (1) As the number of freeze–thaw cycles increases, the peak strength loss rate gradually increases, and the strength deterioration of saturated loess becomes more and more obvious. (2) The freeze–thaw cycle will lead to the development of pores and cracks in the sample, accompanied by the generation of new cracks, which will cause the deterioration of the pore structure of the sample as a whole. (3) The response of strength damage and porosity deterioration of saturated undisturbed loess is roughly similar under the freeze–thaw cycle. The change in porosity can be measured to better reflect the strength deterioration of saturated loess. Therefore, the change of pore structure of undisturbed loess under freeze–thaw cycle conditions is tested by field sampling and indoor tests to reflect the phenomenon of strength deterioration, thereby analyzing the stability of loess slopes.