Effect Of Freeze-thaw Cycles Research Articles

Investigation of the effects of biochar amendment on soil under freeze‒thaw cycles and the underlying mechanism

Biochar (BC) is widely utilized as a soil amendment; however, for widely distributed seasonally frozen soils, the effect of BC on soil and the optimal utilization of BC during the freeze‒thaw process are still unclear. In this study, the effects of freeze‒thaw aged biochar (FT-BC) and BC on soil properties and wheat cultivation were systematically investigated, and the underlying interaction mechanism between BC and soil was explored. The results show that FT-BC dramatically reduces the adverse effects of freeze‒thaw cycles on soil, enhances wheat growth, and increases dry matter yield by 17.5 %, which is mainly attributed to the ability of FT-BC to maintain soil structure, reduce water loss rates to below 0.20 g/h, and decrease nitrogen leaching by more than 20 % during freeze‒thaw cycles. Additionally, fresh BC had a greater effect on the fixation of cadmium than FT-BC in the soil, reducing its accumulation in wheat by 22.5 %. Multiple characterizations revealed that the freeze‒thaw process increased the porosity and specific surface area of FT-BC, providing more sites for water and nitrogen adsorption, whereas the dissolved organic matter released from fresh BC had a better ability to trap cadmium. These findings provide insights into the interactions between BC and soil components during the freeze‒thaw process and suggest the optimized utilization of fresh BC and FT-BC for different soil repair purposes.

Effects of coupled biochar and snow cover on soil carbon components and CO2 emissions in seasonally frozen soil areas under climate change conditions

Global warming is profoundly altering soil freeze–thaw cycle (FTC) patterns, and the formation of different thicknesses and durations of snow cover by snowfall results in heterogeneity of environmental and biological factors, which can have complex effects on soil water and carbon cycle processes. In order to better develop rational regulation strategies to increase the potential of soil carbon sequestration and emission reductions under climate change conditions, a three-year in situ control trial of field snow was set up to simulate climate scenarios using two treatments: snow removal and natural snow. The effects of FTCs and biochar on soil CO2 emission flux (CO2 Flux) were analyzed by constructing a driven coupling model between soil hydrothermal environmental factors, unstable organic carbon components and stable organic carbon components. The results showed that CO2 Flux decreased by 9.36% to 11.34% for 1% biochar treatment, while CO2 Flux increased by 15.41% to 18.32% for 2% biochar treatment. Moreover, the snow removal treatment increased CO2 Flux by 9.86% to 13.99% compared to the natural snow treatment. The snow during freezing and thawing has a dual effect on soil hydrothermal dynamics, with snow removal making the freeze–thaw action more intense in perturbing the soil carbon matrix, while the interfacial behavior of biochar with soil minerals protects the stability of the soil structure. Biochar reduces soil carbon emissions thanks to its highly stabilized components and unique surface structure, which enhances the carbon sequestration and emission reduction effect by increasing the proportion of inert organic carbon, promoting the formation of organic–inorganic complexes, and encapsulating and adsorbing soil organic matter. The results of the study can provide important theoretical support and practical models for the assessment of the environmental effects of biochar and the reduction of carbon sequestration in agriculture under climate change conditions.

Deterioration of dynamic fracture properties of granite under the coupled effects of hydrochemical solutions and freeze-thaw cycles

Fractured rock mass is a kind of complex rock mass widely existing in engineering projects, which is often subjected to erosion by different pH hydrochemical solutions such as surface water, acid rain, acidic and alkaline wastewater discharge, and deicing salts. When the rock project in a cold region suffers from the coupled effects of hydrochemical solutions and freeze-thaw (FT) cycles, the frost-heave-thaw-shrinkage characteristics of rocks are different from ordinary FT under dynamic loads, and the effect of FT cycles may be enlarged or reduced in different hydrochemical solutions. How to determine the effect of FT cycles on the expansion and changes of rock fractures, which is related to the safety and stability of many engineering rock masses in cold regions. In this study, the microstructure changes of specimens induced by hydrochemical solutions and cyclic FT were measured using nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). The dynamic fracture tests were conducted using single cleavage triangle (SCT) granite specimens. Crack propagation gauge (CPG) was applied to examine crack propagation speed (CPS). The findings indicate that the mineral composition of the granite did not vary large with the hydrochemical solutions and FT cycles, but the maximum diffraction intensity of each mineral composition changed. For the granite under the coupling effect of hydrochemical solutions and FT cycles, the granite specimen in NaOH solution with 100 FT cycles has the highest dynamic fracture toughness and is 10.76 MPa·m1/2, dynamic fracture toughness of H2O, HNO3 and Na2SO4 solutions are only 0.94, 0.91 and 0.93 of that of NaOH solution. With increasing FT cycle times, the dynamic fracture toughness and crack speed decrease, whereas the porosity increases. For the specimen in NaOH solution and 100 FT cycles, dynamic fracture toughness decreased by 18.12 % without FT cycles and crack speed decreased by 34.18 %, the porosity increases by 26.42 %.

Effect of freeze‒thaw cycles on root-Soil composite mechanical properties and slope stability.

Natural disasters such as landslides often occur on soil slopes in seasonally frozen areas that undergo freeze‒thaw cycling. Ecological slope protection is an effective way to prevent such disasters. To explore the change in the mechanical properties of soil under the influence of both root reinforcement and freeze‒thaw cycles and its influence on slope stability, the Baijiabao landslide in the Three Gorges Reservoir area was taken as an example. The mechanical properties of soil under different confining pressures, vegetation coverages (VCs) and numbers of freeze‒thaw cycles were studied via mechanical tests, such as triaxial compression tests, wave velocity tests and FLAC3D simulations. The results show that the shear strength of a root-soil composite increases with increasing confining pressure and VC and decreases with increasing number of freeze‒thaw cycles. Bermuda grass roots and confining pressure jointly improve the durability of soil under freeze‒thaw conditions. However, with an increase in the number of freeze‒thaw cycles, the resistance of root reinforcement to freeze‒thaw action gradually decreases. The observed effect of freeze‒thaw cycles on soil degradation was divided into three stages: a significant decrease in strength, a slight decrease in strength and strength stability. Freeze‒thaw cycles and VC mainly affect the cohesion of the soil and have little effect on the internal friction angle. Compared with that of a bare soil slope, the safety factor of a slope covered with plants is larger, the maximum displacement of a landslide is smaller, and it is less affected by freezing and thawing. These findings can provide a reference for research on ecological slope protection technology.

Effects of freeze–thaw cycles on the physicochemical and in vitro digestibility of starch in pre‐fermented frozen raw dough

SummaryIn this study, pre‐fermented frozen raw dough (PFRD) was subjected to freeze–thaw cycling (FTC) to explore the deterioration mechanism of PFRD, after which the physical quality, chemical properties and in vitro digestion characteristics of starch in the dough were analysed. The results showed that after the 5th FTC, the surface area of the dough and starch exhibited obvious depression deformation, and the damaged starch content increased by 38.21%. The random mechanical damage caused by ice crystals also had no significant regularity in the water retention and the short‐range order of starch. Moreover, the breakdown of the double helix structure of starch led to the dissolution of amylose, and the expansion and gelatinization enthalpy increased. In addition, the in vitro digestion results showed that freeze–thaw cycle twice increased the digestibility of the starch, and the hydrolysis rate reached 75.16%, Therefore, the effects of FTC twice on the starch of PFRD are controllable. This study provides a theoretical basis for the development of prefabricated frozen starch food industry technology in the future.

Experimental study on bond durability of GFRP bar/engineered cementitious composite exposed to freeze-thaw environments

Glass fiber reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) present better structural performance as compared to conventional concrete with reinforcing steel bars. However, the bond behavior of the GFRP bar to ECC matrix under freeze-thaw (FT) cycles in cold climates remains underexplored. Therefore, this study aims to investigate the bond durability of GFRP bars and ECC under FT conditions. An experiment was conducted with 33 pullout specimens, categorized according to concrete types (normal concrete and ECC), compressive strengths (30 MPa and 50 MPa) and the number of FT cycles (0, 100, 150, and 200 cycles). Assessment parameters included surface degradation, failure modes, mean bond strength, weight loss, and the relative dynamic modulus of elasticity. Results indicated ECC specimens exhibited greater durability compared to normal concrete specimens, with no significant improvement in durability observed with increased compressive strength. Specifically, the mean bond strengths of N30 (30 MPa normal concrete) specimens, E30 (30 MPa ECC) specimens, and E50 (50 MPa ECC) specimens decreased by 88.41 %, 38.86 %, and 58.21 % after 150 FT cycles, respectively. Failure modes correlated strongly with concrete type and the number of FT cycles. SEM and composition analyses revealed the effects of FT cycles on the concrete matrix, the bond interface, and the GFRP bars. The ascending branches in the bond stress-slip curves of specimens subjected to FT cycles were effectively modeled using Malvar's model. Based on the declining relative dynamic modulus of elasticity and the correlation between laboratory and natural FT cycles, the estimated fatigue lives for GFRP bar/E30 specimens subjected to 250 FT cycles are 35.7, 71.4, and 46.2 years in Beijing, Detroit, and Vancouver, respectively. This research provides insights on GFRP bar/ECC's longevity in practical engineering contexts.

Experimental study on the dealkalization of red mud using the freeze-thaw and acid washing method

The strong alkalinity of red mud is a key reason that threatens the environment and restricts the secondary use of red mud. Freeze-thaw (FT)-acid washing (AW) is proposed to remove alkali to improve the dealkalization efficiency of red mud. FT-AW tests were performed using red mud with oxalic acid (OA) and citric acid (CA) to examine the effect of FT cycles and eluent concentration on the dealkalization efficiency. Results showed that the FT-AW method significantly increased the dealkalization efficiency under the synergy of FT and AW. After 5 times of FT-AW, the alkali removal efficiencies of red mud with OA and CA as eluents reached 97.5% and 95.5%, which were 27.3% and 18.9% higher than those of the control group, respectively. The effect of OA on dealkalization was more sensitive than that of CA. The results of SEM-EDS and XRD showed that FT cycles destroyed the crystal structure of red mud and released part of the bonded alkali. The FT-AW method provides a novel idea for future large-scale red mud dealkalization by using FT alternation in seasonally frozen soil areas.

644. "Impact of heat inactivation and freeze-thaw cycles on detection of influenza A and influenza B antigens and RNA when assessing novel multiplex diagnostic assays"

Abstract Background Advances in diagnostics since the emergence of COVID-19 has resulted in easy availability of rapid antigen tests (RAT). Building on this, multiplex tests for simultaneous detection of Flu A, Flu B, and SARS-CoV-2 are being evaluated as part of NIH’s Rapid Acceleration of Diagnostics (RADx) program. Critically important for assay development and assessment are viral panels prepared under validated conditions to evaluate new tests. These panels may contain live virus or may be inactivated to promote biosafety. They also may undergo freeze-thaw cycles during storage and transport. We characterized the effect of heat inactivation (HI) on detection of Flu A and B using two RATs, and the effect of freeze-thaw cycles on a point-of-care (PoC) molecular assay already on the market. Methods Panels were prepared by serially diluting Flu A or B strains obtained from BEI Resources. Both live and HI panels were prepared. HI was achieved in-house (60°C, 30 minutes). Panels with and without HI were used to assess two RATs by performing triplicate tests and determining limit of detection (LOD) as the lowest TCID50 at which 3 of 3 replicates were positive. Additionally, a molecular-based PoC assay was evaluated by recording cycle threshold (Ct) values before and after freeze-thaw of specimens. All assays were performed according to the manufacturer’s instructions. Results Both RATs detected Flu A with similar sensitivity (2-fold increase in LOD) before and after heat inactivation (Figure 1), whereas Flu B was not detected by either RAT after heat inactivation. These results were consistent across both RATs and two strains of each virus. Live Flu A and B were stable and consistently detected up to four freeze-thaw cycles in the molecular assay with minor attrition of Ct values (Figure 2). Results of LOD characterization for two independent RATs with influenza A and B with and without heat inactivation. Correlation of Flu A and Flu B Ct values for fresh samples versus after four cycles of freeze thaw measured using a PoC molecular assay. Conclusion Pre-treatment and storage of testing material plays a crucial role in the assessment of diagnostic tests used for Flu A and B detection. Loss of reactivity in Flu B antigen tests after inactivation suggests that heating may denature a critical epitope recognized by immunoassays. Selection of live versus HI samples and degradational effects of freeze thaw cycles must be considered by laboratorians and engineers creating or validating diagnostic tests. Disclosures All Authors: No reported disclosures

Enhanced freeze-thaw cycles facilitate the antibiotic resistance proliferation and dissemination risk under global climate change

Antibiotic resistance genes (ARGs) and antibiotic resistant bacteria are considered as emerging contaminants, whose proliferation and dissemination are highly related to the climate conditions. Freeze-thaw cycles (FTC) is a natural phenomena that widely occurred in terrestrial ecosystem for high latitude environments, and frequent FTC has been revealed under global climate change. However, the effects of FTC on the resistome in soil are still not clear. Thus, a simulation experiment was performed to illustrate the profiles of ARGs and mobile genetic elements (MGEs) under FTC exposure. It was found that, 56.4–73.2% of the shared 71 core ARG subtypes were enriched after FTC treatment, and the abundance of ARGs in total had a significant positive linear correlation with the number of FTC in spite of the declined number of ARG subtypes (r = 0.986, p = 0.002). This can explained by the selection pressure exert by freeze-thaw on bacterial community structure and promoted horizontal gene transfer (HGT). The bacterial classeses within phylum Actinobacteria, one of the dominate bacterial phylum accounting for 36–54% of the total bacteria, were enriched because of their spore and filamentous producing attributes, and enormous ARGs were presented in this kind of antibiotic-synthesising bacteria. Moreover, the survived Actinobacteria could serve as ARG donors and receptors, which profit the HGT of ARGs. The present study revealed the facilitation posed by FTC on the proliferation and dissemination of ARGs, and the accordingly findings provide new sights for well understanding of the environmental behaviour of ARGs.

Responses of Nitrous Oxide Emissions and Bacterial Communities to Experimental Freeze-Thaw Cycles in Contrasting Soil Types.

Nitrous oxide (N2O) pulse emissions are detected in soils subjected to freeze-thaw cycles in both laboratory and field experiments. However, the mechanisms underlying this phenomenon are poorly understood. In this study, a laboratory incubation experiment that included freeze-thaw cycles (FTC), freezing (F) and control (CK) treatments was performed on three typical Chinese upland soils, namely, fluvo-aquic soil (FS), black soil (BS) and loess soil (LS). A higher similarity in soil properties and bacterial community structure was discovered between FS and LS than between FS and BS or LS and BS, and the bacterial diversity of FS and LS was higher than that of BS. FTC significantly increased the denitrification potential and the proportion of N2O in the denitrification gas products in FS and LS but decreased the denitrification potential in BS. Accordingly, with the increasing number of freeze-thaw cycles, the bacterial community composition in the FTC treatments in FS and LS diverged from that in CK but changed little in BS. Taxa that responded to FTC or correlated with denitrification potential were identified. Taken together, our results demonstrated that the effects of FTC on N2O emissions are soil-type-dependent and that the shift in the microbial community structure may contribute to the elevated N2O emissions.

Effect of FTC on the interface between soil materials and asphalt concrete using a direct shear test

The process of freezing and thawing has a great effect on different aspects of materials in cold regions. Due to the complex behavior of materials under the impact of freezing and thawing, several studies conducted on the individual behavior of soil materials or asphalt concrete on this condition. In the present study, the impact of freezing and thawing on the strength characteristics and interaction ratio of soil materials from classes GC (clayey gravel) and GP (poorly graded gravel) at the interface between asphalt and soil materials was assessed. The particle size distribution of the aggregate used in this study was within the grading range recommended by the International Commission on Large Dams (ICOLD) and Fuller's ideal grading curve used in the construction of Mijran Dam, Mazandaran Province, Iran. First, granular materials and asphalt concrete were subjected to weight loss test and durability study, respectively, according to AASHTO-T103 and Iranian Standard 12728. Then, utilizing a large-scale direct shear machine, the contact surface element (interface between granular materials and asphalt concrete) was evaluated under dry and saturated conditions as well as under various freeze-thaw cycling (FTC). The results demonstrate that an increase in the number of FTC let to a decrease in the maximum shear stress under dry and saturated circumstances for both clayey gravels and poorly graded gravels materials at interference with asphalt concrete. In GC materials at the contact surface with asphalt concrete, the interaction ratio reduces by 0.22 % under dry conditions and by 0.54–1.2 % under saturated conditions, relative to its value in the tenth cycle, as the number of FTC increases. In GP materials at the interface with asphalt concrete, as the number of FTC increases, the interaction ratio drops between 9.2 % and 33.61 % in dry conditions and by 20.62 % in saturated situations compared to the value that occurred in 10 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.

Effect of Freeze-Thaw Cycles on Mechanical Properties of an Embankment Clay: Laboratory Tests and Model Evaluations

Freeze-thaw (FT) cycling is a crucial issue in seasonal frozen regions and it will influence the mechanical properties of soils, which must be strictly considered for embankment engineering. This study conducted a series of unconsolidated and undrained triaxial tests under various closed-system FT cycles to investigate the mechanical properties of a typical embankment clay from China. Results indicated that the stress-strain curves changed from strain hardening or stabilization to softening during FT cycles. The elastic modulus was obviously weakened by FT cycles and declined sharply after the first FT action. The failure strength gradually reduced with the accumulation of FT cycles and eventually tended to be stable when the FT cycles reached 10, and the attenuation range was approximately 6–22% compared with the condition before FT cycles. Moreover, a phenomenological model on the failure strength was established by results of the tested clay in this study and validated to be robust through multiple sets of different clays data from other published literatures. Based on that, combined with the Mohr stress circle equation and envelope theory, an innovative method for rapidly obtaining the shear strength was proposed. The ensuing discoveries were that the cohesion was damaged in the course of the first few FT cycles and then kept basically constant after 10 cycles, while the internal friction angle was not sensitive to FT cycles. The normalized empirical formula was deduced and can simultaneously apply to the strain hardening, stabilization, and softening curves given the effect of FT cycles.

Effect of freezing-thawing cycles on the physical and mechanical properties of fired and unfired earth bricks

This paper presents the results from a campaign of unconfined compression tests on unfired and fired earth bricks exposed to freezing-thawing cycles. Three types of unfired earth bricks were manufactured by (a) light compaction of unamended earth at the standard Proctor optimum, (b) hypercompaction of unamended earth at a pressure of 100 MPa and (c) hypercompaction of amended earth with hemp fibres at a pressure of 100 MPa. For sake of comparison, the same tests were also performed on standard fired earth bricks exposed to freezing-thawing cycles. All bricks were equalised at a temperature of 23 °C and a relative humidity of 95% before being exposed to 0 (i.e. no freezing at all), 1, 3, 6, 9 and 12 freezing-thawing cycles under dry conditions. The bricks were subsequently subjected to unconfined compression tests to measure the changes of stiffness and strength. Results show that freezing-thawing hardened the unfired earth bricks (especially the lightly compacted Proctor bricks), which exhibited an improved mechanical performance with increasing number of cycles. Only negligible changes of mechanical response were instead measured for the fired bricks after exposure to freezing-thawing. These results suggest that unfired earth bricks can be used for construction in cold regions with sub-zero temperatures without loss of mechanical performance, provided that water uptake close to saturation is prevented by an appropriate architectural design.

Fungal community diversity dominates soil multifunctionality in freeze-thaw events

Global climate change has altered soil freeze-thaw (FT) patterns but less is known about the responses of soil microbial diversity, soil multifunctionality, and their relationship to FT events. Daxing'an Mountains in China, located in high-latitude permafrost ecosystems, are one of the most sensitive areas to climate change and FT patterns. Here, simulated FT conditions were used to determine the impact of FT events on soil microbial diversity and multifunctionality as well as to elucidate the relationships between bacterial and fungal diversity and multifunctionality. Community composition, α-diversity index, and co-occurrence network complexity of fungi significantly changed during FT events, whereas the same parameters did not exhibit significant alterations for bacteria. Soil fungal communities were more sensitive to FT events than soil bacterial communities. FT events significantly affected soil multifunctionality. A random forest analysis showed that the fungal diversity index was the main predictor of soil multifunctionality. Moreover, changes in soil abiotic factors also affected the relationship between soil microbial diversity and multifunctionality. Soil multifunctionality was also constrained by fungal community network complexity. Structural equation model showed that the FT amplitude and FT cycles exerted different impact paths on soil multifunctionality. The effect of FT cycles on soil multifunctionality (0.289) was greater than that of FT amplitude (0.080). As global climate change is expected to accelerate in the future, extension of the FT period in high-altitude and high-latitude regions may have a severe impact on soil function compared to extreme low temperatures caused by the presence of thin snow cover.

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.

Experimental study on the fracture and fatigue behaviors of flawed sandstone under coupled freeze–thaw and cyclic loads

This paper investigates the effects of coupled freeze–thaw (FT) cycles and cyclic loads on the mechanical properties, cracking behaviors and fatigue damage mechanism of flawed rocks. The digital image correlation technology is used to monitor the real-time cracking process and to analyze the evolution characteristics of deformation fields for tested samples. The effects of FT cycles and ligament angles on the mechanical evolution properties of flawed rocks subjected to cyclic loads are first analyzed. Secondly, the cracking processes of flawed rocks with different ligament angles subjected to FT cycles are studied in detail. Seven types of cracks including anti-wing crack, wing crack, oblique secondary crack, far-field crack, out-of-plane shear crack, out-of-plane tensile crack and quasi-coplanar secondary crack are observed. Two crack initiation modes including wing crack initiation and anti-wing crack initiation are registered, and seven crack coalescence types in tested samples are discriminated. The apparent displacement fields can be employed to reveal the fracture mechanism of flawed rocks under coupled FT cycles and cyclic loads. Finally, the fatigue damage mechanism of FT cycles coupling with cyclic loading and unloading is discussed in detail. The experimental results are very meaningful to evaluate the safety and stability of rock engineering in cold regions.

Effect of Freezing-Thawing Cycles on the Elastic Waves’ Properties of Rocks

Freezing thawing cycles are known to play an important role in fracture propagation on rock mass and thus in rock slope instabilities. In laboratories, this phenomenon can be studied through the measurement of the velocities of elastic waves. Seven types of rocks differing by their mineralogy and texture were tested (gneiss, basalt, amphibolite, dolomite, sandstone, marble limestone and calcite). Five samples of each rock were tested. All samples were submitted to freezing/thawing cycles following the European Standard describing the tests to determine the frost resistance of natural stone. Elastic waves were recorded on the samples every 14 cycles. The experimentation continued until the rock was macrofissurated. The evolution of the weight of the samples, the velocities of elastic waves, the evolution of the shapes of the waves were recorded to characterize changes over freeze-thaw cycles. In addition, signal processing on the waves allows to compute energy variations as well as the evolution of natural frequencies of the samples.

Research on fatigue performance of composite crumb rubber modified asphalt mixture under freeze thaw cycles

To study the effect of freeze thaw cycles on the fatigue damage characteristics of composite crumb rubber modified asphalt mixture (CCRMA), the semicircle bending fatigue test and the digital speckle correlation method (DSCM) were combined and the fatigue damage characteristics of CCRMA and styrene–butadienestyrene-modified asphalt mixture (SBSMA) under freeze thaw cycles were analyzed. The plateau valve (PV) of the stiffness modulus degradation ratio curve of the asphalt mixture is proposed as the analysis index to evaluate the macroscopic fatigue damage evolution of the asphalt mixture. The horizontal strain density (DE value) obtained through analyzing the horizontal strain characteristic cloud map of the main crack zone is identified as an index to evaluate the mesoscopic fatigue damage evolution of the asphalt mixture. The results show that after a freeze thaw cycle, the PV increases, DE decreases, fatigue damage rate accelerates, and fatigue resistance decreases. CCRMA has better freeze thaw resistance and fatigue resistance than SBSMA. The fatigue damage model established has high fitting accuracy and can effectively reflect the fatigue damage evolution degree of an asphalt mixture. A correlation analysis of PV and DE values reveals that there is a good linear correlation between them, indicating that applying the DSCM method to semicircle bending fatigue tests for studying the fatigue damage characteristics of asphalt mixtures is reliable.

Effects of freezing-thawing cycles on porosity and geometric configuration of an artificial soils in laboratory modeling

Variation in physical properties of soil depends heavily on freezing process during seasonal changes. Seasonal changes in cold humid regions lead to increasing of soil transformation speed. In the late autumn, soil profile is saturated with water through fallout. During winter, soil solution freezing leads to soil volume increasing due to water transition into the ice. Soil solution freezes in larger pores and the moment water flow stops, water phase transition leads to smaller pores and capillary deformation. Intensity of pore and capillary depletion will define extent of density changes during freezing. Rapidly developing urbanization process requires expansion of urban greening and tree planting, which can be successfully done by sustainable artificial soil implementation for each region, according to its climate conditions and pedogenesis. In order to observe possible porosity and structure changes in artificial soils and change rate due to freeze-thaw phenomenon, we have performed an experiment with a use of artificial soil models and then we have applied X˗Ray computer microtomography method to analyse soil pore space and its composition. As a result, we have seen significant compaction and pore diameter differentiation, as well as geometrical configuration changes.