Increase Of Freeze-thaw Cycles Research Articles

Investigation on the evolution of concrete pore structure under freeze-thaw and fatigue loads

Hydraulic concrete structures in seasonal frozen regions serve under freeze-thaw cycles and cyclic loading conditions which cause notable alterations in the concrete pore structure and a significant reduction in the mechanical properties and durability of concrete. To understand the macroscopic and mesoscopic damage processes and mechanism of concrete subjected to freeze-thaw cycles and cyclic loading lead, the compressive experiment and computed tomography test of concrete after freeze-thaw and fatigue loading tests were conducted. And the influences of freeze-thaw cycle damage and cyclic loading damage on the pore structure of concrete were analyzed. The relationships between concrete pore fractal dimension, compressive strength, and elastic modulus were revealed. The concrete average pore size can be regarded to grows linearly under freeze-thaw and cyclic loading. The porosity, pore volume, and pore surface area increase with the increase in freeze-thaw cycles, and their relationship can be represented by a quadratic function. However, they first decrease and then increase with the increase of loading cycles after a specific freeze-thaw cycles number. Under the combined action of freeze-thaw cycles and cyclic loading, the non-uniformity degree of concrete pore distribution decreases, and the overall structure is more regular. The distribution of single pore morphology tends to be spherical and banded, respectively. The cyclic loading promotes the extension of the internal pores and cracks of freeze-thaw-damaged concrete which aggravates damage of concrete. Under freeze-thaw cyclic loading, the concrete compressive strength and elasticity modulus is linearly and positively correlated with fractal dimension. With the increase of loading cycles number after freezing and thawing, the fractal dimension and compressive strength decrease, and the elasticity modulus has a larger dispersion. The relationship model between concrete compressive strength and fractal dimension can well describe the macroscopic and mesoscopic evolution of concrete under freeze-thaw and cyclic loading. The results can provide a scientific basis for improving the design and maintenance of concrete and benefit extending the long-term service life of hydraulic concrete structures in cold climates.

Experimental study on deformation characteristics of seasonal subgrade soil under dynamic load.

In Northwest China, the highway infrastructure often faces challenges due to the widespread presence of subgrade soil. This soil undergoes significant changes in performance under cyclic loading and freeze-thaw cycles. To effectively design and construct highways in these regions, it is crucial to understand the impact of various factors on the deformation characteristics and mechanical properties of subgrade soil. This study aims to investigate the influence of freeze-thaw cycles, water content, confining pressure, and loading rate on the deformation behavior and mechanical properties of subgrade soil under cyclic loading conditions. Experimental tests were conducted to analyze the deformation characteristics and mechanical properties of the subgrade soil. The test results revealed the following: 1) Dynamic loading leads to a noticeable decrease in the strength of subgrade soil, resulting in a softening effect on the stress-strain curve. The cumulative strain of the soil is positively correlated with the number of freeze-thaw cycles and water content, while negatively correlated with confining pressure. The final cumulative strain remains below 1%. 2) The failure stress of subgrade soil decreases exponentially with an increase in freeze-thaw cycles, dropping from 224.52 kPa to 196.76 kPa. 3) An increase in water content linearly decreases the failure stress of subgrade soil, ranging from 377.1 kPa to 151.5 kPa. 4) Confining pressure exhibits a linearly increasing relationship with the failure stress of subgrade soil, ranging from 151.6 kPa to 274.5 kPa. 5) The failure stress of subgrade soil demonstrates a linear increase with the loading rate, ranging from 200.46 kPa to 210.62 kPa. These findings provide valuable insights for the design and construction of highways in seasonal frozen areas. They also offer guidance for preventing and mitigating subgrade freeze-thaw issues in the future.

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.

Physical property responses of soils subjected to different degrees of erosion and seasonal freeze-thaw cycles in Northeast China

Changes in soil pores and aggregate stability due to freeze-thaw cycles (FTCs) are important causes of increased soil erosion during snowmelt. Soil erosion causes spatial redistribution of soils, enhancing soil heterogeneity and potentially impacting soil responses to FTCs. Nonetheless, there is minimal knowledge of the responses of soils subjected to different degrees of erosion to seasonal FTCs. To reveal the impact of seasonal FTCs, the dynamic variations of pore characteristics and aggregates of soils with four different degrees of erosion (original, degraded, deposited and parent soil) were measured, and the connections between influencing factors and soil properties were analyzed. The results showed that FTCs altered the structure of the soils and weakened their resistance to erosion and that soils with different degrees of erosion responded differently to FTCs. After seasonal FTCs, soil porosity increased (0.4 %-11.9 %) to some extent in all soils, with greater changes observed in the more eroded soils. Notably, capillary porosity exhibited a complex changing trend compared to total porosity. Degraded and parent soils showed a stable bulk density, while the original soil showed a decrease (2.1 %) in bulk density and the deposited soil showed an increase (18.4 %) in bulk density. With the increase of FTCs, the field capacity of original, degraded, and deposited soils exhibited a gradual decrease (15.1 %-18.5 %), while that of the parent soil slightly increased (0.9 %). After seasonal FTCs, the saturated hydraulic conductivity decreased for original and deposited soils (19.5 %-41.5 %), while it increased for degraded and parent soils (29.2 %-41.6 %). Throughout the FTCs, the proportion of the large aggregates decreased and the small aggregates increased, and the transformation was greater on the less eroded soils. The mean weight diameter and geometric mean diameter of the soils gradually decreased with increasing FTCs, while the change was smaller for the more eroded soils. After seasonal FTCs, the less eroded soils were at greater risk of erosion. Our results demonstrated that the number of FTCs had a more significant impact on soil physical properties compared to the temperature difference and soil water content. Overall, freeze-thaw action reinforced the spatial heterogeneity of soil properties, potentially intensifying soil erosion. These findings help reveal the effects of FTCs on the physical properties of soils with different degrees of erosion and deepen the understanding of the mechanism of FTCs on soil erosion processes.

Influence of Polypropylene Fiber on Concrete Permeability under Freeze-Thaw Conditions and Mechanical Loading.

Polypropylene fiber reinforcement is an effective method to enhance the durability of concrete structures. With the increasing public interest in the widespread use of polypropylene fiber reinforced concrete (PFRC), the necessity of evaluating the mechanism of polypropylene fiber (PF) on the permeability of concrete has become prominent. This paper describes the influence of PF on the concrete permeability exposed to freeze-thaw cycles under compressive and tensile stress. The permeability of PFRC under compressive and tensile loads is accurately measured by a specialized permeability setup. The permeability of PFRC under compressive and tensile loads, the volume change of PFRC under compressive load, and the relationship between compressive stress levels at minimum permeability and minimum volume points of PFRC are discussed. The results indicate that the addition of PF adversely affects the permeability of concrete without freeze-thaw damage and cracks. However, it decreases the permeability of concrete specimens exposed to freeze-thaw cycles and cracking. Under compressive load, the permeability of PFRC initially decreases slowly and follows by a significant increase as the compressive stress level increases. This phenomenon correlates with the volume change of the specimen. The compressive stress level of the minimum permeability point and compressive stress level of the minimum volume point of PFRC exhibit a linear correlation, with a fitted proportional function parameter γ ≈ 0.98872. Under tensile load, the permeability of PFRC increases gradually with radial deformation and follows by a significant increase. The strain-permeability curves of PFRC under loading are studied and consist of two stages. In stage I, the permeability of PFRC gradually decreases with the increase of strain under compressive load, while the permeability increases with the increase of strain under tensile load. In stage II, under compressive load, the permeability of PFRC increases with the increase of freeze-thaw cycles, whereas under tensile load, the permeability gradually decreases with the increase of freeze-thaw cycles. The reduction of PF on the permeability of PFRC under tensile load is greater than that under compressive load. In future research, the relationship between strain and permeability of PFRC can be integrated with its constitutive relationship between stress and strain to provide a reference for the application of PF in the waterproofing of concrete structures.

Study on meso-deformation and failure mechanism of rock mass with micro-cracks under freeze-thaw loading

The long-term freeze-thaw effect leads to the development of rock fractures and strength degradation in cold region engineering construction, which poses a serious challenge to the stability of the project. In this paper, the microscopic model of sandstone freeze-thaw cycles was established using a particle flow code (PFC2D). Through numerical simulation, the variation law of mechanical properties of rock mass with micro-cracks is systematically studied from the aspects of displacement, crack development, strain and strength. The results show that: (i) The freeze-thaw loading displacement is concentrated on both sides of the initial micro-cracks, and the crack development is not controlled by it. When the number of freeze-thaw cycles is greater than 17, the displacement and crack development are significant. The crack increases with the increase of the crack distance ratio. (ii) When the number of freeze-thaw cycles is less than 15, the compressive crack develops at the end of the initial micro-crack, and the development is controlled by it. When the number of freeze-thaw cycles is greater than 21, the crack increases sharply, and the development is no longer controlled by the initial micro-cracks. When the number of freeze-thaw cycles is less than 15, the damage strain shows minimal variation but decreases sharply with the increase of freeze-thaw cycles. (iii) Under each crack distance ratio, the strength changes in three stages: when the number of freeze-thaw cycles is less than 15, the strength changes little, and the strength decreases sharply with the increase of freeze-thaw cycles. With the increase of the crack distance ratio, it increases first and then decreases. And it is more significant when the number of freeze-thaw cycles is greater than 17. The research results can provide theoretical support for the influence and evaluation of rock freeze-thaw action in cold regions.

Effects of reduced snowpack due to climate warming on abiotic and biotic soil properties in alpine and boreal forest systems

Reduction in snow cover, depth, onset, and duration of seasonal snow in mid-latitude regions due to climate warming has multiple global and local scale ecosystem impacts. These effects include modulations of the hydrological cycles and increases in land surface solar radiation absorption due to decreased albedo. Changes in snow cover characteristics also affect underlying soils. Snow has an insulating effect on soils by decoupling air and soil temperatures, thus seasonal snow cover reduction leads to overall lower soil temperatures and an increase in freeze-thaw cycles. This is especially prominent during the fall and spring thaw seasons when the snow cover is not as extensive. This in turn has downstream impacts on soil physical, chemical, and biological properties. Among these impacts are soil moisture reduction, temperature, frost regimes, soil pH shifts, and alteration in nutrient flux dynamics during winter, snowmelt period and the following summer growing season. These changes in soil physicochemical properties due to snowpack reduction can then impact the biological soil properties via increased plant root mortality, reduced abundance and diversity of soil arthropods, and shifts in composition, abundance and activity of soil microbial communities. All these soil biotic factors can in turn alter the dynamics of soil nutrient fluxes and future greenhouse gas emissions. Here, we integrate data on the effects of snow cover reduction on abiotic and biotic soil properties, with focus on temperate alpine and forest ecosystems and with an outlook on future impacts.

Degradation of RC short beams under monotonic and repeated loads after cryogenic freeze-thaw cycles

ABSTRACT To investigate the effects of cryogenic freeze-thaw cycles and repeated loading on the bearing capacity and deformation properties of reinforced concrete (RC) short beams, RC short beams with different reinforcement ratios were subjected to Minus 160°C cryogenic freeze-thaw cycles. Subsequently, a four-point bending tests were carried out under monotonic and repeated loading with the aim of exploring the performance characteristics of the test beams, such as failure mode, load‐deflection response, and ductility. Experimental results showed that the failure mode of RC short beams changed from ductile bending to brittle shear failure after cryogenic freeze-thaw cycles. Additionally, the load-carrying capacity, deformation properties and energy dissipation performance exhibited a significant degradation trend. There is decreasing trend for the ductility and ultimate bearing capacity of beams with the increase in freeze-thaw cycles, and the decrease degree was most obvious in the first three cycles. Moreover, compared with monotonic loading, the ductility index of normal temperature beam and freeze-thaw cycle short beam decreased more significantly under repeated loading, and the bearing capacity decreases more obviously under the last stage of multi-level loading and unloading cycles.

Thawed drip and its membrane-separated components: Role in retarding myofibrillar protein gel deterioration during freezing-thawing cycles

Myofibrillar proteins are crucial for gel formation in processed meat products such as sausages and meat patties. Freeze-thaw cycles can alter protein properties, impacting gel stability and product quality. This study aims to investigate the potential of thawed drip and its membrane-separated components as potential antifreeze agents to retard denaturation, oxidation and gel deterioration of myofibrillar proteins during freezing-thawing cycles of pork patties. The thawed drip and its membrane-separated components of > 10 kDa and < 10 kDa, along with deionized water, were added to minced pork at 10 % mass fraction and subjected to increasing freeze–thaw cycles. Results showed that the addition of thawed drip and its membrane separation components inhibited denaturation and structural changes of myofibrillar proteins, evidenced by reduced surface hydrophobicity and carbonyl content, increased free sulfhydryl groups, protein solubility and α-helix, as compared to the deionized water group. Correspondingly, improved gel properties including water-holding capacity, textural parameters and denser network structure were observed with the addition of thawed drip and its membrane separation components. Denaturation and oxidation of myofibrillar proteins were positively correlated with gel deterioration during freezing-thawing cycles. We here propose a role of thawed drip and its membrane separation components as cryoprotectants against myofibrillar protein gel deterioration during freeze-thawing cycles.

Experimental Study on Salt-Bearing Sandstone Samples Under the Change of Temperature and Humidity Cycle

ABSTRACT Salt crystallization is a common type of disease in grottoes. Due to the change in temperature and humidity, the soluble salt originally existing in sandstone will have a negative impact on the protection of rock relics. In this study, sandstone samples containing Na2SO4 solution and distilled water were used to study the difference in sample damage under the condition of temperature and humidity cycle changes. It was found that the damage degree of samples containing soluble salts was much higher than that of salt-free samples, especially under the influence of freeze-thaw cycles. With the increase of freeze-thaw cycles, the internal friction angle and wave velocity of sandstone decrease linearly, while the surface hardness, tensile strength, and cohesion decrease exponentially. In addition, the damage caused by freeze-thaw cycles and dry-wet cycles develops from the inside to the outside of the rock sample, which is manifested by the increase in the number of macropores and the emergence of new pores. The different combinations of several effects lead to different changes in pore structure and mineral composition of the samples under the four conditions. The research results are helpful in providing a scientific basis for the disease control of stone cultural relics.

Experimental study on the frost resistance of molybdenum tailings concrete

The research aims to experimentally investigate the frost resistance of molybdenum tailings concrete (MoTC), involving C30 and C60 grade, with varying molybdenum tailings replacement ratios and freeze-thaw cycles. The results indicated that with an increase in the number of freeze-thaw cycles, both C30 and C60 grade MoTC showed an aggravated deterioration in strength and failure morphology. However, the deterioration of C60 grade MoTC was less severe than C30 grade. The more than 25% addition of molybdenum tailings significantly improved the frost resistance of C30 grade MoTC, but had minor effect on that of C60 grade MoTC. The mass loss ratio, cubic compressive strength, and dynamic elastic modulus of both C30 and C60 grade MoTC decreased with the increase in freeze-thaw cycles. The highest mass loss ratio for C30 grade MoTC was 100%, with the total loss of the dynamic elastic modulus and cubic compressive strength. For C60 grade MoTC, the highest mass loss ratio was 2.13%, with dynamic elastic modulus and cubic compressive strength reaching 12.8 and 23.79 MPa, respectively. Based on the test data, a predictive formula for the dynamic elastic modulus of C30 grade MoTC with considering the molybdenum tailings replacement ratios and freeze-thaw cycles was proposed, which shows good agreement between the results.

Changing of mechanical property and bearing capacity of strongly chlorine saline soil under freeze-thaw cycles

Freeze-thaw cycles and compactness are two critical factors that significantly affect the engineering properties and safety of building foundations, especially in seasonally frozen regions. This paper investigated the effects of freeze-thaw cycles on the shear strength of naturally strongly chlorine saline soil with the compactness of 85%, 90% and 95%. Three soil samples with different compactness were made. Size and mass changes were measured and recorded during freeze-thaw cycles. Shear strength under different vertical pressures was determined by direct shear tests, and the cohesion and friction angle were measured and discussed. Microstructure characteristic changes of saline soil samples were observed using scanning electron microscopy under different freeze-thaw cycles. Furthermore, numerical software was used to calculate the subsoil-bearing capacity and settlement of the electric tower foundation in the Qarhan Salt Lake region under different freeze-thaw cycles. Results show that the low-density soil shows thaw settlement deformation, but the high-density soil shows frost-heaving deformation with the increase in freeze-thaw cycles. The shear strength of the soil samples first increases and then decreases with the increase in freeze-thaw cycles. After 30 freeze-thaw cycles, the friction angle of soil samples is 28.3%, 29.2% and 29.6% lower than the soil samples without freeze-thaw cycle, the cohesion of soil samples is 71.4%, 60.1% and 54.4% lower than the samples without freeze-thaw cycle, and the cohesion and friction angle of soil samples with different compactness are close to each other. Microstructural changes indicate that the freeze-thaw cycle leads to the breakage of coarse particles and the aggregation of fine particles. Correspondingly, the structure type of soil changes from a granular stacked structure to a cemented-aggregated system. Besides, the quality loss of soil samples is at about 2% during the freeze-thaw cycles. Results suggest that there may be an optimal compactness between 90 and 95%, on the premise of meeting the design requirements and economic benefits. This study can provide theoretical guidance for foundation engineering constructions in seasonally frozen regions.

Freeze-Thaw Damage Characterization of Cement-Stabilized Crushed Stone Base with Skeleton Dense Gradation.

The skeleton dense graded cement-stabilized crushed stone base is a widely used material for road construction. However, this material is susceptible to freeze-thaw damage, which can lead to degradation and failure, for which there is still a lack of an in-depth understanding of the freeze-thaw damage characteristics. This study aims to assess the mechanical performance and the freeze-thaw damage characteristics of the cement-stabilized crushed stone base with skeleton dense gradation based on a mechanical test and acoustic technology in a laboratory. There is a gradually increasing trend in the mass loss rate of the base material with an increase in freeze-thaw cycles. The curve steepens significantly after 15 cycles, following a parabola-fitting pattern relationship. The compressive strength of the cement-stabilized crushed stone base also decreased with a parabola-fitting pattern, and the decrease rate may accelerate as the freeze-thaw cycles increase. The resilience modulus of the base material decreased with increasing freeze-thaw cycles, following a parabolic trend. This suggests that the material's resistance to freeze-thaw damage decreases with increasing cycles. The ultrasonic wave velocity decreased with increasing freeze-thaw cycles, exhibiting a parabolic trend. This decline can be attributed to microcracks and defects developing within the material, offering insights for monitoring and predicting its service life. The damage progression of the cement-stabilized crushed stone base was found to occur in three stages: initial, stationary, and failure. The duration of stage I increased with freeze-thaw cycles, while the duration of stage III decreased. The findings provide valuable insights into the mechanisms and processes of freeze-thaw damage in a cement-stabilized crushed stone base with skeleton dense gradation.

Freeze-Thaw Damage Characteristics of Concrete Based on Compressive Mechanical Properties and Acoustic Parameters.

Concrete is a versatile material widely used in modern construction. However, concrete is also subject to freeze-thaw damage, which can significantly reduce its mechanical properties and lead to premature failure. Therefore, the objective of this study was to assess the laboratory performance and freeze-thaw damage characteristics of a common mix proportion of concrete based on compressive mechanical tests and acoustic technologies. Freeze-thaw damage characteristics of the concrete were evaluated via compressive mechanical testing, mass loss analysis, and ultrasonic pulse velocity testing. Acoustic emission (AE) technology was utilized to assess the damage development status of the concrete. The outcomes indicated that the relationships between cumulative mass loss, compressive strength, and ultrasonic wave velocity and freeze-thaw cycles during the freezing-thawing process follow a parabola fitting pattern. As the freeze-thaw damage degree increased, the surface presented a trend of "smooth intact surface" to "surface with dense pores" to "cement mortar peeling" to "coarse aggregates exposed on a large area". Therefore, there was a rapid decrease in the mass loss after a certain number of freeze-thaw cycles. According to the three stages divided by the stress-AE parameter curve, the linear growth stage shortens, the damage accumulation stage increases, and the failure stage appears earlier with the increase in freeze-thaw cycles. In conclusion, the application of a comprehensive understanding of freeze-thaw damage characteristics of concrete based on compressive properties and acoustic parameters would enhance the evaluation of the performance degradation and damage status for concrete structures.

Combined deterioration effects of freeze–thaw and corrosion on the cyclic flexural behavior of RC beams

Reinforced concrete (RC) stands as the predominant construction material, and with the growing prevalence of aging infrastructure, the safety assessment of deteriorating structures has emerged as a pressing and critical concern. This study presents an experimental investigation into the combined effects of freeze–thaw cycles (100, 200, and 300 cycles) and corrosion (corrosion ratio: 3% and 10%) on the cyclic behavior of RC beams. Seven RC beam specimens with varying types and levels of deterioration were fabricated, and static tests were conducted using a four-point bending method to assess the behavior of RC beams under each degradation factor. The experimental results revealed that increasing freeze–thaw cycles significantly impact RC beam behavior, leading to intensified crack formation due to cyclical frost-heaving pressure. This ultimately results in reduced yield loads ranging from 3% to 11% and peak loads reduced by 1–2% compared to the reference specimen A-0-0. Corrosion of steel bars in RC beams alters failure modes, with corroded specimens (C-0-3 and C-0-10) experiencing substantial decreases in yield load, a 15% reduction in C-0-3, and a 26% decrease in C-0-10, compared to A-0-0. Displacement at yield load and peak load also decreased, highlighting the detrimental impact of corrosion on beam mechanical properties. The combined deterioration from freeze–thaw cycles and corrosion further exacerbates these reductions, resulting in a substantial decrease in yield load (32%) and peak load (24%) in D-3-10 compared to the reference specimen A-0-0. Additionally, energy dissipation capacity and cumulative energy dissipation capacity exhibit dynamic changes influenced by the progression of freeze–thaw cycles, corrosion, and their combined effects.

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.

Study on the freeze-thaw damage characteristics of skarn based on CT three-dimensional reconstruction

To study the mesoscopic damage evolution characteristics of skarn under freeze-thaw cycles, based on CT technology, the skarn samples under freeze-thaw action were scanned by CT, and the image data of skarn were segmented by Avizo software. The digital model of the three-dimensional structure of skarn was established, and the evolution law of the internal structure of skarn during the freeze-thaw cycle was quantitatively analyzed. The box dimension algorithm calculates the fractal dimension of the pore structure under freeze-thaw conditions. The relationship between fractal dimension, pore volume fraction, and freeze-thaw cycles was studied. According to the statistical results of the pore size distribu-tion of skarn, the change characteristics of pore structure in the rock under the influence of freeze-thaw were studied. Based on the theory of rock damage mechanics, the damage variable of skarn was defined using the concept of the effective bearing zone, and the freeze-thaw damage evolution of skarn was studied. The results show that the three-dimensional reconstructed model can directly show each medium’s meso-pore structure and spatial distribution. There is a positive correlation between pore volume fraction and fractal dimension under freeze-thaw conditions. The fractal dimension satisfies the exponential growth law. The skarn damage variable increases with the increase of freeze-thaw cycles, which is consistent with the development trend of pore structure. The exponential function can better reflect the damage evolution of skarn under freezing and thawing.

A Study on Chloride Corrosion Resistance of Reactive Powder Concrete (RPC) with Copper Slag Replacing Quartz Sand under Freeze-Thaw Conditions.

In order to study the influence of freeze-thaw cycles on chloride ion corrosion resistance of RPC with copper slag (CS) instead of quartz sand (QS), the 28d uniaxial compressive strength (UCS) of CSRPC with a different CS substitution rate was investigated by unconfined compression tests. The electric flux test method was used to study the chloride ion diffusion resistance of CSRPC after freeze-thaw cycles, and the pore size distribution was obtained through the nuclear magnetic resonance (NMR) method. Then, a mathematical relationship between the chloride ion diffusion coefficient and the pore fractal characteristic parameter T was established to study the effect of freeze-thaw cycles on chloride ion diffusion. Finally, SEM/EDS, XRD, and DTG methods were combined to study the influence of the distribution of Friedel's salts generated after freeze-thaw cycles on chloride ion diffusion in CSRPC. The results indicate that CS has a micro aggregate effect and pozzolanic activity, which can effectively improve the chloride ion diffusion resistance of CSRPC after freeze-thaw cycles. In addition, the electric flux of CSRPC decreases with the increase in freeze-thaw cycles, and the chloride diffusion coefficient is closely related to the pore fractal dimension.

Investigation of the Deterioration of Basu Granite Mechanical Properties Caused by Freeze–Thaw Cycles in High-Altitude Mountains in the Eastern Part of the Tibetan Plateau, China

Mountains composed of granite are generally regarded as stable geological formations. However, in Alpine and high-altitude mountains in the eastern part of the Tibetan Plateau, geological hazards such as collapses and landslides occur frequently due to the deterioration of granite mechanical properties caused by the freeze–thaw cycles. To investigate this phenomenon, a freeze–thaw cyclic mechanical test is conducted on granite from the Basu area, and the rock’s damage trend during the freeze–thaw process is analyzed through wave velocity and nuclear magnetic resonance (NMR) tests. The results indicated that the internal damage of granite increases and its wave velocity decreases significantly with increasing the freeze–thaw cycles, implying a decline in the rock’s integrity. Furthermore, the development pattern of the NMR T2 relaxation time distribution indicates that the crack size range of naturally weathered rock samples further increased after freeze–thaw cycles, whereas less-weathered rocks showed a more concentrated range of crack sizes. Triaxial compression tests conducted on rock samples after the freeze–thaw cycles showed that parameters such as the uniaxial compressive strength, elastic modulus, internal friction angle, and cohesion of the rock decreased with increasing freeze–thaw cycles, while a significant change of Poisson’s ratio was not observed. Based on the test data and theoretical analysis, a freeze–thaw damage constitutive model of the Basu granite can be established to simulate and predict the overall variation in rock stress and strain under various confining pressures and freeze–thaw cycles. Hopefully, the present study will provide useful guidance for research on the hazard mechanism and hazard prevention of granite sand-sliding slopes in the Basu area.

Effect of ultra-low temperature freeze-thaw cycle on the flexural performance of hybrid fiber RC beams subjected to monotonic and repeated loading

This study investigates the effects of Ultra-low temperature freeze-thaw cycles on the cracking behavior and deformation performance of steel fiber, basalt fiber, and hybrid fiber reinforced concrete beams under monotonic and repeated loading. Firstly, the freezing temperature and freeze-thaw cycles on the compressive and splitting tensile strength of steel fiber, basalt fiber and hybrid fiber reinforced concrete were tested respectively; Then a four-point bending tests under monotonic and repeated loading were carried out on 12 fiber reinforced concrete beams after ultra-low temperature freeze-thaw cycles. Experimental results are reported in terms of their failure modes, flexural strength, load-deflection response, cracking behavior and ductility. The test results show that both the compressive and splitting tensile strength of all kinds of fiber reinforced concrete decreases with the progressive freeze-thaw cycles and lowering freezing temperature. The addition of fiber could significantly mitigate the concrete damage caused by freeze-thaw cycle, and the hybrid fiber reinforced concrete shows the most significant strength enhancement. With the increase of freeze-thaw cycles and the decrease of freezing temperature, the freeze-thaw damage of the beam is more serious. The ductility and energy absorption of the beam shoes different degrees of decrease. The degradation of flexural load-bearing capacity, deformation capacity, cracking performance and ductility of beams are inhibited by adding fibers.