Freeze-thaw Cycles Research Articles

Mechanical, Durability, and Microstructure Characterization of Pervious Concrete Incorporating Polypropylene Fibers and Fly Ash/Silica Fume

Pervious concrete, because of its high porosity, is a suitable material for reducing the effects of water precipitations and is primarily utilized in road pavements. In this study, the effects of binder-to-aggregate (B/A) ratios, as well as mineral admixtures with and without polypropylene fibers (PPFs) (0.2% by volume), including fly ash (FA) or silica fume (SF) (10% by substitution of cement), on the mechanical properties and durability of pervious concrete were experimentally observed. The experimental campaign included the following tests: permeability, porosity, compressive strength, splitting tensile strength, and flexural strength tests. The durability performance was evaluated by observing freeze–thaw cycles and abrasion resistance after 28 d curing. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA-DTA), and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) were employed to investigate the phase composition and microstructure. The results revealed that, for an assigned B/A ratio identified as optimal, the incorporation of mineral admixtures and fibers mutually compensated for their respective negative effects, resulting in the effective enhancement of both mechanical/microstructural characteristics and durability properties. In general, pervious concrete developed with fly ash or silica fume achieved higher compressive strength (>35 MPA) and permeability of 4 mm/s, whereas the binary combination of fly ash or silica fume with 0.2% PPFs yielded a flexural strength greater than 6 MPA and a permeability of 6 mm/s. Silica fume-based pervious concrete exhibited excellent performance in terms of freeze–thaw (F-T) cycling and abrasion resistance, followed by fiber-reinforced pervious concrete, except fly ash-based pervious concrete. Microstructural analysis showed that the inclusion of fly ash or silica fume reduced the harmful capillary pores and refined the pore enlargement caused by PPFs in the cement interface matrix through micro-filling and a pozzolanic reaction, leading to improved mechanical and durability characteristics of pervious concrete.

Establishment and Validation of Fecal Secretory Immunoglobulin A Measurement for Intestinal Mucosal Health Assessment in Wild Lemurs.

The measurement of biomarkers in blood and excreta can enable immune status assessment and provide prognostic information on individual health outcomes. In this respect, the fecal measurement of secretory immunoglobulin A (sIgA), the primary mammalian antibody for mucosal defense, has recently received increased interest in a few anthropoid primates, but a fecal sIgA assay for use in strepsirrhine primates has not yet been reported. Here, we develop and analytically validate a cost-effective in-house sandwich enzyme immunoassay for the extraction and measurement of sIgA in feces of redfronted lemurs (Eulemur rufifrons). We also tested a simple method for sIgA extraction that can be used under remote field conditions and undertook experiments to assess the robustness of sIgA concentrations to variation in processing and storage conditions of fecal extracts. Our analytical validation revealed that the assay recognizes immunoreactive sIgA in redfronted lemur feces, that sIgA can be measured accurately with no potential interference from the fecal matrix, and that assay reagents and performance are highly stable over time. The field-friendly extraction procedure produced sIgA results strongly correlated with those generated by a standard laboratory extraction method. Short-term storage at room temperature resulted in a slight decline in sIgA concentrations, whereas freezing extracts at -20°C kept sIgA levels stable for at least 3 months. Longer-term storage of >5 months, however, led to a significant decline of sIgA concentrations. Multiple freeze-thaw cycles did not affect sIgA levels. This study, therefore, provides the basis for measuring fecal sIgA in lemurs and possibly other strepsirrhines. When samples are processed properly and stored frozen, and when sIgA analysis can be performed within 3 months upon sample collection, fecal sIgA measurements can become a valuable tool for monitoring aspects of immunity and health in both zoo-housed and wild-living lemurs.

Synthesis and evaluation of self‐healing polyvinyl alcohol‐tannic acid membranes for skin bio‐applications

AbstractAutonomic self‐healing films have shown limited mechanical strength, hindering their application as biomaterials, particularly in skin bioengineering. To address this challenge, we developed polyvinyl alcohol (PVA)‐tannic acid (TA)‐based membranes with improved self‐healing properties and strong mechanical performance. Using a blade coating method and freeze–thaw cycles (−10°C for 1 h, followed by room temperature thawing), the synthesized membranes demonstrated a tensile strength of 8.8 MPa before healing and 7.6 MPa after healing, achieving an 88% healing efficiency. Membrane thickness showed a slight reduction from 465 to 432 μm posthealing. After 3000 bending cycles at a 1 cm radius, the membranes maintained flexibility with no significant changes in water vapor transmission rate (WVTR) (7.66 g/m2·day) or oxygen transmission rate (OTR) (0.13 cm3/m2·day·bar). These results underscore the membranes' suitability for dynamic skin environments, combining robust mechanical properties with excellent self‐healing capabilities. The PVA‐TA membranes present a promising solution for advanced skin bioengineering applications.

Effects of freeze–thaw on the detachment capacity of soils with different textures on the Loess Plateau, China

Soil detachment capacity (Dc) is a crucial indicator for quantifying erosion intensity. However, the combined actions of freeze–thaw and water flow complicate the erosion process, leaving the variation mechanism of Dc under this condition systematically unexplored. This study examined five loess soils from a seasonal freeze–thaw area. The mechanism driving changes in Dc was quantified through freeze–thaw simulation combined with flow scouring tests, and a Dc prediction model was established. The results revealed that the shear strength (τm), cohesion (Coh), and internal friction angle (φ) in silt loam were higher than in sandy loam. After freeze–thaw cycles (FTC), τm, Coh, and φ of the five loess soils decreased by 1.02–1.37, 1.07–9.15, and 0.92–1.05 times, respectively. As FTC increased, τm and Coh gradually stabilized, while φ showed minimal fluctuation, indicating that FTC had a cumulative effect on the deterioration of soil mechanical properties. During FTC, Dc in Wuzhong sandy loam was the largest, being 1.14–3.24 times greater than in other soils, suggesting a significant main effect of soil type on Dc variation, with a contribution rate of 19.27 %. Dc eventually stabilized with increasing, indicating a critical FTC of around 10 for its impact on Dc. Compared to unfrozen soils, Dc increased by 33.69 %–102.40 % under the combined effects of freeze–thaw and water flow, clarifying that FTC aggravated soil instability. Effective stream power was the optimum hydraulic parameter, contributing the most to Dc (45.94 %). FTC (6.41 %) and initial soil moisture content (8.59 %) were less influential, as FTC initially degraded soil properties, and then the combined action with water flow intensified soil damage, causing the role of freeze–thaw factors to be obscured by other variables. A Dc prediction model using a general flow intensity index estimated well Dc, with both R2 and NSE at 0.94. Model performance comparison emphasized the need for validation when extending the application range beyond development conditions. These findings provide new insights into the detachment mechanisms of different textured soils under compound freeze–thaw and hydrodynamic influence in freeze–thaw region.

Gap defect and freeze-thaw cycles effects on mechanical characteristics of concrete-filled steel tube stub columns with experimental and theoretical investigation

As concrete-filled steel tube (CFST) structures become more prevalent in engineering, their durability garners significant attention. Mechanical characteristics of concrete-filled steel tube stub columns under the combined influence of gap defect and freeze-thaw cycles is presented with experimental and theoretical investigation in the paper. Twenty-six concrete-filled steel tube stub columns were designed to study the combined effects on failure mechanisms, axial compression-strain response, strength, and ductility. The experimental results indicate that as the number of freeze-thaw cycles and gap ratio increase, the deformation of the specimen increases and the deformation time advances. The specimen's strength and ductility are decreased by the combined effect of these factors. In the most severe cases, the specimen's overall strength and ductility are reduced by 29.4 % and 44.0 %, respectively. Subsequently, a finite element numerical model is established to parametrically analyze the concrete-filled steel tube stub column. Results show that the degree of restraint in the concrete-filled steel tube significantly influences the reduction in strength and ductility of the specimens. The stronger the restraining effect, the less the degradation of strength and ductility caused by the combined impact of the two factors. Therefore, it is crucial to effectively restrain the concrete within the concrete-filled steel tube to ensure structural safety and durability.

Long-term stability of five atypical antipsychotics (risperidone, olanzapine, paliperidone, clozapine, quetiapine) and the antidepressant mirtazapine in human serum assessed by a validated SPE LC-MS/MS method.

Long-term sample stability of five atypical antipsychoticdrugs risperidone, paliperidone, clozapine, quetiapine and olanzapine and the antidepressant drug mirtazapine in serum was studied by use of a newly developed and validated analytical method based on solid-phase extraction and liquid chromatography-tandem mass spectrometry. Ascorbic acid was used as an antioxidative agent to stabilize olanzapine during storage and sample preparation. We assessed analyte stability on long-term storage in serum samples at 25°C, 5°C, -20°C and -80°C, and during five freeze-thaw cycles. Analytes were stable for 23 days at room temperature except for olanzapine and mirtazapine (17 days). All analytes were stable for at least 30 days at 5°C. All analytes were stable for 270 days at -20°C, except for paliperidone and mirtazapine with 60 days and 180 days, respectively. All analytes were stable for 270 days at -80°C. Furthermore, all analytes were stable for five freeze-thaw cycles. We recommend storage at -80°C when samples drawn for analysis of antipsychotic drugs are stored for more than 60 days, whereas a temperature of -20°C is sufficient for storage less than 60 days.

Spatiotemporal Evolution Analysis of Surface Deformation on the Beihei Highway Based on Multi-Source Remote Sensing Data

Under the interference of climate warming and human engineering activities, the degradation of permafrost causes the frequent occurrence of geological disasters such as uneven foundation settlement and landslides, which brings great challenges to the construction and operational safety of road projects. In this paper, the spatial and temporal evolution of surface deformations along the Beihei Highway was investigated by combining the SBAS-InSAR technique and the surface frost number model after considering the vegetation factor with multi-source remote sensing observation data. After comprehensively considering factors such as climate change, permafrost degradation, anthropogenic disturbance, and vegetation disturbance, the surface uneven settlement and landslide processes were analyzed in conjunction with site surveys and ground data. The results show that the average deformation rate is approximately −16 mm/a over the 22 km section of the study area. The rate of surface deformation on the pavement is related to topography, and the rate of surface subsidence on the pavement is more pronounced in areas with high topographic relief and a sunny aspect. Permafrost along the roads in the study area showed an insignificant degradation trend, and at landslides with large surface deformation, permafrost showed a significant degradation trend. Meteorological monitoring data indicate that the annual minimum mean temperature in the study area is increasing rapidly at a rate of 1.266 °C/10a during the last 40 years. The occurrence of landslides is associated with precipitation and freeze–thaw cycles. There are interactions between permafrost degradation, landslides, and vegetation degradation, and permafrost and vegetation are important influences on uneven surface settlement. Focusing on the spatial and temporal evolution process of surface deformation in the permafrost zone can help to deeply understand the mechanism of climate change impact on road hazards in the permafrost zone.

Investigation of Adhesion and Stripping Properties in Asphalt–Aggregate Systems: Impact of NaCl Solubility and Freeze–Thaw Cycles

Investigation of Adhesion and Stripping Properties in Asphalt–Aggregate Systems: Impact of NaCl Solubility and Freeze–Thaw Cycles

Strength Analysis and Microstructural Characterization of Calcined Red Mud Based-Geopolymer Concrete Modified with Slag and Phosphogypsum

This research aims to comprehensively investigate the combined use of calcined red mud (RM), calcium sulfate dihydrate (CSD), and ground granulated blast furnace slag (GGBFS) in geopolymer concrete (GC), demonstrating how their optimized proportions improve GC's fresh, mechanical, durability, and microstructural properties. This study investigated the influence of partially replacing calcined red mud (RM) with GGBFS and Phosphogypsum or CSD in GC. The test program included tests on the fresh, mechanical, and durability properties of these blends, including slump value, compressive strength, ultrasonic pulse velocity, water absorption and porosity, rapid chloride penetration, electrical resistivity, mass loss due to freeze-thaw cycles, and resistance to sulfate attack. Material characterization of the GC blends was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential thermogravimetric analysis (DTG). One-way ANOVA analysis was also used to examine the significance of variation between the results due to the replacement of calcined RM with GGBFS and CSD. The results showed that the mix R40-G45-C15, with 40% calcined red mud, 45% GGBFS, and 15% CSD, demonstrated the highest density at 2401 kg/m³, 15.93% greater than the R70-G15-C15 mix, and achieved a compressive strength 73.40% higher at 28 days. Additionally, R40-G45-C15 showed superior durability, with water absorption and porosity reductions of 87.42% and 83.86%, an 85.78% reduction in charge passed at 7 days, and a 40.94% lower mass loss from freeze-thaw cycles compared to R70-G15-C15. SEM analysis confirmed the formation of and gels in the blends, contributing to improved density and strength. XRD tests indicated the nominated peaks of calcite, quartz, and portlandite in the blends, with increased portlandite intensity due to higher RM content. These results indicate that partially substituting the calcined RM with CSD and GGBFS in GC could be a viable alternative option, offering potential contributions to sustainable construction with improved structural performances.

Novel high-strength, recyclable, microbial-resistant, and freeze-thaw dual topological network hydrogel cooling media

The demand for multifunctional hydrogels, offering high mechanical strength, efficient cooling, and antimicrobial properties, is growing in food preservation. Here, a dual-network (DN) hydrogel PM@Cur, which includes curcumin, is fabricated through chemical crosslinking and hydrogen bonding interactions. The resulting hydrogels can withstand more than five freeze-thaw cycles at −80 °C, and resist brittleness after liquid nitrogen treatment. PM@Cur also exhibits surface hydrophobicity (contact angle >90°) for both water and organic solvents. These properties meet the mechanical, anti-fouling, and recyclable demands for hydrogel coolants. The antimicrobial assays in vitro confirmed that the inclusion of curcumin provided the PM@Cur with photodynamic antimicrobial capacity. Finally, the prepared PM@Cur hydrogel ice cubes have been confirmed to exhibit better anti-melting properties than traditional ice cubes, thus enabling the preservation of strawberries and shrimp. This study presents an innovative solution for producing advanced functional integrated hydrogels, offering a promising and safer option for food coolants.\\.

Effect of anionic polyacrylamide amendment on the climatic durability of solidified waste rock fine

In order to improve the climatic durability of solidified waste rock fine (WRF), anionic polyacrylamide (APAM) was innovatively introduced to amend solidified WRF in this study. The effects of APAM content, freeze-thaw (F-T), and wet-dry (W-D) cycles on the mechanical behaviors of solidified WRF were explored. After that, zeta potential, fourier transform infrared (FTIR) spectroscopy, and scanning electron microscope (SEM) tests were initiated to understand the behavioral mechanisms of APAM. The results show that APAM can significantly improve the mechanical properties and durability of solidified WRF, and there exist a threshold content of APAM (0.3%~0.8% in this study), beyond which the strength will decrease. The microscopic test shows that the bridging effect and the filming effect induced by APAM are considered to be the two decisive factors affecting the mechanical behavior of S-WRF. On the one hand, the linear APAM long chain enables the cohesion between particles to be stronger through ion bridging, on the other hand, the long chains cross-link with each other to form a network interwoven inside the structure, thus playing a microfabric reinforcement role and enhancing the crack resistance of the solidified matrix. In addition, life cycle assessment (LCA) further confirmed the advantages of using industrial by-products combined with APAM to amend solidified-WRF. These results provide a theoretical basis for using APAM as trace additives to mitigate climatic durability-related issues.

Investigation of coupled thermo-hydro-mechanical processes on soil slopes in seasonally frozen regions

Freeze-thaw cycles significantly affect slope stability in seasonally frozen regions, posing serious threats to the functionality and safety of infrastructure. This study developed a coupled thermo-hydro-mechanical (THM) model of frozen soils that accounts for water migration, water-ice phase change, groundwater recharge, frost heave and thaw settlement deformation. The accuracy and reliability of the model was verified based on soil column test results. The change of temperature, water content, and displacement of a soil slope during freeze-thaw process was investigated. The results show that the water-heat transfer and deformation mainly occur in the shallow soils of the slope with changes in air temperature. The temperature fluctuations at the shoulder and face of the slope are more pronounced than those at the toe and crest of the slope. Water migration from the unfrozen zone to the freezing front due to the temperature gradient results in an increase in water content in the frozen zone. The slope shoulder exhibits the largest temperature fluctuations, leading to increased water migration and greater deformation. The rising groundwater table increases the total water content at the slope toe and base, exacerbating the frost heave and thaw settlement deformation, and reasonable groundwater table control intervals are provided. This study elucidates the thermo-hydro-mechanical coupling process and deformation mechanism of seasonally frozen soil slopes, and summarizes the failure modes, which provides a reference for the stability assessment and disaster prevention of soil slopes in cold regions.

The axial compression mechanical performance of CFRP-confined fully replaced nonnatural coal gangue aggregate columns after freeze[sbnd]thaw cycles

With the continuous mining of coal worldwide, the accumulation of coal gangue, a byproduct of coal production, has increasingly posed severe environmental challenges. To mitigate the environmental pollution caused by coal gangue, this paper proposes the use of processed coal gangue as a replacement for coarse aggregates in concrete. Additionally, carbon fiber-reinforced polymers (CFRP) are employed to confine these square concrete columns, with the aim of expanding the application of nonnatural coal gangue concrete in freezethaw environments. Taking the number of CFRP layers, number of freezethaw cycles, and concrete strength grade as variables, a total of 54 samples were designed. Experimental and theoretical analyses were conducted to investigate the mechanical behavior of CFRP-confined fully replaced nonnatural coal gangue aggregate (FNCGA) columns. The specific conclusions are as follows: (1) Under a freezethaw environment, the stressstrain behavior of the CFRP-confined FNCGA columns undergoes three stages: an elastic ascending stage, a plastic descending stage, and a plastic ascending stage. (2) When the number of freezethaw cycles increases from 100 to 300, the Poisson's ratio of the elastic stage of the sample exhibiting an upward trend. (3) For the three-layer CFRP confined sample, the volumetric strain is positive (in compression), and the bearing capacity of the sample exceeds that of the unconfined concrete by approximately 10%. (4) Compared with existing models and experimental results, the bearing capacity and stressstrain model proposed in this study have greater accuracy, enabling better simulation of the mechanical performance of CFRP-confined FNCGA columns.

Effect of ionic soil stabilizer on the properties of lime and fly ash stabilized iron tailings as pavement base

The large use of iron tailings is in urgent need given its huge emissions and pollution to environment. This paper sought to utilize a large quantity of iron tailings with fly ash and lime to prepare road base materials, and use ionic soil stabilizer (ISS) to improve its pavement performance. Different dosage ISS content of was added to the lime-fly ash stabilized iron tailing materials to improve the mechanical strength, frost resistance properties and decrease the dry shrinkage. The results show that the UCS of the specimen with 0.67 % ISS represents enhancement of 195.5 % compared to the control sample at 7 d. After undergoing 15 freeze-thaw cycles, the residual UCS ratio remains at 76.6 %, whereas the control sample exhibits signs of failure. Additionally, the dry shrinkage strain at 30 d was 66.3 % lower than that of the control sample without ISS. The mechanisms underlie that the adsorbed ISS onto iron tailings can reduce the repulsion between total fine particles by lowering the general zeta potential, thus decreasing the porosity of the road base materials. Besides, the ISS can hinder the phase transformation from ettringite (AFt) to monosulfoaluminate (AFm) and its hydrophobic groups can prevent the infiltration and migration of water. The findings reveal that ISS significantly enhances the pavement performance of the stabilized iron tailings, thereby presenting a novel approach for the incorporation of iron tailings in road construction endeavors.

Tailoring structural and mechanical properties of konjac glucomannan/curdlan composite hydrogels by freeze-thaw treatment

To improve the gelling properties of konjac glucomannan/curdlan (KGM/CUD) composite hydrogels, KGM/CUD composite hydrogels were treated by freeze-thawing. Herein, we focus on the effects of freeze-thaw cycles, freezing temperature, and freezing time on the structural and mechanical properties of KGM/CUD composite hydrogels. SEM and SAXS results showed that ice crystals generated by freezing extruded the molecular chains and increased the cross-linking density between molecular chains, which resulted in a denser gel microstructure. Among them, the freeze-thaw treatment at −20 °C for 12 h can effectively reduce the correlation length (ξ). According to mechanical testing, freeze-thawed gels for 48 h reached 408-, 826-, and 840-fold of the hardness, gumminess and chewiness of unfrozen, respectively. After freeze-thaw treatment, the energy storage modulus (G') of the gel increased to 9872 Pa, the residual mass after heating was up to 27.9 %, the water holding capacity (WHC) was reduced to 80.85 %. In addition, low-field nuclear magnetic resonance results confirmed that the freeze-thaw treatment promoted the formation of ice crystals from water molecules, which realized the transition of the water state, thus reducing the water mobility of the gel. This study provides a facile and efficient strategy for designing hydrogels products with exceptional texture and sensory characteristics.

Consolidation behavior and modified model of Qinghai-Tibetan clay subjected to freeze-thaw cycles

Consolidation behavior and modified model of Qinghai-Tibetan clay subjected to freeze-thaw cycles

Evidence for stability of cardiac troponin T concentrations measured with a high sensitivity TnT test in serum and lithium heparin plasma after six-year storage at-80 °C and multiple freeze-thaw cycles.

As high-sensitivity cardiac troponin T (hs-cTnT) is making the transition from diagnostic to prognostic use, a long-term stability study of 5th generation hs-cTnT according to EFLM CRESS recommendations was set up for investigation of frozen clinical specimens (two matrices). Study samples collected in serum tubes and lithium heparin tubes with gel from patients admitted for suspected minor myocardial damage were measured directly after completion of the study (0 years), and after 3-year and 6-year storage at-80 °C, and recovery of hs-cTnT concentrations after long-term storage (%hs-cTnT concentration compared to 0-year) was calculated. Hs-cTnT changes were also compared to decisive delta changes, such as the ones proposed in the ESC NSTEMI 0 h/1 h algorithm (<3 or >5 ng/L for ruling out and ruling in suspected NSTEMI patients). Eighty-six patients were included in the study, whereof 28 both lithium heparin plasma and serum samples were collected simultaneously, in others only serum (n=30) or plasma (n=28). Multiple aliquots per patient were made, so that 479 serum and 473 plasma samples were available for analysis. Across the overall hs-cTnT measuring range, median recovery after 6 years was 105.4 % and 106.2 % for serum and plasma, respectively. Based on these decisive delta changes, serum showed consistent results upon long term storage (max 0.8 % of samples above delta threshold of >5 ng/L) as compared to heparin plasma (up to 19.2 % of samples above threshold). Over 6 years of storage at-80 °C, recovery of hs-cTnT in serum and heparin plasma was similar and within common lot-to-lot variation. Yet, when evaluating absolute delta increments around hs-cTnT clinical decision points, long-term stored sera displayed better clinical performance compared to heparin plasma samples.

Study on Performance Deterioration of Asphalt and Asphalt Mixtures Containing Mafilon under Internal Salt Freeze-Thaw Cycles

The purpose of this work is to determine the implications of internal salt freeze-thaw cycles on performance deterioration to asphalt and asphalt mixtures containing Mafilon (MFL). The deterioration to different numbers of F-TCs and different MFL contents on asphalt properties and mechanism were investigated by physical properties tests and microcosmic tests. Then the damages of road performance indexes of asphalt mixtures containing different MFL contents were studied by road performance tests. The experimental results show that asphalt containing MFL after F-TCs has a remarkable decline in ductility and penetration, while growth in softening point. Internal salt F-TCs are most damaging to the cryogenic properties of asphalt. Chemical reactions and salt aging effects occur in salt F-TCs, raising the glass transition temperature of asphalt. Road performance tests indicate the deterioration of internal salt F-TCs to high temperature stability and water stability is the most pronounced, with 29.18% and 21.78% reduction, respectively.

Investigation on mesostructural characteristics of different pore types within asphalt mixtures under freeze–thaw cycles using CT scanning technology

The distribution of water within asphalt pavement contributes to water-induced damage, with pores serving as the primary conduit for water infiltration. However, understanding the microstructural changes in various pore types amid extreme water conditions remains limited. This study focuses on three type asphalt mixtures which common used in the surface-layer of asphalt pavement and utilises Computed Tomography (CT) technology to categorise internal pores in asphalt mixtures into isolated, semi-connected, connected, and open pores. Examining the impact of freeze–thaw cycles, the research quantifies the connectivity and evolution of each pore type in asphalt concrete. The findings reveal that after freeze–thaw cycles, small isolated pores emerge while some larger isolated pores amalgamate with open pores, leading to a reduction in isolated pores. Volumetric alterations predominantly occur in open pores, where semi-connected pores either expand autonomously or merge with existing connected pores. Overall, the pore network enlarges, yet its complexity remains relatively stable. Notably, microstructural parameters of isolated and semi-connected pores exhibit a weaker correlation compared to total and open pores, with the most robust correlation found between average coordination number, volume, and other microstructural characteristics. Among the pore types, open pores demonstrate the highest sensitivity to freeze–thaw cycles. Substantial variations in correlation coefficients and freeze–thaw sensitivity are observed across different pore types and within the same pore type with distinct microstructural parameters. Thus, a comprehensive analysis encompassing multiple microstructural parameters across diverse pore types is imperative for a thorough evaluation of pore micro characteristics.

Shear behavior of cold region clay-concrete interface under temperature-controlled direct shear tests

The shear properties of the permafrost-structure interface play a crucial role in analyzing the performance of engineering structures in cold regions. Direct shear tests were carried out on the permafrost-concrete structural interface by means of self-improved and optimized temperature-controlled direct shear apparatus to investigate the effects of temperature, moisture content and freeze-thaw cycles. Test results were used to establish a shear characteristic model under coupled influence of temperature and humidity. Preparation of specimens consisting of precast C30 concrete blocks and soil samples taken from borehole cores of the pile foundation of the Middle Bridge No. 3 on the road from Sai Township to Qiuluo Village, Sakya County, Tibet, China, and were treated to different effective confining pressure (σn = 300 kPa, 400 kPa, 500 kPa and 600 kPa), different temperatures (T = −20 °C, −15 °C, −5 °C, 0 °C, 5 °C, 15 °C, and 20 °C), different moisture contents (ω = 5 %, 10 %, 15 %, and 20 %), and different numbers of freeze-thaw cycles (N = 0, 1, 3, 5, 7and11) from −15 °C to 15 °C, test results are given and analyzed. The peak shear stress (τp) is significantly higher than the residual stress (τr) at negative temperature, τp is greater than 1.5 times to 3.2 times of τr. τp is greatly affected by temperature changes, τp under negative temperature is 17 % higher than that under positive temperature, because the water in the soil freezes at negative temperatures, forming a concrete-ice-soil bond interface, which increases the peak strength of the interface. While τr is insensitive to temperature changes. At negative temperatures, the cohesion (c') changes less with increasing water content (ω), and the effect of ω on the external friction angle (φ′) is more significant. At positive temperature, the cohesion decreases with increasing ω, and the effect of ω on the external friction angle is not significant. When N < 5, the cohesion increases with the increase of N; when N = 5, c' reaches the maximum value; when N > 5, c' decreases with the increase of N. Moreover, regardless of the type of shear behavior, the first five freeze-thaw cycles have the greatest impact on the external friction angle. Compared with the sample that has not experienced freeze-thaw cycles, when N = 5, the total decrease in the external friction angle of the sample is 25.6 %.