Unidirectional Freezing Research Articles

A unified model for frost wedging in an open fissure under unidirectional freezing

The propagation of joints and fissures, included by the frost heaving pressure arising from the water-ice phase transition is considered as frost wedging. This process is widely observed and plays a crucial role in weathering of jointed hard rocks in cold regions. Despite some fundamental results achieved in former experimental studies, a unified theoretical model is still absent, hindering a thorough understanding of this process. To further explore the mechanism of frost wedging during the freezing process, this paper firstly carries out a frost heave test on a rock block bearing a single open fissure. The results indicate that the evolution of frost heaving pressure in the fissure can be divided into four stages: sealing of the open fissure by ice wedge, ice wedge slipping, crack propagation, as well as stabilization of the ice-filled fissure. Based on the laboratory test results, a unified model for the frost heaving pressure in a single open fissure is established, which comprehensively takes into account the mechanical interaction between ice, water and rock. The model is validated by the test result, and it can reasonably describe the formation of the sealing conditions and the process of crack propagation. Fracture of the ice-rock interface near the free surface increases the likelihood of ice wedge slip, while frost wedging mainly damages geological bodies during crack propagation.

Bidirectional anisotropic bacterial cellulose/polyvinyl alcohol/MXene aerogel phase change composites for photothermal conversion enhancement

The issues of inherent low thermal conductivity, slow heat transport rate and easy leakage are critical challenges for accelerating solar-thermal energy harvesting and storage for organic solid-liquid phase change materials (PCMs). Aerogel carriers with thermal conductivity enhancement based on ice temple methods show favorable potential for PCMs solar thermal applications. Comparing with disordered and unidirectional freezing, bidirectional freezing can assemble efficiently in multiple dimensions and result in long-range ordered structures. In this paper, bacterial cellulose/polyvinyl alcohol/MXene aerogels were constructed by bidirectional freezing. The anisotropic PCMs composites were from vacuum impregnation PEG into aerogel networks. By controlling crystallization and growth of ice crystals through the dual temperature gradients, the PCMs composites obtained enhanced heat transfer efficiency in horizontal and vertical directions. Bidirectional aligned PCMs with PDMS wedge angle of 0° and 20° exhibit high thermal conductivity of 0.716 W m−1 K−1 and 0.768 W m−1 K−1, which were 184% higher than that of PEG, and photothermal conversion efficiency of 55.17% and 76.91%. Remarkably, the PCMs composites with a 20° PDMS wedge angle also exhibited a high PCM loading capacity (96.3%) and a high enthalpy (157.7 J/g). The results show that bidirectional anisotropic PCMs composites have excellent overall performance and are expected to improve solar thermal application.

High-aligned oppositely-charged nanocellulose/MXene aerogel membranes through synergy of directional freeze-casting and structural densification for osmotic-energy harvesting

Optimization of ion-transport paths can considerably improve ion-transport capabilities in charged nanochannels. Thus, the assembly of high-charge-density one- and two-dimensional nanomaterials into aligned nanochannels is necessary for high-performance osmotic-energy harvesting. Herein, we prepared cellulose/MXene aerogel membranes with opposite charges and aligned nanochannels via chemical modification on algal cellulose nanofibers and MXene nanosheets, unidirectional freeze casting, and structural densification to considerably enhance the ionic conductivity in low-concentration solutions (maximum conductivity of 2.88 × 10−3 S cm−1). In particular, the aligned membrane had an output power density of 2.97 and 4.89 times higher than membranes used for suction filtration and isotropic nanochannels, respectively, demonstrating the necessity for nanostructure control. In addition, due to the photothermal effect of MXene, the positively–negatively (P–N) charged unit produced a maximum output power density of 8.87 W m−2 under a concentration gradient of artificial seawater and river water and simulated sunlight. Moreover, the unit maintained 90.4% of its original output capacity after 168 h of operation. As a proof of concept, we created nine series of P–N units and successfully powered an electronic calculator with an output voltage of 1.85 V. This study reveals improvements in developing renewable materials with an aligned nanostructure for high-performance osmotic-energy conversion.

Numerical Study of Pore Water Pressure in Frozen Soils during Moisture Migration

Frost heaving in soils is a primary cause of engineering failures in cold regions. Although extensive experimental and numerical research has focused on the deformation caused by frost heaving, there is a notable lack of numerical investigations into the critical underlying factor: pore water pressure. This study aimed to experimentally determine changes in soil water content over time at various depths during unidirectional freezing and to model this process using a coupled hydrothermal approach. The agreement between experimental water content outcomes and numerical predictions validates the numerical method’s applicability. Furthermore, by applying the Gibbs free energy equation, we derived a novel equation for calculating the pore water pressure in saturated frozen soil. Utilizing this equation, we developed a numerical model to simulate pore water pressure and water movement in frozen soil, accounting for scenarios with and without ice lens formation and quantifying unfrozen water migration from unfrozen to frozen zones over time. Our findings reveal that pore water pressure decreases as freezing depth increases, reaching near zero at the freezing front. Notably, the presence of an ice lens significantly amplifies pore water pressure—approximately tenfold—compared to scenarios without an ice lens, aligning with existing experimental data. The model also indicates that the cold-end temperature sets the maximum pore water pressure value in freezing soil, with superior performance to Konrad’s model at lower temperatures in the absence of ice lenses. Additionally, as freezing progresses, the rate of water flow from the unfrozen region to the freezing fringe exhibits a fluctuating decline. This study successfully establishes a numerical model for pore water pressure and water flow in frozen soil, confirms its validity through experimental comparison, and introduces an improved formula for pore water pressure calculation, offering a more accurate reflection of the real-world phenomena than previous formulations.

Simulation of Temperature Field in Railway Embankment Filling in Seasonal Frozen Areas

In order to examine the temperature field changes of railway roadbed in seasonal frozen areas under different filling heights, a typical cross-sectional model of Chagan Lake Station railway was established using the finite element numerical simulation software ANSYS. The temperature parameters of the roadbed were calculated based on the atmospheric temperature of local meteorological data, and the temperature fitting curve was used as the temperature boundary condition. Under different filling quantities, the temperature field of the roadbed was simulated for a freeze-thaw cycle, and the temperature curve changes were analyzed. The results indicate that as the filling height increases, the freezing depth line also increases accordingly. When the filling height is 2.5m, the maximum freezing depth at the roadbed is 1.7m. In a freeze-thaw cycle, the freezing process of soil develops from top to bottom, and the melting process develops in two directions: from top to bottom and from a certain depth of soil upwards, with the characteristics of "unidirectional freezing and bidirectional melting". The freezing period starts from early December of each year to the end of March of the following year, and completely melts until the end of April. Melting develops faster than freezing.

Effects of Freeze-Drying Processes on the Acoustic Absorption Performance of Sustainable Cellulose Nanocrystal Aerogels.

Cellulose aerogels have great prospects for noise reduction applications due to their sustainable value and superior 3D interconnected porous structures. The drying principle is a crucial factor in the preparation process for developing high-performance aerogels, particularly with respect to achieving high acoustic absorption properties. In this study, multifunctional cellulose nanocrystal (CNC) aerogels were conveniently prepared using two distinct freeze-drying principles: refrigerator conventional freezing (RCF) and liquid nitrogen unidirectional freezing (LnUF). The results indicate that the rapid RCF process resulted in a denser CNC aerogel structure with disordered larger pores, causing a stronger compressive performance (Young's modulus of 40 kPa). On the contrary, the LnUF process constructed ordered structures of CNC aerogels with a lower bulk density (0.03 g/cm3) and smaller apertures, resulting in better thermal stability, higher diffuse reflection across visible light, and especially increased acoustic absorption performance at low-mid frequencies (600-3000 Hz). Moreover, the dissipation mechanism of sound energy in the fabricated CNC aerogels is predicted by a designed porous media model. This work not only paves the way for optimizing the performance of aerogels through structure control, but also provides a new perspective for developing sustainable and efficient acoustic absorptive materials for a wide range of applications.

Tuning the properties of all natural polymeric scaffolds for tendon repair with cellulose microfibers

Rotator cuff injuries affect a large percentage of the population worldwide. Surgical repair has rates of failure of up to 70%, and existing materials used in the reinforcement of injuries often lack appropriate mechanical properties and biodegradability. There is a clinical need for tendon biomaterials that enable cell attachment and proliferation, while supporting mechanically the injury site. In this work, we develop a novel all-natural polymeric scaffold for applications in the supraspinatus tendon of the shoulder. The unidirectional freezing technique is applied to a chitosan-gelatine matrix containing varying cellulose concentrations, followed by crosslinking with genipin. The viability of the technique using a custom 3D printed mould is evaluated. The scaffolds' morphology and mechanical properties are extensively characterized: the ultimate tensile strength of the material with 20% cellulose was found to increase 6-fold compared to scaffolds without cellulose; significant effects on the microstructure of the scaffold were evidenced via scanning electron microscopy. Furthermore, the biocompatibility of the materials was characterized with both porcine tendon derived cells and normal human dermal fibroblasts. All scaffolds are highly biocompatible, the incorporation of cellulose results in higher cell metabolic activity values and density of cells on the surface of the material. Scaffolds containing 20% cellulose fibers were found to possess the optimal biomechanical properties for applications in rotator cuff tendon repair.

Low–temperature superelastic, anisotropic, silane-crosslinked sodium alginate aerogel for thermal insulation

Bio-aerogels have attracted much attention owing to their remarkable properties, but their brittle and poor elasticity has limited their further applications. Here, we propose a strategy of in-situ silanization crosslinking combined with unidirectional freeze casting (SUFC) to prepare superelastic sodium alginate (SA) aerogels. The resulting aerogel was ultra-light (0.048 g/cm3), high porosity (96.86 %), and self-extinguishing from fire. Aerogels exhibited anisotropic properties, such as low-temperature elasticity (500 g compression at −70 °C 10-cycle, 99.6 % recovery), exceptional fatigue resistance (100-cycle at 50 % strain), and excellent thermal insulation (0.0696 W·m−1·K−1). Thus, the SUFC strategy provides considerable freedom for constructing multi-material, lamellar/honeycomb structured alginate-based aerogels, which pave the way to thermal insulation development at low temperatures.

Self-weighting of the overlying soil horizon catalyzed by freeze–thaw cycles leads to silt particle enrichment in the soil profile

Freeze–thaw cycles, as a strong weathering effect, can cause changes in the soil particle size and content, which can affect changes in the geological environment of the soil. A zone of silt enrichment was found at certain depths in the soil profile of the study regions. To understand and analyze the causes of this substratum phenomenon, a unidirectional freeze–thaw test on soil under static loading was designed and simulated in the laboratory in accordance with actual field conditions to investigate the process of changes in the physical index parameters after freeze–thaw cycles when the soil is under pressure. The changes in the parameters in the upper, middle and lower parts of the test soil column after 6, 10, 20, 40 and 50 freeze–thaw cycles were measured for the three regions. The test results show that the mechanical composition of the soil changes significantly after freeze–thaw cycles, the sand content decreases significantly, the clay and silt contents increase, and the particle frequency curve moves in the direction of particle size reduction. The freeze–thaw process is always accompanied by the fragmentation and aggregation of soil particles, and the fractal dimension is used to describe the distribution width of the soil particle population and to compare the clay content. The larger the fractal dimension is, the higher the clay content in the sample. Kvar(Coefficient of granulometric variation) decreases as the number of freeze–thaw cycles increases, the soil particles change from high-intensity to low-intensity variation, and the soil particles gradually transition to silt particles. The occurrence of silt-rich zones is the result of a combination of freeze–thaw action and static loading. This study can provide a new reference and vision for the freeze–thaw evolution process and tectonic development of soil in middle- and high-latitude cold regions.

Influence of anionic polyacrylamide on the freeze–thaw resistance of silty clay

Freeze–thaw (FT) alternation can severely affect the properties of fine–grained soils, often leading to the failure of foundation backfill projects, such as open canals and roads in cold regions. To address these problems, a water–soluble anionic polyacrylamide (APAM) was used to improve the properties of fine–grained soils, particularly silty clay. This study aims to analyze the effects of the APAM polymer on the physico–mechanical and microstructural properties of silty clay under both unfrozen and FT cycles. For this purpose, different addition dosages and FT cycle numbers were determined, and then a series of zeta potential, thermal conductivity, permeability, triaxial compression, and scanning electron microscopy (SEM) tests were conducted on the soil samples. Additionally, a unidirectional freezing test was constructed to investigate the coupled thermo–hydro–mechanical processes of APAM–treated soil samples under subzero temperature conditions. The results showed that the addition of the APAM polymer significantly enhanced the macroscopic engineering properties and microstructural characteristics of silty clay. This improvement was attributed to the charge neutralization, adsorption bridging effect, and hydrophobic interaction provided by the APAM polymer. However, all the soil samples showed a significant deterioration in their engineering properties during FT cycles, especially after the third FT cycle. It was notable that APAM–treated soil samples were superior to the untreated sample in terms of FT resistance. During the unidirectional freezing process, the pore water migrated from the unfrozen zone towards the freezing front due to the temperature gradient. The treated sample's pore water migration volume was considerably lower than that of the untreated sample, resulting in a 55.25% reduction in total frost heave when the APAM dosage was 0.30%. The findings of this paper may be utilized to mitigate the risk of frost damage to foundation backfill projects in cold regions, as well as to get a better understanding of the stabilization mechanism of the eco–friendly APAM polymer.

Unidirectional Freezing of Polymer Solution Droplets.

Ice templating provides a means of generating textures with a well-defined topography. Recent applications involve the freezing of water droplets, with or without colloids, on flat or textured surfaces. An interesting feature of water droplets freezing on a substrate is the formation of a pointy tip at a constant angle, regardless of the substrate temperature, surface energy, or droplet volume. Here, by adding the polymer to water, we demonstrate how to manipulate and even prevent the formation of such an icy tip. We find that the sharpness of the tip decreases with increasing polymer concentration until completely disappearing above the overlap concentration, while the total freezing time increases concomitantly. Building on these observations, we combined simple geometrical arguments with heat flux measurements to model and connect the spatial and temporal evolution of polymer droplets under unidirectional freezing. Together our results provide new ways to control the shape of frozen droplets for ice templating or microstructure fabrication, with applications in tissue engineering, separation membranes, and soft robotics.

High-performance flexible reduced graphene oxide/polyimide nanocomposite aerogels fabricated by double crosslinking strategy for piezoresistive sensor application

Flexible conductive polyimide aerogels used for piezoresistive pressure sensors in harsh environments are often limited by brittleness, structural collapse, low elastic recovery, low sensitivity, and narrow pressure detection range. Herein, we report a simple and green method of ice-templating unidirectional solidification combined with freeze-drying and thermal imidization to obtain a flexible reduced graphene oxide/polyimide (rGO/PI) nanocomposite aerogels with a double crosslinked structure, which achieve a significant transformation of PI aerogels from brittleness to high flexibility. The strong layered structure and dense interlaminar porous network are established by the covalent crosslinking of 1,3,5-triaminophenoxybenzene (TAB) and the hydrogen bonding crosslinking of graphene oxide (GO), imparting the double crosslinked rGO/PI aerogels with unique “porous honeycomb” structure and excellent mechanical properties. Due to the synergistic effect of TAB, rGO, PI, and unidirectional freezing process, the double crosslinked rGO/PI nanocomposite aerogel shows low density (25 mg/cm3), high compression cycle stability (3000 cycles), wide pressure detection range (0–85.1 kPa), extremely short response time (about 129 ms) and excellent environmental resistance (maintaining high structural stability and pressure response even at high temperatures of 180 °C and low temperatures of −50 °C), suitable for detecting various motion signals. It is proved that the elastic double crosslinked rGO/PI nanocomposite aerogels have potential applications serving as candidate materials for piezoresistive sensors and wearable electronic protective equipment in the fields of national defense, military industry, aerospace, and other fields in extreme environments.

Rationally designed conductive wood with mechanoresponsive electrical resistance

Porous cellular foams, combining lightweight, high strength, and compressibility, hold great promise in a wide range of advanced applications. Here, the native structure of pine wood was modified by in-situ lignin sulfonation and unidirectional freezing, resulting in an alveolate structure inside the wood cell wall with arrays of sub-100 nm channels. The obtained wood foam exhibited highly enhanced permeability while retaining the native cellular arrangement and high lignin and hemicellulose content. Such engineered cellular foam contributed to superior mechanical performance with compressive strength of 9 MPa and Young’s modulus of 344 MPa in the longitudinal direction. The high porosity allowed homogeneous infiltration of conductive polymer PEDOT:PSS inside the wood cell wall. The resulting composite exhibited high conductivity, sponge-like compressibility and the ability to modulate electrical resistance in a reversible manner in the radial direction. This rationally designed conductive wood demonstrated potential in durable and ultrasensitive pressure-responsive devices and strain sensors.

Dual cross-linked and vertically oriented MXene/polyvinyl alcohol aerogel for ultrabroadband electromagnetic interference shielding and thermal camouflage

Lightweight and porous conductive aerogels have demonstrated great potential in electromagnetic interference (EMI) shielding and thermal camouflage, while the poor mechanical properties and structural stability usually limit their applications. Herein, vertically oriented and physically/chemically dual cross-linked Ti3C2TX MXene/polyvinyl alcohol (PVA) composite aerogel is prepared by ice-templated unidirectional freezing process and subsequent glutaraldehyde (GA) treatment. GA induced covalent crosslinking leads to the significantly enhanced structural stability and mechanical strength of the resultant MXene/PVA composite aerogels, which also endows them with desirable flame retardancy. The honeycomb-like structure of the composite aerogel contributes to its good anisotropic absorption-dominated EMI shielding performance over an ultrabroadband frequency range (8.2–40 GHz) with a low MXene content of 3.81 vol%. Furthermore, the excellent thermal insulation properties and low infrared emissivity of the highly oriented arranged MXene sheets bring the composite aerogel promising applications in thermal camouflage. Therefore, the lightweight and robust MXene/PVA composite aerogel demonstrates great potential in multi-scenario applications as a high-performance multifunctional EMI shielding material.

Cyclic freeze–thaw induced stiffness anisotropy of sandy silt under all-round and unidirectional freezing modes

The stiffness anisotropy of soil is a critical factor that influences the deformation characteristics of soil in landform evolution, geological disaster mitigation and engineering applications. However, the effects of freeze–thaw cycles on the stiffness anisotropy of soil have not been clearly understood. In this study, a new thermal boundary-controlled triaxial testing system equipped with bender elements is developed to investigate the effects of cyclic freeze–thaw on the stiffness of a sandy silt under both unidirectional and all-round freezing modes. It is revealed that under all-round freeze–thaw cycles, the shear wave velocity in the horizontal and vertical planes undergoes a continuous increase of 14% and 8%, respectively. In contrast, unidirectional freeze–thaw leads to a non-monotonic evolution of shear wave velocity, eventually resulting in a 3% reduction in the horizontal plane and a 16% reduction in the vertical plane after 10 freeze–thaw cycles. The increase in shear stiffness anisotropy of the sandy silt after freeze–thaw cycles is more significant in the unidirectional freeze–thaw condition (from 1.11 to 1.49) compared with the all-round freeze–thaw condition (from 1.13 to 1.19). This study illustrates the significance of unidirectional freeze–thaw in the evolution of mechanical anisotropy of soils in cold regions.

Biomimetic cryogel promotes the repair of osteoporotic bone defects through altering the ROS niche via down-regulating the ROMO1

Osteoporosis is a systemic bone disease that is prone to fractures due to decreased bone density and bone quality, and delayed union or nonunion often occurs in osteoporotic fractures. Therefore, it is particularly important to develop tissue engineering materials to promote osteoporotic fracture healing. In this study, a series of biomimetic cryogels prepared from the decellularized extracellular matrix (dECM), methacrylate gelatin (GelMA), and carboxymethyl chitosan (CMCS) via unidirectional freezing, photo- and genipin crosslinking were applied for the regeneration of osteoporotic fractures. Specifically, dECM extracted from normal or osteoporotic rats was applied for the preparation of the cryogels, named as GC-Normal dECM or GC-OVX dECM, respectively. It was verified that the GC-Normal dECM demonstrated superior performance in promoting the proliferation of BMSCs isolated from osteoporotic rats (OVX-BMSCs), and the differentiation of OVX-BMSCs into osteoblasts both in vitro and in vivo. RNA sequencing and further verifications confirmed that GC-Normal dECM cryogel could scavenge the intracellular reactive oxygen species (ROS) in OVX-BMSCs to accelerate the regeneration of osteoporotic fracture by down-regulating the reactive oxygen species modulator 1 (Romo1). The results indicated that by regulating the ROS niche of OVX-BMSCs, biomimetic the GC-Normal dECM cryogel was expected to be a clinical candidate for repairing osteoporotic bone defects.

Preparation of robust and light‐weight anisotropic polyimide/graphene composite aerogels for strain sensors

AbstractThis study reports the fabrication of a serious of anisotropic composite aerogels comprising polyimide and graphene (PI/G) through a simple and eco‐friendly technique. Poly(amic acid) ammonium salt/graphene dispersion, which was produced through the mixture of poly(amic acid), graphene aqueous dispersion, triethylamine, and water, was utilized in the process of creating PI/G composite aerogels employing unidirectional freezing, freeze‐drying, and thermal imidization. The PI/G aerogels displayed anisotropic mechanical properties, thermal insulation, and electrical conductivity. The PI/G aerogels with an anisotropic microstructure demonstrated notable rigidity and a high compressive modulus (52.7 MPa) along the axial direction, while displaying favorable flexibility and a low modulus (18.2 MPa) along the radial direction. Furthermore, the PI/G aerogel exhibited anisotropic thermal conductivity (axial: 64 mW m−1 K−1; radical: 55 mW m−1 K−1). These properties enable the PI/G aerogel to have a wider range of potential applications, especially strain sensors. The research presented herein establishes a simple and eco‐friendly strategy for the production of anisotropic PI/G‐based composite aerogels.

Effect of freezing conditions on the microstructure and compressive response of alumina/epoxy nacre-type composites

An attempt is made to fabricate nacre-type alumina/epoxy (cerepoxy) composites using ice-templated alumina scaffolds. A polydimethylsiloxane (PDMS) wedge with varying angles (0°, 5°, 10°, and 20°) is used to modulate the temperature gradients during the freezing. While a 2D nucleation is observed in uni-directional freezing (0° wedge angle), bi-directional freezing in non-zero wedge angles shows 1D nucleation. The lamellae thickness and interlamellar spacing increase with the increase in PDMS wedge angle. Moreover, the density of scaffolds varies along the freezing direction, with denser microstructure recorded at the bottom location (closer to the cold finger). The quasi-static and high strain rate compression testing reveals the anisotropy in the compressive mechanical properties of cerepoxy samples. The compressive strength and energy-absorbing capacity increase at higher loading rates. Finally, the present study establishes the structure-property relationship and shows that bi-directional freezing is an efficient route to design and fabricate cerepoxy composites having nacre-type microstructure.

Experimental study on frost heave characteristics and micro-mechanism of fine-grained soil under dynamic load for heavy-haul railway subgrades in seasonally frozen regions

In seasonally frozen regions, there is frequent uneven frost heave of heavy haul railway subgrades, which reduces the smoothness of the track and affects the operational safety of trains. To clarify the frost heave characteristics and micro-mechanism of subgrade filling under the action of unidirectional freezing and dynamic loading, unidirectional freezing tests were performed on a fine-grained subgrade filling under open conditions, and the frost heave characteristics under different initial water contents and dynamic loads were analyzed. The particle image velocimetry (PIV) technique was applied to analyze the development of local deformation at different locations in the samples. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were performed on the samples before and after freezing to reveal the development mechanism of the microstructure. The test results showed that with the increase in the initial water content and load amplitude, the frost heave increased, while the water replenishment and frost depth decreased. Combined with the PIV results, it was found that the soil in the frozen and unfrozen areas exhibited frost heave and compressive deformation, respectively, during the freezing process, further revealing the local deformation law of the soil. The samples mainly contained small pores and micropores before freezing and small pores and medium pores after freezing, indicating that the effect of freezing and swelling had the greatest influence on the small and medium pores inside the soil. The higher the initial water content, the higher the porosity of the sample after freezing; with the increase in the load amplitude, the porosity of the frozen samples decreased. The negative temperature effect of the change in phase from water to ice drove the particle movement, thereby increasing the inter-particle pore space, leading to a macroscopic frost heave deformation of the soil samples. Our results can serve as a basis in the maintenance and safety of railway subgrades in cold regions.

Frost-heaving characteristics and formation mechanism of saturated sandstone under unidirectional freezing conditions

In this study, a series of frost-heaving experiments were conducted on saturated sandstone at varying cooling rates under unidirectional freezing conditions. The frost-heaving strain in the freezing process was examined using a novel laboratory testing methodology. The results showed that the frost-heaving behavior of the saturated sandstone was significantly affected by the freezing direction and rate. Specifically, the rapid freezing of sandstone parallel to the freezing direction resulted in a more pronounced frost-heaving strain than that perpendicular to the freezing direction. The rock freezing rate had a positive correlation with the peak frost-heaving strain parallel to the freezing direction, and a negative correlation with that perpendicular to the freezing direction. A microstructure-based conceptual model is proposed to determine the frost-heaving pressure. The conceptual model showed that the ice pressure, determined by the pore-water pressure and capillary force, resulted from the crystallization of the pore water within the pore structure. A nonlinear relationship was observed between the ice pressure and crystallization rate. Capillary forces were more significant for slow crystallization processes, resulting in a larger difference between ice and water pressures. At high crystallization rates, the hydraulic pressure acted on the pore structure before the capillary forces become significant, leading to a smaller difference between the water and ice pressures. Rapid crystallization processes resulted in the uneven distribution of ice pressure within the pore structure, with subsequent re-equilibration occurring with the migration of unfrozen water. The proposed conceptual model presents a new perspective for obtaining an improved understanding of the microscopic frost-heaving mechanism involved in the freeze-thaw damage of porous rocks. It provides an evaluation method for the behavior of rocks during weathering by frost heave in cold regions.