Freeze-thaw Conditions Research Articles

Detecting soil freeze-thaw dynamics with C-band SAR over permafrost in Northern Sweden and seasonally frozen grounds in the Tibetan Plateau, China

ABSTRACT The soil freeze-thaw (FT) state plays a significant role in cold ecosystems by influencing hydrology, geomorphology, ecology, thermodynamics, and soil chemistry. As climate change alters the frequency and timing of FT events, regions, such as the Tibetan Plateau and other subarctic permafrost zones, face significant environmental shifts, including land subsidence, altered hydrological processes, and carbon balance disturbances. This study aimed to detect frozen, thawed, and transition periods, with a particular emphasis on the identification of critical transition periods. A new approach called Percentile-based Freeze-Thaw Identification (PFTI) was applied to identify the three FT periodsusing C-band Synthetic Aperture Radar (SAR) data, specifically using Sentinel-1 VV and VH polarizations in both ascending and descending orbits. The PFTI approach is based on the Seasonal Threshold Approach (STA) with some modifications. We assessed the performance of PFTI against STA and validated it using the in-situ soil FT index. PFTI slightly improved the STA by 4% to 6% in detecting FT cycles over the Nagqu area of the Tibetan Plateau and Stordalen Mire in northern Sweden from 2017 to 2022. Moreover, PFTI demonstrated an accuracy of 94% without and 70% with transition periods in the Stordalen Mire, and 77% without and 50% with transition periods in the Nagqu area, as validated by in situ measurements. This study demonstrates the potential of PFTI on a monthly scale for detecting frozen, thawed, and transition periods on a regional scale to better monitor shifts due to the impacts of climate change in the most vulnerable regions.

Effect of hollow glass microspheres (HGM) on improving self-heating capability of cement composites exposed to various deterioration conditions

Cement-based self-heating composites play a crucial role in addressing the need for intelligent road and pavement systems capable of efficient de-icing in severe weather conditions. However, the self-heating capability of these composites can be adversely affected by various deteriorating factors such as water ingress, nitric and sulfuric attacks, and freeze-thaw conditions. In this study, we propose the use of hollow glass microspheres (HGM) to enhance the self-heating capability of cement composites exposed to such deteriorating conditions. The initial investigation focused on observing the effects of HGM incorporation on changes in compressive strength, electrical conductivity, and thermal conductivity. Subsequently, the self-heating capability of these composites was systematically examined under cyclic heating conditions following exposure to deterioration factors. Microstructural analysis, including mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), was conducted. The results indicated that the inclusion of HGM can effectively safeguard the conductive networks from external solutions, thereby preventing potential disconnection of these networks. Consequently, the incorporation of HGM is anticipated to enhance both the electrical stability and self-heating capability of cement composites exposed to diverse deteriorating conditions.

Experimental analysis of frost resistance and failure models in engineered cementitious composites with the integration of Yellow River sand

Abstract This study investigates the potential use of Yellow River sand (YRS) sourced from the lower reaches of the Yellow River in China as a sustainable and cost-effective substitute for quartz sand in engineered cementitious composites (ECCs). This region accumulates around 400 million tons of sand annually. The study evaluates the impact of different YRS replacement percentages (0, 25, 50, 75, and 100%) on mechanical and microstructure properties under freeze-thaw conditions, focusing on assessing the ECC durability during cooling cycles. The results show that YRS exhibits a smaller normal distribution of particle sizes compared to that of quartz sand and a 5.77 times greater specific surface area, affecting the ECC particle size distribution. After 300 cooling cycles, the R25 group maintains 97.5% of the initial mass and 79.4% of flexural strength, indicating superior durability. The R25 group also demonstrates a minimal decrease of 11.5% in equivalent bending strength, reaching a level of 104.4% compared to R0. The R25 group’s porosity is 30.80%, with an average pore size of 20.47 mm, showing 1.3% and 6.7% decreases compared to the R0 group. Additionally, this study establishes a failure progression equation using the Weibull probability distribution model, with calculated values closely aligning with measured values. Overall, this study recommends using YRS as a sustainable ECC material.

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.

An experimental investigation on freeze-thaw resistance of fiber-reinforced red mud-slag based geopolymer

This study aims to investigate the influence of different fiber types, lengths, and contents on their performance in freeze-thaw environments. Indoor freeze-thaw tests were conducted to evaluate the flexural strength, compressive strength, and mass loss of fiber-reinforced geopolymer materials. Additionally, SEM and XRD analyses were performed to examine the internal structure of the geopolymer composites. The results demonstrated that the incorporation of different fibers significantly improved various properties, particularly the flexural strength of the specimens. With an increasing number of freeze-thaw cycles, surface cracks became more prominent in the geopolymer specimens, leading to a gradual decrease in frost resistance. However, the addition of an appropriate amount of fiber effectively enhanced frost resistance. Following freeze-thaw exposure, an increase in fiber content initially resulted in a decrease and subsequently an increase in relative flexural strength, compressive strength, and mass loss. Notably, studies revealed that polypropylene fibers with a length of 9 mm and a content of 0.9 % exhibited minimal mass and strength loss. SEM analysis indicated uniform distribution of fibers within the geopolymer matrix, contributing to improved flexural strength and enhanced frost resistance in fiber-reinforced structures. XRD results indicate that red mud-slag based geopolymers produce high-strength hydrated calcium (aluminosilicate) silicate and hematite phases, which enhances the mechanical properties and durability of the specimens. In conclusion, this study highlights that incorporating suitable fibers can enhance the durability and performance of red mud-slag based geopolymers under freeze-thaw conditions. The findings provide valuable insights for optimizing fiber type, length, and content to achieve superior mechanical properties and frost resistance in geopolymer composites.

Effect of tracheid on water absorption behavior of Cunninghamia lanceolata under freeze-thaw conditions

Effect of tracheid on water absorption behavior of Cunninghamia lanceolata under freeze-thaw conditions

Effects of Freeze-Thaw Cycles on Bioaccessibilities of Polycyclic Aromatic Hydrocarbons.

The bioaccessibility of particle-bound hydrophobic organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), and the factors influencing their re-release are crucial for assessing potential human health risks via inhalation and hand-mouth exposure. However, the mechanisms by which various factors affect the re-release of PAHs in body fluids, particularly in response to environmental changes like freeze-thaw cycles, remain unclear. To obtain a better understanding, an in vitro method was employed to investigate the re-release processes of PAHs from different soil types (ferrallitic soil and calcareous soil) in simulated body fluids (simulated lung fluid and simulated saliva) under varying freeze-thaw conditions (0, 15, and 30 cycles). The findings indicated that the bioaccessibilities of phenanthrene and pyrene decreased with the frequency of freeze-thaw cycles, which were constrained by soil nature and simulated body fluids compositions as well. Additionally, this study observed that the portion of reversible adsorption of PAHs declined after exposure to freeze-thaw cycles in a nonlinear manner, suggesting that the potential human health risk associated with PAHs could be mitigated due to the "aging effect" which occurred as PAHs became less bioaccessible over time. These results underscore the importance of considering the characteristics of pollutants, body fluids, and environmental media when conducting a precise assessment of the human health risks posed by such contaminants.

Freeze-Thaw Cycle Durability and Mechanism Analysis of Zeolite Powder-Modified Recycled Concrete.

The inferior mechanical performance and freeze-thaw (FT) resistance of recycled concrete are mostly due to the significant water absorption and porosity of recycled coarse particles. In this study, different dosages of zeolite powder were used in recycled concrete. A series of macroscopic tests were used to evaluate the workability and FT durability of zeolite powder-modified recycled concrete (ZPRC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to reveal the micro-mechanisms of FT resistance in ZPRC. The results show that the increase in zeolite powder content leads to a decrease in the slump and water absorption of ZPRC. Additionally, ZPRC with 10% zeolite powder has superior mechanical characteristics and tolerance to FT conditions. The higher strength and FT resistance of the ZPRC can be attributed to the particle-filling effect, water storage function, and pozzolanic reaction of zeolite powder, which results in a denser microstructure. The particle-filling effect of zeolite powder promotes the reduction of surface pores in recycled coarse aggregates (RCAs). The water storage function of zeolite powder can provide water for the secondary hydration of cement particles while reducing the free water content in ZPRC. The pozzolanic reaction of zeolite powder can also promote the generation of hydrated calcium silicate and anorthite, thereby making the microstructure of ZPRC more compact. These results provide theoretical guidance for the engineering application of recycled concrete in cold regions.

Alternative material recommendation for facade cladding: High silica-containing stonepaste ceramics

This study investigated the potential of using stonepaste ceramics, which were widely preferred as a coating and decoration material on the facades of architectural buildings in ancient times and continues to be produced on a workshop scale today as a cladding material on building facades. Stonepaste ceramics, made from a mixture prepared with a high amount of crystalline quartz as well as frit, plastic clay, and bentonite raw materials, were hand-shaped and sintered at 930 °C after glazing. The physico-mechanical properties of stonepaste ceramics, their behaviour under various environmental conditions (resistance to chemicals, frost, and thermal shock), and their microstructures have been characterized. The characterization results were compared with the properties of commonly used facade cladding materials. It was determined that stonepaste ceramics had a very low firing shrinkage value (2.84 %) compared to that of other ceramic cladding materials, a higher water absorption value (11.79 %) than that of porcelain tiles and floor tiles, and close to wall tiles, and a flexural strength value (33.64MPa) higher than wall tiles and close to porcelain tiles despite the high-water absorption value. Ten cycles of thermal shock resistance showed that the body and glaze layer of the stonepaste ceramic material are well bonded to each other, and there is no significant thermal expansion mismatch between them. One hundred cycles of freeze-thaw conditions indicated that the stonepaste ceramic had good adhesion and thermal expansion compatibility between the glaze and the body but only chipping damage under the action of tensile forces caused by the freezing of water entering the pores of the body. In terms of behaviour against various chemicals, stonepaste ceramics were found to be highly resistant to high and low concentrations of household chemicals, swimming pool salts, and alkalis but less resistant to low concentrations of HCl and citric acid and high concentrations of HCl and lactic acid compared to other chemicals. The results show that stonepaste ceramics, despite their high-water absorption potential, have properties close to those of traditional ceramic tiles and, like these materials, can serve for significant periods in various environmental conditions when used as facade cladding. Consequently, it has been revealed that stonepaste ceramics can be used as a facade cladding material in sustainable, long-lasting, contemporary architectural facades thanks to their technical and protective properties.

Effects of Salt Content and Freeze-Thaw Conditions on Dynamic characteristics and its microscopic mechanism of Chloride Silty Clay

Generally, artificial ground freezing (AGF) technology is utilized to guarantee tunnel safety during construction. However, the soil structure changes significantly after freeze-thaw, resulting in uneven deformation of the tunnel under traffic loading from subway vibration. To solve this problem effectively, it is necessary to consider the combined impact of freeze-thaw, salt, and traffic loading damage that marine soft soil must withstand simultaneously. For this reason, cyclic triaxial test and NMR test were performed on the silty clay saturated with NaCl solution in this study. The influence of three main factors on dynamic properties has been thoroughly investigated, namely freeze-thaw, salt content, and confining pressure. According to cyclic triaxial test, the shape of the hysteresis loop of the specimens after freeze-thaw changed more significantly with increasing loading cycles. The dynamic elastic modulus was weakened by freeze-thaw, while improved by the addition of NaCl. Damping ratio was consistent with the dynamic elastic modulus law. It was worth noting that the different freezing temperatures (−10 °C, −20 °C and − 30 °C) had only a slight impact on dynamic elastic modulus, as well as damping ratio. Mathematical models were proposed to forecast the dynamic elastic modulus and damping ratio regarding marine soft clay. NMR test indicated that the addition of salt made the internal pore environment of the specimens tend to be consistent and enhanced the water-solid interaction. The increase in porosity resulted in the decrease in dynamic elastic modulus. The results have provided valuable insights into the mechanical characteristics of marine soft clay when AGF technology is applied.

Response of soft rock and sand compound soil structure to freeze-thaw cycles in Mu Us Sandy Land, China

In order to accurately understand the relationship between soil structure and climate feedback in the frozen soil area of Mu Us Sandy Land, China, and to explore the key control factors for the structural stability of soft rock and sand compound soil under freeze-thaw environment, the indoor freeze-thaw simulation experiment was applied. The results show that the freeze-thaw period, clay content, organic matter and their interactions have significant effects on the stability of composite soil aggregates. After 10 freeze-thaw cycles, the aggregate content in the 1:0, 1:1, 1:2, and 1:5 composite soil with a diameter greater than 1 mm decreased by 55%, 34%, 44%, and 57%, while the aggregate content with a diameter less than 1 mm increased by 91%, 70%, 66%, and 87%, and the aggregate composition of each particle size is mainly concentrated in the range of 0.25–0.5 mm. Under freeze-thaw conditions, the changes of clay and aggregate content in different proportions of composite soil is the same, all showing 1:1>1:2:>1:5, and 1:1 composite soil with >0.25 mm aggregate content is the highest. Under freeze-thaw alternations, 1:1, 1:2 and 1:5 composite soil aggregates (<0.5 mm) showed a significant positive correlation with soil organic matter, while there is no significant correlation between large aggregates (>1 mm) and soil organic matter. In conclusion, the freeze-thaw cycle reduces the structural stability of composite soil aggregates, and clay are the key controlling factors for the formation and structural stability of composite soil aggregates.

Evaluation of fracture indices of warm mix asphalt (WMA) modified with nano-additive under pure shear and pure tear deformations

Cracks located on the road edge and curve are two pavement crack types that can reduce road safety. Providing a solution to control this type of crack can solve a large part of the concern in this case. This study innovatively bridges the research gap by evaluating the efficacy of nano-reduced graphene oxide powder (NRGOP) in enhancing the fracture resistance of warm mix asphalt (WMA) under various environmental conditions, a critical aspect previously unexplored in the pavement engineering literature. For this goal, asphalt mixtures containing different ratios of NRGOP were constructed. Then, a level of aging and damage induced by freeze–thaw were applied to the semicircular bend (SCB) and edge-notched disc bend (ENDB) specimens to understand how the changes in fracture strength, fracture crispiness, and fracture stiffness are under modes III and II (at + 15 °C and −15 °C). The finding revealed that the introduction of NRGOP increased the fracture properties of WMA mixtures, such as fracture energy (FEII or FEIII) and fracture toughness (KIIC or KIIIC), as well as fracture stiffness under pure shear and pure tear deformations. Laboratory findings at low temperatures showed that it is necessary to investigate KIIC and FEII for asphalt mixtures under non-conditions and freeze–thaw conditions. However, KIIC and FEIII were suggested for aging conditions. Therefore, in two-thirds of the results, FEII was critical, and in 100 % results, KIIIC was critical. At + 15 °C, KIIC and FEIII were more crucial for non-treated and freeze–thaw conditions, while KIIC and FEII were more critical for aging, respectively. Therefore, in two-thirds of the results, FEIII was critical, and in 100 % results, KIIC was critical. The results of this research provide insights to advance the socio-economics of pavements by controlling surface cracks in tropical and subtropical regions, which in turn increases ride quality, driver safety, and pavement maintenance costs.

Effect of Nano-TiO2 and Polypropylene Fiber on Mechanical Properties and Durability of Recycled Aggregate Concrete

In order to promote the engineering application of recycled concrete, the effects of PPF and nano-TiO2 dioxide on the mechanical properties and durability of recycled concrete were studied.Polypropylene fiber recycled concrete(PRAC) and nano-TiO2 recycled concrete(TRAC) were prepared by adding different volume contents of PPF and nano-TiO2. The experimental findings demonstrated that the PPF and nano-TiO2 improved the splitting tensile strength of RAC better than the compressive strength. When the volume content of nano-TiO2. and PPF is 0.8% and 1.0%, respectively, the corresponding splitting tensile strength of concrete reaches the maximum value(3.4 and 3.7 MPa). The contribution rates of nano-TiO2 and PPF with different volume contents to the mechanical properties of RAC have optimal values, which are 0.4 and 1.0%, respectively. The incorporation of nano-TiO2 and PPF can effectively inhibit the loss of RAC mass and the generation of pores under freeze–thaw conditions, and slow down the decrease of dynamic elastic modulus. When the volume content of PPF is 1.0% and the volume content of nano-TiO2 is 0.4%, the protection effect on the internal structure of RAC is better, and its carbon resistance is better. The results of RSM model analysis and prediction show that both PPF and nano-TiO2 can be used as admixture materials to improve the mechanical properties and durability of RAC, and the comprehensive improvement effect of PPF on RAC performance is better than that of nano-TiO2.

Study on the shear characteristics of the cemented soil-concrete interface after artificial freeze-thaw under vibration loading

Underground construction has reduced underground space. Consequently, engineering construction is being done near existing structures. The artificial ground freezing (AGF) method is effective in such projects, and cement is often used to reduce frost heave and thaw settlement. A cemented soil-concrete interface is formed around underground structures. The interface serves as the primary medium for interaction between the two materials. Therefore, the shear characteristics of the cemented soil–concrete interface after artificial freeze–thaw cycles under the influence of the surrounding vibration load in underground engineering must be understood. This study conducted large-scale interface shear tests of a cemented soil–concrete interface with vibration loading. The effects of curing time and artificial freeze–thaw cycles on interface shear characteristics were studied. Furthermore, unconfined compressive tests of the cemented soil under artificial freeze–thaw conditions were conducted. The shear strength of the interface increased with curing time. The shear strength of the interface and the unconfined compressive strength of the cemented soil increased rapidly in the early stage of curing and gradually slowed after seven days. Artificial freeze–thaw reduced the shear strength of the interface with vibration loading. The results enrich ongoing research on the shear characteristics of cemented soil-concrete interfaces.

Exploring the in vitro stability of insulin degrading enzyme as a potential biomarker for neurocognitive disorders and Alzheimer's disease risk

Insulin degrading enzyme (IDE) plays a critical role in degrading insulin and beta-forming proteins, implicating its significance as a biomarker in metabolic dysfunction and neurocognitive disorders, including Alzheimer's disease (AD). Understanding the impact of pre-analytic conditions of in vitro IDE levels is imperative for reliable biomarker assessment. This study explored the influence of freeze-thaw cycles, storage temperature, and storage time on IDE levels in human serum.Serum samples from seven healthy volunteers were subjected to various storage conditions, including refrigeration (4 °C) and freezing (−20 °C and −80 °C) for 24 h and six months, with differing freeze-thaw cycles. In vitro IDE levels were measured at 24 h and after 6 months using ELISA.Results indicate that while short-term storage at either −20 °C or −80 °C yielded similar IDE levels, prolonged storage and multiple freeze-thaw cycles significantly impacted IDE stability, with colder temperatures exhibiting better preservation.Although further research with larger cohorts and longer storage time is warranted to establish clinical significance, our study suggests preferential use of unthawed samples or consistent freeze-thaw conditions for accurate IDE assessment. Thus, optimizing sample storage conditions is paramount for reliable IDE biomarker analysis in clinical and research settings.

Enhancing concrete durability in chloride-rich environments through manual application of healing agents

Concrete structures in chloride-rich environments are prone to deterioration, especially when ions can intrude via cracks towards the steel reinforcement. Self-healing concrete could significantly extend the service life of reinforced concrete. Hence, selecting appropriate healing agents to improve the durability is a critical challenge for the construction industry. This study investigates the use of three potential healing agents: water-repellent agent (WRA), sodium silicate (SS), and polyurethane (PU). The agents are tested separately under two conditions: exposure to a 3.3 % NaCl concentration at 20 °C and exposure to cyclic freeze-thaw conditions. The agents are manually injected into the cracks and evaluated for their healing efficiency using the capillary absorption test and microscopy analysis. Additionally, their resistance to freeze-thaw cycles by monitoring mass loss and chloride bulk diffusion is measured using sprayed silver nitrate, titration, and EDX mapping. The results demonstrate the effectiveness of PU in completely preventing chloride ingress and withstanding the freeze-thaw cycles. On the other hand, WRA showed a significant reduction in scaling, being the only healing agent to keep scaling below the appropriate scaling level of 1 kg/m2. Although WRA had the best performance in the scaling test and prevented chloride ingress, some influence was observed from the freeze-thaw cycles with regard to chloride ingress. Samples treated with SS performed better than the reference samples but did not show the same effectiveness as samples treated with PU or WRA in preventing chloride ingress. Overall, the study highlights the potential of healing agents in improving the durability of concrete structures in chloride-rich environments, with PU and WRA being the most promising for further development and optimization.

Evaluation of freeze-thaw resistance of geopolymer concrete incorporating GFRP waste powder

This study investigates the use of glass fiber reinforced polymer (GFRP) waste powder as a partial replacement for cementitious materials in the synthesis of geopolymer concretes (GPCs), focusing on their durability under freeze-thaw (F-T) conditions. Two types of binary GPCs were synthesized: GFRP powder/ground granulated blast furnace slag (GGBS)-based GPC and GFRP powder/fly ash (FA)-based GPC, with a GFRP powder weight content of 30 %. Single GFRP powder-based, GGBS-based and FA-based GPCs were prepared as reference materials. The F-T resistance was evaluated through mass loss and residual compressive strength (RCS), as well as examining the microstructure using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). Results demonstrated that the mass loss of all GPC samples remained below the critical value of 5 % after 300 cycles. The incorporation of 30 wt% GFRP powder into GGBS-based GPC resulted in improved resistance to F-T damage, increasing the number of cycles endured from 200 to 300. Similarly, adding 30 wt% GFRP powder to FA-based GPC demonstrated enhanced resistance to F-T deterioration, with the number of cycles increasing from 150 to 175. The pore distributions of GFRP powder/FA-based GPC remained relatively unchanged before 200 F-T cycles, indicating it effective resistance against F-T conditions. GFRP powder/GGBS-based GPC exhibited a more uniform and denser microstructure with a reduced presence of pores, even after enduring 300 F-T cycles, making it better equipped to withstand F-T cycles. Furthermore, prediction models were developed to estimate RCS and damage evolution due to F-T conditions, producing accurate results compared to test data. This study presents an effective method for the utilization of GFRP waste as a building material in cold environments.

Improving freeze resistance of cement-based materials with modified graphite-paraffin composite low-temperature microencapsulated phase change materials

This study examines the influence of microencapsulated phase change materials (MPCM) on enhancing the freeze-thaw resistance of cementitious structures, overcoming the limitations commonly associated with traditional phase change materials (PCM), such as insufficient thermal conductivity and non-optimal phase change temperatures. The research focused on developing MPCM with improved thermal conductivity and lower phase transition points, utilizing a binary mixture of tetradecane and hexadecane as the core material, supplemented by modified graphite. The phase change performance and physicochemical stability of the prepared MPCM were thoroughly assessed. Cement specimens, incorporating different contents of MPCM, were then subjected to a series of tests under both room temperature and simulated freeze-thaw conditions. These tests included mechanical testing, temperature response experiments, and monitoring of internal damage. The findings identified the optimal MPCM formulation as a 9:1 mixture of tetradecane and hexadecane, with an addition of 2 % hydrophobically modified graphite, which exhibited a phase change temperature near 0 °C and a range exceeding 6.7 °C, along with stable physicochemical properties. When 3 % MPCM was included in cement specimens cured for 28 days under freeze-thaw conditions, a significant reduction in internal damage caused by freeze-thaw cycles was observed, leading to an increase in compressive strength by 0.12 % and in flexural strength by 11.77 %. Additionally, temperature tests confirmed the efficacy of MPCM in stabilizing internal temperature fluctuations within the cement specimens. The results of this study present a viable approach to enhance the durability of cement-based infrastructure in cold climates.

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

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

Potential for Recycling Metakaolin/Slag-Based Geopolymer Concrete of Various Strength Levels in Freeze-Thaw Conditions.

Geopolymer concrete (GPC) represents an innovative green and low-carbon construction material, offering a viable alternative to ordinary Portland cement concrete (OPC) in building applications. However, existing studies tend to overlook the recyclability aspect of GPC for future use. Various structural applications necessitate the use of concrete with distinct strength characteristics. The recyclability of the parent concrete is influenced by these varying strengths. This study examined the recycling potential of GPC across a spectrum of strength grades (40, 60, 80, and 100 MPa, marked as C40, C60, C80, and C100) when subjected to freeze-thaw conditions. Recycling 5-16 mm recycled geopolymer coarse aggregate (RGAs) from GPC prepared from 5 to 16 mm natural coarse aggregates (NAs). The cementitious material comprised 60% metakaolin and 40% slag, with natural gravel serving as the NAs, and the alkali activator consisting of sodium hydroxide solution and sodium silicate solution. The strength of the GPC was modulated by altering the Na/Al ratio. After 350 freeze-thaw cycles, the GPC specimens underwent crushing, washing, and sieving to produce RGAs. Subsequently, their physical properties (apparent density, water absorption, crushing index, and attached mortar content and microstructure (microhardness, SEM, and XRD) were thoroughly examined. The findings indicated that GPC with strength grades of C100, C80, and C60 were capable of enduring 350 freeze-thaw cycles, in contrast to C40, which did not withstand these conditions. RGAs derived from GPC of strength grades C100 and C80 complied with the criteria for Class II recycled aggregates, whereas RGAs produced from GPC of strength grade C60 aligned with the Class III level. A higher-strength grade in the parent concrete correlated with enhanced performance characteristics in the resulting recycled aggregates.