Search Results (13)

Wood–textile composites (WTCs), consisting of polypropylene and woven willow wood, have potential for both interior and exterior applications. However, their basic materials are not inherently resistant to outdoor weathering. This study examines the impact of various climatic conditions on the material behavior of WTCs. The composite and its components were aged under different scenarios, including kiln-drying, frost, standard and tropical climate, and artificial weathering and water storage, and analyzed for dimensional stability, chemical changes (FTIR), mechanical damage (µ-CT), and mechanical performance. While kiln-drying, frost, and tropical climates had only minor effects, water storage caused swelling-related damage, resulting in a 45% decrease in Young’s modulus but increased elongation at break (+88%) and impact strength (+75%). Artificial weathering led to significant degradation: tensile strength declined by 28%, Young’s modulus by 49%, and impact strength by 26%. In the medium term, this degradation compromises the integrity of the composite. The results highlight the need for effective stabilization measures—such as polymer modification or structural protection—to ensure the long-term durability of WTCs in outdoor use. Full article

In several geotechnical and geoenvironmental projects, fines containing expandable clay minerals such as expansive clay (EC) were added to sand as sealing materials to form liners or hydraulic barriers. Liner layers are generally exposed to different climatic conditions such as freeze-thaw (FT) during their service lifetime. The hydromechanical behavior of these layers under such circumstances is of great significance. In this study, the impact of fine contents of expansive soil on swelling, consolidation characteristics, and hydraulic conductivity under FT conditions is examined. Different clay liners with 20%, 30%, and 60% of EC content were designed. The specimens were initially subjected to successive FT cycles up to 15 in close system criteria. The results revealed that volumetric strains attained during successive FT cycles are proportional to the content and nature of expanding minerals (i.e., montmorillonite) and reached a 4.5% magnitude value for the liner with 60% clay. Vertical strains during wetting conditions have been reduced by about 90% after the first FT cycles, which implies significant destruction in the soil structure. The yield stress indicated a 60% change, along with increasing FT cycles. The hydraulic conductivity during an extended period of 100 days shows significant changes and deterioration due to FT actions. The outcome of this study will help to predict the lifetime behavior and performance of the liner, taking into account the stability under frost conditions. Full article

Exposed to seasonal climate changes, the loess in the Ili region of Xinjiang, which has variable engineering properties, frequently undergoes freezing–thawing (F-T) and wetting–drying (W-D) cycles. In the present research, a series of uniaxial compression tests were conducted to investigate the collapsibility characteristics of the representative loess slope in the Ili region. In parallel, scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) tests were conducted. The test results obtained from the research indicated that both F-T cycles and W-D cycles exacerbate the deterioration of the loess, with the most severe effects observed after 6–10 cycles. Under the combined physical cycles, the microstructure of the loess progressively evolves from the relatively aggregated state to the dispersed one. Meanwhile, the porosity of the loess exhibited an initial increase with the number of W-D cycles, followed by an obvious decrease. Note that the pattern of the loess experiences fluctuation, which was achieved at the given point with the increased number of F-T cycles. It is suggested that the variability in loess wetting collapse is attributed to the irreversible alteration in the microstructure attributed to the combined cycles. The main reasons for the occurrence of loess collapse are the frost heaving force and the swelling–shrinking action. The impacts of W-D and F-T cycles on the loess obtained from this research can make a contribution to the in-depth understanding about loess collapse in the Ili valley. Full article

We report the synthesis of poly(acrylamide-co-acrylic acid)/sodium carboxy methyl cellulose (PAMAA/CMC-Na) hydrogels, and subsequent fabrication of dual-network polymer hydrogels (PAMAA/CMC-Na/Fe) using as-prepared via the salt solution (FeCl₃) immersion method. The created dual-network polymer hydrogels exhibit anti-swelling properties, frost resistance, high conductivity, and good mechanical performance. The hydrogel swells sightly when immersed in solution (pH = 2~11). With the increase in n_AA:n_AM, the modulus of elasticity experiences a rise from 1.1 to 1.6 MPa, while the toughness undergoes an increase from 0.18 to 0.24 MJ/m³. Furthermore, the presence of a high concentration of CMC-Na also contributes to the enhancement of mechanical strength in the resulting hydrogels, ascribing to enhanced physical network of the hydrogels. The minimum freezing point reaches −21.8 °C when the CMC-Na concentration is 2.5%, owing to the dissipated hydrogen bonds by the coordination of Fe³⁺ with carboxyl (-COO⁻) in CMC-Na and PAMAA. It is found that the conductivity of the PAMAA/CMC-Na/Fe hydrogels gradually decreased from 2.62 to 0.6 S/m as the concentration of CMC-Na rises. The obtained results indicates that the dual-network hydrogels with high mechanical properties, anti-swelling properties, frost resistance, and electrical conductivity can be a competitive substance used in the production of bendable sensors and biosensors. Full article

The Qinghai–Tibet Plateau is the main permafrost area in China. Concrete structures constructed on permafrost are affected by the early negative-temperature environment. In particular, the negative-temperature environment seriously affects the strength growth process and the frost resistance of concrete (FRC). Therefore, this study considered the influence of the gas content, water–binder ratio (w/b), age, and other factors on the strength variation law and FRC under −3 °C curing conditions. Nuclear magnetic resonance (NMR) was used to analyze the pore structure of concrete before and after freeze–thaw cycles (FTCs). The results showed that the compressive strength of the concrete (CSC) under −3 °C curing was only 57.8–86.4% of that cured under standard conditions. The CSC under −3 °C curing showed an obvious age-lag phenomenon. The FRC under −3 °C curing was much lower than that under standard curing. The porosity of the concrete under −3 °C curing was greater, with a higher percentage of harmful and multi-harmful pores than that under standard curing. The concrete properties deteriorated primarily because curing at −3 °C hindered the hydration reaction compared with standard methods. This hindrance resulted in diminished hydration development, weakening the concrete’s structural integrity. Under both curing conditions, when the gas content was between 3.2% and 3.8%, the frost resistance was the best. This is because a gas content within this range effectively enhances the internal pore structure, therefore relieving the swelling pressure caused by FTCs. Based on the freeze–thaw damage (FTD) model proposed by previous authors, a new model for the CSC under −3 °C curing reaching that of the concrete under standard curing for 28 d was established in this study. This advanced model was capable of accurately assessing the FTD of concrete structures in permafrost regions. Finally, the life expectancy of concrete in Northwest China was predicted. The life of the concrete reached 46.9 years under standard curing, while the longest life of the concrete under −3 °C curing was only 12.9 years. Therefore, attention should be paid to constructing and curing concrete structures in cold environments. Full article

A steel slag porous asphalt (SSPA) mixture, as the surfacing layer of permeable asphalt pavements, not only ensures the pavement surface drainage and noise reduction functions, but also improves the comprehensive utilization of steel slag resources and the inherent protection of the ecological environment. However, compared with ordinary asphalt mixtures, SSPA is more susceptible to water damage, such as scouring and frost swelling caused by external rainwater intrusion, resulting in the deterioration of the pavement performance. Therefore, it is of good practical imperative to study the water stability and moisture damage mechanism of SSPAs. In this study, the water stability of SSPA, that was subjected to a series of time–temperature H₂O-immersion schemes, was investigated using the pull-out and H₂O-immersion Marshall tests, whilst the microscopic mechanism of moisture damage was studied using the scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD) tests. The corresponding results showed that: (a) with the increase in the H₂O immersion time, the water stability of SSPA first increased and then decreased; and (b) the water stability of SSPA was strong under medium-temperature H₂O-immersion or short-term high-temperature H₂O-immersion. SEM, on the other hand, showed that the transition zone spacing was closely related to the chemical adhesion mechanism between the asphalt and steel slag aggregate. Additionally, the FTIR analysis further showed that the steel slag asphalt mastic spectra had new absorption peaks at 3200~3750 cm⁻¹, inherently indicating the existence of chemical bonding between the asphalt and steel slag, with the XRD results showing that CaSO₄·2H₂O had a beneficial effect on the water stability of SSPA. Full article

To investigate the load-bearing characteristics of anchor rods under asymmetric freezing conditions such as those in cold regions and the effect of frost swelling, a model test device was developed using a controlled-temperature environmental box and a hydraulic actuator. Laboratorial pull-out model tests of anchor rods in soil layers were conducted at different moisture contents and freezing temperatures, the changes in anchor rod pull-out force before and after freezing were quantitatively described, load–displacement relationship curves were prepared, and the frost swelling displacement of anchor rods under asymmetric freezing conditions and the stress evolution of surrounding soil were observed and recorded. The shear strength of the anchor–soil interface increased with decreasing temperature, and the ultimate values of the pull-out force at 0, −3 and −7 °C were 4, 17.04 and 18.1 times greater than those at room temperature, respectively, for 10% water content. The pull-out force of the frozen anchor increased with increasing water content. The bolts were displaced by the freezing expansion force. Their lateral displacements at 0, −3 and −7 °C were 2.9, 3.2 and 3.5 mm, respectively, and their vertical displacements were 0.2, 3.5 and 4.3 mm, respectively, for 10% water content. The total displacement increased with increasing moisture content, and the maximum transverse displacements were 3.5, 3.65 and 3.8 mm for 10, 12 and 14% water contents, respectively, and 4.3, 5.1 and 5.5 mm in the vertical direction, respectively. The ultimate pull-out forces after freezing and thawing were 71, 68 and 52% of that before freezing for 10, 12 and 14% water, respectively. Full article

In order to study the bearing safety and influencing factors of the support structures of hydraulic tunnels in cold regions under the action of low-temperature frost heave, a mechanical model of the support structure and surrounding rock was established. Taking a hydraulic tunnel of a hydropower station in Xinjiang as the research object, a combination of field measurement and a numerical simulation method was adopted to study the bearing safety of the support structure during a period of freezing weather. Based on this model, the effects of different thermal expansion coefficients, temperature differences, and surrounding rock porosity on the bearing safety of the support structure in the low-temperature region were studied. From the calculation results, it was concluded that the simulation results of the numerical model established by using the mechanical model in this paper were in good agreement with the actual measurement results of the project. The circumferential freezing and compressive stresses at the arch waist of the supporting structure of the project were the largest, and significant plastic strain was generated near the arch waist. The displacement at the arch of the supporting structure was the largest, while the weak points were at the arch waist and arch top of the supporting structure. The coefficient of thermal expansion, greater temperature difference, and increased porosity of the surrounding rock all led to an increase in the rock freezing and swelling force to varying degrees, thus reducing the load-bearing safety of the supporting structure. The research results could provide a theoretical basis and a reliable mechanical and numerical simulation model for establishing the bearing safety of tunnels in the cold region. Full article

The mining industry manages large volumes of tailings, sludge, and residues that represent a huge environmental issue. This fact has prompted research into valorization of these wastes as alternative aggregates for concrete production, embankments, pavement material, etc. The use of mining wastes as a resource for construction presents two benefits: conserving natural resources and reducing the environmental impacts of mining. In the case of road construction, the use of mining wastes has not yet been developed on a large scale and there is a major lack of specific legislation. This gap is due to the variety of exploited rocks, the diversity of tailings, mine residues, or valuable by-products slated for valorization, and the environmental specifics. This paper presents a review on recycling mine wastes as road construction material, including waste rock and mine tailings. Those materials were mostly used in infrastructure where soils had initially poor geotechnical properties (low bearing capacity, frost susceptibility, swelling risk, etc.). Different mining wastes were used directly or stabilized by a hydraulic binder through geopolymerization or, in some cases, with bituminous treatment. Overall, the use of mine wastes for road construction will have a considerable environmental impact by reducing the volume of waste and offering sustainable raw materials. Full article

When the buried pipeline passes through the permafrost zone, the phenomenon of frost swelling occurs in the permafrost zone, which causes a certain degree of bending and deformation of the pipeline. As a result, the pipeline’s structural safety is compromised, and the pipeline finally fails during operation, posing a serious hazard to the natural gas pipeline’s operation. Whereas the theoretical research on soil frost heave is relatively comprehensive, the applied research on engineering problems is not yet complete. Therefore, it is necessary to predict frost heaving through experiments and numerical simulation, and put forward reasonable control measures for existing or potential problems. For the problem of pipeline damage caused by frost swelling of soil in the natural gas high-pressure regulator station in a river and creek region, the Drucker–Prager elastic-ideal plastic model of soil was selected for finite element analysis, and a reasonable finite element model of pipe-soil was established in this paper. Through the temperature field analysis, it was found that the soil around the buried pipe is affected by the pipeline and is lower than its freezing temperature, which makes the soil freeze and swell. Furthermore, through the thermal–structural coupling analysis, it was found that the buried pipe is affected by the freezing and swelling of the soil and the structure is greatly likely to be damaged. In addition, by analyzing the temperature distribution and frost heave deformation of the soil around the pipeline, as well as the deformation and force of the pipeline at different pipe temperatures, this paper also determined the ideal temperature for preventing frost heave damage to natural gas at high-pressure regulator stations as −1 °C. Finally, based on the results of the abovementioned analysis, the heating method was determined to improve the frost damage phenomenon at the high-pressure regulator. The results of the anti-frost and swell study were used to conduct field trials at natural gas high-pressure regulator stations where frost and swell had occurred. By adding heating furnace to increase inlet temperature, frost heaving of gas transmission pipeline can be effectively prevented. The results of the research provide a reference for both existing and new natural gas pipelines, and also accumulate experience for winter maintenance design and construction of pipeline engineering in seasonally frozen soil areas. Full article

In this study, the effect of lithium slag (LS) on the frost resistance of cement-soil was evaluated. The results of freeze–thaw damage on the surface of the cement-soil, freeze–thaw mass loss, unconfined compression strength, triaxial shear strength, cohesion, and internal friction angle were tested at various freeze–thaw cycles after 90 days of curing when LS was incorporated into the cement-soil at different proportions (0%, 6%, 12%, and 18%). Combining nuclear magnetic resonance (NMR) T₂ distribution and scanning electron microscopy (SEM) microscopic images, the mechanism of the effect of LS on the cement-soil was also analyzed. The experiment confirmed that the surface freeze–thaw damage degree and mass loss value of the cement-soil decreased after incorporating different LS contents, and that the unconfined compression strength, triaxial shear strength, cohesion, and internal friction angle also improved significantly compared with the specimens without LS. In this experiment, the optimization level of the cement-soil performance with different LS content was ranked as 12% > 18% > 6% > 0%. According to the NMR and SEM analysis results, the LS content of 12% can optimize the internal pore structure of the cement-soil and strengthen the bond between aggregate particles, hence inhibiting the extension of freeze-swelling cracks induced by freeze–thaw cycles. In conclusion, LS can effectively enhance the frost resistance of cement-soil, and the optimum content in this experiment is 12%. Full article

The rate of bank retreat was measured using erosion pins on the alluvial banks of the rivers in the Podhale region (the boundary zone between Central and Outer Carpathians) during the hydrological year 2013/2014. During the winter half-year (November–April), the bank retreat was mainly caused by processes related to the freezing and thawing of the ground (swelling, creep, downfall). During the summer half-year (May–October), fluvial processes and mass movements such as lateral erosion, washing out, and sliding predominated. The share of fluvial processes in the total annual amount of bank retreat (71 cm on average) was 4 times greater than that of the frost phenomena. Erosion on bank surfaces by frost phenomena during the cold half-year was greatest (up to 38 cm) on the upper parts of banks composed of fine-grained alluvium, while fluvial erosion during the summer half-year (exceeding 80 cm) mostly affected the lower parts of the banks, composed of gravel. The precise calculation of the relative role of frost phenomena in the annual balance of bank erosion was precluded at some stations by the loss of erosion pins in the summer flood. Full article

Most previous studies of the Qinghai-Tibet engineering corridor (QTEC) have focused on the impacts of climate change on thaw-induced slope failures, whereas few have considered freeze-induced slope failures. Terrestrial laser scanning was used in combination with global navigation satellite systems to monitor three-dimensional surface changes between 2014 and 2015 on the slope of permafrost in the QTEC, which experienced two thawing periods and a freezing period. Soil temperature and moisture sensors were also deployed at 11 depths to reveal the hydrological–thermal dynamics of the active layer. We analyzed scanned surface changes in the slope based on comparisons of multi-temporal point cloud data to determine how the hydrological–thermal process affected active layer deformation during freeze–thaw cycles, thereby comprehensively quantifying the surface deformation. During the two thawing periods, the major structure of the slope exhibited subsidence trends, whereas the major structure of the slope had an uplift trend in the freezing period. The seasonal subsidence trend was caused by thaw settlement and the seasonal uplift trend was probably due to frost heaving. This occurred mainly because the active layer and the upper permafrost underwent a phase transition due to heat transfer. The ground movements occurred approximately in the soil temperature conduction direction between the top of the soil and the permafrost table. The elevation deformation range was mainly −0.20 m to 0.20 m. Surface volume increases with heaving after freezing could have compensated for the loss of thawing twice and still led to the upward swelling of the slope. Thus, this type of slope in permafrost is dominated by frost heave. Deformation characteristics of the slope will support enhanced decision making regarding the implementation of remote sensing and hydrological–thermal measurement technologies to monitor changes in the slopes in permafrost adjacent to engineering corridors, thereby improving the understanding and assessment of hazards. Full article