Freeze-thaw Effect Research Articles

Effect of Freeze-Thaw on Compressive Strength of Clayey Soils Reinforced with Wool

ABSTRACT Reinforcing clayey soil using synthetic and natural fibers has been widely used as soil improvement methods in recent years. The usage of wool, which is inside the natural fibers, as a reinforcing material is seen as an economic, sustainable, and environmentally friendly solution. The compressive strength parameters of clayey soils (CS) equipped with wool were determined by a series of free pressure strength tests before and after freeze-thaw (F-T). The F-T cycle was repeated 12 times in cycles 1, 7, and 28 days. The highest strength increase was attained after 28 days of curing. The compressive strength increase of CS samples prepared with four different wool additives (0.5%, 1%, 1.5%, and 2% dry weight) occurred between 16.9–68.7% and 13.3–62.7% before and after F-T, respectively. The highest compressive strength increase before and after F-T occurred in CS+1.5% wool mixture. In addition, the wool ratio and the number of freeze-thaw cycles were determined to be important parameters in the increase in compressive strength. In summary, it is concluded that wool-supported CS can be used in the basic design of engineering structures and in shallow depths especially in regions with cold climates.

Geomechanical, durability–hygrothermal and thermal shock properties of Kocaeli Kandira stone used as building stone in historical structures

This study investigated the mineralogical, chemical, physical, mechanical, durability–hygrothermal, thermal shock properties, and economic aspects of the Kandira stone, one of the well-known natural building stones, commonly used in many historical structures in the Marmara and Thrace regions. Especially, it has been preferred to Malta stone in historical structures in Istanbul due to economic reasons at the beginning of the 1900s. A similar appearance and lithology with Malta stone and closeness of the Kandira stone to Istanbul made it attractive to be used as natural building stone in historical monuments and new structures. The mean physico-mechanical properties of Kandira stone yielded 2.24 g/cm3 apparent density, 2.72 specific gravity, 19.21% total porosity, 5.8% water absorption by weight, 48 MPa compressive strength, 11.4 MPa bending strength. In terms of durability properties, Kandira stone has high resistance to aging by CaCl salt mist and no or low resistance to SO2 aging in a humid environment. Also, the freeze–thaw test of Kandira stone yielded an exceptionally low mass loss (0.11%) indicating that the stone is resistant to freeze–thaw effect. Thermal shock tests indicated that Kandira stone is mainly resistant to thermal shock cycles. Economically, the calculated probable reserve of Kandira stone resulted in 40.8 × 106 tons of material and the potential economic value based on the probable reserve is calculated around 54.672 × 109 TL (approximately €7.2B). In conclusion, this study defined the petrographic, geomechanical, durability–hygrothermal and thermal shock properties essential for the use of Kandira stone as building stone and restoration material.

Mechanistic Investigation of Typical Loess Landslide Disasters in Ili Basin, Xinjiang, China

In the period from 2010 to 2018, a total of 302 geological disasters occurred in the Xinjiang Autonomous Region, China, of which 136 occurred in the Ili Basin. Compared with those in other regions, the loess landslides in the Ili Basin are strongly influenced by the seasonal freeze–thaw effect. Taking the No. 2 Piliqinghe landslide as an example and based on the field geological investigation, it was found in the present study that the main triggering factors of this landslide were the snowmelt erosion of the slope toe and meltwater infiltration into the trailing edge of the slope. The mechanism of loess landslide instability was studied using numerical simulation. The results showed that (1) the Piliqinghe landslide disaster was formed through a process composed of the local sliding of the leading edge → the creep sliding and tension cracking of the slope surface → the overall sliding stage; (2) the infiltration of snowmelt was the direct cause of the landslide formation; (3) the fluvial erosion and softening caused the soil of the slope toe to slide. The results can be used as a reference for the analysis of the disaster mechanism and movement characteristics of similar loess landslides.

Effect of freeze-thaw cycles on soil engineering properties of reservoir bank slopes at the northern foot of Tianshan Mountain

The instability of soil bank slopes induced by freeze-thaw cycles at the northern foot of Tianshan Mountain is very common. The failure not only caused a large amount of soil erosion, but also led to serious reservoir sedimentation and water quality degradation, which exerted a lot of adverse effects on agricultural production in the local irrigation areas. Based on field investigations on dozens of irrigation reservoirs there, laboratory tests were carried out to quantitatively analyze the freeze-thaw effect on the soil engineering characteristics to reveal the facilitation on the bank slope instability. The results show that the softening characteristics of the stressstrain curves gradually weaken, the effective cohesions decline exponentially, the seepage coefficients enlarge, and the thermal conductivities decrease after 7 freeze-thaw cycles. The freeze-thaw effect on the specimens with low confining pressures, low dry densities and high water contents is more significant. The water migration and the phase transition between water and ice result in the variations of the soil internal microstructures, which is the main factor affecting the soil engineering characteristics. Sufficient water supply and the alternation of positive and negative temperatures at the reservoir bank slopes in cold regions make the water migration and phase transition in the soil very intensely. It is easy to form a large number of pores and micro cracks in the soil freezing and thawing areas. The volume changes of the soil and the water migration are difficult to reach a dynamic balance in the open system. Long-term freeze-thaw cycles will bring out the fragmentation of the soil particles, resulting in that the micro cracks on the soil surfaces are developing continuously. The soil of the bank slopes will fall or collapse when these cracks penetrate, which often happens in winter there.

模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

森林凋落物分解是森林生态系统物质循环的重要环节，季节性冻融交替是影响凋落物分解的重要环境因素之一，但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响，以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料，从凋落物基质质量、冻融环境等影响凋落分解的因素着手，采用模拟冻融循环过程（-5-5℃），研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现，3中典型林型凋落物经过不同冻融处理后，其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势，而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下，3种林型的凋落物碳绝对含量呈波动下降的趋势，说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下，有机碳释放有显著差异（P<0.05）。其中，冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放，但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下，亚高山森林土壤冻融事件频发将加快凋落物的分解，但变化程度受到凋落物质量控制。;In this study, we address the effects of freeze-thaw cycles on the process of litter decomposition in subalpine forests. In a microcosm experiment, we measured the dynamics of litter moss loss rates and organic carbon by controlling the freeze-thaw environment (-5-5℃) in three typical forests in the sub-alpine region in western Sichuan. The three forest types including coniferous, coniferous-broadleaf, and broadleaf forest were selected for our experiment design based on the criteria of their abundance in the study area. Our results showed that clear and significant differences (P<0.05) in all measured litter types were all observed due to the freeze-thaw treatments. Specially, the mass loss rate of litter in both coniferous-broadleaf and coniferous forests showed a slow-fast-slow trend. In contrast, in the broadleaf forests, the mass loss rates exhibited a gradual decrease trend. This fluctuation phenomenon implies that there is a balance between microbial-fixed exogenous carbon and substrate-released carbon. In conclusion, the increase of globally average temperature would accelerate the freeze-thaw cycles and thus significantly change the process of mass loss and nutrient cycles in the subalpine forests, but both the magnitude and direction of the freeze-thaw effects varied with initial litter quality.

Thermal shock and freeze-thaw resistance of different types of carbonate rocks

In this study, the physical, mechanical and index properties of 6 different carbonate rocks, taken from quarries in the East Anatolian region of Turkey and commonly used for decorative purposes in buildings, were investigated after the thermal shock (T-S) and freeze thaw (F-T) effects. Compared to room temperature conditions, attempts were made to determine the variation in physical and mechanical properties like porosity, mass loss, roughness, gloss, Schmidt hardness (SH), P-wave velocities (Vp) and uniaxial compressive strength (UCS) occurring in carbonate rocks as a result of T-S and F-T cycles. Additionally, SEM analysis was performed on 2 rocks with worst and best physical and mechanical properties at room temperature and the causes of variations in the microstructure of these carbonate rocks were discussed. According to the obtained results, as the number of T-S and F-T cycles increase, the degradation of the internal structure of the carbonate rocks increases and as a result, resistance to physical and mechanical effects significantly reduces. Additionally, the F-T effect was determined to negatively affect the internal structure of the carbonate rocks in greater amounts compared to the T-S effect. It was determined that UCS of the carbonate rocks decreased between 16.14-28.65% and 22.96–45.66% after 50 T-S and F-T cycles, respectively. As the L4 rock sample (Tamara Bej) has fewer flaws in the internal structure compared to other rocks, it was identified to be more favorable for decorative use in buildings.

Experimental research on the development of residual strain in seasonal frozen soil under freezing-thawing and impact type traffic loads

Vehicle load is among the main factors affecting the deformation of subgrade soil. In this research study, the concept of impact type traffic load is introduced to investigate the effects of vehicle load based on the dynamic stress and displacement time histories acquired from seasonal frozen subgrade soils. Using freezing-thawing and dynamic triaxial tests and considering the amplitude and loading sequence of impact type traffic load, the residual deformation characteristics of subgrade soil under impact type traffic loads and freezing-thawing cycles is studied. It was found that under impact type traffic load, the residual deformation of soils increased sharply as the amplitude of impact type traffic load increased. It was also found that the increase in the amplitude of impact type traffic load led to the increase of residual deformation in a scale of power and exponential function. The amplitudes of impact type traffic load affect the development stress-strain path of the residual strain. After the soil experienced the proper amount of pre-vibration of the light load, residual deformation decreased by 15%. After freezing-thawing, the residual strain of soil increased as the amplitude of the impact type traffic loads increased. Also, when the amplification effect of freezing-thawing on the residual strain was basically stable, the residual deformation increased by about 10%. The peak impact type traffic load had a large effect on soil deformation after the freezing-thawing process, leading to the observation that of the earlier the peaks, the stronger the effect of freezing-thawing. After the soil was subjected to preloading with a small load, the influence of the freezing-thawing cycles gradually stabilized. The results may be useful in preventing and controlling the risk of subgrade soil failure when construction takes place spring thaw periods.

Freeze-thaw effects on erosion process in loess slope under simulated rainfall

Seasonal freeze-thaw processes have led to severe soil erosion in the middle and high latitudes. The area affected by freeze-thaw erosion in China exceeds 13% of the national territory. So understanding the effect of freeze-thaw on erosion process is of great significance for soil and water conservation as well as for ecological engineering. In this study, we designed simulated rainfall experiments to investigate soil erosion processes under two soil conditions, unfrozen slope (UFS) and frozen slope (FS), and three rainfall intensities of 0.6, 0.9 and 1.2 mm/min. The results showed that the initial runoff time of FS occurred much earlier than that of the UFS. Under the same rainfall intensity, the runoff of FS is 1.17–1.26 times that of UFS; and the sediment yield of FS is 6.48–10.49 times that of UFS. With increasing rainfall time, rills were produced on the slope. After the appearance of the rills, the sediment yield on the FS accounts for 74%–86% of the total sediment yield. Rill erosion was the main reason for the increase in soil erosion rate on FS, and the reduction in water percolation resulting from frozen layers was one of the important factors leading to the advancement of rills on slope. A linear relationship existed between the cumulative runoff and the sediment yield of UFS and FS (R2>0.97, P<0.01). The average mean weight diameter (MWD) on the slope erosion particles was as follows: UFS0.9 (73.84 µm)>FS0.6 (72.30 µm)>UFS1.2 (72.23 µm)>substrate (71.23 µm)>FS1.2 (71.06 µm)>FS0.9 (70.72 µm). During the early stage of the rainfall, the MWD of the FS was relatively large. However, during the middle to late rainfall, the particle composition gradually approached that of the soil substrate. Under different rainfall intensities, the mean soil erodibility (MK) of the FS was 7.22 times that of the UFS. The ratio of the mean regression coefficient C2 (MC2) between FS and UFS was roughly correspondent with MK. Therefore, the parameter C2 can be used to evaluate soil erodibility after the appearance of the rills. This article explored the influence mechanism of freeze-thaw effects on loess soil erosion and provided a theoretical basis for further studies on soil erosion in the loess hilly regions.

Comparison of Soil Greenhouse Gas Fluxes during the Spring Freeze–Thaw Period and the Growing Season in a Temperate Broadleaved Korean Pine Forest, Changbai Mountains, China

Soils in mid-high latitudes are under the great impact of freeze–thaw cycling. However, insufficient research on soil CO2, CH4, and N2O fluxes during the spring freeze–thaw (SFT) period has led to great uncertainties in estimating soil greenhouse gas (GHG) fluxes. The present study was conducted in a temperate broad-leaved Korean pine mixed forest in Northeastern China, where soils experience an apparent freeze–thaw effect in spring. The temporal variations and impact factors of soil GHG fluxes were measured during the SFT period and growing season (GS) using the static-chamber method. The results show that the soil acted as a source of atmospheric CO2 and N2O and a sink of atmospheric CH4 during the whole observation period. Soil CO2 emission and CH4 uptake were lower during the SFT period than those during the GS, whereas N2O emissions were more than six times higher during the SFT period than that during the GS. The responses of soil GHG fluxes to soil temperature (Ts) and soil moisture during the SFT and GS periods differed. During the SFT period, soil CO2 and CH4 fluxes were mainly affected by the volumetric water content (VWC) and Ts, respectively, whereas soil N2O flux was influenced jointly by Ts and VWC. The dominant controlling factor for CO2 was Ts during the GS, whereas CH4 and N2O were mainly regulated by VWC. Soil CO2 and N2O fluxes accounted for 97.3% and 3.1% of the total 100-year global warming potential (GWP100) respectively, with CH4 flux offsetting 0.4% of the total GWP100. The results highlight the importance of environmental variations to soil N2O pulse during the SFT period and the difference of soil GHG fluxes between the SFT and GS periods, which contribute to predicting the forest soil GHG fluxes and their global warming potential under global climate change.

Evaluation of the impact of freeze-thaw cycles on pore structure characteristics of black soil using X-ray computed tomography

Freeze-thaw cycles extensively and intensely occur in northeast China and generate significant effects on soil pore structure. The objective of this study was to obtain three-dimensional (3D) images of soil pore structures utilizing industrial X-ray microtomography and to apply image analysis techniques to visually and quantitatively evaluate the impact of the freeze-thaw effect on pore characteristics of black soil. The soil samples were subjected to zero (T0), one (T1), five (T5), ten (T10), fifteen (T15), and twenty (T20) freeze-thaw cycles and were then scanned at a 25-μm resolution to construct pore-throat network images. The results showed that the freeze-thaw effect increased the porosity of the soil 3D microstructure and that the pore-throat networks became increasingly complex with a greater number of freeze-thaw cycles. The total porosity and macroporosity increased significantly with an increase in the number of freeze-thaw cycles (p < 0.05). The soil in the T20 treatment displayed the greatest total porosity and macroporosity, which were 247.8 and 251.1 % greater, respectively, than in the T0 treatment. In freeze-thaw processes, contraction of the solid phase is induced by thawing of ice crystals but is insufficient to counteract the displacement induced by the freezing expansion of ice crystals. Macroporosity contributes to most of the increase in total porosity between each treatment. The numbers of pore throats and paths were significantly and positively correlated (p < 0.05) with the number of macropores. The freeze-thaw effect mainly affected those pores with greater effective diameters, which may include more branch paths and throats. The findings of this study can help to improve the understanding of soil dynamic processes under freeze-thaw cycles and further enable the utilization of pore morphology in monitoring the quality of soil structure.

Deterioration of non-persistent rock joints: A focus on impact of freeze–thaw cycles

Existing research on rock freeze-thaw mainly focuses on a single freeze-thaw process, while little attention is paid to the cumulative effect of cyclic freeze-thaw on rock mass joints. However, the accumulated freeze-thaw effects are precisely the leading cause of rock mass deterioration and damage in severe cold regions. This study aims to investigate the use of a novel laboratory testing method, i.e., membrane pressure sensors in the joint, to demonstrate the impact of cyclic frost-thaw on jointed rocks. With the sensors, the change of frost-heaving pressure in the joint under cyclic process is continuously monitored. The measurements indicate that under freeze-thaw cycles, the initiation of frost-heaving pressure is critical, which is followed by an explosion, stability, and ablation stages. In these stages, the maximum frost-heaving pressure is observed to emerge at the early stage of the freeze-thaw cycle. Based on the experimental observations, frost-heaving pressure evolution law and damage mechanism of jointed rock masses are analyzed. For example, the peak frost-heaving pressure increases exponentially with the decrease of temperature and decreases exponentially with the increase of freeze-thaw cycles. Also, the pressure has a positive linear relationship with the geometric size of the joint. In essence, the deterioration of freeze-thaw cycles on jointed rock masses is mainly due to crack propagation caused by the frost-heaving pressure.

Effects of freeze-thaw on dissolved nitrogen pool, nitrogen transformation processes and diversity of bacterial community in temperate soils

Soil freeze-thaw could affect nitrogen (N) availability. The N transformation is closely related with soil microbes. The effect of soil freeze-thaw on the soil bacterial communities in the temperate zone is still not clear. We hypothesized that freeze-thaw events could affect the diversity and composition of bacterial communities, thereby changing the contents of soil dissolved nitrogen pools as well as the N transformation process. In this study, microcosms with different freeze-thaw cycles (six and fifteen cycles) were designed, with the constant temperature at 2 ℃ as the control. The results showed that the contents of dissolved total nitrogen, dissolved inorganic nitrogen, microbial biomass nitrogen and net nitrogen mineralization rate were decreased significantly in response to increasing cycles of freeze-thaw. The number of freeze-thaw cycles did not affect bacterial α diversity. In contrast, the duration of incubation was positively correlated with bacterial α diversity including Chao1 and Shannon indices. Freeze-thaw treatment significantly affected the function and composition of bacterial communities, but the number of freeze-thaw cycles had little effect on the bacterial community structure. The partial redundant analysis showed that under freeze-thaw treatments, both the composition and function of bacterial community were significantly related to soil dissolved N pools and N transformation processes.

Effect of Freeze-Thaw on the Stability of a Cutting Slope in a High-Latitude and Low-Altitude Permafrost Region

In order to study the influence of freeze-thaw cycles on the stability of cutting slopes in high-latitude and low-altitude permafrost regions, we selected a cutting slope (the K105+700–800 section of National Highway 332) in the Elunchun Autonomous Banner in Inner Mongolia as the research object. Located in the Greater Xing’an Mountains, the permafrost in the Elunchun Autonomous Banner is a high-latitude and low-altitude permafrost. The area is also dominated by island-shaped permafrost, which increases the difficulty of dealing with cutting slopes, due to its morphological complexity. Surface collapse, caused by freeze-thaw erosion in this area, is the main reason for the instability of the cutting slope. Indoor freeze-thaw tests, field monitoring, and an ABAQUS numerical simulation model were conducted so as to quantify the decrease in rock strength and slope stability under freeze-thaw conditions. The following conclusions were drawn. (1) As the number of freeze-thaw cycles increased, the compressive strength of the rock specimens obtained from this slope gradually decreased. After 50 freeze-thaw cycles, the uniaxial compressive strength measured by the test decreased from 40 MPa to 12 MPa, a decrease of 37%. The elastic modulus value was reduced by 47%. (2) The safety factor of the slope—calculated by the strength reduction method under the dynamic analysis of coupled heat, moisture, and stress—gradually decreased. After 50 freeze-thaw cycles, the safety factor of the slope was only 0.74. (3) Reasonably reducing the number of freeze-thaw cycles, reducing the water content of the slope, slowing down the slope, and increasing the number of grading steps can effectively improve the stability of the slope. The results of this study can provide a reference for the design and stability analysis of slopes in permafrost regions of the Greater Xing’an Mountains.

Analysis of Capillary Water Migration Law of Compacted Loess in Ningxia

Capillary water is the main cause of freezing damage and collapsible damage of compacted loess. Therefore, researching capillary water migration law of compacted loess is the key to solve various damage in the infrastructure construction of loess. Different regions have different climatic conditions, which make the physical and mechanical properties of the loess is different. In order to reveal the capillary water migration law of compacted loess in Ningxia, the moisture migration law of compacted loess with different degrees of compaction was studied by using standpipe method. The results show that the migration rate of capillary water is rapid at the early stage and gradually became slower with the increase of time, which is negatively related to the degree of compaction and migration height. The maximum migration height of capillary water increases exponentially with the increase of compactness. Migration rate and migration height of capillary water are related to capillary water potential, gravitational potential, and pipe-resistance of capillary. In this study, the relational equation can predict capillary water distribution and the migration height of compacted loess was newly established. This equation can also provide a reference to reduce various damage and freeze-thaw effect in compacted loess.

Analysis on Composite Erosion Process Based on Multi Dynamic Erosion Environment Simulation

Using the compound erosion experimental device developed by ourselves, the compound erosion process simulation experiment of 35° steep slope were carried out under different combination modes of freeze-thaw, wind, rainfall. The runoff and sediment yield change process of Pisha sandstone slope under different dynamic combination environment were studied. The results show that the superposition of wind, freeze-thaw and rainfall conditions obviously promotes the occurrence of slope erosion, among which the effect of freeze-thaw increased the collapse phenomenon obviously in the erosion process.

Evolution of dynamic flow behavior in asphalt mixtures exposed to freeze-thaw cycles

This study aims to understand the evolution of dynamic moisture flow in asphalt mixtures exposed to freeze-thaw cycles. X-ray CT was utilized to capture the moisture dynamics in unsaturated asphalt mixtures during simulated rainfall events. Three main characteristics of the dynamic flow behaviors within asphalt mixtures were measured and monitored, including wetting front position, directional velocity of wetting front, and inertia influence region. It was found that at a specific infiltration rate, freeze-thaw cycles increased the vertical flow penetration and decreased the horizontal flow penetration for both wetting front position and directional velocity, suggesting that seepage anisotropy was exacerbated in asphalt mixtures. The initial inertia of water droplet was mostly converted towards the vertical direction under freeze-thaw effect. As a result, the shape of water transmission was converted from a hemispherical shape to a slender shape under freeze-thaw cycles. Linear regression analysis between direction velocity growth rate in particular samples and freeze-thaw cycles to pore structure was conducted, and it was found that compared with dense-graded mixtures, open-graded mixtures displayed larger slopes for horizontal flow, and smaller slopes for vertical flow, demonstrating the non-negligible effect of pore structure on dynamic flow evolution under freeze-thaw cycles.

Rapid and Detergent-Free Decellularization of Cartilage.

The use of decellularized tissues or organs as cell culture scaffolds has proven to be a promising approach for tissue engineering and regenerative medicine, as these decellularized tissues can provide the instructive niche for cell differentiation and functions. Cartilage is a largely avascular tissue with limited regenerative capacity. Lesions caused by arthritis can lead to severe cartilage degeneration. Previous studies have indicated that decellularized cartilage can be used as scaffolds that support the chondrogenic differentiation of adult stem cells. However, these decellularization protocols all require the use of denaturing agents, such as high salt and detergents, that lead to the artifactual disruption of the chemical and physical integrity of the tissue microenvironment. Here, we established a new decellularization method for cartilage, through a combined effect of freezing-thawing, sectioning, and sonication in water. This protocol achieved the complete removal of cells within minutes, instead of hours or days required by existing procedures, and does not use any detergent. The resulting decellularized cartilage preserved the native ultrastructure and biochemical contents, including glycosaminoglycans, which is typically depleted by traditional decellularization methods. Human mesenchymal stem cells could readily adhere onto the decellularized cartilage. Together, this work unveils a simple new method for decellularizing cartilage, which will be useful in studying how tissue microenvironment supports chondrocyte growth and functions. Impact statement In this study, we develop a simple, fast cartilage decellularization method that does not require any detergent, so that the decellularized cartilage chemistry is preserved. Traditional detergent-based decellularization removes the tissue biochemical contents (i.e., glycosaminoglycans). In this new water decellularization protocol, the biochemical contents of cartilage can be preserved. This allows the study of biochemistry and physical content in extracellular matrix as a whole, and this protocol would definitely be useful for studying the effect of tissue microenvironment in supporting chondrocyte growth and functions.

Soil Water Contents Control the Responses of Dissolved Nitrogen Pools and Bacterial Communities to Freeze-Thaw in Temperate Soils.

Background Freeze-thaw influences soil-dissolved nitrogen (N) pools due to variations in bacterial communities in temperate regions. The availability of soil water is important to soil biogeochemical cycles under frozen conditions. However, it is unclear how soil water content (SWC) mediates the effects of freeze-thaw on soil-dissolved N pools and bacterial communities. Method In this study, freeze-thaw microcosms were incubated at three levels of SWC, including 10% (air-dried soils), 15% (natural SWC), and 30% (wet soils). In addition to measuring soil-dissolved N pools, variations in bacterial communities were examined using high-throughput sequencing. Results and Conclusions. Total dissolved N (TDN), NO3−-N, NH4+-N, microbial biomass N (MBN), and net N mineralization rate (NNMR) were significantly influenced by SWC, freeze-thaw, and their interaction (NH4+-N excluded). N immobilization was inhibited under both low and high SWC, which was accompanied by varied bacterial community composition. However, only higher SWC substantially modified the freeze-thaw effects on the soil-dissolved N pools, characterized by a decrease in N mineralization (especially for the content of NO3−-N and NNMR) and an increase in N immobilization (MBN). These scenarios could be significantly correlated to variations in bacterial community composition based on redundancy analysis, especially by species belonging to Bacteroidetes, Nitrospirae, Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Bacteroidetes, Nitrospirae, Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Nitrospirae, Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Alphaproteobacteria, Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Gemmatimonadetes, and Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.Verrucomicrobia (Spearman's correlations). In conclusion, bacterial species passed through biotic (bacterial species) and abiotic filters (soil N pools) in response to freeze-thaw under varied SWC.

Experimental Investigation on the Freeze-Thaw Resistance of Steel Fibers Reinforced Rubber Concrete.

The reuse of rubber in concrete results in two major opposing effects: an enhancement in durability and a reduction in mechanical strength. In order to strengthen the mechanical properties of rubber concrete, steel fibers were added in this research. The compressive strength, the four-point bending strength, the mass loss rate, and the relative dynamic elastic modulus of steel fiber reinforced rubber concrete, subjected to cyclic freezing and thawing, were tested. The effects of the content of steel fibers on the freeze–thaw resistance are discussed. The microstructure damage was captured and analyzed by Industrial Computed Tomography (ICT) scanning. Results show that the addition of 2.0% steel fibers can increase the compressive strength of rubber concrete by 26.6% if there is no freeze–thaw effect, but the strengthening effect disappears when subjected to cyclic freeze–thaw. The enhancement of steel fibers on the four-point bending strength is effective under cyclic freeze–thaw. The effect of steel fibers is positive on the mass loss rate but negative on the relative dynamic elastic modulus.

Mechanical and electrical properties of coarse-grained soil affected by cyclic freeze-thaw in high cold regions

To evaluate the geotechnical properties of coarse-grained soil affected by cyclic freeze-thaw, the electrical resistivity and mechanical tests are conducted. The soil specimens are prepared under different water contents, dry densities and exposed to 0-20 freeze-thaw cycles. As a result, the stress-strain behavior of the specimen (w =14.0% and ρd=1.90 g/cm3) changes from strain-hardening into strain-softening due to the freeze-thaw effect. The electrical resistivity of test specimen increases with the freeze-thaw cycles change, but the mechanical parameters (the unconfined compressive strength qu and the deformation modulus E) and brittleness index decrease considerably at the same conditions. All of them tend to be stable after 7−9 cycles. Moreover, both the dry density and the water content have reciprocal effects on the freeze-thaw actions. The failure and pore characteristics of specimens affected by freeze-thaw cycles are discussed by using the image analysis method. Then, an exponential function equation is developed to assess the electrical resistivity of specimens affected by the cyclic freeze-thaw. Linear relations between the mechanical parameters and the electrical resistivity of specimens are established to evaluate the geotechnical properties of the soil exposed to freeze-thaw actions through the corresponding electrical resistivity.