Freeze-thaw Conditions Research Articles

Effect of Thaw Depth on Nitrogen and Phosphorus Loss in Runoff of Loess Slope

Seasonal freeze-thaw erosion is a form of soil erosion caused by the topographical characteristics and climatic factors of the hilly and gully loess regions. Seasonal freeze-thaw can damage the soil pores and cause its bulk density to change. The effects of thawing depth on runoff and Nitrogen and Phosphorus loss on the rainfall erosion of an artificial slope filled with loess soil were analyzed after a rainfall test that simulated the spring thaw period in China. The results showed that: (1) The maximum runoff yield was 33.35 mm at 4 cm thawing depth, and the minimum was 12.95 mm at 6 cm thawing depth. With the increase in runoff time, the slope infiltration rate had a decreasing trend. The loss rate of available and total Phosphorus increased with the increase in runoff rate. The rate of increase was fastest when the thawing depth was 4 cm. (2) The relationships between runoff rate and Nitrogen loss and Phosphorus loss rate can be explained by linear regression equations, and the loss rate increased as the runoff rate rose for all thawing depths. Within the 0–6 cm thawing depths, the loss of total phosphorus was the largest when the thawing depth was 4 cm, and the loss of available phosphorus was the smallest when the thawing depth was 6 cm. At the shallower thawing depths, the available Nitrogen loss represented a smaller proportion of the total Nitrogen loss compared to nitrate Nitrogen loss. However, there was a gradual rise in the available Nitrogen proportion in the total amount of inorganic Nitrogen as the thawing depth increased. (3) Total Phosphorus was the available Phosphorus with a quadratic function relationship with runoff energy and runoff power. Runoff energy mainly affected the total Nitrogen and available Nitrogen loss in runoff, whereas runoff power mainly affected total Nitrogen loss in runoff. The results of this paper can improve the understanding of runoff and Nitrogen and Phosphorus loss caused by runoff during freeze-thaw conditions.

Comparison of hydrogeochemical characteristics of thermokarst lake water in the Qinghai–Tibet Plateau under active layer freeze–thaw conditions

Abstract With the gradual increase of global temperature, thermokarst lakes are widely developed and become major environmental disasters in the Tundra Plateau which have impacted the stability of the project such as the Qinghai–Tibetan highway. In this study, some typical thermokarst lakes in the Qinghai–Tibet Plateau (QTP) were selected as the research object. And four samples were taken from different freezing–thawing processes of the lakes in 2019 to analyze the hydrogeochemical process of the thermokarst lake in the context of climate change. Results show that the main hydrogeochemical types of the lake water in the northern part of the study area were HCO3·Cl − Na·Ca·Mg or Cl·HCO3 − Na·Mg, whereas in the central and southern parts were mainly Cl − Na·Mg. The variations of hydrogeochemical concentration in thermokarst lake water are mainly affected by evaporation concentration, rock differentiation, freezing desalination in the active layer, and plant photosynthesis, which are mainly due to temperature changes. Furthermore, the results of the saturation index (SI) show that dolomite and calcite leaching control the hydrogeochemical composition in thermokarst lakes. In addition, the evaporation-to-inflow (E/I) ratios of the lake reach the maximum in the middle and later periods of the active layer thawing. On the contrary, the E/I values of the lakes decrease during the initial thawing or freezing periods of the active layer.

Evaluating the effects of styrene-butadiene rubber (SBR) and polyphosphoric acid (PPA) on asphalt adhesion performance

The styrene-butadiene rubber (SBR) latex and polyphosphoric acid (PPA) are extensively utilized alone or together to optimize the properties of base asphalt to tackle the booming traffic loads and volumes. In this paper, the influences of SBR, PPA, and SBR&PPA on the adhesion performance of base asphalt were evaluated by atomic force microscopy (AFM), surface free energy (SFE), binder bond strength (BBS), and split tensile strength tests from multiple scales under dry or moisture conditions. Finally, the one-way analysis of variance (ANOVA) was conducted. According to the results, both SBR and PPA dosages show significant influence on the adhesion performance of the asphalt binder and its mixture. Specifically, at the nanoscale, the PPA and SBR modifiers are beneficial to improving the adhesion force of base asphalt from 17nN to 21-30nN. At the asphalt scale, both PPA and SBR modifiers enhance the SFE of base asphalt. However, only asphalts modified with 1% PPA, 1.5% PPA, 3% SBR, and 1.5% SBR&2% PPA are less prone to ravel. At the asphalt-aggregate and mixture scales, the SBR modifier enhances the pull-off strength of base asphalt significantly from 1.83 MPa to about 4 MPa, as well as the dry tensile strength (TSD). However, after the freeze–thaw condition, the PPA&SBR modified asphalt demonstrates the most satisfying freeze–thaw tensile strength (TSFT) and the tensile strength ratio (TSR). Considering the unfavorable moisture damage resistance of asphalt and its mixture when being modified with a single modifier, the asphalt modified with 1.5% SBR&2% PPA is recommended and could improve the adhesion performance between asphalt and aggregate even under moisture conditions.

Effect of Silica Fume and Polyvinyl Alcohol Fiber on Mechanical Properties and Frost Resistance of Concrete

To improve the mechanical properties and frost resistance of concrete, silica fume, and polyvinyl alcohol fiber compounded in concrete. The mechanical and frost resistance of concrete were comprehensively analyzed and evaluated for strength change, mass loss, and relative dynamic elastic modulus change by compressive strength test, flexural strength test, and rapid freeze-thaw test. The results showed that with the incorporation of silica fume and polyvinyl alcohol fiber, the compressive and flexural strengths of concrete were improved, and the decrease in mass loss rate and relative dynamic elastic modulus of concrete after freeze-thaw cycles were significantly reduced, which indicated that the compounding of silica fume and polyvinyl alcohol fiber improved the frost resistance of concrete. When the content of silica fume was 10% and the volume content of polyvinyl alcohol fiber was 1%, the comprehensive mechanical performance and frost resistance of concrete is the best. The compressive strength increased by 26.6% and flexural strength increased by 29.17% compared to ordinary concrete. Based on the test data, to study the macroscopic damage evolution of concrete compound silica fume and polyvinyl alcohol fiber under repeated freeze-thaw conditions. The Weibull distribution probability model and GM (1, 1) model were established. The average relative errors between the predicted and actual data of the two models are small and very close. It is shown that both models can reflect well the development of concrete damage under a freeze-thaw environment. This provides an important reference value and theoretical basis for the durability evaluation and life prediction of compound silica fume and polyvinyl alcohol fiber concrete in cold regions.

Experimental Study on Freeze-Thaw Effects on Creep Characteristics of Rubber Concrete

Crumb Rubber Concrete (CRC) can exhibit high freeze-thaw resistance, but its long-term creep behavior under various freeze-thaw conditions remains unclear, which is essential for the safety of pavement engineering in the severe cold zone. In this study, the freeze-thaw effects on the creep behavior of CRC under different stress levels were systematically analyzed by testing the compressive strength, the uniaxial creep under different stress levels, and the dynamic elastic modulus. To simulate real conditions of the road environment in the cold area, the lowest temperature of −20°C, six freeze-thaw cycles of 0, 30, 60, 90, 120, and 150, and seven different stress levels of 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 of the compressive strength were employed in this study. The test results showed that the mass loss rate was 6%–11.2% and the compressive strength decreased by 6.51%–47% after 30–150 freeze-thaw cycles. When the stress level reached its critical value, the relative dynamic elastic modulus decreased with the number of freeze-thaw cycles. After 150 freeze-thaw cycles, failure did not appear when the stress level was lower than 50%, above which the creep failure was determined by the stress level and the number of the freeze-thaw cycles. Meanwhile, it was found that the cracking and interfacial debonding between the matrix and the crumb rubber particle were the main reasons for the degradation of CRC creep performance. Finally, a Weibull distribution-based empirical creep damage model was established to predict the failure of CRC, which can enhance its application to related engineering.

冻融条件下生物结皮覆盖对土壤饱和导水率的影响

生物结皮（BSC）是广泛分布的地被物，每逢冬春季节，受冻融交替作用影响，结皮土壤的理化性质和水文学特征明显改变且与裸土差异显著，从而影响该地区土壤可蚀性评估和土壤侵蚀防治。采用室内模拟实验，以蓝藻结皮土壤为对象，研究不同冻融交替次数和初始含水量下，土壤三相对温度变化的响应特征并定量分析结皮覆盖土壤在此条件下饱和导水率（Ks）的变化趋势和突变点。结果表明：初始含水量对Ks无显著影响（P>0.05），冻融交替次数对Ks有极显著影响（P<0.01），冻融条件下裸土的平均Ks为1.941 mm/min，结皮覆盖土壤平均Ks为0.325 mm/min，两者具有极显著差异（P<0.01），且随交替次数增加，Ks差异逐渐增大，并在10次时达到最大值为10.13倍。不同冻融含水量下的结皮土壤的Ks在冻融10-20次时趋近，平均值为0.219mm/min。冻融作用显著改变土壤结构，且在冻融7次时土壤结构变化较明显，冻融过程中<0.1 mm的土壤颗粒显著变化。试验条件下，Ks受因子影响程度大小为：冻融交替次数 > 土壤结构 > 结皮厚度 > 结皮容重 > 下层土壤容重 > 冻融初始含水量；冻融次数与结皮厚度、结皮容重、冻融初始含水量的交互效应对Ks有显著影响。;Biological crust is a kind of ground cover which distributes widely. Due to their special physiological mechanisms, algae and moss can thrive and grow under the extreme cold and low light conditions so as form crusts. Biological crust (BSC) exists in various types of climatic region, soil and vegetation, the type of crust reflects the local water conditions and soil nutrient status, meanwhile, the formation of biological crust has an important influence on the occurrence and development of soil, hydrology and erosion processes, affects the physical and chemical properties of the soil, which manifests as the degree of influence of different types of crusts. However, the effect of biological crusts on soil infiltration is still controversial, on the one hand, biological crusts increase the roughness of the soil surface and correspondingly extend the retention time of water on the soil surface, which is not conducive to water infiltration, on the other hand, biological crusts improve soil structure and create water flow channels that are conducive to water infiltration. In this study, we used indoor simulation experiments, took the cyanobacteria crust-covered soil as research object to study the response characteristics of three relatives of soil under different freeze-thaw cycles and initial water contents, then quantitatively analyzed the trend and change point of the saturated hydraulic conductivity of crust-covered soil (Ks). The results show that the initial water content has no significant effect on Ks (P>0.05), and the number of freeze-thaw alternation has a very significant effect on Ks (P<0.01). The average Ks of bare soil under freeze-thaw conditions is 1.941 mm/min, the average Ks of crust-covered soil is 0.325 mm/min, and there is a very significant difference between them (P<0.01). With the increase of the number of alternation, the difference of Ks gradually increase, the Ks of bare soil reaches a maximum of 10.13 times of crust soil at 10 times. The Ks of crust soil under different initial water contents is approaching a similar level after 10-20 freeze-thaw alternations, with an average value of 0.219 mm/min. The effects of freezing and thawing significantly change the soil structure, especially after 7 times, and the soil particles lower than 0.1 mm, changing significantly. Under the experiment conditions, the degree of influence of Ks by the factors is as follows:number of freeze-thaw cycles > soil structure > crust thickness > crust bulk density > lower soil bulk density > initial freeze-thaw water content. The interactive effects of freeze-thaw cycles and crust thickness, crust bulk density, and the initial water content have the significant impact on Ks.

Informing Improvements in Freeze/Thaw State Classification Using Subpixel Temperature

Freeze/thaw (FT) processes at the earth’s surface can have a considerable effect on global carbon, energy, and hydrologic cycles. Therefore, an accurate representation of FT is valuable to adequately monitor and model these processes. In this study, we assess the relationship between satellite-based FT products and modeled surface and soil temperatures over North America. In addition, hourly land surface temperature (LST) from the Geostationary Operational Environmental Satellite (GOES) system is also compared to FT classifications. Utilizing the higher spatial resolution temperatures (~5 km), we assess subgrid-scale variability and its relationship to coarser microwave FT classifications (>25 km). We also examine product agreement and subpixel characteristics across the land cover, climate, and topography. FT classifications are shown to vary widely depending on these variables, leading to an ambiguous definition of frozen and thawed states. Our results suggest that current products can characterize FT transitions with consistent subfreezing surface characteristics in far northern regions (>50 °N). However, uncertainty associated with FT classifications is shown to increase considerably as latitude decreases. Our results also suggest that fractional FT products, utilizing data inputs, such as LST, would provide a considerable improvement in mountainous regions with high intergrid cell heterogeneity, in regions characterized by ephemeral FT events (i.e., regions < 40 °N), as well as during freeze and thaw onset periods. This study also provides insight to improving the representation of surface FT state by providing a clearer definition of the subpixel scale temperature characteristics that govern existing frozen classifications.

Effects of Arctic Wetland Dynamics on Tower-Based GNSS Reflectometry Observations

A tower-based global navigation satellite system reflectometry (GNSS-R) experiment is set up in an Arctic wetland environment for investigating the possibility of monitoring wetland inundation and freeze/thaw (FT) dynamics which are additionally impacted by snow on the ground. Effects of inundation, snow cover, and soil FT state on observed GNSS-R signal-to-noise ratios (SNRs) are analyzed for horizontal (H) and vertical (V) polarizations. A simple classification approach is suggested to detect the inundated, frozen, or thawed soil state. A simple forward reflectivity model is formulated to evaluate the influence of snow cover, overlying frozen, or thawed soil, on the reflected GNSS signals. Reflectivity time series are simulated in H- and V-polarizations using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> observations of the Arctic wetland site. The simulations are used to verify the tower-based observations, which show a significant impact of wet snow on reflectivity during melting conditions in spring. The observed SNR is strongly correlated with the Sentinel-1 backscatter coefficient. Generally, soil states detected by GNSS-R are in high agreement with ground truth soil states, especially for inundated and frozen soils. Wet snow conditions, however, complicate the correct timing estimation of soil thawing by inducing reflectivities of a similar order as thawing soil. It is recommended that GNSS-R land application models and retrieval algorithms consider snow cover effects to reduce false classification, especially in FT detection. Overall, the outcome of this study is relevant to the upcoming ESA HydroGNSS mission.

Runoff and drainage trade‐offs from cover crops exposed to freeze–thaw events

AbstractWinter cover crops are widely promoted for multiple ecosystem services although nutrient leaching from the plant biomass and subsequent transport of those nutrients is possible after freeze–thaw events. The objective of this study was to determine the effect of freeze–thaw conditions on both runoff and drainage or leachate water quality from two common cover crops. Rainfall simulations were performed on packed columns (20 cm diam.; 56 cm length) that included triplicate combinations of cereal rye (Secale cereale L.), forage radish (Raphanus sativus L. var. longipinnatus), and bare soil and a heavy, light, and no freezing treatment. The two cover crops reduced runoff total suspended solids concentrations and nitrate leaching compared with a bare soil control, confirming many cover cropping benefits. The heavy freezing conditions (including two nights of &lt;–15 °C) resulted in significantly higher total phosphorus and nitrate concentrations in both runoff and leachate from the cereal rye, which had been killed, compared with unfrozen cereal rye. Some of the conditions tested in this lab‐scale study could be considered extreme (e.g., 10.1 cm h−1 rainfall × 2 h, −15.7 °C) but these results nonetheless help demonstrate the importance of effective conservation practices for both surface and subsurface flows as well as for multiple water quality parameters in the face of increasing weather variability.

Satellite Retrievals of Probabilistic Freeze-Thaw Conditions From SMAP and AMSR Brightness Temperatures

The freeze-thaw (FT) status of soil regulates ecological and hydrologic processes and is therefore a vital component of land surface models. This study utilizes a Hidden Markov Model (HMM) to retrieve surface FT status from L-band (SMAP) and Ka-band (AMSR) satellite microwave brightness temperatures in cold-constrained lands north of 45 °N. The HMM, parameterized on a per-gridcell basis such that there are two possible states and emissions probabilities are assumed to be a two-component Gaussian Mixture, produces the posterior probability (a continuous variable between 0 and 1) that the surface is frozen given the radiometer input. HMM classification accuracy, averaged over five core validation networks, is acceptable (Ap > 80 %) when judged against in situ air and soil temperature measurements from individual validation sites and is comparable to that of current FT products that produce a discrete state. Patterns in performance across variable land class, open water fraction, and elevation are assessed from 91 sparse network weather stations within 87 gridcells in the domain. The resulting satellite data record provides a continuous variable estimate of the daily probability of frozen conditions over northern land areas experiencing widespread thawing of permafrost and a shrinking frozen season due to global warming.

A Novel Freeze-Thaw State Detection Algorithm Based on Passive L-Band Microwave Remote Sensing

A Novel Freeze-Thaw State Detection Algorithm Based on Passive L-Band Microwave Remote Sensing

Freeze/thaw onset detection combining SMAP and ASCAT data over Alaska: A machine learning approach

In the context of global warming, permafrost degrades gradually. To cope with the instability of the cryosphere, it is very important to strengthen the monitoring of the seasonal freeze–thaw cycle. At present, active and passive microwave remote sensing data are widely used in freeze/thaw (F/T) onset detection. There is some potential to improve accuracy through the combination of active and passive microwave data. Compared with the traditional method for combination, the machine learning algorithm has a stronger nonlinear expression ability. Therefore, it is advisable to use machine learning to combine multi-source data for freeze/thaw onset detection. In this study, the temporal change detection method is applied to SMAP data and ASCAT data respectively for preliminary detection. Then the Random Forest algorithm (RF) is used to combine the preliminary results of active and passive microwave data with site observation to estimate the freeze/thaw onsets more accurately. The method is validated with data obtained in Alaska from 2015 to 2019. The accuracy evaluation shows that the proposed method can effectively improve the accuracy of freeze/thaw onset detection. The predicted distribution of the freeze/thaw cycle indicates that the variation of the freeze–thaw cycle is closely related to latitude. In general, the proposed method based on machine learning is promising in the research of freeze–thaw state monitoring.

Spatiotemporal characteristics of the soil freeze-thaw state and its variation under different land use types - A case study in Northeast China

With global warming, the soil freeze-thaw state has greatly changed, which has profoundly impacted the balance between water resources, ecological security and regional agriculture and forestry production in frozen regions. Based on daily soil freezing/thawing depth data in Heilongjiang Province over the last 60 years, Mann-Kendall trend analysis, Sen's slope and Hurst exponent were performed to analyze the spatiotemporal characteristics of the soil freeze-thaw state, and the effects of nonclimatic factors "land use types" and snow cover on the change in the soil freeze-thaw state were discussed. The results indicated that (1) the soil freeze-thaw state significantly changed over the past 60 years. The maximum seasonally frozen depth decreased approximately by 48 cm, the first freezing date was delayed by approximately 10 d, the first thawing date and last date advanced approximately by 6 and 27 d, respectively, the freezing and thawing periods decreased by approximately 17 and 21 d, respectively, and the duration and actual number of freezing days decreased by 38 and 34 d, respectively. (2) The soil freeze-thaw state changed abruptly in 1988 and exhibited a significant trend after the 1990s. The Hurst exponent of the soil freeze-thaw state variables at approximately 2/3 of the stations reached the strong persistence level. (3) In forestland and grassland areas, vegetation coverage reduced the climate warming impact on the soil freeze-thaw state. In addition, the maximum snow depth was significantly correlated with the soil freezing depth and first thawing date, and the change in snow depth also offset the effects of temperature rise on soil freezing depth and first thawing date to a certain extent. Changes in the soil freeze-thaw state have both advantages and disadvantages on agricultural production. Therefore, it is necessary to strengthen agricultural monitoring and use territorial knowledge to reasonably regulate agricultural production.

Investigation on the Effect of Seawater Condition, Sulphate Attack, Acid Attack, Freeze–Thaw Condition, and Wetting–Drying on the Geopolymer Concrete

Investigation on the Effect of Seawater Condition, Sulphate Attack, Acid Attack, Freeze–Thaw Condition, and Wetting–Drying on the Geopolymer Concrete

Seasonal Performance Evaluation of Pavement Base Using Recycled Materials

Using recycled pavement materials to construct new pavement base is currently an important construction strategy bringing improved sustainability. This study investigates the long-term performance of pavement bases constructed with recycled concrete aggregate (RCA), reclaimed asphalt pavement (RAP), and blends with natural aggregates in a seasonal frost region. The stabilization effect of fly ash on RAP was studied as well. In situ falling weight deflectometer (FWD) tests were routinely conducted to provide seasonal deflection data, which were used to back-calculate the layer modulus. Seasonal changes in the base layer modulus along with the pavement ride quality were monitored. One of the two lanes at the test sections was consistently subjected to traffic loading, whereas the other one was not. Findings from this field research indicated that after undergoing over 8 years of naturally seasonal freeze-thaw conditions, 100% RCA, 50% RCA, plus 50% natural aggregates, and 100% RAP, presented improved performance over 100% natural aggregates. However, 50% RAP blended with 50% natural aggregates performed comparably to natural aggregates only, and fly ash did not provide considerable improvement on the long-term performance of 50% RAP plus 50% natural aggregate base. Seasonal climatic variations turned out to affect pavement performance more critically than traffic loading.

Cover crop mixtures: A powerful strategy to reduce post-harvest surplus of soil nitrate and leaching

Cover cropping is a practice with potential to reduce post-harvest surplus of soil nitrate (NO3-), a mobile form of nitrogen naturally susceptible to losses. Increased soil NO3- leaching occurs when high soil NO3- coincides with high drainage events – a common occurrence during the non-growing season in cold and humid climates. The potential of cover crops to reduce NO3- leaching can be affected by the performance of the cover crop and by edaphic-climatic conditions (e.g., freeze-thaw cycles, soil type) and is subjected to interannual variation. Here, we evaluate soil type and crop rotation effects on soil parameters (i.e., NO3- concentration, temperature, water content) and on NO3- leaching under freeze-thaw conditions, using a high-frequency weighing lysimeter system. The soil type consisted of silt loam (SIL) and loamy sand (LS) soils and the crop rotation consisted of a rotation with a mixture of leguminous/non-leguminous cover crops (+CC) and no cover crop (-CC). This research was conducted during periods of 2017/2018 and 2018/2019 subjected to significant drainage. Our results indicated that cover crops did not affect drainage but affected soil temperature, with warmer soils observed over the winter when cover crops were used (+CC) than without cover-crops (-CC). Moreover, the cereal-crucifer-legume mixture after spring wheat reduced soil NO3- content by 80% compared to -CC during 2017/2018. For 2018/2019, due to poor establishment of the cereal-legume mixture under-seeded to corn, no reduction in soil NO3- content was observed. The reduction in soil NO3- in +CC plots for 2017/2018 translated to a significant reduction (by 67%) in NO3- leaching averaged across soil types. Soil drainage, NO3- content and NO3- leaching were not affected by soil type, an effect in part influenced by the boundary controls of the lysimeter system which mimicked soil conditions of a non-LS adjacent/reference field. To expand our results, we estimated the potential drainage of a hypothetical excessively drained LS (ED-LS) – a soil naturally subjected to high hydraulic conductivity and low water holding capacity. Overall, our results indicated that cover cropping can reduce NO3- leaching independent of soil type but the effect can be pronounced for ED-LS.

Degradation of Mechanical Behavior of Sandstone under Freeze-Thaw Conditions with Different Low Temperatures

This study investigated the effects of freezing temperature under freeze-thaw cycling conditions on the mechanical behavior of sandstone. First, the sandstone specimens were subjected to 10-time freeze-thaw cycling treatments at different freezing temperatures (−20, −40, −50, and −60 °C). Subsequently, a series of density, ultrasonic wave, and static and dynamic mechanical behavior tests were carried out. Finally, the effects of freezing temperature on the density, P-wave velocity, stress–strain curves, static and dynamic uniaxial compressive strength, static elastic modulus, and dynamic energy absorption of sandstone were discussed. The results show that the density slightly decreases as temperature decreases, approximately by 1.0% at −60 °C compared with that at 20 °C. The P-wave velocity, static and dynamic uniaxial compressive strength, static elastic modulus, and dynamic energy absorption obviously decrease. As freezing temperature decreases from 20 to −60 °C, the static uniaxial compressive strength, static elastic modulus, dynamic strength, and dynamic energy absorption of sandstone decrease by 16.8%, 21.2%, 30.8%, and 30.7%, respectively. The dynamic mechanical behavior is more sensitive to the freezing temperature during freeze-thawing cycling compared with the static mechanical behavior. In addition, a higher strain rate can induce a higher dynamic strength and energy absorption.

Study on failure mechanism of concrete subjected to freeze-thaw condition in airport deicers

The rapid freeze–thaw test about ordinary Portland cement concrete (PCC) was performed in the deicers of water, 3.5% ethylene glycol, 3.5% NaCl and 3.5% calcium magnesium acetate (CMA). The ice pressure (Ip) of deicer was tested, and the concept of the ice pressure impulse (IPI) was proposed. A crack density model was employed to describe the freeze–thaw damage process of concrete. Results indicated that the freeze–thaw damage of PCC in CMA deicer was the mildest. The Ip value of water was the highest but its IPI value was the lowest. The freeze–thaw microcracks inside concrete was induced by the Ip of deicer restrained in concrete pores. The freeze–thaw crack density decreased with the relative depth of specimen. The value of superficial critical crack density was 0.85 ∼ 0.88, when the exterior mortar of concrete began spalling. The value of central critical crack density was 0.32 ∼ 0.34, when the interior freeze–thaw failure of concrete occurred.

Sustainable and Reusable Gelatin-Based Hydrogel “Jelly Ice Cubes” as Food Coolant. II: Ideal Freeze–Thaw Conditions

Sustainable and Reusable Gelatin-Based Hydrogel “Jelly Ice Cubes” as Food Coolant. II: Ideal Freeze–Thaw Conditions

Cryopreservation of Infant Gut Microbiota with Natural Cryoprotectants.

A growing body of evidence has demonstrated the importance of the gut microbiome in human health. In general, fecal microbial samples are used to study the mechanisms of relevant diseases. In this context, it is worth mentioning that an optimized cryopreservation method is urgently needed to successfully perform clinical diagnosis, therapy, and scientific investigations of the gut microbiome without affecting its viability and biological activity. In this study, we aimed to test the relative cryopreservation efficiency of different nontoxic natural cryoprotectants using infant fecal and meconium samples. First, we selected two facultative and two obligate anaerobic bacteria as the experimental gut microbial strain to compare these cryoprotectants' toxicity and concentration-dependent bacteria viabilities after cryopreservation, then the viabilities and bacterial diversity of mixed facultative and obligate anaerobic bacteria. Finally, we explored the effects of optimized cryoprotectants for meconium and infant feces after cryopreservation using 16S rRNA sequencing analyses. In addition, to better understand the effectiveness of these cryoprotectants, we used different freeze-thaw conditions mimicking real-life situations in the process of distribution. We found that the better choice for the infant fecal sample's cryopreservation was 100 mg/mL trehalose, whereas 200 mg/mL trehalose/betaine was the optimum choice for meconium cryopreservation. We hope that our results will shed light on the importance of natural cryoprotectants toward the long-term and stable viability of invaluable human gut microbial specimens.