Quantification of the concrete freeze–thaw environment across the Qinghai–Tibet Plateau based on machine learning algorithms

The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering managers should take into account. In this paper, we propose a more realistic method to calculate the number of concrete freeze–thaw cycles(NFTCs) on the QTP. The calculated results show that the NFTCs increase as the altitude of the meteorological station increases with the average NFTCs being 208.7. Four machine learning methods, i.e., the random forest(RF) model, generalized boosting method(GBM), generalized linear model(GLM), and generalized additive model(GAM), are used to fit the NFTCs. The root mean square error(RMSE) values of the RF, GBM, GLM, and GAM are 32.3, 4.3, 247.9, and 161.3, respectively. The R^(2) values of the RF, GBM, GLM, and GAM are 0.93, 0.99, 0.48, and 0.66, respectively. The GBM method performs the best compared to the other three methods, which was shown by the results of RMSE and R^(2) values. The quantitative results from the GBM method indicate that the lowest, medium, and highest NFTC values are distributed in the northern, central, and southern parts of the QTP, respectively. The annual NFTCs in the QTP region are mainly concentrated at 160 and above, and the average NFTCs is 200 across the QTP. Our results can provide scientific guidance and a theoretical basis for the freezing resistance design of concrete in various projects on the QTP.

Stress-Strain Relationship and Failure Criterion for Concrete after Freezing and Thawing Cycles

The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out. Based on the damage mechanics theory, the dsmage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained. Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies tile rationality of tile damage-based one-dimensional stress-strain relationship proposed.

Calculation of salt-frost heave of sulfate saline soil due to long-term freeze−thaw cycles

Based on salt-frost heave tests of sulfate saline soil under repeated freeze−thaw cycles,this paper discusses the mechanism of the salt-frost heave under long-term freeze−thaw cycles.The results show that the salt-frost heave can be restricted considerably by loads,and there is a critical load for the salt-frost heave cumulative effect.Under this load,peak values of salt-frost heave approach a constant,and the residual values become 0.There is no longer structure heave or cumulative effect of saline soil exposed to freeze−thaw cycles under the critical load.Taking cumulative effect into account in calculations of salt-frost heave,a salt-frost heave model under freeze−thaw cycles is developed.

Freeze–thaw resistance of eco–material stabilized loess

In the Loess Plateau in Northern China,repeated freeze–thaw(FT)cycles deteriorate the strength and structure of loess as a foundation soil,resulting in the instability or failure of supporting structure.Lignosulfonate is an eco–material,utilized as an effective and nontraditional stabilizer to improve the engineering properties of metastable soils.A series of laboratory tests,including unconfined compression tests,cyclic loading–unloading tests and scanning electron microscopy,on calcium lignosulfonate(CL)-and sodium lignosulfonate(SL)-stabilized loess were performed to investigate the stabilization effect,deterioration mechanisms of the FT cycles,and the resistance to FT cycles.Two traditional stabilizers,quicklime(QL)and sodium silicate(SS),were selected,and the engineering properties of QL-and SS-stabilized loess were compared with those of CL-and SLstabilized loess.The results showed that the strength values of CL-and SL-stabilized loess specimens decreased by 34.2%and 50%respectively,after 20 FT cycles,whereas those of the traditionally SS-and QL-stabilized specimens decreased by 85.3%and 82.87%,respectively.The elastic moduli of SL-and QL-stabilized loess specimens decreased by 22.1%and 92.0%,respectively.The mean energy dissipations of nontraditionally treated specimens also decreased significantly less than those of traditionally treated specimens.Overall,the results showed CL and SL had better stabilization effects on engineering properties of loess than QL and SS,and their stabilized loess specimens exhibited stronger resistance to FT cycles.The study findings demonstrated the significant potential of lignosulfonate for extensive application in cold loess areas.

Responses of soil microbial communities to freeze–thaw cycles in a Chinese temperate forest

Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but their responses to freeze–thaw cycles(FTCs)are poorly understood.We conducted a feld freeze–thaw experiment in a natural Korean pine and broadleaf mixed forest in the Changbai Mountain Nature Reserve,China,to determine the dynamic responses of soil microbial communities to FTCs.Results:Bacteria were more sensitive than fungi to FTCs.Fungal biomass,diversity and community composition were not signifcantly afected by freeze–thaw regardless of the stage.Moderate initial freeze–thaw resulted in increased bacterial biomass,diversity,and copiotrophic taxa abundance.Subsequent FTCs reduced the bacterial biomass and diversity.Compared with the initial FTC,subsequent FTCs exerted an opposite efect on the direction of change in the composition and function of the bacterial community.Soil water content,dissolved organic carbon,ammonium nitrogen,and total dissolved phosphorus were important factors determining bacterial community diversity and composition during FTCs.Moreover,the functional potentials of the microbial community involved in C and N cycling were also afected by FTCs.Conclusions:Diferent stages of FTCs have diferent ecological efects on the soil environment and microbial activities.Soil FTCs changed the soil nutrients and water availability and then mainly infuenced bacterial community composition,diversity,and functional potentials,which may disturb C and N states in this temperate forest soil.This study also improves our understanding of microbial communities regulating their ecological functions in response to climate change.

Influence of fines content on the anti-frost properties of coarse-grained soil

This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows： （1） the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; （2） the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; （3） with increasing numbers of freeze-thaw cycles, the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engi- neering design values; and （4） considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway sub,fade coarse-~rained soil fillings in frozen re^ions.

Compressive Mechanical Characteristics of Multi-layered Gradient Hydroxyapatite Reinforced Poly(Vinyl Alcohol) Gel Biomaterial

Functional gradient materials provided us a new concept for artificial articular cartilage design with gradient component and gradient structure where one side of the material is high free water content thereby providing excellent lubrication function and the opposite side of the material is high hydroxyapatite content, thereby improving the bioactivity of the material and stimulating cell growth. The goal of the present study was to develop a multi-layered gradient HA/PVA gel biocomposites through layer-by-layer casting method combing with freeze/thaw cycle technology. The various influence factors on the compressive strength and modulus of the multi-layered gradient biocomposites were investigated. The results showed that the compressive mechanical characteristics of the biocomposites were similar to that of natural articular cartilage. Both the compressive strength and modulus of the multi-layered gradient HA/PVA gel biocomposites increased exponentially with the rise of compressive strain ratio. Both the compressive strength and average compressive modulus of the biocomposites improved with the rise of freeze/thaw cycle times and total concentration of HA particles in the biocomposites, but they showed decreasing tendency with the rise of HA concentration difference between adjacent layers.

Winter survival of microbial contaminants in soil:An in situ verification

The aim of the research was to evaluate, at site scale, the influence of freezing and freeze/thaw cycles on the survival of faecal coliforms and faecal enterococci in soil, in a climate change perspective. Before the winter period and during grazing, viable cells of faecal coliforms and faecal enterococci were detected only in the first 10 cm below ground, while,after the winter period and before the new seasonal grazing, a lower number of viable cells of both faecal indicators was detected only in some of the investigated soil profiles, and within the first 5 cm. Taking into consideration the results of specific investigations, we hypothesise that the non-uniform spatial distribution of grass roots within the studied soil can play an important role in influencing this phenomenon, while several abiotic factors do not play any significant role. Taking into account the local trend in the increase of air temperature, a different distribution of microbial pollution over time is expected in spring waters, in future climate scenarios. The progressive increase in air temperature will cause a progressive decrease in freeze/thaw cycles at higher altitudes, minimising cold shocks on microbial cells, and causing spring water pollution also during winter.