Mechanical behaviour and microstructural evolution of organic material-stabilized sandy soil under freeze‒thaw cycles

Uniaxial compressive mechanical properties and stress–strain model for roller-compacted concrete with initial damage subjected to freeze–thaw cycles

The effect of microstructural evolution on the permeability of sandstone under freeze-thaw cycles

Engine turbine blades are subjected to high-temperature and high-speed fragment impacts during use, and the ability of the blades to resist shocks affects their reliability. At present, there are few studies on the ability to withstand shocks of Ni-based single crystal alloys, especially with regards to their mechanical behaviour and microstructural evolution under shock loading. The solutions to the above problems can further help us understand the mechanisms of the mechanical responses and microstructural evolution of Ni-based single crystal alloys under shock loading. Thus, we study the mechanical behaviour and microstructural evolution characteristics of Ni-based single crystal alloys with different crystal orientations under shock loading using molecular dynamics simulations. We find that the (001) phase interface has the strongest impediment ability due to its dislocation network structure and the expansion of dislocations, which lead to the greatest reinforcing effect on the matrix. The penetration force of the (001) phase interface is the greatest with fragment penetration. Moreover, the energy dissipation capacity of the (001) phase interface is the highest with fragment penetration because it has the strongest resistance to shock loading. The second highest is the (110) phase interface, and the minimum dissipation capacity comes from the (111) phase interface. This study has an important theoretical significance for the in-depth understanding of the failure mechanisms of Ni-based single crystal alloys under shock loading.

Influence of freeze-thaw cycles on change of arsenic speciation and toxic effects to bacteria in paddy soil.

Quantification of hepatitis B virus (HBV) DNA and hepatitis C virus (HCV) RNA often is performed in specimens that have been frozen and thawed more than once. To ensure optimal therapeutic and prognostic value, it is important to establish whether viral load measurements are affected by repeated freeze-thaw (FT) cycles. We therefore evaluated the effect of multiple FT cycles on HBV DNA and HCV RNA quantification by testing serum specimens subjected to one (baseline), two, four, and eight FT cycles with the appropriate Chiron Quantiplex assay. Linear regression analysis showed minor increases of 1.7% per FT cycle for both HBV DNA and HCV RNA. The rise in HCV RNA levels was more pronounced among low-concentration samples, since further analysis revealed an increase of 3.2% per FT cycle among samples with 0.2 to 3.86 Meq of HCV RNA per ml. Given that the coefficient of variation for the Quantiplex assays is generally 10 to 15%, the minor increases in HBV DNA and HCV RNA levels with progressive FT cycles for the specimens tested were recognized only because analysis of variance revealed a statistically significant trend (P < 0.05). Due to the minor statistical trend, the clinical impact for individual patient specimens is likely to be limited, but it may deserve further study. In conclusion, the concentration of HBV DNA and HCV RNA in serum specimens subjected to up to eight short-term FT cycles was stable.

Pavement failure in seasonal frozen areas is mainly accelerated by the periodic freezing–thawing cycles. This study investigates the suitability of cement and household waste product such as wood ash as stabilizing agent to improve the strength behaviour of soil subjected to seasonal freeze–thaw cycles. Test samples were prepared by blending the frost affected soil with 2%, 4% and 6% cement as well as 5%, 10%, 15% and 20% wood ash and combination of both, respectively. Unconfined compressive tests were performed on Soil+Cement, Soil+Wood ash and Soil+Cement+Wood ash samples after 0, 3, 7, 14 and 28 days of curing periods and 28 freeze–thaw cycles. The results show a noteworthy increase in the strength of “Soil+cement+wood ash” mix over “soil+cement” or “soil+wood ash” mix when subjected to freeze–thaw cycles and strength improvement is augmented with curing periods. The highest UCS value was found to be of soil treated with 6% cement and 20% wood ash, with an increase of UCS value from 258 kPa of untreated soil to 4405 kPa of treated soil for non-freeze–thaw cycle and 237–4572 kPa for 28 days freeze–thaw cycles. Further, scanning electron microscope and energy-dispersive X-ray spectrometer tests were conducted to comprehend the mechanism involved in the stabilization process. Change in soil structure and formation of cementitious compounds were observed on addition of cement and wood ash.KeywordsFreeze–thawWood AshUCSSEMEDX

The continuous increase in the emissions of iron ore tailings (IOTs) has caused serious pollution to the environment and raised costly IOT management costs. For protecting the environment and decreasing the economic cost, the fiber-reinforced tailing mortar was prepared with 50% IOTs, polyacrylonitrile fiber (PANF), and basalt fiber (BF). The mass loss, porosity, ultrasonic velocity, mechanical strength, and pore structure of tailing mortar after different treatments, including 100 freeze–thaw (FT) cycles and 90 sulfate attack (SA) cycles were analyzed to investigate the effect of PANF and BF on the durability. The test results indicated that BF and PANF have great bridging effects and cracking resistance to improve the durability properties. The B0.25P0.05 (BF: 0.25% and PANF: 0.05%) specimens possess the minimum mechanical strength loss, particularly the uniaxial compressive strength (UCS) only decreased by 5.58% after 100 FT cycles and 2.73% after 90 SA cycles. The B0.25P0.05 specimens also have the smallest dynamic elastic modulus loss, and the reduction was only 7.24% after 100 FT cycles and 0.76% after 90 SA cycles. For 120-day long-term tests, the B0.25P0.05 specimens have the maximum increment in the UCS (22.04%) and dynamic elastic modulus (5.60%). Besides, the mechanical strength of tailing mortar undergoing FT and SA cycles can be predicted accurately by dynamic elastic modulus (prediction error ≤5%). From a microscopic view, the nuclear magnetic resonance (NMR) test demonstrated that fibers significantly decrease the large pores and improve the pore microstructure, and thus raise the mechanical properties. Finally, the ranking of durability is B0.25P0.05 > B1.00P0 > B0P0.08 > B0P0. The hybrid fibers of rigid BF (6 mm) and flexible PANF (12 mm) in tailing mortar cross-climb to generate a denser network structure. Besides, BF and PANF in the mortars can effectively fill the pores and bear expansion stress caused by FT and SA cycles. Therefore, these effects remarkably limit the deformation with different sizes.

Evolution of soil-water and shrinkage characteristics of an expansive clay during freeze-thaw and drying-wetting cycles

In the Loess Plateau, seasonal freeze and thaw cause great damage to the mechanical behavior and microstructure of soil, which leads to frequent geological disasters during winter and spring. To investigate the influence of freeze‐thaw (FT) cycling (FTC) on the shear strength and microstructure of intact loess, triaxial shear, nuclear magnetic resonance, and scanning electron microscope tests were carried out on soil samples after target FT cycles. The results indicate that the FTC has limited changes to the soil stress‐strain curve, but has a significant attenuation effect on the peak deviatoric stress. The peak deviatoric stress was attenuated by FTC but changed insignificantly after ten cycles. The cohesive force decays exponentially with the number of FT cycles, while the internal friction angle increases slightly. Moreover, under FTC, the T2 hydrogen spectra of soil samples showed a multimodal distribution, with the main peak appearing to have two obvious upward shifts that occurred at 6 and 10 FT cycles. Indeed, a depolarization phenomenon related to the directional frequency of soil particles was observed, and the mass fractal dimension of the pore network increased slightly. In an FT environment, the shear strength declines due to accumulated internal microstructural damage. These findings contribute to a better understanding of the response of loess to FTC and provide novel ideas for the prevention of frost damage in loess areas.

The effect of adding polypropylene fibers on the freeze-thaw cycle durability of lignosulfonate stabilised clayey sand

Seasonal freeze-thaw cycle (FTC) is one of the key processes that affect heavy metal behaviors in soil. However, previous studies are mainly focused on extreme FTC treatments which may exaggerate the real FTC effects in the field. This study aimed to compare the effects of different FTC conditions on the adsorption and desorption behaviors of Cd in the surface black soil. Different minimum freezing temperatures (- 2, - 5, and - 15°C), FTC rates (1 and 20°Ch-1), freezing lengths (2 and 24h), and FTC frequencies (1, 3, and 9) were investigated. The thawing temperature was set at 5°C. The amplitude for the FTC rate, length, and frequency experiments ranged from 5 to - 2°C. Our results indicated that the adsorption amounts of Cd presented an order of - 2°C > - 15°C > - 5°C and 24h > 2h for different FTC amplitude- and freezing length-treated soils, and the adsorption amounts decreased with increasing FTC rate and frequency. Soil maximum adsorption amount of Cd increased with the increases of FTC frequency, freezing length, and FTC rate, while it decreased with the decreases of freezing temperature. Soil Cd desorption ratio decreased with the increases of FTC frequency, freezing length, and TFC rate, and it increased with the increasing freezing temperature. Our results suggested that FTC conditions can significantly influence the adsorption and desorption behaviors of heavy metal in soil.

Expansion and contraction of clogged open graded friction course exposed to freeze-thaw cycles and degradation of mechanical performance

Effect of freeze-thaw cycles on engineering properties of biocemented sand under different treatment conditions

The frost weathering of three French limestones [Lens (LS), Migne (MI) and Savonnieres (SA)], with different physico-mechanical properties, during the freeze–thaw cycles was studied. The weathering evolution in stone samples undergoing the freeze–thaw cycles was monitored by measurement of following properties: total porosity, P-wave velocity, static elastic moduli, uniaxial compressive strength and toughness. The thermo-mechanical behaviour of stones was also studied by measurement of the strain and temperature (in surface and centre of sample) during one freeze–thaw cycle. These results, mainly the weathering observed for SA(73) with a degree of saturation of 73 % and a lack of weathering for LS with a degree of saturation of 90 %, show that it is impossible to define a unique critical degree of saturation for different stones and this varies from stone to stone. The shrinkage and (or) the expansion of samples during the crystallization phase were determined. The shrinkage is related to the migration of water away from tiny pores towards larger cavities where ice has already formed. The expansion is attributed on the one hand to the rise in pressure that comes from the water which flows towards the ice front and on the other hand to the relatively important quantity of ice formed when thermal contraction and the contraction due to migration dominate. The elastic moduli (static moduli and dynamic moduli) was found to be affected the most by frost weathering and is a real sensor of first micro-crack initiation, whereas the uniaxial compressive strength and the porosity were found to be affected the least.

Cracked rock masses in cold regions are subjected to freeze–thaw cycles over extended periods, resulting in freeze–thaw deformation. The combined effects of freeze–thaw cycling and the depth of cracks significantly influence the stability and durability of underground rock engineering in these regions. In some cold regions with minimal annual rainfall, rock masses are unable to absorb external water during freeze–thaw cycles. As freeze–thaw deformation progresses, the rock transitions naturally from a saturated state to an unsaturated state. To investigate the deformation damage mechanisms and evolution patterns of saturated red sandstone with initial non-penetrating cracks of varying depths (20 mm, 30 mm, 40 mm) under freeze–thaw cycling conditions without external water replenishment and with naturally varying saturation levels, relevant freeze–thaw cycle experiments and strain monitoring were conducted. The results indicate that cracked red sandstone experiences residual strain in each freeze–thaw cycle, which gradually accumulates, leading to irreversible freeze–thaw damage deformation. The cumulative residual strain of the rock specimen after 45 freeze–thaw cycles was 40.69 times greater than the residual strain from the first cycle. Additionally, the freeze–thaw strain characteristic values exhibited a clear correlation with crack depth. These findings provide experimental methods and data references for analyzing the deformation and failure mechanisms of cracked rock induced by freeze–thaw damage in cold regions.