The physicochemical combination method (PCCM) is a new integrated method for treating and reusing large volumes of slurry-like mud (MS). To study the effects of freezing-thawing (FT) cycles on the mechanical properties of MS treated by the PCCM, unconfined compression tests (UCTs) and microstructural tests are both conducted on PCCM-treated MS samples with different combinations of FT cycles, initial water contents (wei), and cementitious binder contents (wc). The experimental results indicate that the unconfined compressive strength (UCS) and the elastic modulus (E) of PCCM-treated MS decrease exponentially when the FT cycles increase from 0 to 15. For the PCCM-treated MS samples subjected to 15 FT cycles, the reduction degree of their strength, as well as deformation resistance, is more sensitive to the variation of wc compared to that of wei. Meanwhile, the UCS and E of PCCM-treated MS samples are higher than those of the corresponding MS samples treated by the conventional cement solidification method (CCSM). The superior resistance to FT cycles of PCCM-treated MS is attributed to the presence of APAM, which not only facilitates the aggregation of soil particles but also enhances the dewatering efficiency of MS. Notably, the E/UCS value of CCSM-treated MS is 1.25 times larger than that of PCCM-treated MS, indicating the application of PCCM can significantly enhance the toughness of the treated MS.

The waste tire rubber may be incorporated with the cement soil to improve its frost resistance. However, it remains a significant challenge to optimise the rubber content between its mechanical strength and durability under freeze-thaw conditions. In this study, the macroscopic mechanical properties of ordinary cement soil and rubber-cement soil (with particle sizes of 30 and 60 mesh) were explored under different freeze-thaw cycles (0, 3, 6, 9, 15) by taking the wave propagation and unconfined compressive strength (UCS) tests. Subsequently, a series of scanning electron microscope (SEM) and X-ray diffraction (XRD) tests were conducted to analyse the microstructure of the specimens, further clarifying the freeze-thaw damage mechanisms in rubber-cement soil. The results show that freeze-thaw cycles cause irreversible internal damage to the cement soil, leading to continuous reductions in both wave velocity and UCS. After 15 freeze-thaw cycles, the wave velocity loss rates are 95%, 72.2%, and 89.7% for ordinary cement soil, cement soil mixed with 30-mesh and 60-mesh rubber particles, respectively. The corresponding UCS loss rates are 95.4%, 82.7%, and 89.2%, respectively. The above results suggest that 30-mesh rubber-cement soil exhibits superior frost resistance. From a microstructural perspective, the rubber particles delay and inhibit the propagation of frost heaving cracks, forming a denser spatial structure for calcium silicate hydrates (C-S-H) gel, thereby improving the freeze-thaw resistance. By integrating macroscopic mechanical testing and microstructural analysis, this study reveals the mechanical properties and damage mechanism of rubber-cement soil under freeze-thaw conditions, providing valuable insights for its engineering applications.

Insight into the growth of internal microstructure and surface morphology is critical for understanding the robustness of red sandstone artifacts in frigid environments. Since freeze-thaw (F-T) cycles can exacerbate the surface deterioration of water-bearing sandstone, a series of investigation on fresh and weathered water-bearing sandstone samples with different F-T cycle numbers (i.e. 0-100) is performed in this study, including three-dimensional (3D) laser scanning, scanning electron microscope (SEM) and computed tomography (CT) scanning tests, thermal property tests, Brazilian tests, and multi-field numerical simulations. Our results demonstrate that with increasing F-T cycles, the surface fractal dimension and specific surface area of red sandstone samples increase, and the pore size distribution inside rocks shifts from ultrananopores (10-100 nm) to micro-pores (0.1-100 mm) and ultramicropores (100 mm & thorn;). Spatially, the pores generated by the F-T cycles are more prominent near the surfaces of rock samples. Numerical simulation indicates that the uneven pore distribution leads to surface degradation. After 100 F-T cycles, the intergranular (IG) cement of the samples cracks, and the IG fractures are widened; eventually, due to the structural integrity weakening, the tensile strength is drastically reduced by over half. The thermal properties of the water-saturated sandstone can be improved during the F-T cycles, and a strong coefficient of determination of 0.98 exists between the fractal dimensions of sandstone surface and the tensile strength. When assessing the mechanical properties of stone artifacts under F-T cycles, the morphological damage of red sandstone should first be investigated when in situ sampling is inappropriate. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

In the current study, the durability of a clayey-sand stabilized with copper-slag (CS)-based geopolymer and alkaline activator solution (AAS) is investigated in freezing-thawing (F-T) cycles. For this purpose, tests including Atterberg limits, pH, standard Proctor compaction, unconfined compressive strength (UCS), accumulated loss of mass (ALM), swell and shrinkage, ultrasonic P-wave velocity, the toxicity characteristic leaching procedure (TCLP), and scanning electron microscopy (SEM) analysis were conducted. Various contents of CS (i.e., 0, 10%, and 15%) and 8 and 11 M NaOH were assessed in 0, 1, 3, 6, 9, and 12 cycles. The AAS contained 70% of Na2SiO3 and 30% of NaOH. Also, the weight ratio of CS to ASS was 1 (CS/ASS = 1). According to the TCLP test, the CS-based geopolymer stabilized samples have no environmental hazards. The results illustrated that the strength and stiffness of untreated soil increased with an increase in F-T cycles until cycle 3. For samples with 11 M NaOH concentration, loss of strength and stiffness were observed due to F-T cycles. Furthermore, the sample with 8 M NaOH showed hybrid behavior (i.e., an increase in strength and stiffness until cycle 3), similar to that of untreated soil, and then declined until cycle 9, similar to soil treated with 11 M NaOH. Based on the microstructural analysis, higher microcracks were observed in the 8 M sample compared with the 11 M sample due to soft-strain behavior. Furthermore, a higher microcrack formation resulted in a higher potential for swell mass and volume change.

Foam concrete is characterized by lightweight, self-compacting and high flowability, thereby widely used as a subgrade bed filler. High-speed railway subgrades usually experience inhomogeneous deformation due to the occurrence of freezing-thawing cycles in seasonally frozen soil areas. It is essential to study the deformation behavior of foam concrete under the coupling effect of freezing-thawing cycles and dynamic loading. In this paper, dynamic triaxial tests were performed to study the accumulative deformation of the foam concrete under different numbers of freezing-thawing cycles, freezing temperatures, amplitudes and frequencies of dynamic loading. Based on the scanning electron microscopy (SEM) tests, the characteristics of the pore structure were analyzed quantitatively by introducing the directional distribution frequency and fractal dimension. The research results illustrate that the damage caused by freezing-thawing progress to the pore structure results in more significant deformation of the foam concrete subjected to dynamic loading. There exists an accumulative damage effect induced by the coupling action of long-term dynamic loading and freezing-thawing progress on the microstructure and mechanical properties of foam concrete. The development of the fractal dimension agrees with that of the accumulative strain, indicating a close connection between the microstructure and the dynamic behavior of foam concrete. The findings concluded in this study contribute to a sufficient understanding of the performance of foam concrete used as high-speed railway subgrade fillers subjected to seasonal freezing.

Sludge-cured lightweight soils have unique advantages in roadbed treatment due to their properties such as low density and high strength. Its long-term mechanical law based on the superposition of drying-wetting and freezing-thawing (D-W-F-T) is studied through creep experiment. The test results show that: with the increase of the number of D-W-F-T, the deformation of the soil gradually increases, and the deformation tends to be stable when it reaches a certain number of times; the stress-strain isochronous curves are obviously nonlinear in general; The long-term strength increases with the increase of density and confining pressure, and decreases with the increase of the number of D-W-F-T; by comparing the isochronous stress-strain curve cluster method and the steady state creep rate vs. The comparative analysis suggests that the steady state creep rate versus stress level curve method be used to determine the long term strength.

Soil freezing-thawing cycle (FTC) is an important factor controlling C dynamics in mid-high latitude regions, especially in the permafrost regions impacted by global warming. Nonetheless, the response of C cycling in the deeper active layers of permafrost regions to FTC remains far from certain. We aimed to characterize the emission of CO2 from soils of multiple depths as impacted by FTC and its relationship with active organic C (OC) and enzyme activities. We collected soil samples from three soil layers (0-15, 15-30, and 30-45 cm) of an undisturbed peatland in the Da Xing'anling Mountains, NE China, and then subjected them to various freezing (10 to -10 degrees C) and thawing (-10 to 10 degrees C) cycles. Soil CO2 emissions, two active OC fractions, and activities of three enzymes were monitored during incubation periods. At the thawing stage of the first FTC, CO2 emission rates in the three soil layers presented transient peaks being approximate to 1.6-1.7 times higher than those of the unfrozen control sample. Although FTC did not change the overall patterns of decreasing CO2 emission along the soil profile, FTC significantly reduced the amount of CO2 emission when compared with the unfrozen control sample, possibly because the small CO2 emission at the freezing stage neutralized the peak of CO2 emission at the thawing stage. This study suggests that in the active layer of permafrost peatlands, CO2 emission during FTCs may be lower than the emission under higher temperatures, but experiment with more temperature gradients should be encouraged to verify this conclusion in the future. Meanwhile, FTC significantly increased water extracted OC release from the three soil layers, approximate to 1.2-1.6 times higher compared to the unfrozen control sample, indicating that soil carbon loss in the form of leachate may increase during freezing-thawing periods. Additionally, the CO2 emissions impacted by FTCs were significantly correlated with active OC fractions and enzyme activities, which indicated that active OC and enzymes were sensitive to FTCs, and surviving microbes and enzymes might use the increased liable substrates and induce the CO2 emission during freezing-thawing periods.