In the northwestern saline soils and coastal areas, cement soil (CS) materials are inevitably subjected to various factors including salt erosion, dry-wet cycle (DWC), temperature fluctuations and dynamic loading during its service life, which the coupling effect of these unfavourable factors seriously threatened the durability and engineering reliability of CS materials. Additionally, combined with the substantially extensive application prospects of rubber cementitious material, as a resource-efficient civil engineering material and fibre-reinforced composites, consequently, in order to address aforementioned issues, this investigation proposed to consider the incorporation of rubber particles composite basalt fiber (BF) to CS materials as an innovative engineering solution to effectively enhance the mechanical and durability properties of CS materials for prolonging its service life. In this study, sulphate ions were utilized to simulate external erosive environment and basalt fibre rubber cement soil (BFRCS) specimens were subjected to various DWC numbers (0, 1, 4, 7, 11 and 15) in diverse concentrations (0 g/L, 6 g/L and 18 g/L) of Na2SO4 solution, and specimens that had completed the corresponding DWC number were then conducted both unconfined and dynamic compressive strength tests simultaneously to analyze static and dynamic stress-strain curves, static and dynamic compressive strength, apparent morphological deterioration characteristics and energy absorption properties of BFRCS specimens. Furthermore, further qualitative and quantitative damage assessments of pore distribution and microscopic morphology of BFRCS specimens under various DWC sulphate erosion environments were carried out from the fine and microscopic perspectives through pore structure test and scanning electron microscopy (SEM) test, respectively. The test results indicated that the static, dynamic compressive strength and specific energy absorption (SEA) of BFRCS specimens exhibited a slight increase followed by a progressive decline as DWC number increased. Additionally, compared to 4 mm BFRCS specimens, those with 0.106 mm rubber particle size demonstrated more favorable resistance to DWC sulphate erosion. The air content, bubble spacing coefficient and average bubble chord length of BFRCS specimens all progressively grew as DWC number increased, while the specific surface area of pores gradually decreased. The effective combination of BF with CS matrix significantly diminished pores and weak areas within specimen, and its synergistic interaction with rubber particles efficiently mitigated the stresses associated with expansive, contraction, crystallization and osmosis subjected by specimen. Simultaneously, more ettringite (AFt) had been observed within BFRCS specimens in 18 g/L sulphate erosive environments. These findings will facilitate the design and construction of CS subgrade engineering in northwestern saline soils and coastal regions, promoting sustainable and durable solutions while reducing the detrimental environmental impact of waste rubber.

High-strength mortar (HSM) gradually has wide applications due to its exceptional strength, micro-expansion properties, and excellent fluidity. Behavior deterioration of structures in saline soil areas is primarily attributed to freeze-thaw cycles and sulfate attack. In this study, the coupling effect of freeze-thaw cycles and sulfate attack on the appearance, mass loss, and relative dynamic elastic modulus of HSM was investigated during erosion. Then, compressive experiments were conducted to assess the mechanical properties of HSM subjected to both freeze-thaw cycles and sulfate attack. The influences of coupling freeze-thaw cycles and sulfate attack on the compressive properties of HSM were quantified through regression analysis of experimental results. Empirical models for compressive stress-strain curves and damage constitutive behavior of HSM were developed, taking the coupled adverse effect into account. The results indicate that the coupled effect of freeze-thaw cycles and sulfate attack causes performance deterioration of HSM. The empirical models reproduce the compressive behaviors of HSM subjected to freeze-thaw cycles and sulfate attack.

A novel thermo-hydro-mechanical-chemical (THMC) coupling model grounded in thermodynamic dissipation theory was established to unravel the intricate behavior of unsaturated sulfate-saline soils during cooling crystallization. The model quantifies energy transfer and dissipation during crystallization and introduces a method to calculate the amount of sulfate crystallization. It intricately captures the interdependencies between crystallization, pore water pressure, crystallization pressure and volumetric expansion, while also accounting for the dynamic feedback of latent heat from phase transitions on heat conduction. The reliability of the model was validated through experimental data. Numerical simulations explored the effects of cooling paths, thermal conductivity, initial salt content and initial porosity on the crystallization behavior and mechanical properties. The model provides theoretical support for optimizing the engineering design and facility maintenance of sulfatesaline soils.

To study the failure mechanism of high ductile coagulation (HDC) under sulfate attack in cold saline soil area, cement-based cementing material (cement: fly ash: sand: water reducing agent: water = 1:1:0.72:0.03:0.58) and 2 % polyvinyl alcohol fiber (PVA) were used to prepare HDC sample, to increase the density and ductility of concrete. a 540-day sulfate-long-term immersion test was performed on HDC specimens under two low-temperature curing environments and different sulfate solution concentrations (5 %, 10 %). Using a combination of macro and microscopic methods, according to the principle of energy dissipation, To study the relationship between the evolution of energy (total damage energy U, dissipated energy Uds, elastic strain energy Ues) and the deterioration of strength and the change of pore structure during the compression process of HDC. According to the characteristics of stress-strain curves during HDC compression, the damage evolution characteristics of characteristic stress points during HDC compression are summarized, establish energy storage indicators Kel to evaluate the degree of internal damage of HDC. The results show that during the compression damage process of HDC after long-term soaking in sulfate solution under low temperature environment, Uds and Ues of HDC at characteristic stress points both increase first and then decrease, Kel are reduced first and then increased. The development trend of elastic strain energy and dissipative energy of HDC in 10 % sulfate solution is more drastic than that in 5 % sulfate solution. Compared with the other three groups, the D group energy storage level rises and falls more violently, and the HDC has a smaller ability to resist damage under this condition. Through the study of the correlation between macro and micro changes of HDC in cold saline soil areas and energy evolution, to provide a reference for the stable operation of highly ductile concrete in cold saline soil areas.

The fundamental cause of frost heave and salt expansion of saline soil is the water condensation and salt crystallization during the freezing process. Therefore, controlling the water and salt content is crucial to inhibit the expansion behaviors of saline soil. Recently, electroosmosis has been demonstrated to accelerate soil dewatering by driving hydrated cations. However, its efficiency in mitigating the salt-induced freezing damages of saline soil requires further improvement. In this study, a series of comparative experiments were conducted to investigate the synergistic effects of electroosmosis and calcium chloride (CaCl2) on inhibiting the deformation of sodium sulfate saline soil. The results demonstrated that electroosmosis combined with CaCl2 dramatically increased the cumulative drainage volume by improving soil conductivity. Under the external electric field, excess Na+ and SO42- ions migrated towards the cathode and anode, respectively, with a portion being removed from the soil via electroosmotic flow. These processes collectively contributed to a significant reduction in the crystallization-induced deformation of saline soil. Additionally, abundant Ca2+ ions migrated to cathode under the electric force and reacted with OH- ions or soluble silicate to form cementing substances, significantly improving the mechanical strength and freeze-thaw resistance of the soil. Among all electrochemical treatment groups, the soil sample treated with 10 % CaCl2 exhibited optimal performance, with a 71 % increase in drainage volume, a 180 similar to 443 % enhancement in shear strength, and a 65.1 % reduction in freezing deformation. However, excessive addition of CaCl2 resulted in the degradation of soil strength, microstructure, and freeze-thaw resistance.

In this study, ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used as binders, while NaOH (NH) and Na2SiO3 (NS) served as alkali activators. Seawater (SW) was used instead of freshwater (FW) to develop a SW-GGBS-FA geopolymer for solidifying sandy soils. Geopolymer mortar specimens were tested for unconfined compressive strength (UCS) after being curing at room temperature. The results showed that the early strength of the seawater group specimens increased slowly less than that of the freshwater group specimens, while the late strength was 1.16 times higher than that of the freshwater group specimens. Factors including seawater salinity (SS), the GGBS/FA ratio, curing agent (CA) content, and the NH/ NS ratio were examined in this experiment. The results showed that the strength of the specimens was higher for SS of 1.2 %, G90:F10, CA content of 15 %, activator content was 15 %, and NH: NS of 50:50. The pore structure of the mortar specimens was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and computerized tomography (CT), revealing the mechanisms by which various factors influenced the microstructure. XRD indicated that SW-GGBS-FA geopolymer mortar newly produced Friedel salt and calcium silicate sulfate hydrate (C-S-S-H). The microstructures observed by CT and SEM showed that the pore radius of the seawater specimens was mainly less than 10 mu m, and the maximum crack length was 92.55 mu m. The pore radius of freshwater specimens was larger than that of seawater specimens, and the largest crack was 148.44 mu m, which confirmed that Friedel salt and C-S-S-H fill the pores and increase the UCS of the specimens.

Sulfate saline soil is considered as an inferior subgrade construction material that is highly susceptible to damage from salt heaving and dissolution. Polyurethane/water glass (PU/WG) is an efficient grouting material widely used in underground engineering; however, its application in saline soil reinforcement has not yet been reported. In this study, PU/WG was used to solidify sulfate-saline soils. The influence of the dry density, curing agent ratio, and salt content on the strength was evaluated. The mechanical properties of the solidified soil were determined by conducting uniaxial compression strength tests, and crack development was detected using acoustic emission technology. The reinforcing mechanism was revealed by scanning electron microscopy tests and mercury intrusion porosimetry. The results indicated that the peak stress, peak strain, and ultimate strain increased with increasing dry density and PU/WG content, whereas they decreased with increasing salt content. The relationship between the peak stress, density, and PU/WG can be described using linear functions. The relationship between the peak stress and salt content can be described by a second-order polynomial function. The larger the dry density and the higher the PU/WG content, the steeper the stress-strain curves and the lower the ductility. Further, the higher the salt content, the higher the ductility. Soil with a higher dry density, more PU/WG, and less salt content exhibited higher brittleness. Thus, PU/WG can fill in the original disorganized and large pores, thereby increasing the complexity of the internal pore structure via organic-inorganic gel reactions.

Ultra-high performance concrete (UHPC), due to its superior mechanical and durability properties, is extensively applied in saline soil areas. In this paper, the damage evolution process and constitutive relationship of UHPC under sulfate dry-wet cycling were investigated through mechanical property tests combined with acoustic emission (AE) technology. The results showed that With the increase in erosion cycles and SO42- content, the proportion of low-amplitude (<= 50 dB) AE events exhibited a decreasing trend. In contrast, the fraction of medium-and high-amplitude AE events gradually increased, suggesting that large-scale damage began to play a dominant role in the specimen's deterioration process. Based on AE characteristic parameters, the damage evolution model of UHPC under uniaxial compression was established, the model can effectively characterize the uniaxial compression damage evolution behavior of UHPC under sulfate dry-wet cycling, providing theoretical support for the service performance evaluation of UHPC structures in saline soil areas.

The engineering diseases caused by seasonal sulfate saline soil in Hexi region of Gansu Province seriously affect the local infrastructure construction and operation maintenance. To address this issue, this study explored the thermal mass transfer law, pore fluid phase transition, soil deformation and microstructure of unsaturated sulfate saline soil under the open system. Firstly, based on the theories of porous media mechanics and continuum mechanics, combined with the conservation equations of mass, energy and momentum and considering the phase transition of pore fluid, a multi-field coupled mathematical model of hydro-thermal-salt-gas-mechanical for unsaturated sulfate saline soil was established. Secondly, basic unknown variables such as pore water pressure, concentration, temperature, porosity, and displacement were selected to perform numerical simulation analysis on the equation system by Comsol Multiphysics finite element method. Finally, a comparative analysis was conducted between the on-site measured data and the numerical simulation results. The results show that the water and salt phase transitions caused by temperature change could lead to soil salt heave and frost heave, alter the pore structure of the soil, and reduce the compactness of the soil, ultimately being reflected in the changes in soil porosity. The influence of external temperature on soil temperature gradually decreases with increasing depth, and the sensitivity of frozen areas to external temperature is much higher than that of unfrozen areas. This study not only enriches the theoretical results of thermal mass transfer law and deformation of unsaturated sulfate saline soil, but also provides practical guidance for the prevention and control of engineering diseases in local sulfate saline soil.

Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.