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.

In regions with sandy soft soil strata, the subway foundation commonly undergoes freeze-thaw cycles during construction. This study focuses on analyzing the microstructural and fractal characteristics of frozen-thawed sandy soft soil to improve our understanding of its strength behavior and stability. Pore size distribution curves before and after freeze-thaw cycles were examined using nuclear magnetic resonance technology. Additionally, fractal theory was applied to illustrate the soil's fractal properties. The strength properties of frozen remolded clay under varying freezing temperatures and sand contents were investigated through uniaxial compression tests, indicating that soil strength is significantly influenced by fractal dimensions. The findings suggest that lower freezing temperatures lead to a more dispersed soil skeleton, resulting in a higher fractal dimension for the frozen-thawed soil. Likewise, an increase in sand content enlarges the soil pores and the fractal dimension of the frozen-thawed soil. Furthermore, an increase in fractal dimension caused by freezing temperatures results in increased soil strength, while an increase in fractal dimension due to changes in sand content leads to a decrease in soil strength.

Concrete is subject to the combined erosive effects of physical and chemical activities in cold, salty soil regions. In this work, durability tests of recycled concrete (RC) subjected to sulfate freeze-thaw cycles were conducted. The macroscopic performance deterioration law of RC under the influence of the replacement rate (0%, 50%, 100%) and the moisture content of coarse recycled concrete aggregate (CRCA) (0%, 50%, 100%) was investigated by analyzing the change characteristics of apparent damage, mass loss rate, and Relative dynamic modulus of elasticity (RDME) of RC during the erosion process. At the same time, nuclear magnetic resonance (NMR) and microhardness testing equipment were used to examine the multi-parameter evolution features such as porosity, pore distribution, interfacial transition zone (ITZ) width, and strength. The findings indicate that the main cause of the variation in the degree of damage to the RC surface layer is the variance in the effective water-cement (w/ c) ratio of the mortar due to replacement rate and moisture content. The strength and area of erosion damage increase when the CRCA replacement rate rises due to the easier inward penetration of the sulfate solution. CRCA with a 50% moisture content could increase the strength of the mortar by decreasing the mortar's effective w/c ratio. The rate and effectiveness of salt solution replenishment inward were simultaneously slowed down by the improved ITZ performance. In erosive situations, the fractal dimension of RC reduces to varying degrees. This is due to the expansion of the pore structure. The porosity/fractal dimension is employed as the comprehensive pore parameter eta in this research so as to take into account the integrity of the pore structure and the specificity of the pore distribution. The improved microstructure damage variables can reflect the erosive microstructure deterioration process of RC.

The traditional rock and soil frost heave deformation characteristics analysis test is time-consuming and expensive. Therefore, an experimental study method of rock and soil frost heave deformation characteristics based on the pore distribution model is proposed. The pore distribution model was constructed to calculate the stress intensity factor formed by the point force and the distributed gravity, and then the frost heave displacement was obtained, and the frost heave deformation characteristics were analysed. The test results show that the running time of this study is saved by at least 2 min, and the average test cost is 14,951 million Yuan. Through the results of soil strain energy release rate and soil moisture content obtained, the effectiveness of the frost heave deformation characteristic test of rock and soil is fully verified.

This study investigates the modification of red clay with calcium carbonate. The pore distribution was obtained using a combination of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) techniques. The influence of calcium carbonate content, density, confining pressure, and shear strain on the pores was studied. Introducing pore classification to assess the extent of the damage under different conditions and the relationship between different types of pores. The results show that the content of added calcium carbonate has little effect on pore distribution when the density is low (1.4 and 1.5 g/cm(3)). The content of calcium carbonate has an influence on pore distribution when the density is high (1.6 g/cm(3)). With the density increases, the number of macropores and mesopores between soil particles decreases, while the small pores increase. The confining pressure results in the preferential drainage of free water from macropores. The porosity decreases as the confining pressure increases. Under the same confining pressure, as the shear strain increases, the large pores decrease while the small pores increase. Based on the analysis of damage degree, the shear strain is positively linearly related to the damage degree of intragranular mesopores, which forms a convex function relationship with intragranular macropores and intergranular mesopores (except under a confining pressure of 100 kPa).