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.

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.

This study explores the application of calcium carbide residue, desulfurization gypsum, and ground granulated blast slag as curing agents to solidify sludge. Through indoor experiments simulating dry-wet cycles and sulfate erosion, using unconfined compressive strength (UCS), X-ray diffraction, and scanning electron microscope as testing methods, the durability of solidified sludge against dry-wet cycles and sulfate erosion was studied. The objective is to provide technical support for the application of solidified sludge in engineering projects and promote the resource utilization of industrial solid waste. The results indicate that solidified sludge exhibits excellent durability against dry-wet cycles and sulfate erosion, with improved durability as the dosage of curing agent increases. In terms of dry-wet cycles, UCS initially increases but experiences a certain degree of decline as the number of dry-wet cycles increases, with the strength change rate exceeding - 35%, and failure strain gradually increases. As for sulfate erosion, UCS initially decreases following 1 day of erosion and subsequently shows a gradual improvement as the erosion time progresses. Higher sulfate concentrations lead to higher UCS, with strengths reaching up to 2.102 MPa, and failure strain gradually decreases. Microscopic tests revealed that, although dry-wet cycles initially weaken the structure and network of solidified sludge, increasing dry-wet cycles numbers leads to enhanced hydration reactions, resulting in higher content of hydration products and a denser microstructure. Experimental results indicate that using calcium carbide residue, desulfurization gypsum, and ground granulated blast slag as curing agents for sludge results in excellent resistance against dry-wet cycles and sulfate erosion.

Tumushuke, a significant node of the China-Pakistan Economic Corridor and the Silk Road Economic Belt, is strategically located in the southern region of Xinjiang. Due to the widespread distribution of its salty soils, concrete construction safety is significantly compromised. The construction of this project used sulfate-resistant cement, which was costly to construct. Six groups with varying sulfate immersion concentrations were set up to perform sulfate erosion tests and sulfate freeze-thaw coupling tests, respectively, based on the survey of the distribution of sulfate concentration in the area. The Tumushuke area's concrete erosion kinds were classified using a microanalysis of the degraded concrete. The findings indicate that the concrete primarily exhibits gypsum-type erosion when the sulfate concentration is greater than 20,000 mg/kg, ettringite-gypsum-type erosion when the sulfate concentration is between 15,000 and 20,000 mg/kg, and ettringite-gypsum-type erosion when the sulfate concentration is less than 15,000 mg/kg. The erosion product, carbon-sulfur silica-calcite, also occurs under sulfate freeze-thaw coupling. In the Tumushuke area, ettringite-type erosion damage is primarily found in low-sulfate areas in the southwest and a small portion of the northeast. In contrast, higher-sulfate areas in the central northward area are primarily affected by ettringite-gypsum and gypsum-type erosion damage. The results of this study can provide a basis for adopting different anti-sulfate erosion measures for engineering construction in different regions.