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.

A series of large-scale shaking table tests were carried out to investigate the seismic performance of different cement-soil reinforced pile groups in liquefiable sands. Specifically, sinewave scanning was performed on three cement-soil reinforced 3 x 3 pile groups and one conventional (unimproved) 3 x 3 pile group. In this study, the bending moment of group piles, the horizontal displacement of the superstructure, pore water pressure into soils, and the settlement and acceleration response of piles and the ground under different earthquake intensities were recorded. The natural frequency of the ground and the dynamic stress-strain relationship of the soils around piles were obtained. The results show that the acceleration response of the improved pile groups before soil liquefaction is significantly smaller than that of the unimproved pile group. However, the acceleration attenuation of the unimproved pile groups after soil liquefaction is substantially greater than that of the improved pile group. In addition, the lateral displacement of the superstructure, the settlement of pile heads, the bending moment of pile shafts, and the dynamic shear strain of the soils around piles in improved cases are all smaller than those in the unimproved case. In particular, the improved cases significantly suppressed the pile bending moment at the interface between the liquefied layer and the non-liquefied layer. The spatial layout of cement-soils significantly impacts the natural frequency and stress changes of the pile-soil Winkel elastic foundation beam systems.

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.

This paper aims to investigate the effects of zeolite and palm fiber on the strength and durability of cement soil. Based on the findings of previous research, optimal proportions of zeolite, palm fiber, and cement, as well as the appropriate curing age, were determined. Subsequently, unconfined compressive strength tests, dry-wet cycle tests, and freeze-thaw tests were conducted, utilizing NaCl and Na2SO4 solutions over the specified curing period. The strength and durability characteristics of the samples were evaluated by assessing mass and strength loss, taking into account the combined effects of NaCl and Na2SO4 solution erosion. The test data also provide a fitting relationship between strength and the number of cycles under the influence of different solutions, thereby offering a basis for theoretical predictions without the need for additional experiments. Finally, the microscopic mechanisms were analyzed using scanning electron microscopy (SEM). The results indicate that the cement soil composite of zeolite and palm fiber, when combined in optimal proportions, exhibits the best durability and minimal loss of strength and mass, irrespective of whether exposed to clean water or salt erosion, as well as during dry-wet or freeze-thaw cycles.

This paper performs the strength properties of bio-enzyme improved high liquid limit soil (HLLS) treated with 4% (by weight) content of cement or lime cured for 28 days. A series of consolidated undrained (CU) triaxial tests and unconfined compressive (UC) strength tests were conducted on plain soil (untreated by cement or lime), cement-treated and lime-treated HLLS specimens improved with different bio-enzyme content (i.e., 0%, 0.2%, 0.4%, 0.6% and 0.8% by weight) to investigate the effect of bio-enzyme content on the strength properties of tested soil. The results indicate that the stress-strain relationship of bio-enzyme improved plain soil specimens exhibit strain-hardening behavior and ductile failure mode. The other specimens exhibit strain-softening behavior and brittle failure mode. Adding 0.6% bio-enzyme, the values of undrained shear strength of CS specimens are about 1.7 times, 1.8 times, and 1.9 times of LS specimens at sigma 3 = 100 kPa, 200 kPa and 300 kPa. The residual strength is about 40.5% on average the peak strength for CS specimens, and 37.0% for LS specimens. The cohesion c increased 258.6% and 220.7%, and the internal friction angle phi increased 38.57% and 39.05% for CS and LS specimens respectively. The UC strength of CS specimen is 1.69 times that of LS specimen. The magnitudes of CU strength, UC strength, cohesion and internal friction angle of three types of soil specimens followed the same increase trend when the bio-enzyme content increased from 0 to 0.6%, and peak values can be observed at 0.6% bio-enzyme content. The use of bio-enzyme to improve the strength behavior of HLLS treated with cement or lime is an innovative and attractive solution in geotechnical engineering. The effectiveness of bio-enzyme in improving the strength of HLLS treated with cement or lime was studied based on a laboratory investigation.Adding cement or lime in HLLS provided a significant increase in strength and strength parameters at a certain bio-enzyme content, where the treatment effect of cement is better than that of lime.The bio-enzyme content of 0.6% can achieve the most economical effect on enhancing the strength and the strength parameters of HLLS improved by 4% cement or lime.

Sugarcane bagasse ash is a kind of agricultural waste with a large quantity and good volcanic ash reactivity, it is necessary to find a way to reasonably utilize it to prevent environmental pollution caused by long-term accumulation. In this paper, the effect of sugarcane bagasse ash on the short-term mechanical properties of coastal cement soil were studied, and unconfined compressive tests and triaxial shear tests were carried out. The sugarcane bagasse ash content was set to 0 %, 1 %, 2 %, 3 %, 4 % and 5 %, respectively, the cement content was set to 5 %, and the curing age was set at 7d. The test results show that sugarcane bagasse ash can effectively improve the unconfined compressive strength and triaxial shear strength of cement soil, exhibiting a trend of increasing first and then decreasing with the increase of its content. When the sugarcane bagasse ash content is 1 %, the unconfined compressive strength reaches the maximum value of 2040 kPa, which is 56 % and 8 % higher than that of cement soil with 5 % and 7 % cement content, respectively. Compared with cement soil with 5 % cement content, the triaxial shear strength increases by 12 %similar to 17 %, the internal friction angle phi and cohesion c increases by 3 %similar to 8 % and 2 %similar to 11 %, respectively. The SEM test results show that the addition of bagasse ash can promote the hydration of cement to produce hydrated calcium silicate and other hydration products, fill the internal pores of the sample, and make the microstructure of the modified cement soil tend to be dense. The research results provide a reference for the application of sugarcane bagasse ash modified cement soil in practical engineering.

In saline-alkali and coastal areas, cement soil faces various threats from salt erosion, and these environmental conditions can significantly impact the mechanical properties of cement soil. To counter external erosion, the addition of graphene oxide (GO) nanomaterials to cement soil is considered an effective solution. This study systematically investigates the strength variations of GO cement soil after erosion in different concentrations of NaCl solution (0 g/L, 4.5 g/L, 18 g/L, 30 g/L), Na2SO4 (0 g/L, 4.5 g/L, 18 g/L, 30 g/L), and a composite salt solution of both (0 g/L, 4.5 g/L, 18 g/L, 30 g/L) at different times (7d, 14d, 30d, 60d) through salt immersion tests, unconfined compressive strength tests, and SEM scanning electron microscope tests. Simultaneously, the study analyzes the mass change rate, stress-strain curves, peak stress of unconfined compressive strength, and modulus of elasticity changes in cement soil samples after erosion. The internal erosion mechanism of cement soil samples is explored at the microscopic level. When the GO cement soil was eroded in different concentrations of NaCl solution for 14 days, a consistent trend of mass decrease was observed. However, after 7, 30, and 60 days of erosion in various concentrations of NaCl solution, the mass showed an increasing trend. When immersed in pure water for 7d, 14d, 30d, and 60d, as well as in a 4.5 g/L NaCl solution for 7d and 14d erosion, the peak stress of GO cement soil samples shows an increasing trend, while it decreases under other conditions, especially significantly in Na2SO4 solution. Simultaneously, Na2SO4 has the greatest impact on the modulus of elasticity of cement soil. SEM test results reveal that due to nucleation effects, GO promotes the generation of hydration product C-S-H, enhancing the resistance of cement soil samples to external erosion. Furthermore, it is observed that under the influence of SO42-, C-S-H undergoes decalcification to generate AFt, while the impact of Cl- on C-S-H is relatively small.

In coastal and saline-alkali regions, cement soil materials face significant challenges from salt erosion and both dynamic and static loads, threatening their structural stability. To enhance the mechanical properties of cement soil, this study explores the incorporation of graphene oxide (GO). We subjected GO cement soil specimens to various concentrations of a composite salt solution (with a NaCl to Na2SO4 mass ratio of 1:1) in erosion experiments lasting 7 and 30 days. The specimens were analyzed through unconfined compressive strength tests, split Hopkinson pressure bar (SHPB) tests, and scanning electron microscopy (SEM) to examine changes in stressstrain curves, peak stress, and energy dissipation. The results indicate that the dynamic and static peak stresses, energy absorption, and energy absorption efficiency of the GO cement soil specimens are inversely related to the concentration of the mixed salt solution. Notably, in a 4.5 g/L erosion environment after 7 days, an increasing trend was observed in static peak stress, energy absorption, and energy absorption efficiency. Additionally, when the salt concentration was fixed, these properties showed a positive correlation with impact gas pressure. SEM analysis revealed that the nucleation effect of GO and its strong bonding with the cement matrix significantly improved the microstructure of the specimens by reducing pores and defects, thus enhancing density and overall performance. Furthermore, in an 18 g/L erosion environment, a notable presence of ettringite (AFt) was identified in the GO cement soil specimens.

A universal testing machine and a 50 mm split Hopkinson pressure bar (SHPB) were used to conduct salt erosion and freeze -thaw (F -T) cycle coupling tests on cement soil specimens with 0.5% polyvinyl alcohol (PVA) fiber and without fiber in order to study the effects of salt solution and F -T cycles on the dynamic and static mechanical properties of cement soil. In four distinct solution settings (clear water, 9 g/L sodium sulphate solution, 9 g/L sodium chloride solution, and 9 g/L sodium sulphate and sodium chloride mixed solution). After F -T cycles, the cement soil specimens underwent the unconfined compressive strength (UCS) test, SHPB test, and SEM test. The findings indicate that as the number of F -T cycles increases, the dynamic and static mechanical properties of cement soil specimens decrease, and the rate of decline is rapid followed by slow. After five F -T cycles, the combined solution ' s unconfined compressive strength dropped to 15.91% (without fiber) and 29.41% (with fiber), respectively. After five F -T cycles, the dynamic compressive strength in sodium sulphate solution fell by 95.17% (without fiber) and 93.86% (with fiber). Fibers help to some degree by preventing salt erosion and F -T cycles. With more F -T cycles, the absorbed energy declines exponentially, and the order of the solutions ' effects on the absorbed energy is: mixed sodium chloride and sodium sulphate solution > sodium chloride solution > sodium sulphate solution > clear water.

Studies show that adding carbon fiber to concrete to form a conductive network can make concrete feel its own stress, strain, cracks, and damage according to the change of conductive network, and improve the strength and durability of concrete. In view of the self-sensing characteristics of carbon fiber, carbon fiber reinforced cement-based composites are put forward as a new intelligent sensing material. Through unconfined compressive strength test, resistivity test, microscopic test, and model test, the influence of fiber volume fraction and fiber length on unconfined compressive strength and resistivity change rate of carbon fiber reinforced cement-based composites are studied. A carbon fiber reinforced cement-based composites sensor is made according to the optimal ratio, which is implanted into cement-based composites components to establish the functional relationship between the sensor resistivity change rate and the stress of cement-based composites components, so as to realize the stress monitoring of cement-based composites components by the sensor. The results show that, in the study of the strength of carbon fiber reinforced cement-based composites, the unconfined compressive strength of carbon fiber reinforced cement-based composites is affected by both carbon fiber volume fraction and carbon fiber length, and the compressive strength increases first and then decreases with the increase of both. In the test range, 2% is the optimal volume fraction and 6 mm is the optimal fiber length. In the study of the resistivity change rate of carbon fiber reinforced cement-based composites, when the carbon fiber volume fraction is 1% and the fiber length is 3 mm, the resistivity change rate of the specimen is the largest, and the self-sensing sensitivity of carbon fiber reinforced cement-based composites is the best. There is an obvious exponential relationship between the resistivity change rate of the sensor embedded in the component and the stress of the cement-based composites component. Through establishing a stress prediction formula based on resistivity change rate, the stress state monitoring of the cement-based composites structure can be realized.