In salt lake areas, the cast-in-situ concrete structure has been corroded by the combination of sulfate and chloride for a long time. The incorporation of basalt fiber materials into concrete helps to improve the durability of concrete. In this paper, experiments were conducted to study the corrosion deterioration mechanisms of basalt fiber-reinforced cast-in-situ concrete under sulfate, chloride, and combined attack. The appearance, size, mass, flexural, and compressive strength of specimens were investigated during the immersion period to determine the changes in the physical and mechanical properties of specimens. Moreover, the microstructure and mineral changes of specimens during the immersion period were observed by Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD), and Thermogravimetric (TG)/ Derivative Thermogravimetric (DTG) analyses. Results show that premixed chloride has a significant detrimental influence on the strength development of cast-in-situ concrete, with concrete powder spalling occurring on the surface of the specimen. Severe corrosion degradation of specimens occurs under the external sulfate and internal chloride combined attack, resulting in lower flexural and compressive strength. The compressive strength and flexural strength of the corroded specimens decreased by 15.4% and 24.8%, respectively, compared with the control group at 28 days. Moreover, premixed basalt fiber has a beneficial influence on cast-in-situ concrete. When the basalt fiber content is 0.5%, the flexural strength of the specimen is increased by 16.2%. The filling and bridging effect of basalt fiber alleviates the negative effects caused by corrosion. In addition, increasing fiber content is beneficial for enhancing its effectiveness when the fiber content is less than 0.5%. This paper provides a valuable reference for the application of basalt fiber-reinforced cast-in-situ concrete under the condition of sulfate–chloride compound corrosion.

Collapsible loess is characterized by its unique soil-forming environment, mineral composition, and microstructure, resulting in poor engineering properties such as high water sensitivity, high collapsibility, high compressibility, and low strength. To improve the poor engineering properties of collapsible loess, we selected a suitable eco-friendly material—guar gum (GG)—for its improvement and reinforcement, and investigated the improvement effect of different GG dosages (0.5~1.5%) and curing ages (0~28 days) on collapsible loess. The mechanical properties of soil samples were determined by direct shear tests, unconfined compressive strength tests, and splitting tests. The water stability of soil samples was evaluated by both cube and sphere crumb tests. SEM and EDS analyses were also conducted to determine the microstructural and mineral changes in soil. The results indicate that the incorporation of GG is beneficial to inhibit the collapsibility of the soil and improves the water stability and strength of the soil. The collapsibility coefficient of loess is reduced to below 0.015 when 0.75% and above of GG is admixed, which is considered a complete loss of its collapsibility. When the GG dosage increases from 0% to 1.25%, the compressive strength and tensile strength of the soil samples increase by 43.5% and 34.9%, respectively. However, by further increasing the GG dosage to 1.5%, the compressive strength and tensile strength decrease by 3.8% and 6% compared to those with 1.25% GG. This indicates that the strength of the specimens shows an increasing trend and then a decreasing trend with the increase in GG dosage, and 1.25% GG was found to be the best modified dosage. Microstructural and mineral analyses indicate that the addition of GG does not change the mineral composition of loess, but, rather, it significantly promotes the agglomeration and bonding of soil particles through cross-linking with Ca²⁺ ions in the soil to form a biopolymer network, thus achieving a reliable reinforcement effect. Compared with the existing traditional stabilizers, GG is a sustainable and eco-friendly modified material with a higher low-carbon value. Therefore, it is very necessary to mix GG into collapsible loess to eliminate some of the poor engineering properties of loess to meet engineering needs. This study can provide test support for the application and promotion of GG-modified loess in water agriculture and road engineering.

Early degradation of cast-in-situ concrete induced by multiple internal–external sulfate combined attacks significantly affects the development of concrete strength. An experimental study regarding the effects of Ca²⁺ on the early degradation of cast-in-situ mortars subjected to internal–external sulfate and magnesium combined attacks is investigated in this paper. In particular, a specific method for accurately simulating the degradation of cast-in-situ structures was proposed in this experiment. Physical properties (including weight, size changes, and porosity), mechanical properties (including flexural strength and compressive strength), sulfate concentration, and microstructural properties were monitored during 28 days of immersion. The results show that an internal sulfate and magnesium combined attack (ISA-IMA) obviously retards the development of early strength and accelerates the degradation induced by external sulfate attack (ESA). The diffusion path of sulfate ions from outside is blocked by flake-shaped magnesium hydrates, delaying the penetration of external sulfate attacks. However, it is far from neutralizing the strength loss induced by an internal magnesium attack (IMA) at an early age. Premixed excessive Ca²⁺ would improve the strength development and pore structure of concrete or mortar, enhancing durability against corrosive conditions.

When the finite element-strength reduction method is used for two-dimensional slope stability analysis for elastic-perfectly plastic material, the failure criterion usually adopts the criterion of plastic zone penetration. That is, when the slope is in the limit equilibrium state, the plastic zone goes through the slope from the toe to the top. Meanwhile, the critical slip surface is composed of a series of points of maximum equivalent plastic strain along the depth direction. By deploying a set of parallel lines approximately perpendicular to the slope surface and picking out the points of these lines with the maximum equivalent strain points, we obtain a series of points taking on a wave shape, which constitutes a signal function. Subsequently, the wavelet packet analysis is used to smooth these points, i.e., locating the critical slip surface. The analysis of classic examples and comparison with Spencer’s method show that the proposed method in this paper is reasonable and effective.

Using industrial by-product lithium slag (LS) as a raw material for ultra-high performance concrete (UHPC) is an important way to achieve low-carbon prefabricated structures. However, existing studies lack a constitutive model for LS-UHPC and its application in prefabricated beam connection nodes. To fill this gap, this paper first established a tensile-compressive constitutive model for LS-UHPC through mechanical tests; then it was embedded into the finite element model to simulate the bending performance of the connection nodes of the post-cast LS-UHPC prefabricated beams and verified by the test results. Finally, parameter analysis is carried out. The results show that moderately increasing the diameter of longitudinal reinforcement can significantly improve the flexural bearing capacity of the connection node, but when the diameter exceeds 18 mm and HRB500 high-strength steel bars are used, the node exhibits over-reinforced failure characteristics; increasing the strength grade of ordinary concrete has a limited effect on the improvement of flexural bearing capacity (<5%). This study clarified the mechanical constitutive relationship of LS-UHPC, revealed the failure mechanism and bearing capacity evolution law of its prefabricated connection nodes under parameter changes, and provided a theoretical basis and design suggestions for the application of low-carbon lithium slag UHPC in prefabricated assembly structures.

With the continuous expansion of the lithium industry, lithium slag (LS) has been generated in large quantities, and its potential reuse in cement-based materials has become increasingly important. In this work, LS was introduced into ultra-high-performance concrete (UHPC) as a partial substitute for cement to explore its applicability in low-cement UHPC systems. The fresh properties of UHPC, including flowability and setting behavior, were measured, and its mechanical performance was evaluated through compressive and flexural strength tests. In addition, early-age autogenous shrinkage was monitored to clarify the effect of LS on dimensional stability. To further reveal the mechanisms associated with the macroscopic performance changes, isothermal conduction calorimetry, backscattered electron microscopy (BSE), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and mercury intrusion porosimetry (MIP) were adopted. These techniques were used to characterize the hydration behavior, phase composition, hydration product evolution, and pore-structure characteristics of UHPC containing different LS contents. Results demonstrate that LS incorporation effectively reduces autogenous shrinkage and accelerates setting. An optimal LS content enhances long-term strength development; however, LS incorporation compromises early-age compressive strength and flowability. Calorimetric, thermogravimetric, and BSE analyses collectively reveal that LS retards early hydration heat release and delays initial strength gain, attributable to its dilution effect, but exhibits latent pozzolanic reactivity, consuming Ca(OH)₂ and promoting secondary C–S–H formation, thereby increasing the 28-day degree of cement hydration. Pore-structure analysis further confirms that an appropriate LS content significantly reduces total porosity, average pore diameter, and the volume fraction of pores with PD > 50 nm, leading to a more refined and compact microstructure. Integrated macroscopic and microscopic evidence identifies 20 wt.% LS as the optimal replacement level: relative to the reference mixture LS0, the 28-day compressive and flexural strengths of LS20 are increased by 10.86% and 27.93%, while flowability decreases by 13.97%, initial setting time shortens by 10.54%, and autogenous shrinkage is reduced by 57.41%. The results provide a scientific basis for the resource utilization of lithium slag in UHPC and contribute to the development of cement-reduced UHPC mixtures with improved mechanical and microstructural characteristics.