Conventional materials necessitate a layer-by-layer rolling or tamping process for subgrade backfill projects, which hampers their utility in confined spaces and environments where compaction is challenging. To address this issue, a self-compacting poured solidified mucky soil was prepared. To assess the suitability of this innovative material for subgrade, a suite of performance including flowability, bleeding rate, setting time, unconfined compressive strength (UCS), and deformation modulus were employed as evaluation criteria. The workability and mechanical properties of poured solidified mucky soil were compared. The durability and solidification mechanism were investigated. The results demonstrate that the 28-day UCS of poured solidified mucky soil with 20% curing agent content reaches 2.54 MPa. The increase of organic matter content is not conducive to the solidification process. When the curing temperature is 20 degrees C, the 28-day UCS of the poured solidified mucky soil with curing agent content not less than 12% is greater than 0.8 MPa. The three-dimensional network structure formed with calcium silicate hydrate, calcium aluminate hydrate, and ettringite is the main source of strength formation. The recommended mud moisture content is not exceed 85%, the curing agent content is 16%, and the curing temperature should not be lower than 20 degrees C.

Ground granulated blast furnace slag (GGBS), calcium carbide slag (CS), and phosphogypsum (PG) were combined in a mass ratio of 60:30:10 (abbreviated as GCP) to solidify dredged sludge (DS) with high water content. The long-term strength characteristics of solidified DS under varying curing agent dosage and initial water contents, as well as its durability under complex environmental conditions, were investigated via a series of mechanical and microstructural tests. The superior performance of GCP-solidified DS (SDS-G) in terms of strength and durability was demonstrated in comparison to solidified DS using ordinary Portland cement (SDS-O). The results indicated that the unconfined compressive strength (UCS) of SDS-G was approximately 3.0-4.5 times greater than that of SDS-O at the same dosage and curing ages, exhibiting a consistent increase in strength even beyond 28 days of curing. Additionally, the strength and deformation modulus (E50) of SDS-G increased initially and then decreased during wet-dry cycles, with reductions in mass, volume, and strength significantly were smaller than those observed in SDS-O. Furthermore, the reductions in UCS and E50 induced by freeze-thaw cycles were considerably smaller for SDS-G than for SDS-O, with strength losses of 50.7 % and 88.3 %, respectively, after 13 freeze-thaw cycles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the enhancements observed in SDS-G were attributed to the formation of ettringite (AFt), which effectively fills larger pores between agglomerated soil particles, thereby creating a denser and more stable microstructure in conjunction with hydrated calcium aluminosilicate (C- (A)-S-H) gels.

Salinized loess exhibits poor engineering properties, including low strength, salt migration, and instability, due to the combined characteristics of loess and saline soil. This poses serious threats to the safety and stability of buildings, roads, and other infrastructure. To address this issue, this study aims to solidify salinized loess using geopolymer produced through alkali activation of industrial waste, including slag powder and fly ash. An orthogonal experimental design was used to systematically investigate the mechanical properties, microstructural characteristics, and solidification mechanism of geopolymer solidified salinized loess. The tests included unconfined compressive strength (UCS), direct shear, pH, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate the influences of different factors on the solidification effect. The results showed that the sodium silicate solution modulus was the primary factor affecting the strength of solidified salinized loess, followed by the amounts of fly ash and slag powder. The Baume degree (degrees Be) had the least impact. Under the optimal conditions (1 modulus, 35 degrees Be, slag powder and fly ash ratio of 1:0), the UCS of the sample at 28 days reached 3204.06 kPa, which increased by 16.32 times compared with the unsolidified sample. Lowering the modulus and increasing the proportion of slag powder and the Baume degree increased the sample pH. Micro-analysis revealed that the strength increase was mainly due to the bonding of soil particles by gel substances (C - S - H, N - A - S - H, and C - A - S - H) formed during alkali activation, as well as the filling effect of unreacted slag powder and fly ash. The findings of this study provide valuable theoretical and practical insights for treating salinized loess in engineering, offering essential references for optimizing geopolymer solidifier ratios.

Currently, solid waste accumulates significantly, including red mud (RM) and fly ash (FA). Meanwhile, traditional cement-based curing agents pose challenges due to their high energy consumption and substantial pollution during the remediation of heavy metal-contaminated soil. In light of the need for resource utilization of solid waste and demands for energy conservation and emission reduction, this study investigates the stabilization/solidification of Cu2+-contaminated loess using a novel curing agent. This agent comprises low-energy, environmentally friendly high-belite sulfoaluminate cement (HBSAC) and quicklime (CaO) mixed with RM and FA. The study evaluates the samples across various metrics, including mechanical properties, permeability, pH, conductivity, leached ion concentration, and microstructure, to systematically investigate the curing effect and mechanism of the new curing agent on contaminated soil. It conducts an assessment related to the economics and carbon emissions of the solidified body. The results show that the optimal ratio for the curing agent consists of RM and FA, CaO, and HBSAC at 20%, 5%, and 7%, respectively, with a water-to-solid ratio of 0.38 and a mass ratio of RM to FA at 13:2. This new curing agent not only possesses superior properties but also offers excellent economic benefits and reduces carbon emissions. It holds significant potential for applications in the remediation of Cu2+-contaminated soils.

To accurately assess the safety of excavation and its impact on deformation settlement in soft soil areas, it is essential to conduct stability analysis and investigate the solidification mechanism of improved soft soil. This study involved a comprehensive series of laboratory tests, such as direct shear, dry-wet cycles, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests, encompassing a wide range of working conditions. Based on the findings, an optimal construction scheme for solidifying the soil was proposed, utilizing data from the Zhuhai Tunnel project. The test results indicated that the curing time and proportion significantly influenced the shear strength of the amended soil. It was determined that a 10% cement and 9% stabilizer curing for 28 days represented the optimal proportion. The stabilizer primarily enhanced the shear strength by increasing the cohesion of the soil. Furthermore, the improved soil exhibited excellent stability even after undergoing seven dry-wet cycles. Additionally, microscopic analysis was conducted to explore the chemical reactions and solidification mechanism occurring between particles in the improved soft soil. The stabilizer induces the migration of water molecules to the soil surface and continuously supplies hydration to the cement, promoting its secondary hydration and generating more calcium silicate hydrate gel (C-S-H) and ettringite (AFt). The gelation and filling effects of the hydration products between particles resulted in a densified structure, thereby enhancing the mechanical strength and stability of the improved soil. This research offers valuable guidance for the application of soil improvement in construction and engineering projects in soft soil areas.

Various problems are often encountered during the backfilling process of deep foundation pits. The development of low-cost and efficient solidified materials for the preparation of fluidized solidified soil is currently an ideal solution. This article used industrial solid waste (granulated blast furnace slag, fly ash, carbide slag, etc.) as the main raw material to study the hydration hardening properties of solidified materials and the construction feasibility of fluidized solidified soil prepared from solid waste materials. The results are as follows: Compared with cement-based materials, solid waste-based solidified materials had lower early activity. The cumulative heat release within 72 h was less than 200 J/g. Different solid wastes, such as fly ash and carbide slag, had different effects on the properties of solidified materials. Overall, they had the potential to prepare fluidized solidified soil. The prepared fluidized solidified soil had a fluidity greater than 350 mm, a 28d compressive strength greater than 3 MPa, and exhibited good workability and excellent mechanical properties. Hydration products such as CS -H and AFt were filled in the soil structure. The 28d compressive strength well above the design requirements of general engineering projects. Meanwhile, the prepared fluidized solidified soil had good adaptability to conventional water reducers (fluidity could be increased by more than 40%) and early strength agents (1d compressive strength could be increased by more than 60%).