The objective of this study was to enhance the mechanical properties of gravelly soil and to consider the binding and filling effects of xanthan gum and calcium lignosulfonate. To this end, gravelly soil samples were prepared with various dosages of xanthan gum and calcium lignosulfonate, and their curing effects were investigated. The mechanical properties and strength parameters of the cured gravelly soil were investigated using unconfined compressive strength (UCS) tests and conventional triaxial compression tests. Furthermore, scanning electron microscopy (SEM) was employed to examine the microstructure and curing mechanisms of the gravelly soil treated with these additives. The findings demonstrate that as the dosage increases, both xanthan gum and calcium lignosulfonate markedly enhance the compressive strength and shear strength of the gravelly soil. The curing effect of xanthan gum was found to be more pronounced with higher dosages, while the optimal curing effect for calcium lignosulfonate was achieved at a dosage of 4%. The gravelly soil treated with xanthan gum exhibited superior performance compared to that treated with calcium lignosulfonate when the same dosage was used. Moreover, at elevated confining pressures, the binding effect of xanthan gum and calcium lignosulfonate on the gravelly soil was less pronounced than the strength effect imparted by the confining pressure. This suggests that the impact of dosage on the shear strength of the gravelly soil is diminished at higher confining pressures. The stabilization of crushed stone soil by xanthan gum is a complex process that involves two main mechanisms: bonding and cementation, and filling and film-forming. The curing mechanism of calcium lignosulfonate-cured gravelly soil can be summarized as follows: ion exchange, adsorption and encapsulation, and pore filling and binding effects. The findings of this research offer significant insights that are pertinent to the construction of high earth-rock dams and related engineering applications.

The effective utilization of phosphogypsum (PG) and industrial waste soil is of paramount importance in the real world. The combination of phosphogypsum and soil in a single mixture can simultaneously utilize both materials. In this study, a novel green road material was developed according to the concept of synergistic utilization of multiple solid wastes, which is based on conventional cement stabilized soil. The GGBS was employed to gradually replace cement to stabilize PG-soil mixtures. The curing effect of GGBS replacing cement and the modification effect of PG on stabilized soil were evaluated in three aspects: mechanical properties, water stability, and environmental performance. This evaluation was conducted using the unconfined compressive strength (UCS), softening coefficient, and ionic concentration of heavy and trace metals. Furthermore, microscopic characterization techniques, including a pH meter, UV-visible spectrophotometer, FTIR, XRD, SEM, and EDS, were used to perform further analyses of the curing mechanism. The objective was to enhance the UCS of stabilized soil by incorporating an optimal amount of PG, avoiding the necessity for a complex and costly pretreatment process for PG. The UCS reached approximately 8 MPa in 7 days without immersion in water curing and 4 MPa in 7 days with 1 day immersion in water curing. Despite the decline in water stability resulting from the incorporation of PG, the stabilized soil exhibits superior mechanical properties compared to the majority of studies on the application of PG to stabilized soils. The monitoring of contaminant ions in the stabilized soil over a period of 28 days demonstrated compliance with EPA requirements, indicating that PG-based stabilized soil does not negatively impact the surrounding environment in the presence of water. Additionally, the optimal ratio of GGBS to cement is 1:1. Meanwhile, excessively high or low cement content has a detrimental impact on the properties of stabilized soil. Lastly, the practical engineering application of this novel green road material was achieved, and its mechanical properties and economic benefit were demonstrated to be superior to those of conventional cement stabilized soil. The study of PG in stabilized soil was transformed into the utilization of realworld projects without the necessity for a complex pretreatment process for PG. Concurrently, the replacement of GGBS for cement results in a reduction in both carbon emissions and economic costs, due to an enhanced utilization of solid waste. Additionally, it offers a more detailed analysis of the curing mechanisms in stabilized soils with respect to strength, water stability, and harmful ions.

To address the issues of low early strength in cement-stabilized soft soil, as well as the high pollution, energy consumption, and costs associated with cement binder application, one-part geopolymer (OPG) is prepared by using solid sodium silicate (Na2O center dot SiO2, NS) to activate a mixture of binary precursors, namely fly ash (FA) and ground granulated blast furnace slag (GGBFS), along with water. The factors, including FA dosage, solid NS molarity, alkali molar concentration, and water-cement ratio, are considered for assessing the physical and mechanical properties of OPG. Based on this, optimized proportioning tests were conducted to determine the best mixing ratio of OPG for soft soil stabilization. The effects of the FA/GGBFS ratio in the precursor and curing ages on the unconfined compressive strength (UCS), porosity, and pore size distribution of OPG-stabilized soft soil were further investigated. Micro-analysis was performed using mercury intrusion porosimetry (MIP), scanning electron microscope-energy dispersive spectrometer (SEM-EDS) to reveal the stabilization mechanism. The results indicated that the OPG prepared with solid NS could effectively stabilize soft soil, with hydrated gels (N-A-S-H, C-A-H, C-S-H, and C-A-S-H) effectively bonding soil particles and contributing to the formation of a denser soil skeleton. The mixing proportion of FA/GGBFS of 0.1, water-cement ratio of 0.8, NS molarity of 1.0, and molar concentration of 3 mol/L was found to be optimal for soft soil stabilization. The corresponding OPG had good workability and achieved a UCS of 4.4 MPa. This study extends the application of solid sodium silicate-inspired one-step geopolymers in deep mixing techniques, providing guidance on the theoretical basis for the reinforcement treatment of soft ground foundations.