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.

Solidified soil (SS) is widely applied for resource utilization of excavated soil (ES), however the waste solidified soil (WSS) may pose environmental hazards in future because of its high pH (>10). WSS is unsuitable for landfill but can be raw materials for preparing recycled solidified soil (RSS) with better mechanical properties than SS. This investigation used OPC and alkali-activated slag (AAS) as binders to solidify ES and WSS and prepare RSS. The mechanical properties of RSS were experimentally verified to be better than SS, increased by over 76 %. The mechanism is that the clay particles in WSS have been solidified to form sand-like particles or adhere to natural sand, resulting in increasing content of sand-sized particles, and the residual clay particles undergo cation exchange under the high pH and Ca2 + content, resulting in a decrease in zeta potential, reducing diffusion layer thickness. As a result, the flowability of RSS increases under the same liquid to solid ratio. The residual unreacted binder particles and high pH in WSS are beneficial for the early and final compressive strength increase of RSS, which allows preparing RSS with lower cost and carbon emission. Finally, the utilization of WSS has significant environmental benefits.

Sulfate saline soil is considered as an inferior subgrade construction material that is highly susceptible to damage from salt heaving and dissolution. Polyurethane/water glass (PU/WG) is an efficient grouting material widely used in underground engineering; however, its application in saline soil reinforcement has not yet been reported. In this study, PU/WG was used to solidify sulfate-saline soils. The influence of the dry density, curing agent ratio, and salt content on the strength was evaluated. The mechanical properties of the solidified soil were determined by conducting uniaxial compression strength tests, and crack development was detected using acoustic emission technology. The reinforcing mechanism was revealed by scanning electron microscopy tests and mercury intrusion porosimetry. The results indicated that the peak stress, peak strain, and ultimate strain increased with increasing dry density and PU/WG content, whereas they decreased with increasing salt content. The relationship between the peak stress, density, and PU/WG can be described using linear functions. The relationship between the peak stress and salt content can be described by a second-order polynomial function. The larger the dry density and the higher the PU/WG content, the steeper the stress-strain curves and the lower the ductility. Further, the higher the salt content, the higher the ductility. Soil with a higher dry density, more PU/WG, and less salt content exhibited higher brittleness. Thus, PU/WG can fill in the original disorganized and large pores, thereby increasing the complexity of the internal pore structure via organic-inorganic gel reactions.

Soft soil foundations need to be reinforced because of their low bearing capacity and susceptibility to deformation. Ordinary portland cement (OPC) is widely used in foundation treatment due to its strong mechanical properties. However, the production process for OPC curing agents involves high energy consumption and significant CO2 emissions. Given these problems, this paper proposes a fly ash-slag-based geopolymer to replace OPC curing agents, which can solidify soil while reducing OPC consumption. Another issue is that variability in environmental conditions influences the strength of soil solidified with fly ash-slag-based geopolymer, leading to subpar mechanical properties. However, by adding desulfurized gypsum as an admixture, the rich SO42- can react with Ca2+ and active silicate in the geopolymer to form Aft, thereby improving the mechanical properties. In the experiment, desulfurized gypsum is added as an admixture to a fly ash-slag-based geopolymer curing agent, and the resulting solidified soil is investigated through various macroscopic and microscopic tests. These tests include unconfined compressive strength measurements, water stability tests, scanning electron microscopy analyses, and X-ray diffraction tests. The results of these tests are combined with the response surface method to optimize the alkali-solid ratio, the modulus of the alkali activator, and the amount of desulfurized gypsum to 0.6%, 0.809%, and 15.96%, respectively. On this basis, an optimal mixing ratio was proposed and applied to form a geopolymer-solidified soil. The compressive strength and microstructure of this soil were then investigated using the single-variable method. An unconsolidated undrained triaxial test was performed on geopolymer-solidified soils of different curing times to investigate their shear performance. The water stability test was carried out to explore the influence of soaking time on the strength of solidified soil. Through microscopic observation, it was found that the fly ash-slag-based geopolymer generated significant amounts of (N, C)-A-S-H and C-S-H in solidified soil. With the addition of desulfurized gypsum, soil particles become filled with Aft and the solidified soil becomes more brittle instead of plastic, resulting in a significant increase in compressive strength. In addition, the cohesion and internal friction angle increase with curing time. With the increase of soaking time, the softening effect of long-term water soaking reduced the strength of the solidified soil.

To address the low utilization rate of construction waste soil and the environmental impact of traditional cement solidification, this study investigates the effect of desulfurized gypsum and silica fume in synergy with cement for construction waste soil. The effects of solidifying material dosage, liquid-to-solid ratio, and mixing ratio on mechanical properties were analyzed. Optimal performance was achieved with the dosage of solidifying material was 20%, the liquid-to-solid ratio was 0.2, and the mixing ratio of desulfurized gypsum, silica fume, and cement was 2:1:1, meeting the requirements of the technical specification for application of road solidified soil (T/CECS 737-2020). This formulation is referred to as FS-C type solidified soil. A self-fabricated carbonation device was employed to assess carbonation methods, time, and curing age on the mechanical properties of solidified soil. Carbonation for 6 h post-molding significantly enhanced strength, while carbonation in a loose state led to strength reduction. SEM analysis revealed a denser microstructure in carbonated samples due to calcium carbonate and silica gel formation. Compared to traditional cement solidification, FS-C type solidified soil reduces cement consumption by 15%, decreases CO2 emissions by 299.25 g/m(3), and sequesters 85 g/m(3) of CO2. These findings highlight the potential of FS-C type solidified soil as an environmentally friendly alternative for construction applications.

In order to study the cement-industrial waste-based synergistic curing of silt soil, orthogonal design tests were used to prepare a new curing agent using cement, fly ash, blast furnace slag, and phosphogypsum as curing materials. In order to evaluate the cement-industrial waste-cured soils, unconfined compressive strength tests, fluidity tests, wet and dry cycle tests, and electron microscope scanning tests were carried out. The mechanical properties and microstructure of the cement-industrial slag were revealed and used to analyze the curing mechanism. The results showed that, among the cement-industrial wastes, cement and blast furnace slag had a significant effect on the unconfined compressive strength of the specimens, and the optimal ratio for early strength was cement-fly ash-slag-phosphogypsum = 1:0.11:0.44:0.06; the optimal ratio for late strength was cement-fly ash-slag-phosphogypsum = 1:0.44:0.44:0.06. In the case of a 140% water content, the 28d compressive strengths of curing agent Ratios I and II were 550.3 kPa and 586.5 kPa, respectively. When a polycarboxylic acid water-reducing agent was mixed at 6.4%, the mobilities of curing agent Ratios I and II increased by 32.1% and 35.8%, and the 28d compressive strengths were 504.1 kPa and 548.8 kPa, respectively. When calcium chloride was incorporated at 1.5%, the early strength of the cured soil increased by 33% and 29.1% compared to that of the unadulterated case year on year, and the mobility was almost unchanged. From microanalysis, it was found that the cement-industrial waste produced the expansion hydration products calcium alumina (AFt) and calcium silicate (C-S-H) during the hydration process. The results of this study provide a certain basis and reference value for the use of marine soft soil as a fluid filling material.

Research on the performance of solidified soil in capillary water absorption seawater environments is necessary to reveal the durability under conditions such as above seawater level in coastal zones. Taking soda residue-ground granulated blast furnace slag-carbide slag (SR-GGBS-CS) and cement as marine soil solidifiers, the deterioration characteristics of solidified soil resulting from capillary seawater absorption were elucidated systematically through a series of tests including capillary water absorption, unconfined compressive strength, swelling, local strain, and crystallization. The microscopic mechanism was analysed through nuclear magnetic resonance and X-ray diffraction tests. The results showed that cement-solidified soil exhibited higher water absorption and faster swelling compared with SR-GGBS-CS solidified soil in the one-dimensional seawater absorption state. In the three-dimensional seawater absorption state, solidified soil with low GGBS dosage experienced a significant transition from vertical shrinkage to swelling during the capillary water absorption process, leading to a substantial decrease in strength after 7 days of crystallization. Cement-solidified soil displayed non-uniform and anisotropic swelling, along with the formation of more external salt crystals. Overall, the soil solidified with 25% SR, 10% GGBS, and 4% CS demonstrated robust resistance to capillary absorption deterioration in a seawater environment due to its minimal water absorption and swelling, uniform surface strain, weak salt crystallization, and limited strength deterioration caused by capillary water absorption.

Salt-frost heaving of canal foundation saline soils is the primary cause of damage to the lining structures of water conveyance channels in the Hetao Irrigation District, China. Chemical solidification of saline soils can mitigate frost heave; however, application studies exploring the salt-frost heave resistance of saline soils solidified through the synergistic use of multiple industrial solid wastes in the Hetao remain limited. This study employs a sustainable solidifying material composed of slag, fly ash, coal gangue, coal-based metakaolin, carbide slag, and potassium silicate activator. The optimal mix ratio was determined using Response Surface Methodology (RSM). Unidirectional freezing tests evaluated the effects of solidification material content, curing period, and salt content on salt-frost heave development. Unconfined compressive strength tests assessed salt-frost heave durability of high-salinity solidified saline soils. Microstructural characteristics were analyzed using Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TG) to investigate resistance mechanisms. Results indicated that the industrial waste materials exhibited synergistic effects in an alkaline environment, with the optimal mix ratio of slag, fly ash, coal gangue, coal-based metakaolin, carbide slag, and potassium silicate at 21:25:33:8:7:6. Increasing solidified material content and curing time significantly enhanced salt-frost heave resistance, as evidenced by improved freezing temperature stability, deeper freezing front migration, and reduced salt-frost heave rate. The optimal group (35 % solidifier, 7 days curing) showed a 5.53 degrees C increase in stable freezing temperature, a 3.78 cm upward migration of the freezing front, and a 3.94 % reduction in salt-frost heave rate. Salt-frost heave durability of highsalinity soils improved post-solidification, with a gradual decrease in the degradation of unconfined compressive strength, achieving a minimum weakening of 21.13 %. Hydration products C-S-H, C-A-H, and AFt filled voids between soil particles, restricting water and salt migration. Hydration of industrial wastes reduced free water and SO24 content, decreasing water-salt crystallization and mitigating salt-frost heave. The findings provide an engineering reference for in-situ treatment of salt-frost heaving in saline soils of water conveyance channels in the Hetao Irrigation District.

Coral sand is characterized by low cohesion and high porosity, posing a potential liquefaction risk. Thus, coral sand stabilization is necessary in coastal construction projects. Polyurethane, with its excellent toughness, rapid reaction speed, and strong adhesive properties, is an ideal choice for reinforcing coral sand. However, the diffusion range of non-water reacting foamed polyurethane in coral sand is limited. This study explored the use of water-reacting polyurethane (PRP) to solidify coral sand. PRP is known for its high permeability and bonding strength. Despite its potential, the dynamic mechanical properties and reinforcing mechanism of PRP-solidified coral sand, which are crucial for site seismic analysis and seismic design, have not yet been fully understood. Thus, the resonance column and uniaxial compression tests were conducted to investigate the variations in dynamic shear strain, dynamic shear modulus, damping ratio, and uniaxial compressive strength of the solidified material under different confining pressures, PRP incorporation ratios, and mass moisture contents of coral sand. To further investigate the underlying mechanisms of the variations in its mechanical properties, scanning electron microscopy (SEM) and mercury intrusion tests were conducted to analyze the morphology and pore characteristics of the PRP-solidified material. The results show that, at a constant moisture content, increasing the PRP proportion enhanced the dynamic shear modulus, damping ratio, and uniaxial compressive strength of the coral sand. However, excess moisture content reduced these properties. The pore ratio decreased with the increase of PRP and moisture content, with a larger reduction before drying and a smaller one after drying. The tortuosity of the specimens was mainly affected by the incorporation ratio of PRP, which increased with the increase of the incorporation ratio. However, the moisture content of coral sand had a fewer effect on the tortuosity. The permeability gradually decreased with the increase of the PRP incorporation ratio and the moisture content of coral sand. PRP strengthened the coral sand, primarily through its covering, filling, and bonding effects, enhancing the friction and mechanical occlusion. These findings are significant for the applications of PRP in future coastal engineering projects.

The application of alkali-activated slag (AAS) cementing material to the curing of soft soil foundations has a good engineering application prospect and is economical and environmentally friendly. In this study, three different activators (Na2OnSiO(2), NaOH, Ca(OH)(2)) were used to alkali-activate slag powder to solidify and improve soft soil in inland port areas. In order to explore the mechanical properties and strength formation mechanism of AAS-solidified soil under different activators, mechanical properties, and microscopic tests were carried out. Firstly, with unconfined compressive strength as the evaluation index, an orthogonal test of three factors, such as the type of activator, the amount of activator, and the amount of slag powder, was designed. Then, the unconfined compressive strength, resilience modulus, shear strength, and compression modulus of AAS-solidified soil were tested with the three activators under optimal dosage. Finally, phase composition, SEM-EDS, TG-DTG, and FT-IR analyses were carried out with the three AAS-solidified soils. The results show the following: (1) The factors affecting the unconfined compressive strength of AAS-solidified soil are ordered as follows: the type of activator > the amount of activator > the amount of slag powder. In addition, the optimal factors were as follows: activator type: Na2OnSiO(2); amount of activator: 3%; and amount of slag powder: 20%. (2) In considering the macroscopic mechanical properties, the effect of the activator is Na2OnSiO(2) > NaOH > Ca(OH)(2), and the Na2OnSiO(2) AAS-solidified soil has good early strength. (3) The hydration products of AAS are mainly C-A-S-H gel, N-A-S-H gel, and C-S-H gel, which increase the strength and cohesion of solidified soil. The results show that AAS-solidified soil with 0.7-modulus Na2OnSiO(2) as the activator has good engineering characteristics and can be used for curing soft soil foundations.