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.

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.

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.

Geopolymer has being emerged as a promising alternative to traditional Portland cement in geotechnical engineering, particularly for subgrade applications in cold regions, owing to its eco-friendly and high-performance characteristics. However, exposing geopolymer solidified soils (GSSs) to cold environments can deteriorate the mechanical properties. Hence, it is crucial to improve the mechanical properties and freeze-thaw resistance of the GSSs. In this study, the unconfined compressive strength (UCS), hydro-thermal-deformation characteristics, and microstructure of the nano-silica geopolymer solidified soils (NSGSSs) were experimentally investigated, and the sustainability of the NSGSSs was assessed. The results showed that under the same strain condition, the stresses of the NSGSSs were larger than those of the GSSs. Besides, the UCS of the NSGSSs firstly increased and then decreased with nano-silica (NS) content, with the GSSs containing 3 wt% NS demonstrating the highest peak stress. The UCS loss rate increased with the freeze-thaw cycles (FTCs) and then stabilized, with the first FTC having the most significant impact on the UCS of the soil samples. During the FTCs, the NSGSSs exhibited a larger amplitude of soil temperature variation and residual volumetric unfrozen water content compared to the GSSs. However, the vertical deformation, frost heave and thaw settlement rates of the NSGSSs were markedly smaller than those of the GSSs. After the 9th FTC, the NSGSSs with 3 wt% NS content showed a denser structure and excellent freeze-thaw resistance. Moreover, although adding NS to GSSs increased carbon emissions and costs, the low values of the carbon emission index and economic efficiency index indicated that the substantial improvement in mechanical properties outweighed these negative aspects, particularly for the NSGSSs exposed to the FTCs. This study would provide valuable insights into the development of new eco-friendly materials and offers a novel approach for frost heave prevention and control in cold region geotechnical engineering.

Solidified soil prefabricated pile (PPSS) is a new type of pile formed by extruding solidified soil with hydraulic equipment. The PPSS includes two parts: precast pile and core pile, which can be used to strengthen soft foundation. To study the deformation characteristics of PPSS under vertical load, the nonlinear mechanical behaviour of the double-contact interface of PPSS is analyzed by using the bond slip model and hyperbolic model. A settlement calculation method is proposed considering the displacement coordination of the doublecontact interfaces, e.g., interface between precast pile and surrounding soil, and interface between core pile and precast pile. The bearing characteristics of the double-contact interfaces are studied by using the numerical results. Based on the numerical results, the effects of elastic modulus ratio, diameter ratio, length and initial cohesion on the deformation characteristics of PPSS are analyzed.

Binders can enhance soil properties and improve their suitability as subgrade fillers; however, the cementing effect and strength properties of solidified soil are highly susceptible to external environmental factors. This study evaluated the strength and durability of solidified sludge soil (PSCS) with varying binder (PSC) contents through unconfined compressive strength (UCS) tests combined with drying-wetting (D-W) and freezing-thawing (F-T) cycles, and identified the optimal binder content for performance enhancement. Additionally, mercury intrusion porosimetry (MIP) tests were conducted to analyze pore structure changes and explore the synergistic effects between hydration reactions and moisture variations induced by D-W/F-T cycles. Results indicate that binder content > 15 % significantly enhances PSCS strength and durability, with 15 % content (PSCS15) demonstrating the best economic advantage. During D-W/F-T cycles, the synergy between hydration reactions and moisture variations affects the pore structure, resulting in strength changes. For example, during D-W cycles, moisture movement causes the collapse of pores > 30 mu m, while hydration products fill the pores, decreasing the porosity of 5-30 mu m. Subsequently, moisture variations weaken the cementation effect, leading to a increase in the porosity of 5-30 mu m. This process causes the strength to fluctuate, showing a first decrease, followed by an increase, and then another decrease, with an overall reduction of 21.6 %. During the drying stage of D-W cycles, moisture evaporation inhibits hydration reactions in soil. In contrast, during F-T cycles, moisture remains in different physical states (e.g., solid ice crystals and liquid water). These moisture variations causing the collapse of pores >30 mu m, while hydration products fill the larger pores, increasing the porosity of 1-10 mu m. The strength first decreases and then increases, with an overall increase of 38.7 %. Furthermore, this study demonstrates that until the hydration process is completed, D-W cycles have a more significant negative impact on PSCS compared to F-T cycles.