Search Results (1,537)

Gravelly soil is widely used in western China but suffers from poor gradation, low water stability, and weak freeze–thaw resistance. Traditional cementitious stabilizers involve high energy and carbon emissions. To address these issues, a novel, eco-friendly gravelly soil stabilizer was prepared from waste foamed concrete (WFC) via crushing, ball milling, and high-temperature calcination. This study systematically evaluated stabilization performance and mechanisms. Results indicate that the WFC stabilizer significantly enhances soil properties. At the optimal 30% dosage, the 28-day unconfined compressive strength (UCS) reached 6.5 MPa (a 333% increase), and water stability was significantly improved. Under freeze–thaw conditions, the 30% dosage yielded a mere 2% mass loss after five cycles, with the UCS reaching 9.56 MPa (a 437% increase). Microstructural analyses (XRD, SEM) revealed that hydration generates calcium silicate hydrate (C-S-H) gel and katoite (Ca₃Al₂(SiO₄)_3−x(OH)_4x). These products effectively fill soil pores and the spaces of the particles, optimizing the microstructure. This study provides a sustainable pathway for WFC recycling and offers a relatively lower energy consumption, low-carbon and high-performance stabilizer for reinforcing gravelly soil subgrades in cold regions. Full article

Solid-waste-based cementitious materials have been widely applied in soil stabilization. However, their durability in practical engineering applications remains inadequate, which may lead to performance degradation and challenges for long-term serviceability. In this study, the durability of solid waste-based cementitious materials (CSD)-solidified soil was improved by adding RL and polypropylene fibers (PP). The research results indicate that the addition of RL hinders the ingress of water into the sample, which is beneficial for improving the water stability and resistance to dry–wet cycles of CSD solidified soil. The addition of PP can suppress crack propagation and effectively enhance the freeze–thaw cycle resistance of solidified soil. When the dosage of RL and PP is both 0.2%, CSD-RP solidified soil exhibits excellent durability performance. After 28 days, the water stability coefficient reached 82.8%, representing a 9.5% increase compared to the control group. After undergoing dry–wet and freeze–thaw cycles, the strength loss of the samples was 36.7% and 47.3%, which was 8.6% and 10.5% lower than that of the control group. Microscopic test results show that cyclic failure promotes the formation of pores and cracks in the sample, while the hydration products generated by the reaction of cementitious materials densify the soil. Compared with the control group, the total porosity of CSD-RP samples decreased by 2.45% and 2.19% after wet–dry and freeze–thaw cycles, further indicating that co doping of RL and PP is beneficial for reducing the degree of structural degradation of the samples. Full article

High-liquid-limit clay exhibits pronounced water sensitivity due to the strong electrostatic repulsion and weak interparticle bonding within its microstructure, which often limits its direct engineering uses and complicates the reuse of excavated clayey soils generated during the construction of transportation infrastructure. In this study, inorganic salts (KCl, CaCl₂ and FeCl₃) and carboxyl-containing polymers (PAAS, HPMA and CMC) were screened to construct organic–inorganic composite stabilization systems. Based on the screening results, an organic–inorganic composite system composed of CaCl₂ and sodium polyacrylate (PAAS) was developed to regulate interfacial interactions and induce microstructural reconstruction in clay. The synergistic mechanisms governing particle aggregation and dispersion were systematically investigated through Atterberg limit tests, zeta potential measurements, DLVO theoretical calculations, particle size analysis, scanning electron microscopy (SEM) and immersion disintegration experiments, combined with multivariate statistical modeling. Among the tested salt–polymer formulations, a composite system with 2% CaCl₂ and 0.1% PAAS showed the most favorable overall performance, achieving an optimal balance between electrostatic compression and steric stabilization, leading to enhanced structural integrity and delayed water-induced disintegration. Ca²⁺ ions compress the diffuse double layer and promote particle flocculation, whereas adsorbed PAAS chains introduce steric hindrance and interfacial modification. Their synergistic interaction reconstructs the pore–aggregate framework and regulates the interparticle potential energy landscape. DLVO analysis indicates that the optimized system attains a moderate critical interaction distance (h_c = 7.31 nm) and primary minimum depth (DPM = −2.72 × 10⁻¹⁶ J), reflecting a balanced interfacial bonding state. Multivariate statistical analyses further reveal a dual control pathway, in which consistency primarily governs disintegration duration, with additional contributions from surface electrochemical properties, while surface properties, soil structure and consistency collectively influence disintegration initiation. These findings elucidate the interfacial regulation and structural evolution mechanisms in organic–inorganic composite systems and provide insights into the design of composite modifiers for water-sensitive particulate materials, particularly for the resource reuse of high-liquid-limit clay excavated during the construction of transportation infrastructure and related geotechnical engineering applications. Full article

In the cement-based stabilization of organic soil, the alkaline environment produced by cement hydration dissolves organic matter from the soil skeleton while simultaneously promoting the precipitation of neophases. This study investigates the coupled effects of structural deterioration and neophase compensation on the microstructural and mechanical properties of organic soil. Organic soil was treated with an alkaline Ca(OH)₂ solution (pH = 12.0) utilizing a model testing apparatus over an 80-day duration. Consolidation and permeability tests were combined with microstructural analyses (FTIR, XRD, and SEM-EDS) to elucidate the fundamental mechanisms. The results show that humus acid in organic soil was dissolved in an alkaline environment, significantly enlarging soil pores and forming interconnected dissolution channels. Consequently, the permeability coefficient and additional settlement increased by 49.21% and 18.07%, respectively, compared to the pristine soil samples. Concurrently, within the OH⁻-and Ca²⁺-rich environment, clay minerals underwent a pozzolanic reaction, generating C-(A)S-H gels. Dissolved humus acid formed complexes with Ca²⁺ ions. While these formed neophases provide microstructural compensation for the organic soil, their compensatory effect is limited. These findings provide a critical theoretical framework for understanding the coupled deterioration–compensation mechanisms, which is essential for optimizing engineering design and promoting the long-term durability of alkaline-reinforced organic geotechnical environments. Full article

Thallium (Tl) and cadmium (Cd) are highly toxic heavy metals that frequently co-occur in sulfide ores, posing a serious food safety risk through accumulation in rice. Although calcium-based (Ca-based) amendments have been widely applied to remediate heavy metal-contaminated soils, their effectiveness in Tl–Cd co-contaminated paddy soils remains unclear. A pot experiment was conducted to evaluate four Ca-based amendments—limestone powder, dolomite powder, hydrated lime, and oyster shell powder—on Tl and Cd bioavailability and uptake in paddy soil near a mining area. Ca-based amendments effectively reduced Tl and Cd bioavailability, with DTPA-Tl reducing by 11.2–17.2% and DTPA-Cd by 8.9–21.3%. These reductions were attributed to increased soil pH and decreased DOC, Fe, and Mn in the pore water. Additionally, Ca-based amendments shifted Tl and Cd from acid-extractable to residual fractions, reducing mobility. Additionally, Ca-based amendments promoted Fe/Mn plaque formation on rice roots, reducing Tl and Cd uptake. Consequently, Tl and Cd concentrations in brown rice decreased by over 14%, with the lowest levels observed under oyster shell powder. However, Cd concentrations still exceeded the maximum permissible limit, indicating that, although Ca-based amendments show considerable potential for in situ remediation of Tl–Cd co-contaminated paddy soils, further optimization and additional measures are required to achieve safe production. Full article

Increasing total soil porosity and optimizing pore distribution improve soil water-holding capacity, thereby alleviating drought impacts on crop yields in semi-arid regions. A three year split-plot field experiment was conducted, with organic fertilizer (sheep manure) rates as main plots and water-retaining agent (WRA) rates as subplots. Four organic fertilizer (0, 45, 60, and 75 Mg hm⁻²) and four WRA rates (0, 0.3, 0.6, and 0.9 Mg hm⁻²) were set, resulting in 16 combined treatments. Undisturbed soil samples were collected to analyze pore distribution and water availability using the soil water retention curve. The results showed significant variations in ameliorative effects with soil depth. Individual applications of either organic fertilizer or WRA significantly improved topsoil pore distribution and water availability but exerted negative effects on the subsoil. Combined application enhanced both soil layers, with a stronger synergistic effect in the subsoil. The combination of 45 Mg ha⁻² organic fertilizer + 0.9 Mg ha⁻² WRA achieved optimal soil improvement in the 0–20 cm layer, increasing aeration porosity by 21.89% compared to organic fertilizer alone; this improvement led to 14.99% and 15.65% increases in plant available water (PAW) and readily available water (RAW), respectively. For the 20–40 cm layer, the combination of 60 Mg ha⁻² organic fertilizer + 0.9 Mg ha⁻² WRA was optimal, increasing total, aeration, and capillary porosity by 24.18%, 183.50%, and 56.73%, respectively, compared to organic fertilizer alone. Consequently, subsoil water availability was enhanced, resulting in 57.53% and 61.18% higher PAW and RAW than the control without WRA. These findings highlight the necessity of layer-specific regulation and differentiated management. The optimal combinations (OF45+W0.9 for 0–20 cm and OF60+W0.9 for 20–40 cm) effectively optimize pore distribution and increase water availability through the complementary synergistic effects of organic fertilizer and WRA. Consequently, this strategy alleviates drought stress on crop yields in semi-arid regions. Full article

This study investigates the valorization of dredged sludge as a sustainable subgrade fill material through stabilization with a nano-calcium carbonate–cement composite. Unconfined compressive strength (UCS) tests were systematically conducted to determine the optimal dosage of nano-CaCO₃ as a supplementary additive at a fixed cement content of 8% by dry soil mass. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and quantitative pore structure analysis were employed to elucidate the underlying solidification mechanisms. The results demonstrate that the addition of 2% nano-CaCO₃ yields the highest 28-day UCS of 721 kPa, representing a statistically significant 21% improvement over the cement-only reference (596 kPa) and a more than threefold increase relative to untreated sludge (213 kPa). Conversely, increasing the nano-CaCO₃ dosage to 2.5% leads to a significant strength reduction, attributed to nanoparticle agglomeration and hindered cement hydration. Microstructural characterization reveals that the optimal nano-CaCO₃ dosage accelerates early-age hydration through a nucleation effect, promotes the consumption of portlandite, and enhances the formation of calcium silicate hydrate (C–S–H) gel. Semi-quantitative XRD analysis further confirms the conversion of less stable monosulfate (AFm-SO₄) into stable monocarboaluminate (AFm-CO₃) phases. These synergistic mechanisms—nucleation, physical pore filling, and chemical reaction—result in a densified matrix with a refined pore structure, reduced total porosity, and a more homogeneous pore-size distribution. The findings provide a robust theoretical basis for the resource-oriented utilization of dredged sludge and the design of low-carbon composite stabilizers for soft soil treatment. Full article

Water-induced deterioration of silty soil subgrade in the lower Yellow River floodplain poses a critical, long-standing engineering challenge. Most existing studies on silty soil modification prioritize strength enhancement via traditional cementitious binders (i.e., cement, lime), yet these strategies fail to fundamentally block water migration in the soil matrix. A distinct scientific gap persists: the capillary water inhibition mechanism of nano-superhydrophobic modified Yellow River alluvial silt, along with the correlation between its microstructural evolution and macroscopic engineering performance, has yet to be systematically elucidated. To fill this gap, we conducted hydrophobic modification of the targeted silt using a nano-superhydrophobic material (NSHM), and performed a systematic suite of laboratory tests to characterize its hydrophobicity, mechanical properties, water stability, and microstructural characteristics. Quantitative experimental results demonstrate that NSHM imparts remarkable water resistance to the silt: at an NSHM dosage ≥0.5%, the modified soil exhibits stable superhydrophobicity across all tested compaction degrees, with over a 99% reduction in saturated hydraulic conductivity. Notably, the hydrophobic modification only incurs a <12% reduction in the dry unconfined compressive strength (UCS) of the silt. Microscopic characterization results reveal that NSHM modifies the silt via two core pathways: uniform particle encapsulation and pore infilling, without altering the inherent mineral functional groups of the soil. This microstructural regulation reduces the average pore diameter by 38.2% and total porosity by 15.6%, while optimizing the uniformity of pore size distribution. Based on comprehensive evaluation of overall performance, a minimum NSHM dosage of 0.5% is recommended for in situ application in local silty soil subgrade. This study provides critical theoretical guidance and technical support for water damage mitigation in alluvial silty soil subgrade. Full article

To enhance the engineering performance of fine-grained composite soils with unbalanced particle gradation, high plasticity, and poor water stability, a synergistic stabilization strategy combining particle structure regulation and microbially induced calcium carbonate precipitation (MICP) was proposed. The particle size distribution and fundamental engineering properties of a titanium gypsum–clay (TSC) composite soil were first optimized through systematic single-factor blending tests. The results indicate that a TS:C ratio of 60:40 significantly improved gradation characteristics, reduced plasticity, and enhanced both compaction behavior and load-bearing capacity. Based on the optimized gradation framework, MICP treatment was subsequently introduced to further enhance water stability. The effects of key parameters, particularly the type of calcium source, on the evolution of water stability were systematically investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to elucidate the underlying reinforcement mechanisms. The results demonstrate that the water stability coefficient increased markedly from 0.35 to 0.83 following MICP treatment, while strength degradation under water immersion was effectively mitigated. Microscopic observations reveal that microbially precipitated calcite fills pore spaces and forms a continuous cementation network via particle bridging and interfacial bonding, leading to an approximately 32% reduction in porosity. Overall, the proposed synergistic strategy offers an effective and sustainable approach for improving the water stability and structural integrity of complex fine-grained composite soils. Full article

Granite residual soil slopes are highly water-sensitive and prone to rapid collapse, strength degradation, and rainfall-induced erosion. This study investigates the improvement effects and underlying mechanisms of carboxymethyl cellulose (CMC) on the water stability, mechanical properties, and rainfall erosion resistance of granite residual soil from Fuzhou, Fujian Province, China. Laboratory tests, including unconfined compressive strength (UCS) tests, direct shear tests, disintegration tests, slope rainfall scouring model experiments, X-ray diffraction test (XRD) and scanning electron microscopy (SEM) observations, were conducted to evaluate the performance and microstructural behavior of CMC-stabilized soils. The results indicate that the addition of CMC significantly enhances soil resistance to disintegration: the 24 h disintegration ratio decreased to 0.5% at 0.5% CMC content. The incorporation of CMC can significantly enhance the unconfined compressive strength (UCS) of the soil and lead to an increase in cohesion, while its effect on the internal friction angle is limited. Under simulated rainfall conditions (30° slope, 120 mm·h⁻¹ rainfall intensity, 60 min duration), slopes stabilized with 0.5% CMC exhibited suppressed rill formation and a 47.5% reduction in sediment yield, accompanied by delayed moisture increase at different depths and reduced infiltration rates. Microstructural analyses reveal that CMC hydration forms gel-like films and filamentous bridges, promoting particle aggregation and pore filling, thereby constructing a denser particle network without generating new chemical compounds. This microstructure collectively enhances soil disintegration resistance, mechanical strength, and slope erosion resistance. Full article

Cement-based grouts used in anchorage engineering often suffer from insufficient flowability, bleeding, and inadequate early-age strength, which may impair grout filling quality and interfacial bonding. This study investigated the synergistic use of fly ash (FA) and metakaolin (MK) to optimize the fresh properties, strength development, microstructure, and early-age anchorage performance of cement-based grouts. Rheological behavior, bleeding rate, and compressive strength were evaluated for grouts with different FA and MK contents, and the overall performance was ranked using the entropy-weighted TOPSIS method. X-ray diffraction and scanning electron microscopy were further employed to clarify the underlying microstructural evolution, and laboratory pull-out tests were conducted to verify the early-age anchorage effectiveness of the selected optimal mixtures. The results showed that the optimal performance was achieved at 15–20% FA and 3–6% MK. Within this range, grout viscosity decreased from 0.24 to 0.16 Pa·s, bleeding rate decreased from 13% to 2%, and compressive strength increased markedly at both 7 and 28 days. The optimized grout also increased the peak interfacial shear stress from 0.440 to 0.978 MPa. These improvements were associated with accelerated hydration, reduced CH and residual clinker phases, and a denser hydration-product network. The pull-out specimens failed predominantly along the grout–rock/soil interface, and the improved anchorage response was attributed to a denser hydration-product network that reduced pores and interfacial defects and promoted more efficient shear-stress transfer. Full article

The chemical equilibria of metal ions between soil solution and solid phases govern the solubility of metals in soil. However, the identity of these controlling phases remains poorly understood in historically polluted environments. This study aimed to identify the dominant mineral phases regulating the activities of Zn²⁺, Cd²⁺, Pb²⁺, and Ni²⁺ in soils subjected to long-term contamination from sewage sludge, municipal solid waste, river water, and industrial effluents across India. The soil samples were collected from various locations historically polluted by sewage sludge, municipal solid waste, polluted river water and industrial effluents. The free ion activities of Zn²⁺ (pZn²⁺), Cd²⁺ (pCd²⁺), Pb²⁺ (pPb²⁺) and Ni²⁺ (pNi²⁺) in soil pore water were estimated using the geochemical speciation model WHAM-VII. The metal ion activities were higher in industrial effluents and solid waste-treated soils as compared to other contaminated soils. The solubility of Zn and Cd in soils contaminated with Zn-smelter effluents was controlled by franklinite (ZnFe₂O₄) in equilibrium with goethite (α-FeOOH) and otavite (CdCO₃), respectively. Identification of minerals further reveals that nickel ferrite (NiFe₂O₄) in equilibrium with lepidocrocite (γ-FeOOH) governs the activity of Ni²⁺ in cycle factory effluent-irrigated soils of Sonepat, Haryana. At the municipal solid waste-contaminated site, the Pb²⁺ activity was controlled by exchangeable Pb in soils, whereas Zn²⁺ activity was governed by willemite (Zn₂SiO₄) in equilibrium with quartz (SiO₂). These findings provide new insights into mineralogical controls on heavy metal solubility under diverse contamination scenarios. Formation of highly soluble minerals like otavite, willemite, and nickel ferrite suggested the potential ecological risk of Cd, Zn, and Ni, respectively, in polluted soils. Full article

With the requirement for reducing carbon footprint in engineering construction, porous vegetation concrete is increasingly receiving attention for use in completed slope restoration. Cemented soil is introduced after the completion of porous vegetation concrete stabilization and functions mainly as a revegetation substrate. An important consideration for cemented soil in this application is its ability to maintain strength and water stability and possess moisture retention capacity, without causing much increase in alkali release or diffusion. This present study investigated a newly developed twofold stabilization system involving both cement binders and organic waterborne epoxy resin to meet the requirements of synthetically enhancing slope stabilization and restoration. Changes in the unconfined compressive strength and water stability were analyzed, whilst mineralogical composition and microstructure characteristics were investigated. The results indicated that moderate incorporation of triethylenediamine (TETA)-cured epoxy resin (1–2% by soil mass) moderately reduced strength and increased water stability with controlled alkali release in cemented soil. Mineralogical and microstructural analysis revealed that TETA-cured epoxy resin retarded cement hydration and refined particle bonding, exhibiting less consolidated pore structure characteristics. The twofold stabilization was exceptional in enhancing structural stability exposed to repeated humidity variation, albeit it yielded increased strength reduction rate from <7% to 9–16% under UV irradiation. Potentials of calcium sulfoaluminate cement and Portland slag cement were also investigated. A pilot-scale vegetation trial with representative plant species gave general agreement with effects observed in the laboratory in alkali reduction and moisture retention. The results provided an ecological approach for better restoring completed slopes that were stabilized using porous vegetation concrete. Full article

In order to investigate the effects of bentonite and glass fiber on the macroscopic mechanical properties and microscopic mechanisms of cement soil in dry environments, a series of laboratory tests were conducted in this study, including drying tests under controlled environments (30 °C, 50% humidity), unconfined compressive strength (UCS) tests, digital image processing technology, and scanning electron microscopy (SEM) analyses. The moisture evaporation law, surface crack development process, UCS variation, and microstructure evolution of cement soil with different mix proportions (bentonite content: 0–9%; glass fiber content: 0–0.5%) were systematically analyzed. The results show that bentonite can significantly enhance the water retention capacity of cement soil, reduce the water evaporation rate, and increase the unconfined compressive strength by filling internal pores to densify the microstructure. Glass fibers form a three-dimensional network structure in the matrix, exerting a bridging effect to inhibit crack initiation and propagation, and optimize the mechanical properties. The unconfined compressive strength increases significantly with an increase in bentonite content (3–9%), and the optimal fiber content for strength improvement is determined as 0.3%. The synergistic effect of bentonite and fibers optimizes the interfacial bonding force between fibers and the matrix, which remarkably improves the anti-cracking performance of cement soil. Specifically, when the bentonite content is 6–9% and the fiber content is 0.3–0.5%, the cement soil maintains complete integrity after drying, with no obvious cracks on the surface. SEM analysis reveals that the addition of bentonite and fibers inhibits the expansion and connection of internal voids, avoiding the cycle of “void enlargement–stress concentration–crack propagation”. This study provides a scientific basis for the engineering application of cement soil in a dry environment. Full article

The swell-shrink behavior of expansive soil strongly affects the long-term stability of subgrades and other geotechnical infrastructures. This study investigated the effects of three nanomaterial additives, namely nano-lime, nano-calcined clay, and hydrophobic nano-silica, on expansive soil. A series of laboratory tests was performed to evaluate the swell-shrink behavior of nanomaterial-treated soils under varying initial water contents and curing durations. Additionally, microstructural analyses were conducted to reveal the underlying stabilization mechanisms. The results showed that all three nanomaterials reduced the swell-shrink potential of the expansive soil, but their improvement effects were strongly dependent on the initial water content. Nano-lime exhibited the strongest overall stabilization effect, especially under relatively high initial water contents, and its performance became more pronounced with curing. Nano-calcined clay provided a moderate but relatively stable improvement. In contrast, hydrophobic nano-silica performed better under relatively low initial water contents, indicating a distinct moisture-dependent behavior. Nano-lime and nano-calcined clay were more effective in refining the pore structure and promoting a denser soil fabric, whereas nano-silica mainly modified particle surface conditions and showed limited pore-refinement capacity under wet conditions. These findings highlight the novelty of the present study in terms of the moisture-dependent stabilization performance and comparative mechanisms of three representative nanomaterials under a unified low dosage, and they provide useful guidance for the improvement of expansive soil subgrades in engineering practice. Full article