Search Results (691)

Lime-based stabilization of clayey soils remains a cornerstone of ground improvement, yet the high carbon footprint of lime production drives the search for sustainable supplementary binders derived from industrial and quarrying wastes. Volcanic tuff waste (VTW), a fine powder by-product of wet cutting of ignimbritic tuff blocks, is an underutilized quarrying residue, already fine enough to use directly without grinding or thermal processing, yet its use as a supplementary binder in lime-stabilized clays has not been systematically investigated. This study evaluates VTW sourced from Ahlat (Bitlis, Türkiye) in kaolin clay stabilized with 6% lime, with VTW added at 0%, 10%, 15%, and 20% by dry weight. Mixtures were characterized through Atterberg limits, compaction, unconfined compressive strength (UCS) at 1–28 days, California Bearing Ratio (CBR), XRD, SEM, and FTIR. VTW reduced plasticity index, increased maximum dry density, and lowered optimum moisture content. The 15% VTW mixture achieved the highest 28-day UCS of 4296 kPa, a 17.2% improvement over the lime-only control, and the highest CBR of 80%. XRD revealed Tobermorite 9 Å formation, while SEM and FTIR confirmed cementitious gel phases consistent with pozzolanic reactions. The findings demonstrate that ignimbritic VTW, used directly without processing, is an effective supplementary binder that partially replaces carbon-intensive lime, supporting low-carbon, cost-effective stabilization and the valorization of quarrying waste within a circular economy framework. Full article

The valorization of drinking water treatment sludge (DWTS) and eggshell waste represents a promising route for reducing landfill disposal and developing alternative stabilized materials for geotechnical applications. This study aimed to evaluate the mechanical and microstructural behavior of DWTS stabilized with commercial lime (CL) and eggshell-derived hydrated lime (EHL), including alkali-activated EHL systems. EHL was produced from locally collected eggshell waste through washing, drying, grinding, calcination at 1000 °C for 4 h, hydration, drying, and sieving. The mixtures were prepared with lime contents of 5%, 8%, 11%, and 14%, while NaOH solutions of 0.5, 1.0, and 1.5 M were used for the activated systems. A total of 120 cylindrical specimens were compacted under controlled dry unit weight and moisture content and cured for 7 and 28 days. The stabilized DWTS was evaluated through unconfined compressive strength (q_u), SEM–EDS analysis, and multifactorial ANOVA. The highest q_u for CL-treated specimens was 4561.72 kPa at 14% lime and 28 days, while EHL reached its best response at 11% lime and 7 days, with a q_u of 3195.13 kPa. In general, EHL showed a competitive performance at intermediate and high lime contents, although increasing NaOH molarity tended to reduce strength. Full article

This study investigates the effect of nano-zeolite and lime on the resistance of reconstituted soil using an integrated experimental and explainable machine learning framework. Soil samples were prepared with varying proportions of nano-zeolite, lime, and fines, and cured under controlled temperature and time conditions. Soil resistance (q) was measured to evaluate the mechanical performance of each mixture. Eight machine learning models, including artificial neural networks (ANN), random forest (RF), random tree (RT), random committee–random tree (RC-RT), M5Rules, KStar, RBFS, and additive regression–decision stump (AR-DS), were developed using Weka 3.8.6 to predict soil resistance based on the input parameters. Model performance was assessed using SSE, MAE, MSE, RMSE, Error %, Accuracy %, R², correlation coefficient, Willmott Index, Nash–Sutcliffe Efficiency, Kling–Gupta Efficiency, and SMAPE. ANN and RF achieved superior accuracy (R² ≥ 0.98) with minimal prediction error, effectively capturing the nonlinear interactions between stabilizer content, curing time, and environmental conditions. Sensitivity analyses using the analysis index and SHAP values revealed that nano-zeolite, lime, and curing time were the dominant factors influencing soil resistance, while fines content and curing temperature had secondary effects. The results demonstrate that nano-zeolite and lime significantly enhance soil resistance and that explainable machine learning models can reliably predict and interpret soil performance, providing a data-driven framework for optimized soil stabilization in geotechnical engineering applications. Full article

Acidic subsoils can restrict root growth and nitrogen (N) uptake and increase the risk of N loss; however, the extent of genotypic variation remains unclear. We evaluated two bread wheat cultivars, Haruyokoi and Harukirari, and one spelt line, KU-1025, under limed and acidic subsoil treatments to clarify whether maintaining root growth in acidic subsoil contributes to greater N capture and lower N loss. After 78 days, we measured shoot dry weight, shoot N uptake, root dry weight, total root length, soil nitrate (NO₃-N) concentration, and cumulative N leaching. The acidic subsoil reduced shoot N uptake, root length in the subsoil, deep-root ratio, and NO₃-N depletion, indicating that it restricted root proliferation and N acquisition. KU-1025 showed the greatest shoot dry weight, shoot N uptake, root dry weight, and total root length under both treatments. It also maintained a high deep-root ratio under acidic subsoil conditions and showed lower soil NO₃-N concentrations and less N leaching than the two wheat cultivars. Across genotypes and treatments, shoot N uptake was positively correlated with root dry weight and total root length, whereas N leaching was negatively correlated with these traits. These results suggest that maintaining a large root system, rather than deep rooting alone, is important for improving N capture and reducing N loss under acidic subsoil conditions, and that KU-1025 may provide useful genetic variation for breeding wheat adapted to acidic subsoil environments. Full article

Red clay in humid-hot environments suffers from severe water sensitivity and rainfall-induced slope instability, while traditional cement/lime stabilization faces high carbon emission challenges. Existing studies on plant ash-modified red clay mainly focus on basic mechanical properties, while systematic research on water retention characteristics and slope stability under extreme rainfall in humid-hot climates remains insufficient. To address this gap, this study proposes a sustainable stabilization method using agricultural waste-derived plant ash for red clay modification in humid-hot regions. Red clay exhibits distinct engineering behaviors owing to its unique physicochemical properties, leading to compromised slope stability and reduced resistance to rainwater infiltration. In this study, red clay was stabilized with 5%, 10%, 15%, and 20% plant ash. Laboratory tests evaluated compaction characteristics, shear strength, and water retention, supported by microstructural analysis via scanning electron microscopy (SEM). Slope stability under rainfall conditions was further simulated using ABAQUS 2022 software. Key findings include: (1) The addition of plant ash significantly altered the compaction properties. As the plant ash content increased from 0% to 20%, the maximum dry density of the modified red clay decreased linearly from 1.68 g/cm³ (unmodified soil) to 1.53 g/cm³, while the optimum moisture content rose from 21.86% to 23.85%. (2) The mechanical properties exhibited a non-linear response, peaking at 10% ash content. At this optimum dosage, the unconfined compressive strength, cohesion, and internal friction angle increased by 70.4%, 83.0%, and 37.1%, respectively, compared to untreated soil. (3) Plant ash enhanced water retention capacity, shifting the soil-water characteristic curve (SWCC). The modified soil demonstrated faster dehydration at low suction but improved water retention at high suction. The permeability coefficient decreased by an order of magnitude. Microstructural analysis revealed reduced porosity and fracture infilling by cementitious gels. (4) Numerical simulations confirmed that 10% plant ash reduced maximum slope displacement from 0.96 m to 0.61 m under heavy rainfall (90 mm total precipitation over 36 h, peak intensity 90 mm/day), elevating the safety factor from 0.85 to 1.45. Failure modes transitioned from deep-seated slip to localized shallow erosion. These results demonstrate that plant ash is a sustainable and effective additive for red clay slope stabilization in tropical climates. Full article

In the face of the raw materials crisis and environmental concerns, sustainable waste management has become a priority for current and future generations. Recycling waste from wastewater treatment plants in a closed loop protects natural resources, reduces landfill volumes, and lowers disposal costs. This paper presents the results of tests on the physical, filtration, and mechanical properties of mixtures of washed mineral waste (WMW) from grit chambers with fly ash from the thermal treatment of municipal sewage sludge (SSA) in a fluidized bed furnace. Additionally, radiological tests of the mixture components were conducted. Based on the conducted tests, the possibility of sustainable use in civil engineering, such as soil backfills and embankment construction materials, was assessed. The possibility of safely using waste materials in the indicated construction solutions was demonstrated for mixtures with dominant WMW content (90% and 70% by total weight). The waste mixtures correspond to poorly or medium-grade sands with a small amount of silt (uniformity coefficients of 3.33, 3.50, and 8.00). They are characterized by maximum dry densities of 1.542, 1.770, and 1.780 g/cm³; optimal moisture contents of 12.54, 12.86, and 20.25%; permeability coefficients of 0.08, 0.22, and 0.39 m/d; and internal friction angles of 38.4, 39.5, and 40.1°. The values of the determined parameters of some mixtures are similar to those of natural sands used as construction aggregates. All mixtures meet the geotechnical criteria for use in road embankments, below frost depth, and in flood embankment bodies. Mixtures with a 90% mass fraction of WMW were also approved for application as backfill for installation trenches. However, none of the mixtures met the hydraulic conductivity threshold required for the upper layers of embankments nor for backfill of abutments and retaining structures without the use of an additional binder (cement or lime), which is considered a prerequisite for these applications. Full article

Argillaceous siltstone is widely distributed along expressways in southern China; however, its strong water sensitivity and slaking properties severely restrict its utilization as subgrade fill, particularly under wet–dry cyclic conditions where bearing capacity deteriorates sharply. Existing studies have predominantly focused on mechanical performance evaluation of stabilizers, while systematic comparisons of lime and cement improvement effects and durability evolution under wet–dry cycles remain insufficiently understood. Drawing on the Yongjin Expressway reconstruction and expansion project, this study systematically investigates the durability of lime- and cement-improved argillaceous siltstone fill. Through unconfined compressive strength (UCS) tests, California bearing ratio (CBR) tests, and five wetting–drying cycles, the evolution differences in strength development, water stability, and durability between the two improvement schemes are revealed. Results indicate that, under identical stabilizer contents (3–7%) and curing conditions, the UCS and CBR of cement-improved soil are significantly higher than those of lime-improved soil. At the same dosage, the strength of cement-improved soil is approximately 1.5–1.7 times that of lime-improved soil, and the absolute strength gap further widens with increasing dosage. Both stabilizers effectively inhibit water immersion swelling, but the swelling rate of lime-improved soil is about 1.3–1.5 times that of cement-improved soil at the same dosage. At 7% dosage, the swelling rates of cement- and lime-improved soils decrease to 0.40% and 0.60%, respectively, both meeting subgrade fill swelling control requirements. After five wet–dry cycles, the UCS retention rate of 7% cement-improved soil is 78.3%, while that of lime-improved soil is 69.0%; the residual strengths are 507.0 kPa and 303.6 kPa, respectively, both satisfying general subgrade engineering strength requirements. However, the 3% lime-improved soil declines to 47.5 kPa after cycling, falling below the engineering threshold. Integrating strength, deformation, and durability indices, high-grade highway roadbeds and other high-load-bearing sections should prioritize 7% cement improvement, whereas general subgrade sections and locations emphasizing crack resistance may adopt 7% lime improvement as an alternative. Low-dosage (<5%) lime improvement is not recommended for argillaceous siltstone subgrade engineering. The findings provide a scientific basis for the engineering application of argillaceous siltstone as subgrade fill and for optimization of improvement schemes. Full article

Soil pH is a key regulator of soil chemical processes, organic matter transformation, and ecosystem functioning in acid soils. This study examines how pH gradients induced by long-term liming affect soil chemical properties, aluminum dynamics, and soil organic carbon (SOC) stabilization in Retisols under plant-derived organic inputs. The study was conducted at six soil pH levels (pH_KCl from 3.9–4.0 to 6.5–6.7), which reflect a gradient of acidity conditions. Soil chemical parameters, SOC content and fractions, humic substance composition, aluminum forms, and soil respiration (CO₂ release under laboratory conditions) were analysed. Increasing soil pH significantly reduced aluminum concentrations (by up to 59%) and improved nitrogen and phosphorus availability, indicating a gradual reduction in chemical limitations associated with soil acidity. Soil pH strongly controlled both SOC content and quality. The highest SOC content was observed at pH 6.0–6.1, and strongly acidic conditions favored the accumulation of more labile carbon forms. As the pH increased, there was a clear shift towards more stable organic matter, as indicated by higher humic acid content, an increased HA/FA ratio, and a threefold increase in the organic carbon stability index. At the same time, the reduced water-extractable organic carbon content indicated reduced carbon mobility and improved physicochemical stabilization. Microbial activity increased with increasing pH, but showed a nonlinear response, reflecting a balance between increased mineralization and carbon stabilization processes. These data indicate that soil pH primarily determines SOC stabilization pathways, rather than just total carbon accumulation. These results suggest that soil pH may influence SOC stabilization through changes in aluminum dynamics, organo-mineral interactions, and microbial processes, supporting previously reported mechanisms of carbon stabilization in acid soils. The optimal pH range of 5.5–6.1 promotes favorable interactions between nutrient availability, microbial processes, and organic–mineral associations, supporting long-term soil functionality. This study highlights liming as a key strategy for regulating soil biogeochemical processes and improving the sustainability of acid soil management. Full article

Ecological carrying capacity (ECC) is a vital indicator for regional sustainable development, reflecting an ecosystem’s support for human activities while maintaining core functions. Research on ECC has largely focused on static assessment, while exploration of dynamic prediction has been relatively limited. This study constructed a comprehensive evaluation system using the AHP-EW model with multidimensional indicators and developed a CAXO hybrid model for multi-scenario ECC projection of China. ECC patterns were classified into five levels, with SHAP and LIME adopted to interpret ECC changes. The results show that China’s ECC exhibits a “high in the southeast and low in the northwest” spatial pattern and has improved continuously from 2000 to 2020, with the proportion of Level V areas increasing from 10.86% to 14.61%. Significant regional disparities exist, with more favorable ECC conditions east of the Hu Huanyong Line and poorer conditions in the west. The CAXO model achieves reliable performance (OA = 90.01%, Kappa = 87.11%) and outperforms traditional models. SHAP analysis identifies NDVI (2.17) as the most critical driving factor, followed by soil moisture (0.53) and precipitation (0.52), while LIME reveals heterogeneous factor contributions across ECC levels. Northwestern China faces severe ecological constraints (Level I: 53.96%), whereas eastern China exhibits the optimal ECC status (Level V: 70.07%). Multi-scenario projections to 2050 show that Level V areas will reach 28.22% under SSP1-2.6, Level III will account for 27.70% under SSP2-4.5, and Level I will rise to 22.44% under SSP5-8.5. The proposed ECC framework and CAXO model provide scientific support for ecological security early warning and sustainable development policy-making. Full article

Stabilizing weak soils is a well-known pavement and geotechnical engineering technique. This technique involves introducing minimal cementitious materials to improve the soil’s geotechnical characteristics. This paper investigates the use of recycled industrial polymer waste (IPW) as a reinforcement material in the presence of cementitious binders to stabilize weak silty sand soil (SM), supporting sustainable engineering practices. The randomly distributed IPW were added as percentages of 0%, 5%, and 10% to a mixture of lime soil and cement soil, with varying amounts of 0% to 6% of lime (L) and 0% to 6% of ordinary Portland cement (OPC), respectively. The laboratory experiments were conducted on natural and stabilized samples in wet (unsoaked) and submerged (soaked) conditions. The experimental program included Proctor compaction, California bearing ratio (CBR), unconfined compressive strength (UCS), durability tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction analyses. The resilient modulus (Mr) was estimated using an empirical equation. The outcomes of this experimental study show that adding a combination of IPW shreds with a small amount of L and/or OPC to the SM soil provides a significant increase in the UCS, CBR, durability and Mr values compared with case of SM with only L, which allows for superior characteristics and increases strength and stiffness parameters throughout any phase of earthwork construction design, resulting in stronger and stiffer subgrades. These results were reinforced by microstructural observations from SEM, EDS, and DRX, confirming the formation of cementitious gels and chemical compounds, consistent with the macro-scale mechanical improvements. The expected practical outcomes include potential reductions in pavement thickness, which can help lower pavement stabilization costs and extend its service life. Additionally, the use of waste materials to replace raw materials contributes to decreased energy consumption and emissions, although detailed assessments are needed to quantify these effects. Full article

The problem of industrial waste disposal is becoming increasingly pressing. For a long time, one of the primary methods of managing hazardous industrial waste was to dispose of it for long periods (decades) in engineered landfills. However, over time, due to various climatic, geological, and other changes, landfills begin to cause significant harm to the environment and human health. Old landfills, many built in the mid-20th century, pollute the air, soil, and groundwater. Therefore, the issue of decommissioning “old” landfills is becoming increasingly pressing. This study aimed to develop technological solutions for the safe extraction and processing of hazardous liquid waste from an aged industrial landfill. An integrated treatment chain was designed, comprising extraction, multi-barrier water treatment, vacuum evaporation, and lithification. Optimal lithification compositions were identified: for the salt concentrate–sludge–spent media mixture, a ratio of 68.2% sorbent D, 28.0% salt concentrate, and 3.8% dewatered sludge/spent media yielded a loose granular geocomposite; for oil-containing waste, the optimal ratio using lime and opoka was 1:0.9:0.5 (bottom sediments/CaO/opoka). Biotesting confirmed that the lithified waste is Hazard Class V (non-hazardous), whereas the untreated waste is Class III (moderately hazardous). The resulting geocomposite is suitable for on-site technical reclamation, closing the material cycle. Full article

Surface and subsurface acidity (pH < 4.4) limit nutrient availability, restrict root exploration, and impair crop yields in agricultural and agropastoral systems. Subsurface acidity (0.4–0.8 m layer) is a critical limiting factor for mature tropical soils. Methodologies that provide amelioration of surface and subsurface acidity and improvements in soil chemical fertility are necessary to decrease production costs and increase crop yields. This study evaluated the long-term ability of different methodologies for applying calcium (Ca) compounds (limestone (LS), phosphogypsum (PG), and hydrated lime (HL)) to ameliorate surface and subsurface acidity and improve soil chemical fertility. The results showed that the correction of surface acidity by treatments T2 (no-till/LS + PG), T3 (conventional tillage/LS + PG), T5 (no-till/HL + PG) and T6 (minimum tillage/HL + PG) persisted two years after application, as evidenced by higher pH and base saturation (BS) and lower total acidity in the 0.0–0.2 m layer compared with the control. By contrast, the improvement in acidity in the 0.4–0.8 m layer that was previously observed after subsurface application of HL in the 2017–2018 season (T6 and T7, minimum tillage/HL + PG) was lost. Moreover, the improvements in Ca²⁺ content and Ca²⁺/cation exchange capacity (CEC) observed after applying LS plus PG persisted in the 0.0–0.1 m layer only. However, the improvements in Mg²⁺ content and Mg²⁺/CEC after applying HL plus PG were not maintained. In addition, the positive effects of Ca compounds on sulfate-S (S-SO₄²⁻) content throughout the soil profile (0.0–0.8 m) did not persist. By contrast, after two seasons, Ca compound application had residual positive effects on P content in the 0.1–0.8 m layer and organic matter (OM) content in the 0.2–0.8 m layer, which were previously not observed. Full article

Sewage sludge (SS) is a by-product of wastewater treatment processes (WWTPs) and is rich in organic matter and essential nutrients like nitrogen, phosphorus, and potassium, making it a potential fertilizer for agricultural use. However, its application is often limited due to the presence of pathogenic bacteria, viruses, metals, and organic contaminants that can accumulate in soils and crops, raising concerns about food safety. Sewage sludge is additionally challenging to handle due to its high moisture content, low density, and odor emission. To mitigate environmental risks and enhance its usability as a soil fertilizer, SS must be stabilized. Various techniques, including chemical, physical, and biological, can be used to stabilize SS. The addition of lime and composting has received particular attention among these techniques owing to the benefits they offer. Both methods effectively control and eliminate pathogens and reduce metal bioavailability, thus improving their agricultural utility. This review emphasizes the importance of using SS for agricultural purposes, placing particular focus on the procedures of composting and liming to stabilize and enhance the quality of SS, hence promoting its safety. Full article

Published laboratory data on soil stabilisation are abundant, yet they remain fragmented across studies and are often difficult to reuse because of inconsistent reporting formats, heterogeneous testing conditions, and incomplete metadata. This article presents a curated experimental dataset compiled from 20 published studies on fine-grained soils, comprising 560 records, including 397 unconfined compressive strength (UCS) results and 163 California Bearing Ratio (CBR) results. The dataset is defined by the inclusion of laboratory studies designed around biopolymer-based two-additive stabilisation frameworks, while intentionally retaining untreated and single-additive comparator records reported within the same experimental programmes. This design is a key distinguishing feature of the dataset because it enables analysis of baseline soil behaviour, isolated additive effects, and combined-additive responses within a traceable study context. Across the included studies, the treatment systems cover a wide range of biopolymer- and lignin-related materials, including xanthan gum, guar gum, chitosan, sodium lignosulfonate, and electrolyte lignin stabiliser, together with complementary additives such as cement, lime, fly ash, ground granulated blast-furnace slag, rice husk ash, glass powder, concrete waste, nano-additives, and natural or synthetic fibres. In addition to UCS and CBR outcomes, the dataset preserves key contextual variables required for meaningful secondary reuse, including soil classification, grain-size fractions, Atterberg limits, compaction properties, curing duration, additive identities and dosages, and source-level traceability. The data are distributed as a structured Excel workbook comprising two cleaned outcome-specific sheets (CBR_clean and UCS_clean) and four supporting documentation sheets (StudyInventory, DataDictionary, VocabularyMap, and QC_Log). Record-level identifiers, DOI-linked source fields, inferred-curing flags, and qualified outcome descriptors are retained to support auditability, selective filtering, and reproducible reuse. The resulting dataset provides a practical foundation for comparative assessment of stabilisation strategies, pavement and subgrade engineering studies, meta-analysis, and machine learning applications in geotechnical engineering. Full article

Eggshell waste generated by the poultry processing industry represents a significant yet underutilized biogenic resource with substantial potential for sustainable agricultural and environmental applications. Globally, several million metric tons of eggshell residues are produced annually, consisting predominantly of calcium carbonate (CaCO₃) in the form of calcite, along with minor quantities of organic matrices and trace minerals. These physicochemical characteristics make eggshells a promising renewable alternative to conventional mineral sources for use as fertilizers, soil amendments, and biomaterials. Recent studies have shown that finely ground eggshell powder (ESP) is an effective liming material that can regulate soil chemical conditions and improve agronomic performance under acidic soil conditions. Furthermore, eggshell-derived materials have been incorporated into composting systems, biochar composites, and nanostructured fertilizers to enhance nutrient dynamics, immobilization of contaminants, and microbial activity. Advances in nanotechnology have facilitated the synthesis of nano-calcium carbonate (NCC) and nanohydroxyapatite (nHAP) fertilizers with improved nutrient supply and controlled-release properties. However, challenges associated with nanosafety evaluation, large-scale processing technologies, regulatory harmonization, and long-term field validation remain. Therefore, this review critically synthesizes the structural, biochemical, and physicochemical properties of eggshells and eggshell membranes, examines their applications in sustainable agriculture and environmental remediation, and identifies the key research priorities required to advance eggshell valorization within circular bioeconomy strategies. Full article