Search Results (1,025)

Rubber particles have been proven to have the advantages of improving the energy absorption effect and enhancing the friction between soil particles when used to modify the soil. The rubber-modified soil technology also provides a new solution for the pollution-free disposal of waste rubber. However, when rubber particles are used to modify collapsible loess, they cannot significantly enhance its strength. Previous studies have not systematically clarified whether combining rubber particles with different cementation mechanisms can overcome this limitation, nor compared their shear mechanical effectiveness under identical conditions. In view of this, a dual synergistic strategy is implemented by combining rubber with lime and rubber with enzyme-induced calcium carbonate precipitation (EICP). Direct shear tests and scanning electron microscopy are used to evaluate four modification approaches: rubber alone, lime alone, rubber with EICP, and rubber with lime. Accordingly, shear strength, cohesion, and internal friction angle are quantified. At a vertical normal stress of 100 kPa and above, samples modified with rubber and lime (7–9% lime and 6–8% rubber) achieve peak shear strength values of 200–203 kPa, representing an 86.4% increase compared to rubber alone. Microscopic analysis reveals that calcium silicate hydrate gel effectively anchored rubber particles, forming a composite structure with a rigid skeleton and elastic buffer. In comparison, the rubber and EICP group (10% rubber) shows a substantial increase in internal friction angle (24.25°) but only a modest improvement in cohesion (16.5%), which is due to limited continuity in the calcium carbonate bonding network. It should be noted that the performance of EICP-based modification is constrained by curing efficiency and reaction continuity, which may affect its scalability in conventional engineering applications. Overall, the combination of rubber and lime provided an optimal balance of strength, ductility, and construction efficiency. Meanwhile, the rubber and EICP method demonstrates notable advantages in environmental compatibility and long-term durability, making it suitable for ecologically sensitive applications. The results offer a framework for loess stabilization based on performance adaptation and resource recycling, supporting sustainable use of waste rubber in geotechnical engineering. Full article

Revealing the evolution of micropore structure in industrial by-product solidified sludge is essential for elucidating strength development mechanisms and promoting the engineering utilization of industrial wastes. In this study, a series of tests, including unconfined compressive strength (UCS), low-field nuclear magnetic resonance, direct shear, and scanning electron microscopy coupled with energy-dispersive spectroscopy, were conducted on granulated blast furnace slag–carbide slag–titanium gypsum (GCT)-solidified sludge (GSDS) and cement-solidified sludge (CSDS). The results demonstrate that GSDS exhibits significantly superior compressive strength, deformation resistance, and pore-filling capacity compared with CSDS. With increasing curing age, both materials show logarithmic increases in UCS and mesopore volume fraction, accompanied by power-law decreases in total pore volume and the most probable pore size. On this basis, quantitative relationships between micropore characteristics and macroscopic mechanical properties are established for both solidified sludges. Microscopic analyses reveal that strength development in GSDS is primarily attributed to the formation of abundant C-(A)-S-H gels and expansive ettringite crystals, which effectively cement soil particles and refine interparticle pores. The synergistic solidification mechanism of GCT, involving ion exchange, cementitious bonding, and pore filling, promotes particle aggregation, enhances interparticle bonding, and refines pore structure, thereby markedly improving structural integrity and macroscopic strength in GSDS. Full article

Offshore wind farm construction faces significant geotechnical challenges posed by tidal mudflat sediments, including high moisture content, low bearing capacity, and high sensitivity to disturbance. Utilizing MgO—a material characterized by abundant raw materials, low embodied energy, and environmental compatibility—for the stabilization of such soft soils represents a promising and sustainable approach worthy of further investigation. This study elucidates the carbonation-induced stabilization mechanism of coastal mucky soil from Ningbo, Zhejiang Province, through systematic monitoring of reaction temperature and unconfined compressive strength (UCS) testing under varying levels of reactive MgO content, carbonation duration, and initial moisture content. Microstructural characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to reveal the evolution of mineralogical and pore structure features associated with carbonation. The results indicate that increasing MgO content leads to higher peak reaction temperatures and shorter time-to-peak values. However, the rate of reduction in time-to-peak diminishes beyond 20% MgO. A secondary temperature rise is commonly observed between 3–3.5 h of carbonation in most specimens. When the MgO content is below 30%, UCS peaks within 6–10 h, with the peak time decreasing as MgO content increases. When MgO exceeds 45%, strength deterioration occurs due to structural damage. The correlation between deformation modulus and UCS is found to be comparable to that of conventional cement-stabilized soils. Microstructural analysis reveals that, with increased MgO dosage and prolonged carbonation, carbonation products progressively fill voids and bind soil particles, resulting in reduced total porosity and a refinement of pore size distribution—evidenced by a leftward shift in the most probable pore diameter. Nevertheless, at excessively high MgO levels (e.g., 50%), crystallization pressure from rapid product formation may generate macro-pores, compromising soil fabric integrity. This study presents a low-carbon and efficient ground improvement approach for access road construction in tidal mudflat wind farm developments. Full article

The Yellow River Floodplain region of Shandong Province is dominated by silty soils that challenge geotechnical construction. Drilling–Mixing–Jetting (DMJ) Deep Cement Mixing Pile groups have been adopted to improve the geotechnical properties of the soil. This study conducted field tests to evaluate column strength and numerically investigated the effects of area replacement ratio (7.10%, 10.66% and 14.21%) and column spacing. It is observed that the DMJ-integrated columns demonstrate enhanced soil–cement strength in the Yellow River Floodplain region, with sample strengths varying between 2 and 8 MPa. The electrical resistivity of soil–cement shows a strong linear correlation (Pearson’s R > 0.75) with unconfined compressive strength. Settlement reduction ratios range between 32.11% and 94.75% and increase with higher area replacement ratio (ARR) and applied stress but decrease with larger column spacing. Bearing capacity improvement factors are found to be increased with ARR, while column spacing has minimal effect, with values between 423.89 kPa and 431.61 kPa. Lateral displacement decreased with column installation and increasing area replacement ratio (ARR), while the effect of column spacing was confined to depths near the column head. Full article

This study evaluated the influence of soil preparation method and initial moisture content on the compressive strength of cement-stabilized rammed earth (CSRE). Cube samples stabilized with 7–12% cement were compacted using a manual rammer, cured for up to 28 days, and tested according to adapted EN 12390-3 procedures. These results indicated that eliminating the powdering step improved laboratory efficiency and produced specimens more representative of field practice. These findings demonstrate that labor-intensive powdering of natural soils is unnecessary, provided that moisture is accurately determined, thereby improving both laboratory efficiency and consistency with field practice. The outcomes contribute to optimizing laboratory methodologies for earthen construction materials. Full article

Riverbank erosion is a significant natural disaster that is prevalent in the deltaic regions in Bangladesh, resulting in loss of land, crops, and settlements. This research work is concentrated on the Satkhira Koyra area and is oriented towards a comparative assessment of the functionality of geo-bag and cement concrete (CC) blocks for erosion control purposes. The results showed that a geogrid could be used on the riverbank slope for more soil stability. The proposed approach is that the geogrid is used as a base layer for the slope. The sand-filled geo-bags are more cost-effective with this combination. Field monitoring and hydraulic model testing were used to identify their performance under natural flow conditions. Lined with geotextile fabric and filled with sand, the geo-bags were located in the most susceptible riverbank areas. The empirical results showed that the geo-bags provide the same levels of hydraulic resistance as those provided by CC blocks, but with substantial economic benefits and installation accomplished by local labor. When used in combination with a geogrid base layer, the geo-bag construction ensured excellent slope stability and allowed the establishment of natural vegetation, thus contributing to an environmentally friendly restoration. While CC blocks remain the optimal solution for high-value structures, the combined geogrid and geo-bag system offers a more flexible, cost-effective, and environmentally friendly alternative for stable erosion protection. Full article

The Otukpo Burnt Brick Factory has remained dormant for more than three decades despite repeated government interventions. In this context, the present study investigates the suitability of soils from Otukpo, Benue State, Nigeria, for unfired brick production and as supplementary cementitious materials (SCMs). Four representative samples (OT1–OT4) were subjected to X-ray fluorescence (XRF), thermogravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD), unconfined compressive strength (UCS), cube strength, shrinkage, and water absorption tests. The results revealed high reactive oxide contents (SiO₂ + Al₂O₃ + Fe₂O₃ > 93%) with low SO₃ and moderate loss on ignition (~6%), thus indicating strong pozzolanic potential. PSD residues on the 45 µm sieve ranged from 6.8 to 17%, which is well below the ASTM C618 limit of 34%. XRD confirmed quartz and kaolinite as dominant phases. Strength activity indices showed that only OT3 and OT4 exceeded Nigerian (NIS 693:2007) and Indian (IS 1725:2023) standards when stabilized with 5 wt.% cement or sodium hydroxide; while OT1 and OT2 were below these thresholds. Water absorption values for OT3 (18.69%) and OT4 (19.04%) marginally satisfied Indian standards but failed Nigerian requirements, which is reflective of high porosity. Linear shrinkage (~14%) met IS 1498 marginally, and pH values (6.14–6.34) were consistent with lateritic soils. Overall, OT3 and OT4 demonstrated promise for low-energy SCMs and unfired brick applications, though they must be restricted to non-load-bearing uses unless further stabilization is applied. Full article

Soil permeability is an important factor in the mining and geotechnical industry, impacting slope stability and tailings management. It directly influences the stability of structures, the control of water in tailings ponds, and the safety of workers. Various additives, such as cement kiln dust (CKD), bentonite, fly ash, polymers, lime, and asphalt, are incorporated into soil structures to improve permeability and stability. Any significant changes in soil permeability will alter the soil’s behavior. However, the long-term effect of most additives on structures remains unexplored. This study investigates the long-term impact of CKD on the permeability of a CKD-treated slope. The slope surface was treated with 0%, 5%, 10%, and 15% of CKD by the dry weight of the soil in 2008 and was evaluated in 2024. The permeability test results of the collected soil sample from the slope (2024) showed that the permeability of the soil decreases with an increase in the soil CKD content. The coefficient of permeability, k, is more than 100 times less for a CKD content of 15% by the dry weight of the soil compared to the permeability of the untreated native soil. The treated soil becomes almost impermeable when the CKD content increases to 20% (by the dry weight of the soil). However, the treated slope’s permeability increased over time, possibly due to erosion, resulting in a reduction in CKD content. The surface permeability of the slope exhibits an irregular distribution, resulting from the evolving spatial distribution of Cement Kiln Dust over time. Full article

Conducting laboratory tests in geotechnical engineering is a costly, time-consuming, and labor-intensive process. As an alternative solution, this study employs various machine learning methods to predict the unconfined compressive strength (UCS) of fine-grained soils stabilized by combining chemical additives (such as Portland cement, lime, and industrial and agricultural waste) and nanosilica. After preparing a comprehensive database of a collection of studies from the literature, ten machine learning models were developed for modeling, and their performances were compared using various metrics. After comparing the performance of the models in predicting the UCS with experimental results, the CatBoost model was determined as the optimal model. The variables of curing time, liquid limit of soil, and additive contents were identified as the most effective parameters on the stabilized soil’s UCS. The best-performing model on the applied dataset was determined and compared with experimental models. After determining the effective parameters for predicting the strength of stabilized soil, the nonlinear relationships between the most important variables and the stabilized soil’s UCS were analyzed and investigated. Full article

Rapid urban growth in South Indian coastal cities such as Chennai has intensified the Urban Heat Island (UHI) effect, with paved parking lots, walkways, and open spaces acting as major heat reservoirs. This study specifically compares conventional construction materials with natural and low-thermal-inertia alternatives to evaluate their relative ability to mitigate Surface Urban Heat Island (SUHI) effects. Unlike previous studies that examine isolated materials or single seasons, this pilot provides a unified, multi-season comparison of nine urban surfaces, offering new evidence on their comparative cooling performance. To assess practical mitigation strategies, a field pilot was conducted using nine surface types commonly employed in the region—concrete, interlocking tiles, parking tiles, white cooling tiles, white-painted concrete, natural grass, synthetic turf, barren soil, and a novel 10% coconut-shell biochar concrete. The rationale of this comparison is to evaluate how conventional, reflective, vegetated, and low-thermal-inertia surfaces differ in their capacity to reduce surface heating, thereby identifying practical, material-based strategies for SUHI mitigation in tropical cities. Surface temperatures were measured at four times of day (pre-dawn, noon, sunset, night) across three months (winter, transition, summer). Results revealed sharp noon-time contrasts: synthetic turf and barren soil peaked above 45–70 °C in summer, while reflective coatings and natural grass remained 25–35 °C cooler. High thermal-mass materials such as concrete and interlocked tiles retained heat into the evening, whereas grass and reflective tiles cooled rapidly, lowering late-day and nocturnal heat loads. Biochar concrete performed thermally similarly to conventional concrete but offered co-benefits of ~10% cement reduction, carbon sequestration, and sustainable reuse of locally abundant coconut shell waste. Full article

Expansive soils undergo significant volume changes with moisture fluctuations, posing persistent challenges for infrastructure due to heave, settlement, and loss of bearing capacity. Stabilization is a common mitigation strategy, though traditional binders, such as cement and lime, are associated with high energy consumption and considerable CO₂ emissions. In this context, identifying low-carbon alternatives is essential. This study evaluates the short-term behavior of expansive marly clays from southern Spain stabilized with volcanic ash generated during the 2021 Tajogaite eruption (La Palma, Canary Islands, Spain). Volcanic ash was incorporated in different proportions to assess its performance as a natural pozzolan, while natural hydrated lime was used both as a direct stabilizer and as an activator to enhance ash reactivity. A key methodological contribution of this research is the monitoring of lime reactivity throughout storage, using XRD and TGA to quantify portlandite loss and partial carbonation before mixing—an aspect seldom addressed in stabilization studies. The experimental program included chemical and mineralogical characterization, compaction, Atterberg limits, free swelling, unconfined compressive strength, and direct shear tests on natural and stabilized mixtures. The results show that volcanic ash, particularly when lime-activated, substantially improves volumetric stability. Free swelling decreased from 11.9% in the natural soil to values as low as 1.7%, while dry density increased and plasticity decreased. Strength gains were modest under short-term conditions, consistent with the limited time for pozzolanic reactions to develop. The combined use of volcanic ash and lime reduced the lime demand required to achieve equivalent volumetric control, offering an eco-efficient and technically viable alternative for stabilizing expansive marly clays. Full article

To promote the resource utilization of industrial solid waste, this study developed a multi-source industrial solid waste cementitious material (MSWC) for fluidized solidified soil (FSS), which consists of steel slag (SS), granulated blast furnace slag (GBFS), circulating fluidized bed fly ash (CFBFA), desulfurization gypsum (DG) and ordinary Portland cement (OPC). Firstly, the influence of industrial solid waste contents on the unconfined compressive strength (UCS) of FSS solidified with MSWC (MSWC-FSS) was studied, and the optimal proportion for MSWC was determined as SS:GBFS:CFBFA:DG:OPC = 20:40:15:5:20. Then, the effects of water reducers (PCE and FDN) and early-strength agents (Na₂SO₄ and CaCl₂) on the flow expansion, setting time and UCS of MSWC-FSS were studied. With the increase of PCE and FDN, the flow expansion, setting time and UCS of MSWC-FSS increased. With the increase of Na₂SO₄ and CaCl₂, the flow expansion and setting time of MSWC-FSS decreased, and 3 d and 7 d UCS increased, and 28 d UCS first increased and then decreased. The best mixing scheme of water reducer and admixture is 0.5% PCE and 1% Na₂SO₄, respectively. Finally, the sustainability of MSWC-FSS was assessed. The heavy metal leaching of MSWC-FSS met the safety requirements. For FSS cementitious materials, the cost and carbon emissions of MSWC were only 43.9% and 22.4% of OPC, respectively. Full article

Stabilisation of weak subgrades in mining and infrastructure projects traditionally relies on cement and lime, leading to high embodied energy and carbon emissions. Although waste glass powder (GP) has been explored in previous studies, existing work has primarily focused on isolated mechanical or material characteristics, with limited emphasis on integrated performance metrics. This study addresses this gap by establishing a mechanical–energy–carbon evaluation framework for assessing GP as a low-carbon stabiliser for black cotton (BC) and kaolinite clay (KC) soils. Laboratory investigations were conducted to evaluate the index, compaction, strength, and swelling characteristics at GP dosages ranging from 0% to 20%. Results showed a marked decrease in liquid limit (from 76% to 61% for BC and 45% to 32% for KC) and optimum moisture content, accompanied by a concurrent increase in maximum dry density. Strength improved substantially, with UCS reaching 95 kN/m² (BC) and 100 kN/m² (KC) at 15% GP. CBR values increased threefold, while DFSI decreased by 45–75%, indicating improved volumetric stability. Energy accounting revealed an 80–85% lower embodied energy compared to cement, with carbon savings of approximately 52 kg CO₂/t. The proposed Energy Performance Index confirmed superior strength per unit energy efficiency of GP. Valorising post-consumer glass aligns with circular economy principles and UN SDGs 9, 12, and 13, offering a low-carbon stabilisation strategy for energy-efficient mining operations. Full article

This study systematically investigates the engineering characteristics of lead-contaminated red clay stabilized by calcium lignosulfonate and ordinary Portland cement composite binders. A series of experiments were conducted to evaluate the effects of lignosulfonate contents (0%, 0.25%, 0.5%, 1%, 2%), cement content (4%, 6%, 8%, 10%), and lead ion concentration (0%, 0.1%, 1%) on the mechanical properties, permeability characteristics, and leaching behavior. Key findings include the following. (1) Based on the highest mean UCS values observed in this study, the best-performing formulations were 1% lignosulfonate + 4% cement for uncontaminated soil, 0.5% lignosulfonate + 4% cement for 0.1% lead, and 0.25% lignosulfonate + 10% cement for 1% lead. (2) The permeability coefficient initially decreases and then increases with lignosulfonate addition, with maximum reductions of 65.9% and 44.4% for 0.1% and 1% lead contamination under their respective best-performing formulations under these specific test conditions. (3) The leaching concentration of 0.1% lead-contaminated soil met the national standard (<5 mg/L). Critically, however, the 1% lead-contaminated soil failed the TCLP test, with a leaching concentration of 37.3 mg/L, vastly exceeding the regulatory limit. This constitutes a treatment failure for environmental safety purposes, rendering the concurrent mechanical strength improvement irrelevant. (4) Microstructural and X-Ray Diffraction analyses (SEM and XRD) suggest that lignosulfonate improves soil structure by promoting the formation of C-S-H gel and ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O), whereas high lead concentrations inhibit ettringite formation. This research provides a theoretical foundation for the multi-criteria evaluation and application of lignosulfonate–cement composites in lead-contaminated soil remediation. Full article

This study evaluates the mechanical performance and predictive modeling of fine-grained soils stabilized with crushed aggregate residue (CAR) or crushed limestone waste (CLW) and Portland cement by integrating the porosity–binder index ($\eta /C_{\mathrm{i}\mathrm{v}}$) and Machine Learning (ML) techniques. Laboratory testing included unconfined compressive strength (q_u) and small-strain shear modulus (G_o) measurements on mixtures containing 15% and 30% CAR and 3% and 6% cement, compacted at dry unit weights between 1.69 and 1.81 g·cm⁻³ and cured for 7 and 28 days. Results revealed that strength and stiffness increased significantly with both cement and CAR contents. The mixture with 30% CAR and 6% cement exhibited the highest mechanical performance at 28 days (q_u = 1550 kPa and G_o = 6790 MPa). When mixtures are compared within the same curing period, the role of CAR and cement becomes evident. At 28 days, increasing CAR from 15% to 30% led to a moderate rise in q_u (from 1390 to 1550 kPa) and G_o (from 6220 to 6790 MPa). Likewise, at 7 days, increasing cement from 3% to 6% at 15% CAR produced significant gains in q_u (207 to 693 kPa) and G_o (2090 to 4120 MPa). The porosity–binder index showed strong correlations with q_u (R² = 0.94) and G_o (R² = 0.92). The ML models further improved accuracy, achieving R² values of 0.99 for q_u and 0.97 for G_o. Although the index already performed well, the additional gain provided by ML is meaningful because it reduces prediction errors and better captures nonlinear interactions among mixture variables. This results in more reliable estimates for mix design, confirming that the combined use of $\eta /C_{\mathrm{i}\mathrm{v}}$ and ML offers a robust framework for predicting the behavior of soil–cement–CAR mixtures. Full article