Search Results (130)

The fatigue resistance of cement-stabilized macadam (CSM) plays a vital role in ensuring the long-term durability of pavement structures. However, limited cementitious material (CM) content often leads to high packing voids, which significantly compromise fatigue performance. Existing studies have rarely explored the coupled mechanism between pore structure and fatigue behavior, especially in the context of solid-waste-based CMs. In this study, a cost-effective alkali-activated sludge gasification slag (ASS) was proposed as a sustainable CM substitute for ordinary Portland cement (OPC) in CSM. A dual evaluation approach combining cross-sectional image analysis and fatigue loading tests was employed to reveal the effect pathway of void structure optimization on fatigue resistance. The results showed that ASS exhibited excellent cementitious reactivity, forming highly polymerized C-A-S-H/C-S-H gels that contributed to a denser microstructure and superior mechanical performance. At a 6% binder dosage, the void ratio of ASS–CSM was reduced to 30%, 3% lower than that of OPC–CSM. The 28-day unconfined compressive strength and compressive resilient modulus reached 5.7 MPa and 1183 MPa, representing improvements of 35.7% and 4.1% compared to those of OPC. Under cyclic loading, the ASS system achieved higher energy absorption and more uniform stress distribution, effectively suppressing fatigue crack initiation and propagation. Moreover, the production cost and carbon emissions of ASS were 249.52 CNY/t and 174.51 kg CO₂e/t—reductions of 10.9% and 76.2% relative to those of OPC, respectively. These findings demonstrate that ASS not only improves fatigue performance through pore structure refinement but also offers significant economic and environmental advantages, providing a theoretical foundation for the large-scale application of solid-waste-based binders in pavement engineering. Full article

In order to broaden the means of resource utilization of waste soil and steel slag produced in the process of urban construction, in this study, steel slag was used to replace part of the cement with waste soil, to prepare flowable waste soil. Through unconfined compressive strength (UCS), permeability, and dry–wet cycle tests, the mechanical properties of flowable waste soil under different steel slag replacement ratios and moisture contents were studied. The results show that the UCS of the flowable waste soil increases with the increase in curing age. When the steel slag replacement ratio is less than 66.7%, the UCS of the sample after 7 days of curing is more than 100 kPa. When the moisture content of the sample is 58% and the steel slag replacement ratio is 58.3%, the UCS can reach 101 kPa after 1 day of curing, which can meet the requirements of rapid construction. The UCS, resistance to the dry–wet cycle, elastic modulus, failure stress, and failure strain of flowable waste soil all decrease with the increase in the moisture content and steel slag substitution ratio. The permeability coefficient of the steel slag mixed sample decreased from 2.1 × 10⁻⁶ cm/s to 7.4 × 10⁻⁷ cm/s, and the permeability coefficient of the flowable waste soil after 28 d curing extended below 6 × 10⁻⁶ cm/s, indicating that the flowable waste soil has good impermeability and can be applied well in engineering. Full article

The 2014 Mt. Ontake eruption in Japan highlighted the need for improved volcanic shelters. To contribute to their reinforcement, this study focuses on the energy absorption characteristics of pumice, particularly artificial pumice made from waste glass. Compression tests were conducted under unconfined and oedometric conditions using a universal testing machine, drop-weight testing machine, and split Hopkinson bar across a wide strain rate range (10⁻³ to 10² s⁻¹). The deformation behavior was categorized into two types: one with a distinct initial peak followed by stress drop and another with a continuous transition to plateau deformation. Regardless of deformation type, the absorbed energy showed a positive dependence on strain rate. The average absorbed energy increased from approximately 1.6 MJ/m³ at 10⁻³ s⁻¹ to over 4.3 MJ/m³ at 10² s⁻¹. A simple predictive model was proposed to evaluate the energy absorption capacity of pumice reinforcement. The model’s predictions were in good agreement with experimental results for pumice layers up to 150 mm thick. These findings provide fundamental insights into the high strain rate behavior of artificial pumice and its potential application as a passive energy-absorbing material for impact-resistant volcanic shelters. Full article

Lateritic clay is widely distributed in southern China, and its strength is greatly affected by water content. The elevated moisture content in lateritic clay during monsoon periods frequently results in insufficient shear strength for standard engineering applications. Large quantities of solid waste, including steel slag, fly ash, and granulated blast furnace slag, are produced as industrial by-products. This paper is based on the backfilling resource utilization of steel slag, fly ash, and ground-granulated blast-furnace slag as lateritic clay improvement admixtures, along with the stress–strain behavior, strength characteristics, and microstructure of steel-slag-modified lateritic clay, fly-ash-modified lateritic clay, and ground-granulated blast-furnace slag-modified lateritic clay, by combining uniaxial compression tests, straight shear tests, and scanning electron microscopy observation. The experimental results were analyzed to determine the appropriate dosages of three kinds of solid waste and their mechanisms in lateritic clay modification. The results indicate that the unconfined compressive strength of SS-modified lateritic clay exhibited an increase with an increase in SS dosage in the range of 1–7%, the unconfined compressive strength of FA-modified lateritic clay showed an increase with an increase in FA dosage in the range of 1–5%, and the unconfined compressive strength of GGBFS-modified lateritic clay increased with an increase in the use of GGBFS in the range of 1–5%. Under the condition of a 7-day curing age, the unconfined compressive strength of lateritic clay modified with 7% SS increased by approximately 397%, while that modified with 5% FA and 5% GGBFS exhibited increases of about 187% and 185%, respectively. The stress–strain relationship of fly-ash and blast-furnace slag-modified lateritic clays showed elastic–plastic deformation. But the stress–strain behavior of steel-slag-modified lateritic clay at a steel slag dose greater than 5% and a maintenance age greater than 7 days showed elastic deformation. Analyzing the SEM images shows that the more hydration products are generated, the relatively higher the unconfined compressive strength of modified lateritic clay is, and the form of deformation of modified lateritic clay is closer to elastic deformation. Through comparative analysis of modified lateritic clay samples, this study elucidates the property-altering mechanisms of waste powder additives, guiding their engineering utilization. Full article

This study aimed to assess the mechanical and morphological properties of rigid polyurethane foams (RPUFs) reinforced with cellulose nanocrystals (CNC) at varying concentrations, exploring also effects of expansion under confinement for use in sandwich panels. RPUFs with 1%, 3%, and 5% CNC were tested, with the 3% CNC content delivering the best combination of mechanical performance and cellular structure. While the RPUF with 5% CNC showed a 78% increase in cell length, its compressive strength dropped by 55%, likely due to CNC agglomeration. Confining the RPUF during expansion improved the density by 23%, which in turn led to an approximately 90% increase in core shear stress. Flexural tests revealed that confined panels exhibited better force-displacement responses, with core shear strength rising by 55% compared to unconfined panels. These results suggest that CNC-reinforced and confined RPUFs are well-suited for structural applications requiring both strength and insulation. Full article

Root exudates play a crucial role in shaping rhizosphere soil structure, water dynamics, and adaptation to environmental stress. This study investigated the effects of environmental temperature (5 °C, 15 °C, and 25 °C) on water retention and soil strength in rhizosphere versus non-rhizosphere soils, simulated by adding glucose or deionized water to soil samples. Over a 10-day drying period, changes in soil water content, evaporation rate, water repellency, penetration resistance, and unconfined compressive strength were measured. The results showed that simulated root exudates significantly enhanced water retention at 15 °C (by 21.5%), but this effect diminished at 25 °C (to 8.3%) and was negative at 5 °C (by −8.9%). Additionally, root exudates improved soil mechanical stability, with the effect being more pronounced at higher temperatures. These changes were attributed to increased organic carbon decomposition and a higher proportion of micropores (<100 μm). These findings highlight the temperature-dependent role of root exudates in regulating soil properties, with implications for agricultural management and ecosystem resilience under climate change. Full article

The shear strength and compression properties of stiff Boom clay from Belgium at a depth of about 16.5 to 28 m were investigated by means of cone penetration and laboratory testing. The latter consisted of index classification, constant rate of strain, triaxial, direct simple shear and unconfined compression tests. The Boom clay samples exhibited strong swelling tendencies. The suction pressure was measured via different procedures and was compared to the expected in situ stress. The undrained shear strength profile determined from cone penetration tests (CPTs) was not compatible with the triaxial and direct simple shear measurements, which gave significantly lower undrained shear strength values. Micro-computed tomography (μCT) scans of the samples showed the presence of pre-existing discontinuities which may cause inconsistencies in the comparison of the laboratory test results with in situ data. The experimental data gathered in this study provide useful information for analyzing the mechanical behaviour of Boom clay at shallow depths considering that most investigations in the literature have been carried out on deep Boom clay deposits. Full article

In order to study the strength characteristics of organic-matter-contaminated red soil and the improvement effects of different modifiers, the red soil in the Yulin area was taken as the research object, and triaxial compression tests were carried out to study the effects of different mass fractions (0%, 2%, 4%, 6%, 8%) of organic matter (sodium humate) on the strength characteristics of red soil. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) tests were carried out to study the improvement effects of different amounts of lignin, fly ash, and xanthan gum on organic-matter-contaminated red soil (organic matter content of 8%). The results of the tests showed that the cohesion and internal friction angle of red soil both tended to decrease with the increase in organic matter content. When the organic matter content increased from 0% to 8%, the cohesion of the red soil decreased from 60.98 kPa to 40.07 kPa, a decrease of 34.29%; and the internal friction angle decreased from 17.42° to 7.28°, a decrease of 58.21%. The stress–strain relationship curves of organic-matter-contaminated red soil all show a hardening type. Under different confining pressures, as the organic matter content increased, the shear strength of the red soil decreased continuously. The unconfined compressive strength of organic-matter-contaminated red soil increased with the increase in lignin content, and increased first and then decreased with the increase in fly ash content and xanthan gum content. Through comparative analysis, it was found that the fly ash with a content of 15% had the best improvement effect. The lignin-amended red soil enhanced the connection of soil particles through reinforcement, reduced pores, and improved soil strength. Fly ash improved the acidification reaction, and the hydrates filled the pores and enhanced the soil strength. Xanthan gum improved the red soil by absorbing water and promoting microbial growth, further enhancing the bonding force between soil particles. This study can provide a reference for engineering construction and red soil improvement in red soil areas. Full article

The flexural behavior of geogrid-reinforced foamed lightweight soil (GRFL soil) is investigated in this study using unconfined compressive and four-point bending tests. The effects of wet density and reinforcement layers on flexural performance are analyzed using load–displacement curves, damage patterns, load characteristics, unconfined compressive strength, and flexural strength. A variance study demonstrates that increasing the wet density significantly increases unconfined compressive strength. Bond stress mechanisms enable geogrid integration, efficiently reroute stresses internally, and greatly increase flexural strength. With a maximum unconfined compressive strength of 3.16 MPa and a peak flexural strength increase of 166%, this reinforcement increases both strength and ductility by changing the damage pattern from brittle to ductile. The principal load is initially supported by the foamed lightweight soil, and in later phases, geogrids take over load-bearing responsibilities. Additionally, the work correlates the ratio of unconfined compressive to flexural strength with wet density and informs the development of predictive models for unconfined compressive strength as a function of reinforcing layers and wet density. Full article

In recent decades, rapid urbanization has generated a large amount of waste soft soil and construction debris, resulting in severe environmental pollution and posing significant challenges to engineering construction. To address this issue, this study explores an innovative approach that synergistically applies recycled fine aggregate (RFA) and soil stabilizers to improve the mechanical properties of soft soil. Through laboratory experiments, the study systematically examines the effects of different mixing ratios of RFA (20%, 40%, 60%) and soil stabilizers (10%, 15%, 20%) with red clay. After standard curing, the samples underwent water immersion maintenance for varying durations (1, 5, 20, and 40 days). Unconfined compressive strength (UCS) tests were conducted to evaluate the mechanical performance of the samples, and the mechanisms were further analyzed using scanning electron microscopy (SEM) and particle size distribution (PSD) analysis. The results indicate that the optimal performance is achieved with 20% RFA and 20% stabilizer, reaching the highest UCS value after 40 days of water immersion. This improvement is primarily attributed to the formation of a dense reticulated structure, where RFA particles are effectively encapsulated by clay particles and stabilized by hydration products from the stabilizer, forming a robust structural system. Unconsolidated undrained (UU) tests reveal that peak deviatoric stress increases with confining pressure and stabilizer content but decreases when excessive RFA is added. Shear strength parameter analysis demonstrates that both the internal friction angle (φ) and cohesion (c) are closely related to the content ratios, with the best performance observed at 20% stabilizer and 20% RFA. PSD analysis further confirms that increasing stabilizer content enhances particle aggregation, while SEM observations visually illustrate a denser microstructure. These findings provide a feasible solution for waste soft soil treatment and resource utilization of construction debris, as well as critical technical support and theoretical guidance for geotechnical engineering practices in high-moisture environments. Full article

Understanding the mechanical and physical behavior of aged CPB under cyclic loading is a significant area of research. Many parameters such as cementation (hydration) and the microstructure, which dictate the arrangement of particles and permeability, affect the mechanical features of cemented paste backfill (CPB). The impact of a wide range of external energy sources within the mining environment, such as cyclic loading resulting from long-term blasting, can significantly alter the applied stresses on the backfill mass. This paper aims to delve into this crucial area of research. A series of uniaxial cyclic tests were conducted on CPB, utilizing samples made from tailing materials sourced from a copper mine in South Australia. Different loading levels were applied at various curing times. All samples exhibited cyclic loading hardening behavior for cyclic loading levels between 80% and 93% of monotonic unconfined compressive strength (UCS), and a cyclic loading damage behavior was observed for 96% of UCS loading level for both 14- and 28-day curing periods. To further investigate these findings, scanning electron microscope analysis as well as sonic velocity tests were conducted for capturing microstructural changes in the samples before and after tests. These findings can be used to indicate a safe firing distance to a filled mass. Full article

Using silty clay as roadbed filling can lead to roadbed diseases. In this paper, silty clay was modified with lignin and BFS (GGBS). Then, the mechanical properties, freeze-thaw characteristics, and microscopic mechanisms were investigated using unconfined compression tests, California bearing ratio tests, rebound modulus tests, freeze-thaw cycling tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that as the curing age increased, the unconfined compressive strength (UCS) of modified silty clay gradually increased, and the relationship between the stress and axial strain of the samples gradually transitioned from strain-softening to strain-hardening. As the lignin content decreased and the BFS content increased, the UCS, California bearing ratio (CBR), and rebound modulus of the modified silty clay first increased and then tended to stabilize. Adding lignin and BFS can effectively resist volume increase and mass loss during freeze-thaw cycles. When the ratio of lignin to BFS was 4%:8%, the growth rate of the UCS, CBR, and rebound modulus was the largest, the change rate in volume and mass and the loss rate of the UCS under the freeze-thaw cycle were the smallest, and the silty clay improvement effect was the most significant. The microscopic experimental results indicated that a large amount of hydrated calcium silicate products effectively increased the strength of interunit connections, filled soil pores, and reduced pore number and size. The research results can further improve the applicability of silty clay in roadbed engineering, protect the environment, and reduce the waste of resources. Full article

Identifying suitable sites for urban, industrial, and tourist development is important, especially in areas with increasing population and limited land availability. Kharga Oasis, Egypt, stands out as a promising area for such development, which can help reduce overcrowding in the Nile Valley and Delta. However, soil and various environmental factors can affect the suitability of civil engineering projects. This study used Geographic Information Systems (GISs) and a multi-criteria decision-making approach to assess the suitability of Kharga Oasis for construction activities. Geotechnical parameters were obtained from seismic velocity data, including Poisson’s ratio, stress ratio, concentration index, material index, N-value, and foundation-bearing capacity. A comprehensive analysis of in situ and laboratory-based geological and geotechnical data from 24 boreholes examined soil plasticity, water content, unconfined compressive strength, and consolidation parameters. By integrating geotechnical, geomorphological, geological, environmental, and field data, a detailed site suitability map was created using the analytic hierarchy process to develop a weighted GIS model that accounts for the numerous elements influencing civil project design and construction. The results highlight suitable sites within the study area, with high and very high suitability classes covering 56.87% of the land, moderate areas representing 27.61%, and unsuitable areas covering 15.53%. It should be noted that many settlements exist in highly vulnerable areas, emphasizing the importance of this study. This model identifies areas vulnerable to geotechnical and geoenvironmental hazards, allowing for early decision-making at the beginning of the planning process and reducing the waste of effort. The applied model does not only highlight suitable sites in the Kharga Oasis, Egypt, but, additionally, it provides a reproducible method for efficiently assessing land use suitability in other regions with similar geological and environmental conditions around the world. Full article

A cementitious paste fill (CPF) ensures the long-age stability of underground cavities. Recently, superplasticizers, specifically ones that are polycarboxylate ether-based, have been incorporated to enhance CPF performance, yet their long-term effects on permeability, mechanical properties, and microstructures remain unclear. This study investigates these effects with CPF samples containing varying superplasticizer dosages (0%, 1%, 3%, 5%) that have been cured for up to 150 days. Rheological assessments (slump cone, vane shear tests), unconfined compressive strength testing, microstructural characterization (MIP, SEM), and hydraulic conductivity measurements were performed alongside XRD and thermal analyses (TAns) on high w/c (2) cement paste samples. The results showed that superplasticizer addition reduced CPF water content by 23% and yield stress by six times, aiding slurry transport. Long-term strength was enhanced by up to 2.4 times compared to the control samples, indicating improved underground stability. Superplasticizers altered the CPF samples stress–strain responses, increasing their load-bearing capacity. TG/DTG and XRD analyses revealed that hydration product development increased and porosity decreased in the presence of a superplasticizer. Hydraulic conductivity and permeability also decreased significantly. SEM and MIP analyses showed that the superplasticizer enhanced denser microstructures with fewer pores and fractures. These findings offer promising implications for designing CPFs with improved strength, durability, and environmental sustainability. Full article

The purpose of this study was to fully explore the mechanical properties of five different doses of an Argon–Oxygen Decarburization slag mixture in an unconfined compressive strength test. The peak stress, elastic modulus, and stress–strain curve of the mixture were studied for 90 days. Based on the experimental data and according to the theory of damage mechanics, the concept of damage threshold (t) was introduced to construct a damage constitutive model. Referring to the damage threshold of concrete, that of the mixture was determined to be 0.7 times higher than the peak strain, and the correlation coefficient between the established model and the test curve was above 0.85. These results indicate that the addition of AOD slag and fly ash can cause hydration reactions, increase the quantity of hydration products, and enhance the peak stress and elastic modulus of the mixture. The maximum increases were 94.9% and 43.1%, respectively. Parameters a and b reflect the peak stress and brittleness of the mixture, respectively. The incorporation of Argon–Oxygen Decarburization slag can make the mixture less brittle and improve its properties. The incorporation of Argon–Oxygen Decarburization slag can protect the mixture from damage. The maximum decrease is 40.2%. Full article