Search Results (122)

The Artemis program led by NASA aims to establish a sustained human presence at the lunar south pole, increasing the need to characterise the mechanical behaviour of polar regolith, particularly within the highland terrains that dominate the lunar crust. This study investigates the compressive, shear and tensile strengths of the frozen lunar highland simulant LHS-1E under controlled moisture contents of 5–13 wt%, representing ice-bearing conditions reported in permanently shadowed regions. Freezing serves as a controlled terrestrial proxy for assessing ice-cemented behaviour, although full lunar vacuum and cryogenic conditions are not replicated. Results show systematic strengthening with increasing moisture content. Namely, the unconfined compressive strength increased from 1.09 MPa to 6.31 MPa, the Young’s modulus from 66 MPa to 238 MPa, the friction angle from 35° to 45°, and the tensile strength from 286 kPa to 463 kPa, while the cohesion remained between 6 and 8 kPa and the Poisson’s ratio decreased from 0.19 to 0.09. These findings capture and quantify the mechanical transition from friction-dominated to ice-bonded granular behaviour and provide strength bounds relevant to infrastructure development and excavation in ice-bearing lunar polar regolith. Full article

In a calcined clay rotary cooler, the flow behavior and heat transfer characteristics of the granular bed are key factors determining the cooling efficiency. In this study, an Euler–Euler multiphase model coupled with the kinetic theory of granular flow (KTGF) was used to simulate the granular bed flow and heat transfer in a rotating drum of a rotary cooler. Unlike conventional large-particle beds, the 11 μm calcined clay particles interact more strongly with the gas phase, resulting in stratification and fluidization in the fine-particle bed. The effects of rotational speed, baffle configuration, and number of baffles on the flow and heat transfer behavior of the calcined clay granular bed were investigated. The results show that L-shaped baffles provide superior cooling, achieving a granular bed temperature and heat transfer coefficient (HTC) of 656.88 K and 151.15 W/(m²·K), respectively. At 2 rpm, the maximum temperature decrement and HTC increment are 5.73 K and 46.30 W/(m²·K), whereas excessive rotational speeds intensify bed fluidization. Additionally, increasing the number of L-shaped baffles has limited influence on expanding the fluidized region. With 12 L-shaped baffles, the temperature decrement peaks at 2.86 K and the HTC increment reaches a relatively high 33.27 W/(m²·K). This study provides a theoretical basis for the design and optimization of industrial-scale rotary cooling equipment for fine-particle beds. Full article

The circular economy (CE) concept promotes the maximization of the use of waste-derived materials, particularly construction and demolition waste (CDW), as secondary raw materials in the production of new construction materials. One of the promising approaches for their valorization is the incorporation of recycled aggregates (RA) into cement-bound granular mixtures (CBGM), which are widely used in road pavement structures. This paper presents the results of laboratory-scale investigation on the mechanical performance of CBGM containing recycled aggregates. The study focused on evaluating the influence of secondary raw materials on the compressive strength and overall mechanical performance of the mixtures. The obtained results indicate that the incorporation of recycled aggregates not only represents an effective strategy for the management and reuse of construction waste, but also contributes to the improvement of the mechanical properties of CBGM. The findings confirm the potential of recycled materials as a viable and technically effective component of cement-bound mixtures, thereby supporting the development of sustainable road engineering and the implementation of circular economy principles. Full article

Enhancing the freeze–thaw resistance of cement-based materials in a green and efficient manner is crucial for hydraulic structures in cold regions. This study investigated the effects of soybean antifreeze protein (AFP) on the freeze–thaw durability of cement mortar through mechanical testing, low-temperature microscopy, NMR analysis, and frost-heaving stress monitoring. The results show that AFP improves freeze–thaw durability, with 0.5% dosage outperforming 1.0%. Relative to the control, the relative ice content at −20 °C decreased from 62.81% to 40.01%, and frost-heaving stress declined from 321.15 kPa to 123.04 kPa. Microscopy and pore structure analyses revealed that AFP transforms ice crystals from needle-like to fine granular forms, inhibiting ordered growth and retarding pore coarsening. A frost-heaving stress model based on the Gibbs–Thomson effect and ice-crystal fractal characteristics indicated that AFP suppresses stress development by reducing effective ice formation, weakening stress transfer, and increasing ice-crystal boundary complexity. This study offers insights for developing green antifreeze admixtures for cement-based materials in cold regions. Full article

Asphalt pavement on rigid base (cement concrete) differs significantly from traditional granular base pavement. To investigate its mechanical behavior, a viscoelastic–viscoplastic damage constitutive model for asphalt mixtures is proposed and verified. A user-material subroutine (UMAT) is developed to implement the model, and a three-dimensional finite element model is established to analyze pavement responses under various working conditions. Key numerical results include the following: the asphalt layer primarily experiences compressive–shear failure, with peak shear stress (τ₁₂) reaching 141.6 kPa under rigid base conditions; emergency braking increases τ₁₂ to approximately 270.3 kPa, a 91% increase; increasing vehicle speed from 15 m/s to 35 m/s raises τ₁₂ by 36.7%; based on stress analysis alone, the recommended asphalt layer thickness is between 0.10 m and 0.14 m, as thickness beyond 0.10 m yields diminishing stress reduction. The findings provide references for performance prediction, structural design, and material development of asphalt pavement on a rigid base. Full article

To systematically investigate the combined effects of moisture content, confining pressure, and loading rate on the mechanical properties of weakly cemented soft rock, this study focuses on the Jurassic coal measures from the Hoxtolgay coalfield in Xinjiang. A series of uniaxial and triaxial compression tests were conducted under varying moisture states, loading velocities, and confining pressures. Complementary X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brazilian splitting tests were performed to analyze the microstructural evolution and tensile failure characteristics. The experimental results demonstrate that moisture content acts as the primary governing factor for mechanical degradation; increased hydration promotes clay mineral swelling and attenuates inter-granular cementation, leading to a continuous reduction in both compressive and tensile strengths, as well as the elastic modulus. Conversely, confining pressure consistently enhances these macroscopic mechanical parameters by restricting lateral deformation. While the loading rate alters the mechanical response, its impact is secondary compared to the definitive effects of moisture and stress constraints. Furthermore, by utilizing established stress–strain-based indices, the study quantitatively evaluates the brittleness characteristics, confirming that hydration fundamentally drives the rock mass from a brittle state toward ductility. This research elucidates the coupled degradation mechanisms of highly sensitive soft rock, providing a theoretical foundation for stability design and risk assessment in underground geotechnical engineering. Full article

Against the backdrop of dual-carbon goals and resource constraints, the high-value utilization of recycled fine aggregates (RFAs) remains limited, leading to inconsistent engineering performance and insufficient durability. Enzyme-induced carbonate precipitation (EICP) represents a promising low-carbon cementation method, yet its deposition uniformity and cementation efficiency are influenced by the pore structure of granular media and associated mass transfer pathways. This study employs a two-stage experimental design to investigate the synergistic effects of particle size distribution characteristics, represented primarily by d₅₀, and fiber addition on EICP-cemented RFA. Phase I (fiber-free; d₅₀ = 0.67–1.14 mm) results indicate that, across the tested gradation schemes, the CaCO₃ content generally decreased from 9.49% to 7.72% as the representative d₅₀ increased, while the dry density changed only slightly (1.637–1.617 g/cm³). However, the unconfined compressive strength (UCS) decreased from 1000 kPa to 541 kPa (45.9% reduction), indicating that strength is primarily governed by the connectivity of the cementation network rather than solely by the degree of densification. In Phase II, glass fiber (GF), polypropylene fiber (PPF), and jute fiber (JF) were incorporated into the ERFA4 gradation scheme selected for fiber modification. All three systems exhibited a unimodal optimum pattern: the peak CaCO₃ contents reached 10.71% (GF 0.5%), 10.11% (PPF 0.7%), and 11.46% (JF 0.7%), corresponding to peak UCS values of 1917, 1874, and 2450 kPa, respectively. Microscopic analysis suggested that fiber bridging coupled with CaCO₃ deposition may contribute to the formation of a “fiber-CaCO₃-particle” stress-transfer network, which is consistent with the observed enhancements in load-bearing capacity, ductility, and post-peak stability. Full article

In recent decades, the need to embrace the concepts of the circular economy and ecological transition has become increasingly apparent, especially in the civil engineering sector. This research aims to study a Cement-Bound Granular Material (CBGM) pavement layer using the industrial by-product Anhydrous Calcium Sulphate (ACS) as a partial replacement for Portland Cement (PC) by weight. The dual objective is to reduce environmental impact and ensure long-term high mechanical performance. Mechanical tests conducted at different curing periods (7, 28, 96, and 120 days) showed compressive strength gains of up to 180%. The evolution of the mechanical behavior was correlated with the formation of the gypsum dihydrate and ettringite hydrated phases, found by quantitative XRD analysis, to reinforce the cement matrix. Finite element simulations and fatigue life predictions using Miner’s rule over pavement lifespans of 15, 20, and 30 years indicated an increase in durability by a factor of 4.68 for the ACS-enhanced mixture compared to traditional PC-only formulations. Leaching tests show the material performs within acceptable environmental thresholds, even if its classification and acceptance may differ across regulatory systems, suggesting a solid basis for its application in sustainable practices. Full article

For the metal deposits exploited by the open-stope subsequent filling method, the goaf roof is prone to large-scale caving when the stope ore is not fully mined. This further results in the accumulation of a thick layer of waste rock on the goaf floor due to the caving of surrounding rocks. In the treatment using cemented filling, it is essential to ensure that the filling slurry fully permeates into the granular pile, and that the granular-cemented backfill possesses sufficient strength to guarantee the production safety of adjacent stopes. Taking the caving goaf of Shirengou Iron Mine as the engineering background, the effects of slurry concentration, cement–tailing ratio, height of the granular pile, and particle size of the granular rock on seepage laws are investigated by means of a self-developed simplified filling test device. The filling slurry concentration that meets the on-site requirements for fluidity and permeability is thereby determined. Meanwhile, by prefabricating the granular-cemented backfill, the characteristics of the self-supporting capacity and strength of the backfill are studied, considering factors such as different slurry concentrations, cement–tailing ratios, and curing ages. The results indicate that the cement–tailing ratio exerts the least influence on the seepage law, yet it has the most significant impact on the strength of the granular-cemented backfill. When the cement–tailing ratio of the filling slurry ranges from 1:8 to 1:4 with a concentration of 68%, the filling slurry can completely seep and cement the waste rock layer. At this point, the granular-cemented backfill strength can reach 1~2 MPa, which satisfies the seepage and cementation requirements for the waste rock inside the caving goaf of Shirengou Iron Mine. Full article

The Transylvanian Basin is an intra-Carpathian sedimentary unit displaying complex tectonic and sedimentary evolution that started in the Late Cretaceous. This study presents a geotechnical characterization of three Paleogene lithostratigraphic units located in the northwestern part of the basin, i.e., Brebi, Mera, and Moigrad. These formations record the transition from marine carbonate facies to brackish and subsequently fluvial environments, controlled by tectonic uplifts, marine regressions, and fluctuations in sediment supply. A total of 583 soil samples were collected through geotechnical boreholes and analyzed in the laboratory according to EN ISO standards, assessing natural moisture content, bulk density, grain size distribution, Atterberg limits, carbonate content, unconfined compressive strength, and shear strength parameters. Characteristic values of these properties were determined based on probabilistic distributions. The analyzed formations exhibit well-differentiated lithological and geotechnical characteristics, primarily governed by the degree of plasticity and the presence of calcium carbonate. The Brebi Formation predominantly consists of medium-plasticity clays with highly to very highly carbonate content, indicating a partially cemented microstructure. The Mera Formation is mainly composed of high-plasticity clays having a variable content of carbonates, with frequent sandy intercalations, resulting in significant variability in mechanical properties. The Moigrad Formation consists of two distinct lithological complexes: a clay-rich complex composed of variably plastic calcareous clays spanning all four plasticity classes and a sandy unit made up of weakly cohesive sediments with a granular structure and locally developed carbonate microcementation. Full article

Cemented granular materials (CGMs) represent a transitional class of geomaterials where mechanical behavior is governed by the interplay between a discrete granular skeleton and a continuous cementitious matrix. While previous studies have focused on idealized spherical particles, this study aims to quantify the influence of the cement filling ratio (ranging from 10% to 100%) on the mechanical constitutive behavior of CGMs fabricated with large, irregular granitic aggregates (14–20 mm). Unconfined compressive tests and splitting tensile tests were conducted to evaluate the evolution of strength, stiffness, and failure modes. The results reveal a distinct mechanical transition governed by the cement filling ratio (${\rho }_m$). The elastic modulus and splitting tensile strength exhibited a linear increase with ${\rho }_m$ (R2 > 0.95), indicating a direct dependence on the volume fraction of the binding phase. In contrast, the unconfined compressive strength (UCS) and peak strain displayed a bilinear growth pattern with a critical inflection point at ${\rho }_m$ = 80%. For the specific irregular granitic aggregate skeleton investigated, this threshold marks the transition from contact-dominated stability to matrix-dominated continuum behavior. Below this threshold, strength gain is limited by the stability of discrete particle contacts; above 80%, the material behaves as a continuum, with UCS increasing rapidly to a maximum of 41.78 MPa at 100% filling. Furthermore, the dispersion of stress–strain responses significantly decreased as ${\rho }_m$ exceeded 50%, attributed to the homogenization of stress distribution within the specimen. These findings provide a quantitative basis for optimizing cement usage in ground reinforcement applications, identifying 80% as a critical design threshold. Full article

Circulation is one of the most prevalent and severe complications during the drilling and completion of deep and ultra-deep wells, especially in fractured and karstic formations. In regions such as the Sichuan Basin, bottom-hole temperatures exceeding 200 °C, limited formation strength, and frequent lithological alternations significantly reduce the effectiveness of conventional granular materials under high-temperature and long open-hole conditions. Bridging-type plugging systems based on particle gradation or principles often exhibit low success rates due to fiber softening, rubber aging, and erosion-induced deterioration of the sealing structure. In this study, a high-temperature-resistant bridging composite system was developed to meet the extreme conditions in deep and ultra-deep wells. By incorporating temperature-resistant bridging particles and flexible reinforcing components, the slurry establishes a synergistic “bridging–filling–densification” sealing mechanism. Meanwhile, the combined use of retarders, fluid-loss reducers, and rheology modifiers ensures stable pumpability and adequate curing densification at 200 °C. Overall, the results provide new insights and experimental evidence for the design of high-temperature cement-based plugging materials, offering a promising approach for improving loss-control effectiveness and wellbore strengthening in complex intervals. Full article

This study compares the mechanisms of organic (Hydroxypropyl Methyl Cellulose, HPMC) and inorganic (bentonite) thickeners in regulating the bleeding behavior and surface homogeneity of cement pastes. In situ low-field nuclear magnetic resonance (LF-NMR) was employed to monitor water migration, while X-ray diffraction (XRD), scanning electron microscopy (SEM), and carbonation tests were conducted to evaluate the property disparities between the top surface and bottom layers. Results indicate fundamentally different working modes: HPMC reduces bleeding by swelling to block capillary channels, exhibiting a saturation threshold at 0.2% dosage. Beyond this point, as the primary transport channels are effectively sealed, additional HPMC merely densifies the polymer “plugs” without further suppressing the bleeding rate. XRD and SEM analyses reveal that despite the reduction in total bleeding, HPMC-modified pastes still exhibit significant stratification; the top layer retains a loose, granular morphology with higher carbonation susceptibility compared to the dense bottom layer. In contrast, bentonite mitigates bleeding through a volume-filling mechanism and thixotropic structuring, demonstrating a continuous, dosage-dependent efficacy up to 1.2%. At a 0.6% dosage, bentonite effectively eliminates microstructural disparities, yielding a top surface with a dense matrix and hydration product distribution nearly identical to the bottom layer. These findings demonstrate that the specific inorganic thickener (bentonite) utilized in this work is more effective in restoring surface homogeneity and enhancing carbonation resistance than the evaluated organic polymer (HPMC). Full article

Severe lost circulation frequently occurs in deep and ultra-deep wells under high-temperature/high-pressure (HPHT) conditions and in fracture-cavity composite loss channels. Conventional lost-circulation materials (LCMs) often fail because of premature loss of mobility, insufficient residence in loss paths, and irreversible failure after solidification. Cement-based sealing systems, owing to their ability to plug large leakage channels and their cost-effectiveness, have become the mainstream solution. To improve their performance under extreme downhole conditions, recent studies have focused on base-cement design, reinforcement phases, and property regulation strategies-including the use of granular/fibrous/nanoscale additives for bridging reinforcement, rheology and thickening control to enhance injectability and residence, and chemical/functional modifiers to improve compactness and durability of the hardened matrix. Significant progress has been achieved in terms of HPHT resistance, densification design, regulation of rheological properties and thickening behavior, and self-healing/responsive sealing functions. However, most existing studies still focus on improving individual properties and lack a cross-scale, holistic design and unified mechanistic perspective for fracture-cavity coupled flow and long-term sealing stability. Distinct from previous reviews that mainly catalogue material types or discuss single-performance optimization, this review is framed by fracture-cavity composite loss channels and long-term sealing requirements under HPHT conditions, systematically synthesizes the material design strategies, reinforcement mechanisms and applicability boundaries of cement-based plugging systems, builds cross-scale linkages among these aspects, and proposes future research directions toward sustainable plugging design. Full article

The growing accumulation of glass waste and the limited availability of natural aggregates present major challenges for sustainable road construction. This study aimed to evaluate the influence of the glass cullet content (GC) in the range of 0–30% on the mechanical and compaction properties of cement-bound granular mixtures (CBGM 31.5 mm, R_c class C_5/6) intended for the road base and subbase layers. Laboratory tests were carried out to analyze the effect of GC on the optimum moisture content (OMC), the maximum dry density (ρ_d,max), and the compressive strength after 7 and 28 days (R₇, R₂₈). The results showed a systematic decrease in OMC and ρ_d,max with increasing GC content, by approximately 18% and 2.8%, respectively, for the mixture containing 30% glass. All CBGM mixtures met the strength requirements for class C_5/6 (R_c = 6–10 MPa), with the highest value of R28 obtained for the mixture containing 20% GC (9.4 MPa), representing a 24% increase compared to the reference mix. The relationship between GC content and compressive strength was best described by a second-degree polynomial function (R² = 0.60–0.65), indicating an optimum within the 10–20% range. Strength enhancement was attributed to synergistic effects of physical mechanisms (filler effect and improved particle packing) and chemical activity (pozzolanic reactivity of fine glass fractions). The 30% GC mixture provided the minimum required strength while achieving the highest level of waste utilization and environmental benefit. Therefore, the optimal GC content should be determined as a balance between mechanical performance and sustainable use of secondary materials in the temperate climatic conditions of Central Europe. Full article